But...the 70-200mm f/2.8L IS II really is the best lens for what you describe... You discount the f/2.8 non-IS for sharpness, not weight - the IS II is not significantly different is size/weight from the non-IS.Originally Posted by DavidEccleston
I'm puzzled by Rich's statements about slower focusing, too. The aperture doesn't directly affect focus speed, AFAIK. While an f/2.8 lens provides more precise AF, that precision does come at a slight cost in speed - that's why the majority of the data used to drive the AI Servo calculations actually come from the f/5.6 sensor lines - they have a faster response time (similarly, with the high-precision AF points, the AF system uses the co-located f/5.6 line(s) for a 'coarse focus' then refines that with the f/2.8 line(s).
The main problem (perhaps that's too strong a term) with a variable aperture zoom is when you shoot in M mode, since zooming changes exposure. You're shooting with a 7D, though - if you use M mode but set ISO to Auto, the camera will adjust the ISO to provide metered exposure in M mode (and the forthcoming 7D firmware update will allow you to set a cap on Auto ISO lower than 3200, if you prefer).
No idea about focus hunting with the 70-300mm, but that issue notwithstanding, I'd pick the 70-300mm f/4-5.6L IS over the 70-200mm f/4L IS.
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