Summary: I have only had this lens for a few days and I compare it with Canon's 70-200mm f4L which I have had for a couple years. For the price, this is a great lens, especially if you can really use the 200-300mm range. I however have little need for that much zoom.
Summary: I've used this lens for 4-5 years for many High School prom and senior photo shoots as well as sports and while there are slight limitations in aperture, most of the photography I've shot was with good light. I left a couple of pictures on the main page to see for reference.
Summary: All summer I have been taking pictures of dragonflies and damselflies. The detail is amazing! I can see the hair on the legs of dragonfly! Wonderful! A little slow to focus sometimes but overall the picture quality is so much better than a Tamron my spouse was using.
Conclusion: This lens still surprises me. Sometimes it is very sharp, but sometimes I am not satisfied with the images it produces. Good for trekking, when weight is an issue. But remember fast shutterspeed, tripod or enough light.
Conclusion: Bought this as my first telephoto from a friend who upgraded to the 70-200mm f4L world. This lens has served me well for 4 years, and has been a GREAT motorsports lens. The fast AF is really nice when panning and tracking race cars and motorcycles. This is probably the best bang for the buck.
Pros: -FAST autofocus -Compact design -Good for the money
Cons: -Not as solid feeling as a L lens (but it's not one, so there!)
Conclusion: This is an excellent lens for a bargain price. The AF is fast, the IQ is good, and it's not expensive. Sure, the AF isn't as fast as my 70-200 f4L, but honestly, it's pretty close. It has ring USM with FTM (full time manual) focusing - a feature usually not found in lenses of this price range.