Originally posted by: Muse
When you people talk about fast or slow lenses are you referring to the widest available aperture at various focal lengths (i.e. lower number for aperture translates to faster shutter speed at the same exposure setting) or the speed of the lens's autofocus mechanisms? I presume the former, but it's a point of confusion for me.
the former. and fast is relative. f/4 is fast for a 600 mm lens, middling for a 200 mm lens, and ridiculously slow for a 50 mm lens.