Archived posting to the Leica Users Group, 2000/09/15
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]A rangefinder lens requires a focusing cam to couple with the camera's rangefinder. The camera's rangefinder is designed to couple correctly to the natural focus movement of a 50mm lens. All other focal lengths require a compensating mechanism to: increase the focusing cam's movement as compared to the wide angle lens' natural focusing movement; or, decrease the focusing cam's movement as compared to the long lens' natural focusing movement. If you are making an SLR lens into a rangefinder this will require designing a completely new focusing mount. As rangefinder cameras constitute a limited market, production numbers are fairly low. The Pentax "limited" production run of 2000 may well take many years to sell out. The problem with converting M lenses to LTM is that the M lenses were designed to be physically longer so that you could mount the shorter LTM lens on to a M camera using an adapter. You cannot just unscrew the M mount and screw on a LTM mount, the rear of the lens has to have 1mm machined off. That is not much but Leica has not been in the habit of designing in extra space just in case! So, again, a new focusing mount has to be designed and, again, demand will be low. The new mount designs required and low production runs mean higher costs. The Cosina/Voitlander lenses are often touted as low cost but that is only compared to Leica prices not regular SLR prices. Except, of course, in the super wide angles where you can design an uncoupled rangefinder lens to be much less expensive to produce than a complicated mirror clearing retrofocus SLR design. John Collier > From: Dante A Stella <dante@umich.edu> > > Just a thought > > Why are LTM versions of other lenses so expensive? Do the Summicrons require > rengineering of the barrel body due to some problem with the difference in > film-flange distance that wouldn't allow you to switch the mount plates (I've > never > disassmbled an M lens, so I can't tell)? (Why couldn't you just adjust the > focus > on the lens cells if that were the case)? Is this why the Pentax is so > expensive, > too (to say nothing of the Ricoh GR-1 lens and the Hexanon 60/1.2L)? Or is it > milking the LTM user/collector / maven / afficionado / admirer? > > The actual lens mount in LTM is a pretty simple threaded piece of metal that's > chrome plated, certainly something that seems like it could be made cheaply by > a > competent machine shop (LTM ffd is 28mm +/2 0.2mm). Actually, with modern CNC > equipment it doesn't seem like it should be that hard to make the "more > complicated" M mount, either. It would seem that to produce a short run of > LTM > wouldn't justfy the massive price increase like $400-500. > > By the way, has anyone ever converted an M lens to SM? > > It would be nice if you could specify LTM or M mount as an option. Think of > how > much new life could be breathed into so many old IIIgs and IIIfs. >