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Ultravid & ED Glass; Help me understand. (1 Viewer)
- Thread starter Buz
- Start date
NoSpringChicken
Well-known member
The latest Ultravid HD range uses FL or Fluorite glass which is more or less the same thing as ED glass. I am sure someone else will provide a more technical explanation than this in due course.
Ron
Ron
Last edited:
Kevin Purcell
Well-known member
Leica Ultravid HD binoculars (and scopes) use "Fluoride glass" or more correctly fluophosphate glass in their objectives.
http://en.wikipedia.org/wiki/Fluorophosphate_glass
Fluorite (with a T) is much abused term by marketers and really means calcium fluorite (CaF2) ... it's not a glass it's a calcium fluorite crystal. It's brittle, absorbs water (so it's not used as the outer element) and it's expensive. It's never used in binoculars and rarely used in spotting scopes today, Kowa were the last, I think).
The explosion in equivalent marketing terms (mixed with technical terms) for low dispersion glasses just confuses the consumer: ED, HD, XD, FL, L, LD, UL, LD, SLD, ULD, etc. But I suspect that's the point ("We have HD glass but Zeiss is just FL").
http://en.wikipedia.org/wiki/Low_dispersion_glass
It's up there with APO.
http://en.wikipedia.org/wiki/Fluorophosphate_glass
Fluorite (with a T) is much abused term by marketers and really means calcium fluorite (CaF2) ... it's not a glass it's a calcium fluorite crystal. It's brittle, absorbs water (so it's not used as the outer element) and it's expensive. It's never used in binoculars and rarely used in spotting scopes today, Kowa were the last, I think).
The explosion in equivalent marketing terms (mixed with technical terms) for low dispersion glasses just confuses the consumer: ED, HD, XD, FL, L, LD, UL, LD, SLD, ULD, etc. But I suspect that's the point ("We have HD glass but Zeiss is just FL").
http://en.wikipedia.org/wiki/Low_dispersion_glass
It's up there with APO.
Tvc15_2000
Well-known member
I saved this some time ago off the web, I searched for it again and could not locate the article intact. So here it is with the images seperated from the article.
Stephen Ingraham writes:
White light, ordinary daylight, is a mixture of all the individual colors in the rainbow. When light passes through glass, even the glass of the best lens, each color of light is bent at a slightly different angle, so that daylight is broken up into its individual colors. We call that “dispersion.” White light is “dispersed” into its individual colors. Because of the difference in how much each color is bent, no lens can bring all three primary colors to the same focus. Therefore you get fringes of out-of-focus color around every object in the image. They show up best at the high contrast edges of things. We call this effect: Chromatic Aberration.
Way back at the dawn of glass optics, designers discovered that using two different kinds of glass in lenses carefully ground and matched to each other, and then cemented together, could “cure” much of this aberration. In essence, the first part of the lens produces a normal “dispersion” of the light into its spectrum (rainbow), but then the second lens is ground to compliment the first (bowing in where the other bows out) and so to reverse the dispersion—to, in effect, pull the different colors of light back to the same focus. Carefully selecting the refractive index (the amount the glass bends the light) of the two lens elements produces a lens that is more or less color corrected for two of the three primary colors. We call such a cemented, color corrected lens an achromat, or an achromatic doublet.
The human eye is very forgiving. We tend to tune out the narrow greenish-yellow and reddish-purple lines on either side of light and dark edges that remain in even the best achromatic lens designs. I had to actually teach myself to see it in binoculars, after readers of BVD complained that I was not commenting on it. (Do yourself a favor. If you don’t see it, don’t teach yourself to. You will regret it.) However, the reality is that even at low powers, all that unfocused color tends to “muddy” the colors and reduce the visible detail in the image. It is not an effect you notice without comparing the achromat to a system with a better design, but it is visible when you do, primarily as an added “snap” or “vividness” to the whole image. The better corrected a system is, the “cleaner” the colors, and the whole image, will look.
As magnification and the focal length of the objective (the big lens) increase, however, as in a spotting scope, the color fringes themselves become objectionably noticeable. The longer the focal length of the objective, the more space the colors have to spread, and, of course, the fringes and the muddying effect are magnified right along with the image. Still, a properly designed and manufactured achromat can produce very satisfying images, especially at lower powers.
