14x17 ULF Lens Help

[SawyerK]

Hey Yall! Not native to forums but I was hoping someone could help me out. I recently built a 14x17" ULF to shoot CTX green lat xray film and it was perfect, almost. I was looking to build a lighter, collapsable, monorail field camera but I am having trouble wrapping my head around lenses. I've read that most people shooting ULF use 500mm lenses with ease. However, I am a broke medical student and want to try to use my Schneider-Rodenstock 150mm f5.6 or my Caltar ii-N APO 210mm lens. Is there a way to use them? I have a 52cm rail so I dont think racking out will be a problem but I can't for the life of me find any formula or a simulator or anything on DIY ULFs and lenses/conversions. the 150mm len is charted, focus at infinity @f16 to have a image size of ~8" and that's at ~6" distance lensboard to plate. I think racking out the bellows will give me the coverage I need but I can't seem to get any straight answers on if i'll be able to focus at all with 150mm or 210mm lenses. From my understanding, which is really poor when it comes to optics, is that at 150mm from lens to board I will be focused at infinity and to focus on things infinitely closer I need to rack it out. But is there a tried and true formula for what that distance would be for focusing between ~8' and 20'? Does anyone know anything? I'd rather troubleshoot and get my distances right before I make the bellows. Yall are just wonderful, thank you for the help!

 

[NedL]

Welcome to photrio!
Yes there is a simple formula. If u is the distance from the film to the lens, and v is the distance from the lens to the subject, and f is the focal length of the lens, then:

1/u + 1/v = 1/f

( when focused at infinity, the 1/v term becomes 0, so 1/u = 1/f and u = f, the focal length of your lens )

So if you rack out to twice your focal length, you get 1:1 reproduction of subject onto film and the distance from the film to the lens is the same as the distance from the lens to the subject, which is 2*f. i.e:

1/2f + 1/2f = 1/f


I don't have your lenses, so I don't know about them, but some lenses can be used at a longer focal length by removing the front or rear elements ( with some loss of aberration corrections ). Maybe someone here will know if your lens can be used that way.

Have fun!

 

[awty]

0.7mm pinhole will cover 14x17 at a focal length of 280mm, giving you a 90 degree angle of view at f500.
I just built a camera and it covers.

 

[Dan Fromm]

Lessee now. 14x17's diagonal is 22 inches = 559 mm. OP, you need a lens that will cover at least 22 inches. Neither of your lenses will come close to that at infinity.

You're in the wrong forum for the advice you want. APUG, sorry, photrio, is weak on LF. Run, do not crawl, to http://www.largeformatphotography.info/forum/. At the least, look at the link in the first post in this http://www.largeformatphotography.i...to-look-for-information-on-LF-(mainly)-lenses discussion. It has a link to a discussion on how to calculate coverage at nearer distances given coverage at infinity. There are other links that will direct you to information about the relationship between focal length, magnification and extension.

Short version, you're toast. To use your camera effectively you're going to need a lens with high coverage. This means a long process lens or one of Reinhold Schable's meniscus lenses or a pinhole, as was suggested in post #3 above. Whichever you choose, you're still toast. The pinhole excepted, these are all narrow angle lenses so you'll need a focal length much longer than 520 mm to cover y'r X-ray film. This means a longer rail to focus at infinity and an even longer one to focus closer.

 

[Rick A]

The short answer here is YES you can use your lenses, IF you don't mind circular images on the film. Your lenses will not cover 14x17 and massive vignetting will result.

 

[Andrew O'Neill]

If you cannot afford to get a lens that will cover 14x17, then stick with pinhole until you can. I shoot 14x17, by the way. Several of my lenses cover that format, but are extremely wide to just slightly longer than normal FL. My longest lens is Fujinon 600C. Lots of people here are LF shooters, so it's not that "weak".

 

[desertrat]

Several years ago I bought a Wollensak Apochromatic Raptar in 21-1/2" focal length, for about $125, on Ebay. I believe it will cover 14X17. It is not a dialyte like the Artar, but a 4 element double gauss design and has more coverage than an Artar. I own several of the these lenses, the shortest being 10-3/4", and it will cover 8X10 at f22 and smaller all the way into the corners with good image quality. At the LF forum, in the paper negative thread, a member posted an 8X10 image taken with this lens.

 

[koraks]

The short answer here is YES you can use your lenses, IF you don't mind circular images on the film. Your lenses will not cover 14x17 and massive vignetting will result.

Indeed. His lenses will only cover at very close distances. They may be sort of usable for extreme close ups if the odd wide-angle perspective isn't a problem.