Nikon D5100 - Not my father's F mount. Or mine

[semi-ambivalent]

Hi all!

My son has a new Nikon D5100 dslr. It's been great. We're both also analog users.

Just now we mounted, without issue at first, a 24mm F/2.8 AiS manual focus lens. But this lens cannot go to F/22 because a little tab on the aperture ring, which I think is an artifact of the Nikon FA days, hits a small protrusion on the D5100's lens mount. We have as yet been unable to find anything on the net about what this protrusion actually does. There is no mention of it in the 5100 manual. It appears to be spring loaded and can be pushed back into the mount. Can anyone here explain what this thing does?

Thanks,

s-a

 

[PhotoJim]

That protrusion sounds like the AI metering tab that is supposed to be moved as the aperture ring turns. That tab on the aperture ring is supposed to interface with it.

Truthfully though you would not want to use f/22 as you will get a lot of diffraction softness.

 

[semi-ambivalent]

That protrusion sounds like the AI metering tab that is supposed to be moved as the aperture ring turns. That tab on the aperture ring is supposed to interface with it.

Truthfully though you would not want to use f/22 as you will get a lot of diffraction softness.

No, although I wasn't clear. The protrusion is not the AI coupler. That usually rests at about 2:00 on the face of the lens mount when no lens is mounted. The one I'm talking about is at 8:00 and sits just a bit outboard of the lens mount itself. I get what you're saying about diffraction but, strictly speaking, diffraction is a function of aperture, not aperture ratio. In lenses of modest focal length, yes, f/22 usually does not perform very well at all. I'm just ticked off that there's this thing on the camera that is not even referenced in the user manual that came with the camera. Lazy lazy Nikon.