I wish Canon made an IS version of their small 85 and 100mm f/2.0.
That tamron isn't going to be much smaller than my zoom. The tamron would need to have perfect AF, the DOF is going to be razor thin.
I understand why Tamron their AF system isn't that great now, Phase detect isn't that simple to implement, the camera needs lens-specific information, when the phase detect sensor isn't in phase, it need to be able to tell the lens, exactly how far it should move its elements. I believe most Tamron and Sigma lenses often can only use contrast detect, that's why focus often bounces back and forth like a point and shoot.
The camera shares information between the phase detect system and the chip inside the lens. Tamron has to reverse engineer what the camera is saying. But each time Canon updates their chips, or makes a new camera, it says something that the chip in the Tamron lens might not understand. This is why Tamron lenses that focus on one camera, often stop focusing at all on newer cameras.
