WA lenses for 12x20greenspun.com : LUSENET : Large format photography : One Thread
I am looking for a wide angle (around 200 mm) to cover 12"x20". Failing an existing lense, how would I go about making such a lense? Reference works on optics? Lense design software?
-- Greg Twombly (email@example.com), October 13, 1998
I was curious to see any answers to this. Probably everybody has been stunned into silence.
Going by diagonals, a 200mm on 20x12" would cover 112 degrees, and is equivalent to 55mm on 5x4", or 15mm on 35mm. It is possible, but I suspect there is too little demand for such a lens to be commercially viable. But, of course, the results would be wonderful.
A standard text is Sidney F. Ray, "Applied Photographics", Focal Press. This gives good detail about the theory of lens types, aberrations and how they are corrected (or traded-off), materials, lens types, and uses. The second edition is 1994 (maybe there is a more recent edition), and doesn't mention the more recent optics, such as the Schneider Super-Angulon XL 47mm for 5x4". Scale this lens up four times, and your needs may be fulfilled. If you can afford it, perhaps Herr Schneider would make one for you.
Making your own lens is trivially simple. Take a 200mm magnifying glass, restrict the aperture, and there you are. But your negative is 600mm across diagonals, and the quality of this optic would be dreadful. You might be better off with a pinhole or zone plate.
Ray's book does not discuss the practical details of designing and constructing a lens. Some of his references do. Grinding your own lenses is possible: follow an astronomy trail, there are many books on the subject. But astronomers use long focal-length (i.e. narrow- field) lenses, which are much easier. To make a 200mm lens for 20x12" that competes on quality with the "big boys" would need a powerful computer and very good manufacturing techniques.
If you are serious about constructing your own lens, I suggest you start with an easier one, say around 3000mm.
-- Alan Gibson (firstname.lastname@example.org), October 18, 1998.
I seem to remember seeing, maybe a year or so ago, in one of the Lens & Repro Company's ads in View Camera, a listing for a superwide lens manufactured (maybe one-of-a-kind) by one of the large makers and 20x12 (or larger?) dedicated camera. I think it had a fan filter. My vague recollection is that the whole rig cost about $10,000. You might call Lens & Repro in New York to track this down.
-- Chris Patti (email@example.com), October 21, 1998.
I use a 12" CP 300mm (uncoated) Goertz Dagor on my 12x20 straight on...It seems to work well.I don't use movements,don't focus on infinity and 5top down to f64. Outside it seems to work well enough hyperfocal. Sharp lens and wide.I Also use 240f10 nikkor barrel wide angle for closeups...8" or closer and it will cover 12x20.Low contrast lens...process type...cheap...no shutter.Only drawback is f32 max.But you can get quite a bit closer than the dagor with it.
-- Emile de Leon (firstname.lastname@example.org), June 29, 2001.
Lens and Repro from time to time has Hypergon (Goerz version) lenses for sale. A 6" Hypergon will cover 12x20 nicely. They do have a 200 mm Hypergon for sale now. It will cover 24x28. Call Jeff at (212) 675-1900. It will probably cost you a small fortune. I would drill a small hole on my lensboard to make a "pinhole". Good light!
-- Geoffrey Chen (DB45TEK@AOL.COM), June 29, 2001.
I have seen these Hypergon critters advertised. What the hey is the "fan"???
-- Wayne (email@example.com), June 29, 2001.
I meant to say that the 240 f10 nikkor barrel lens covers 12x20 at 2'10" or closer in my last entry.
-- Emile de Leon (firstname.lastname@example.org), June 30, 2001.
The Hypergon was designed by von Hoegh - its almost spherical and covers about 130 degrees at f/40. This is probably the widest undistorted field covered by any lens.
The fan is the equivalent of a center filter - it is to help with the falloff in illumination in the corners, which would be damned dramatic for stuff this wide. The basic idea is that the fan covers more in the center than at the peripheries (think angular speeds - the same thickness would have to move faster at the adges i.e., cover things for smalleer amounts of time). I believe, typically, exposures were divided into two parts, about the three quarters being made through the fan and then the fan drops away and the rest of the exposure is made without the fan. The photographer would have to blow through a hose or squeeze a bulb to set the fan spinning.
From a Goerz catalogue - "The Hypergon holds a unique place among wide-angle lenses on account of its incomparable covering power. It is a symmetrical double anastigmat, consisting of two very thin hemispherical single glasses. Astigmatism, spherical aberration and curvature of field are completely corrected, and the definition is sharp to the very edges of the plate. The chromatic aberration is not corrected, but is eliminated after focusing by the use of the smaller diaphragm stop, f/31. The symmetrical design of the Hypergon insures complete freedom for distortion of straight lines. The diminution of light toward the margin of the image, unavoidable in a lens cutting such an extraordinary angle, is corrected by an ingenious device in the form a a star diaphragm, which is rotated in front of the lens, by means of a bulb and tube attachment, during the exposure.
-- N Dhananjay (email@example.com), June 30, 2001.