EF 70-300 f4-5.6 L IS USM - Is it a Lemon?

Started Mar 9, 2011 | Discussions thread
aomcm Regular Member • Posts: 158
Re: Is it a lemon 70-300 L IS Usm

When I had my Rebel T1i, I was disappointed in the performance of some of my lenses. I checked and discovered I had a front focus issue. I think this is fairly common in Rebels. It was worse on some lenses than others and I even had one lens that back focused, so you can have the problem in one lens and not others. I sent my camera and all my lenses to Canon and had them focus calibrated together. It took a week and was free because it was still under warranty. Made a significant difference and one of my lenses even needed a new circuit board. No matter how great a lens is optically, it will obviously not perform if it is misfocusing. Misfocusing is much more common, especially in Rebels, than an optically defective lens. It is also easily corrected.

There is lots of stuff on the web about how to check for focus accuracy (Google "Front Focus"), but you can start by setting a ruler at a 45 degree angle. Shoot it wide open from as far away as you can and see if the out of focus area is symmetrical. If it is not, get in touch with a Canon Service Center to send it in for calibration. Might solve your problem.

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