Originally posted by Balticbelle It might be possible to dress the offending portion of this ring with an appropriate miniature file capable of cutting the material in a small amount of time. If the adjacent areas are masked appropriately the fine adjustment which is probably no longer than two centimeters could avoid having to send the lens back to Sigma. It is also likely that since the mount is silver in color, that no one would ever know
No good idea, besides your mixup of millimetres and centimetres.
First, the offending ring is made from plated brass. Once the plating is removed (due to wear and tear or due to other mechanical reasons), the brass will be visible.
Second, except for the most adept file handlers, this will have some kind of 3rd-world-hack feeling. Ugly scratches and dents. Should you ever think about selling a lens that looks as if somebody held a file to it's bayonet ring - forget it.
Third, even with most careful application of masking tape, it's close to impossible to hinder small metal flakes to fall in places where they don't belong.
No, don't do this at home, and don't do this in your workshop, should you happen to have one.
A way to handle this would be removing the ring from the lens and fitting it to a lathe, but this would need some extra effort just to fix it precisely in plane. Your run-of-the-mill three-jaw chuck won't be the perfect tool for the job.
And even then, the first two points would still be valid - visible (and oxidizing brass) and a klunky "fumbled with in an inappropriate way"-feeling for a precision optical instrument.
Nah. Don't. Let's wait for details on what Sigma wants for
replacing that ring with a modified ring. That's the only way to let these lenses keep some of their value intact.