Stepping away from the baiting of the JCO entity for a moment. ---
On Oct 19, 2006, at 7:00 AM, William Robb wrote: > ... They are both changes to the mount, done for purely economic > reasons. > Had Canon so desired, they could have left the register distance > alone, > and it should have allowed adapting FD lenses to EOS cameras, > though the > lenses themselves may have needed modification. ... Canon increased the mount register to allow for a mirror that was a few mm longer, useful to prevent the imaging cutoff that FD series cameras had with long lenses. There was insufficient space in the FD mirror box even with a cantilever mirror lifting linkage for the required longer mirror. Increasing the register 2mm allowed for a 4mm longer reflex mirror. The EOS mount has both more register and a wider diameter to allow for the needs that Canon perceived as the future requirements in fast, long lenses. The people at Canon are not stupid. I am certain they debated these changes for years knowing how it would affect their customers. But they were up against the wall with the FD mount, it was hampering both optical and mechanical design of the lens line. Pentax changes to K-mount over the years have been less dramatic. The register originally chosen and the diameter have been sufficient and not a hindrance to optical development, like Nikon's bayonet mount as well. The removal of mechanical couplings for aperture sensing is an economic move as well as a functional improvement: electronic sensing of aperture position is less likely to need adjustment and service, and removing the aperture ring and follow cam mechanism from the lens allows for simplification, more reliability, less service as well. The addition of power couplings in KAF2 allows for the possibility of removing the mechanical iris actuation as well: future lenses could be completely servo driven internally with the electronic couplings for iris actuation, dispensing with the ambiguities involved in the current aperture regulation mechanism ... this is what I would expect with the next set of upgrades to the Pentax K-mount. The obvious reasons why they have not yet gone this step are backwards compatibility and cost ... it keeps the price of the lenses down to have the mechanical actuator, prevents having two different actuation mechanisms to support, and it gives them the backwards compatibility that Pentax customers want. --- Please do go on now. ;-) Godfrey -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net
