by With the release of the Sony Alpha SLT-A55 and SLT-A33 in late 2010, Sony created a new category of camera, similar to a conventional digital SLR in many respects (same sensor size, lens mounts, general form factor) but with an ingenious technical twist in the way it uses the camera’s internal mirror. The A55 and A33 were bleeding-edge products whose novelty was impressive enough to overshadow some of their usability shortcomings. With the release of the Alpha SLT-A77, however, Sony has almost fully realized the promise of the earlier cameras. The 24-megapixel, 12-frames-per-second SLT-A77 is a grown-up, ready-to-work, 21st-century machine.
The speedy, accurate phase-detect autofocus keeps up with fast-moving subjects, and the A77’s 24-megapixel resolution provides detail to spare, even at higher ISOs and after cropping.
Shooting at 12 fps fills the camera’s buffer pretty quickly. I got this shot of the cowboy hitting the dirt the old-fashioned way: I clicked the shutter at the right moment.
Resolution and noise
As noted in the Macworld review of the Sony Alpha SLT-A55, the new Sony SLT (single-lens translucent) cameras use a fixed translucent or “pellicle” mirror that lets most of the light coming through the lens go straight to the sensor, while also continuously bouncing a little of the light up to an ultrafast phase-detect autofocus sensor.
The SLT design does mean a little less light reaches the imaging sensor than in a conventional SLR. Sony says the light loss is about half a stop. That sounds like a lot, but as a practical matter, it isn’t. To compensate for the loss of light that the fixed translucent mirror causes, Sony increased the gain on the sensor slightly; that is, it made the sensor a little more sensitive.
The downside of this new technology, as Macworld’s testing verifies, is that the A77 is a little noisier than DSLR counterparts such as the Nikon D7000 or Canon 7D, especially above ISO 1600.
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