Mysterious Anastigmats

[JOSEPH ANDERSON]

I remember reading in a late 1940s Popular Photography magzine that the last of the
Kodak anastigmats were coated on the inner surface just like the early Ektars.This was
not Kodak's claim. It was the writer of the artical. I was woundering if these are the
lenses Paul Fitzgerald and Dan Fromm were refering to in responce to my question.
(Are 203 Ektars apochromatic) These lenses didn't carry the Ektar name. I guess
only Kodak knows why. They were idsntical as far as I know.

Thanks again for your input.
Joe A

[Glenn Thoreson]

I have heard of some anastigmats with internal coating. I don't think I've seen any, though. That would be war time era and some strange stuff was going on then. It's a mystery.

[E. von Hoegh]

Quite a few early coated lenses were coated only on the interior surfaces. This was due to the lack of durability of the early coatings.

"Anastigmat" was a name that Kodak used on many different types of lens. I've always thought it was first used to distinguish the Zeiss/Kodak (Tessar) lenses from the rapid-rectilinear type in the early 20th C..

Where the name "Ektar" came from, I have no idea.

[Dan Fromm]

Joseph, my 203/7.7 dialyte type Kodak Anastigmat s/n EC 222 (EC means made in 1941) is not coated inside or out and shows no signs of having been coated inside or out.

Some madness struck in Rochester shortly after WWII. Kodak renamed their top-of-the-line lenses, many of which has been sold previously as Kodak Anastigmats, as Ektars. Wollensak renamed their Velostigmats as Raptars.

Bill, rapid rectilinears aren't anastigmats. Tessars are anastigmats. So are most relatively modern (most lenses designed since the mid-1890s) lenses. Ole Tjugen will shortly chime in with the news that RRs and Petzvals can be sharper centrally than most older anastigmats. To which I will add, in advance, that some of the sharpest lenses used by the USAF for aerial photography are Petzval types, used as very narrow angle lenses. Correcting lenses for astigmatism was a major advance.

Ektar is a made-up trade name that means "our best," was applied to many many design types. In general, lens names, except perhaps meniscus, are made up.

[Ole Tjugen]

Ektar = Eastman Kodak -tar, I guess?

The -tar seems to be a common suffix for lots of anastigmats.

Dan has preempted the rest of my post, but I would like to state that I don't believe RRs are as sharp as the very best Aplanats, and that the very best Aplanats are sharper centrally than any early anastigmat. My 1915 Hugo Meyer Aristoplanat 270mm resolves detail finer than the theoretical limit...

[Glenn Thoreson]

I may have missed this, but anastigmat means simply that the lens is corrected for astimatism. I didn't notice anyone saying that, so far. Anyhoo, it's not a proprietary term. The anastigmat design was the first major "improvement" in photographic lenses. It enabled the making of much faster lenses than the RR or Aplanat, et al. All modern lenses are anastigmats in one form or another. Anastigmats were, for long time, labeled as such purely to distinguish them from earlier designs. Probably a certain amount of prestige involved, too. ( Hey, look, you guys! I got me one o' them new fangled Eastman Kodak - tars! ) :D

[Ole Tjugen]

Anyhoo, it's not a proprietary term. The anastigmat design was the first major "improvement" in photographic lenses.

It was a proprietary term for 20 years, when it was covered by the Zeiss patent. A while after the term "anastigmat" became open, Zeiss patented "Protar" as their term for "anastigmat".

Considering the time span of Aplanat/RR production (1868 to well into the 1930s), I believe the Aplanat was the third major improvement. The Petzval Portrait Lens was the second, and much of the mathematics behind that is still fundamental to modern lens design.

The first place has to go to the achromat. ;)


... All modern lenses are anastigmats in one form or another.
Surprisingly, you're wrong here. There are several lenses in production which are not anastigmats; the Rodenstock Imagon is only the best known of them.


Anastigmats were, for long time, labeled as such purely to distinguish them from earlier designs.

"Anastigmat" meant for a long time "not Aplanat". Very many lenses sold as "anastigmats" were nothing of the sort, but they were not Aplanats/Rapid Rectilinears. Strangely enough a good Aplanat will outperform any but a very few of the very latest anastigmats at f:11 and down...

[Jim Galli]

Ektar = Eastman Kodak -tar, I guess?

The -tar seems to be a common suffix for lots of anastigmats.

Dan has preempted the rest of my post, but I would like to state that I don't believe RRs are as sharp as the very best Aplanats, and that the very best Aplanats are sharper centrally than any early anastigmat. My 1915 Hugo Meyer Aristoplanat 270mm resolves detail finer than the theoretical limit...

I'll take issue here so perhaps I can learn something;

I don't believe RRs are as sharp as the very best Aplanats,

RR's and Aplanats are the same design. :confused:

Very many lenses sold as "anastigmats" were nothing of the sort,

name one? These mfr's knew what anastigmat meant. Tessar's argueably, but that will rile Dan up.

[Murray]

Somewhere (I think a 5-volume encyclopedia of Optics & Optical Engineering edited by Rudolph Kingslake), I read that the anastigmatic name (I guess in the opinion of the writer at the time it was written), on a lens, indicated it was highly corrected for a few different things, not just astigmatism, and applied to some 3 and 4 element lenses. I don't remember if there was an commentary on the disuse of the name with later designs.

I will have access to that library hopefully in a week or so and will look to see how badly I butchered my recollection of the above.

