Hot Mirrors – heat control filters, heat removal, infrared, ... - mirror hot

 2024-10-12 09:12:45

Wow! This can be one of the most helpful blogs we have ever come across on thesubject. Basically wonderful info! I am also an expert in this topic therefore I can understand your hard work.

When it comes to the telescopes and the accessories that we review or recommend, our editorial board (which is comprised entirely of astronomers) makes unbiased judgments. Read our telescope testing methodology or read about us.

Hello! I simply would wish to supply a huge thumbs up for the wonderful info you might have here for this post. I am returning to your blog post for additional soon.

Glass prism

When you consider that air is more like crown glass than flint glass, and that the deflection produced by the whole atmosphere is (usually) only about half a degree, you can see why the dispersion of atmospheric refraction is only perceptible under unusual circumstances. © 2002, 2004 – 2008, 2012, 2014 Andrew T. Young Go back to the ... main optics page astronomical refraction page GF home page

Theoretically, it should be able to offer near-perfect alignment accuracy, just as good as collimating on a defocused star at high magnification.

The Apertura laser collimator uses a 45-degree window like the Hotech SCA laser, though we’ll need to provide our own 1.25” to 2” adapter.

However, compared to the Glatter, it is a little harder to see very small amounts of misalignment, and the family of accessories and other products is not as diverse as what is offered for the Glatter.

Types of opticalprisms

The figure was constructed using the actual dispersion curve of BK 7 crown glass, similar in its optical properties to ordinary window glass. Although the angle was chosen to give a large deflection, the dispersion is barely visible on your screen. You can see that ordinary glass produces very little dispersion. When dispersion is really wanted, a different type of glass (called “flint” glass, from one of the ingredients originally used in making it) is used. Yet even the highest-dispersion flint glasses have only 2 or 3 times as much dispersion at the same angular deflection as crown glass. When you consider that air is more like crown glass than flint glass, and that the deflection produced by the whole atmosphere is (usually) only about half a degree, you can see why the dispersion of atmospheric refraction is only perceptible under unusual circumstances. © 2002, 2004 – 2008, 2012, 2014 Andrew T. Young Go back to the ... main optics page astronomical refraction page GF home page

However, the SVBONY laser’s screws are hidden behind rubbery coverings, which I just poked through and destroyed to access the adjustment screws with a hex key.

What is prism in Physics

In optics, prisms made for the purpose of dispersing light are usually made with bases that are equilateral triangles, so that the angles between adjacent sides of the prism are 60°. However, prisms are also often used to re-direct light by using internal reflection; these often have bases that are isosceles right triangles, with angles of 45°-90°-45°. As optical technology developed, opticians found uses for more complicated pieces of glass with plane entrance, exit, and reflecting or refracting faces; but these are often not “prisms” in the geometric sense, but more complicated polyhedra, or even more complex shapes, with unused corners cut or rounded off to reduce weight. However, for our present purpose, the interesting prisms are those that deviate light by refraction, not reflection, and these are triangular. The ones used for dispersing light sometimes have only two adjacent faces polished; the third side and the bases are often left in a rough-ground state, and may be painted black to absorb unwanted reflections. The angle between the two polished faces is called the refracting angle. If the prism is to be used for its dispersion, the refracting angle is usually about 60°. On the other hand, refracting prisms are sometimes used to produce a very small angular deviation. These have a small refracting angle, and are often called wedges (although they do not have a sharp edge, which would be fragile and easily broken). If we are to compare the effects of atmospheric refraction — which typically produces an angular deviation (even at the horizon) of only half a degree, and never more than a few degrees — with a glass prism, one of these wedges would be the appropriate form. Sometimes a very thick wedge is used (e.g., the “Dove prism” used as an image rotator) to produce a small angular deviation by refraction, and the dispersion is merely a nuisance. For small angles, the deviation of a glass prism is about 1/3 of the prism angle, so a wedge angle of only a degree and a half would suffice to mimic the horizontal refraction of the standard atmosphere. An example Here's a beam of white light, coming vertically upward through a prism (shown in gray here) with a refracting angle of 38°. The bases of the prism are parallel to your screen. One side of the prism is horizontal, so the beam is not deviated when it enters the prism (at the bottom of the picture). When the light leaves the glass at the inclined face and enters the air, it is refracted, and the beam is deflected to the right; the deflection is larger at shorter (bluer) wavelengths. The figure was constructed using the actual dispersion curve of BK 7 crown glass, similar in its optical properties to ordinary window glass. Although the angle was chosen to give a large deflection, the dispersion is barely visible on your screen. You can see that ordinary glass produces very little dispersion. When dispersion is really wanted, a different type of glass (called “flint” glass, from one of the ingredients originally used in making it) is used. Yet even the highest-dispersion flint glasses have only 2 or 3 times as much dispersion at the same angular deflection as crown glass. When you consider that air is more like crown glass than flint glass, and that the deflection produced by the whole atmosphere is (usually) only about half a degree, you can see why the dispersion of atmospheric refraction is only perceptible under unusual circumstances. © 2002, 2004 – 2008, 2012, 2014 Andrew T. Young Go back to the ... main optics page astronomical refraction page GF home page

