On Mon, 23 Dec 2002 16:23:49 GMT, Logan McMinn wrote:

>One reason for opting for a fast lens is that it can allow quicker and
>more accurate focusing. As others have said, the faster the lens, the
>less the depth of field. This has a benefit in that when manually
>focusing, the image will snap into focus more precisely than with a
>slower lens.

This has an exception: when the VF focus screen is
optimized for a slower lens (many are, for the slow
common zooms), stopping an f1.4 lens down to f2 or
even f2.8 (with DOF preview) can make it easier to
focus...

>I don't know if it improves the accuracy of autofocusing,
>though; that could depend more on other factors.
>
>The image in the viewfinder will be slightly brighter as well, which
>can be useful in marginal lighting conditions.