Re: 50mm Rigid Summicron or 50mm Summitar for M8?
CMIIW,
5cm equals 50mm. probably in the past they used to have the focal lengths in cm instead of mm.
As for the infinity lock, i dont know. I guess probably for better gripping when someone's changing lens, or probably required to have the focus locked at infinity when someone's want to dismount the lens. Again, CMMIW.
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