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I wasn't sure how well the technique is used nowadays given the many other ways of improving contrast. However, a web search for 'oblique illumination' shows that some of the mainstream microscope makers mention this form of lighting as a feature in some of their models (particularly metallurgical), so presumably it does still have a worthwhile role. The oblique patch stop is certainly a cheap and cheerful way for the amateur to improve contrast for some subjects, especially at medium powers where patch stops for dark-field get trickier to make. I was also intrigued to see that at least one manufacturer, 'Edge', market a microscope with 'patented Multiple Obliquetm Illumination' which apparently gives 3D images. Visit the Edge web site for details and read the theory behind the technique for 3D imaging. Comments on the article to the author Dave Walker welcomed. References 1) 'Under the Microscope' by A. Curry, R. F. Grayson and G. R. Hosey, (Blandford Press, UK, 1982), Chapter 8. Now out of print, but worth looking out for in second-hand bookshops as it gives clear explanations of many techniques and principles, especially the use of polarised light. 2) 'The Microscope Past and Present' by S. Bradbury. Pergamon Press, UK, 1968, pp. 180-183. A compact but thorough overview of the history of the microscope and it's development. Illustrates and discusses the Ross Radial and Ross / Zentmayer microscope and the fad for oblique illumination. Microscopy UK Front Page Micscape Magazine Article Library Text and images © David Walker. © Onview.net Ltd, Microscopy-UK, and all contributors 1995 onwards. All rights reserved. Main site is at www.microscopy-uk.org.uk with full mirror at www.microscopy-uk.net.

1) 'Under the Microscope' by A. Curry, R. F. Grayson and G. R. Hosey, (Blandford Press, UK, 1982), Chapter 8. Now out of print, but worth looking out for in second-hand bookshops as it gives clear explanations of many techniques and principles, especially the use of polarised light. 2) 'The Microscope Past and Present' by S. Bradbury. Pergamon Press, UK, 1968, pp. 180-183. A compact but thorough overview of the history of the microscope and it's development. Illustrates and discusses the Ross Radial and Ross / Zentmayer microscope and the fad for oblique illumination. Microscopy UK Front Page Micscape Magazine Article Library Text and images © David Walker. © Onview.net Ltd, Microscopy-UK, and all contributors 1995 onwards. All rights reserved. Main site is at www.microscopy-uk.org.uk with full mirror at www.microscopy-uk.net.

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If you have a condenser and filter tray, a simple stop can be made as shown left. Just cut out a piece of opaque card to fit the filter tray and experiment with various sizes of sector cut out of the disc for a given objective to allow light from an angle to reach the subject. Normal axial illumination should be setup first. As for dark field, the condenser iris should be fully open and the condenser focus adjusted to get the best effect. You may need to experiment with the size of the notch for a given objective. The orientation of the notch with respect to the subject should also be changed to see what achieves the best effect. If you have a rotating stage this is easier than rotating the patch stop in the filter tray. If the filter tray is a swing out type, also experiment with the extent the filter is swung in, as well as varying the orientation of the notch in the filter tray. Condenser with oblique illumination Buying a condenser specifically for oblique illumination is probably not justified, but this is a feature found in some condensers. My Russian Biolam microscope is supplied with a modest Abbe condenser, but for critical work I use the better quality Russian aplanatic condenser (N.A. 1.4). As a bonus this also has an oblique illumination feature, see image right. (Supplementary low power lens N.A. 0.3 also shown). The iris can be moved up to 10mm off-axis in opposite directions, which also rotates in the mount to change the orientation of the light to the subject. The latter feature, as mentioned above for the oblique patch stop, is important as the off-axis lighting often works best in a specific orientation to a subject e.g. for non-symmetric diatoms like Pleurosigma. Historical footnote In the late19th century but before the advent of high numerical aperture objectives, oblique illumination was quite popular and some makers developed microscopes especially to exploit the benefits of the technique. One of the first models was shown by Zentmayer of Philadelphia in 1876 at an Exposition in this city. It had a swinging substage, i.e. the whole substage assembly swung about an axis in the same plane as the stage. An image of this microscope is in the Moody Medical Library On-line (item 1.028 in catalogue). (This site illustrates a wonderful selection of historical microscopes from the famous Moody collection, most makers are represented). Some makers designed microscopes that took oblique illumination to rather extreme limits. The classic example is the Ross Radial microscope built by the famous English maker Ross to a design by Wenham. This is a superb example of quality engineering and optics by a respected maker, but a rather bizarre microscope nevertheless. Almost every conceivable plane and axis of the microscope limb, body and substage has the facility to be tilted or rotated (see ref. 2 or similar history of microscopes where this model is often illustrated). An image of this microscope is also in the Moody Medical Library On-line (item 1.031 in catalogue). The technique fell out of favour towards the end of the 19th century as high numerical aperture objectives became available with the ability to resolve the fine detail of diatoms etc. with good axial illumination. A firmer understanding of the requirements for a critical image with axial illumination were also realised. I wasn't sure how well the technique is used nowadays given the many other ways of improving contrast. However, a web search for 'oblique illumination' shows that some of the mainstream microscope makers mention this form of lighting as a feature in some of their models (particularly metallurgical), so presumably it does still have a worthwhile role. The oblique patch stop is certainly a cheap and cheerful way for the amateur to improve contrast for some subjects, especially at medium powers where patch stops for dark-field get trickier to make. I was also intrigued to see that at least one manufacturer, 'Edge', market a microscope with 'patented Multiple Obliquetm Illumination' which apparently gives 3D images. Visit the Edge web site for details and read the theory behind the technique for 3D imaging. Comments on the article to the author Dave Walker welcomed. References 1) 'Under the Microscope' by A. Curry, R. F. Grayson and G. R. Hosey, (Blandford Press, UK, 1982), Chapter 8. Now out of print, but worth looking out for in second-hand bookshops as it gives clear explanations of many techniques and principles, especially the use of polarised light. 2) 'The Microscope Past and Present' by S. Bradbury. Pergamon Press, UK, 1968, pp. 180-183. A compact but thorough overview of the history of the microscope and it's development. Illustrates and discusses the Ross Radial and Ross / Zentmayer microscope and the fad for oblique illumination. Microscopy UK Front Page Micscape Magazine Article Library Text and images © David Walker. © Onview.net Ltd, Microscopy-UK, and all contributors 1995 onwards. All rights reserved. Main site is at www.microscopy-uk.org.uk with full mirror at www.microscopy-uk.net.

References 1) 'Under the Microscope' by A. Curry, R. F. Grayson and G. R. Hosey, (Blandford Press, UK, 1982), Chapter 8. Now out of print, but worth looking out for in second-hand bookshops as it gives clear explanations of many techniques and principles, especially the use of polarised light. 2) 'The Microscope Past and Present' by S. Bradbury. Pergamon Press, UK, 1968, pp. 180-183. A compact but thorough overview of the history of the microscope and it's development. Illustrates and discusses the Ross Radial and Ross / Zentmayer microscope and the fad for oblique illumination. Microscopy UK Front Page Micscape Magazine Article Library Text and images © David Walker. © Onview.net Ltd, Microscopy-UK, and all contributors 1995 onwards. All rights reserved. Main site is at www.microscopy-uk.org.uk with full mirror at www.microscopy-uk.net.

In the late19th century but before the advent of high numerical aperture objectives, oblique illumination was quite popular and some makers developed microscopes especially to exploit the benefits of the technique. One of the first models was shown by Zentmayer of Philadelphia in 1876 at an Exposition in this city. It had a swinging substage, i.e. the whole substage assembly swung about an axis in the same plane as the stage. An image of this microscope is in the Moody Medical Library On-line (item 1.028 in catalogue). (This site illustrates a wonderful selection of historical microscopes from the famous Moody collection, most makers are represented). Some makers designed microscopes that took oblique illumination to rather extreme limits. The classic example is the Ross Radial microscope built by the famous English maker Ross to a design by Wenham. This is a superb example of quality engineering and optics by a respected maker, but a rather bizarre microscope nevertheless. Almost every conceivable plane and axis of the microscope limb, body and substage has the facility to be tilted or rotated (see ref. 2 or similar history of microscopes where this model is often illustrated). An image of this microscope is also in the Moody Medical Library On-line (item 1.031 in catalogue). The technique fell out of favour towards the end of the 19th century as high numerical aperture objectives became available with the ability to resolve the fine detail of diatoms etc. with good axial illumination. A firmer understanding of the requirements for a critical image with axial illumination were also realised. I wasn't sure how well the technique is used nowadays given the many other ways of improving contrast. However, a web search for 'oblique illumination' shows that some of the mainstream microscope makers mention this form of lighting as a feature in some of their models (particularly metallurgical), so presumably it does still have a worthwhile role. The oblique patch stop is certainly a cheap and cheerful way for the amateur to improve contrast for some subjects, especially at medium powers where patch stops for dark-field get trickier to make. I was also intrigued to see that at least one manufacturer, 'Edge', market a microscope with 'patented Multiple Obliquetm Illumination' which apparently gives 3D images. Visit the Edge web site for details and read the theory behind the technique for 3D imaging. Comments on the article to the author Dave Walker welcomed. References 1) 'Under the Microscope' by A. Curry, R. F. Grayson and G. R. Hosey, (Blandford Press, UK, 1982), Chapter 8. Now out of print, but worth looking out for in second-hand bookshops as it gives clear explanations of many techniques and principles, especially the use of polarised light. 2) 'The Microscope Past and Present' by S. Bradbury. Pergamon Press, UK, 1968, pp. 180-183. A compact but thorough overview of the history of the microscope and it's development. Illustrates and discusses the Ross Radial and Ross / Zentmayer microscope and the fad for oblique illumination. Microscopy UK Front Page Micscape Magazine Article Library Text and images © David Walker. © Onview.net Ltd, Microscopy-UK, and all contributors 1995 onwards. All rights reserved. Main site is at www.microscopy-uk.org.uk with full mirror at www.microscopy-uk.net.

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You may need to experiment with the size of the notch for a given objective. The orientation of the notch with respect to the subject should also be changed to see what achieves the best effect. If you have a rotating stage this is easier than rotating the patch stop in the filter tray. If the filter tray is a swing out type, also experiment with the extent the filter is swung in, as well as varying the orientation of the notch in the filter tray. Condenser with oblique illumination Buying a condenser specifically for oblique illumination is probably not justified, but this is a feature found in some condensers. My Russian Biolam microscope is supplied with a modest Abbe condenser, but for critical work I use the better quality Russian aplanatic condenser (N.A. 1.4). As a bonus this also has an oblique illumination feature, see image right. (Supplementary low power lens N.A. 0.3 also shown). The iris can be moved up to 10mm off-axis in opposite directions, which also rotates in the mount to change the orientation of the light to the subject. The latter feature, as mentioned above for the oblique patch stop, is important as the off-axis lighting often works best in a specific orientation to a subject e.g. for non-symmetric diatoms like Pleurosigma. Historical footnote In the late19th century but before the advent of high numerical aperture objectives, oblique illumination was quite popular and some makers developed microscopes especially to exploit the benefits of the technique. One of the first models was shown by Zentmayer of Philadelphia in 1876 at an Exposition in this city. It had a swinging substage, i.e. the whole substage assembly swung about an axis in the same plane as the stage. An image of this microscope is in the Moody Medical Library On-line (item 1.028 in catalogue). (This site illustrates a wonderful selection of historical microscopes from the famous Moody collection, most makers are represented). Some makers designed microscopes that took oblique illumination to rather extreme limits. The classic example is the Ross Radial microscope built by the famous English maker Ross to a design by Wenham. This is a superb example of quality engineering and optics by a respected maker, but a rather bizarre microscope nevertheless. Almost every conceivable plane and axis of the microscope limb, body and substage has the facility to be tilted or rotated (see ref. 2 or similar history of microscopes where this model is often illustrated). An image of this microscope is also in the Moody Medical Library On-line (item 1.031 in catalogue). The technique fell out of favour towards the end of the 19th century as high numerical aperture objectives became available with the ability to resolve the fine detail of diatoms etc. with good axial illumination. A firmer understanding of the requirements for a critical image with axial illumination were also realised. I wasn't sure how well the technique is used nowadays given the many other ways of improving contrast. However, a web search for 'oblique illumination' shows that some of the mainstream microscope makers mention this form of lighting as a feature in some of their models (particularly metallurgical), so presumably it does still have a worthwhile role. The oblique patch stop is certainly a cheap and cheerful way for the amateur to improve contrast for some subjects, especially at medium powers where patch stops for dark-field get trickier to make. I was also intrigued to see that at least one manufacturer, 'Edge', market a microscope with 'patented Multiple Obliquetm Illumination' which apparently gives 3D images. Visit the Edge web site for details and read the theory behind the technique for 3D imaging. Comments on the article to the author Dave Walker welcomed. References 1) 'Under the Microscope' by A. Curry, R. F. Grayson and G. R. Hosey, (Blandford Press, UK, 1982), Chapter 8. Now out of print, but worth looking out for in second-hand bookshops as it gives clear explanations of many techniques and principles, especially the use of polarised light. 2) 'The Microscope Past and Present' by S. Bradbury. Pergamon Press, UK, 1968, pp. 180-183. A compact but thorough overview of the history of the microscope and it's development. Illustrates and discusses the Ross Radial and Ross / Zentmayer microscope and the fad for oblique illumination. Microscopy UK Front Page Micscape Magazine Article Library Text and images © David Walker. © Onview.net Ltd, Microscopy-UK, and all contributors 1995 onwards. All rights reserved. Main site is at www.microscopy-uk.org.uk with full mirror at www.microscopy-uk.net.

