Quote Originally Posted by PhotoMaxi
However the site's ISO 12233 Chart 100% crops show this lens to be a far cry from being sharp.


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StapledPhoto already explained why that is incorrect, so I wont go into it. Here is a site that has reviewed both lenses on the same camera:



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http://www.photozone.de/canon-eos/184-canon-ef-24-70mm-f28-usm-l-test-report--review?start=1



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http://www.photozone.de/canon-eos/178-canon-ef-s-17-55mm-f28-usm-is-test-report--review?start=1


It shows that the 17-55 is noticeably sharper in the center as well as the corners at all overlapping focal lengths at f/2.8. At f/4 their performance is closer together.