Sony SLT Alpha A55 In-depth Review
Overall handling and operation
The overall handling of the new SLT Alpha A33 and A55 is very similar to Sony's Alpha DSLRs in most respects, but the differences, where they exist, are largely a consequences of the difference in core technology (and the full-time live view it brings). Inevitably, the A55 handles more like a 'bridge' camera than a conventional DSLR, and in very general terms, the experience of using the new SLT Alphas is similar to that of shooting with Panasonic's G1, GH1 and G2.
Specific handling issues
In general, the A55 handles very well indeed. Unlike most other Alpha DSLRs its viewfinder projects far enough behind the camera to avoid squashing your face against the LCD screen, and an efficient switch immediately activates the LCD as soon as you remove your eye from the EVF. Full-time live view is a necessary consequence of the unique way in which the A33 and A55 are designed, and it works very well, with no perceptible 'lag' and plenty of detail visible on both the LCD and EVF. This single way of working also means you don't get any of the warning messages about mode incompatibility that could be so disconcerting on Sony's live view DSLRs.
Any concerns about lack of detail on even a high resolution EVF should be overcome with the two-step magnification option. Once activated, using the delete button, it ensures accurate focus in either manual or AF modes - a huge benefit for anyone that needs ultra-precise control over focusing, when shooting macro subjects, for instance.
The A55's EVF has a very high effective resolution of 1.15 million dots, and is crisp and detailed enough for accurate manual focusing using the 15x magnification option. It is a shame though that screen magnification is not automatic when manual focusing is selected. Even with an SSM lens mounted, this feature must be indicated using the slightly hard to locate (with your eye to the EVF) delete button.
Oddly, the aspect ratio of the EVF display is closer to 16:9 than the 'standard' 3:2 ratio of a 16.2MP sensor. The disparity is made obvious by the fact that the EVF's optics appear to have been designed to provide close to a 4:3 ratio view through the finder, which leaves a lot of space at the top and bottom of the image, which you can see as black in the (simulated) view below.
|3:2 (16.2MP)||16:9 (14MP)|
This image shows a simulated view through the A55's electronic viewfinder. The black border around the edges shows a masked off area around the 'active' portion of the screen. The gray area represents the 1.15 million dot active area of the LCD display, and is shown here for illustration only. As you can see, in the 3:2 aspect ratio, some of the area at either side is essentially wasted, and plays host only to the focus confirmation and SteadyShot INSIDE indicators. When the A55 is switched to 16:9 ratio capture (or to Sweep Panorama mode) a greater proportion of the EVF is used, and the scene to be captured almost fills the available display area laterally.
Considering that the A55 represents Sony's first attempt at a completely new type of camera, it feels impressively polished, and its performance is overall extremely good. The A55 is impressively well-featured, and in general, it makes good on the promise of its headline specifications. In everyday shooting the A55 is a far more agreeable companion than most of its DSLR cousins in the Alpha range too, thanks largely to its generously sized and well-implemented EVF and LCD screen.
Startup time is reasonably quick for a camera which doesn't have an optical finder, at approximately 1 second, and when the camera is turned off, the EVF and LCD are extinguished immediately. The camera's access light only goes out after sensor-cleaning though around one second after the power switch is turned to 'off.' Shot to shot time in single-frame advance is roughly 0.5 seconds but this increases to approximately 1.5 seconds when automatic image review is turned on. Obviously in continuous shooting modes, shot-to-shot times are faster.
The A55 suffers from the same problem as the company's NEX models in that considerable delays are introduced if you turn image review on (the usual state for most cameras). Turning image review on does add around a two second delay before the review image appears and there's no way of getting back to live view during that time. Oddly, though, it doesn't feel like such a big issue in this situation. Working through the EVF, DSLR users are unlikely to expect a review image to appear, so it doesn't feel as unusual to not have one.
Overall PerformanceWe'll discuss AF performance in more detail further down this page, but the A55's other key systems (metering and white balance) are generally very reliable. Metering, especially, is more or less infallible when left in multi-zone mode, and with 1200 zones in total it should be. Even in very poor artificial light the A55 is capable of accurate exposures with a minimum of manual intervention.
The A55's AWB system isn't quite as solid though, and whilst perfectly happy in daylight, it has a tendency to slightly under-neutralise tungsten light, especially in relatively dark conditions. The same could be said though of most cameras of this class. Less of an issue is the A55's inability to deliver perfectly neutral results from a custom white balance setting. This is a major annoyance in the studio, where a lot of trial and error is required to get a completely neutral result under artificial light, but unlikely to be a problem in day to day (non-technical) shooting.
