Though video recording has become commonplace among SLRs since the Nikon D90 first introduced the feature in 2008, Sony has been late to the party, introducing video-free dSLRs as recently as June of this year. Well, the electronics giant has finally burst onto the scene with three new dSLRs that shoot video. Overshadowing its announcement of a new Sony Alpha SLR-A560 is the debut of the Sony Alpha SLT-A55V and SLT-A33, two ground-breaking cameras that don't just play catch up with video features--they promise to revolutionize the SLR category with an innovative translucent mirror design.
The SLT denomination stands for Single Lens Translucent and both cameras utilize a special semi-transparent stationary mirror (aka a pellicle mirror) rather than the flip-up mirrors in conventional SLRs. Although most light passes through the lens to the image sensor, the translucent mirror diverts some of it to a phase-detection autofocus sensor. Because there's no raising and lowering of the mirror between shots, the AF works while images are captured (rather than having to focus between shots). This allows the camera to quickly and continuously autofocus while shooting stills and video, enabling burst-mode shooting of up to 10fps (on the A55V) or 7fps (on the A33), though you can only achieve the maximum by locking the aperture open (otherwise the max is 6fps for both cameras). But where the fast, continuous AF ability really stands out is for shooting video. Most dSLRs don't even offer continuous AF in video-shooting mode because lenses make focus adjustments too slowly (and they make too much noise) to produce smooth results on video. According to Sony, its mirror technology enables the cameras to use faster continuous phase detect AF, which greatly reduces (or eliminates) these issues in video-shooting mode (with full 1920x1080 HD recording in AVCHD format).
The mirror technology also enables full-time Live View and both cameras offer fully articulating 3-inch, 921,600-dot LCDs as well as electronic viewfinders with 100 percent coverage and 1.1x magnification, which should give you a huge amount of shooting flexibility in various lighting situations and shooting angles.
The A55V has a 16.2-megapixel Exmor HD CMOS sensor and built-in GPS and will be priced at $750 (body-only) when it comes on the market in October. The A33 bumps resolution down to 14.2-megapixel (also an Exmor HD CMOS) and skips the GPS to bring pricing down to $650 (body-only) and will hit the market a bit earlier, in September.