Raythemanroe
Bullet Whisperer
Awesome, but you should not have used a period after "most. but". You know if you are in the business of corrections..
Ray
ED Glass
- Thread starter mike a
- Start date
Ray
We've all figured out that your intellect is much more sophisticated than ours and so is your BS. A typo is a typo no matter how many times it's incorrect. Means nothing. You can continue your lesson somewhere else or stop being so condescending. Wrong forum.
Turbulent Turtle
F-TR competitor
Excellent. I'll be keeping my eye (behind fluorite glass) on you.
Turbulent Turtle
F-TR competitor
No, that's not correct. A typo is when you fumble the keys, have a frain bart or similar. When you write the word incorrectly EVERY SINGLE TIME, that's ignorance.
At any rate, I'm done with this. You guys want to call it flourite, have at it.
Raythemanroe
Bullet Whisperer
"Excellent, I'll be"Excellent. I'll be keeping my eye (behind fluorite glass) on you.
I fixed it for you.
Ray
Raythemanroe
Bullet Whisperer
Flourite
Ray
Ray
Raythemanroe
Bullet Whisperer
Floorite
Ray
Ray
Fred Bohl
Gold $$ Contributor
As I understand it, the labels of LD, ED, SLD or UD are the marketing terms. The families of low dispersion glass are graded by having relatively low Chromatic Dispersion (lower Refractive Index, and high Abbe Number) also high internal spectral Transmittance.
The material composition of these glasses features Fluorophosphate as an ingredient but of equal and even more importance is the processing. Controlling the melt temperature profile, sequence and amounts of mineral additions, as well as cooling temperature profile are all critical to achieving the desired properties.
Edit - Corrected thanks to Justin Credible
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Turbulent Turtle
F-TR competitor
That is also close to my understanding for the vast majority of ED glass claims. However, I do know that Nikon's Super-ED glass is a follow-on to their ED glass and as I understand it there is more fluorite material in the Super-ED compared to the ED glass. I haven't a clue about the wizardry used to make the glass in the first place; no ideas on how many eyes of newt, bees knees, and unicorn farts are required and in what sequence.
After reading through the comments here I feel like I should try and clear a few things up. I have worked in the precision optics industry making, and training others to make, precision optics in the U.S., Europe, and Asia for almost 20 years. I have seen a lot of things! I do have a BS degree in optics but am not a designer, just a lens maker with some knowledge of design. I'm not going to nit-pick on things like the spelling of fluorite or bad punctuation, I'm an engineer and screw those things up all the time, I just want to clear some things up as there is not really a good online resource for this stuff and there is a lot of incorrect info out there as well. I'll try not to be too long winded, but will likely fail, and I'll address things in more or less the order I see them in the comments and they pop in my head.
I have no scopes with ED lenses that I know of, I don't believe they are needed for sling shooting, so I won't comment on if they are worth it or not. I can certainly see a possible benefit for those shooting bench or F-class.
First, when I say "glass" I mean actual glass. If I mean a lens I will say "lens". Calling a lens glass is like calling your barrel steel. People rarely want to know who made the steel, they want to know the barrel maker. There are few major players in making glass with Schott, Hoya, and Ohara being the big ones for high quality stuff, and a LOT more companies that grind and polish glass (I work for one). The glass makers do relatively little lens making compared to the volume of glass they make. Seeing Schott or whoever on your optic just means they made the glass, they probably did not grind and polish the lens. The glass might not have even been made in Germany! Lens prints will say something like "N-BK7 or equivalent" as each maker has their own version of many glasses with a different name. Ohara can make stuff as good as Schott, though each does have some unique glasses. And just like with barrel making you can take high quality material and make a bad product, but you can't take bad material and make a high quality product.
ED, HD, etc. glass is essentially a marketing term. There is no official definition of it that I have ever come across, but you will see some makers put it in their glass names. For simplicity I will use ED glass as generally used here and elsewhere, a very low dispersion glass. Some of the lower quality makers of rifle scopes (very cheap scopes) use the term more loosely...
