Fresnel screenvs ALRscreen

While examining a slide or an object in a microscope, the lens closest to it is called the objective lens, which collects light and increases the magnification of the object being examined.

Microscopic lenses result in higher magnification of the object under examination to the observer. At higher magnification, it becomes easy to analyze even minute details of the object. By using multiple lenses in a microscope, object image becomes clearer and easier to examine. With the help of multiple lenses, an object image can even be magnified more than 1000 times.

Optical glass is often used to create microscopic lenses. It is considerably more uniform and has higher purity than conventional glass.

Ahmed, Usman. "What is the Role of Lenses in Microscopy?". AZoOptics. https://www.azooptics.com/Article.aspx?ArticleID=2339. (accessed November 25, 2024).

To drive air bubbles to the surface, the temperature is raised to 1550 °C. The mixture is then steadily cooled to 1000 °C with continuous agitation.

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You may be able to find Fresnel lenses to fit view cameras, but it will be difficult, if possible at all, to find ones for SLRs and TLRs. In large part, because their viewing systems/focussing screens already are equiped with Fresnel lenses. ;-)

The Speed here has been used for many decades for astro stuff; where the focus was done with the GG/Fresnel combo; with lenses wide open; often big fast ones. On a properly non messed with speed the back panel is very accurate. One does have a slight focus shift on some lenses if one stops down ; one with the scan backs can do a minor tweak if wanted.

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Anything between the GG and the lens affects the focus. Just by refraction, the effective distance is increased by about 1/3rd of the thickness, and the Fresnel refraction adds to that. When focusing a view camera, hundredths (perhaps thousandths) of an inch matter at the focal plane.

There is a problem though with the optical tricks (and those include using a Fresnel lens): because being directional, they have a focus, and assume your eye will be in a certain place. And not only that: they also assume that the exit pupil of the lens is in a certain place (that's why some manufacturers supplied different focussing screens for use with long lenses).

On Ebay Speed Graphics mine are really two piles; perfect GG/Fresnel setups; OR ones with a focus error ; due to the Kilroy factor ( GG and Fresnel in backward; or only GG in a GG/Fresnel type focus panel)

A conventional microscope employs numerous lenses and a light source to significantly enhance the image of the object under examination.

Thanks, Q.G. I`m now thinking that I`m probably into this assumption because time ago, I used to use some screens from Beattie; these were one-piece plastic fresnel+groundglass. I remember to have this ones installed on a 4x5" and on the F3 as well.

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Some viewing screens have both a Fresnel and convex lens. That's one reason the Nikon F3 has such an extraordinarily clear viewfinder. The ground surface of an Hasselblad "Acute-Matte" screen is actually composed of microscopic prisms angled to redirect light toward the center, in addition to a conventional Fresnel lens. Screens for autofocus cameras (e.g., Nikon) are bright because they are ground less aggressively (in addition to a Fresnel lens), which passes more light but makes them somewhat hard to use for manual focusing.

Very interesting. Certainly I never know what to do with the fresnel while focusing on the Sinar. Thanks God it`s made in plastic.

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On the 4x5 Speed graphic here GG with Fresnel is very accurate; it is what I use to scan artwork with our 35 and 50 Megapixel Phase One scan backs; where never the RF is used.

Fowler, S. A., & Allansmith, M. R. (1981). The Effect of Cleaning Soft Contact Lenses: A Scanning Electron Microscopic Study. Archives of Ophthalmology, 99(8), 1382–1386. https://jamanetwork.com/journals/jamaophthalmology/article-abstract/633879

The blank is clamped into a vice and kept in place beneath a diamond-tipped, cylinder-shaped cutter that spins at high speed. The blank's surface is trimmed with this cutter in the desired curvature.

A common thrown around tolerance is that the film plane to GG error on some LF cameras is can be +/- .007 inches on some folks cameras. On a press camera the; the tolerance really has to be tighter; one is using faster lenses like my 210mm F3.5 Xenar and focusing on the back screen; ie the GG/Fresnel combo; it NOT tiny apertures but big ones.

Shorter lenses needs fresnels for better viewing, longer lenses could be used without them. Depending on the lens availability, the manufacturer could offer different solutions. As far as I know, Yashicas are fixed lens cameras, then it`s a closed camera system. If on Rolleis lenses are interchangeable, the user could choose one or another configuration.

And that's the only way to make a screen brighter: making sure most of the light hitting it goes in a direction where it will be seen. The coarseness (or fineness) of a scattering surface would make no difference.

Ahmed, Usman. 2022. What is the Role of Lenses in Microscopy?. AZoOptics, viewed 25 November 2024, https://www.azooptics.com/Article.aspx?ArticleID=2339.

The compound microscope uses a series of lenses to magnify the image. These lenses are made of optical glass, which is significantly purer and clearer than regular glass.

The GG with Fresnel also works well with the old 178mm F2.5 wide open; a lens that I have used for astro work for about 3+ decades.

Putting the Fresnel lens on the side of the lens isn't really creating a big problem. And being on the other side instead of between you and the screen itself, it does make inspecting the screen image easier.

