I purchased this item on the Internet thinking it might be a catadioptric (mirror) lens but when I got it home I found it has no mirrors, just two large, heavy convex lenses. The beast is 3.5 inches long and across and weighs over 2 pounds. (My postal sale only goes to two pounds.) I have a 500mm mirror lens and it is much lighter and smaller. There are no markings on it whatsoever. There are fine screw threads on each end. If I look through either end objects about four inches from the other end are in focus. In the attached photo it looks like there is a round center plate in the middle of the lens, like mirror lenses have, but this is an optical delusion. Both ends look just about the same. Any ideas?
There ar no markings so I have no idea of the focal length or anything else. It is 3.5 inches from front to back. If I hold my hand four inches away from one end and look into the other my hand is in focus and maganified just a little. The concave lenses on the ends both face out.
Hold a piece of white paper up against a wall in a darkish area that faces a window. Then, move the lens back and forwards until it throws an image of what's outside onto the paper. This will give you an approximate FL.
To determine if you can use that lens easily on a film camera, measure the focal length, aperture and image circle. You will have to do it yourself because you will just get a bunch of wild guesses in response to your post .
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