KOWA 90mm 1:1 Huge Fast Glass

[bigdog]

I just picked up a KOWA 90mm 1:1 lens on Ebay. This is a huge industrial looking chunk of glass that I believe may be used as an X-Ray at the dentist kind of application? This is a fixed aperture fixed focus lens.

Does anyone have any experience with mounting this lens on a Canon EOS or other SLR body? The rear element sticks way out but this diameter seems to be close to that of a Pentax M42 screw mount. The lens' actual screw mount is threaded on the same outside diameter as the glass which is huge!

Another issue may be the distance from the rear element to the film plane to maintain focus. Holding the lens up to the light, it appears to come in to focus with my eye only when the lens is held a good foot or so from my eye.

 

[venchka]

Sounds like a job for a view camera.

 

[Sonnar Brian]

Better to put a piece of paper on a table, and focus on a lamp. You will probably find that the back focus is tiny. That is the case of the 42mm F0.75, 50mm F1, and others made for CRT and X-Ray cameras that I have.

 

[raid]

I once bought a Leica huge optic. It just sat there on the floor, until today!
I gave the lens to the Physics Department at UWF, and one faculty member told me today that he wants to use that lens in some laser experiment. He acknowledged that such lenses would be very costly to order.

 

[Sonnar Brian]

You did not say it right.

Pinky to Lip: "LASUHR"...

I have a custom manufactured lens from the 1980's, made for an optical computer using "LASUHRS" that was $40,000 to manufacture. The computer was roughly $1M. Now an expensive paperweight.

 

[bigdog]

So when you say the back focus is tiny, I would have to mount the lens so the rear element just about touches the shutter? I was thinking I would need a bellows set up to focus and gain distance from the film plane but from what you are telling me this lens needs to be very close to the film plane?

I thought formats larger than 35mm may have lots of light fall off on the perimeter. This is already getting a bit too technical. I guess I should try the paper test and I will be able to see the image circle on the paper to determine back focus and image size?

I think I will need a machinist to thread the back element to go in to a 42mm Pentax to Canon adapter I have, but who the heck knows what the results will be. I only paid $50 but it may be an expensive paperweight ha ha!

I wonder what this sucker would look like mounted on my FED 2 body?

 

[Sonnar Brian]

Did you try to form an image with the lens? Looking though it does not give the back-focus. Just take a piece of white paper, set flat on a table, and aim at ceiling light. That will give some indication. My Wray 50/1 CRT lens has to be a few millimeters from the film plane.

 

[bigdog]

Yes, I got a perfect circle of light when I held the rear element about 1/2 to 1/4 inch or closer to the rear element ...moving the paper any greater distance from the rear element created an oblong shape. It also appears that the lens may only focus in a macro fashion, from approx. 2 inches to a foot from the subject.

 

[bo_lorentzen]

Point the lens to a light-source a few rooms away, kill the light where the lens are and then move the paper until you have a clear picture of the light-source that is roughly the film plane.🙂


Bo

www.bophoto.typepad.com

 

[wjgorham]

This type of high aperture lens of about 90mm focal lengh was used in projetion tv sets.