Sony’s new Translucent Mirror cameras look like a D-SLR, feel like a D-SLR, and produce D-SLR image quality, but since their mirror boxes lack the traditional D-SLR components, they do not technically fall into that category.
Translucent Mirror cameras do come with a host of benefits, but there’s a caveat.
For many, the new Sony Alpha a33 and a55 Translucent Mirror cameras offer a feature set that could be more compelling than Sony’s D-SLR counterpart, the Sony Alpha a560. The new Sony’s have access to the phase detection auto-focus sensor, which lets them deliver extremely fast auto-focusing. The key is that you can get this fast, continuous auto-focusing no matter what mode you are in; specifically burst shooting (10 frames per second on the a55) and HD video recording. The Sony a560 D-SLR can auto-focus just as fast, but not in burst mode. It also does not auto-focus during video recording.
The a33 and a55 Translucent Mirror cameras are also more compact and weigh less than the a560 D-SLR. Sony said the Translucent cameras are 23 percent smaller and 26 percent lighter than last year’s Sony Alpha a550 D-SLR, the predecessor to the a560. Though the new devices have smaller builds, image quality is identical since they have the same size image sensor; APS-C.
The overall feature set is nearly identical on a33 and a560 cameras: HD video capture (1080i60 AVCHD), gorgeous high-resolution articulating, 3-inch LCD (921,600 dots), and 14.2-megapixel captures. Price is identical too: both will sell for $650 (body only) and $750 (with an 18-55mm lens).
So why wouldn’t you be interested in the Translucent Mirror cameras over the D-SLR? Here’s the catch: there’s no optical viewfinder. In place of the optical viewfinder is an electronic viewfinder (EVF), which is a tiny high-resolution LCD (.46-inch with 1,152 000 dots). An EVF is not for everyone. I personally can’t stand them, but times are changing, and many people might not mind the EVF or prefer to use a camera with a large, 3-inch LCD.
My only gripe with the a560 D-SLR is that it completely lacks any auto-focus during video recording. While it’s not technically possible for it to access the fast phase-detection auto-focus sensor while recording video, Nikon has released the 31000 D-SLR, which can continuously auto-focus during video recording – but not as the Translucent Mirror cameras. It does so by processing image information from the main, large image sensor.
source: http://www.pcmag.com/article2/0,2817,2368300,00.asp
A+ would read again