« on: May 25, 2012, 11:23:42 AM »
I have the f4 IS and have rented the f2.8 II. The f2.8 II is considered to be one of the best zooms available from any manufacturer and was very sharp. However, the f4 is super sharp also and very little difference in real world viewing can be seen. The f4 is half the price and readily available for around $1000 used also. It is also half the weight. It's a very compact, easy to carry lens for what it provides. The f2.8 II is a beast. Bigger and heavier. You do not need a tripod collar to make the f4 work on a tripod, which is good since Canon doesn't provide one.
The f2.8 II is metal construction, the f4 is not, but build quality is still excellent. Cheaper 67mm filters for the f4 vs 77mm for the f2.8 II, although I find many of the popular lenses that you find in many bags, such as the 17-40 and 24-105, 300 f4 etc are also 77mm filter size, so the 77mm may be a plus.
If someone offered me one or the other, I would take the f2.8 II, but in the $2500 range new, the f4 looks all the better in the real world. If you like to hike or travel, the size and weight of the f4 is a real plus.
Both lenses are great.