I am in the process of designing my first darkroom. The kit I bought included 2 x componon-s lenses for a vivitar v1 enlarger. However, the guy I got it from, who was selling loads of gear, apologised that the retaining rings for the lenses to mount them on the lens boards had accidentally been included in another lot. No big deal really. The lenses have 39mm threads. I bought a 39-42 stepdown filter adapter as I thought this would work just fine as a retaining ring. it does, up to a point - I can screw the ring on far enough to make it work, but it is obvious the threads are not the same pitch, which I find surprising, as I thought all photo lens threads were the same. on both lenses the rings "nip up" before they bottom out on the threads. Can anyone confirm that a 39mm enlarger lens mount thread really is a different pitch to a 39mm filter thread?