View Full Version : questions about modifying a Fotoman lens cone, ffd's, & helical adjustment

John Schneider
18-Jan-2010, 22:57
I have a 612 cone that was made for a 135 Sironar-S (bought it for anticipated future use when they were closing up shop). For a number of reasons I've decided to use it with a 135 Xenotar, which is (based on specs published by Schneider and on the Ebony website) about 7mm shorter in flange focal distance.

I have a plan for how to enlarge for helical to take a Copal 1 and how to mill off the top of the cone and install a flange to mount the helical. My question concerns how much to mill off. Do I mill off the exact difference in published ffd's, or is the actual ffd of my 135 Xenotar apt to be different enough from the spec for me to remove a bit of the cone, install and test my lens, and repeat? Concomitant with this issue is the question of how much adjustment the Fotoman helical has if my Xenotar's actual ffd is a bit longer or shorter than the published spec?