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Message: <blockquote data-quote="PaulD" data-source="post: 1844725" data-attributes="member: 11840">I've always found the lens reviews on Photozone to be very good. Their first test with a Canon 100-400 produced very indifferent results. They ended up redoing the test with another copy of the same lens and got much better results. I believe there was a gap of a few years or so between the tests but can't find any confirmation of that. Either way it does seem to confirm the frequent suggestion that quality control was a problem with early copies of this lens.Here's a quote from the summary at the end of the test:-"The Canon EF 100-400mm f/4.5-5.6 USM L IS is a very good performer with few weaknesses ... that's assuming you get a good sample - the first tested sample was mediocre whereas the second one performed very fine. The resolution of the lens is on a very high level throughout the zoom range with only a marginal performance penalty at 400mm." The full test can be found at:-<a href="http://www.photozone.de/canon-eos/204-canon-ef-100-400mm-f45-56-usm-l-is-test-report--review" target="_blank">http://www.photozone.de/canon-eos/204-canon-ef-100-400mm-f45-56-usm-l-is-test-report--review</a></blockquote>