Help me identify this lens mount. Nikon?

[ghostman]

I got a used Peleng 8mm fisheye recently. It came with a detachable M42 mount and an M42-to-Canon-EOS adapter. I use this on my Canon XTi and it works wonderfully.

It also came with this other detachable mount and I can't figure out which lens system it is for. I did some research and it appears to be a Nikon mount. In fact, a lot of Peleng fisheye's ship with an M42 mount and a Nikon mount. So that seemed settled... except...

The mount doesn't fit on my old (and no longer used) Nikon EM 35mm film SLR. This camera took Nikon E Series lenses, which, to my limited understanding of Nikon mounts, is an iteration of the Nikon F mount. So if the Peleng mount was for Nikon, shouldn't it fit the EM SLR?

Here's a photo I took with the Peleng mount and my Nikon E Series 50mm lens, side-by-side.

http://homepages.nyu.edu/~tn282/public/pelengnikon.jpg

Perhaps someone more knowledgeable of Nikon (or Pentax or Olympus) lenses can help clue me in. I have no other Nikon bodies to test it on.

 

[996GT2]

The mount doesn't look like it has the AI groove, so maybe it only works on non-AI mounts? Just a guess

Also, did you measure the throat diameter at 44mm? That's the diamater for the Nikon F mount...however it's not a ton of help since a lot of other lens mounts have similar throat diameters.

 

[ghostman]

Indeed, the throat diameter measures approximately 44mm. It seems to slip onto the Nikon SLR just fine, but it won't turn and clip into place. In fact, it won't turn at all. I wonder if the Nikon EM was just a bizarre camera.