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View Full Version : Lenses covering 20 x 24



Stewart Ethier
2-Jun-1998, 14:50
Since both Wisner and Lotus View make 20 x 24 cameras, there must be lenses that cover this format. This means an image circle of diameter at least 800mm, pref erably 900mm to allow for movements. Does anyone know what's available? In par ticular, what is the choice of focal lengths?

Sean Donnelly
4-Jun-1998, 00:18
The Lens and Repro Equipment Corp. has advertised a 150 mm Goerz Hypergon that c overs 20 x 24". I believe ther are also many long focal length process lenses t hat would cover this size.

Stewart Ethier
1-Sep-1998, 15:35
I can now answer my own question to some extent, in case anyone's interested. I just found in my basement a 1969 Burke & James catalog, with something like 40 pages devoted to lenses. First, there are 7 Goerz Red Dot Artar lenses that cov er 20 x 24, with focal lengths of 19, 24, 30, 35, 42, 47.5, and 70 inches. The first two are available in Acme M-X synchro shutters, while the last 5 are avail able only in barrel. The coverages of the 7 lenses are respectively 20 x 24, 24 x 32, 30 x 40, 36 x 45, 48 x 56, 48 x 64, and 72 x 90 inches. Actually, the ca talog says "covers at same size", but I'm not sure exactly what this means. Doe s it mean at 1:1? Are these lenses intended for close-up work?

The catalog contains 7 pages of anastigmat lenses, but only two cover 20 x 24: both Goerz Dagor Series III f/7.7 in barrel. The 24 inch version covers 18 x 36 , while the 30 inch version covers 30 x 40.

Finally, there are two pages of process and copy lenses, and I counted 24 of the m that cover 20 x 24 or more. Manufacturers include Goerz, Rodenstock, Carl Zei ss, Boyer, Metra, Taylor Cooke, Ross, and Wray.

Presumably, most of these lenses are available on the used market. The prices i n the catalog seem very low---I guess there's been some inflation in the past 30 years!

Boyd Hecker
26-Jan-2000, 10:32
Wisner has a 20 X 24 Lens Guide (posted 4/30/99) listing "classic" lenses with a promise to add 'certain recent production lenses to this table in the near future.' http://wisner.com/20x24lens.htm

John Hicks
27-Jan-2000, 21:54
Artars are process lenses, intended for 1:1 or so, which is most likely what tha t coverage spec refers to.

Tracy Storer
15-Dec-2001, 13:14
Stewart, "covers at same size" DOES mean 1:1, You would need an Artar of 30" or more to cover 20x24 at infinity. Dagors from 16.5"(no movement) and up will do nicely. Zeiss wide angle Protars in longer focal lengths(rare) are great. Fujinon 600 C is my main lens for infinity to 1.5:1. Tracy Storer www.mammothcamera

Murph
6-May-2012, 15:23
Good information.

RichardRitter
7-May-2012, 04:45
Wisner has a 20 X 24 Lens Guide (posted 4/30/99) listing "classic" lenses with a promise to add 'certain recent production lenses to this table in the near future.' http://wisner.com/20x24lens.htm
The Wisner site is no longer on line.

Tracy Storer
9-May-2012, 17:56
73363Screenshot courtesy the wayback machine.....

Mark Sawyer
9-May-2012, 18:53
Just out of curiousity, has anyone ever tried popping a good negative diopter on a lens, thereby increasing its focal length and coverage?

cosmicexplosion
9-May-2012, 20:08
I just learnt that a dagor goerz 19" converts to a 33"!!

Tracy Storer
10-May-2012, 09:33
Not yet, but have had the same thought. Planning on looking into this when things settle down for me in a couple months.


Just out of curiousity, has anyone ever tried popping a good negative diopter on a lens, thereby increasing its focal length and coverage?

Hermes07
10-May-2012, 13:05
Just out of curiousity, has anyone ever tried popping a good negative diopter on a lens, thereby increasing its focal length and coverage?

a GOOD negative diopter would have to be achromatic to avoid introducing a lot of fringing and aberrations. In my experience, it's very hard to find decent, coated, negative achromats in large diameters. Anyone have a source?

