I wouldn't put it on a lathe. I think your idea is good. Use a slitting saw on a rotary table. To protect the lens use something like Dip Seal you can paint on the glass or at the very least some green or blue masking tape.
A co-worker would like me to make a modification to a "vintage" 1960's wide angle lens. The difference between modern cameras and what this is designed for causes vignetting in the image. A common mod to this lens is to cut down the tube that extends forward of the front glass. It is similar to this lens. The front, where it says Paris, gets shortened.
I have an SX1 mill converted to CNC. I also have a 4 jaw mounted on a manual turn table. My plan is to make and slit a doughnut out of aluminum to hold it by the small end with the lens facing up. Then use a thin HSS Slitting Saw in the spindle. Use the turntable to rotate the lens and cut a ring off the front. I am thinking with plenty of suction I can keep the chips out of the lens.
My concern is rigidity. But if I go fast on the blade and do very light cuts I should be OK. Any thoughts on this plan? Other ideas?
I don't have a lathe yet so that's out.
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I wouldn't put it on a lathe. I think your idea is good. Use a slitting saw on a rotary table. To protect the lens use something like Dip Seal you can paint on the glass or at the very least some green or blue masking tape.
The owner is thinking painters tape to protect the lens. They do have some sort of coating. I am not sure what it is or if a lens that old has much anyway. I looked into the Dip Seal and I think the application temp is too high.
I still need to find out if it is aluminum or steel. I don't currently have a slitting saw or arbor. Am I better off with a thick or thin saw blade? Small diameter and high tooth count I assume?
Is that a Angénieux 1.8 / 5.9mm Type R wide angle lens for C mount? That's what it looks like...
I don't know which camera the lens is made for (size of film frame and flange back distance) and which camera he intends to use this lens on. My guess is that the vignetting is caused by the format differences between the original camera and his present one, NOT the part he wants you to cut off. If the ring would cause the vignetting it would have caused it also on the original camera.
Your decision, but I'd not do it. If it is the lens I think it is then it is a valuable lens (350-500 EUR second hand value) and if anything bad happens to the front element or any other part then he will not be happy. A tiny scratch can render it into paper weight... Your friend needs to get a proper adapter. As him to register on this forum:
https://www.dpreview.com/forums
That is the place to discuss lens conversion and what to do about vignetting. Many wide angle lenses have vignetting "by default" and is not possible to fix that with such fixes.
https://www.youtube.com/c/AdaptingCamera/videos
https://adapting-camera.blogspot.com
Last edited by tjbaudio; 12-17-2017 at 09:49 AM. Reason: pictures did not take