Contrast-detection autofocus systems have come a long way since the first live view attempts on DSLRs, and even in the short time that compact system cameras have been around.
By increasing the output channels and speeds from the sensor and tweaking algorithms, the best contrast AF systems are difficult to distinguish from phase-detection versions in good light and are often more accurate in their focus.
The system on the NEX-7 is about as quick as we’ve seen, matching that of the latest Panasonic and Olympus models, while in low light it seems to offer even better performance, even using the relatively small-aperture kit lens.
Using the flexible-spot AF it is possible to get a precise position for the focus in a scene and only very rarely did it show any sign of hunting backwards and forwards.
When shooting in extreme low-light conditions it seemed to switch to a more general area AF when focusing couldn’t be achieved, which meant I could continue shooting. For continuous shooting a lack of focus seems to stall the burst rate.
The object-tracking and continuous-focusing systems work well together for maintaining a lock on a moving subject, but the performance starts to struggle in low light. When compared to other contrast AF systems, the NEX-7’s is way ahead of the competition and will even give some DSLRs with phase detection a run for their money.