All four varieties of the Canon 70-200mm "L" zoom are renowned for being ultra-sharp. This is the f/2.8 IS version, the Rolls Royce of the range - until it was superseded by the Mk II version of the lens in 2010.  It's the longest of the four, and the widest, and the heaviest and by far the most expensive. It's also the most flexible - if you're prepared for the weight and the expense, you don't need to choose between the constant f/2.8 or the IS - you can have both. If you're shooting moving subjects though, then IS isn't much of a help, and you might find the f/2.8 non-IS version a better choice.

This lens can be used very well with a Canon Extender (teleconverter). The 1.4x Extender makes it a 100-280mm f/4 zoom, and the 2x Extender makes it a 140-400mm f/5.6 zoom. With either Extender, the lens will still autofocus on all EOS cameras.