fluorite glass in medium format lenses?

[william_h._wiley]

Are any medium format cameras using fluorite glass in their lenses?

The best 35mmm lenses in Nikon & Canon are fluorite, and the results

are amazing. Other than cost, why haven't medium format manufactures

developed lenses with fluorite for optimal optics?

[Robin Smith]

William

 

Do not get too obsessed with flourite lenses and ED glass etc. etc. Fancy lenses needing high refractive index glass for their design often utilize such glasses as they are an integral part of the design of many fast large range zooms and so on. Super telephoto lenses too often use them. I suspect that quite a few MF lenses do have these fancy elements in them, but often not so much is made of them. When Zeiss say that the 350mm is a superachromat - my guess is that it has special glass. Likewise the Mamiya 645 APO lenses. It seems very likely to me that the Zeiss 110mm/2 has such glass in it and so on. The trouble with making a big deal about fancy glass is that when a lens does not need it to achieve the stated aim then it can look like a disadvantage compared to one that you can say is an FL/ED etc. lens. In many ways describing a lens as apochromatic is actually more useful as it tells you specific things about the lens' lack of chromatic abberation. Many Leica lenses are designated as apochromats with not a word about fluorite glass, for example. I think it is important to realize that Japanese lens manufacturers are excellent marketeers and know that stressing such things as flourite elements and so on attracts buyers. The German tradition is more that the quality will speak for itself without giving people a lot of guff about low-dispersion elements, etc.

 

In short FL lenses and such are not unknown in the MF world, but less marketing breath is spent on them. It also bears remembering that fluorite lenses have been around for at least 25 years - they are not a new thing at all. Just like multicoating.

[bobatkins]

Canon was the first, and I think still the only 35mm lens manufacturer, to use fluorite (which is technically a crystal, not a glass) in their lenses. At the time (70's) it was a real breakthrough, but new glasses have been formulated over the last 25 years which are almost as good. I don't think any MF lenses have fluorite elements, but I could be wrong. Nikon certainly don't use fluorite elements.

 

Of course it doesn't really matter. There are other "special" (low or anomolous dispersion) glasses which can be used to allow highly aphochromatic lenses to be designed, though you usually need more "special" glass elements than fluorite elements to do a similar job.

[jeff_drew3]

FWIW: A non-scientific explanation based on a SWAG . . . Ceramics and plastics are now used extensively and in combination. Formulae are different than they were 20 years ago, and in many ways lenses have improved despite their increased complexity. I have a flourite refractor telescope and can see the difference in use. The WOW factor is there, but at a much higher (almost double) cost than a regular one, all other features being equal. Comparing a 350mm regular vs 350mm SuperApochromat gets to be a very fine argument of value to cost. If both lenses are of high quality manufacture, the argument may be tougher still, although on rare occasions, I've seen the differences. With todays' films and improved lens elements, I've seen better images from lesser expensive combinations than 20 years ago, but that's purely anecdotal. My real opinion is, if the additional cost of rare earth elements is added to the process and a significant improvement is made AND the market will buy it, the R&D/mgmnt will ratify the deal and we would routinely see it.

[steve_rasmussen]

A lot of good points here and I agree that having fluorite lens elements is not essential for excellent color correction. Let me clarify a couple of misconceptions about color correction. APO is not a guarantee of superior color correction. It just says that three colors are coming to a focus at the film plane. It says nothing about how far from the film plane the uncorrected colors will fall. It also doesn't tell you the degree spherochromatism (change in spherical aberration by color)the lens has. Telephoto designs can only be corrected for one zone in which all the designated colors will be corrected. Because of this, the uncorrected zones will have more longitudinal chromatic than the corrected zone. The benefit of low dispersion glass combined with an APO level of correction is that the uncorrected zones have much less tertiary spectrum due to reduced spherochromatism. Can long telephotos be made using normal glass that won't color fringe? Yes, but they would have to be superachromatic(4 colors)or super APO(proposed name). Actually, low dispersion glass designations are more meaningful about degree of color correction than the terms achromatic, APO, etc. This is because these terms(LD) imply low spherochromatism. There is a fluorite Zenzanon 500mm from Bronica. Pentax's ED is probably similar in performance to fluorite. SR

[mike_rott]

Zeiss uses phospho-fluorite glass in their 35mm APO lenses and I would assume also for their 3 Superachromat lenses in MF. As far as I know, they were the first to use this type of glass (mircoscope lenses). Canon uses calcium-fluorite in their tele lenses, a bit different but with similar characteristics and perhaps easier to make.

