> When you get a spec. for a lens, for example: 24-70mm f3.5/5.6 > I know the f3.5 is the speed of the lens, but why is the 5.6 listed? Steve, Because the lens's maximum aperture changes as the lens is zoomed. Typically it would be (in this case) f/3.5 when the lens is at 24mm and only f/5.6 when it is at 70mm. This is something that early zoom lens designs avoided but seems to be a matter of course with many less expensive zoom designs of the present. Since auto exposure systems automatically compensate for loss of maximum aperture (up to the limits) as the lens is zoomed this is not a major problem these days. I have a follow-up question though. What about the minimum aperture on these lenses ... does it too drop in corresponding fashion? It would seem so but not necessarily, no? I don't have one of these variable aperture zooms. andy
