Viggo said:
It's not about the lack of skills, it's matter of not violating patents Canon own.
Canon made fast EF compatible glass over 17 years ago, all relevant patents must have expired by now, if they ever existed. A few years ago there was a long thread in some german photo forum about the Canon EF lens protocol and the way Sigma reverse engineered it. The conclusion was that Sigma did not put much effort into it and as a result had AF problems that seemed to have pestered them forever. This may have been ok when they made mostly cheaper substitutes for Canon/Nikon accessories, but with their new ambition towards optical excellence they clearly have some homework to do.
kphoto99 said:
I have been thinking about this also and I'm beginning to suspect that Canon has software in the body to prevent the third party lenses from focusing consistently. Basically if the camera does not recognize the lens as Canon it would insert random miss focusing.
Or alternately if the lens is miss identified by the camera as some other Canon lens, it is apply a correction which is appropriate for the Canon lens but not good for the Sigma.
If a Canon camera indeed introduced targeted random focus shifts for third party glass, then it would be fraudulent for third party manufacturers to sell lenses as fully functional. Somehow I doubt this, and the fact that so many people seem to be happy with third party accessories seems to confirm my doubt. But here's the thing: even if they perfectly reproduced Canon's protocol, if their HSM drive loses steps due to sticky surfaces or whatnot, they would have inconsistent focusing. Remember that regular AF is a single effort process. This would more likely explain why poor AF performance seems to be so random.
If the camera sends some lens specific corrections, these are either fixed parameters, or based on parameters sent by the lens to the camera. In both cases the lens should have full control how it responds to data sent by the camera.
AcutancePhotography said:
If that came out to be true, a lot of people will lose what respect they had for Canon and the other manufacturers would jump on this.
The last major incident happened with the introduction of the 10D, when a range of Sigma lenses stopped working. It has been proven conclusively, that Canon introduced a pointless protocol change, just to become incompatible with Sigma lenses ("the work ain't done until Sigma won't run"). People still blame this on Sigma and only use it as a justification to stick to Canon accessories, even if it limits their options and, on average, is more expensive. Rarely do you see "bad Canon, stop messing pointlessly with your protocol!" postings.
