I have a 1.4 on my Nikon set up,and coupled up with my 300mm lense its incredible sharp, and AF works fine..I had a bigma on the same camera, and the 300mm + converter produces far better images. Yes Ive lost a stop, but my camera is designed to give good results in low light, the results speak for themselves..the second robin isnt bad for what your using, and for early attempts
Because of where and in the way canon converters are mounted, image quality sharpness and contrast will be affected with all but the best lenses, and loosing 2 stops is a lot for most lenses. To get the best results