Originally Posted by
dubaiphil
When you say 'candid' I presume you're not going in with flash firing. Therefore it all depends on the light levels, focal length and distance to the subjects.
Lower light and you'll be needing a larger aperture and higher ISO - you'll have to focus more critically and you'll need to use a cross point for focusing if you're selecting it yourself.
Better light and you won't necessarily need such a large aperture, your depth of field will be larger and you won't have to focus so critically.
Watch your shutter speeds though - as the subjects won't be posing for you, you'll have to ensure that your shutter speed is fast enough to stop any subject movement.
So - what light levels are you talking about, and which autofocus lenses are you talking about?