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Differing Grades of ED/HD glass (1 Viewer)
- Thread starter jgraider
- Start date
Nope, although I do recall that discussion. But at the risk of seeming presumptious, there are three grades of fluoride bearing abnormal "ED" glass, referred to by some makers ( cross referenced to other maker's nomenclature, all of whom share the same final numerical suffixes) as FPL51, FPL52, and FPL53, in ascending order of abnormality. Only very slightly better than FPL53 is pure calcium fluorite crystal, commonly called "fluorite".
When paired with the best mating element in a doublet lens, FPL51, 52, and 53 provide reductions of color error, compared to a normal crown/flint doublet, of factors of about 2, 4, and 8 respectively.
I am not posing as an optics expert by any means, but have read some things on this subject at the amateur level (I would recommend Rutten and van Venrooij's "Telescope Optics"), due to my interest in astronomical telescopes. My scope being, after all that, a crown/flint doublet!
Otherwise, to find that original thread, I would search on "Abbe number".
Ron
When paired with the best mating element in a doublet lens, FPL51, 52, and 53 provide reductions of color error, compared to a normal crown/flint doublet, of factors of about 2, 4, and 8 respectively.
I am not posing as an optics expert by any means, but have read some things on this subject at the amateur level (I would recommend Rutten and van Venrooij's "Telescope Optics"), due to my interest in astronomical telescopes. My scope being, after all that, a crown/flint doublet!
Otherwise, to find that original thread, I would search on "Abbe number".
Ron
henry link
Well-known member
Just to expand a little on Ron's information, most every glass maker seems to make an Ohara FPL51 equivalent with an Abbe# around 82, but AFAIK the only Fluorite equivalent glass in current production is FPL53 made only by Ohara with an Abbe number of 95. Ohara FPL52 (Abbe# around 90 I think) is no longer in production and I don't think there is an equivalent glass available from anyone else.
We aren't often told what glass is used in spotting scopes or binoculars, but since they (especially binoculars) represent a low magnification non-critical use it's probably safe to assume that most "ED" glass used in them is an FPL51 equivalent. I've heard of one spotting scope that is said to use FPL53 (Kowa 773/4) and no binoculars. I noticed one binocular maker specifying Schott FK5 with an Abbe# of 70, which barely qualifies as ED at all.
As Ron mentioned, the ED glass type determines the potential color correction, but the mating glass types and the overall design will determine if that potential is reached.
We aren't often told what glass is used in spotting scopes or binoculars, but since they (especially binoculars) represent a low magnification non-critical use it's probably safe to assume that most "ED" glass used in them is an FPL51 equivalent. I've heard of one spotting scope that is said to use FPL53 (Kowa 773/4) and no binoculars. I noticed one binocular maker specifying Schott FK5 with an Abbe# of 70, which barely qualifies as ED at all.
As Ron mentioned, the ED glass type determines the potential color correction, but the mating glass types and the overall design will determine if that potential is reached.
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henry link
Well-known member
The 883/884 uses Fluorite crystal, not glass. If the 773/774 really does use FPL53 there should be no significant difference in color correction, assuming optimum mating glass and design in both cases.
RJM
Don't Worry, Be Happy!
The Kowa 77x being a slightly slower scope, F6.6 vs F5.8 for the 88x, might display some other optical benefits too. Too bad this scope has never been sussed more by our sports optics cognoscenti. I'd like it to be FPL-53, but my spidy sense tells me "XD" is FPL-51. No matter as it seems to be an excellent optic in a very compact package.
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lilcrazy2
Well-known member
Alpen had sent me an email saying the ED glass they use in the Wings ED binos is an H-FK61 based material with an Abbe # of 81.5. They also sent this chart that shows some other grades of lesser glass. Perhaps they use different glass for their highest end Ranier ED's.
Tom
Tom
brocknroller
porromaniac
Henry,
Let me see if I'm understanding you correctly. You're saying, in regard to the ED glass used in binoculars, is that "most every" ED-glass binoculars, regardless of the name under which it's marketed (FL, HD, ED, XYZ) contains Ohara FPL51 or the equivalent ED glass. Correct?
That means that whether you buy a lower-priced Legend HD or a mid-priced Zen Ray ED3 or an uber-priced Nikon EDG or a "fluoride ion glass" Zeiss FL or Leica HD, or SV EL/SLC-HD, the ED components are all essentially the same?
