I bought a Canon EOS M to shoot video, mostly talking heads stuff so I simply set to the camera to AF Face tracking and had no problems.
I recently purchased the DSLR lens adapter and the cheap Canon f/1.8 50mm to use with the camera and the results are terrible. It just refuses to stay in focus for more than a second, even with someone sat still and not moving. It hunts none stop, creating a lot of off putting noise.
I understand that an STM lens will reduce the noise and the jerky movement, but do they affect AF as well? Is the lack of STM why I can't get solid AF?