Screwdriver AF doesn't require a lens to be compatible with any particular mode of AF control. Hell, it doesn't even need any embedded electronics associated with focusing, save for distance reporting not critical to focus operation. These lenses can just be dumb mechanisms following the camera body's instructions. Compatibility is no issue at all.
Focus by wire is entirely a different kettle of fish. The lens is an integral part of the 'brain' of the system, and who other than the designers knows what requirements need to be fulfilled. But I can offer this observation. My old EVF style camera has CDAF focusing. When it focuses, the gross movements happen at a fast motor speed, but when it approaches correct focus the motor slows considerably for the last fine focusing. Clearly, this focusing motor has variable speeds. My DSLR is the "bottom feeder" model from Olympus, the E-410 which has only PDAF (CDAF not being added until the 420 mode, AF during live view is achieved by a quick mirror flip into reflex view, and back into live view all in about a second). Even considering the humble status of this camera, the AF flies like shit off a shovel. It will snap into focus in a trice with no hunting. But my observation is that the motors in the two consumer zooms I have run only at a single high speed. I'm guessing that CDAF needs AF motors that slow down as they approach correct focus, and that the cheaper lenses weren't enabled for this mode in their original firmware versions. Someone with the better 4/3 lenses might comment on their operation. IMO this thread is a storm in a teacup, because Olympus has issued firmware updates to enable CDAF in live view with the "incompatible" lenses. Problem solved. Regards, Anthony Farr > -----Original Message----- > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of > Adam Maas > Sent: Sunday, 14 September 2008 7:17 AM > To: Pentax-Discuss Mail List > Subject: Re: panasonic's new micro four/thirds camera: G1 > > When everybody elses lensed designed "years" before Live View and CDAF > work just fine? Yup. Canon and Nikon had much more significant hurdles > to get 20 year old lenses to AF with CDAF than Oly did with at most 5 > year old lenses designed for a focus-by-wire application like CDAF. > Nikon, with it's obsolete screwdriver-drive AF pulled it off, and both > Nikon and Canon have achieved it on lens-motor based lenses, despite > their specs dating back to ancient times (the Nikon lens-motor control > spec dates to 1983, the Canon to 1987). Wasn't 4/3rds supposed to be > the 'modern, future-proof' mount? > > I don't expect the same level of AF speed from the older lenses as the > new ones designed for the application, but the bloody things should be > able to AF in the first place. Especially since Olympus designed them > to be firmware-upgradable. Frankly I doubt this is even an engineering > issue per se. More likely it's just a budgeting issue and they didn't > spend the money to implement the necessary support either in the > bodies or via firmware upgrades. > > Heck, despite all that I'm still enthused for the G1 and am seriously > considering buying one once the 20/1.7 becomes available. > > -Adam > -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
