I have a 210mm Sironar-N lens mounted in a Copal shutter. It had a shim behind the front cell; it was mounted that way when I purchased it. A few months ago, I was out shooting in the field; it started to rain; I was trying to remove a tight filter from the front of the lens and mistakenly unscrewed the lens cell from the shutter - - losing the shim in the knee-high weeds.
While I cannot see a difference in the focus without the shim, either at infinity or up close, I am certain that the shim was there for a reason. I also tried to see if I could detect any change by examining the image with a loupe focused on ifinitiy, close to 1:1 and at the midpoint, adjusting the position of the front cell in the shutter by screwing it in and out. My thought was that perhaps I could calculate what size shim it needed by knowing how far out I had unscrewed the cell. Again, I could not see a difference, but I am certain that it is needed.
So my questions are: who can do the necessary testing or how do I determine what size shim it might need and where would I get said shim? Is there someone who does that kind of testing?
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