Modern SLR AF don't use IR, it is CCD TTL phase detection. Need
available light or assistant beam to work not IR. The old one detect
vertical lines and later one with sensors for horizontal lines too. It
is called passive focus and IR (active focus) is used on compact AF
cameras. I don't know the very detail about phase detection but it is
something like split image finder theory.
C.H.Ling
bsandyman@xxxxxxx wrote:
>
> Ok, I think that AF cameras send out a IR square wave and then look for
> reflections of the same frequency as the square wave. The difference in phase
> of
> the reflected light and the source light can be used to calcuate the
> difference.
> Is this what you mean?
>
> Why would this have a problem in low light conditions? Since the camera
> carries
> it's own little IR source...
>
> Or maybe something else is meant by phase?
>
>
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