Oblique illumination also works well on single cells such as protozoa. One book I referred to (ref. 1) illustrates that the internal vacuoles are particularly distinctive in this sort of illumination. If you haven't tried the technique, how can it be achieved? A few methods are given below. Knock the mirror! As commented above, if you have a microscope with a mirror, moving the mirror (plane side) so that light is shone off-axis can achieve the effect. This one of the few techniques for improving contrast that the owner of a simple microscope without a condenser can achieve i.e. unlike dark-field or phase contrast. I first spotted the effect myself as a ten year old with a no-frills toy microscope, and I got into the habit of rocking the mirror on its axis when studying transparent live pond-life to see if more details were revealed. Simple stop for the condenser filter tray If you have a condenser and filter tray, a simple stop can be made as shown left. Just cut out a piece of opaque card to fit the filter tray and experiment with various sizes of sector cut out of the disc for a given objective to allow light from an angle to reach the subject. Normal axial illumination should be setup first. As for dark field, the condenser iris should be fully open and the condenser focus adjusted to get the best effect. You may need to experiment with the size of the notch for a given objective. The orientation of the notch with respect to the subject should also be changed to see what achieves the best effect. If you have a rotating stage this is easier than rotating the patch stop in the filter tray. If the filter tray is a swing out type, also experiment with the extent the filter is swung in, as well as varying the orientation of the notch in the filter tray. Condenser with oblique illumination Buying a condenser specifically for oblique illumination is probably not justified, but this is a feature found in some condensers. My Russian Biolam microscope is supplied with a modest Abbe condenser, but for critical work I use the better quality Russian aplanatic condenser (N.A. 1.4). As a bonus this also has an oblique illumination feature, see image right. (Supplementary low power lens N.A. 0.3 also shown). The iris can be moved up to 10mm off-axis in opposite directions, which also rotates in the mount to change the orientation of the light to the subject. The latter feature, as mentioned above for the oblique patch stop, is important as the off-axis lighting often works best in a specific orientation to a subject e.g. for non-symmetric diatoms like Pleurosigma. Historical footnote In the late19th century but before the advent of high numerical aperture objectives, oblique illumination was quite popular and some makers developed microscopes especially to exploit the benefits of the technique. One of the first models was shown by Zentmayer of Philadelphia in 1876 at an Exposition in this city. It had a swinging substage, i.e. the whole substage assembly swung about an axis in the same plane as the stage. An image of this microscope is in the Moody Medical Library On-line (item 1.028 in catalogue). (This site illustrates a wonderful selection of historical microscopes from the famous Moody collection, most makers are represented). Some makers designed microscopes that took oblique illumination to rather extreme limits. The classic example is the Ross Radial microscope built by the famous English maker Ross to a design by Wenham. This is a superb example of quality engineering and optics by a respected maker, but a rather bizarre microscope nevertheless. Almost every conceivable plane and axis of the microscope limb, body and substage has the facility to be tilted or rotated (see ref. 2 or similar history of microscopes where this model is often illustrated). An image of this microscope is also in the Moody Medical Library On-line (item 1.031 in catalogue). The technique fell out of favour towards the end of the 19th century as high numerical aperture objectives became available with the ability to resolve the fine detail of diatoms etc. with good axial illumination. A firmer understanding of the requirements for a critical image with axial illumination were also realised. I wasn't sure how well the technique is used nowadays given the many other ways of improving contrast. However, a web search for 'oblique illumination' shows that some of the mainstream microscope makers mention this form of lighting as a feature in some of their models (particularly metallurgical), so presumably it does still have a worthwhile role. The oblique patch stop is certainly a cheap and cheerful way for the amateur to improve contrast for some subjects, especially at medium powers where patch stops for dark-field get trickier to make. I was also intrigued to see that at least one manufacturer, 'Edge', market a microscope with 'patented Multiple Obliquetm Illumination' which apparently gives 3D images. Visit the Edge web site for details and read the theory behind the technique for 3D imaging. Comments on the article to the author Dave Walker welcomed. References 1) 'Under the Microscope' by A. Curry, R. F. Grayson and G. R. Hosey, (Blandford Press, UK, 1982), Chapter 8. Now out of print, but worth looking out for in second-hand bookshops as it gives clear explanations of many techniques and principles, especially the use of polarised light. 2) 'The Microscope Past and Present' by S. Bradbury. Pergamon Press, UK, 1968, pp. 180-183. A compact but thorough overview of the history of the microscope and it's development. Illustrates and discusses the Ross Radial and Ross / Zentmayer microscope and the fad for oblique illumination. Microscopy UK Front Page Micscape Magazine Article Library Text and images © David Walker. © Onview.net Ltd, Microscopy-UK, and all contributors 1995 onwards. All rights reserved. Main site is at www.microscopy-uk.org.uk with full mirror at www.microscopy-uk.net.

Simple stop for the condenser filter tray If you have a condenser and filter tray, a simple stop can be made as shown left. Just cut out a piece of opaque card to fit the filter tray and experiment with various sizes of sector cut out of the disc for a given objective to allow light from an angle to reach the subject. Normal axial illumination should be setup first. As for dark field, the condenser iris should be fully open and the condenser focus adjusted to get the best effect. You may need to experiment with the size of the notch for a given objective. The orientation of the notch with respect to the subject should also be changed to see what achieves the best effect. If you have a rotating stage this is easier than rotating the patch stop in the filter tray. If the filter tray is a swing out type, also experiment with the extent the filter is swung in, as well as varying the orientation of the notch in the filter tray. Condenser with oblique illumination Buying a condenser specifically for oblique illumination is probably not justified, but this is a feature found in some condensers. My Russian Biolam microscope is supplied with a modest Abbe condenser, but for critical work I use the better quality Russian aplanatic condenser (N.A. 1.4). As a bonus this also has an oblique illumination feature, see image right. (Supplementary low power lens N.A. 0.3 also shown). The iris can be moved up to 10mm off-axis in opposite directions, which also rotates in the mount to change the orientation of the light to the subject. The latter feature, as mentioned above for the oblique patch stop, is important as the off-axis lighting often works best in a specific orientation to a subject e.g. for non-symmetric diatoms like Pleurosigma. Historical footnote In the late19th century but before the advent of high numerical aperture objectives, oblique illumination was quite popular and some makers developed microscopes especially to exploit the benefits of the technique. One of the first models was shown by Zentmayer of Philadelphia in 1876 at an Exposition in this city. It had a swinging substage, i.e. the whole substage assembly swung about an axis in the same plane as the stage. An image of this microscope is in the Moody Medical Library On-line (item 1.028 in catalogue). (This site illustrates a wonderful selection of historical microscopes from the famous Moody collection, most makers are represented). Some makers designed microscopes that took oblique illumination to rather extreme limits. The classic example is the Ross Radial microscope built by the famous English maker Ross to a design by Wenham. This is a superb example of quality engineering and optics by a respected maker, but a rather bizarre microscope nevertheless. Almost every conceivable plane and axis of the microscope limb, body and substage has the facility to be tilted or rotated (see ref. 2 or similar history of microscopes where this model is often illustrated). An image of this microscope is also in the Moody Medical Library On-line (item 1.031 in catalogue). The technique fell out of favour towards the end of the 19th century as high numerical aperture objectives became available with the ability to resolve the fine detail of diatoms etc. with good axial illumination. A firmer understanding of the requirements for a critical image with axial illumination were also realised. I wasn't sure how well the technique is used nowadays given the many other ways of improving contrast. However, a web search for 'oblique illumination' shows that some of the mainstream microscope makers mention this form of lighting as a feature in some of their models (particularly metallurgical), so presumably it does still have a worthwhile role. The oblique patch stop is certainly a cheap and cheerful way for the amateur to improve contrast for some subjects, especially at medium powers where patch stops for dark-field get trickier to make. I was also intrigued to see that at least one manufacturer, 'Edge', market a microscope with 'patented Multiple Obliquetm Illumination' which apparently gives 3D images. Visit the Edge web site for details and read the theory behind the technique for 3D imaging. Comments on the article to the author Dave Walker welcomed. References 1) 'Under the Microscope' by A. Curry, R. F. Grayson and G. R. Hosey, (Blandford Press, UK, 1982), Chapter 8. Now out of print, but worth looking out for in second-hand bookshops as it gives clear explanations of many techniques and principles, especially the use of polarised light. 2) 'The Microscope Past and Present' by S. Bradbury. Pergamon Press, UK, 1968, pp. 180-183. A compact but thorough overview of the history of the microscope and it's development. Illustrates and discusses the Ross Radial and Ross / Zentmayer microscope and the fad for oblique illumination. Microscopy UK Front Page Micscape Magazine Article Library Text and images © David Walker. © Onview.net Ltd, Microscopy-UK, and all contributors 1995 onwards. All rights reserved. Main site is at www.microscopy-uk.org.uk with full mirror at www.microscopy-uk.net.

