Nikon AI Conversion
Minimum aperture signal post
Camera bodies that don't support metering with AI lenses have a small switch
to detect whether the aperture ring of a non-G AF lens is set to the minimum aperture.
This switch does not need to be activated for lenses without a CPU, but it can be
damaged when mounting pre-AI lenses. All that is necessary to prevent that is to file
down the aperture ring in the general location of the switch.
But while you're at it, I would highly recommend doing a real AI conversion - this will raise the value of the lens and if you ever get a body with AI metering, you don't have to work on the lens a second time.
The post on the aperture ring is officially called “Minimum aperture signal post (EE servo coupling post).” Originally, it was used for the automatic aperture accessory for the Nikon F2, which explains the old name in parentheses.
To see the switch in action, move the mouse pointer over the image.
Position of the post
The correct position of the post is 124° offset from the minimum aperture:
To mark the position on the aperture ring, print out this template, and cut out the middle part. Align with the minimum aperture, and mark the post position:
The marked section must remain when filing down the aperture ring. For the actual work, see the page on AI conversion.