The core technology of the A57 is, of couse, its SLT fixed mirror design. By using an electronic viewfinder, Sony removes the need to reflect light away from the image sensor and into an optical finder. This means that most of the light can be sent directly to the image sensor and there's no need for a complex moving mirror mechanism.
What makes the design distinct from 'mirrorless' camera designs is that the SLT still has a fixed, semi-transparent mirror constantly redirecting light onto the camera's DSLR-style phase-detection AF sensor. This not only means that it can quickly focus all Sony and Minolta A-mount lenses, but can continue to do so both while continuous shooting and shooting movies. Conventional DSLRs have to wait for the mirror to reset before they can take another focus measurement, meaning high speed continuous shooting tends to be reserved for professional level cameras.
The cost of having a mirror permanently in the optical path is a loss of light to the sensor. However, in the tests we've conducted so far, the 0.5EV increase in noise is negligable in real-world shooting.
Although Sony has never publicly stated that improvements were made to the A65 and A77 to prevent the occasional 'ghosting' (an offset double-image visible on where bright highlights were repeated over dark regions), it has hinted that the A57 could logically be expected to see any component improvements that those cameras had.
Although the A57 continues to use the same LCD panel as the A55 for its viewfinder, it features revised viewfinder optics, allowing use of a larger area of the panel. The A57 has two viewfinder modes, a 'Maximum Magnification' mode that uses the full 800 x 600 resolution display and a 'Standard' mode that uses a smaller subset of the screen to give a longer eye-point (the distance from which the entire display can be seen), allowing easier use by wearers of glasses.
The magnification figure for the Maximum Magnification mode is 1.04x - slightly down on the 1.1x offered by the A55, but using the equivalent of 1.44 million dots, rather than the A55's 0.97 million (though it's not entirely what this figure relates to - Sony quoted 1.15 million at the A55's launch). Either way, it's an improvement over the A55.
The LCD itself is a field-sequential device - it shows red, then green, then blue information rather than being able to show them all at the same time. The result is that you will sometimes see colorful tearing, often in your peripheral vision if you quickly look around the frame or blink. The degree to which you find this disconcerting is likely to be a personal issue, but it's another way in which the A57's viewfinder is inferior to the OLED unit in the A65.
Auto Portrait Framing
Continuing the camera's beginner-friendly theme, the A57 gains an 'Auto Portrait Framing' mode that will try to re-crop images containing faces, if it thinks there's a better portrait image to be had from it. Based on a combination of face detection and the rule-of-thirds, Auto Portrait Framing will identify where the subject's eyes are and crop the image, to put the eyes one third of the way down the frame.
This crop frame is shown on the rear display, just after you've taken your picture, so that you can see how the camera thinks you should have composed the shot. It then takes the cropped region of the photo and resizes it back up to full resolution and saves this resized image alongside your original one. The system will attempt to leave more of the background image on the side that the subject is facing, so that you don't end up with pictures of people staring into the edge of the frame.
|Original image||Camera re-cropped and upscaled portrait image|
Clear View Zoom
When the A57 does up-scale images - either in Auto Portrait Framing mode or in its Intelligent Zoom mode (which offers up to 2x magnification), it uses the 'By Pixel Super Resolution Technology' Sony has included in its recent compact cameras. The theory is that it intelligently interpolates between pixels as it up-sizes. By comparing each image element to a database of patterns it can attempt to add more detail than simple upscaling would allow.
We'll look at the feature more closely in our full review, but Sony's statement that the quality of this digital zooming is 'nearly equivalent' to optical zooming with the kit zoom is either a rather grand claim or a bit of a dig at the quality of the kit zoom.
The A57 features much improved video specifications, compared with the A55. The most obvious change is its ability to capture 1080 video at 60 frames per second (whereas the 55 captured 30 frames per second and presented them as 60 interlaced fields per second). This highest-definition video is captured in the AVCHD 2.0 standard.
Because the AF sensor needs a fairly wide aperture to make sure it's fully illuminated, the camera will only autofocus in P mode, but if you're happy to do without AF, you can take more control of the exposure settings in A, S or M modes. You have the choice of setting ISO manually (between 100 and 3200), or engaging Auto ISO across the same range. As with stills mode, there's no option to control the range over which Auto ISO operates.
We rather liked the A55 but are aware not everybody appreciated its small hand grip. We also found the short battery life a little frustrating (its battery wasn't significantly smaller than most of its rivals' but the added power demands of always running the screen or viewfinder just ate through batteries). Both of these things have been addressed, leaving us essentially with a slightly cut-down (Gold Award-winning) A65 built around the excellent 16MP Sony sensor. And that's a good place for any camera to start.
While we're not fully convinced about all the A57's special features, there are a couple (such as sweep panorama) that we rather like. It'll certainly be interesting to see how it stacks up against its conventional DSLR competition.