If, like the author, you own a microscope with a mirror for external lighting, you may well have accidentally discovered the benefit of oblique illumination for studying some subjects. Microscope mirrors are occasionally knocked out of alignment at some stage during viewing, with the result that the subject is lit with an off-axis light source. This oblique illumination is in fact a useful way of improving the visibility of some low contrast subjects like protozoa and the details on diatoms. Essentially oblique illumination works by accentuating any phase gradients within a transparent specimen. It's an easy form of lighting to achieve up to medium powers (e.g. 40x objectives) with most microscopes with or without a mirror, and is a 'cheap and cheerful' technique the amateur can use to improve visibility when studying low contrast subjects, especially if you're not fortunate enough to possess phase contrast or high power dark field illumination. To illustrate its effect, the image right shows part of the classic diatom Pleurosigma angulatum using a 40x achromatic objective (Russian, NA 0.65 dry). This is one of the cheapest 40x objectives you can buy, but is perfectly capable of resolving the dots i.e. the fine detail on the silica shell, but in normal brightfield this detail is quite difficult to see. Only the central 'raphe' (on the right of the image) and an edge of the diatom frustule at the left can be made out. It's not resolution that's the problem, it's contrast. If the diatom is studied with an oblique patch stop in the filter tray (see below) the image right is seen. The dots which are fine markings on the diatom frustule are now clearly seen. (Incidentally I have to push my ancient image capture card to the limit to capture these sort of images, so they are a lot less convincing than the visual image down the microscope). It's also possible to resolve the dots under dark-field with this objective, but I have never found using home-made patch stops for a 40X dry objective very easy and have achieved less than successful dark-field, so oblique illumination is an easier alternative to improve contrast. In a second example, the image left and right shows the classic epithelial cells taken by scraping the inside of the cheek lightly with the finger nail and mounting the saliva under a cover slip (again using the 40x dry objective). The image left is in brightfield with the iris stopped down more than normal to improve contrast - it's an acceptable image but rather flat. The same view with the oblique patch stop gives a very pleasing depth to the cell especially the nucleus, cell granules and folding of the cell (again, the visual image is a lot clearer than in the captured image). Oblique illumination also works well on single cells such as protozoa. One book I referred to (ref. 1) illustrates that the internal vacuoles are particularly distinctive in this sort of illumination. If you haven't tried the technique, how can it be achieved? A few methods are given below. Knock the mirror! As commented above, if you have a microscope with a mirror, moving the mirror (plane side) so that light is shone off-axis can achieve the effect. This one of the few techniques for improving contrast that the owner of a simple microscope without a condenser can achieve i.e. unlike dark-field or phase contrast. I first spotted the effect myself as a ten year old with a no-frills toy microscope, and I got into the habit of rocking the mirror on its axis when studying transparent live pond-life to see if more details were revealed. Simple stop for the condenser filter tray If you have a condenser and filter tray, a simple stop can be made as shown left. Just cut out a piece of opaque card to fit the filter tray and experiment with various sizes of sector cut out of the disc for a given objective to allow light from an angle to reach the subject. Normal axial illumination should be setup first. As for dark field, the condenser iris should be fully open and the condenser focus adjusted to get the best effect. You may need to experiment with the size of the notch for a given objective. The orientation of the notch with respect to the subject should also be changed to see what achieves the best effect. If you have a rotating stage this is easier than rotating the patch stop in the filter tray. If the filter tray is a swing out type, also experiment with the extent the filter is swung in, as well as varying the orientation of the notch in the filter tray. Condenser with oblique illumination Buying a condenser specifically for oblique illumination is probably not justified, but this is a feature found in some condensers. My Russian Biolam microscope is supplied with a modest Abbe condenser, but for critical work I use the better quality Russian aplanatic condenser (N.A. 1.4). As a bonus this also has an oblique illumination feature, see image right. (Supplementary low power lens N.A. 0.3 also shown). The iris can be moved up to 10mm off-axis in opposite directions, which also rotates in the mount to change the orientation of the light to the subject. The latter feature, as mentioned above for the oblique patch stop, is important as the off-axis lighting often works best in a specific orientation to a subject e.g. for non-symmetric diatoms like Pleurosigma. Historical footnote In the late19th century but before the advent of high numerical aperture objectives, oblique illumination was quite popular and some makers developed microscopes especially to exploit the benefits of the technique. One of the first models was shown by Zentmayer of Philadelphia in 1876 at an Exposition in this city. It had a swinging substage, i.e. the whole substage assembly swung about an axis in the same plane as the stage. An image of this microscope is in the Moody Medical Library On-line (item 1.028 in catalogue). (This site illustrates a wonderful selection of historical microscopes from the famous Moody collection, most makers are represented). Some makers designed microscopes that took oblique illumination to rather extreme limits. The classic example is the Ross Radial microscope built by the famous English maker Ross to a design by Wenham. This is a superb example of quality engineering and optics by a respected maker, but a rather bizarre microscope nevertheless. Almost every conceivable plane and axis of the microscope limb, body and substage has the facility to be tilted or rotated (see ref. 2 or similar history of microscopes where this model is often illustrated). An image of this microscope is also in the Moody Medical Library On-line (item 1.031 in catalogue). The technique fell out of favour towards the end of the 19th century as high numerical aperture objectives became available with the ability to resolve the fine detail of diatoms etc. with good axial illumination. A firmer understanding of the requirements for a critical image with axial illumination were also realised. I wasn't sure how well the technique is used nowadays given the many other ways of improving contrast. However, a web search for 'oblique illumination' shows that some of the mainstream microscope makers mention this form of lighting as a feature in some of their models (particularly metallurgical), so presumably it does still have a worthwhile role. The oblique patch stop is certainly a cheap and cheerful way for the amateur to improve contrast for some subjects, especially at medium powers where patch stops for dark-field get trickier to make. I was also intrigued to see that at least one manufacturer, 'Edge', market a microscope with 'patented Multiple Obliquetm Illumination' which apparently gives 3D images. Visit the Edge web site for details and read the theory behind the technique for 3D imaging. Comments on the article to the author Dave Walker welcomed. References 1) 'Under the Microscope' by A. Curry, R. F. Grayson and G. R. Hosey, (Blandford Press, UK, 1982), Chapter 8. Now out of print, but worth looking out for in second-hand bookshops as it gives clear explanations of many techniques and principles, especially the use of polarised light. 2) 'The Microscope Past and Present' by S. Bradbury. Pergamon Press, UK, 1968, pp. 180-183. A compact but thorough overview of the history of the microscope and it's development. Illustrates and discusses the Ross Radial and Ross / Zentmayer microscope and the fad for oblique illumination. Microscopy UK Front Page Micscape Magazine Article Library Text and images © David Walker. © Onview.net Ltd, Microscopy-UK, and all contributors 1995 onwards. All rights reserved. Main site is at www.microscopy-uk.org.uk with full mirror at www.microscopy-uk.net.

The iris can be moved up to 10mm off-axis in opposite directions, which also rotates in the mount to change the orientation of the light to the subject. The latter feature, as mentioned above for the oblique patch stop, is important as the off-axis lighting often works best in a specific orientation to a subject e.g. for non-symmetric diatoms like Pleurosigma. Historical footnote In the late19th century but before the advent of high numerical aperture objectives, oblique illumination was quite popular and some makers developed microscopes especially to exploit the benefits of the technique. One of the first models was shown by Zentmayer of Philadelphia in 1876 at an Exposition in this city. It had a swinging substage, i.e. the whole substage assembly swung about an axis in the same plane as the stage. An image of this microscope is in the Moody Medical Library On-line (item 1.028 in catalogue). (This site illustrates a wonderful selection of historical microscopes from the famous Moody collection, most makers are represented). Some makers designed microscopes that took oblique illumination to rather extreme limits. The classic example is the Ross Radial microscope built by the famous English maker Ross to a design by Wenham. This is a superb example of quality engineering and optics by a respected maker, but a rather bizarre microscope nevertheless. Almost every conceivable plane and axis of the microscope limb, body and substage has the facility to be tilted or rotated (see ref. 2 or similar history of microscopes where this model is often illustrated). An image of this microscope is also in the Moody Medical Library On-line (item 1.031 in catalogue). The technique fell out of favour towards the end of the 19th century as high numerical aperture objectives became available with the ability to resolve the fine detail of diatoms etc. with good axial illumination. A firmer understanding of the requirements for a critical image with axial illumination were also realised. I wasn't sure how well the technique is used nowadays given the many other ways of improving contrast. However, a web search for 'oblique illumination' shows that some of the mainstream microscope makers mention this form of lighting as a feature in some of their models (particularly metallurgical), so presumably it does still have a worthwhile role. The oblique patch stop is certainly a cheap and cheerful way for the amateur to improve contrast for some subjects, especially at medium powers where patch stops for dark-field get trickier to make. I was also intrigued to see that at least one manufacturer, 'Edge', market a microscope with 'patented Multiple Obliquetm Illumination' which apparently gives 3D images. Visit the Edge web site for details and read the theory behind the technique for 3D imaging. Comments on the article to the author Dave Walker welcomed. References 1) 'Under the Microscope' by A. Curry, R. F. Grayson and G. R. Hosey, (Blandford Press, UK, 1982), Chapter 8. Now out of print, but worth looking out for in second-hand bookshops as it gives clear explanations of many techniques and principles, especially the use of polarised light. 2) 'The Microscope Past and Present' by S. Bradbury. Pergamon Press, UK, 1968, pp. 180-183. A compact but thorough overview of the history of the microscope and it's development. Illustrates and discusses the Ross Radial and Ross / Zentmayer microscope and the fad for oblique illumination. Microscopy UK Front Page Micscape Magazine Article Library Text and images © David Walker. © Onview.net Ltd, Microscopy-UK, and all contributors 1995 onwards. All rights reserved. Main site is at www.microscopy-uk.org.uk with full mirror at www.microscopy-uk.net.

A CPL offers more versatility and works better with digital cameras. Both linear and circular polarizers look the same, and they both do the same thing – reduce reflections on non-metallic surfaces such as water, glass and wet surfaces, and they increase colour saturation too. A CPL filter is essentially a linear polariser with an extra glass element that allows you to adjust your lens filter to block polarised light from different directions.

Urth Circular Polarizing Filters (CPL Filters) cut reflections, boost colour saturation and increase ... Read more Read less

It's also possible to resolve the dots under dark-field with this objective, but I have never found using home-made patch stops for a 40X dry objective very easy and have achieved less than successful dark-field, so oblique illumination is an easier alternative to improve contrast. In a second example, the image left and right shows the classic epithelial cells taken by scraping the inside of the cheek lightly with the finger nail and mounting the saliva under a cover slip (again using the 40x dry objective). The image left is in brightfield with the iris stopped down more than normal to improve contrast - it's an acceptable image but rather flat. The same view with the oblique patch stop gives a very pleasing depth to the cell especially the nucleus, cell granules and folding of the cell (again, the visual image is a lot clearer than in the captured image). Oblique illumination also works well on single cells such as protozoa. One book I referred to (ref. 1) illustrates that the internal vacuoles are particularly distinctive in this sort of illumination. If you haven't tried the technique, how can it be achieved? A few methods are given below. Knock the mirror! As commented above, if you have a microscope with a mirror, moving the mirror (plane side) so that light is shone off-axis can achieve the effect. This one of the few techniques for improving contrast that the owner of a simple microscope without a condenser can achieve i.e. unlike dark-field or phase contrast. I first spotted the effect myself as a ten year old with a no-frills toy microscope, and I got into the habit of rocking the mirror on its axis when studying transparent live pond-life to see if more details were revealed. Simple stop for the condenser filter tray If you have a condenser and filter tray, a simple stop can be made as shown left. Just cut out a piece of opaque card to fit the filter tray and experiment with various sizes of sector cut out of the disc for a given objective to allow light from an angle to reach the subject. Normal axial illumination should be setup first. As for dark field, the condenser iris should be fully open and the condenser focus adjusted to get the best effect. You may need to experiment with the size of the notch for a given objective. The orientation of the notch with respect to the subject should also be changed to see what achieves the best effect. If you have a rotating stage this is easier than rotating the patch stop in the filter tray. If the filter tray is a swing out type, also experiment with the extent the filter is swung in, as well as varying the orientation of the notch in the filter tray. Condenser with oblique illumination Buying a condenser specifically for oblique illumination is probably not justified, but this is a feature found in some condensers. My Russian Biolam microscope is supplied with a modest Abbe condenser, but for critical work I use the better quality Russian aplanatic condenser (N.A. 1.4). As a bonus this also has an oblique illumination feature, see image right. (Supplementary low power lens N.A. 0.3 also shown). The iris can be moved up to 10mm off-axis in opposite directions, which also rotates in the mount to change the orientation of the light to the subject. The latter feature, as mentioned above for the oblique patch stop, is important as the off-axis lighting often works best in a specific orientation to a subject e.g. for non-symmetric diatoms like Pleurosigma. Historical footnote In the late19th century but before the advent of high numerical aperture objectives, oblique illumination was quite popular and some makers developed microscopes especially to exploit the benefits of the technique. One of the first models was shown by Zentmayer of Philadelphia in 1876 at an Exposition in this city. It had a swinging substage, i.e. the whole substage assembly swung about an axis in the same plane as the stage. An image of this microscope is in the Moody Medical Library On-line (item 1.028 in catalogue). (This site illustrates a wonderful selection of historical microscopes from the famous Moody collection, most makers are represented). Some makers designed microscopes that took oblique illumination to rather extreme limits. The classic example is the Ross Radial microscope built by the famous English maker Ross to a design by Wenham. This is a superb example of quality engineering and optics by a respected maker, but a rather bizarre microscope nevertheless. Almost every conceivable plane and axis of the microscope limb, body and substage has the facility to be tilted or rotated (see ref. 2 or similar history of microscopes where this model is often illustrated). An image of this microscope is also in the Moody Medical Library On-line (item 1.031 in catalogue). The technique fell out of favour towards the end of the 19th century as high numerical aperture objectives became available with the ability to resolve the fine detail of diatoms etc. with good axial illumination. A firmer understanding of the requirements for a critical image with axial illumination were also realised. I wasn't sure how well the technique is used nowadays given the many other ways of improving contrast. However, a web search for 'oblique illumination' shows that some of the mainstream microscope makers mention this form of lighting as a feature in some of their models (particularly metallurgical), so presumably it does still have a worthwhile role. The oblique patch stop is certainly a cheap and cheerful way for the amateur to improve contrast for some subjects, especially at medium powers where patch stops for dark-field get trickier to make. I was also intrigued to see that at least one manufacturer, 'Edge', market a microscope with 'patented Multiple Obliquetm Illumination' which apparently gives 3D images. Visit the Edge web site for details and read the theory behind the technique for 3D imaging. Comments on the article to the author Dave Walker welcomed. References 1) 'Under the Microscope' by A. Curry, R. F. Grayson and G. R. Hosey, (Blandford Press, UK, 1982), Chapter 8. Now out of print, but worth looking out for in second-hand bookshops as it gives clear explanations of many techniques and principles, especially the use of polarised light. 2) 'The Microscope Past and Present' by S. Bradbury. Pergamon Press, UK, 1968, pp. 180-183. A compact but thorough overview of the history of the microscope and it's development. Illustrates and discusses the Ross Radial and Ross / Zentmayer microscope and the fad for oblique illumination. Microscopy UK Front Page Micscape Magazine Article Library Text and images © David Walker. © Onview.net Ltd, Microscopy-UK, and all contributors 1995 onwards. All rights reserved. Main site is at www.microscopy-uk.org.uk with full mirror at www.microscopy-uk.net.

