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Features

Full-time phase-detection AF

The advantage of the SLT design - and the reason why Sony uses it - is that it always redirects light to a DSLR-style phase-detection AF sensor. Phase detection has two great advantages over contrast detection systems - firstly, it is able to determine exactly how to move the lens to achieve focus from a single reading (contrast-detect AF has to move the lens through its focus range to find focus) but, more importantly, phase detection technology is more refined - around 40 years of research and development has been applied to PDAF in SLRs.

This (Sony supplied) diagram shows the SLT-A77 imaging and focusing systems but the technology is identical on the A57. Light coming in through the lens is split by the fixed, semi-transparent mirror - a portion feeds the phase-detection AF sensor, and the majority hits the main imaging sensor for live view and image capture.

As with the implementation in previous SLT models, the A57's AF module does not work at apertures smaller than f/5.6, so although the A57 offers aperture-priority, shutter-priority and manual exposure modes for video recording, these are not compatible with AF. You can use full-time (continuous) AF during video shooting but only in program AE mode. If you initiate movie recording in any of the conventional PASM modes, the A57 will switch to program AE regardless of your current exposure settings.

Sony claims the A57 is free of the overheating concerns during movie shooting that affected the A55 (recording times could drop as low as 6 min at 30°C with SteadyShot switched on). Sony estimates the A57 can shoot for its full 29 minutes at 30°C, dropping to 13 minutes only when the ambient temperature rises to 40°C.

Flash

The A57's built-in flash has a guide rating of 10m at ISO 100. You can control output via flash exposure compensation of +/-2 stops EV.

The A57's flash has done a good job here, and this portrait is nicely exposed with no red-eye.

Auto Portrait Framing

Continuing the camera's beginner-friendly theme, the A57 introduces a JPEG-only 'Auto Portrait Framing' mode that will re-crop images containing faces, if it thinks there's a better portrait image to be had. 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 place them one third of the way down the frame.

With Auto Portrait Framing enabled, you get onscreen confirmation that the camera recognizes a face and the effect will be engaged via a large green face detection square and an autocrop icon when you half-press the shutter button. Once the image is captured, a temporary crop frame is overlaid (in both the EVF and rear display) indicating the new composition.

This cropped region of the photo is then resized back up to full resolution using 'clear image zoom' technology which we'll discuss in a moment. In a welcome move your uncropped original is saved to the card as well, so you always have recourse to it if you don't care for the camera's decision.

In practice, the system is smart enough to leave more of the background image on the side that the subject is facing (see the example below), so that you don't end up with pictures of people staring into the edge of the frame. And while the camera is pre-disposed to create a portrait-oriented crop, when subjects occupy a relatively small area of the frame it will create a landscape-oriented crop, minimizing the amount of upsampling needed to create the final image.

Original image Cropped and upscaled
Original image Cropped and upscaled

In scenes with the subject facing the lens and centered in the frame (as in the example directly above), the preference clearly seems to be to crop the subject along the right side of the frame. Yet there are times when a near identical original framing results in a crop with the subject on the left side of the frame. There is little obvious rhyme or reason as to what determines placement of front-facing subjects, so you must be willing to give up a considerable degree of compositional control.

In our testing, we found that the likelihood of a portion of the subject's face being cropped off is high. As a teaching tool, we find this a useful and easily implemented approach for those new to compositional techniques, but more experienced shooters will understandably be reluctant to put such an important decision in the hands of a software algorithm. Of course, you still have the original shot if you don't like the cropped version.

Clear Image Zoom

When the A57 does up-scale images - either in Auto Portrait Framing mode or in its Clear Image Zoom mode (which offers up to 2x magnification), it uses the 'By Pixel Super Resolution Technology' Sony has included in its recent Cyber-shot 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.

In the samples below, we've photographed a distant scene using the optically excellent Sony 24-70mm F2.8 ZA SSM Carl Zeiss Vario-Sonnar T* lens at an aperture of f/6.3.

The original scene shot at a focal length of 52mm equivalent. A 100% crop of a 2x Clear Image Zoom.
A 100% crop of a 2x upsampling using Photoshop's Bicubic Automatic setting. A 100% crop of the scene shot at a focal length of 105mm equivalent.

While we noted some image quality benefit to this upsampling technology in our Sony DSC-RX100 review, we're less impressed with results on the A57. As you can see in the samples above, there is nothing to be gained using Clear Image Zoom that cannot be accomplished with even a default upsampling in Photoshop. And, Sony's marketing claims aside, Clear Image Zoom is notably inferior to results you get by optically zooming the lens. This function's only real benefit compared to upsampling in Photoshop is convenience. But while it may save a trip into image editing software, you've also permanently deleted pixels outside of your chosen zoom range, which seriously limits the usefulness of the resulting images.

Sweep Panorama

The A57 includes an automatic sweep panorama mode that allows you to create large, high-resolution panoramas in-camera.

Handheld Sweep panorama (8192 x 1856)

Sweep Panorama works very well, and while the files suffer in resolution compared to single shot images, they are certainly usable for both onscreen viewing and small to medium-sized prints. Automated stitching can be prone to areas of softness along seams, but overall the results are quite pleasing. Of course the results are best without sgnificant movement of subjects between frames.

The A57 also offers a 3D panorama mode, which produces files compatible for viewing on 3D TVs. This features works exactly the same as on previous cameras and you can read about it in detail in our Sony SLT-A55 review.

Lens corrections

The A57's JPEG processing engine includes three separate lens correction options that can be turned on and off in the camera's setup menu. You can correct for vignetting (what Sony refers to as 'shading'), chromatic aberration and lens distortion. While this ability has been a staple of previous models like the NEX-5N and SLT-A65, its inclusion here represents an upgrade compared to the A55.

Of the three correction modes, only the distortion option is disabled by default. Sony warns of decreased performance with it enabled, but in our daily use, we've seen nothing more than slightly reduced image bursts in the fastest continuous shooting modes. In a majority of shooting situations, we see little downside to having it enabled as a general rule.

All three lens corrections work essentially as advertised, noticeably reducing the optical flaws. You can read more details about their use as well as view before/after comparisons in our in-depth review of the Sony NEX-7.

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