9 out of 10 points and recommendedIS, IQ, fast autofocus, light, cheapRequired considerable work with micro AF adjustment, F8 is required at the telephoto end
I got this originally when I was using a Rebel XSI and a Sunpak PZ40XII flash, because I'm disabled and its light weight was very attractive. It took fairly good pictures, and I was happy for the price.reviewed April 14th, 2009 (purchased for $300)
I missed a few far-off pictures where the focus wasn't perfect, to the point I missed an incredibly impressive 12-point buck on a forest path. Sigh.
Then I got my 50D, and oh, how things changed...
It took about 3 weeks. I tried all the tutorials for micro AF adjustments online - use an LCD monitor, a printed target, etc., but never got consistent results. So I just took notes out in the field (later I learned that wasn't necessary - the AF microadjustment used is logged in the EXIF - doh!) Anyway, I finally settled on +7. Now, when used properly (F8, 1/400th of a second or higher), the pictures *can be* on par with my mom's 300mm f/2.8L on the same body! The IQ is amazing.
Of course, F8 is very limiting, both light-wise and simply having to manage the lens. I have a 580EX2 with a Better Beamer now, which helps with the light, when flash is allowed - in many instances it is not, and I might choose instead my 70-200mm f/2.8L IS (which seems to have inferior quality (!?)) with a tripod, say at a horse show or such. Plus, you can't put two 2x extenders on it like the 300mm f/2.8L IS and have a frankly amazing reach (by the way, my mom's 300mm f/2.8L IS with 2 2x extenders still outresolves my 15mp 1.6x 50D... what great glass!). On the other hand, that thing is like 5 pounds. I like to do up-close wildlife work, and the ability to actually CARRY this lens and use it without a tripod is great.
If you can AF-microadjust, or take it back repeatedly 'til you get one that focuses PERFECTLY (I recommend testing on deer or a dog or something far-off that fills only a small portion of the frame over any of the methods I found online), this is an amazing lens with *perfect* sharpness all the way out to 250mm (at f8) at the center, even with the ridiculous pixel density of the 50D, and pretty sharp corners. It resolves 15mp of detail, if not a bit more. If you can't micro-AF adjust or bring it back ad naseum, you might be slightly disappointed, but it's still great, especially for the price. And I personally think its "cheap plastic" construction is a huge plus.
I totally also use the hood 100% of the time. This lens needs it. This, the Tamron 28-75mm f/2.8, and the Tokina 12-24 ATX are my mainstay lenses, plus the Canon 85mm f/1.8 and 50mm f/1.4 for portraiture and very low-light work.
I'd also like to add: the Raynox DCR-250 (2.5x) macro lens works wonders with this. VERY good image quality, filling the whole frame with a grain of rice if you want. Much less expensive than getting that kind of special purpose macro lens like the MP-E. Not perfect, but for $300 for this plus $40 for that, you get stupendous results.