Archived posting to the Leica Users Group, 1998/06/10
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Charles, The cam difference between Leica CL lenses and Leica-M/Minolta CLE lenses is tough to visualize without an example of each in front of you. The lens mount for both types of lenses is the same, and both focus in a similar manner with the rangefinder wheel rolling on the back of the helical (I'm not sure if helical is the right term---or, come to think of it, what the "cam" in rangefinder cam refers to). The difference is simply that the Leica-M/CLE helical moves "evenly" fore and aft, always perfectly parallel to the lens mount, while the CL helical is cut and moves at an angle. Hold your Summicron 40/2.0 and any of your other standard-mount M lenses in your hands, turn the focus ring and, from the top of the lens, watch how the helical moves. Leica has stated that this difference in helical/cam movement can lead to focusing inaccuracy; many LUG member have reported finding no focusing problems. I suspect there may be a difference between theoretical and actual use, or perhaps between "usual use" and "super-critical use." Leica designs lenses to quite severe standards. It may well be that an Elmar-C 90/4.0 on a Leica-M, mounted on a tripod, using slow film, exposed at 4.0, focused at certain distances, with the resulting negatives examined at 30x, shows some focusing inaccuracy that is attributable to the cam/helical. I seldom use my Leica on a tripod, and when I used a Rokkor-C 40/2.0 on my M body I never saw evidence of focusing inaccuracy in my prints. Your mileage may vary..... =20 I'm not sure I understand your reference to "non-rotating cam arrangement."=20 Reards, PB On Tue, 09 Jun 1998 19:24:06 -0500, Charles Babington <cbabing3@swbell.net> wrote: >I've seen this statement, about different kinds of cams, before >(probably on Gandy's site), but I've been a bit mystified because on >"most" of my M lenses the rangefinder wheel simply rides on the back of >the rotating focusing helical in the lens - as on the 40 Summicron. =20 [snip] >So in my experience, most lenses have the rotating >type of cam. Is my experience too narrow, or do most of the other short >lenses use the non-rotating cam arrangement? =20 Paul C. Brodek Kobe, Japan pcb@iac.co.jp