Canon EF 17-40 mm f/4.0L USM
10. Autofocus
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Just like any other L-grade model, the Canon 17-40 mm is equipped with a quiet high quality, yet fast and dependable USM motor. As far as being fast and quiet the lens is perfect. But when talking about its accuracy it is a whole different story. We were very surprised to see that in testing conditions the Canon 17-40 mm can fail in as many as 10% of cases. It might not be a very bad result but we expect more from an L-grade USM motor equipped lens…
Fortunately, the lens did not have a tendency for front or back focusing and when it missed it was done rarely and by chance.