Polarizing filters Physics

Microscopy UK Front Page Micscape Magazine Article Library Text and images © David Walker. © Onview.net Ltd, Microscopy-UK, and all contributors 1995 onwards. All rights reserved. Main site is at www.microscopy-uk.org.uk with full mirror at www.microscopy-uk.net.

Comments on the article to the author Dave Walker welcomed. References 1) 'Under the Microscope' by A. Curry, R. F. Grayson and G. R. Hosey, (Blandford Press, UK, 1982), Chapter 8. Now out of print, but worth looking out for in second-hand bookshops as it gives clear explanations of many techniques and principles, especially the use of polarised light. 2) 'The Microscope Past and Present' by S. Bradbury. Pergamon Press, UK, 1968, pp. 180-183. A compact but thorough overview of the history of the microscope and it's development. Illustrates and discusses the Ross Radial and Ross / Zentmayer microscope and the fad for oblique illumination. Microscopy UK Front Page Micscape Magazine Article Library Text and images © David Walker. © Onview.net Ltd, Microscopy-UK, and all contributors 1995 onwards. All rights reserved. Main site is at www.microscopy-uk.org.uk with full mirror at www.microscopy-uk.net.

A brief survey of the benefits of using off-axis lighting to view some subjects, and how it can be easily accomplished without cost for most microscopes. Also a look at some rather bizarre 19th century microscopes which took the use of oblique illumination a bit too far!

In a second example, the image left and right shows the classic epithelial cells taken by scraping the inside of the cheek lightly with the finger nail and mounting the saliva under a cover slip (again using the 40x dry objective). The image left is in brightfield with the iris stopped down more than normal to improve contrast - it's an acceptable image but rather flat. The same view with the oblique patch stop gives a very pleasing depth to the cell especially the nucleus, cell granules and folding of the cell (again, the visual image is a lot clearer than in the captured image). Oblique illumination also works well on single cells such as protozoa. One book I referred to (ref. 1) illustrates that the internal vacuoles are particularly distinctive in this sort of illumination. If you haven't tried the technique, how can it be achieved? A few methods are given below. Knock the mirror! As commented above, if you have a microscope with a mirror, moving the mirror (plane side) so that light is shone off-axis can achieve the effect. This one of the few techniques for improving contrast that the owner of a simple microscope without a condenser can achieve i.e. unlike dark-field or phase contrast. I first spotted the effect myself as a ten year old with a no-frills toy microscope, and I got into the habit of rocking the mirror on its axis when studying transparent live pond-life to see if more details were revealed. Simple stop for the condenser filter tray If you have a condenser and filter tray, a simple stop can be made as shown left. Just cut out a piece of opaque card to fit the filter tray and experiment with various sizes of sector cut out of the disc for a given objective to allow light from an angle to reach the subject. Normal axial illumination should be setup first. As for dark field, the condenser iris should be fully open and the condenser focus adjusted to get the best effect. You may need to experiment with the size of the notch for a given objective. The orientation of the notch with respect to the subject should also be changed to see what achieves the best effect. If you have a rotating stage this is easier than rotating the patch stop in the filter tray. If the filter tray is a swing out type, also experiment with the extent the filter is swung in, as well as varying the orientation of the notch in the filter tray. Condenser with oblique illumination Buying a condenser specifically for oblique illumination is probably not justified, but this is a feature found in some condensers. My Russian Biolam microscope is supplied with a modest Abbe condenser, but for critical work I use the better quality Russian aplanatic condenser (N.A. 1.4). As a bonus this also has an oblique illumination feature, see image right. (Supplementary low power lens N.A. 0.3 also shown). The iris can be moved up to 10mm off-axis in opposite directions, which also rotates in the mount to change the orientation of the light to the subject. The latter feature, as mentioned above for the oblique patch stop, is important as the off-axis lighting often works best in a specific orientation to a subject e.g. for non-symmetric diatoms like Pleurosigma. Historical footnote In the late19th century but before the advent of high numerical aperture objectives, oblique illumination was quite popular and some makers developed microscopes especially to exploit the benefits of the technique. One of the first models was shown by Zentmayer of Philadelphia in 1876 at an Exposition in this city. It had a swinging substage, i.e. the whole substage assembly swung about an axis in the same plane as the stage. An image of this microscope is in the Moody Medical Library On-line (item 1.028 in catalogue). (This site illustrates a wonderful selection of historical microscopes from the famous Moody collection, most makers are represented). Some makers designed microscopes that took oblique illumination to rather extreme limits. The classic example is the Ross Radial microscope built by the famous English maker Ross to a design by Wenham. This is a superb example of quality engineering and optics by a respected maker, but a rather bizarre microscope nevertheless. Almost every conceivable plane and axis of the microscope limb, body and substage has the facility to be tilted or rotated (see ref. 2 or similar history of microscopes where this model is often illustrated). An image of this microscope is also in the Moody Medical Library On-line (item 1.031 in catalogue). The technique fell out of favour towards the end of the 19th century as high numerical aperture objectives became available with the ability to resolve the fine detail of diatoms etc. with good axial illumination. A firmer understanding of the requirements for a critical image with axial illumination were also realised. I wasn't sure how well the technique is used nowadays given the many other ways of improving contrast. However, a web search for 'oblique illumination' shows that some of the mainstream microscope makers mention this form of lighting as a feature in some of their models (particularly metallurgical), so presumably it does still have a worthwhile role. The oblique patch stop is certainly a cheap and cheerful way for the amateur to improve contrast for some subjects, especially at medium powers where patch stops for dark-field get trickier to make. I was also intrigued to see that at least one manufacturer, 'Edge', market a microscope with 'patented Multiple Obliquetm Illumination' which apparently gives 3D images. Visit the Edge web site for details and read the theory behind the technique for 3D imaging. Comments on the article to the author Dave Walker welcomed. References 1) 'Under the Microscope' by A. Curry, R. F. Grayson and G. R. Hosey, (Blandford Press, UK, 1982), Chapter 8. Now out of print, but worth looking out for in second-hand bookshops as it gives clear explanations of many techniques and principles, especially the use of polarised light. 2) 'The Microscope Past and Present' by S. Bradbury. Pergamon Press, UK, 1968, pp. 180-183. A compact but thorough overview of the history of the microscope and it's development. Illustrates and discusses the Ross Radial and Ross / Zentmayer microscope and the fad for oblique illumination. Microscopy UK Front Page Micscape Magazine Article Library Text and images © David Walker. © Onview.net Ltd, Microscopy-UK, and all contributors 1995 onwards. All rights reserved. Main site is at www.microscopy-uk.org.uk with full mirror at www.microscopy-uk.net.

PolarizingFilterSheet

Knock the mirror! As commented above, if you have a microscope with a mirror, moving the mirror (plane side) so that light is shone off-axis can achieve the effect. This one of the few techniques for improving contrast that the owner of a simple microscope without a condenser can achieve i.e. unlike dark-field or phase contrast. I first spotted the effect myself as a ten year old with a no-frills toy microscope, and I got into the habit of rocking the mirror on its axis when studying transparent live pond-life to see if more details were revealed. Simple stop for the condenser filter tray If you have a condenser and filter tray, a simple stop can be made as shown left. Just cut out a piece of opaque card to fit the filter tray and experiment with various sizes of sector cut out of the disc for a given objective to allow light from an angle to reach the subject. Normal axial illumination should be setup first. As for dark field, the condenser iris should be fully open and the condenser focus adjusted to get the best effect. You may need to experiment with the size of the notch for a given objective. The orientation of the notch with respect to the subject should also be changed to see what achieves the best effect. If you have a rotating stage this is easier than rotating the patch stop in the filter tray. If the filter tray is a swing out type, also experiment with the extent the filter is swung in, as well as varying the orientation of the notch in the filter tray. Condenser with oblique illumination Buying a condenser specifically for oblique illumination is probably not justified, but this is a feature found in some condensers. My Russian Biolam microscope is supplied with a modest Abbe condenser, but for critical work I use the better quality Russian aplanatic condenser (N.A. 1.4). As a bonus this also has an oblique illumination feature, see image right. (Supplementary low power lens N.A. 0.3 also shown). The iris can be moved up to 10mm off-axis in opposite directions, which also rotates in the mount to change the orientation of the light to the subject. The latter feature, as mentioned above for the oblique patch stop, is important as the off-axis lighting often works best in a specific orientation to a subject e.g. for non-symmetric diatoms like Pleurosigma. Historical footnote In the late19th century but before the advent of high numerical aperture objectives, oblique illumination was quite popular and some makers developed microscopes especially to exploit the benefits of the technique. One of the first models was shown by Zentmayer of Philadelphia in 1876 at an Exposition in this city. It had a swinging substage, i.e. the whole substage assembly swung about an axis in the same plane as the stage. An image of this microscope is in the Moody Medical Library On-line (item 1.028 in catalogue). (This site illustrates a wonderful selection of historical microscopes from the famous Moody collection, most makers are represented). Some makers designed microscopes that took oblique illumination to rather extreme limits. The classic example is the Ross Radial microscope built by the famous English maker Ross to a design by Wenham. This is a superb example of quality engineering and optics by a respected maker, but a rather bizarre microscope nevertheless. Almost every conceivable plane and axis of the microscope limb, body and substage has the facility to be tilted or rotated (see ref. 2 or similar history of microscopes where this model is often illustrated). An image of this microscope is also in the Moody Medical Library On-line (item 1.031 in catalogue). The technique fell out of favour towards the end of the 19th century as high numerical aperture objectives became available with the ability to resolve the fine detail of diatoms etc. with good axial illumination. A firmer understanding of the requirements for a critical image with axial illumination were also realised. I wasn't sure how well the technique is used nowadays given the many other ways of improving contrast. However, a web search for 'oblique illumination' shows that some of the mainstream microscope makers mention this form of lighting as a feature in some of their models (particularly metallurgical), so presumably it does still have a worthwhile role. The oblique patch stop is certainly a cheap and cheerful way for the amateur to improve contrast for some subjects, especially at medium powers where patch stops for dark-field get trickier to make. I was also intrigued to see that at least one manufacturer, 'Edge', market a microscope with 'patented Multiple Obliquetm Illumination' which apparently gives 3D images. Visit the Edge web site for details and read the theory behind the technique for 3D imaging. Comments on the article to the author Dave Walker welcomed. References 1) 'Under the Microscope' by A. Curry, R. F. Grayson and G. R. Hosey, (Blandford Press, UK, 1982), Chapter 8. Now out of print, but worth looking out for in second-hand bookshops as it gives clear explanations of many techniques and principles, especially the use of polarised light. 2) 'The Microscope Past and Present' by S. Bradbury. Pergamon Press, UK, 1968, pp. 180-183. A compact but thorough overview of the history of the microscope and it's development. Illustrates and discusses the Ross Radial and Ross / Zentmayer microscope and the fad for oblique illumination. Microscopy UK Front Page Micscape Magazine Article Library Text and images © David Walker. © Onview.net Ltd, Microscopy-UK, and all contributors 1995 onwards. All rights reserved. Main site is at www.microscopy-uk.org.uk with full mirror at www.microscopy-uk.net.

