> The AF sensors depend on angular information, interpreted as
contrast
> by 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,
why
> would you want a readout???
Henning

Have 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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