When a scope does use ED lenses in the design it is typically only 1 to maybe 3 of the dozen or so lenses in the scope. A scope made with only ED lenses would not only be very expensive, as the material is pricey and a pain to grind/polish, but would also have very poor performance. It would actually end up with a considerable amount of chromatic aberration as well as all other sorts of aberrations. An ED lens has less dispersion (basically how much different colors of light bend relative to each other) but there is still some there. This is countered by using lenses with high dispersion (e.g. achromat)! The advantage of using ED lenses is that it allows better pairing with high dispersion lenses to give a better overall color correction (less chromatic aberration) and less creation of other errors. The bad thing with ED glass is that it has a LOW index of fraction, meaning it bends light less than higher dispersion glass. One effect of this is that for a given focal length the lens must have a steeper curve, which leads to other aberrations such as spherical that degrade the image quality. Optical system design is all about compromise and using subsequent lenses to correct for aberrations created in the earlier lenses. Glass choice is critical in this and a scope with a dozen elements may have 10 different glass types (of hundreds available)! I THINK the reason Unertl and Lyman scopes were so long was the gentler curves created less spherical aberration, but that is an educated guess on my part. Unertl definitely used achromats.
There ARE current production rifle scopes with fluorite lenses. I guarantee it. I would wager most/all of the high dollar, high magnification, scopes do but I have not seen all of the lens prints for them so I can't say for sure. The fluorite lenses currently used are easier (that is a very relative term...) to process and relatively more resilient to shock, temperature, etc. when compared to older stuff. The material is also cheaper, like a Ferrari being cheaper than a Bugatti.
I have seen rifle scope designs with aspheric elements (making aspheres is my specialty), but cannot say if any are on the market. They are useful in telescope designs as they are excellent at correcting spherical aberration, which can be more of an issue when using low index ED glass. A good one is also expensive.
I have seen Nikon credited with inventing ED glass, and that might very well be the case but I do not know, but all the makers have their own versions of ED glass with fluorite being a common part of that. And just because it says Nikon on it does not mean Nikon even made the glass, or maybe even the lenses!
Coatings do indeed make a HUGE difference in overall optical performance. ED glass does tend to have better transmission as less light is lost at the air-glass boundary with its lower index of refraction, but good coatings can make all glasses transmit about equally for the thicknesses used.
The screenshot shared by Ledd Sligner is wrong (I don't know what website it is from) in that describes fluorite as a flint glass. It is WAY into the crown spectrum. To make an achromat you take a crown glass (such as fluorite, but the common BK7 is one as well) that has relatively low dispersion and pair it with a flint glass with relatively high dispersion to create the desired level of chromatic (and other) aberration for that set of lenses.
ED lenses have low dispersion which means that the Abbe Number (calculated from the actual refractive index at various wavelengths) is high but the refractive index is LOW. As a general trend a higher Abbe number means a lower refractive index.
I think that sums it up, hopefully I didn't screw up and make a mistake as well! I'm not trying to put anyone down with this, if you are not in the industry this stuff is not obvious and not easy to find accurate info on.
Let me know if I can clarify!
Justin
I have no scopes with ED lenses that I know of, I don't believe they are needed for sling shooting, so I won't comment on if they are worth it or not. I can certainly see a possible benefit for those shooting bench or F-class.
First, when I say "glass" I mean actual glass. If I mean a lens I will say "lens". Calling a lens glass is like calling your barrel steel. People rarely want to know who made the steel, they want to know the barrel maker. There are few major players in making glass with Schott, Hoya, and Ohara being the big ones for high quality stuff, and a LOT more companies that grind and polish glass (I work for one). The glass makers do relatively little lens making compared to the volume of glass they make. Seeing Schott or whoever on your optic just means they made the glass, they probably did not grind and polish the lens. The glass might not have even been made in Germany! Lens prints will say something like "N-BK7 or equivalent" as each maker has their own version of many glasses with a different name. Ohara can make stuff as good as Schott, though each does have some unique glasses. And just like with barrel making you can take high quality material and make a bad product, but you can't take bad material and make a high quality product.
ED, HD, etc. glass is essentially a marketing term. There is no official definition of it that I have ever come across, but you will see some makers put it in their glass names. For simplicity I will use ED glass as generally used here and elsewhere, a very low dispersion glass. Some of the lower quality makers of rifle scopes (very cheap scopes) use the term more loosely...
