Therefore, while technically the aperture does not
> change, for metering and AF purposes the "effective aperture" does
change, since
> less light reaches the sensors. Since with AF what matters is the
amount of
> light that reaches the sensors (no?),
Mmmm...
I'm not sure: I expect it is a function of the amount of light for
sure. But I'm not sure if the effective "width" of the beam is also a
factor. I.E. is AF efficiency at f2.8 with an ND 0.6 (2 stop) filter
the same as no filter on an f 5.6 lens?
need someone really clever to answer that ;o)
For macro (sob, that *begins* at 1:1) AF remains irrelavent ... though
I do use the focus-confirm indicator on occasion. The central sensor
is a non issue anyway as dead centre is seldom where I'm focusssing
and focus-frame does not work at macro scales: unless you tripod
happens to rotate about the right point.
Bob
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