For visible light, which property changes with color

Prisms are usually classified by the shapes of the bases; so we have triangular, rectangular, hexagonal and other types of prism. The kind Newton experimented with were triangular; usually these are made with rather short side faces. In optics, prisms made for the purpose of dispersing light are usually made with bases that are equilateral triangles, so that the angles between adjacent sides of the prism are 60°. However, prisms are also often used to re-direct light by using internal reflection; these often have bases that are isosceles right triangles, with angles of 45°-90°-45°. As optical technology developed, opticians found uses for more complicated pieces of glass with plane entrance, exit, and reflecting or refracting faces; but these are often not “prisms” in the geometric sense, but more complicated polyhedra, or even more complex shapes, with unused corners cut or rounded off to reduce weight. However, for our present purpose, the interesting prisms are those that deviate light by refraction, not reflection, and these are triangular. The ones used for dispersing light sometimes have only two adjacent faces polished; the third side and the bases are often left in a rough-ground state, and may be painted black to absorb unwanted reflections. The angle between the two polished faces is called the refracting angle. If the prism is to be used for its dispersion, the refracting angle is usually about 60°. On the other hand, refracting prisms are sometimes used to produce a very small angular deviation. These have a small refracting angle, and are often called wedges (although they do not have a sharp edge, which would be fragile and easily broken). If we are to compare the effects of atmospheric refraction — which typically produces an angular deviation (even at the horizon) of only half a degree, and never more than a few degrees — with a glass prism, one of these wedges would be the appropriate form. Sometimes a very thick wedge is used (e.g., the “Dove prism” used as an image rotator) to produce a small angular deviation by refraction, and the dispersion is merely a nuisance. For small angles, the deviation of a glass prism is about 1/3 of the prism angle, so a wedge angle of only a degree and a half would suffice to mimic the horizontal refraction of the standard atmosphere. An example Here's a beam of white light, coming vertically upward through a prism (shown in gray here) with a refracting angle of 38°. The bases of the prism are parallel to your screen. One side of the prism is horizontal, so the beam is not deviated when it enters the prism (at the bottom of the picture). When the light leaves the glass at the inclined face and enters the air, it is refracted, and the beam is deflected to the right; the deflection is larger at shorter (bluer) wavelengths. The figure was constructed using the actual dispersion curve of BK 7 crown glass, similar in its optical properties to ordinary window glass. Although the angle was chosen to give a large deflection, the dispersion is barely visible on your screen. You can see that ordinary glass produces very little dispersion. When dispersion is really wanted, a different type of glass (called “flint” glass, from one of the ingredients originally used in making it) is used. Yet even the highest-dispersion flint glasses have only 2 or 3 times as much dispersion at the same angular deflection as crown glass. When you consider that air is more like crown glass than flint glass, and that the deflection produced by the whole atmosphere is (usually) only about half a degree, you can see why the dispersion of atmospheric refraction is only perceptible under unusual circumstances. © 2002, 2004 – 2008, 2012, 2014 Andrew T. Young Go back to the ... main optics page astronomical refraction page GF home page

There’s also a pretty good chance the laser will arrive misaligned with the collimator barrel from the factory, making it useless until we adjust it in a V-block with the (thankfully exposed) hex key screws.

However, before buying a Glatter TuBlug, which cost as much as the collimator itself, I had to look into the focuser to check my primary mirror alignment and then go back down to the adjustment screws instead of being able to check the alignment in real time. This was a bit of a pain initially.

Extremely sensitive to mechanical misalignments in the telescope that may not ultimately matter, such as the screws or compression ring in your focuser de-centering or tilting the laser.

