for what you are doing, stick with zone focusing. too much
changing for most AF systems to lock onto in low light.
I'd agree... AF systems are very slow in low light no matter how
fast your lens is.
I don't find that to be the case. It depends very much upon the
particular scene conditions.
Would you consider trying a fast 35mm lens as a compromise?
35mm is about as long a lens on 16x24 format that I can consistently
zone focus in low light due to how wide an aperture I need to use for
proper exposure. And the success rate is substantially less than for
a 24-28mm lens. It's also about the limit of being able to just point
from the hip and get the framing according my previsualization.
If you need a 50mm lens or greater for framing purposes, AF works
quite well most of the time until the scene you're trying to catch is
so low in contrast that it can no longer lock on target. But framing
for 50mm and above, you need to be working with the viewfinder
anyway... manual focus takes over.
Godfrey
