Nikkormat FT3 and GN Nikkor questions

[Trask]

I recently picked up an FT3 (with an odd little rewind knob, but that's another story). The camera came with a Nikon rubber eyecup, which attaches to a round diopter-like screw-in eyepiece. I pulled out a spare +0.50 diopter to see if it would screw in properly and it did, but the outside diameter of the 0.50 is too small for the Nikon eyecup to attach too. I'd kind of like to use the eyecup, just for form's sake, so does anyone know if Nikon made an adapter that newer, smaller diopters could screw into, that was large enough to attach the eyecup?

Second question: I'm moving again, so was packing up all my cameras etc. and was playing around with my various AI and non-AI Nikkors. I noticed that on all my lenses, the lens would always be at f/8 when the ears or the AI ridge were straight up, in the middle (if you know what I mean). All my lenses, that is, except my GN Nikkor, which is at f/11. Now I admit that I bought a Nikkor replacement f-stop ring to conver this non-AI lens to AI, and installed it myself. I'm not all thumbs and I'm pretty sure I did it right, so any ideas why the lens is "correct" at f/11 instead of f/8? (I note that the f-stop ring is a little stiff, so maybe I am all thumbs...)

All thoughts, complementary or otherwise, are welcomed. Thanks.

 

[PhotoJim]

The coupling shoe on the aperture ring should be straight up at f/5.6. However, the AI coupling ridge is a relative device and it records stops down from wide open, not fixed apertures. Therefore, if your lens is stopped down 4 stops, the AI ridge should be in the same position as another lens stopped down 4 stops from maximum. The actual aperture on each lens is irrelevant.

 

[Trask]

That's just what I needed to know -- thanks for sharing your expertise. Dan