I was also intrigued to see that at least one manufacturer, 'Edge', market a microscope with 'patented Multiple Obliquetm Illumination' which apparently gives 3D images. Visit the Edge web site for details and read the theory behind the technique for 3D imaging. Comments on the article to the author Dave Walker welcomed. References 1) 'Under the Microscope' by A. Curry, R. F. Grayson and G. R. Hosey, (Blandford Press, UK, 1982), Chapter 8. Now out of print, but worth looking out for in second-hand bookshops as it gives clear explanations of many techniques and principles, especially the use of polarised light. 2) 'The Microscope Past and Present' by S. Bradbury. Pergamon Press, UK, 1968, pp. 180-183. A compact but thorough overview of the history of the microscope and it's development. Illustrates and discusses the Ross Radial and Ross / Zentmayer microscope and the fad for oblique illumination. Microscopy UK Front Page Micscape Magazine Article Library Text and images © David Walker. © Onview.net Ltd, Microscopy-UK, and all contributors 1995 onwards. All rights reserved. Main site is at www.microscopy-uk.org.uk with full mirror at www.microscopy-uk.net.

Circularlypolarized light

A circular polarizer blocks reflected light from any angle while a linear polarizer only blocks reflected light from one direction.

Urth has two different ranges of filters: Urth (our premium range) and Urth Plus+ (our professional range). Let the quality of your lens guide your decision. If you’ve invested in a professional-quality lens, we recommend you match its quality with our Plus+ range. Our Urth range is the perfect option for all other standards of lens.

"This filter has elevated my photography beyond my expectations. Can't get enough of the colours and contrast." – Javi bought our CPL Plus+.

It's not resolution that's the problem, it's contrast. If the diatom is studied with an oblique patch stop in the filter tray (see below) the image right is seen. The dots which are fine markings on the diatom frustule are now clearly seen. (Incidentally I have to push my ancient image capture card to the limit to capture these sort of images, so they are a lot less convincing than the visual image down the microscope). It's also possible to resolve the dots under dark-field with this objective, but I have never found using home-made patch stops for a 40X dry objective very easy and have achieved less than successful dark-field, so oblique illumination is an easier alternative to improve contrast. In a second example, the image left and right shows the classic epithelial cells taken by scraping the inside of the cheek lightly with the finger nail and mounting the saliva under a cover slip (again using the 40x dry objective). The image left is in brightfield with the iris stopped down more than normal to improve contrast - it's an acceptable image but rather flat. The same view with the oblique patch stop gives a very pleasing depth to the cell especially the nucleus, cell granules and folding of the cell (again, the visual image is a lot clearer than in the captured image). Oblique illumination also works well on single cells such as protozoa. One book I referred to (ref. 1) illustrates that the internal vacuoles are particularly distinctive in this sort of illumination. If you haven't tried the technique, how can it be achieved? A few methods are given below. Knock the mirror! As commented above, if you have a microscope with a mirror, moving the mirror (plane side) so that light is shone off-axis can achieve the effect. This one of the few techniques for improving contrast that the owner of a simple microscope without a condenser can achieve i.e. unlike dark-field or phase contrast. I first spotted the effect myself as a ten year old with a no-frills toy microscope, and I got into the habit of rocking the mirror on its axis when studying transparent live pond-life to see if more details were revealed. Simple stop for the condenser filter tray If you have a condenser and filter tray, a simple stop can be made as shown left. Just cut out a piece of opaque card to fit the filter tray and experiment with various sizes of sector cut out of the disc for a given objective to allow light from an angle to reach the subject. Normal axial illumination should be setup first. As for dark field, the condenser iris should be fully open and the condenser focus adjusted to get the best effect. You may need to experiment with the size of the notch for a given objective. The orientation of the notch with respect to the subject should also be changed to see what achieves the best effect. If you have a rotating stage this is easier than rotating the patch stop in the filter tray. If the filter tray is a swing out type, also experiment with the extent the filter is swung in, as well as varying the orientation of the notch in the filter tray. Condenser with oblique illumination Buying a condenser specifically for oblique illumination is probably not justified, but this is a feature found in some condensers. My Russian Biolam microscope is supplied with a modest Abbe condenser, but for critical work I use the better quality Russian aplanatic condenser (N.A. 1.4). As a bonus this also has an oblique illumination feature, see image right. (Supplementary low power lens N.A. 0.3 also shown). The iris can be moved up to 10mm off-axis in opposite directions, which also rotates in the mount to change the orientation of the light to the subject. The latter feature, as mentioned above for the oblique patch stop, is important as the off-axis lighting often works best in a specific orientation to a subject e.g. for non-symmetric diatoms like Pleurosigma. Historical footnote In the late19th century but before the advent of high numerical aperture objectives, oblique illumination was quite popular and some makers developed microscopes especially to exploit the benefits of the technique. One of the first models was shown by Zentmayer of Philadelphia in 1876 at an Exposition in this city. It had a swinging substage, i.e. the whole substage assembly swung about an axis in the same plane as the stage. An image of this microscope is in the Moody Medical Library On-line (item 1.028 in catalogue). (This site illustrates a wonderful selection of historical microscopes from the famous Moody collection, most makers are represented). Some makers designed microscopes that took oblique illumination to rather extreme limits. The classic example is the Ross Radial microscope built by the famous English maker Ross to a design by Wenham. This is a superb example of quality engineering and optics by a respected maker, but a rather bizarre microscope nevertheless. Almost every conceivable plane and axis of the microscope limb, body and substage has the facility to be tilted or rotated (see ref. 2 or similar history of microscopes where this model is often illustrated). An image of this microscope is also in the Moody Medical Library On-line (item 1.031 in catalogue). The technique fell out of favour towards the end of the 19th century as high numerical aperture objectives became available with the ability to resolve the fine detail of diatoms etc. with good axial illumination. A firmer understanding of the requirements for a critical image with axial illumination were also realised. I wasn't sure how well the technique is used nowadays given the many other ways of improving contrast. However, a web search for 'oblique illumination' shows that some of the mainstream microscope makers mention this form of lighting as a feature in some of their models (particularly metallurgical), so presumably it does still have a worthwhile role. The oblique patch stop is certainly a cheap and cheerful way for the amateur to improve contrast for some subjects, especially at medium powers where patch stops for dark-field get trickier to make. I was also intrigued to see that at least one manufacturer, 'Edge', market a microscope with 'patented Multiple Obliquetm Illumination' which apparently gives 3D images. Visit the Edge web site for details and read the theory behind the technique for 3D imaging. Comments on the article to the author Dave Walker welcomed. References 1) 'Under the Microscope' by A. Curry, R. F. Grayson and G. R. Hosey, (Blandford Press, UK, 1982), Chapter 8. Now out of print, but worth looking out for in second-hand bookshops as it gives clear explanations of many techniques and principles, especially the use of polarised light. 2) 'The Microscope Past and Present' by S. Bradbury. Pergamon Press, UK, 1968, pp. 180-183. A compact but thorough overview of the history of the microscope and it's development. Illustrates and discusses the Ross Radial and Ross / Zentmayer microscope and the fad for oblique illumination. Microscopy UK Front Page Micscape Magazine Article Library Text and images © David Walker. © Onview.net Ltd, Microscopy-UK, and all contributors 1995 onwards. All rights reserved. Main site is at www.microscopy-uk.org.uk with full mirror at www.microscopy-uk.net.

Text and images © David Walker. © Onview.net Ltd, Microscopy-UK, and all contributors 1995 onwards. All rights reserved. Main site is at www.microscopy-uk.org.uk with full mirror at www.microscopy-uk.net.