Spotting scope designers, and especially long camera lens designers, needed a better solution. Films (and now, digital sensors) are as unforgiving as the human eye is forgiving…every color fringe leaps out in a photograph (as many a beginning digiscoper has discovered to his or her grief), and the overall lack of vivid color is really noticeable in high power photos. And, as above, even the human eye and brain reaches the limits of its tolerance for aberration when the powers increase over about 40x. Designers began to experiment with “low dispersion” and “extra-low dispersion glass” (“ED”). ED is glass which has a high “heavy metal” or “rare earth” content, making it very dense, and keeping the various colors of light as close together as possible. Using ED in an achromatic doublet design, or, better yet, in an air spaced triplet design (where the light passes through three lenses before focus), can correct almost all of the chromatic aberration, and produce a very “clean” image.
Unfortunately, ED glass has it drawbacks. The primary one is weight. The same density that gives it its low dispersion also makes it quite a bit heavier than other glass. The heavy metals used in its manufacture are environmentally dangerous, and it does tend to have a slight yellow cast which much be corrected for with proper coatings, or it will color the image.
Sometimes other “low dispersion” materials are used to the same effect. The most common is Calcium Fluoride or, as it is known, Fluorite. Fluorite crystals can be grown big enough in the lab to grind into lens elements of up to 100mm. It is not an easy material to work with, being both fragile and relatively toxic. It is not very stable with changes in temperature either. There are persistent rumors of fluorite elements cracking under field use, though I have to say I have heard of no confirmed reports.
Recently a third alternative has become available to optical designers. FL glass, a special optical glass which is enhanced with fluorine ions, has the advantages of both ED and Fluorite, but without the drawbacks of either. The introduction of FL glass allows the design of systems that are light weight, durable, and which offer superior color correction.
The use of any of these low dispersion materials, especially in multiple element objective designs can produce what we call Apochromatic performance, or a lens that brings all three of the primary colors of light to the same focus. One would think then that the Color Fringing demon is licked.
Unfortunately, to complicate matters, modern wide field eyepieces and optical systems that use them also produce some color fringing of their own, especially away from the center of the field. This off-axis color, or secondary spectrum, is related to spherical aberration: the failure of a spherical lens to focus light that passes through the center of the lens at the same point it focuses light that passes through the edges of the lens. As I understand it, spherical aberration effects each color of light slightly differently, so that, as you approach the edge of the field, the different colors of light spread out again, causing noticeable color fringes.
Therefore the best you can hope for in current modern optics is an elimination of “most” “noticeable” color fringing, at the center of the field. There will always be some visible at the edges. Still, a well designed modern system which uses ED, Fluorite, or FL glass produces an image, especially at higher powers, that is noticeably cleaner than conventional glass optics. The extra vividness increases your pleasure in the image, makes possible the differentiation of finer shades of colors (especially, for some reason, the blues), and, we are discovering, even at the lower powers common in binoculars, increases color perception in low light situations, enhancing the twilight performance of the optics.
Almost all of the high end makers produce a spotting scope that uses some kind of low dispersion material in the objective lens, often in conjunction with a multiple lens design (more than two elements). The use of ED glass in binocular objectives, while not as common, or as well advertised, is happening. Carl Zeiss Sports Optics has just introduced the first binoculars with FL glass, and a multiple lens design, in the objective, producing, what is to my (admittedly somewhat prejudiced) eye, the cleanest, clearest, most vivid binocular image currently available.
Are there improvements yet to be made? One of possible uses of “aspheric” elements in objective and eyepiece design (aspheric means a lens that is shaped to some complex curve that is not a simple section of a sphere) would be to “cure” the last of the secondary off-axis color and produce an image that is as close to color pure as possible. There are already camera lenses that have eliminated all visible color fringing, even in very long 800mm and greater telephotos, and in very complex 1-10x zooms on modern compact digital cameras. The question is: how many spotting scope and binocular customers would be willing to pay what one of those super-tele lenses cost ($8,000-$25,000) for their day-in, day-out optics, or, to put it another way, could any company hope to sell enough binoculars and scopes to equal the production run of your average compact digital camera? It is a matter of market.
Will an absolutely color perfect system be produced? It is only a matter of time, improved manufacturing techniques, new materials, and volume. It will be done. Who will do it? Well that will be the fun part to watch.
Try this:
• Choose any roof prism binocular.
• Look at a high contrast object: one with very dark horizontal or vertical bars against a light background is best. The bars of a window against the light from outside works very well, as do the sharp shadows thrown by architectural edges in buildings in full sun.
• As you focus on the vertical or horizontal edge you will see thin bands of color outlining the edge, similar to the fringes in the photos on the reverse side. If the dark object is thin enough you will see different color fringes on each side of it. If not, swing the binoculars to place the edge on either side of the center of the field and you will see the color change.
• Well corrected optics will show very thin color fringes near the center of the field, with the fringes becoming much wider and more visible as you move the high contrast edge toward the edge of the field, but all optics, especially roof prism binoculars, will show some color fringing.
