On Mon, 31 Oct 2005 18:02:15 -0800, "Joseph Chamberlain, DDS" <drjchamberlain@xxxxxxxxxxxxx> wrote/replied to: >1. I understand that autofocus is only supported (at least by Canon lenses) >if the maximum aperture is f/5.6 or larger. In case I were to add a Canon 2x >extender to a lens that already has f/5.6 as the maximum aperture with the >resulting maximum aperture being smaller than f/5.6 would I still be able to >use the lens in manual focus mode ? In this case would the exposure metering >be preserved through the lens and only the autofocus lost, or would some >kind of exposure compensation have to be used ? I would appreciate if those >with experience using this type of arrangement could share their knowledge >with me. Yes you can manual focus, and yes auto exposure is preserved. Pro EOS bodies can autofocus up to f8. But you can in some cases retain autofocus on the 'lesser' bodies by 'cheating'. Tape over the last contact in the extender and the camera thinks you are still at f5.6. I do this all the time on my 100-400 with 1.4x. Works great for me, at least in decent lighting. >2. I have looked at yet another lens from Canon. The EF 28-300mm f/3.5-5.6L >IS USM seems to be an interesting lens to have. Assuming the image quality >is good (and I would hope so since it is an "L" lens), this would be an >extremely versatile lens to have, specially if one can also carry a 2x >extender in the camera bag (in case the answer to question number 1 above is >yes). Yes, it's a decent lens - expensive and heavy. Look for used lenses, often you can get them at 1/2-3/4 of new price. -- Jim Davis, Owner, Eastern Beaver Company: http://easternbeaver.com/ Motorcycle Relay Kits - Powerlet, Posi-Lock K100RSes on both sides of the planet!
