With its USM autofocus drive, focusing was always fast and spot-on. The ribbed rubber zoom ring, located toward the rear of the lens, is nice and wide (1.5 inches), grips easily, and has a good feel. Manual focusing is very usable for an AF telephoto zoom, and the wide-ribbed rubber focusing ring located toward the front is well dampened. That, along with it relatively thin barrel diameter, makes you feel in control while manually focusing.
Performance and image quality
In our lab tests, the lens was a very good all-around performer. It displayed noticeable pincushion distortion (where objects appear to curve toward the center of the image) at 200mm, its longest; although noticeable in lab tests, it generally won't detract much from your photos unless you shoot lots of horizontal and vertical lines, such as architecture. Beyond that, distortion is less evident as you get wider, with less, but still noticeable, pincushion distortion at 135mm, and minimal barrel distortion (where objects appear to curve away from the center of the image) at 70mm. It delivered very good sharpness at 200mm and excellent sharpness at 135mm and 70mm. There was well-controlled sharpness at the corners of the frame, with minimal sharpness lost at the edges. It exhibited the best corner sharpness results at 135mm, with only minimal loss, and fully zoomed out to 200mm it showed more loss of corner sharpness, but still good for a zoom lens.
There are times--like that amazing safari, or maybe just for your backpacking trips--that you'll demand a high-quality telephoto lens with rugged construction, a light weight, and a manageable size. The 70-200mm f4 IS USM L is a great option over the traditionally large 70-200 f2.8 lenses. Unless you really need some of the things that only the f2.8 lens can provide, such as faster shutter speed options, say for stopping action, or a shallower depth of field, I suggest you only carry the extra weight if you absolutely must. The 70-200mm f4 is 24 ounces lighter and about $600 less than its f2.8 cousin, making it a great option for those who want a well-built, telephoto zoom lens you can hold in your hand.