The aim of this page is to show the deviation of light by a prism, and to indicate how small the dispersive effect really is. Prisms It may be helpful to remind you what a prism really is: a geometric figure bounded by planes, whose bases are equal polygons, similarly oriented in parallel planes. The planes defined by corresponding (and hence parallel) sides of these polygons intersect in lines that are all parallel, so that the side faces of the prism are all parallelograms. Prisms are usually classified by the shapes of the bases; so we have triangular, rectangular, hexagonal and other types of prism. The kind Newton experimented with were triangular; usually these are made with rather short side faces. In optics, prisms made for the purpose of dispersing light are usually made with bases that are equilateral triangles, so that the angles between adjacent sides of the prism are 60°. However, prisms are also often used to re-direct light by using internal reflection; these often have bases that are isosceles right triangles, with angles of 45°-90°-45°. As optical technology developed, opticians found uses for more complicated pieces of glass with plane entrance, exit, and reflecting or refracting faces; but these are often not “prisms” in the geometric sense, but more complicated polyhedra, or even more complex shapes, with unused corners cut or rounded off to reduce weight. However, for our present purpose, the interesting prisms are those that deviate light by refraction, not reflection, and these are triangular. The ones used for dispersing light sometimes have only two adjacent faces polished; the third side and the bases are often left in a rough-ground state, and may be painted black to absorb unwanted reflections. The angle between the two polished faces is called the refracting angle. If the prism is to be used for its dispersion, the refracting angle is usually about 60°. On the other hand, refracting prisms are sometimes used to produce a very small angular deviation. These have a small refracting angle, and are often called wedges (although they do not have a sharp edge, which would be fragile and easily broken). If we are to compare the effects of atmospheric refraction — which typically produces an angular deviation (even at the horizon) of only half a degree, and never more than a few degrees — with a glass prism, one of these wedges would be the appropriate form. Sometimes a very thick wedge is used (e.g., the “Dove prism” used as an image rotator) to produce a small angular deviation by refraction, and the dispersion is merely a nuisance. For small angles, the deviation of a glass prism is about 1/3 of the prism angle, so a wedge angle of only a degree and a half would suffice to mimic the horizontal refraction of the standard atmosphere. An example Here's a beam of white light, coming vertically upward through a prism (shown in gray here) with a refracting angle of 38°. The bases of the prism are parallel to your screen. One side of the prism is horizontal, so the beam is not deviated when it enters the prism (at the bottom of the picture). When the light leaves the glass at the inclined face and enters the air, it is refracted, and the beam is deflected to the right; the deflection is larger at shorter (bluer) wavelengths. The figure was constructed using the actual dispersion curve of BK 7 crown glass, similar in its optical properties to ordinary window glass. Although the angle was chosen to give a large deflection, the dispersion is barely visible on your screen. You can see that ordinary glass produces very little dispersion. When dispersion is really wanted, a different type of glass (called “flint” glass, from one of the ingredients originally used in making it) is used. Yet even the highest-dispersion flint glasses have only 2 or 3 times as much dispersion at the same angular deflection as crown glass. When you consider that air is more like crown glass than flint glass, and that the deflection produced by the whole atmosphere is (usually) only about half a degree, you can see why the dispersion of atmospheric refraction is only perceptible under unusual circumstances. © 2002, 2004 – 2008, 2012, 2014 Andrew T. Young Go back to the ... main optics page astronomical refraction page GF home page

It also has a built-in 45-degree window, so I could use it even while adjusting screws at the other end of the telescope.

I could use the hybrid 2″/1.25″ version with either size focuser without any difficulties or concerns about decentering the laser with an adapter.

One thing I’ve noticed is that it’s a lot less accurate than more expensive lasers due to the lack of a precision 2” adapter, grid lines, and machining tolerances.

The SVBONY laser collimator is similar to the Apertura laser in design and lack of precision, as I’ve used and confirmed. But it’s cheaper and does include a tight-fitting 1.25” to 2” adapter by default.

You can see that ordinary glass produces very little dispersion. When dispersion is really wanted, a different type of glass (called “flint” glass, from one of the ingredients originally used in making it) is used. Yet even the highest-dispersion flint glasses have only 2 or 3 times as much dispersion at the same angular deflection as crown glass. When you consider that air is more like crown glass than flint glass, and that the deflection produced by the whole atmosphere is (usually) only about half a degree, you can see why the dispersion of atmospheric refraction is only perceptible under unusual circumstances. © 2002, 2004 – 2008, 2012, 2014 Andrew T. Young Go back to the ... main optics page astronomical refraction page GF home page

Laser collimators are used for aligning the optics of Newtonian reflector telescopes and some catadioptric and Cassegrain telescopes, if need be.

An amateur astronomer and telescope maker from Connecticut who has been featured on TIME magazine, National Geographic, La Vanguardia, and Clarin, The Guardian, The Arizona Daily Star, and Astronomy Technology Today and had won the Stellafane 1st and 3rd place Junior Awards in the 2018 Convention. Zane has owned over 425 telescopes, of which around 400 he has actually gotten to take out under the stars. These range from the stuff we review on TelescopicWatch to homemade or antique telescopes; the oldest he has owned or worked on so far was an Emil Busch refractor made shortly before the outbreak of World War I. Many of these are telescopes that he repaired or built.

