After the purchase, he was disappointed with him, he pretty much lathered on large focal lengths. I gave the lens for adjustment at the office. Canon service. The procedure is not cheap, but after adjustment, even at 300mm, sharp shots are obtained. Best sharpness at f8-f9.5. So, whoever is not satisfied with its sharpness, bring it into alignment. Regarding its "darkness", at 300mm and f5.6 at a distance of 3m, the depth of field will be only 2 centimeters, and at a distance of 100m the depth of field will be about 20m, so you are unlikely to need a large aperture. And when you need it, then buy an L-ku. Chromatic aberration, if shot in raw, is well treated by DPP. Camera: 650D
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