Hi,
Contrast detection AF has some issues. It works by moving the lens back and forth and measure contrast. It can work very well, but needs lenses built for purpose. For instance Sony's NEX cameras work with Sony SSM (ultra sonic motor) lenses but are said to be terribly slow.
I'm much in favor of EVFs, the Sony A55 I have has an EVF, the viewfinder image can be enlarged 15X which is very useful for exact focusing, but the focusing rings on AF lenses are not really meant for critical AF, to short stroke and to much play. So I would say that
MF with an EVF is exacting but slow. With fast lenses there is also an issue with focus shift, the position of correct focus shifts when stopping down.
Even if the EVF actually shows the sensor image, the sensor may be misaligned with the lens. In that case it's not possible to achieve correct focus across the image.
I'd be pretty certain that EVFs are taking over in a few years, but I don't think we are there yet.
Best regards
Erik
Thanks Eric. Is there anything I've missed out in terms of the AF benefits of a mirrorless system?
At the moment, the only downfall is the AF speed and tracking ability of a contrast detection system?