P-polarizedlight

Essentially oblique illumination works by accentuating any phase gradients within a transparent specimen. It's an easy form of lighting to achieve up to medium powers (e.g. 40x objectives) with most microscopes with or without a mirror, and is a 'cheap and cheerful' technique the amateur can use to improve visibility when studying low contrast subjects, especially if you're not fortunate enough to possess phase contrast or high power dark field illumination. To illustrate its effect, the image right shows part of the classic diatom Pleurosigma angulatum using a 40x achromatic objective (Russian, NA 0.65 dry). This is one of the cheapest 40x objectives you can buy, but is perfectly capable of resolving the dots i.e. the fine detail on the silica shell, but in normal brightfield this detail is quite difficult to see. Only the central 'raphe' (on the right of the image) and an edge of the diatom frustule at the left can be made out. It's not resolution that's the problem, it's contrast. If the diatom is studied with an oblique patch stop in the filter tray (see below) the image right is seen. The dots which are fine markings on the diatom frustule are now clearly seen. (Incidentally I have to push my ancient image capture card to the limit to capture these sort of images, so they are a lot less convincing than the visual image down the microscope). It's also possible to resolve the dots under dark-field with this objective, but I have never found using home-made patch stops for a 40X dry objective very easy and have achieved less than successful dark-field, so oblique illumination is an easier alternative to improve contrast. In a second example, the image left and right shows the classic epithelial cells taken by scraping the inside of the cheek lightly with the finger nail and mounting the saliva under a cover slip (again using the 40x dry objective). The image left is in brightfield with the iris stopped down more than normal to improve contrast - it's an acceptable image but rather flat. The same view with the oblique patch stop gives a very pleasing depth to the cell especially the nucleus, cell granules and folding of the cell (again, the visual image is a lot clearer than in the captured image). Oblique illumination also works well on single cells such as protozoa. One book I referred to (ref. 1) illustrates that the internal vacuoles are particularly distinctive in this sort of illumination. If you haven't tried the technique, how can it be achieved? A few methods are given below. Knock the mirror! As commented above, if you have a microscope with a mirror, moving the mirror (plane side) so that light is shone off-axis can achieve the effect. This one of the few techniques for improving contrast that the owner of a simple microscope without a condenser can achieve i.e. unlike dark-field or phase contrast. I first spotted the effect myself as a ten year old with a no-frills toy microscope, and I got into the habit of rocking the mirror on its axis when studying transparent live pond-life to see if more details were revealed. Simple stop for the condenser filter tray If you have a condenser and filter tray, a simple stop can be made as shown left. Just cut out a piece of opaque card to fit the filter tray and experiment with various sizes of sector cut out of the disc for a given objective to allow light from an angle to reach the subject. Normal axial illumination should be setup first. As for dark field, the condenser iris should be fully open and the condenser focus adjusted to get the best effect. You may need to experiment with the size of the notch for a given objective. The orientation of the notch with respect to the subject should also be changed to see what achieves the best effect. If you have a rotating stage this is easier than rotating the patch stop in the filter tray. If the filter tray is a swing out type, also experiment with the extent the filter is swung in, as well as varying the orientation of the notch in the filter tray. Condenser with oblique illumination Buying a condenser specifically for oblique illumination is probably not justified, but this is a feature found in some condensers. My Russian Biolam microscope is supplied with a modest Abbe condenser, but for critical work I use the better quality Russian aplanatic condenser (N.A. 1.4). As a bonus this also has an oblique illumination feature, see image right. (Supplementary low power lens N.A. 0.3 also shown). The iris can be moved up to 10mm off-axis in opposite directions, which also rotates in the mount to change the orientation of the light to the subject. The latter feature, as mentioned above for the oblique patch stop, is important as the off-axis lighting often works best in a specific orientation to a subject e.g. for non-symmetric diatoms like Pleurosigma. Historical footnote In the late19th century but before the advent of high numerical aperture objectives, oblique illumination was quite popular and some makers developed microscopes especially to exploit the benefits of the technique. One of the first models was shown by Zentmayer of Philadelphia in 1876 at an Exposition in this city. It had a swinging substage, i.e. the whole substage assembly swung about an axis in the same plane as the stage. An image of this microscope is in the Moody Medical Library On-line (item 1.028 in catalogue). (This site illustrates a wonderful selection of historical microscopes from the famous Moody collection, most makers are represented). Some makers designed microscopes that took oblique illumination to rather extreme limits. The classic example is the Ross Radial microscope built by the famous English maker Ross to a design by Wenham. This is a superb example of quality engineering and optics by a respected maker, but a rather bizarre microscope nevertheless. Almost every conceivable plane and axis of the microscope limb, body and substage has the facility to be tilted or rotated (see ref. 2 or similar history of microscopes where this model is often illustrated). An image of this microscope is also in the Moody Medical Library On-line (item 1.031 in catalogue). The technique fell out of favour towards the end of the 19th century as high numerical aperture objectives became available with the ability to resolve the fine detail of diatoms etc. with good axial illumination. A firmer understanding of the requirements for a critical image with axial illumination were also realised. I wasn't sure how well the technique is used nowadays given the many other ways of improving contrast. However, a web search for 'oblique illumination' shows that some of the mainstream microscope makers mention this form of lighting as a feature in some of their models (particularly metallurgical), so presumably it does still have a worthwhile role. The oblique patch stop is certainly a cheap and cheerful way for the amateur to improve contrast for some subjects, especially at medium powers where patch stops for dark-field get trickier to make. I was also intrigued to see that at least one manufacturer, 'Edge', market a microscope with 'patented Multiple Obliquetm Illumination' which apparently gives 3D images. Visit the Edge web site for details and read the theory behind the technique for 3D imaging. Comments on the article to the author Dave Walker welcomed. References 1) 'Under the Microscope' by A. Curry, R. F. Grayson and G. R. Hosey, (Blandford Press, UK, 1982), Chapter 8. Now out of print, but worth looking out for in second-hand bookshops as it gives clear explanations of many techniques and principles, especially the use of polarised light. 2) 'The Microscope Past and Present' by S. Bradbury. Pergamon Press, UK, 1968, pp. 180-183. A compact but thorough overview of the history of the microscope and it's development. Illustrates and discusses the Ross Radial and Ross / Zentmayer microscope and the fad for oblique illumination. Microscopy UK Front Page Micscape Magazine Article Library Text and images © David Walker. © Onview.net Ltd, Microscopy-UK, and all contributors 1995 onwards. All rights reserved. Main site is at www.microscopy-uk.org.uk with full mirror at www.microscopy-uk.net.

Some makers designed microscopes that took oblique illumination to rather extreme limits. The classic example is the Ross Radial microscope built by the famous English maker Ross to a design by Wenham. This is a superb example of quality engineering and optics by a respected maker, but a rather bizarre microscope nevertheless. Almost every conceivable plane and axis of the microscope limb, body and substage has the facility to be tilted or rotated (see ref. 2 or similar history of microscopes where this model is often illustrated). An image of this microscope is also in the Moody Medical Library On-line (item 1.031 in catalogue). The technique fell out of favour towards the end of the 19th century as high numerical aperture objectives became available with the ability to resolve the fine detail of diatoms etc. with good axial illumination. A firmer understanding of the requirements for a critical image with axial illumination were also realised. I wasn't sure how well the technique is used nowadays given the many other ways of improving contrast. However, a web search for 'oblique illumination' shows that some of the mainstream microscope makers mention this form of lighting as a feature in some of their models (particularly metallurgical), so presumably it does still have a worthwhile role. The oblique patch stop is certainly a cheap and cheerful way for the amateur to improve contrast for some subjects, especially at medium powers where patch stops for dark-field get trickier to make. I was also intrigued to see that at least one manufacturer, 'Edge', market a microscope with 'patented Multiple Obliquetm Illumination' which apparently gives 3D images. Visit the Edge web site for details and read the theory behind the technique for 3D imaging. Comments on the article to the author Dave Walker welcomed. References 1) 'Under the Microscope' by A. Curry, R. F. Grayson and G. R. Hosey, (Blandford Press, UK, 1982), Chapter 8. Now out of print, but worth looking out for in second-hand bookshops as it gives clear explanations of many techniques and principles, especially the use of polarised light. 2) 'The Microscope Past and Present' by S. Bradbury. Pergamon Press, UK, 1968, pp. 180-183. A compact but thorough overview of the history of the microscope and it's development. Illustrates and discusses the Ross Radial and Ross / Zentmayer microscope and the fad for oblique illumination. Microscopy UK Front Page Micscape Magazine Article Library Text and images © David Walker. © Onview.net Ltd, Microscopy-UK, and all contributors 1995 onwards. All rights reserved. Main site is at www.microscopy-uk.org.uk with full mirror at www.microscopy-uk.net.

Condenser with oblique illumination Buying a condenser specifically for oblique illumination is probably not justified, but this is a feature found in some condensers. My Russian Biolam microscope is supplied with a modest Abbe condenser, but for critical work I use the better quality Russian aplanatic condenser (N.A. 1.4). As a bonus this also has an oblique illumination feature, see image right. (Supplementary low power lens N.A. 0.3 also shown). The iris can be moved up to 10mm off-axis in opposite directions, which also rotates in the mount to change the orientation of the light to the subject. The latter feature, as mentioned above for the oblique patch stop, is important as the off-axis lighting often works best in a specific orientation to a subject e.g. for non-symmetric diatoms like Pleurosigma. Historical footnote In the late19th century but before the advent of high numerical aperture objectives, oblique illumination was quite popular and some makers developed microscopes especially to exploit the benefits of the technique. One of the first models was shown by Zentmayer of Philadelphia in 1876 at an Exposition in this city. It had a swinging substage, i.e. the whole substage assembly swung about an axis in the same plane as the stage. An image of this microscope is in the Moody Medical Library On-line (item 1.028 in catalogue). (This site illustrates a wonderful selection of historical microscopes from the famous Moody collection, most makers are represented). Some makers designed microscopes that took oblique illumination to rather extreme limits. The classic example is the Ross Radial microscope built by the famous English maker Ross to a design by Wenham. This is a superb example of quality engineering and optics by a respected maker, but a rather bizarre microscope nevertheless. Almost every conceivable plane and axis of the microscope limb, body and substage has the facility to be tilted or rotated (see ref. 2 or similar history of microscopes where this model is often illustrated). An image of this microscope is also in the Moody Medical Library On-line (item 1.031 in catalogue). The technique fell out of favour towards the end of the 19th century as high numerical aperture objectives became available with the ability to resolve the fine detail of diatoms etc. with good axial illumination. A firmer understanding of the requirements for a critical image with axial illumination were also realised. I wasn't sure how well the technique is used nowadays given the many other ways of improving contrast. However, a web search for 'oblique illumination' shows that some of the mainstream microscope makers mention this form of lighting as a feature in some of their models (particularly metallurgical), so presumably it does still have a worthwhile role. The oblique patch stop is certainly a cheap and cheerful way for the amateur to improve contrast for some subjects, especially at medium powers where patch stops for dark-field get trickier to make. I was also intrigued to see that at least one manufacturer, 'Edge', market a microscope with 'patented Multiple Obliquetm Illumination' which apparently gives 3D images. Visit the Edge web site for details and read the theory behind the technique for 3D imaging. Comments on the article to the author Dave Walker welcomed. References 1) 'Under the Microscope' by A. Curry, R. F. Grayson and G. R. Hosey, (Blandford Press, UK, 1982), Chapter 8. Now out of print, but worth looking out for in second-hand bookshops as it gives clear explanations of many techniques and principles, especially the use of polarised light. 2) 'The Microscope Past and Present' by S. Bradbury. Pergamon Press, UK, 1968, pp. 180-183. A compact but thorough overview of the history of the microscope and it's development. Illustrates and discusses the Ross Radial and Ross / Zentmayer microscope and the fad for oblique illumination. Microscopy UK Front Page Micscape Magazine Article Library Text and images © David Walker. © Onview.net Ltd, Microscopy-UK, and all contributors 1995 onwards. All rights reserved. Main site is at www.microscopy-uk.org.uk with full mirror at www.microscopy-uk.net.

Urth Circular Polarizing Filters (CPL Filters) cut reflections, boost colour saturation and increase contrast by cutting out reflected polarized light. Our polarizing filters cut out polarized light, which usually washes out images with silvery reflected light. Our CPL filters cut out 99.9% of reflected light from water, glass, and non-metallic surfaces, uncovering bolder colours. Our CPL filters block diffused light from any direction. Simply rotate the outer element of the filter to adjust the level of polarization based on the direction of the light source. Our CPL filters give you greater creative control when there is excessive reflected light like you’ll experience in outdoor photography and filmmaking. At full polarization, our CPL creates a 1.33 f-stop light reduction. All Urth CPL filters are built with premium quality materials and are guaranteed for life. And each filter plants 1 tree so future generations can enjoy nature as much as we do now. All our circular filters come with a protective travel tin case, a recycled cleaning cloth, and recycled plastic-free packaging. Read more Read less

