rfaspen
[insert pithy phrase here]
Guesstimating from the image in the OP with a ruler included, this fits the scenario. I'm guessing the microscope objective in the OP is a rather old one (perhaps as old as 1920s or 30s?), but appears to be RMS.
This is a Leitz microscope lens, mounted in an M42 lens cap for some kind of photomicrography that I could not get to work. Microscope objectives are tiny little things. And yes, I think that it is an incomplete lens.
Canon F-1 Microphotography hack by Mike Novak, on Flickr
Anthsmith
Established
Unknown lens
Unknown lens
I believe it is an incomplete elmar or such like which is missing its front element and possibly iris, it is not an enlarger or a microscope objective, totally wrong design for that and it has the iris lug on the side-some one has made a bit of a frankenstein in my opinion so I will have to see what I can sort out as i have some leitz front elements in my spares collection..
Unknown lens
I believe it is an incomplete elmar or such like which is missing its front element and possibly iris, it is not an enlarger or a microscope objective, totally wrong design for that and it has the iris lug on the side-some one has made a bit of a frankenstein in my opinion so I will have to see what I can sort out as i have some leitz front elements in my spares collection..