The only reason a Speed Graphic's GG-Fresnels should be off is if a doofus/Kilroy was in the loop; ie one who screwed up the precision settup. This is actually quite common; folks combine cameras; replace screens and then one gets a focus error; ie the Kilroy/ goober factor.

A microscope uses two smaller lenses, i.e., an objective lens near the sample and an ocular lens near the observer. The magnification of both these lenses can be the same or different from one another. Multiplying the magnification of each lens yields the overall magnification of the microscope. With a 10x ocular and a 30x objective, the microscope's total magnification is 300x.

A condenser lens is located between the light source and the slide platform. It focuses the beam of light on the object and further passes it to the objective lens. The diaphragm controls the quantity of light entering the condenser lens. Anytime a different objective lens can be used to view the item, the amount of light entering the lens can be changed. With magnifications of 400x or more, condenser lenses are very useful.

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But i don't think you're right believing that the coarser a screen the brighter it is. The brightness of a screen depends on (as Edward said) how much light is scattered away vs towards your eye. A simple ground glass screen favours no particular direction, and it makes no difference whether coarse or fine.

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The lens the observer looks through when using a microscope is called an ocular lens. It takes light from the objective lens and re-magnifies it to show a large image. In most cases, the ocular lens magnifies 10x or 15x.

Coming back to Thomas question, Rolleicords could be much older cameras than Yashicas, and I bet there are different categories.

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Usman holds a master's degree in Material Science and Engineering from Xian Jiaotong University, China. He worked on various research projects involving Aerospace Materials, Nanocomposite coatings, Solar Cells, and Nano-technology during his studies. He has been working as a freelance Material Engineering consultant since graduating. He has also published high-quality research papers in international journals with a high impact factor. He enjoys reading books, watching movies, and playing football in his spare time.

After cutting, a lens inspection is carried out, and if the required curvature is not achieved, cutting is done again. This process requires a few minutes to well over an hour.

(The first generation Acute Matte screens Hasselblad used, for instance, had too little of the last, so the micro-optical structures were changed to scatter light a bit more again. A little less bright, but a bit easier to focus.)

The optical properties of optical glass depend highly upon its composition, which includes a mixture of boron oxide, sodium oxide, barium oxide, zinc oxide, potassium oxide, or lead oxide.

Whatever the camera you choose, you`ll probably find a fresnel for it. There are several third party fresnel manufacturers that cut fresnels for different cameras.

A microscope is used to magnify the image of tiny objects. The objects are clearly seen with a microscope because at least one lens magnifies the image. This lens refracts the light so that it enters the eye and magnifies distant objects.

A ground glass provides a translucent surface on which a real image can be projected and viewed. The diffusion is not perfect, so much of the light from the lens tends to continue in a straight line, away from the person's viewing eye, making the edges appear darker than the center. A Fresnel lens bends the light so that it converges on the eye, making the corners appear as bright as the center. To this extent, a Fresnel lens acts like a simple, convex lens at the surface of the ground glass, but is much thinner and lighter.

A microscope is an additional lens placed in front of your eye. The microscope lens functions like a magnifying glass, bending light to make the object appear wider to get the desired magnification effect. However, a single large lens provides blurry and dark images.

Most compound microscopes use four objective lenses, including a low-power lens, a high-power lens, a scanning lens, and an oil-immersion lens.

Rolleiflex TLRs are fixed lens cameras too. Early Rolleis probably have one as a separate accessory, simply because they didn't think of building one into the viewing system when they first made the thingies. It came, as it were, as an afterthought.

A shot wide open at F4.7 is sharp at the center; the bag is only about 6 ft from the camera/scanner; thus here one has little if any Frensel issues.

I try to remember that coarser grainier surface, with extremely bright grains on the LF camera. Probably, is that brightness (from the fresnel) what gets me wrong about the grain size issue. On the F3, I try to remember that it was not as noticeable, perhaps a slightly bit brighter than the standard red point? screen. Anyway, I must have stopped using them after a short time.

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These bags were shot for some Attorney Work with the 50 megapixel scan back on the 4x5 Speed Graphic; where the focus is by the GG/Fresnel .
Then one slips in the scan back under the Graflok; then does a prescan; then a scan. With only one 500 watt lamp the lens was not stopped down much; ie about F8 on a 127mm Ektar. On a full scan one can see the fibers in the bags paper.

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Magnesium fluoride is commonly used as an anti-reflective coating on lenses. If a microscope contains a mirror, it is often made up of Pyrex glass. Silica (SiO2) is often used as a protective coating for mirrors, whereas aluminum is used for reflective coatings.

Furthermore, as with anything that has a focus, there is a depth of focus. The result is that there is not just one plane but a range, stretching from a small distance behind to a small distance in front of the plane in which the true image lies, in which the image can be seen to be sharp. So making a screen brighter the only way you can (i.e. by bending light towards one point: your eye) also makes it a bit more difficult to focus using such a screen.

Ahmed, Usman. "What is the Role of Lenses in Microscopy?". AZoOptics. 25 November 2024. .

