Telephoto lens shims

L

lkgroup

Guest
I mentioned the following at the end of a another tread. I'm starting a new tread on the subject of "shims" for telephoto lenses.

quote:"Even so, half a century of wear can take its toll. I have had to "shim" the RF coupling cams of my Steinheil 13.5cm F4.5 and Nikkor 13.5cm F3.5 lenses to focus properly when used wide-open. You can do the same with the Russian Jupiter-11."



Could you explain or list a web site that could explain how to shim the RF cams. I have a couple lens that do not focus correctly.

Leo
 
I use some precision Copper Tape for my Shims. I will try to get some digital close-ups of the RF cams with the Copper tape on it. I will have to find the thickness of the tape. I have also filed down very thin pieces of metal or PCV plastic and epoxied them on before, but I like the copper tape best.

If the lens's actual focus is behind that indicated by the cameras rangefinder, it means that the cam must be pushed in slightly more. This pushes the RF closer to infinity. I have a fixed distance "target" at 15', a lamp that is easy to focus on. Assuming that the lens focus scale is good, and the RF is accurate, a worn cam on the lens can cause problems. It was the "culprit" on two of my 135 lenses, the Nikkor and Steinheil. That is when I put thin copper tape on the lens' RF coupling to build it back up.
 
I would love to see some close ups on where you put the copper. I'm not picturing this in my mind. Do you use a ground glass on the back of camera to see if the focus is right?

Leo
 
I have used a taped down exposed negative with a 15x loupe to check the focus if pictures come back showing the Lens' distance scale cannot be trusted. That has happened twice: I had to change the shims on a Nikon rangefinder: someone re-assembled it improperly; and on the second adjust the mirror on an SLR.
 
The lens on the right has a single layer of copper tape on the RF cam, the lens on the left is fine without it. Both focus to the same 15' distance on my Canon L1 with its RF set to the "high-power" position. Without the tape it is off by about 1 foot at 15 feet.
 
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