When a scope does use ED lenses in the design it is typically only 1 to maybe 3 of the dozen or so lenses in the scope. A scope made with only ED lenses would not only be very expensive, as the material is pricey and a pain to grind/polish, but would also have very poor performance. It would actually end up with a considerable amount of chromatic aberration as well as all other sorts of aberrations. An ED lens has less dispersion (basically how much different colors of light bend relative to each other) but there is still some there. This is countered by using lenses with high dispersion (e.g. achromat)! The advantage of using ED lenses is that it allows better pairing with high dispersion lenses to give a better overall color correction (less chromatic aberration) and less creation of other errors. The bad thing with ED glass is that it has a LOW index of fraction, meaning it bends light less than higher dispersion glass. One effect of this is that for a given focal length the lens must have a steeper curve, which leads to other aberrations such as spherical that degrade the image quality. Optical system design is all about compromise and using subsequent lenses to correct for aberrations created in the earlier lenses. Glass choice is critical in this and a scope with a dozen elements may have 10 different glass types (of hundreds available)! I THINK the reason Unertl and Lyman scopes were so long was the gentler curves created less spherical aberration, but that is an educated guess on my part. Unertl definitely used achromats.
There ARE current production rifle scopes with fluorite lenses. I guarantee it. I would wager most/all of the high dollar, high magnification, scopes do but I have not seen all of the lens prints for them so I can't say for sure. The fluorite lenses currently used are easier (that is a very relative term...) to process and relatively more resilient to shock, temperature, etc. when compared to older stuff. The material is also cheaper, like a Ferrari being cheaper than a Bugatti.
I have seen rifle scope designs with aspheric elements (making aspheres is my specialty), but cannot say if any are on the market. They are useful in telescope designs as they are excellent at correcting spherical aberration, which can be more of an issue when using low index ED glass. A good one is also expensive.
I have seen Nikon credited with inventing ED glass, and that might very well be the case but I do not know, but all the makers have their own versions of ED glass with fluorite being a common part of that. And just because it says Nikon on it does not mean Nikon even made the glass, or maybe even the lenses!
Coatings do indeed make a HUGE difference in overall optical performance. ED glass does tend to have better transmission as less light is lost at the air-glass boundary with its lower index of refraction, but good coatings can make all glasses transmit about equally for the thicknesses used.
The screenshot shared by Ledd Sligner is wrong (I don't know what website it is from) in that describes fluorite as a flint glass. It is WAY into the crown spectrum. To make an achromat you take a crown glass (such as fluorite, but the common BK7 is one as well) that has relatively low dispersion and pair it with a flint glass with relatively high dispersion to create the desired level of chromatic (and other) aberration for that set of lenses.
ED lenses have low dispersion which means that the Abbe Number (calculated from the actual refractive index at various wavelengths) is high but the refractive index is LOW. As a general trend a higher Abbe number means a lower refractive index.
I think that sums it up, hopefully I didn't screw up and make a mistake as well! I'm not trying to put anyone down with this, if you are not in the industry this stuff is not obvious and not easy to find accurate info on.
Let me know if I can clarify!
Justin
Ledd Slinger
Silver $$ Contributor
R.Morehouse
Gold $$ Contributor
Turbulent Turtle
F-TR competitor
Really? Name one. The only one that I have ever heard of that had fluorite lenses was an Hensoldt 6-24x72. This was a few years back and I do remember the MSRP as being upwards of $7,000. It clearly stated it had fluorite lenses in the marketing literature I saw.
So, let me ask you this. What do you consider a high dollar, high magnification scope? The highest magnification scope of which I am aware is the March-X 8-80X56 and it's virtually the same as my March-X 5-50X56; the only difference being the low end magnification being 8X compared to my 5X. I run my March at 40X virtually all the time, so I never had "magnification envy."
The most expensive riflescope (all optics, no electronics involved other than lighting the reticle) in production that I am aware of is the March 6-60X56 Genesis at over $6,000. It has Super-ED lenses, not fluorite. That's about the same price as that Hensoldt fluorite lens scope.
If there is a riflescope maker out there with fluorite lenses, they sure are keeping it a secret. It's not S&B, Swaro, Docter, Kahles, March, NF, Leupold, Zeiss, USO, etc. So, please point us to some of those riflescopes with fluorite lenses.
