At 6:43 AM +0000 10/30/02, Bob Talbot wrote:
Quite true, there isn't as sharp a cutoff as Canon imposes. The exit pupil isn't as completely tied to the aperture as the above would indicate. However, in the case of the D60 (and EOS3) which I have used the f/5.6 for the D60 and f/8 for the EOS3 seem to be hardwired limits. Third party lenses might fare differently, depending on how their electronics interact with the bodies, and manual lenses with adapters might provide focus confirmation at smaller apertures. Only thing is, you would want focus confirmation to provide confirmation, so wouldn't you want to be able to rely on it? Seems slightly dubious.> The AF sensors depend on angular information, interpreted as contrastby the circuitry. When the rear exit pupil of a lens is too small (ie, the side to side angle of the rays hitting the sensors is too narrow), they don't respond correctly anymore. If they could respond correctly, AF would be possible. If they don't respond correctly,whywould you want a readout???HenningHave you actually tried this or is this repeating stuff from the brochure. Not for the D60 I admit, but on other cameras in the EOS range the lenses will autofocus satisfactorily with "slower that f5.6" third part lenses, or with tubes/teleconverters, when the pukka Canon lenses will not. Well, satisfactory in the sense of being in focus, yes. Less reliable with featureless subjects, yes too. I suspect Canon are protecting us from ourselves ... they can't guarantee the AF so they don't let you try. With most things in design, it's not really a cut-off between works or does not but a progressive fall off in performance.... Q
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* Henning J. Wulff
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