Sony Alpha SLT-A77 preview

The Alpha A77 is Sony's flagship SLT camera, boasting a new 24.3 Megapixel sensor, 12fps continuous shooting, Full HD 1080p video and composition with either a 3in articulated screen or a high resolution OLED electronic viewfinder.

Announced in August 2011 alongside the simpler A65, the new A77 becomes Sony's latest camera to employ a fixed semi-transparent mirror instead of the usual moving reflex mirror in a traditional DSLR. This fixed mirror allows most of the light to pass through to the sensor, but reflects a smaller portion to a traditional phase-change AF sensor. This allows the Sony SLT cameras to offer quick and continuous autofocusing even during burst shooting and movie recording, something which eludes traditional DSLRs.
Meanwhile, the fixed position of the mirror, along with some clever sensor electronics, has allowed Sony to deliver fast response times and shooting speeds up to 12fps with continuous autofocus, which (caveats aside) is a quicker rate than Canon's fastest pro sports body, the EOS 1D Mark IV. Couple this with a new 19-point AF system with 11 cross-type sensors, 1080p movies captured at up to 60fps with full manual control over exposures, built-in GPS and tough magnesium alloy build with sealed controls, and you've got one of the most impressively-featured semi-pro bodies on the market and a worthy successor to Sony's popular Alpha A700 DSLR.
In true Sony style, there's so much new technology going on with the A77 that it's easy to be over-whelmed by the numbers and gadgetry, so it's important to take a look at each aspect in turn to see what it means in practice.
Let's start with the headlining 24.3 Megapixel resolution which, shared by the NEX-7, is the highest pixel count offered by an APS-C sized sensor to date; the previous highest resolution APS-C sensor was an 18 Megapixel model belonging to Canon which found itself deployed on the company's most recent DSLRs including the EOS 600D / T3i and EOS 7D.
The SLT-A77 delivers images with 6000x4000 pixels, compared to 5184x3456 pixels on the 18 Megapixel Canons, and the relatively modest-sounding 4912x3264 pixels of the earlier 16 Megapixel SLT-A55. Numerically it's certainly impressive, but of course the question remains whether image quality, in particular dynamic range and noise levels at high sensitivities, is compromised as a result. The NEX-7 may share the same worries with the same sensor, but with the SLT-A77 there's the additional concern of losing around 30% of the incoming light to the semi-reflective mirror - see later.
The sensitivity runs between 100 and 16000 ISO with a 50 ISO expanded option. Sony also includes its innovative and effective Multi Frame Noise Reduction options which stack a burst of images to reduce noise and extend the maximum sensitivity to 25600 ISO. Ultimately I can't comment on image quality until I test a final production sample, but at least Sony has various image stacking modes at its disposal which can reduce noise on static compositions should single exposure prove to be noisy.
Like earlier Alpha bodies (excluding the NEX range), the SLT-A77 features built-in sensor-shift stabilisation which works with any lens you attach - a key advantage it has over rivals which require optically stabilised lenses to eliminate the wobbles.
The new sensor delivers more than just very high resolution images though: it can capture Full HD video at progressive frame rates of 50 or 60fps depending on region. That's double the progressive frame rate of Full HD modes on any video-equipped DSLR to date. This is important for slow motion work, where 60fps footage can be slowed down by 2.5 times for use in a 24fps project, but until now, all video equipped DSLRs could only offer 60fps for 720p video; now Sony offers it for 1080p too. I'm confirming whether SLT-A77's sold in PAL and NTSC regions can offer all the frame rates, or whether PAL models only support 25 and 50fps compared to 24 and 60fps for NTSC.
To support 1080p encoding at 50 or 60fps, the SLT-A77 employs AVCHD version 2, with the additional benefit of higher data rates: 28Mbit/s for the 1080p / 50 / 60 modes, and 24Mbit/s for the 1080p / 24 / 25 modes. Sony's also equipped the SLT-A77 with full manual control over movie exposures, in addition to built-in stereo mics in the head and a standard jack to connect an external microphone. It's nice to find the standard microphone jack on the A77, although with Sony's proprietary Alpha accessory shoe, you'll need an adapter before being able to mount most third-party models, such as those from Rode.
An additional benefit of the new sensor is support for an electronic first shutter curtain, which improves response times as the shutter no longer needs to close before opening again to start the exposure; indeed Sony quotes a shutter lag of just 0.05 seconds.
While the sensor resolution and support for 1080p at high frame rates is impressive, it's the semi-pro aspirations of the A77 which will really turn heads, starting with the fast continuous shooting. Sony's really carving a niche for itself in this respect and has raised the bar with the A77 by exploiting the fact its fixed mirror doesn't need to lift and close between every frame. Indeed with a top speed of 12fps with autofocus, it's quicker than the 10fps of Canon EOS 1D Mark IV which costs over four times more. Sony's cheaper SLT-A65 may be slower than the A77, but even it manages to squeeze out a top speed of 10fps. Sony really is continuing to redefine what we can expect from bodies at these price points in terms of speed.