Canon EF-S 10-22/3.5-4.5 USM Lens Review
I took a number of test shots at 10mm, 16mm and 22mm over a range of apertures from wide open to f8. The overall conclusion is that the lens is sharp and that it does remarkably well wide open. While some lenses need stoping down 1 or two stops to be sharp, especially at the edges, the EF-S 10-22/3.5-4.5 USM isn't one of them. It's a lens you can shoot wide open and still get good results.
The two images below show full frame views at 10mm and 22mm
All of the following samples are 100% crops taken from the original EOS 20D images. No sharpning has been applied.
Center performance at 10mm is very good. There's really very little change in sharpness when stopping down from wide open.
In the extreme corners there is some softness wide open, but away from the corner, even right at the edges of the frame, sharpness is good. You do get a slight sharpness increase by stopping down from f3.5 to f4, and a little more by stopping down to f5.6, but even at f3.5 the results are pretty good for a superwide zoom lens, with the caveat that the extreme corners are soft.
In the image center, things are sharp wide open at f4. Stopping down really doesn't buy you much at all.
Again, at f16, edge/corner performance wide open (f4) is good. You gain slighly be stopping down, but if you need to shoot wide open you really don't need to be too concerned.
In the center of the frame at f22 the image is sharp wide open
At 22mm there's a little corner/edge softness but overall it's not bad. Again stopping down does improve image quality somewhat.
As I mentioned earlier, the impressive thing about the 10-22 is the good performnce wide open over most of the frame. Just for comparison, here are 100% crops from the edge of shots taken with the EF-S 10-22 and the EF-S 18-55, both at 18mm and f4. The 18-55 is stopped down from f3.5 to f4, the 10-22 is wide open at f4. Yes, it's a $700 lens vs. a $100 lens so I know it's not really a fair fight, but it's the only other lens I have that covers this focal length range!
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