Why You Can Trust CNET Sony Alpha SLT-A57 review: Sony Alpha SLT-A57
With a 12-frames-per-second burst mode, punchy colours and loads of detail, there's plenty to like in the dSLR-alike Sony Alpha SLT-A57.
Sony produces two interchangeable lens lines -- traditional dSLR and so-called single-lens translucent (SLT), which uses a translucent mirror with a digital viewfinder. The A57 falls into the latter camp. It looks and works just like a dSLR but it has a faster burst mode for taking rapid sequences of images.
The Good
The Bad
The Bottom Line
The body alone can be bought now for £620, or for £850 with 18-55mm and 55-200mm lenses.
Specs and handling
Stand it beside a dSLR and you can't tell them apart. There's a top-mounted mode selector with direct access to two automatic modes, sweep panorama, movie and regular semi-manual modes with aperture and shutter priority. There are also program and manual modes if you want to be really hands-on. The handy finger wheel around the front handles adjustments.
Its native resolution is 16.1 megapixels on an APC-C-sized sensor, with sensitivity running from ISO 100 to ISO 16,000. The lens mount accepts all Sony dSLR lenses and A-mount bayonet lenses from Minolta and Konica Minolta. So if you have a library of lenses built up before Sony bought that company's camera business, you can recycle them here.
The longest exposure time is 30 seconds, backed up by a bulb option, which holds open the shutter for as long as you keep the button pressed (you'd be advised to buy a remote if you want to use this mode), while the shortest is 1/4,000.
Sony claims that the Bionz processor can handle large amounts of sensor data for high-speed shooting, and that was certainly the case during my tests. A burst mode fires up to 12 shots per second, making it easy to capture motion as a series of stills.
The animation below shows a 21-frame sample shot at that rate, but looped at 10 frames per second, so that actual captured data ran slightly quicker than seen here. For anyone who needs a camera for performance analysis -- say in sports -- the A57 is certainly up to the job.
Stills tests
This is where a camera lives and dies. I performed my tests shooting raw and JPEG images side by side, but I used the in-camera JPEGs for analysis. The results were sharp and crisp on contrasts and extremely smooth across areas of similar tone. Colours were punchy and luminance was well balanced, adding up to an impressive set of results overall.
I performed my tests using the SAL1855 18-55mm kit lens, so the results below are indicative of that particular unit. If you choose a different lens, your own output will differ. This lens behaves like a 27-82.5mm (3x zoom) unit on the APS-C-sized sensor in the A57. It's not an enormous range, but these measurements are pretty standard for a consumer dSLR's bundled lens.
The lens geometry is spot-on, with no evidence of barrel or pin-cushion distortion (parallel lines bowing out or in, respectively) in my tests.
Macro performance with this lens was very impressive. It was easy to isolate the exact part of the shot I was after, despite the minimum focusing distance topping out at around 21cm in my tests. It was quick to focus, and allowed me to pick out this family of aphids living inside a flower -- along with the stamen at the bottom of the petals. Outside of the sweet spot, it threw the surrounding detail gently out of focus, helping draw the eye to the subject.
It did extremely well in the chromatic aberration test. This reveals how effectively a lens focuses each wavelength of light in the visible spectrum in sync with the rest of the spectrum. Lenses that don't focus each tone perfectly in line with the others will render a pink or turquoise fringe around areas of fine detail against sharp contrasts, which is particularly visible in the corners and edges of the frame.
There's no such problem here. The SAL1855 kit lens focused everything perfectly for a crisp set of results. Detail was consistent right across the frame throughout my tests.
Detail was particularly impressive, with the A57 rendering shots packed with fine elements.
In the image below, taken at the widest end of the zoom, the individual leaves on the trees and bricks in the church are easy to distinguish. Meanwhile, the flat rendered front of the tower, despite being largely smooth, has subtle variations in illumination on the sun-facing side, which are accurately reproduced by the camera.
Colour reproduction was excellent throughout my tests, with the A57 making best use of overcast skies. The cottage below was shot without any direct sunlight, yet the roof is a warm red, the garden is characterised by deep, satisfying green, and the white of both the render and the picket fence is clean.
Furthermore, it did an excellent job of retaining both colour and detail in backlit subjects that could otherwise have been lost in silhouette.
The features of the goose below are perfectly captured. There's still enough detail recorded in its plumage to be recovered by reducing the intensity of the shadow by around 10-15 per cent in post-production.
However, in some instances backlit shots could display a small amount of noise. In the example below, of boats on a reservoir, the retained detail at the front of the image, where the boats have their backs to the camera, is good. But looking further into the frame, where the sun is reflecting off the water, reveals evidence of noise on the bows of the furthest boats.
Low-light performance was very good, even at particularly high sensitivities. The image below was shot with sensitivity set to automatic, causing the A57 to choose a very ambitious ISO 3,200. However, it paid off. Colours remained well balanced and closer to the lens, where there was slightly more available light, some of the text on the back of the tins remained legible without too much evidence of noise.
Noise was more obvious towards the back of the frame, where text was less legible due to the lower light level.
Video test
The A57 shoots video in AVCHD (1,920x1,080 50p) and MP4 (1,440x1,080 25fps) format. I used AVCHD in my tests and achieved excellent results, as can be seen below. Colours were just as punchy as they were in my stills, and there was plenty of detail in fast-moving subjects such as flowing water on a weir.
Compensation for changing light levels was excellent, with fast, smooth corrections made for variations in illumination, without any signs of stepping.
While manually controlling the zoom by turning the cuff on the lens unit, there was no evidence on the soundtrack of the slight sighing sound this makes. However, despite switching on wind noise reduction, the passing breeze could still be heard on the audio track -- as could the sound of the auto-focus system maintaining a fix on moving subjects.
Conclusion
The A57 positively flew through my tests, producing consistently sharp, bright images. The 12fps burst mode is particularly impressive and I couldn't fault the level of detail and colour rendered in the above shots.
The only thing it's lacking is an optical viewfinder. Although the in-eyepiece display isn't as true to the finished photo as the rear-mounted LCD, it's fine-grained and detailed enough to show an enormous amount of shooting data.
It's a great camera, and while it looks a touch expensive when stood beside its peers, the quality of output justifies the asking price.