I was puzzled recently when I did some test shots with my Canon A800 by shooting the same (landscape) scene with and without full optical zoom and with the camera program set to SCN - Sunset. (Sunset mode seems to produce really good DOF regardless of aperture and/or shutter speed.) The focus was equally sharp for both and the shutter speed for the zoomed shots was almost consistently double (or more) that of the non-zoomed shots. All of which seems somewhat inconsistent with generally accepted rules of thumb so I wonder if the camera is making some kind of 'intelligent' adjustments.