Somewhere I also picked up an inference or observation that 'tars typically have 'normal' angle of view, and 'gons are wide angle. Along with this claim was a supposed Greek source for the 'gon suffix justifying it's association with wider view...may have been something to do with a globe.

I don't know that this '-gon' argument applies to enlarger lenses...that seems to be a pattern of how many elements...dunno.

[Ole Tjugen]

... I don't believe RRs are as sharp as the very best Aplanats,

RR's and Aplanats are the same design. :confused:

So it would seem; but the differences in performance are too great to be only sample variations. the best Aplanats are painfully sharp; the best RR's (I've seen) are at best adequate. The differences are greatest in the wide angle varieties where the best WW Aplanats are stunning and the best WA Rectilinears are at best "adequate".

Jim;

Rodenstock Hemi-Anastigmat to "name one".

It's "Hemi" but neither half is "anastigmat", and the whole is nowhere near it. ;)

[Dan Fromm]

Murray, I have a 4"/2.0 Taylor Hobson Anastigmat (that's what the engraving reads) that's a 6/4 double Gauss type. As I wrote earlier in this thread, most lenses designed after around 1895 are anastigmats. Lack of astigmatism is usually a good thing.

Wide angle -tars? 65/6.8, 90/6.8 Raptars come to mind instantly.

Long -tars? 250/4.5 Raptar. All of the Commercial Ektars.

-gon seems to derive from Zeiss' usage (Biogon, Topogon), whence the B&L (and many others under contract) Metrogon, seems to be used consistently. The two enlarging Biogons I've touched (40/5.6 and 180/5.6, IIRC, could be wrong about maximum apertures) conform to Bertele's 1952 (I think that's the year) Biogon patent.

Jim, I'm not riled, I'm puzzled. Kodak, remember, made Kodak Anastigmats that were tessar types.

Where you're right is that correction for astigmatism isn't always that good. There are anastigmats and then there are anastigmats. You might enjoy looking at Eric Beltrando's graphs (click on Courbes, i.e., curves). Many of the lenses we think are pretty good have fairly bad astigmatism not that far off-axis. Take a look at this one: http://www.dioptrique.info/objectifs8/00375/00375.HTM . This lens' has nil astigmatism at the aperture Eric did the calculations for in the center and at the edge of the field, but in between, wow! And then look at this one, a graphic arts Heliar from Voigtlaender (back on topic, thread monitors!): http://www.dioptrique.info/objectifs10/00486/00486.HTM . Fine until the edge of the field. Slow heliars can be better, see http://www.dioptrique.info/objectifs5/00202/00202.HTM , another slow heliar type.

Cheers,

Dan

There's astigmatism and then there's astigmatism. I once had a 1000/11 Celestron C-90 with such horrible astigmatism that at its near focus distance it couldn't focus horizontal and vertical wires in a window screen simultaneously anywhere in the field except dead center. What a terrible lens! My humble tessars, including my extremely humble 101/4.5 Ektar, shoot much much better that that waste of money.

[Glenn Thoreson]

Now I'm more befuddled than normal. That's saying a lot. Anyhoo, I have one particular RR that's so killer sharp in the center that it scratcheth the eyeballs just to look at a print from it. Away from center it falls off rapidly and badly. I have one little Emil Busch Detectiv Aplanat that I haven't used yet. Some day. A Hemi Anastigmat? Does that mean they only half corrected it? The Voigtlander Triple Anastigmat I got from you, Ole - does that mean they tried three times before they got it right? (Snappy sharp lens, BTW) I told you I'm befuddled in the cabeza. :D

[Jim Galli]

Ole, I think your USA-Europe prejudices are showing. RR's are typically what we called 'em on this side of the pond and aplanats are what you nice folks called them. I'm digging myself into a hole here because, come to think of it, every RR I've ever kept around the place was made over on your side. The Voigtlaender Euryscop's are spectacular and I have a little Cooke that makes you wonder why anyone ever made a fuss about anastigmats ;)

Dan, I'm not much on Tessar's. They fail in the corners too soon for my liking. If I'm going to limit myself to 30 degrees, why not just use the Aplanat's like Ole says.

[Ole Tjugen]

No, the difference between RRs and Aplanats is that the Aplanats are German, based on Steinheil's 1886 patent; while the Rapid Rectilinear is based on Dallmeyer's 1886 British patent.

The (German) wide angle Aplanats use thicker glass and closer spacing than the typical wide angle Rectilinears, which seems to give a flatter field and better corrections over a far wider angle of view.

"Triple Anastigmat" generally means that the lens is a triplet, unlike "double anastigmat" where each cell is an anastigmat in itself, with at least three elements (one of which is air in the case of dialytes and double-Gauss lenses)...

The Hemi-Anastigmat is a weird one; with a single front element and an achromatic doublet in the rear. And yes, it's only half corrected!

[Murray]

Triple Anastigmat agrees with the book I saw that said essentially anastigmat = 3-or-more elements, highly corrected'.

I will try to find the book, if only to make sure I'm not story-telling and making it better each time.

[Ernest Purdum]

"Gon" derives from the Greek for angle. Lots of lens names have roots in Greek or Latin.

Wollensak originally used "Velostigmat" (rapid stigmat) for their family of anastigmat lenses (with Series numbers to indicate the specific types), but went away from names of classical derivation in the coined word "Raptar". I've heard that they held a contest to pick a new name. I don't know if Eastman held a contest, but "Ektar" is also a coined word covering several very different designs.