For whatever reason Graphlex put the Fresnel on the lens side of the screen, where it affects the focusing distance. Acute-Matte screens are the same, but presumably with compensation for the effect on focusing. My Sinar has a Fresnel on the viewing side, and can be easily removed (not so easily stowed) for critical focusing.

The shape of the lens has a considerable effect on the refraction of light. In microscopes, convex lenses are usually employed because of their ability to concentrate light on a specific spot.

The thing to do is find a compromise, make a screen that combines even illumination (the thing the Fresnel lens provides) with a fine grain structure making fine focus possible (both dependent on Fresnel lens and screen), a way to stop light scattering in 'unproductive' directions thus making the image appear as bright as possible, and still a 'sufficiently definite' plane of focus.

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The Fresnel lens is (also as Edward said) the bit that is responsible for directing light towards the eye. It bends rays coming from the lens that are 'off target' towards your eye. But it can't do much about the scattering by the screen.

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Zhang, Y., & Gross, H. (2017). Systematic Design of Microscopic Lenses. Optical Design and Fabrication 2017 (Freeform, IODC, OFT) (2017), Paper IW4A.1, IW4A.1. https://opg.optica.org/abstract.cfm?uri=IODC-2017-IW4A.1

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The raw materials and specific optical glass are combined in the correct ratios. This cullet (i.e., optical glass) serves as a flux. A flux helps lower the temperature at which raw materials normally react. A glass furnace is typically used for melting this mixture around 1400 °C. The temperature may fluctuate depending on the type of lens being manufactured.

Furthermore, the surface morphology of materials can be observed with the help of a tunneling microscope. Such microscopes use a beam of electrons that can tunnel through the surface of objects at incredibly small distances and form an image of the surface.

Lorenz, K. O., Kakkassery, J., Boree, D., & Pinto, D. (2014). Atomic force microscopy and scanning electron microscopy analysis of daily disposable limbal ring contact lenses. Clinical and Experimental Optometry, 97(5), 411–417. https://www.tandfonline.com/doi/abs/10.1111/cxo

Many of these bigger bags had boilerplate text that recorded poorly with a high end dslr. The bags were to thick to go through our 36" RGB scanner. They are court evidence. The big scan back records the fine type.

The human eye's biological lens is also convex because it focuses light onto the retina, where rod and cone cells are located to enable vision.

There are various kinds of microscopes used for magnification. An optical microscope is the most common type, creating an image from visible light using lenses. Another commonly used type of microscope is an electron microscope which uses an electron beam to form images.

A trick employed by some screens (like the Acute Matte screens) is to not use a scattering structure, but instead use an array of very small optical elements that each direct the light hitting it towards one point. Instead of scattering light in all directions, most then ends up going straight towards your eye. (The way it works is very much the same as how projection screens are made to reflect more light towards the viewing audience, and how 'cat's eye' road markings work)

These lenses provide magnification of 4x, 10x, 40x, and 100x, respectively. Generally, shorter lenses have less magnification power than longer ones.

In a true ground glass, the coarser the grit, the brighter the screen, and the harder to see and focus on fine detail. The finest screens in "the day" were etched with HF vapor, rather than sandblasted (or molded), making their diffusion nearly complete.

In my own Many Speed Graphics I have bought some off of Ebay that did have a focus error because somebody just had a GG' or had the GG/Fresnel sandwitch in wrong.

On a modern 4x5 film holder the reference surface to film I believe is 5mm; ie 0.197 inches. The Graflok frame to its reference is something like 1/8" ; 0.125 ( from memory) then one has the Ektalite Fresnel; plus the GG. The Fresnel and GG are roughly 1/16". The Optical stack of (1) machined surface; (2) Fresnel; (3) N-1/N times Fresnel thickness makes the focus be correct on GG; which faces the subject.

If one removes the Fresnel on one of these properly setup GG-Fresnel combos; the GG has to be shimmed out about 1/16 inch.

I suspect the GG on Speed Graphics was either window dressing, or used only at tiny apertures. Most of the time, the photographer would use a rangefinder for focusing and an optical or sports finder on top of the camera.

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Ahmed, Usman. (2022, November 02). What is the Role of Lenses in Microscopy?. AZoOptics. Retrieved on November 25, 2024 from https://www.azooptics.com/Article.aspx?ArticleID=2339.

On a properly settup Speed Graphic the GG and Fresnel is designed and built from the factory to focus spot on; ie it includes the (N-1)/N shift. This shift was known 400 years ago; thus it would be a total blunder for a person in Optics to not know this and thus compensate for it. The Graflok " frame's reference to seat where the GG/Fresnel combo sits" is different than if only a GG is used.

The mixture becomes a very thick liquid and is poured into lens molds at this stage. The annealing is carried out at 500 °C after cooling the mixture to approximately 300 °C. Annealing helps eliminate the internal stresses developed during the early cooling phase and weakens the glass. The glass is then gradually cooled to room temperature, and pieces are removed from the molds. These pieces are called blanks.