Steve, thank you for mentioning this. I've been scouring the interwebs for information on the "mirror slap" I'm experiencing.
To answer your question, yes, I have noticed this.
I recently got a 50mm f1.4 K1 non-AI lens which I modified myself to work with AI. Now it mounts on my D700 FX DSLR, where I've set it as one of the non-CPU lenses. Metering is perfect, the camera recognizes where I've set the aperture ring and gives me perfect exposures every time.
But there's that wince-inducing shudder every time you take a photograph, and I'm worried about damaging my camera.
I would like to fix the issue - I take it that I have to file off a bit of the stop down lever? Any idea by how much, or how much should the final size be? I have two other lenses, both factory AI (28mm f2.8 and 105mm f2.5) that I can use to compare. Also have a micrometer/vernier to measure.
Technically, "mirror slap" is made of three parts:
- Mirror rising
- Aperture stop-down
- Shutter opening and closing
Unless the mirror actually strikes something on the rear of the lens as it rises and falls (which shouldn't happen with any Nikon lens except for some very old "mirror-up" fisheyes and the Nikkor-O 2.1cm) then mirror slap will be the same regardless of which lens is mounted. Similarly, the shutter opening and closing is independent of the lens used.
The aperture stop-down action is the only thing which could vary for each lens. Here it is useful to understand what happens. When the lens is mounted, the camera holds the lens aperture stop-down lever so the lens is wide open. When the picture is taken, the camera releases stop-down lever. The lens stop-down lever is spring-loaded and closes the aperture down. If the aperture ring was used, the lens stops down to the setting on the aperture ring. If the camera command dial is used, the camera only releases the stop-down lever a precise distance so the aperture closes to the required setting. After the exposure is taken, the camera slams the stop-down lever up again to re-open the lens.
The stop-down part of the process should be fairly gentle since the aperture is only closed down by a small spring inside the lens. Any jarring is more likely to be
after the exposure when the camera re-opens the lens. Even this should be relatively smooth. Take the lens off the camera and compare with your other AI lenses. Set the lens to minimum aperture and flick the stop-down lever, the aperture blades should open and close freely. It's possible the stop-down lever was bent or moved out of alignment when it was AI modified, and is catching on the side of the slot. Could that be the problem? Maybe also try some test shots with very long exposure (1 sec or more) and notice if the shudder is occurring at the start or end of the exposure (or both). If the camera is exposing properly with the lens, then I don't think you need to file the stop-down lever.