The lens was first labeled "Computar" and later "APO-Kyvytar" -- just to confuse people. You know, first Datsun then Nissan, etc. etc.
The lens was first labeled "Computar" and later "APO-Kyvytar" -- just to confuse people. You know, first Datsun then Nissan, etc. etc.
OK, thanks. That's going to be very difficult.Originally Posted by wsit
Hmm. 360 mm or so. Covers >= 800 mm.
OP, you're dreaming. The lens of your dreams is Berthiot's 360/14 Perigraphe VIa, which covers ~ 890 mm at "small apertures." It was cataloged, whether any were made is unclear. Good luck finding one.
The 360/18 Protar that Oren mentioned will also do what you want. Cataloged image circle is 1,160 mm. Another unicorn.
Have you considered using a pinhole?
Computar f/9, Apo-Kyvvtar, and Kowa Graphic are all the same. Being originally marketed as graphics lenses, even the 1:1 specs are for stringent standards at f/22. In typical real-world LF use at smaller stops, the image circles are going to be significantly larger, even at infinity. Note Sandy's previous post relative to focal lengths quite a bit shorter than 360. Even the official specs for G-Claron lenses are cited relative to graphics standards, while the usable real-world image circle is considerably larger than the published one.
A lot also depends on your style of printing. Contact printers can get away with a lot more "usable" image circle than people who enlarge to a significant degree. That's also a factor when comparing similar lenses. Some have less mechanical vignetting due to larger shutters; but all that seeming surplus of image circle might not be of the same quality towards its periphery.
They are not always the same, as discussed in the thread I linked. Some people who have purchased lenses labeled "Graphic Kowa", expecting to get the coverage of a Computar, have been very unpleasantly surprised. Caveat emptor.
I've got my interest in really wide lenses back after I've put my 210mm f/9 Zeiss Dagor into a Compur #2 and tested it. I was impressed and thought it wouldn't be bad at all to have a longer lens as wide. This thread made me look for some information on the Computar / Graphic Kowa lenses that I have not put my hands on yet. The most useful data that I found was in this thread: https://www.largeformatphotography.i...-k-a-coverage). But sorry I agree with Dan Fromm's #4 message in that thread, and I don't consider the shown images sharp. Yes I see motion blur in the ferns but I don't suspect any motion in the big trees' bark as well as on the ground. What I see is an intolerable (for me) amount of astigmatism. That's at 87° and less. This thread is about 96°....
The old extreme wide-angles were to be used stopped down a lot, and that stopped-down coverage was for contact prints only. The f/18 series V Protars are of the same general formula as the f/9 series IIIa Protars but are far less sharp. The IIIa's cover far less but their sharpness is just as far better. The older f/6.8~f/7.7 Dagors usually illuminate more than the newer ones but their sharp coverage is very modestly larger. And that more field sharpness is traded for less mid-field sharpness as the only optical difference in their generations (except for the glass elements diameter that adds to the illuminated field but not to the sharp one) is the tiny difference is the cell spacing (just the same story as the one told about the Computars' spacing by Gordon Hutchings here: https://www.largeformatphotography.i...=1#post1361392). The older Dagors (and especially the Gugo Meyer Doppel-Anastigmat Dagor copies) that sharply cover somewhat more have their cells 0.5mm to 2mm (depending on the focal lengths) closer than the later Dagors that are optimized for the mid-field sharpness and cover less. Anyone can make these lenses' coverage and sharpness distribution exactly the same by changing the cell spacing.... And getting back to the 210mm f/9 Zeiss Dagor: mine is from the last batch manufactured for Luftwaffe. It's not optimized for the maximum field sharpness. It illuminates its nominal 100° but the corners are not sharp at all. The particular specimen is optimized for wide-open f/9 usage (the original barrel had no iris at all), and to get a really sharp image wide open, one has to sacrifice a bit of coverage. I have yet to try changing the cell spacing a bit to find the optimal compromise between the corner and the mid-field sharpness for my own needs with the lens stopped down to about f/22 and f/32.
Another point: with the same lens design, we get all the aberrations larger and more prominent when the lens gets longer in its focal length. A 90mm seris V Protar may make remarkably sharp 4x5" contact prints well stopped down, but a 360mm seris V Protar will have 4 times less sharp images at the same f-stops. For a lens designed for contact prints only, with a long enough focal length, the difference may get visible enough even in the contact prints.
That makes the above suggestion to try pinhole first look very reasonable - especially considering the costs of that big super-wide-angles and the efforts to find them.
sometimes convertible lenses throw a large image circle when converted, I don't know of any that will cover 31-32 inches, that's a big circle. maybe one of Reinhold's Wollaston Meniscus lenses will do that.
Image circle about 800mm would be 20"x24" image format?
The 450mm f9 Nikkor M is a Tessar formula with about 52 degrees of image cone, at f22 it has an image circle of 440mm at f22... not even close to ~800mm and no, stopping down lots will not increase the image circle to any where near 800mm.
For a 360mm focal lenght lens to make about 800mm image circle requires about 95 degrees if image circle cone or a "Biogon" or "wide field gasuss" lens design/formula or similar.. fact and reality IS, not gonna happen or it will be one of those rare single off lenses or have a lens designed specific to this need.
The other importaint bits of info, what exposure aperture, what are the image goal expectations, what about the shutter and all...?
Easier alternative would be to use a ..... pin hole.
Bernice
And a CND filter -- or two!
Oren, there were all kinds of things made under Computar label, and I get the impression that lots of the coverage complaints are either due to Computar Symmetrigon lenses being mistaken for their graphic ones, or else due to mechanical vignetting issues in smaller shutters, or perhaps an economy line of lenses. Graphics lenses by various manufacturers often had multiple series with coverage implications, whether we're talking G-Clarons, or Nikkor process lenses, Goerz, even Rodenstock. The existence of so many improperly listed things on EBAY doesn't help.
I've always wondered if the extra coverage of the old f/7.7 14 inch Dagors in terms of optical design is really any better than the final Kern versions, or simply due to their bigger shutters and less mechanical vignetting. A tradeoff.
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