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Author Message   Glenn Tinkerer Username: Glenn Post Number: 864 Registered: 07-2006 Rating: N/A Votes: 0 Posted on Tuesday, November 16, 2010 - 03:03 pm:    If you are absolutely sure that the shutter releases 100% with no film in, the problem could be due to the resistance of film in the gate/pressure plate or cassette stopping the shutter fully cocking. This certainly can occur in a double stroke M3 that is worn/in need of adjustment. Your statement that the thinner B/W emulsion films did not initially cause this problem would seem to verify this probable cause. You should also make sure that the back of the camera has not been dinted/distorted and that the rewind knob mechanism is completely free to rotate. If you are prepared to sacrifice a few inches of film, the following 'test' can be quite revealing - Load a cassette of film and try to advance some frames through the camera (5/6 should be enough). Now open the camera and cut off the advanced portion of film, then reload the camera with this small length of film, placing the roll loosely in the cassette space. If the reloaded length can be advanced and the shutter released normally, the fault is in the rewind knob or friction in the cassette spool caused by the location points for the cassette. If the shutter still does not release with this short length of film in place, then you should check the feed of film through the gate/pressure plate interface. Only after eliminating film feed problems should you start to dive into this camera. Don't forget to re-trim the end of the film remaining in the cassette!