On the other hand, some spotting scopes come with fluorite glass and their makers are making sure to say so in their marketing literature. The Kowa Prominar 500 Fluorite comes to mind. There are also many spotting scopes sporting ED lenses.
I can assure you that there are people in the shooting world, especially in competition circles, who would drop any amount of money on optics if they saw an advantage or even just for bragging rights.
Fluorite lenses are found in very high-end camera lenses also, and like spotting scopes, these lenses are simply not subjected the repeated massive pounding that riflescope lenses experience.
Excellent, so please explain what an aspheric lens element would provide in a riflescope? As I said earlier, the only aspheric lens elements that I know about in consumer optics are found in wide-angle lenses. I would love to learn more. (Maybe in very short scopes?)
I was the one who brought that up. I am a long time camera enthusiast and that's usually where one first sees the advancements in consumer optics. In 2017, Nikon celebrated its 100th year and I have been a user of their products for several of those decades. Nikon clearly takes the credit for inventing ED glass in the mid-1960s, but that does not mean that others were left behind. Nikon makes a lot of glass and lenses for others and you are totally correct that just because it says Nikon on the scope or camera lens, it does not necessarily mean that the glass or the lens elements are made by Nikon. As a photographers, we have always known that. But when it comes to their higher end camera lenses, especially the ones made in Japan, Nikon has stated that they make the glass and the lens elements. Nikon has factories in many countries, including China, Thailand and The Philippines. They do say that they make the glass and lenses in those countries also, but they do not say they use only their glass and lenses for those optics.
It's actually pretty easy to differentiate; if the lens is affordable, it was not made in Japan and probably does not have Nikon's glass and lenses in it, or certainly not stuff that comes from their Hikari glass factory. I don't believe any of their riflescopes or even most of their fieldscopes are made in Japan, but I could be wrong. And anyway, I believe that is only a small part of their operations.
I'm glad we agree on coatings. Again, this was first seen for consumer optics, in camera lenses and I remember when they were first introduced in the late 60s early 70s. This is when we were first introduced to terms that I discussed earlier, like "coated," "multi-coated," and "fully multi-coated". You needed a dictionary to understand what was being said (we didn't have the Internet in those days.)
Well, just the various questions I have stated up above. Thanks for taking the time.
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Turbulent Turtle
F-TR competitor
I found the scope with fluorite lenses: The Hensoldt 6-24x72 SAM. I amended my prior post.
http://bulletin.accurateshooter.com/2014/10/worlds-most-expensive-scope-12k-hensoldt-6-24x72mm-sam/
http://bulletin.accurateshooter.com/2014/10/worlds-most-expensive-scope-12k-hensoldt-6-24x72mm-sam/
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I can't reveal models or makers. The optics world is very secretive about these things. When I used to train people on using a specific machine to polish optics most of our customers, especially in Japan and Germany, would not allow us to even reveal they had such equipment. Most have now relented though. But talking about their specific products is certainly still off-limits for me.
I think part of the confusion comes from how we are all using "fluorite". I don't follow the camera and astronomy world very closely but I do know there seems to be disagreement on what is and what is not a fluorite glass. In my experience in the lens manufacturing world a fluorite glass is one who receives a substantial performance from fluorine (keep in mind I know very little about the manufacture of glass, just lenses). This means things like the S-FPL series from Ohara and N-FK series from Schott (among others). Some people also refer to them as fluoro or fluoride glasses. Or that crappy glass (in reference to polishing it). These are absolutely used in some rifle scope designs being produced today. Over the years I have personally polished some of those lenses! Now if you are talking the crystal of Calcium Fluoride, I suspect you are, it's a different story. I have worked with it a lot, and other Fuorides, but I know of no rifle scopes using them. I would even be afraid to have a spotting scope with it, though the fear seems to be unwarranted on my part.