To illustrate its effect, the image right shows part of the classic diatom Pleurosigma angulatum using a 40x achromatic objective (Russian, NA 0.65 dry). This is one of the cheapest 40x objectives you can buy, but is perfectly capable of resolving the dots i.e. the fine detail on the silica shell, but in normal brightfield this detail is quite difficult to see. Only the central 'raphe' (on the right of the image) and an edge of the diatom frustule at the left can be made out. It's not resolution that's the problem, it's contrast. If the diatom is studied with an oblique patch stop in the filter tray (see below) the image right is seen. The dots which are fine markings on the diatom frustule are now clearly seen. (Incidentally I have to push my ancient image capture card to the limit to capture these sort of images, so they are a lot less convincing than the visual image down the microscope). It's also possible to resolve the dots under dark-field with this objective, but I have never found using home-made patch stops for a 40X dry objective very easy and have achieved less than successful dark-field, so oblique illumination is an easier alternative to improve contrast. In a second example, the image left and right shows the classic epithelial cells taken by scraping the inside of the cheek lightly with the finger nail and mounting the saliva under a cover slip (again using the 40x dry objective). The image left is in brightfield with the iris stopped down more than normal to improve contrast - it's an acceptable image but rather flat. The same view with the oblique patch stop gives a very pleasing depth to the cell especially the nucleus, cell granules and folding of the cell (again, the visual image is a lot clearer than in the captured image). Oblique illumination also works well on single cells such as protozoa. One book I referred to (ref. 1) illustrates that the internal vacuoles are particularly distinctive in this sort of illumination. If you haven't tried the technique, how can it be achieved? A few methods are given below. Knock the mirror! As commented above, if you have a microscope with a mirror, moving the mirror (plane side) so that light is shone off-axis can achieve the effect. This one of the few techniques for improving contrast that the owner of a simple microscope without a condenser can achieve i.e. unlike dark-field or phase contrast. I first spotted the effect myself as a ten year old with a no-frills toy microscope, and I got into the habit of rocking the mirror on its axis when studying transparent live pond-life to see if more details were revealed. Simple stop for the condenser filter tray If you have a condenser and filter tray, a simple stop can be made as shown left. Just cut out a piece of opaque card to fit the filter tray and experiment with various sizes of sector cut out of the disc for a given objective to allow light from an angle to reach the subject. Normal axial illumination should be setup first. As for dark field, the condenser iris should be fully open and the condenser focus adjusted to get the best effect. You may need to experiment with the size of the notch for a given objective. The orientation of the notch with respect to the subject should also be changed to see what achieves the best effect. If you have a rotating stage this is easier than rotating the patch stop in the filter tray. If the filter tray is a swing out type, also experiment with the extent the filter is swung in, as well as varying the orientation of the notch in the filter tray. Condenser with oblique illumination Buying a condenser specifically for oblique illumination is probably not justified, but this is a feature found in some condensers. My Russian Biolam microscope is supplied with a modest Abbe condenser, but for critical work I use the better quality Russian aplanatic condenser (N.A. 1.4). As a bonus this also has an oblique illumination feature, see image right. (Supplementary low power lens N.A. 0.3 also shown). The iris can be moved up to 10mm off-axis in opposite directions, which also rotates in the mount to change the orientation of the light to the subject. The latter feature, as mentioned above for the oblique patch stop, is important as the off-axis lighting often works best in a specific orientation to a subject e.g. for non-symmetric diatoms like Pleurosigma. Historical footnote In the late19th century but before the advent of high numerical aperture objectives, oblique illumination was quite popular and some makers developed microscopes especially to exploit the benefits of the technique. One of the first models was shown by Zentmayer of Philadelphia in 1876 at an Exposition in this city. It had a swinging substage, i.e. the whole substage assembly swung about an axis in the same plane as the stage. An image of this microscope is in the Moody Medical Library On-line (item 1.028 in catalogue). (This site illustrates a wonderful selection of historical microscopes from the famous Moody collection, most makers are represented). Some makers designed microscopes that took oblique illumination to rather extreme limits. The classic example is the Ross Radial microscope built by the famous English maker Ross to a design by Wenham. This is a superb example of quality engineering and optics by a respected maker, but a rather bizarre microscope nevertheless. Almost every conceivable plane and axis of the microscope limb, body and substage has the facility to be tilted or rotated (see ref. 2 or similar history of microscopes where this model is often illustrated). An image of this microscope is also in the Moody Medical Library On-line (item 1.031 in catalogue). The technique fell out of favour towards the end of the 19th century as high numerical aperture objectives became available with the ability to resolve the fine detail of diatoms etc. with good axial illumination. A firmer understanding of the requirements for a critical image with axial illumination were also realised. I wasn't sure how well the technique is used nowadays given the many other ways of improving contrast. However, a web search for 'oblique illumination' shows that some of the mainstream microscope makers mention this form of lighting as a feature in some of their models (particularly metallurgical), so presumably it does still have a worthwhile role. The oblique patch stop is certainly a cheap and cheerful way for the amateur to improve contrast for some subjects, especially at medium powers where patch stops for dark-field get trickier to make. I was also intrigued to see that at least one manufacturer, 'Edge', market a microscope with 'patented Multiple Obliquetm Illumination' which apparently gives 3D images. Visit the Edge web site for details and read the theory behind the technique for 3D imaging. Comments on the article to the author Dave Walker welcomed. References 1) 'Under the Microscope' by A. Curry, R. F. Grayson and G. R. Hosey, (Blandford Press, UK, 1982), Chapter 8. Now out of print, but worth looking out for in second-hand bookshops as it gives clear explanations of many techniques and principles, especially the use of polarised light. 2) 'The Microscope Past and Present' by S. Bradbury. Pergamon Press, UK, 1968, pp. 180-183. A compact but thorough overview of the history of the microscope and it's development. Illustrates and discusses the Ross Radial and Ross / Zentmayer microscope and the fad for oblique illumination. Microscopy UK Front Page Micscape Magazine Article Library Text and images © David Walker. © Onview.net Ltd, Microscopy-UK, and all contributors 1995 onwards. All rights reserved. Main site is at www.microscopy-uk.org.uk with full mirror at www.microscopy-uk.net.

Polarizing film Roll

polarizing filter中文

Historical footnote In the late19th century but before the advent of high numerical aperture objectives, oblique illumination was quite popular and some makers developed microscopes especially to exploit the benefits of the technique. One of the first models was shown by Zentmayer of Philadelphia in 1876 at an Exposition in this city. It had a swinging substage, i.e. the whole substage assembly swung about an axis in the same plane as the stage. An image of this microscope is in the Moody Medical Library On-line (item 1.028 in catalogue). (This site illustrates a wonderful selection of historical microscopes from the famous Moody collection, most makers are represented). Some makers designed microscopes that took oblique illumination to rather extreme limits. The classic example is the Ross Radial microscope built by the famous English maker Ross to a design by Wenham. This is a superb example of quality engineering and optics by a respected maker, but a rather bizarre microscope nevertheless. Almost every conceivable plane and axis of the microscope limb, body and substage has the facility to be tilted or rotated (see ref. 2 or similar history of microscopes where this model is often illustrated). An image of this microscope is also in the Moody Medical Library On-line (item 1.031 in catalogue). The technique fell out of favour towards the end of the 19th century as high numerical aperture objectives became available with the ability to resolve the fine detail of diatoms etc. with good axial illumination. A firmer understanding of the requirements for a critical image with axial illumination were also realised. I wasn't sure how well the technique is used nowadays given the many other ways of improving contrast. However, a web search for 'oblique illumination' shows that some of the mainstream microscope makers mention this form of lighting as a feature in some of their models (particularly metallurgical), so presumably it does still have a worthwhile role. The oblique patch stop is certainly a cheap and cheerful way for the amateur to improve contrast for some subjects, especially at medium powers where patch stops for dark-field get trickier to make. I was also intrigued to see that at least one manufacturer, 'Edge', market a microscope with 'patented Multiple Obliquetm Illumination' which apparently gives 3D images. Visit the Edge web site for details and read the theory behind the technique for 3D imaging. Comments on the article to the author Dave Walker welcomed. References 1) 'Under the Microscope' by A. Curry, R. F. Grayson and G. R. Hosey, (Blandford Press, UK, 1982), Chapter 8. Now out of print, but worth looking out for in second-hand bookshops as it gives clear explanations of many techniques and principles, especially the use of polarised light. 2) 'The Microscope Past and Present' by S. Bradbury. Pergamon Press, UK, 1968, pp. 180-183. A compact but thorough overview of the history of the microscope and it's development. Illustrates and discusses the Ross Radial and Ross / Zentmayer microscope and the fad for oblique illumination. Microscopy UK Front Page Micscape Magazine Article Library Text and images © David Walker. © Onview.net Ltd, Microscopy-UK, and all contributors 1995 onwards. All rights reserved. Main site is at www.microscopy-uk.org.uk with full mirror at www.microscopy-uk.net.

What is a polarizingfilter

As commented above, if you have a microscope with a mirror, moving the mirror (plane side) so that light is shone off-axis can achieve the effect. This one of the few techniques for improving contrast that the owner of a simple microscope without a condenser can achieve i.e. unlike dark-field or phase contrast. I first spotted the effect myself as a ten year old with a no-frills toy microscope, and I got into the habit of rocking the mirror on its axis when studying transparent live pond-life to see if more details were revealed. Simple stop for the condenser filter tray If you have a condenser and filter tray, a simple stop can be made as shown left. Just cut out a piece of opaque card to fit the filter tray and experiment with various sizes of sector cut out of the disc for a given objective to allow light from an angle to reach the subject. Normal axial illumination should be setup first. As for dark field, the condenser iris should be fully open and the condenser focus adjusted to get the best effect. You may need to experiment with the size of the notch for a given objective. The orientation of the notch with respect to the subject should also be changed to see what achieves the best effect. If you have a rotating stage this is easier than rotating the patch stop in the filter tray. If the filter tray is a swing out type, also experiment with the extent the filter is swung in, as well as varying the orientation of the notch in the filter tray. Condenser with oblique illumination Buying a condenser specifically for oblique illumination is probably not justified, but this is a feature found in some condensers. My Russian Biolam microscope is supplied with a modest Abbe condenser, but for critical work I use the better quality Russian aplanatic condenser (N.A. 1.4). As a bonus this also has an oblique illumination feature, see image right. (Supplementary low power lens N.A. 0.3 also shown). The iris can be moved up to 10mm off-axis in opposite directions, which also rotates in the mount to change the orientation of the light to the subject. The latter feature, as mentioned above for the oblique patch stop, is important as the off-axis lighting often works best in a specific orientation to a subject e.g. for non-symmetric diatoms like Pleurosigma. Historical footnote In the late19th century but before the advent of high numerical aperture objectives, oblique illumination was quite popular and some makers developed microscopes especially to exploit the benefits of the technique. One of the first models was shown by Zentmayer of Philadelphia in 1876 at an Exposition in this city. It had a swinging substage, i.e. the whole substage assembly swung about an axis in the same plane as the stage. An image of this microscope is in the Moody Medical Library On-line (item 1.028 in catalogue). (This site illustrates a wonderful selection of historical microscopes from the famous Moody collection, most makers are represented). Some makers designed microscopes that took oblique illumination to rather extreme limits. The classic example is the Ross Radial microscope built by the famous English maker Ross to a design by Wenham. This is a superb example of quality engineering and optics by a respected maker, but a rather bizarre microscope nevertheless. Almost every conceivable plane and axis of the microscope limb, body and substage has the facility to be tilted or rotated (see ref. 2 or similar history of microscopes where this model is often illustrated). An image of this microscope is also in the Moody Medical Library On-line (item 1.031 in catalogue). The technique fell out of favour towards the end of the 19th century as high numerical aperture objectives became available with the ability to resolve the fine detail of diatoms etc. with good axial illumination. A firmer understanding of the requirements for a critical image with axial illumination were also realised. I wasn't sure how well the technique is used nowadays given the many other ways of improving contrast. However, a web search for 'oblique illumination' shows that some of the mainstream microscope makers mention this form of lighting as a feature in some of their models (particularly metallurgical), so presumably it does still have a worthwhile role. The oblique patch stop is certainly a cheap and cheerful way for the amateur to improve contrast for some subjects, especially at medium powers where patch stops for dark-field get trickier to make. I was also intrigued to see that at least one manufacturer, 'Edge', market a microscope with 'patented Multiple Obliquetm Illumination' which apparently gives 3D images. Visit the Edge web site for details and read the theory behind the technique for 3D imaging. Comments on the article to the author Dave Walker welcomed. References 1) 'Under the Microscope' by A. Curry, R. F. Grayson and G. R. Hosey, (Blandford Press, UK, 1982), Chapter 8. Now out of print, but worth looking out for in second-hand bookshops as it gives clear explanations of many techniques and principles, especially the use of polarised light. 2) 'The Microscope Past and Present' by S. Bradbury. Pergamon Press, UK, 1968, pp. 180-183. A compact but thorough overview of the history of the microscope and it's development. Illustrates and discusses the Ross Radial and Ross / Zentmayer microscope and the fad for oblique illumination. Microscopy UK Front Page Micscape Magazine Article Library Text and images © David Walker. © Onview.net Ltd, Microscopy-UK, and all contributors 1995 onwards. All rights reserved. Main site is at www.microscopy-uk.org.uk with full mirror at www.microscopy-uk.net.