Make us think our secondary mirror is aligned when it’s actually rotated out of alignment and tilted severely. This may be hard to know if we don’t check with a collimation cap or Cheshire first.

Here's a beam of white light, coming vertically upward through a prism (shown in gray here) with a refracting angle of 38°. The bases of the prism are parallel to your screen. One side of the prism is horizontal, so the beam is not deviated when it enters the prism (at the bottom of the picture). When the light leaves the glass at the inclined face and enters the air, it is refracted, and the beam is deflected to the right; the deflection is larger at shorter (bluer) wavelengths. The figure was constructed using the actual dispersion curve of BK 7 crown glass, similar in its optical properties to ordinary window glass. Although the angle was chosen to give a large deflection, the dispersion is barely visible on your screen. You can see that ordinary glass produces very little dispersion. When dispersion is really wanted, a different type of glass (called “flint” glass, from one of the ingredients originally used in making it) is used. Yet even the highest-dispersion flint glasses have only 2 or 3 times as much dispersion at the same angular deflection as crown glass. When you consider that air is more like crown glass than flint glass, and that the deflection produced by the whole atmosphere is (usually) only about half a degree, you can see why the dispersion of atmospheric refraction is only perceptible under unusual circumstances. © 2002, 2004 – 2008, 2012, 2014 Andrew T. Young Go back to the ... main optics page astronomical refraction page GF home page

The Farpoint laser collimator is one great collimator that I noticed to be very similar to the Glatter in basic design and advantages.

I’d actually recommend you use the laser collimators not on their own but in conjunction with other collimation tools and methods, such as a collimation cap/Cheshire. Before using a laser, I always use such a tool to check for coarse secondary mirror alignment.

Types oflight prisms

The Hotech SCA laser collimator fits in either a 1.25” or 2” focuser using its proprietary “self-centering” rubber adapters.

An example Here's a beam of white light, coming vertically upward through a prism (shown in gray here) with a refracting angle of 38°. The bases of the prism are parallel to your screen. One side of the prism is horizontal, so the beam is not deviated when it enters the prism (at the bottom of the picture). When the light leaves the glass at the inclined face and enters the air, it is refracted, and the beam is deflected to the right; the deflection is larger at shorter (bluer) wavelengths. The figure was constructed using the actual dispersion curve of BK 7 crown glass, similar in its optical properties to ordinary window glass. Although the angle was chosen to give a large deflection, the dispersion is barely visible on your screen. You can see that ordinary glass produces very little dispersion. When dispersion is really wanted, a different type of glass (called “flint” glass, from one of the ingredients originally used in making it) is used. Yet even the highest-dispersion flint glasses have only 2 or 3 times as much dispersion at the same angular deflection as crown glass. When you consider that air is more like crown glass than flint glass, and that the deflection produced by the whole atmosphere is (usually) only about half a degree, you can see why the dispersion of atmospheric refraction is only perceptible under unusual circumstances. © 2002, 2004 – 2008, 2012, 2014 Andrew T. Young Go back to the ... main optics page astronomical refraction page GF home page

Prismlightrefraction

Laser collimators project a beam of light down your telescope tube and allow you to make sure your optics are aligned by getting light to hit the center of your primary mirror and bounce back perfectly into the focuser.

Can be rendered nearly useless if the laser itself is not aligned with the barrel of the collimator. This requires adjustment with the laser sitting in some sort of V-block to correct.

The Howie Glatter laser collimator offers superb machining accuracy and a laser that is certain to be dead-on from the factory.

Laser collimators are superior to regular Cheshire collimators and collimation caps. However, laser collimators are not perfect.

Since 2011, as AstronomySource and TelescopicWatch, we've published astronomy-related content and reviews to help guide the community better.

Types of prism

Dispersion oflightthrough prism

Like the Apertura laser, many of these lasers ship misaligned with the barrel, requiring us to adjust the alignment in a V-block.

Very sensitive to misalignment, making them arguably a must-have if you have a telescope with a focal ratio below f/4.5 or so.

