Modifying filters for use on a 180mm lens for a Mamiya C-330

I have seen several threads on the difficulty of putting filters on both lenses of a 180 due to the close tolerances. I solved the problem today by turning down the diameter of two new B+H filters on my lathe. I used the thread protector ring that comes stock with the 180 as the filter holder. I then simply threaded the filter on and turned it down. My initial measurements indicated I had .050 thou of rim thickness to work with (and leave a 0.010 thickness for stability). I ended up taking off 0.042 thou from each filter in multiple steps until I achieved a good fit with about 0.002 clearance between the two filters:

#1. Lens protector chucked on lathe:

#2. Filter threaded on:

Beautiful work, thanks for sharing! :)

The same method should apply for the 65mm f/3.5 lens, which shares the 180mm filters size, fitting issues, and silver protection rings.

Very impressive.

I've thought about this issue, and came up with the idea of a paramender style filter holder-- screws (or clips) onto both barrels and allows the filter to be slid back and forth between the two lenses. That way you could even use circular polarizers-- adjust while the filter is in front of the viewing lens, and then slide it down in front of the taking lens still in the same orientation.