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I have recently acquired a 35/3.5 (marked 3.5 cm) Summaron for my M2. However, as opposed to my Elmar 50/2.8 and my Summicron 90/2.0, the frame seems not matched, i.e. when I mount the 35 mm, the frame contracts to the 50 mm size. Anyone who can shed light on this ?
from the 'Leica Manual' 14th Ed revised 1961 pp14-15
"The Leica M2 accepts all bayont mounted lenses. ... However, in the case of 35mm lenses, it must be noted that older lenses, without Optical Viewing Unit, will bring the 50mm field line into place in the finder, thus showing a smaller area than actually encompased by the lens."
This may be the answer to your question, however the M2 is not a camera that I'm well aquainted with. Others may be more helpful.
Gentlemen, The earliest M mount (1954ish) 35mm Summaron lenses for the M3 were without eyes and activate the 50mm frame lines. A decent technician can file down the proper cam on the lens so the 35mm frame line will show in an M2. Happy snaps,