It may be helpful to remind you what a prism really is: a geometric figure bounded by planes, whose bases are equal polygons, similarly oriented in parallel planes. The planes defined by corresponding (and hence parallel) sides of these polygons intersect in lines that are all parallel, so that the side faces of the prism are all parallelograms. Prisms are usually classified by the shapes of the bases; so we have triangular, rectangular, hexagonal and other types of prism. The kind Newton experimented with were triangular; usually these are made with rather short side faces. In optics, prisms made for the purpose of dispersing light are usually made with bases that are equilateral triangles, so that the angles between adjacent sides of the prism are 60°. However, prisms are also often used to re-direct light by using internal reflection; these often have bases that are isosceles right triangles, with angles of 45°-90°-45°. As optical technology developed, opticians found uses for more complicated pieces of glass with plane entrance, exit, and reflecting or refracting faces; but these are often not “prisms” in the geometric sense, but more complicated polyhedra, or even more complex shapes, with unused corners cut or rounded off to reduce weight. However, for our present purpose, the interesting prisms are those that deviate light by refraction, not reflection, and these are triangular. The ones used for dispersing light sometimes have only two adjacent faces polished; the third side and the bases are often left in a rough-ground state, and may be painted black to absorb unwanted reflections. The angle between the two polished faces is called the refracting angle. If the prism is to be used for its dispersion, the refracting angle is usually about 60°. On the other hand, refracting prisms are sometimes used to produce a very small angular deviation. These have a small refracting angle, and are often called wedges (although they do not have a sharp edge, which would be fragile and easily broken). If we are to compare the effects of atmospheric refraction — which typically produces an angular deviation (even at the horizon) of only half a degree, and never more than a few degrees — with a glass prism, one of these wedges would be the appropriate form. Sometimes a very thick wedge is used (e.g., the “Dove prism” used as an image rotator) to produce a small angular deviation by refraction, and the dispersion is merely a nuisance. For small angles, the deviation of a glass prism is about 1/3 of the prism angle, so a wedge angle of only a degree and a half would suffice to mimic the horizontal refraction of the standard atmosphere. An example Here's a beam of white light, coming vertically upward through a prism (shown in gray here) with a refracting angle of 38°. The bases of the prism are parallel to your screen. One side of the prism is horizontal, so the beam is not deviated when it enters the prism (at the bottom of the picture). When the light leaves the glass at the inclined face and enters the air, it is refracted, and the beam is deflected to the right; the deflection is larger at shorter (bluer) wavelengths. The figure was constructed using the actual dispersion curve of BK 7 crown glass, similar in its optical properties to ordinary window glass. Although the angle was chosen to give a large deflection, the dispersion is barely visible on your screen. You can see that ordinary glass produces very little dispersion. When dispersion is really wanted, a different type of glass (called “flint” glass, from one of the ingredients originally used in making it) is used. Yet even the highest-dispersion flint glasses have only 2 or 3 times as much dispersion at the same angular deflection as crown glass. When you consider that air is more like crown glass than flint glass, and that the deflection produced by the whole atmosphere is (usually) only about half a degree, you can see why the dispersion of atmospheric refraction is only perceptible under unusual circumstances. © 2002, 2004 – 2008, 2012, 2014 Andrew T. Young Go back to the ... main optics page astronomical refraction page GF home page

Prisms It may be helpful to remind you what a prism really is: a geometric figure bounded by planes, whose bases are equal polygons, similarly oriented in parallel planes. The planes defined by corresponding (and hence parallel) sides of these polygons intersect in lines that are all parallel, so that the side faces of the prism are all parallelograms. Prisms are usually classified by the shapes of the bases; so we have triangular, rectangular, hexagonal and other types of prism. The kind Newton experimented with were triangular; usually these are made with rather short side faces. In optics, prisms made for the purpose of dispersing light are usually made with bases that are equilateral triangles, so that the angles between adjacent sides of the prism are 60°. However, prisms are also often used to re-direct light by using internal reflection; these often have bases that are isosceles right triangles, with angles of 45°-90°-45°. As optical technology developed, opticians found uses for more complicated pieces of glass with plane entrance, exit, and reflecting or refracting faces; but these are often not “prisms” in the geometric sense, but more complicated polyhedra, or even more complex shapes, with unused corners cut or rounded off to reduce weight. However, for our present purpose, the interesting prisms are those that deviate light by refraction, not reflection, and these are triangular. The ones used for dispersing light sometimes have only two adjacent faces polished; the third side and the bases are often left in a rough-ground state, and may be painted black to absorb unwanted reflections. The angle between the two polished faces is called the refracting angle. If the prism is to be used for its dispersion, the refracting angle is usually about 60°. On the other hand, refracting prisms are sometimes used to produce a very small angular deviation. These have a small refracting angle, and are often called wedges (although they do not have a sharp edge, which would be fragile and easily broken). If we are to compare the effects of atmospheric refraction — which typically produces an angular deviation (even at the horizon) of only half a degree, and never more than a few degrees — with a glass prism, one of these wedges would be the appropriate form. Sometimes a very thick wedge is used (e.g., the “Dove prism” used as an image rotator) to produce a small angular deviation by refraction, and the dispersion is merely a nuisance. For small angles, the deviation of a glass prism is about 1/3 of the prism angle, so a wedge angle of only a degree and a half would suffice to mimic the horizontal refraction of the standard atmosphere. An example Here's a beam of white light, coming vertically upward through a prism (shown in gray here) with a refracting angle of 38°. The bases of the prism are parallel to your screen. One side of the prism is horizontal, so the beam is not deviated when it enters the prism (at the bottom of the picture). When the light leaves the glass at the inclined face and enters the air, it is refracted, and the beam is deflected to the right; the deflection is larger at shorter (bluer) wavelengths. The figure was constructed using the actual dispersion curve of BK 7 crown glass, similar in its optical properties to ordinary window glass. Although the angle was chosen to give a large deflection, the dispersion is barely visible on your screen. You can see that ordinary glass produces very little dispersion. When dispersion is really wanted, a different type of glass (called “flint” glass, from one of the ingredients originally used in making it) is used. Yet even the highest-dispersion flint glasses have only 2 or 3 times as much dispersion at the same angular deflection as crown glass. When you consider that air is more like crown glass than flint glass, and that the deflection produced by the whole atmosphere is (usually) only about half a degree, you can see why the dispersion of atmospheric refraction is only perceptible under unusual circumstances. © 2002, 2004 – 2008, 2012, 2014 Andrew T. Young Go back to the ... main optics page astronomical refraction page GF home page

