Sony's exclusive Translucent Mirror Technology (TMT) provides real-time, high-speed Phase Detection auto focus. Unlike traditional DSLR cameras, the mirror inside the camera does not move, allowing the a37 and a57 to rapidly auto focus during still photo and video capture. Light passes through the mirror to the image sensor for capture, and at the same time travels up to a large 15-point (including 3 cross-type points) Phase Detection AF sensor.
Conventional DSLRs with moving mirrors cannot focus while the mirror is flipped up. The Sony a37 and a57 can acquire focus all the time - even while capturing video or still shots at up to 7 (a37) or 12 (a57) frames per second!