• Note the brightness, and width of the color fringes near the center of the field and toward the edge of the field.
• Now try the same test with other roofs. Try ED glasses if you can find them. Definitely try the new Zeiss Victory FLs. Can you determine which ones have the best color correction? Does it, to your eye, correlate well with the overall cleanness and vividness of the colors. How does it correlate with the twilight performance of the optics.
• Try the same test with spotting scopes at powers over 40x. With spotting scopes it is relatively easy to find a variety of low dispersion designs.
Stephen Ingraham writes:
White light, ordinary daylight, is a mixture of all the individual colors in the rainbow. When light passes through glass, even the glass of the best lens, each color of light is bent at a slightly different angle, so that daylight is broken up into its individual colors. We call that “dispersion.” White light is “dispersed” into its individual colors. Because of the difference in how much each color is bent, no lens can bring all three primary colors to the same focus. Therefore you get fringes of out-of-focus color around every object in the image. They show up best at the high contrast edges of things. We call this effect: Chromatic Aberration.
Way back at the dawn of glass optics, designers discovered that using two different kinds of glass in lenses carefully ground and matched to each other, and then cemented together, could “cure” much of this aberration. In essence, the first part of the lens produces a normal “dispersion” of the light into its spectrum (rainbow), but then the second lens is ground to compliment the first (bowing in where the other bows out) and so to reverse the dispersion—to, in effect, pull the different colors of light back to the same focus. Carefully selecting the refractive index (the amount the glass bends the light) of the two lens elements produces a lens that is more or less color corrected for two of the three primary colors. We call such a cemented, color corrected lens an achromat, or an achromatic doublet.
The human eye is very forgiving. We tend to tune out the narrow greenish-yellow and reddish-purple lines on either side of light and dark edges that remain in even the best achromatic lens designs. I had to actually teach myself to see it in binoculars, after readers of BVD complained that I was not commenting on it. (Do yourself a favor. If you don’t see it, don’t teach yourself to. You will regret it.) However, the reality is that even at low powers, all that unfocused color tends to “muddy” the colors and reduce the visible detail in the image. It is not an effect you notice without comparing the achromat to a system with a better design, but it is visible when you do, primarily as an added “snap” or “vividness” to the whole image. The better corrected a system is, the “cleaner” the colors, and the whole image, will look.
As magnification and the focal length of the objective (the big lens) increase, however, as in a spotting scope, the color fringes themselves become objectionably noticeable. The longer the focal length of the objective, the more space the colors have to spread, and, of course, the fringes and the muddying effect are magnified right along with the image. Still, a properly designed and manufactured achromat can produce very satisfying images, especially at lower powers.
Spotting scope designers, and especially long camera lens designers, needed a better solution. Films (and now, digital sensors) are as unforgiving as the human eye is forgiving…every color fringe leaps out in a photograph (as many a beginning digiscoper has discovered to his or her grief), and the overall lack of vivid color is really noticeable in high power photos. And, as above, even the human eye and brain reaches the limits of its tolerance for aberration when the powers increase over about 40x. Designers began to experiment with “low dispersion” and “extra-low dispersion glass” (“ED”). ED is glass which has a high “heavy metal” or “rare earth” content, making it very dense, and keeping the various colors of light as close together as possible. Using ED in an achromatic doublet design, or, better yet, in an air spaced triplet design (where the light passes through three lenses before focus), can correct almost all of the chromatic aberration, and produce a very “clean” image.
Unfortunately, ED glass has it drawbacks. The primary one is weight. The same density that gives it its low dispersion also makes it quite a bit heavier than other glass. The heavy metals used in its manufacture are environmentally dangerous, and it does tend to have a slight yellow cast which much be corrected for with proper coatings, or it will color the image.
Sometimes other “low dispersion” materials are used to the same effect. The most common is Calcium Fluoride or, as it is known, Fluorite. Fluorite crystals can be grown big enough in the lab to grind into lens elements of up to 100mm. It is not an easy material to work with, being both fragile and relatively toxic. It is not very stable with changes in temperature either. There are persistent rumors of fluorite elements cracking under field use, though I have to say I have heard of no confirmed reports.
Recently a third alternative has become available to optical designers. FL glass, a special optical glass which is enhanced with fluorine ions, has the advantages of both ED and Fluorite, but without the drawbacks of either. The introduction of FL glass allows the design of systems that are light weight, durable, and which offer superior color correction.
The use of any of these low dispersion materials, especially in multiple element objective designs can produce what we call Apochromatic performance, or a lens that brings all three of the primary colors of light to the same focus. One would think then that the Color Fringing demon is licked.
