Calling all ye brass lens experts....
I have in my possession a lovely 8x10 "telephoto poco C" field camera that I am restoring. It has a mystery lens on it that I wish to identify. The lens is marked Bausch & Lomb, and it has aperture markings to f/8. But focal length isn't indicated. And actually the name Bausch and Lomb is only found on the shutter, as well as "Unicum." No markings on the barrels.
So... I measured the pupil diameter, it is about 35mm. I also measured the bellows length at 1:1 and from that I estimate that the (unconverted) FL is ~280mm, or ~11". This agrees with 280/35=8 as expected by the f/8 marking. With the front element off, the FL is then ~380mm, or 15". (I guess the wide open aperture will be f/11, though there are no extra markings to that effect)
From my measurements I conclude that I have an 11" / 15" convertible... but who's heard of such a thing?! I searched around and found no such lens. So either it is rare or I mismeasured somewhere along the way.
Anybody else have one or know of this particular lens? Or does anybody have some more info on the telephoto poco c? I have another poco, a 5x7 field, and that one is dated 1902; by appearance I assume this one is of similar age.