Canon 70-200 F/4 L is said to be one, if not THE, of the best lenses Canon ever produced. I've bought it a few days ago, and I can estabilish they talked well. This lens is AWESOME.
The IS one is even better because of the stabilizer, but the optic scheme is the same.
Let's view it in the detail.
First, the body of this lens is white. Or should I say beije. Anyway, it's not the usual black. Every Canon L telephoto lens is white, and there's a reason: L lens all have a metal body, and if you use in a hot sunny day the lens itself could get scorching. Not only that, but chronic dilations and costrictions could cause problems with your lens. That's why Canon decided to make them white: bright colours have an albedo (reflective power) far greater than dark ones, and that limits overheating and connected troubles.
For a L series lens, it's rather light, weighing only 705 g.
It mounts a ring USM AF motor, resulting in lightning fast and accurate focus, as well as silent. There's even an option to select the minimum focus distance between 1,2 m (the minimum) or 3 m: this second choice comes in to play in the case you don't want your lens to focus a too near object. Since the minimum focus distance is 1,2 m, and the max focal is 200 mm, it means you CAN'T take macro pictures worth of this name. But come on, this isn't a macro lens =)
Oh, and I didn't mention it's WATERPROOF.
So, let's talk now about quality image. Well, I'll use a single word: OUTSTANDING. This lens is SHARP, gives highly constrasted images, is flare resistant. This lens is so good it is VERY sharp even at maximum diaphragm aperture. Use it at F/4 and you'll be upset by its sharpness; use it at F/5,6 or more and you WON'T BELIEVE YOUR EYES. This lens kicks ass!!! (Sorry for bad language, but I had no other words to describe this quality =))
So... are even there any flaws? Well... it depends on what you're looking for. For example, it's only a F/4 lens. It has not IS (but there's a version, which costs twice as much, that has got it). It doesn't do macro. But they'r not flaws. A perfect lens doesn't exist. All of us would want a 10-800 mm F/1 lens, sharp at any focal range and any aperture, and maybe, why not, cheap. But that's sci fi, not reality.
Canon 70-200 F/4 L USM is a monstrous lens, and if you consider it costs about 600 dollars (here in Italy 590 €) you are served with an exceptional piece of optical art.
If you can afford it, buy the IS one. I didnt' try the 2,8 version, but from what I've read, the F/4 one is much more sharp than it. But I can't make comparisons by myself, so don't take this for biblic truth.
and again, SHARP =))
well... uhmm... =))
I rate it 10 out of 10.
Thank you for reading.