unknown lens coverage?

[johnschlicher]

I picked this lens up at an estate sale for 3 dollars, the previous owner was really into optics, but they were all taken apart this was the only complete lens at the sale.

Anyway getting to my question. It takes 13 inches to bring him into focus on my 8 x 10, I then put it on my argyle 20 x 24 process camera still 13 inches to bring it in focus but it covers the ground glass???

It's a coated lens and I see 7 reflections, has no writing anywhere, no f stop scale, but it does have an iris. I'm thinking maybe this was some sort of copy machine lens??

So how do you determine the image circle on something like this, and does anyone know what type of lens this is.

Thanks John43268

43269

43270

[domaz]

There are no markings so far all we know he made it himself. I think your going to have to test focal length and coverage yourself. Plenty of ways to do that that aren't difficult. To test focal length aim the front of the lens toward bright outdoor surroundings through a window from within a darkened room. You should see the image on the wall. When the image is focused on infinity the distance from the wall to the lens is the focal length more or less. You should be able to get an idea of coverage this way too.

[EdWorkman]

How close was the objected upon which you focussed ? If infinity [ a couple thousand times the fl ] WOW, if close, not so wow. Did you go outside and focus something "far away"?
An object even a couplathree hundred feet away will help clarify. And at what f stop did you do all this? I assume it must have been moderate or you would have had difficulty focussing. Based on what I've learned here, a "useable" image circle of 31+ inches is astounding for a 13 inch lens at infinity, as opposed to the illumination circle. Did you check the corners , long edge , short edge to see if/where you have mush or sharpness on the 20x24 at infinity? For focus indoors you can make the object full size on the gg and you would be extended to 2fl, but the image circle will be say twice-ish what it "really" is [at infinity].