Sony's new SLRs have some special sauce inside.  

They execute Live View mode (when you use the LCD screen as a viewfinder, just like shooting on a compact point and shoot) differently than most cameras. On most SLRs that offer Live View shooting, auto-focus slows down significantly.  But not on Sony's SLRs.

In general, SLR camera auto-focusing systems are much faster than those on point-and-shoot cameras. That's because they have a separate smaller sensor that is dedicated to performing auto-focus.  (See the "optical viewfinder" image, left).

Most SLRs that offer Live View execute this feature by bypassing the dedicated AF sensor  and using the main image sensor to perform AF; and provide an image on the LCD screen, just like on a point and shoot. (See  the "Live View" image). Problem is, using the the main image sensor for Live View slows down auto-focusing, because the sensor is performing two tasks (sending a real-time image to the LCD and perform AF). And the larger the sensor, the longer it takes to process the image, and the longer it takes to auto-focus.

The Sony cameras are able to retain the fast AF speed SLRs offer when using the viewfinder (and dedicated AF sensor) by adding a third sensor near the viewfinder.  When in Sony's Live View, this third sensor provides an image on the LCD (see the "Quick AF Live View" image).

For more info and hands-on images of Sony's new SLRs, see PC Mag.com news story.