The main effect of a prism is to deviate a beam of light. But, because of the dispersion in the refractivity of transparent materials, the deviation is slightly different for light of different colors. This slight difference in the deviation — only one or two percent, typically — is where the dispersive power of a prism comes from. The aim of this page is to show the deviation of light by a prism, and to indicate how small the dispersive effect really is. Prisms It may be helpful to remind you what a prism really is: a geometric figure bounded by planes, whose bases are equal polygons, similarly oriented in parallel planes. The planes defined by corresponding (and hence parallel) sides of these polygons intersect in lines that are all parallel, so that the side faces of the prism are all parallelograms. Prisms are usually classified by the shapes of the bases; so we have triangular, rectangular, hexagonal and other types of prism. The kind Newton experimented with were triangular; usually these are made with rather short side faces. In optics, prisms made for the purpose of dispersing light are usually made with bases that are equilateral triangles, so that the angles between adjacent sides of the prism are 60°. However, prisms are also often used to re-direct light by using internal reflection; these often have bases that are isosceles right triangles, with angles of 45°-90°-45°. As optical technology developed, opticians found uses for more complicated pieces of glass with plane entrance, exit, and reflecting or refracting faces; but these are often not “prisms” in the geometric sense, but more complicated polyhedra, or even more complex shapes, with unused corners cut or rounded off to reduce weight. However, for our present purpose, the interesting prisms are those that deviate light by refraction, not reflection, and these are triangular. The ones used for dispersing light sometimes have only two adjacent faces polished; the third side and the bases are often left in a rough-ground state, and may be painted black to absorb unwanted reflections. The angle between the two polished faces is called the refracting angle. If the prism is to be used for its dispersion, the refracting angle is usually about 60°. On the other hand, refracting prisms are sometimes used to produce a very small angular deviation. These have a small refracting angle, and are often called wedges (although they do not have a sharp edge, which would be fragile and easily broken). If we are to compare the effects of atmospheric refraction — which typically produces an angular deviation (even at the horizon) of only half a degree, and never more than a few degrees — with a glass prism, one of these wedges would be the appropriate form. Sometimes a very thick wedge is used (e.g., the “Dove prism” used as an image rotator) to produce a small angular deviation by refraction, and the dispersion is merely a nuisance. For small angles, the deviation of a glass prism is about 1/3 of the prism angle, so a wedge angle of only a degree and a half would suffice to mimic the horizontal refraction of the standard atmosphere. An example Here's a beam of white light, coming vertically upward through a prism (shown in gray here) with a refracting angle of 38°. The bases of the prism are parallel to your screen. One side of the prism is horizontal, so the beam is not deviated when it enters the prism (at the bottom of the picture). When the light leaves the glass at the inclined face and enters the air, it is refracted, and the beam is deflected to the right; the deflection is larger at shorter (bluer) wavelengths. The figure was constructed using the actual dispersion curve of BK 7 crown glass, similar in its optical properties to ordinary window glass. Although the angle was chosen to give a large deflection, the dispersion is barely visible on your screen. You can see that ordinary glass produces very little dispersion. When dispersion is really wanted, a different type of glass (called “flint” glass, from one of the ingredients originally used in making it) is used. Yet even the highest-dispersion flint glasses have only 2 or 3 times as much dispersion at the same angular deflection as crown glass. When you consider that air is more like crown glass than flint glass, and that the deflection produced by the whole atmosphere is (usually) only about half a degree, you can see why the dispersion of atmospheric refraction is only perceptible under unusual circumstances. © 2002, 2004 – 2008, 2012, 2014 Andrew T. Young Go back to the ... main optics page astronomical refraction page GF home page

