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06-07-2011, 06:16 AM   #1
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Question: How to adjust focus stop on 3M 5CA 500mm mirror lens


Anyone know how to adjust the infinity focus stop in a 3M 5CA 500mm mirror lens like this:?

3M-5CA 8/500 Telephoto Lens

There are instructions on how to adjust the focus stop on a Rubinar mirror here: (at the bottom of the page.)

Rubinars with various cameras

... but I don't know if it's the same procedure on the 3M 5CA. The 3M doesn't have a rubber focusing ring grip to remove like the Rubinar, for starters.

Thanks much,
Bobbo :-)

06-07-2011, 06:21 AM   #2
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Can you not reach infinity? If the lens is focussing past infinity, then do not adjust the stop to have a hard stop at the infinity mark - mirror lenses need a bit of "slop" in their infinity setting to be able to correct for changing temperature conditions.
06-07-2011, 07:35 AM   #3
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Original Poster
Can't quite reach infinity... From what I've gathered, a few others have had the same issue when using this particular lens (and a few other variants) with an M42 adapter.

Bobbo :-)

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