You've got the right idea, but a 5.6 wide open is well...a 5.6. It doesn't
get any faster than its' maximum aperture, and THATS the aperture that the
camera has to use to AF. Throw on a TC, and the maximum aperture is one or
two stops slower, i.e. f/8 or f/11.
Tom P.
> ]
> OK, another newbie, to EOS anyway, question here. I'm having trouble
> visualizing how aperture affects AF. We're always focusing with the
> lens wide open aren't we? It's not like we have the DOF preview
> pressed while focusing. Then I could understand Does the AF
> mechanism respond *as though* the dialed in aperture were effective?
> Sorry if this is a stupid question.
>
>
> Ken Durling
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