Matty (12.11.12, 6:02 PM): Does the 5D3 have this feature?
Andre (12.10.12, 4:07 PM): It's because it doesn't have phase-detection points on the sensor. Both the t4i and the M have them. Really any camera will support the new STM lenses. I've used the 40mm STM on both the 60D and 6D and they work basically the same. I'm not surprised they left it off, I've tested in on my brother's t4i, and it's just not very good. The best solution for video focus is still manual and focus pulls. I suspect Canon assumes people who are serious about video will do that.