Archived posting to the Leica Users Group, 1998/12/21
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Hello, Mark The reason Leica can't/won't guarantee focus of CL lenses on Ms is that the Leica RFDR is ONLY compatible with the focusing movement of a 50mm lens......BELIEVE IT OR NOT! -- ALL other focal lengths have to have their helical movement "converted" to the "movement" of a 50!!!. In the (obviously more expensive) Leica, Canon, other LTM lenses, other than 50s, this is done with a double helical. To simplify, One helical (steep rake for teles, VERY shallow rake for WAs) actually "focuses" the lens, generally in about 180 degrees of rotation (there are exceptions). This helical moves in unison with another helical which emulates the focusing movement of the 50 (!). If you notice, the movement of the "cam" on the back of the lens always moves in or out the same amount to go from infinity to 3' or so. ALso, this movement is PERFECTLY parallel to the lens mount, regardless of the lens. On the CL lenses, only one helical is used, to match that of the needed "movement" of the lens group....the "cam" on the back of the lens is now ground with a "rake" or angle, to simulate the in-out movement of a 50! Cheaper to make, only one helical pair. Herein lies the "problem" -- the movement is now NOT parallel to the lens mount. Part II - Look at the cam follower on your body. Notice it is "nearly" perfectly aligned with the "seal" screw on the top of the lens mount. On M-bodies, the lateral position of this follower is actually the often denied "near" focus adjustment!! -- now for the "concidental compatibility" --- if, as on many (most?) bodies, the follower is EXACTLY centered on the top of the mount, when at infinity, BINGO - the CL lenses focus (more or less) fine! But if your particular RFDR required this adjustment to be offset slightly off center, to achieve near-focus accuracy with "real" m-lenses, the CL lenses will not focus accurately at most or all distances...BTW< the CL RFDR does not have/need this accurate adjustment - it just wasn't precise enough, hence the lack of super-fast lenses made SPECIFICALLY for the CL!! This is because of not only the lack of base-length, but also the (relative) crudeness of the RFDR manufacture/adjustment. AS a former CL owner as well as a (Leica/other) repairman, I can tell you with some certainty that MOST CL lenses >CAN"T< focus perfectly on an M-body. Close enough for mid-far distances with slow lenses? Sure, mostly. Also, although the CL cam-follower location doesn't matter on REAL M-lenses, and it certainly does fine with 2.8 short lenses or 90s at f4 or f5.6, the CL base length plus the visual accuracy/crudeness of manufacture/magnification is a disaster trying to focus a 50 1.4 or 90 f2 at or near maximum aperture/close focus limits. Perhaps another repairman (Sherry?) can express the problem in a simpler manner. In the meantime, think of the CL as "nearly" compatible with M-lenses (certainly with wideangles, where the accuracy of an M body is an absurd excess), and keep those 90s at f4-5.6, depending on the correct adjustment of the CL and your particular visual acutity. Of course, lenses which are "forbidden" on the CL, because of the metering system, should always be avoided. Likewise, with CL lenses on M-bodies, you really need to check the compatibility on a case by case basis -- obviously check infinity focus (after verifying the body with an M-lens) -- then try it at 3 feet, either with a tiny ground glass or on film.....if you have more than one M-body, you really need to verify this compatibility on EACH body. For God's sake, don't even think about adjusting the body to "work" with CL lenses....yes, it can be done, sorta....but you'll sacrifice the accuracy of near focus with M-lenses, particularly long/fast ones at near distances -- exactly where you need the accuracy of a "real" M...... Aside from ruggedness/reliability issues, the CL was a NEAT little camera......had it not been billed as a "LEICA M" !! While I respect retaining an existing lens mount, in this case it led to 20+ years of confusion and half truths!! I LOVED my two CLs -- had great service from them -- but I didn't treat them as Ms, nor did I expect that insanely short-effective-base RFDR to focus my 90 f2 at 3 feet!! (you couldn't see through the damn RFDR anyway!) Compared to most cameras, it's a well built, finely tuned little machine....Compared to an M (or and SP or Canon) -- Well........you know. Hope my techno-babble explanation answered SOMEONE's questions... Have a happy..... Walt in Denton On Mon, 21 Dec 1998, Mark Hammons wrote: > > > > >WWWWWWWWWWWW > >Do you know if the 90mm Elmar-C <<the one for the CL>> would work on a Leica > >M? > >XXXXXXXXXXXXXXXX > >Francois, > > > >I use it all the time, so I hope it works ;-) Leica claim it has a > >different cam for the focus, and "may" not be accurate on the M, but mine > >has been flawless, and this is the usual experience on this group. > > > >Merry Christmas > > > >Alastair Firkin, > > > I have NEVER been able to figure out why the 40mm Summicon-C and > 90mm Elmar-C are supposedly NOT compatible with other M cameras. > Similarly, I have NEVER been able to figure out why all other M ( or SM > lens for that matter ) are supposedly NOT guaranteed compatible with > focusing on CL's. I'm not refering to lens back protruding too far issues > or short rangefinder on the CL issues. Have either or both of these > "dogmas" ever been examined by anyone or explained in more detail > my Leica? > > > Mark Hammons >