E. von Hoegh
10-May-2012, 13:27
a GOOD negative diopter would have to be achromatic to avoid introducing a lot of fringing and aberrations. In my experience, it's very hard to find decent, coated, negative achromats in large diameters. Anyone have a source?

I've seen them at SurplusShed, but you never know what they will have. Certainly not a reliable source. A couple 60" telescope achromats mounted in a barrel would cover 20x24, and good RR type lenses are surprising. Certainly more than adequate for contact prints.

Hermes07
10-May-2012, 14:08
I've been on the lookout at SS for a long time but have never found a decent-sized negative achromat suitably weak to extend the focal length of a lens in the 600mm range.

Given the cost/time/effort of getting the two achromats, mounting them, adding the aperture, e.t.c. It would probably make more sense to just wait for a beat-up or less-hyped aerial or process lens to come along. I've seen telephotos and APO dialytes & tessars around 35" go for very little - whatever their flaws, I'd expect them to hold up lot better than my diy attempts.

E. von Hoegh
10-May-2012, 14:19
I've been on the lookout at SS for a long time but have never found a decent-sized negative achromat suitably weak to extend the focal length of a lens in the 600mm range.

Given the cost/time/effort of getting the two achromats, mounting them, adding the aperture, e.t.c. It would probably make more sense to just wait for a beat-up or less-hyped aerial or process lens to come along. I've seen telephotos and APO dialytes & tessars around 35" go for very little - whatever their flaws, I'd expect them to hold up lot better than my diy attempts.

You're correct about the long process lenses. However, inveterate DIY-er that I am, there will at some point be a brass barrel home made RR on the front of my Deardorff V8. The effort of assembling it will just add to the value, for me.

desertrat
10-May-2012, 16:50
I've seen them at SurplusShed, but you never know what they will have. Certainly not a reliable source. A couple 60" telescope achromats mounted in a barrel would cover 20x24, and good RR type lenses are surprising. Certainly more than adequate for contact prints.
Just a thought, but the achromats in RR lenses had a meniscus shape, and that was required to get a flat field. Telescope achromats might not be meniscus enough to give a flat field when assembled as a RR. A couple of years ago while mending an injured knee, I spent some time with the free version of OSLO, a ray tracing program, looking at the formulas of some classic lenses I found online and in Kingslakes book, Lens Design Fundamentals. I think ordinary telescope achromats would give a pretty curved field. Of course, at f64 it might not be too bad.

sanking
10-May-2012, 17:03
I just learnt that a dagor goerz 19" converts to a 33"!!

True, but the field of view is much narrower so in the end the combined elements and single element cover about the same.

Also, the single element is not well corrected as there is a lot of chromatic aberrations. You can improve quality by the use of a green or orange filter.

Sandy King

Old-N-Feeble
10-May-2012, 17:06
Sandy... if one filters out the longer or shorter rays of light... wouldn't one need to know whether to tweak the focus fore or aft the unfiltered spectrum?

Hermes07
10-May-2012, 17:19
Just a thought, but the achromats in RR lenses had a meniscus shape, and that was required to get a flat field. Telescope achromats might not be meniscus enough to give a flat field when assembled as a RR. A couple of years ago while mending an injured knee, I spent some time with the free version of OSLO, a ray tracing program, looking at the formulas of some classic lenses I found online and in Kingslakes book, Lens Design Fundamentals. I think ordinary telescope achromats would give a pretty curved field. Of course, at f64 it might not be too bad.

I was going to mention this about Aplanats / RRs. Not only is the meniscus shape of the groups important, but I believe it was originally a design where both glasses are flints, with the negative components on the outside of each group and the positive components on the inside. All this is pretty much the opposite of your standard telescope achromat - they tend to be plano-convex (or very close to it) crown-flint designs with the positive component on the outside. The standard Fraunhoffer doublet using N-BK7 and F2 doesn't appear to meet the prescription for a very low difference in the dispersive properties of the two glasses.

You could still get the benefits of symmetry (zero distortion at 1:1, e.t.c.) with a DIY version but I doubt you would be able to get near the performance of a purpose-built Rapid Rectilinear at large apertures.