Buying a condenser specifically for oblique illumination is probably not justified, but this is a feature found in some condensers. My Russian Biolam microscope is supplied with a modest Abbe condenser, but for critical work I use the better quality Russian aplanatic condenser (N.A. 1.4). As a bonus this also has an oblique illumination feature, see image right. (Supplementary low power lens N.A. 0.3 also shown). The iris can be moved up to 10mm off-axis in opposite directions, which also rotates in the mount to change the orientation of the light to the subject. The latter feature, as mentioned above for the oblique patch stop, is important as the off-axis lighting often works best in a specific orientation to a subject e.g. for non-symmetric diatoms like Pleurosigma. Historical footnote In the late19th century but before the advent of high numerical aperture objectives, oblique illumination was quite popular and some makers developed microscopes especially to exploit the benefits of the technique. One of the first models was shown by Zentmayer of Philadelphia in 1876 at an Exposition in this city. It had a swinging substage, i.e. the whole substage assembly swung about an axis in the same plane as the stage. An image of this microscope is in the Moody Medical Library On-line (item 1.028 in catalogue). (This site illustrates a wonderful selection of historical microscopes from the famous Moody collection, most makers are represented). Some makers designed microscopes that took oblique illumination to rather extreme limits. The classic example is the Ross Radial microscope built by the famous English maker Ross to a design by Wenham. This is a superb example of quality engineering and optics by a respected maker, but a rather bizarre microscope nevertheless. Almost every conceivable plane and axis of the microscope limb, body and substage has the facility to be tilted or rotated (see ref. 2 or similar history of microscopes where this model is often illustrated). An image of this microscope is also in the Moody Medical Library On-line (item 1.031 in catalogue). The technique fell out of favour towards the end of the 19th century as high numerical aperture objectives became available with the ability to resolve the fine detail of diatoms etc. with good axial illumination. A firmer understanding of the requirements for a critical image with axial illumination were also realised. I wasn't sure how well the technique is used nowadays given the many other ways of improving contrast. However, a web search for 'oblique illumination' shows that some of the mainstream microscope makers mention this form of lighting as a feature in some of their models (particularly metallurgical), so presumably it does still have a worthwhile role. The oblique patch stop is certainly a cheap and cheerful way for the amateur to improve contrast for some subjects, especially at medium powers where patch stops for dark-field get trickier to make. I was also intrigued to see that at least one manufacturer, 'Edge', market a microscope with 'patented Multiple Obliquetm Illumination' which apparently gives 3D images. Visit the Edge web site for details and read the theory behind the technique for 3D imaging. Comments on the article to the author Dave Walker welcomed. References 1) 'Under the Microscope' by A. Curry, R. F. Grayson and G. R. Hosey, (Blandford Press, UK, 1982), Chapter 8. Now out of print, but worth looking out for in second-hand bookshops as it gives clear explanations of many techniques and principles, especially the use of polarised light. 2) 'The Microscope Past and Present' by S. Bradbury. Pergamon Press, UK, 1968, pp. 180-183. A compact but thorough overview of the history of the microscope and it's development. Illustrates and discusses the Ross Radial and Ross / Zentmayer microscope and the fad for oblique illumination. Microscopy UK Front Page Micscape Magazine Article Library Text and images © David Walker. © Onview.net Ltd, Microscopy-UK, and all contributors 1995 onwards. All rights reserved. Main site is at www.microscopy-uk.org.uk with full mirror at www.microscopy-uk.net.

If you haven't tried the technique, how can it be achieved? A few methods are given below. Knock the mirror! As commented above, if you have a microscope with a mirror, moving the mirror (plane side) so that light is shone off-axis can achieve the effect. This one of the few techniques for improving contrast that the owner of a simple microscope without a condenser can achieve i.e. unlike dark-field or phase contrast. I first spotted the effect myself as a ten year old with a no-frills toy microscope, and I got into the habit of rocking the mirror on its axis when studying transparent live pond-life to see if more details were revealed. Simple stop for the condenser filter tray If you have a condenser and filter tray, a simple stop can be made as shown left. Just cut out a piece of opaque card to fit the filter tray and experiment with various sizes of sector cut out of the disc for a given objective to allow light from an angle to reach the subject. Normal axial illumination should be setup first. As for dark field, the condenser iris should be fully open and the condenser focus adjusted to get the best effect. You may need to experiment with the size of the notch for a given objective. The orientation of the notch with respect to the subject should also be changed to see what achieves the best effect. If you have a rotating stage this is easier than rotating the patch stop in the filter tray. If the filter tray is a swing out type, also experiment with the extent the filter is swung in, as well as varying the orientation of the notch in the filter tray. Condenser with oblique illumination Buying a condenser specifically for oblique illumination is probably not justified, but this is a feature found in some condensers. My Russian Biolam microscope is supplied with a modest Abbe condenser, but for critical work I use the better quality Russian aplanatic condenser (N.A. 1.4). As a bonus this also has an oblique illumination feature, see image right. (Supplementary low power lens N.A. 0.3 also shown). The iris can be moved up to 10mm off-axis in opposite directions, which also rotates in the mount to change the orientation of the light to the subject. The latter feature, as mentioned above for the oblique patch stop, is important as the off-axis lighting often works best in a specific orientation to a subject e.g. for non-symmetric diatoms like Pleurosigma. Historical footnote In the late19th century but before the advent of high numerical aperture objectives, oblique illumination was quite popular and some makers developed microscopes especially to exploit the benefits of the technique. One of the first models was shown by Zentmayer of Philadelphia in 1876 at an Exposition in this city. It had a swinging substage, i.e. the whole substage assembly swung about an axis in the same plane as the stage. An image of this microscope is in the Moody Medical Library On-line (item 1.028 in catalogue). (This site illustrates a wonderful selection of historical microscopes from the famous Moody collection, most makers are represented). Some makers designed microscopes that took oblique illumination to rather extreme limits. The classic example is the Ross Radial microscope built by the famous English maker Ross to a design by Wenham. This is a superb example of quality engineering and optics by a respected maker, but a rather bizarre microscope nevertheless. Almost every conceivable plane and axis of the microscope limb, body and substage has the facility to be tilted or rotated (see ref. 2 or similar history of microscopes where this model is often illustrated). An image of this microscope is also in the Moody Medical Library On-line (item 1.031 in catalogue). The technique fell out of favour towards the end of the 19th century as high numerical aperture objectives became available with the ability to resolve the fine detail of diatoms etc. with good axial illumination. A firmer understanding of the requirements for a critical image with axial illumination were also realised. I wasn't sure how well the technique is used nowadays given the many other ways of improving contrast. However, a web search for 'oblique illumination' shows that some of the mainstream microscope makers mention this form of lighting as a feature in some of their models (particularly metallurgical), so presumably it does still have a worthwhile role. The oblique patch stop is certainly a cheap and cheerful way for the amateur to improve contrast for some subjects, especially at medium powers where patch stops for dark-field get trickier to make. I was also intrigued to see that at least one manufacturer, 'Edge', market a microscope with 'patented Multiple Obliquetm Illumination' which apparently gives 3D images. Visit the Edge web site for details and read the theory behind the technique for 3D imaging. Comments on the article to the author Dave Walker welcomed. References 1) 'Under the Microscope' by A. Curry, R. F. Grayson and G. R. Hosey, (Blandford Press, UK, 1982), Chapter 8. Now out of print, but worth looking out for in second-hand bookshops as it gives clear explanations of many techniques and principles, especially the use of polarised light. 2) 'The Microscope Past and Present' by S. Bradbury. Pergamon Press, UK, 1968, pp. 180-183. A compact but thorough overview of the history of the microscope and it's development. Illustrates and discusses the Ross Radial and Ross / Zentmayer microscope and the fad for oblique illumination. Microscopy UK Front Page Micscape Magazine Article Library Text and images © David Walker. © Onview.net Ltd, Microscopy-UK, and all contributors 1995 onwards. All rights reserved. Main site is at www.microscopy-uk.org.uk with full mirror at www.microscopy-uk.net.

2) 'The Microscope Past and Present' by S. Bradbury. Pergamon Press, UK, 1968, pp. 180-183. A compact but thorough overview of the history of the microscope and it's development. Illustrates and discusses the Ross Radial and Ross / Zentmayer microscope and the fad for oblique illumination. Microscopy UK Front Page Micscape Magazine Article Library Text and images © David Walker. © Onview.net Ltd, Microscopy-UK, and all contributors 1995 onwards. All rights reserved. Main site is at www.microscopy-uk.org.uk with full mirror at www.microscopy-uk.net.

Partnering with a local Australian archival framer, Urth Art prints are framed with sustainably sourced timber to display the artwork, without damaging the environment. And to bring the gallery experience home, Urth Art prints are protected by art-grade acrylic glazing that prevents fading and discolouration.

Urth Circular Polarizing Filters (CPL Polarizing Filters) cut reflected light from any direction. By cutting polarized light, our CPL Filters increase contrast and boost colour saturation and vibrancy. Our polarizing filters also cut reflections from glass and non-metallic surfaces. CPL Filters are a vital tool for outdoor photographer's kit.

To achieve the strongest polarization possible, the reflected light source needs to be at 90-degrees to your CPL. To check this, make an L-shape using your thumb and index finger. Point your thumb at the lens and wherever your index finger is pointed, that is the angle that will achieve maximum polarisation. Sometimes at full polarization, the effect can look unrealistic so we suggest you back it off a bit for a slightly softer polarization.

The technique fell out of favour towards the end of the 19th century as high numerical aperture objectives became available with the ability to resolve the fine detail of diatoms etc. with good axial illumination. A firmer understanding of the requirements for a critical image with axial illumination were also realised. I wasn't sure how well the technique is used nowadays given the many other ways of improving contrast. However, a web search for 'oblique illumination' shows that some of the mainstream microscope makers mention this form of lighting as a feature in some of their models (particularly metallurgical), so presumably it does still have a worthwhile role. The oblique patch stop is certainly a cheap and cheerful way for the amateur to improve contrast for some subjects, especially at medium powers where patch stops for dark-field get trickier to make. I was also intrigued to see that at least one manufacturer, 'Edge', market a microscope with 'patented Multiple Obliquetm Illumination' which apparently gives 3D images. Visit the Edge web site for details and read the theory behind the technique for 3D imaging. Comments on the article to the author Dave Walker welcomed. References 1) 'Under the Microscope' by A. Curry, R. F. Grayson and G. R. Hosey, (Blandford Press, UK, 1982), Chapter 8. Now out of print, but worth looking out for in second-hand bookshops as it gives clear explanations of many techniques and principles, especially the use of polarised light. 2) 'The Microscope Past and Present' by S. Bradbury. Pergamon Press, UK, 1968, pp. 180-183. A compact but thorough overview of the history of the microscope and it's development. Illustrates and discusses the Ross Radial and Ross / Zentmayer microscope and the fad for oblique illumination. Microscopy UK Front Page Micscape Magazine Article Library Text and images © David Walker. © Onview.net Ltd, Microscopy-UK, and all contributors 1995 onwards. All rights reserved. Main site is at www.microscopy-uk.org.uk with full mirror at www.microscopy-uk.net.

Make sure you have the right size filter and you’re all set. All our filters are designed with a super slim rim to minimise any vignetting that can occur with wide-angle lenses. Because of the amount of glass in telephoto and wide-angle lenses, Ous Plus+ range will provide the best image quality.