I don't have specific numbers in mind for high dollar/magnification. There is no hard cut-off there and it depends on the application. For me, being a sling shooter, 25X is high power. No reason to go higher, maybe some good reasons to go lower. This applies to smallbore and out to 1000 yards for centerfire. Big bucks for ED lenses is also not needed for that, I don't think I have spent over $600 on a scope and have set national records. Any issues aiming are from my moving, not because I can't make out the paper fibers. Not that the "better" scopes don't have notably nicer images, they do, I just don't think it's needed for that. For somebody shooting from a rest (on the bench or ground) the game changes, and that version of high magnification is different than mine. I have virtually no experience there but I can see the value in spending big bucks on better lenses there. I know there are scopes under 25X with fluorite lenses, but I do not want to guess at what price point they start using them.
An asphere gives the same benefits in a rifle scope as it does a camera, wide angle or not, minimizing aberrations caused by the other elements to maximize resolution. The primary target is spherical aberration but higher order stuff can be addressed as well. As far as consumer optics, there are lots of aspheres out there but they are mostly inexpensive plastic or glass molded (not my areas of expertise, I grind, polish, and measure). They are common in cell phone cameras and even the Kodak Disc had one. I'm fairly certain Blu-Ray, and maybe DVD/CD's use them as well but I could be wrong on that. Some eyeglasses as well. The quality of all these pale in comparison to the aspheres used in a quality camera lens.
I'm new to this forum so hopefully my quotes and comments display right.....
Justin
Turbulent Turtle
F-TR competitor
Bingo, we were essentially talking at cross purposes. Yes, I was talking about pure fluorite glass crystals. As I understand it, ED glass contains fluorite in it and I believe Super-ED glass contains more than ED glass does and yep, lots of high-end scopes have that in some fashion.
I had kinda gathered that you were not familiar with higher end riflescopes. As a sling shooter, there really is no call for that but in F-Class and similar, that's what it's all about. You would be shocked to see the amount and quality of optics at an F-Class competition. I'm sure it's the same at PRS and BR, I just don't do those.
You did just fine, thank you so much for taking the time and I hope you stick around.
Raythemanroe
Bullet Whisperer
Kowa Floorite:
"XD lens:Optical glass with extra low dispersion. Also called ED, HD, SD, UD or LD lens.
The lens has been developed as an alternative material to fluorite crystal. XD lens can reduce chromatic aberration, although to a lesser extent than with fluorite crystal.
The word "fluorite" is sometimes used to mean optical glass containing fluorite component (fluorite glass).
The XD lens is made of fluorite glass. At Kowa, the name "fluorite" is only used for pure fluorite crystal."
Ray
"XD lens:Optical glass with extra low dispersion. Also called ED, HD, SD, UD or LD lens.
The lens has been developed as an alternative material to fluorite crystal. XD lens can reduce chromatic aberration, although to a lesser extent than with fluorite crystal.
The word "fluorite" is sometimes used to mean optical glass containing fluorite component (fluorite glass).
The XD lens is made of fluorite glass. At Kowa, the name "fluorite" is only used for pure fluorite crystal."
Ray
Raythemanroe
Bullet Whisperer
Kowa Floorite:
"A mysterious stone called fluorite emits light like a firefly when it is heated or exposed to ultraviolet radiation. Chemically, it consists of fluorite (F) and calcium(Ca), comprising a stable halogenide mineral (CaF2). Natural fluorite contains trace amounts of rare earth elements, giving the stone a greenish or purplish color and causing it to emit fluorescence in response to heat or ultraviolet radiation.
The fluorite used in lenses is an artificially made monocrystal. Therefore, it does not contain any impurities, nor does it emit fluorescence when heated or exposed to ultraviolet rays, but it is a highly uniform and clear lens material. Artificial fluorite is chemically stable, and it is easier to make relatively large crystals of very high quality from it. "
Ray
"A mysterious stone called fluorite emits light like a firefly when it is heated or exposed to ultraviolet radiation. Chemically, it consists of fluorite (F) and calcium(Ca), comprising a stable halogenide mineral (CaF2). Natural fluorite contains trace amounts of rare earth elements, giving the stone a greenish or purplish color and causing it to emit fluorescence in response to heat or ultraviolet radiation.
The fluorite used in lenses is an artificially made monocrystal. Therefore, it does not contain any impurities, nor does it emit fluorescence when heated or exposed to ultraviolet rays, but it is a highly uniform and clear lens material. Artificial fluorite is chemically stable, and it is easier to make relatively large crystals of very high quality from it. "
Ray
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