Or did the qualifier of "most every" mean that premium bins use the better and presumably more expensive FPL53 ED glass?
Brock (aka "Eco-Glass Man")
Tom,
Here is Ohara's chart showing the relationship between their FPL51, 52(must be an old chart) and 53. If you click on "Nd-Vd diagram" and dcompare it to the chart you posted, you'll see that what is used in the Alpen Wings ED appears the same as what Ohara calls FPL51.
http://www.optics.arizona.edu/optomech/references/glass/Ohara_Glass_Catalog.pdf
It is good of them to share this information. I wonder what mating element they use.
Ron
Here is Ohara's chart showing the relationship between their FPL51, 52(must be an old chart) and 53. If you click on "Nd-Vd diagram" and dcompare it to the chart you posted, you'll see that what is used in the Alpen Wings ED appears the same as what Ohara calls FPL51.
http://www.optics.arizona.edu/optomech/references/glass/Ohara_Glass_Catalog.pdf
It is good of them to share this information. I wonder what mating element they use.
Ron
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RJM
Don't Worry, Be Happy!
To my knowledge the only Abbe# 95+ Fluorite crystal lens OEM's for consumer optics is Canon Optron and Sumita.
There is only 1 fluor crown optical glass with Abbe# >92, Ohara FPL-53 at Abbe# 94.9.
Fluor crown optical glass between Abbe# 92-90 consists LZOZ OK4, Hikari (Nikon) FKH2, Ohara FPL52(?), Hoya FCD10, and perhaps CDGM's rumored new H-FK70.
I would say these are the top-tier "ED" lens materials available today. Then there is the second tier of ED-type glass that clusters around Abbe# 81 followed by a third tier Abbe#70-ish.
I suspect most, if not all ED binoculars today use second tier Abbe#81-ish materials since there are only a handfull of optical glass OEMs to choose from. Unless, of course, Leica and Swaro melt their own glass without selling to third parties.
There is only 1 fluor crown optical glass with Abbe# >92, Ohara FPL-53 at Abbe# 94.9.
Fluor crown optical glass between Abbe# 92-90 consists LZOZ OK4, Hikari (Nikon) FKH2, Ohara FPL52(?), Hoya FCD10, and perhaps CDGM's rumored new H-FK70.
I would say these are the top-tier "ED" lens materials available today. Then there is the second tier of ED-type glass that clusters around Abbe# 81 followed by a third tier Abbe#70-ish.
I suspect most, if not all ED binoculars today use second tier Abbe#81-ish materials since there are only a handfull of optical glass OEMs to choose from. Unless, of course, Leica and Swaro melt their own glass without selling to third parties.
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henry link
Well-known member
Tom,
H-FK61 is made by the large Chinese glass company CDGM. Roland Christen of Astro-Physics said on the Astromart Forums that it's hardly any more expensive than BK7 which explains why ED glass is turning up in some inexpensive optics. It's probably the "ED" glass in most of the Chinese ED binoculars.
Brock,
I just visited a few glass catalogues. I think we can assume that Zeiss is using Schott glass, Nikon is using glass from its Hikari division and at least for now Pentax is using Hoya glass. I don't know where Leica and Swarovski buy their optical glass.
Schott lists only one ED glass, N-FK51A with an Abbe# of about 84, only slightly higher than FPL51, so its color correction potential isn't much different. That is almost certainly what they call FL glass. Hikari and Hoya each make an ED glass type that is equivalent to FPL51 (Abbe around 81-82) and they also make equivalents of the discontinued Ohara FPL52 with Abbe#'s around 91, so I was wrong about there being no FPL52 equivalents available. None of these companies lists an equivalent to Ohara FPL53.
I wouldn't read too much into these numbers. Ultimately what matters is not the glass type, but how well the chromatic aberrations are corrected in the final design. This is especially true for lateral CA in binoculars which seems to have more complex causes than longitudinal CA. Both longitudinal and lateral CA are things you can test for yourself, even if you don't know anything about what kind of glass is used, if you're willing to go to the trouble to use boosted magnification and a high contrast target under controlled repeatable conditions.
Henry
Edit: I just saw Rick's post above. I agree with all that.
