Are there compatibility problems with any EF lenses made by third party manufacturers?
Sometimes. Unfortunately certain third-party lenses not built by Canon, notably many older Sigma lenses, will not work correctly on some newer EOS camera bodies like the Elan 7/EOS 30/33 and the digital EOS 10D. The most common symptom is the mirror flipping up and then the camera freezing when you try to take a photo. You then have to switch the camera off to unlock it. The only solution to this problem is to see if Sigma will upgrade the lens for you. If they still have inventory of the control chip they apparently will happily do so for free. The only third-party maker of EF-compatible lenses with no major compatibility problems so far is Tamron. Some people have suggested that this is because Tamron have licensed official lens protocol data from Canon, but Canon USA s Chuck Westfall has stated repeatedly in public fora that Canon have never licensed their lens mount protocol to any other manufacturer. So Tamron have either been very lucky or very clever in their reverse-engineering