On the other hand, refracting prisms are sometimes used to produce a very small angular deviation. These have a small refracting angle, and are often called wedges (although they do not have a sharp edge, which would be fragile and easily broken). If we are to compare the effects of atmospheric refraction — which typically produces an angular deviation (even at the horizon) of only half a degree, and never more than a few degrees — with a glass prism, one of these wedges would be the appropriate form. Sometimes a very thick wedge is used (e.g., the “Dove prism” used as an image rotator) to produce a small angular deviation by refraction, and the dispersion is merely a nuisance. For small angles, the deviation of a glass prism is about 1/3 of the prism angle, so a wedge angle of only a degree and a half would suffice to mimic the horizontal refraction of the standard atmosphere. An example Here's a beam of white light, coming vertically upward through a prism (shown in gray here) with a refracting angle of 38°. The bases of the prism are parallel to your screen. One side of the prism is horizontal, so the beam is not deviated when it enters the prism (at the bottom of the picture). When the light leaves the glass at the inclined face and enters the air, it is refracted, and the beam is deflected to the right; the deflection is larger at shorter (bluer) wavelengths. The figure was constructed using the actual dispersion curve of BK 7 crown glass, similar in its optical properties to ordinary window glass. Although the angle was chosen to give a large deflection, the dispersion is barely visible on your screen. You can see that ordinary glass produces very little dispersion. When dispersion is really wanted, a different type of glass (called “flint” glass, from one of the ingredients originally used in making it) is used. Yet even the highest-dispersion flint glasses have only 2 or 3 times as much dispersion at the same angular deflection as crown glass. When you consider that air is more like crown glass than flint glass, and that the deflection produced by the whole atmosphere is (usually) only about half a degree, you can see why the dispersion of atmospheric refraction is only perceptible under unusual circumstances. © 2002, 2004 – 2008, 2012, 2014 Andrew T. Young Go back to the ... main optics page astronomical refraction page GF home page

Can be used to collimate Schmidt-Cassegrain, Ritchey-Chretien, and other Cassegrain-type telescopes if you know what you are doing, though I don’t consider it to be the most intuitive or affordable option.

The TuBlug, if you buy it, can also amplify the sensitivity of your laser to miscollimation. However, it may induce mechanical misalignment/sagging if your focuser cannot handle it.

However, for our present purpose, the interesting prisms are those that deviate light by refraction, not reflection, and these are triangular. The ones used for dispersing light sometimes have only two adjacent faces polished; the third side and the bases are often left in a rough-ground state, and may be painted black to absorb unwanted reflections. The angle between the two polished faces is called the refracting angle. If the prism is to be used for its dispersion, the refracting angle is usually about 60°. On the other hand, refracting prisms are sometimes used to produce a very small angular deviation. These have a small refracting angle, and are often called wedges (although they do not have a sharp edge, which would be fragile and easily broken). If we are to compare the effects of atmospheric refraction — which typically produces an angular deviation (even at the horizon) of only half a degree, and never more than a few degrees — with a glass prism, one of these wedges would be the appropriate form. Sometimes a very thick wedge is used (e.g., the “Dove prism” used as an image rotator) to produce a small angular deviation by refraction, and the dispersion is merely a nuisance. For small angles, the deviation of a glass prism is about 1/3 of the prism angle, so a wedge angle of only a degree and a half would suffice to mimic the horizontal refraction of the standard atmosphere. An example Here's a beam of white light, coming vertically upward through a prism (shown in gray here) with a refracting angle of 38°. The bases of the prism are parallel to your screen. One side of the prism is horizontal, so the beam is not deviated when it enters the prism (at the bottom of the picture). When the light leaves the glass at the inclined face and enters the air, it is refracted, and the beam is deflected to the right; the deflection is larger at shorter (bluer) wavelengths. The figure was constructed using the actual dispersion curve of BK 7 crown glass, similar in its optical properties to ordinary window glass. Although the angle was chosen to give a large deflection, the dispersion is barely visible on your screen. You can see that ordinary glass produces very little dispersion. When dispersion is really wanted, a different type of glass (called “flint” glass, from one of the ingredients originally used in making it) is used. Yet even the highest-dispersion flint glasses have only 2 or 3 times as much dispersion at the same angular deflection as crown glass. When you consider that air is more like crown glass than flint glass, and that the deflection produced by the whole atmosphere is (usually) only about half a degree, you can see why the dispersion of atmospheric refraction is only perceptible under unusual circumstances. © 2002, 2004 – 2008, 2012, 2014 Andrew T. Young Go back to the ... main optics page astronomical refraction page GF home page

