Shortly after its introduction, photography forums started to buzz with posts from people having focusing problems with the new Canon EOS 1D Mark III. This problem was confirmed by some prominent photographers and by numerous others. The problem apparently affects many, but not all, of these cameras. It appears that both servo and one-shot focusing are affected. Comparative tests show that the defective EOS 1D Mark III cameras get significantly fewer sharply focused shots than do the EOS 1D Mark II and EOS 1D Mark II N models that they replace. Some testers have obtained EOS 1D Mark III bodies that are not defective, and the same tests with these cameras show they get more sharply focused shots than than do the previous models, as would be expected. Some users of the defective Canon EOS 1D Mark III cameras report 30% - 50% "soft" or out of focus photos. Other users report the problem only with fast, high contrast lenses. There's lots of conjecture out there as to what the problem may or may not be. The only thing that's certain is that there is a big problem with these cameras. Although the defective cameras give a significantly higher percentage of unsharp photographs, they still take many that are sharp, and the problem may occur less frequently under certain, as yet unknown, conditions. Because the problem is not obvious, a user would need to do some extensive testing in order to realize they paid $4,500 for a camera that does not focus as it should. After all, a high percentage of soft shots can be attributed to many things, including user error.
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No matter what glorious things a DSLR can do, they are all for naught if it will not focus accurately. There is no real work-around for this problem except manual focusing. That won't get you many in-focus action shots either, but it would work for landscapes and still subjects. Otherwise, one just has to shoot and hope that their once in a lifetime shot will be in focus. Making money by shooting with this camera would be something like being a professional gambler.   
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Through all of this Canon has not even acknowledged that a problem exists. This is typical of how they have handled product problems in the past, but this problem is worse than any I can remember. They continue to advertise the camera with full page ads and happily sell it to anyone who does not know about the problem. Perhaps the cameras they are currently selling no longer have the problem, and perhaps they do. Canon is not telling. Through this entire mess, Canon's attitude has been to let their customers function as their quality assurance department, test their own cameras, and return them for repair if they manage to discover a problem. Canon has issued no recalls, and has never halted sales. When customers do discover this problem, I can't imagine how the repair technicians manage to reproduce and fix it. Since a number of shots from the defective cameras are sharp, it's possible at least some will get their defective cameras back with the infamous "No Problem Found" diagnosis. In any case, this problem will certainly diminish Canon's reputation, more due to their lack of properly handling the problem than from the problem itself. After all, problems can happen to anyone, it's how they are handled that really counts.
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I am posting this only to help get the word out, so readers do not buy these cameras without realizing what they may be getting into. Happily, I do not own a Canon EOS 1D Mark III, and I have no personal experience with this problem. Paying a company for the privilege of doing their quality assurance testing isn't my idea of fun. The moral is, never buy a product until it has been on the market for a while and extensively tested. Do your homework, search the Internet for problems like this one, and with that education go make your choices. I personally wouldn't dream of buying one of these cameras until there is a concise statement of what the problem is, and how it is fixed, from Canon.

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Happy focusing,



A few of many references:
http://www.robgalbraith.com/
http://www.prophotohome.com/
http://forums.dpreview.com/
http://en.wikipedia.org/wiki/
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Update August 7, 2007
Canon has released updated firmware for the EOS 1D Mark III. Reports are that while it impoves performance of cameras that are operating properly, it has little or no effect on the focusing problem that has been the topic of so much controversy. See this article to learn about the firmware update, and this article to learn how to test your EOS 1D Mark III camera.
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Update October 30, 2007
It turns out, as many had suspected all along, that many EOS 1D Mark III cameras have a hardware problem. It only took Canon half a year to figure it out. Affected units must be returned to Canon for repair, and Canon is apparently recalling all unsold units from store shelves. Check here for more details.