There is something about being brought up in the English class system and 'knowing your place' that seems to carry into my adult life and into the gear I usually chose to buy and carry. In England, for my generation at least, if you carried professional equipment you damn well better be able to use it. You didn't buy a good cricket bat unless you were a good cricketer. If you turned up to a gig with an American Fender and Marshall Amp you better have the chops to justify it. You didn't carry professional camera equipment unless you were selling pictures.
I was, therefore, brought up with the self-denying attitude that third-party glass was good enough unless you were David Bailey. Fast forward a couple of decades and here I am in America where enthusiastic amateurs have no such hang-ups. I've seen novices unashamedly carrying 5D's in program mode fitted with L lenses. So it took my less inhibited and ultra-supportive, American wife to 'spoil me' and buy me this monster lens. If it were left to me, I would have stuck to the consumer grade 75-300mm IS which worked OK at a pinch but which was often frustratingly soft and uninspiring. So, weather I feel like I deserve it or not, here I am with this beautiful lens on my camera wondering if I can now live up to the lens - there's something a bit comforting about being an amateur with amateur grade gear that you can blame for the short comings in your work. If a Canon lens carries the 'L' badge there are no such excuses; if the image is 'wrong' it's all me now.
So you get the idea; this lens is a bit intimidating both to be behind and in front of. Physically it resembles a piece of military hardware - an effect that is exaggerated by it's light battleship gray paint scheme. Both its size and light color make this a lens impossible to hide. With it's large, included petal lens hood fitted it really does dwarf the digital Rebel camera. It definitely feels like you are handling a lens that has a camera attached to it not the other way around. A fact that Canon seems to acknowledge by including a tripod collar with this lens. I have some pretty solid tripod heads but this lens would sink even the strongest of them if you were to mount the camera to the head rather than the lens via the lens collar. The whole "military hardware" theme is continued by a battery of four switches to control this lens' functions. There's the usual switch to turn the auto-focus on and off. Then there's a switch for the IS mode, one to restrict focus range and one to run the IS feature on and off.
This lens focuses and zooms internally which means that in outward appearance the lens does not change it's proportions based on the focal length chosen and that filters attached to front of the lens will not spin as the lens focuses. The internal mechanics help in the excellent weather sealing of the lens, but their biggest advantage is the speed of focusing and tracking. This lens focuses really quickly and is fantastically sharp at all focal lengths and apertures. I won't pretend that it is better than equivalent primes but it's close.
Canon have no less than four 70-200mm lenses in their professional L range. There is an f4 and an f2.8 and each is available with or without stabilization. If money is an issue (isn't it always?) the f4 non-IS is one of the bargains of the L range. It has the L's legendary sharpness but it will take a little care to get the best out of it and in low-light it is not especially useful. The f4 IS is useful if you want the added IS functionality but you want to watch the weight - it is a great hiking lens. The 2.8 IS is a great portrait lens if you can control the light, for example, in a studio setting. The f2.8 IS is the most expensive and the largest but it is also the most versatile. It is great for portraits wide open at f2.8 even in available light - this makes it a favorite lens of wedding and portrait photographers. On a crop factor DSLR or with a compatible extender it makes a useful zoo or occasional wildlife lens. Out and about it is not very useful as a street lens but for sports and isolated landscape work it shines.
This is the most expensive lens I own. It costs three times what my Digital Rebel cost and mounted to a camera it is worth more than my current car but that probably says more about the age of my car than this lens. However, once you have got past the pain of the cost and its physical size, which you eventually will, the 70-200mm f2.8 IS is such a versatile tool you will find yourself picking it up in situations you had not even imagined it would be useful. This lens quickly became less of a extravagance in my camera bag than it was a necessity.