Many people suppose that the main optical action of a prism is to disperse white light into its component parts, because that's what Isaac Newton used prisms for. But because dispersion is really a very small effect, it isn't the main optical action of a prism; more correctly, it should be looked at a a minor side effect. The main effect of a prism is to deviate a beam of light. But, because of the dispersion in the refractivity of transparent materials, the deviation is slightly different for light of different colors. This slight difference in the deviation — only one or two percent, typically — is where the dispersive power of a prism comes from. The aim of this page is to show the deviation of light by a prism, and to indicate how small the dispersive effect really is. Prisms It may be helpful to remind you what a prism really is: a geometric figure bounded by planes, whose bases are equal polygons, similarly oriented in parallel planes. The planes defined by corresponding (and hence parallel) sides of these polygons intersect in lines that are all parallel, so that the side faces of the prism are all parallelograms. Prisms are usually classified by the shapes of the bases; so we have triangular, rectangular, hexagonal and other types of prism. The kind Newton experimented with were triangular; usually these are made with rather short side faces. In optics, prisms made for the purpose of dispersing light are usually made with bases that are equilateral triangles, so that the angles between adjacent sides of the prism are 60°. However, prisms are also often used to re-direct light by using internal reflection; these often have bases that are isosceles right triangles, with angles of 45°-90°-45°. As optical technology developed, opticians found uses for more complicated pieces of glass with plane entrance, exit, and reflecting or refracting faces; but these are often not “prisms” in the geometric sense, but more complicated polyhedra, or even more complex shapes, with unused corners cut or rounded off to reduce weight. However, for our present purpose, the interesting prisms are those that deviate light by refraction, not reflection, and these are triangular. The ones used for dispersing light sometimes have only two adjacent faces polished; the third side and the bases are often left in a rough-ground state, and may be painted black to absorb unwanted reflections. The angle between the two polished faces is called the refracting angle. If the prism is to be used for its dispersion, the refracting angle is usually about 60°. On the other hand, refracting prisms are sometimes used to produce a very small angular deviation. These have a small refracting angle, and are often called wedges (although they do not have a sharp edge, which would be fragile and easily broken). If we are to compare the effects of atmospheric refraction — which typically produces an angular deviation (even at the horizon) of only half a degree, and never more than a few degrees — with a glass prism, one of these wedges would be the appropriate form. Sometimes a very thick wedge is used (e.g., the “Dove prism” used as an image rotator) to produce a small angular deviation by refraction, and the dispersion is merely a nuisance. For small angles, the deviation of a glass prism is about 1/3 of the prism angle, so a wedge angle of only a degree and a half would suffice to mimic the horizontal refraction of the standard atmosphere. An example Here's a beam of white light, coming vertically upward through a prism (shown in gray here) with a refracting angle of 38°. The bases of the prism are parallel to your screen. One side of the prism is horizontal, so the beam is not deviated when it enters the prism (at the bottom of the picture). When the light leaves the glass at the inclined face and enters the air, it is refracted, and the beam is deflected to the right; the deflection is larger at shorter (bluer) wavelengths. The figure was constructed using the actual dispersion curve of BK 7 crown glass, similar in its optical properties to ordinary window glass. Although the angle was chosen to give a large deflection, the dispersion is barely visible on your screen. You can see that ordinary glass produces very little dispersion. When dispersion is really wanted, a different type of glass (called “flint” glass, from one of the ingredients originally used in making it) is used. Yet even the highest-dispersion flint glasses have only 2 or 3 times as much dispersion at the same angular deflection as crown glass. When you consider that air is more like crown glass than flint glass, and that the deflection produced by the whole atmosphere is (usually) only about half a degree, you can see why the dispersion of atmospheric refraction is only perceptible under unusual circumstances. © 2002, 2004 – 2008, 2012, 2014 Andrew T. Young Go back to the ... main optics page astronomical refraction page GF home page

It comes in a 1.25”/2” hybrid barrel for use in any size focuser without the need for an adapter, just like the Howie Glatter.