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 23, 2008
Although Canon has implemented a hardware "fix", and several different firmware "fixes", focusing problems still plaque Canon's EOS 1D Mark III. Not only that, but the more recently introduced EOS 1Ds Mark III shares the same problems. Some users of these cameras either do not have the problem, or have simply not experienced it because it shows up mostly in fast action with fast wide open lenses and corresponding narrow depth of field. But there are far too many reports of focusing problems with these cameras to ignore or chalk up to user error. The $8000 price tag of the 1Ds3 model is a lot to risk with problems obviously lurking in the camera's design. This is a real disappointment because both camera models are is capable of producing remarkably good files when they focus properly. It appears that Canon has done all they are going to do to correct this issue in the current models. They have indeed improved the situation, but concise field tests by Rob Galbraith indicate the Mark III cameras still do not focus with the consistency and accuracy of the earlier Mark II models. We can only wait a few more years and hope Canon does a better job on the Mark IV.
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To see concise details check the latest, and possibly the last, installment of the exhaustive 22 page test report from Rob Galbraith. The concluding sentence of this very well documented report states "Canon has put considerable effort into correcting and improving EOS-1D Mark III autofocus in the 14 months since the cameras was introduced, but they have not yet made it, or its high-resolution counterpart the EOS-1Ds Mark III, deliver reliable autofocus of subjects in motion."
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It should also be noted that a number of Canon EOS 1Ds Mark III (not the 1D Mark III) cameras were delivered with a viewfinder that is not aligned with the image sensor. In other words an image that looks level in the viewfinder is not level in the file produced by the camera. This is supposedly due to an improper assembly procedure and should be fixed on models currently being shipped. Some have reported buying brand new cameras that show evidence of having been serviced, such as smears on the mirror.
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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 and admit there was anything wrong. 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.
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Update August 7, 2007
Canon has released updated firmware for the EOS 1D Mark III. Reports are that while it improves 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.