On Sep 24, 2013, at 11:28 AM, Larry Colen <[email protected]> wrote: > On Tue, Sep 24, 2013 at 01:14:54PM -0500, Darren Addy wrote: >> What are you calling "traditional Leica glass"? >> M-mount has a 27.8mm flange to film/sensor distance. >> M39 is 28.8. >> Leica R-mount is 47mm (longer than the "kludge" K-mount 45.46.) > When used in a sentence, “traditional Leica glass" is nearly always referring to Leica M-bayonet and Leica Thread Mount (LTM). While the specific mount registration differences are 1mm apart, M-mount is the more universal design as it is the shortest registration and was designed so that LTM could be easily adapted to it (since M-mount bodies followed LTM bodies, it didn’t make sense to design for M-mount adaptation to LTM to Leitz).
Leica R mount lenses are for their SLR line, in which there are five different (but mostly interchangeable) detail differences depending on year of manufacture and the specific lens in question. Leica (and others) also makes adapters to allow R-mount lenses to be used on M-mount, of course without mechanical rangefinder support since R lenses do not have the RF cam. Note: The Leica M (Type 240) allows full-field focusing and viewing with R lenses via Live View using the LCD or optional EVF. In addition to M-bayonet, LTM, and R-bayonet, Leica also has Visoflex mount (version I = 91.3mm, version II, III = 68.8mm), and manufactured longer lenses with these mountings as native so that they could be used on both the RF and SLR cameras using the appropriate adapters. > Oh well, it was a nice theory. Since folks seem to be able to use > Pentax glass on their ricoh m-modules I thought it had a short > registration distance. To use Pentax SLR lenses on the GXR A12 Camera Mount, all you need is a Pentax M42 or K-mount to Leica M-bayonet mount adapter. I have both. You can nearly always adapt a *lens designed for a deep mount register* to a *body with a shorter mount register*. The A12 Camera mount is M-bayonet register depth, 27.8mm. >> I've been thinking about upcoming cameras from a Pentax-centric point >> of view. We keep asking for a Pentax "full frame" camera, and the >> latest rumors seem to have being mirrorless. There are a lot of >> technical advantages in terms of light path to mirrorless, and there is >> the advantage of you see what the sensor sees. >> >> But, using K-mount for mirrorless is a kludge. You lose the short >> registration distance advantage, without kludging lenses that have >> elements that extend past the mount. I agree. >> But the company isn't Pentax, it's Ricoh. And they have already >> made an interchangeable lens camera with a well defined, full >> frame capable, mirrorless mount. The GXR Leica mount module. This should be qualified. Leica, just like Nikon and Pentax, deemed that it was more important to maintain compatibility with their existing lens lines than to redesign the lens mount on the M and F mount bodies, respectively. However, neither M nor F mounts are ideal for 24x36mm digital sensors—they can be made to work, but ideally a lens mount for a digital sensor should be larger diameter relative to the format and a shorter registration distance, to enable more flexibility in lens design for the digital capture medium. Canon was roundly dissed when they obsoleted the FL/FD mount in the 1980s and thereby obsoleted many owners' expensive lens collections. However, they were prescient in developing the EOS mount which is huge diameter (about 51mm) and a relatively short (44mm) register. The change has stood them in good stead in the long term, although it cost them a lot of customers once upon a time. Olympus was unsuccessful in bringing out an auto-focus SLR lineup and had pretty much left their pro system (OM) on the sidelines for years, delivering a couple of new bodies and lenses only for the last decade of its production history. When they started to think SLR with digital capture, they worked with Kodak and developed the FourThirds mount, which has an even shorter register than Canon EOS (38mm) and about the same outer diameter. This lens mount is the only one in production that actually has the ideal sensor size/diameter/register depth combination for digital capture SLRs and lenses up to f/1.4 aperture settings. The Micro-FourThirds design is essentially the same, scaling down the bayonet diameter along with the register depth to maintain the same characteristics, and allowing for more compact body designs—it was only made possible by the invention of high-resolution EVFs and large sensors with Live View capability. >> What if the new high end, full frame sensor, camera coming from >> Ricoh were not a Pentax mount, but a Leica mount? Ideally a mount >> that is mechanically compatible with traditional Leica glass, but >> with contacts for autofocus etc. And what if, just for the hell >> of it, they also sold an adapter that allowed use of K-mount lenses >> in full auto focus? Even if it were just full autofocus on the SDM >> lenses. It’s an interesting thought, but there are some subtleties here too. M-mount was never designed for lenses with electronic control or bidirectional communication with the body other than via the lens focusing cam and body’s mechanical rangefinder cam follower. Leica has gone through some complex efforts to maintain full compatibility with all M and LTM lenses, barring a few that simply project too far into the body cavity to work with the thicker digital capture sensor mechanism, while at the same time creating a communication system between lens and body that at least allows the body to recognize what lens is fitted so as to fill out the EXIF data and estimate the working aperture. They achieve this through a six-bit coding on the lens flange and a reader on the body flange. So if Ricoh were to do this, they would have to extend the M-mount design in ways that were not incompatible with Leica’s extension of the M-mount into the modern era. This would be no simple trick as there’s precious little space on the M lens mount for the usual sets of electrical contacts, potential screwdriver drive, mechanical iris control, etc. All of that stuff would have to be implemented in one way or another. It’s a fun thought exercise, however. Godfrey -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