BTW, Rick, I thought you said that the Kowa 773/774 uses FPL53 in a recent post. Not so?
H-FK61 is made by the large Chinese glass company CDGM. Roland Christen of Astro-Physics said on the Astromart Forums that it's hardly any more expensive than BK7 which explains why ED glass is turning up in some inexpensive optics. It's probably the "ED" glass in most of the Chinese ED binoculars.
Brock,
I just visited a few glass catalogues. I think we can assume that Zeiss is using Schott glass, Nikon is using glass from its Hikari division and at least for now Pentax is using Hoya glass. I don't know where Leica and Swarovski buy their optical glass.
Schott lists only one ED glass, N-FK51A with an Abbe# of about 84, only slightly higher than FPL51, so its color correction potential isn't much different. That is almost certainly what they call FL glass. Hikari and Hoya each make an ED glass type that is equivalent to FPL51 (Abbe around 81-82) and they also make equivalents of the discontinued Ohara FPL52 with Abbe#'s around 91, so I was wrong about there being no FPL52 equivalents available. None of these companies lists an equivalent to Ohara FPL53.
I wouldn't read too much into these numbers. Ultimately what matters is not the glass type, but how well the chromatic aberrations are corrected in the final design. This is especially true for lateral CA in binoculars which seems to have more complex causes than longitudinal CA. Both longitudinal and lateral CA are things you can test for yourself, even if you don't know anything about what kind of glass is used, if you're willing to go to the trouble to use boosted magnification and a high contrast target under controlled repeatable conditions.
Henry
Edit: I just saw Rick's post above. I agree with all that.
BTW, Rick, I thought you said that the Kowa 773/774 uses FPL53 in a recent post. Not so?
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lilcrazy2
Well-known member
Henry
I agree with you and don't really concern myself with the type of glass, and have a non ED glass bino that handles CA as well or better than many of the $500 ED binos.
Many months ago when I did a review of the 8x42 Alpen Wings ED binos, someone asked what type of flourite glass they had. I called Tim Gardner up and asked the question since the box says " ED optics is achieved through the use of flourite glass....". He admitted they were not using flourite glass but some type of composition, and later sent the email stating what they use.
Tom
Tom
I agree with you and don't really concern myself with the type of glass, and have a non ED glass bino that handles CA as well or better than many of the $500 ED binos.
Many months ago when I did a review of the 8x42 Alpen Wings ED binos, someone asked what type of flourite glass they had. I called Tim Gardner up and asked the question since the box says " ED optics is achieved through the use of flourite glass....". He admitted they were not using flourite glass but some type of composition, and later sent the email stating what they use.
Tom
Tom
RJM
Don't Worry, Be Happy!
Perhaps, maybe, could be....heck Henry I don't know for sure! Seems to be some confusion over at their HQ over what the switchover from "ED" to "XD" in their nomenclature a few years back meant for the optics materials-wise. Frankly, the objective lens could made from caliche and I wouldn't care to be the wiser as long as the view was pleasing.8-P
henry link
Well-known member
Rick,
I looked for that post and couldn't find it. Maybe I dreamed it. I have a friend who owns a 773. Maybe I'll try to borrow it and run some tests.
Henry
I looked for that post and couldn't find it. Maybe I dreamed it. I have a friend who owns a 773. Maybe I'll try to borrow it and run some tests.
Henry
Henry and Rick,
My notes based on subjective assessment with the night sky and various daytime targets from a few years back when I tested the Kowa 773 & 883 with my cherry Nikon ED 82 A as a reference had the 883 with the lowest CA I have seen in spotting scopes. The Nikon was better than the 773 but not as good as the 883. Based on this, my guess would be that Kowa does not use FPL 53 and that Nikon might use a Hikari FPL 52 equivalent in their scopes. But this is just guessing.
Kimmo
My notes based on subjective assessment with the night sky and various daytime targets from a few years back when I tested the Kowa 773 & 883 with my cherry Nikon ED 82 A as a reference had the 883 with the lowest CA I have seen in spotting scopes. The Nikon was better than the 773 but not as good as the 883. Based on this, my guess would be that Kowa does not use FPL 53 and that Nikon might use a Hikari FPL 52 equivalent in their scopes. But this is just guessing.
Kimmo
