F. Craig Callahan wrote:
>
> Another question I have pertains to the EF 28-105/3.5~4.5 (old
> version) that I
> just picked up to go with the 7 for hiking/backpacking use (this also
> pertains
> to the 20-35/3.5~4.5): The instructions say to switch to manual mode
> for manual
> focusing, and cautions to not touch the focus ring when focusing using
> the AF.
> Does this mean that this lens does not support full-time manual
> focusing even
> though it's a USM lens?
It does support FTM. The reason for switching it to manual is another
one. With a camera body that doesn't allow to separate AF from the
shutter release, it would not make much sense to focus nanually before
AF has completed his thing. It would override your manully set focus
when you press the shutter release. If in one shot mode, it would not
even allow you to take a picture before the AF thinks it's sharp.
Besides, focusing manually during AF might fool the AF logic. Anyway, if
you think you have to do it, I have occasionally done this by accident
and never had any lens defects.
Thomas Bantel
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