Unfortunately, to complicate matters, modern wide field eyepieces and optical systems that use them also produce some color fringing of their own, especially away from the center of the field. This off-axis color, or secondary spectrum, is related to spherical aberration: the failure of a spherical lens to focus light that passes through the center of the lens at the same point it focuses light that passes through the edges of the lens. As I understand it, spherical aberration effects each color of light slightly differently, so that, as you approach the edge of the field, the different colors of light spread out again, causing noticeable color fringes.
Therefore the best you can hope for in current modern optics is an elimination of “most” “noticeable” color fringing, at the center of the field. There will always be some visible at the edges. Still, a well designed modern system which uses ED, Fluorite, or FL glass produces an image, especially at higher powers, that is noticeably cleaner than conventional glass optics. The extra vividness increases your pleasure in the image, makes possible the differentiation of finer shades of colors (especially, for some reason, the blues), and, we are discovering, even at the lower powers common in binoculars, increases color perception in low light situations, enhancing the twilight performance of the optics.
Almost all of the high end makers produce a spotting scope that uses some kind of low dispersion material in the objective lens, often in conjunction with a multiple lens design (more than two elements). The use of ED glass in binocular objectives, while not as common, or as well advertised, is happening. Carl Zeiss Sports Optics has just introduced the first binoculars with FL glass, and a multiple lens design, in the objective, producing, what is to my (admittedly somewhat prejudiced) eye, the cleanest, clearest, most vivid binocular image currently available.
Are there improvements yet to be made? One of possible uses of “aspheric” elements in objective and eyepiece design (aspheric means a lens that is shaped to some complex curve that is not a simple section of a sphere) would be to “cure” the last of the secondary off-axis color and produce an image that is as close to color pure as possible. There are already camera lenses that have eliminated all visible color fringing, even in very long 800mm and greater telephotos, and in very complex 1-10x zooms on modern compact digital cameras. The question is: how many spotting scope and binocular customers would be willing to pay what one of those super-tele lenses cost ($8,000-$25,000) for their day-in, day-out optics, or, to put it another way, could any company hope to sell enough binoculars and scopes to equal the production run of your average compact digital camera? It is a matter of market.
Will an absolutely color perfect system be produced? It is only a matter of time, improved manufacturing techniques, new materials, and volume. It will be done. Who will do it? Well that will be the fun part to watch.
Try this:
• Choose any roof prism binocular.
• Look at a high contrast object: one with very dark horizontal or vertical bars against a light background is best. The bars of a window against the light from outside works very well, as do the sharp shadows thrown by architectural edges in buildings in full sun.
• As you focus on the vertical or horizontal edge you will see thin bands of color outlining the edge, similar to the fringes in the photos on the reverse side. If the dark object is thin enough you will see different color fringes on each side of it. If not, swing the binoculars to place the edge on either side of the center of the field and you will see the color change.
• Well corrected optics will show very thin color fringes near the center of the field, with the fringes becoming much wider and more visible as you move the high contrast edge toward the edge of the field, but all optics, especially roof prism binoculars, will show some color fringing.
• Note the brightness, and width of the color fringes near the center of the field and toward the edge of the field.
• Now try the same test with other roofs. Try ED glasses if you can find them. Definitely try the new Zeiss Victory FLs. Can you determine which ones have the best color correction? Does it, to your eye, correlate well with the overall cleanness and vividness of the colors. How does it correlate with the twilight performance of the optics.
• Try the same test with spotting scopes at powers over 40x. With spotting scopes it is relatively easy to find a variety of low dispersion designs.
Attachments
Last edited:
Tvc15_2000
Well-known member
Thanks Frank. I miss Stephens’s posts also. I was sad to see the posting could no logger be found. So as not to hijack this thread I will post the other article I scraped off the web in 2006 have in its own thread..
spitfiretriple
Well-known member
Good post Tvc. Steven Ingraham's article deserves to be readily available somewhere, along with some of the posts of certain regualrs here. Maybe we need some sort of "accumulated wisdom" sticky. But maybe that's not how forums work.
I browsed SI's website. Some stunning images of butterflies. I had no idea America had so many beautiful species. I thought you had to go to a rainforest for such colour and variety. I'm amazed all Americans aren't lepidopterists!
I browsed SI's website. Some stunning images of butterflies. I had no idea America had so many beautiful species. I thought you had to go to a rainforest for such colour and variety. I'm amazed all Americans aren't lepidopterists!
Mac308
Well-known member
We're too busy waging a "global war on terrorism." :eek!: :C
The Takahashi Astronomer 22x60, one of the finest binoculars I've ever looked thru, does indeed use Fluorite, and it is the outside element.
edz
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