[bobatkins]

There's a BIG difference between silica bases glasses containing additional elements such as fluorine and Fluorite which is a pure calcium fluoride crystal. It is much more difficult to grow perfect crystals big enough to form 6" diameter elements from (e.g for 600/4 lenses) than it is to make a fluorosilicate or phosphofluorosilicate glass.

[dominique_cesari1]

About Canon exclusivity on fluorite lenses in 35 mm : I thaught that the Hexanon f6,3 300 mm had such a glass?

[jeff_drew3]

More good points, thanks for the info. Yes, Konica had a flourite 300mm lens, and yes it was a beauty. Some of the chrystal growing experiments in space were great starts at providing valuable info on quality control & development etc. US readers, please write your congressman and petition for more funds for Nasa etc. Discoveries from those projects benefit all of us.

[colm boran]

Another interesting tidbit regarding fluorite use in lenses. The "History of Carl Zeiss" claims that Dr. Ernst Abbe was hired by Zeiss in the 1800's and was resposible for introducing fluorite into lenses to correct for chromatic abberation. Don't know if Zeiss still uses it today in their lenses for Hasselblad, Rollei, etc., but if not, they probably have something even better.

 

I have a Word document containing the text of the "History of Carl Zeiss" that I downloaded from Contax's website a while ago. If anyone is interested in this, please e-mail me: cboran@mich.com. It is somewhat interesting how Zeiss management, etc., was taken by the allied forces after WW II because the Zeiss formulae were war secrets, etc.

[christian deichert]

Canon certainly does not enjoy exclusivity in having flourite in its lenses. I call your attention to the Minolta MD 400mm f/5.6 APO lens, produced 20 years ago, which featured a flourite element. See also the Minolta MD 100-500mm f/8 APO and Minolta MD 600mm f/6.3 APO which I believe also had flourite elements.

[russ_arcuri]

All I know is this: when you want a cheap refractor telescope, you go with 'regular' glass. When you want better performance, you go with an APO design, which is more money, frequently uses special low-dispersion glass, and shows a marked improvement over 'regular' glass scopes.<p>

 

And then, when you want the very best, you buy a flourite telescope. Their cost is hideous, but as Jeff Drew already mentioned, there is no substitute. The views through flourite refractors ruin the observer for anything less ever again.

[bobatkins]

(1) It's flUOrite, not flOUrite!! Flourite elements disolve in water, though if you then get then hot enough they make a tasty snack.

<p>

(2) <em>"Don't know if Zeiss still uses it today in their lenses for Hasselblad, Rollei, etc., but if not, they probably have something even better"</em>. Zeiss is best, so of course whatever technology they have, it must be better than everyone else's. Even if I don't know what it is....makes sense to me.

[neal_vaughan]

"<i>The best 35mmm lenses in Nikon & Canon are fluorite, and the results are amazing</i><p>

Just to make something perfectly clear that Bob has aleardy pointed out: Nikon certainly does not use flourite in their lenses. In fact, they rather decisively eschew its use. Read the Nikon Full Line catalog, and nikon states that they dont use it because of certain properties it contains.

[russ_arcuri]

Sincere apologies for misspelling "fluorite." Although a "flourite" telescope might be interesting too...

[christian deichert]

Fluorite and not flourite, eh? No wonder my lenses don't taste like city water...

[michael lepard]

As mentioned Konica did produce a very early fluorite lens in the early 1960's, maybe this was the first commercially available fluorite lens? While it wasn't cheap ($1000USD in 60s currency!) and wasn't fast 300mm f6.3 it did set a very high standard in 35mm lenses. It was also the size of a normal 200mm lens too. The only draw back was the speed of the lens and it was fairly fragile with the flourite elements.

 

Photo: Konica Hexanon 300mm f6.3 Flourite (last version)

 

Mike LePard

The Photography Blue Book website

http://photobluebook.virtualave.net/

[tak_ming_leung]

I have used the Bronica PE 500mm/8 lens extensively in the past 2 years with a ETRsi body and found that this optical marvel produces an absolutely stunning level of performance - even a touch better than the Zeiss SA 250mm/5.6! A friend of mine who works for Tamron in Japan once told me that Zenza Bronica was copying optical formulae from Zeiss for use in their own lenses. They spared no cost and effort in producing one of the best telephoto lenses in medium format in the world - PE 500/8. He also told me that one large-diameter fluorite crystal was incorporated in the design, together with 2 other low dispersion elements. I first encountered this superb lens in Tokyo 3 years ago in a second-hand camera store. I bought it for USD$3,800 and ever since have owned THE BEST lens in my entire Bronica line of optics.