Continuous Shooting and BufferingThe A55's 'headline' 10fps rate is impressive, and is a feat only matched by two other cameras currently on the market, the Canon EOS-1D Mark IV and Nikon D3S. To get the maximum 10fps performance, it is necessary to switch to the dedicated setting on the A55's exposure mode dial. In this mode, exposure is automatic. Setting focus set to 'single' mode gains you the ability to shift the aperture/shutter speed settings and adjust ISO but you lose the ability to refocus between shots, making the mode less useful for many applications.
The A55 has two more continuous shooting settings - continuous high (6fps) and continuous low (3fps). These can be activated from within the PASM modes, where full control over the camera's shooting parameters is possible. Here's how the A55 performs with a 4GB Sandisk Extreme III SDHC card installed.
- JPEG (Fine): around 10 fps for 30 frames then about 2fps dropping to 1.5fps after 37 frames
- RAW: around 10 fps for 19 frames, then around 0.5 fps
- RAW + JPEG: around 10 fps for 20 frames, then about 0.4 fps
- Recovery time: around 50 seconds
- JPEG (Fine): around 6 fps for 47 frames, then around 2.5fps
- RAW: around 6 fps for 20 frames, then around 0.5 fps
- RAW + JPEG: around 6 fps for 18 frames, then about 0.3 fps
- Recovery time: around 50 seconds
- JPEG (Fine): around 3 fps for capacity of card
- RAW: around 3 fps for 22 frames, then around 0.5 fps
- RAW + JPEG: around 3 fps for 21 frames, then about 0.4 fps
- Recovery time: around 50 seconds
Whilst the A55 gives very impressive performance in terms of speed and burst depth, two things let it down when shooting continuous bursts. The first is a recovery time of 50 seconds, for some of which time the camera is essentially unusable - almost all of its available processing power being used to write the images to card. With a fast card installed, the camera never stops shooting unless you remove your finger from the shutter release. However, if after finishing a burst, you try to access image review, the A55 freezes. Both EVF and LCD black out, the camera remains completely frozen (except for AF, oddly, which still operates) for roughly 20 seconds. After this time has elapsed the A55 wakes up again, and allows image review, albeit it with a lag of several seconds between images. Only after the full 50 seconds of recovery time has elapsed does it return to its normal level of responsiveness.
The second major issue with the A55's continuous shooting is that it cannot maintain live view in 10fps and 6fps capture. In 10fps mode the A55 shows a constantly updating slide show of the image you just took, which means that you can't accurately tell where you subject is, - only where it just was. This can be rather disconcerting when panning as you keep being given the impression that the subject is further back than it now actually is.
It behaves differently in 6fps continuous shooting mode though - when set to 6fps the A55 shows a slideshow of images between the last one it just captured, and the one before that. This means that with your eye to the EVF, you're always looking at a stream of snapshots, essentially, each one of which was captured by the camera before the picture it just took. Presumably this is to give an indication of panning accuracy between captured images, but the overall effect is confusing.
Super SteadyShot INSIDE Image Stabilization test
At a range of shutter speeds a total of twenty hand-held shots were taken of a static scene, ten without stabilization, ten with the activated SteadyShot system. For these tests we used the Sony 18-55mm SAM kit lens at 55 mm to produce a 82.5 mm equiv. FOV. The test chart was approximately 5 m away from the camera. We're looking for how much improvement the system offers, not an absolute measurement of 'how low you can go' with the shutter speeds.
The resulting images were then inspected and given a blur score from zero to three where zero represented a very blurred image and three a sharp image with no noticeable blur (see crop examples below). Obviously the amount of blur which is acceptable will depend on your personal taste and the final image size (for instance a '2: Soft' will still look fine as a 4x6 print or in a web gallery). Example crops from these four blur scores can be seen below.
|0: Very blurred||1: Blurred|
|2: Soft||3: Sharp|
Hand-held, no stabilization (18-55 mm kit lens, 82.5 mm equiv. FOV)
With the kit lens at its longest focal length we only were able to get 100% sharp shots at 1/125th sec (which you'd expect). At lower speeds the percentage of sharp shots decreases continuously and at 1/8th sec drops sharply to only two usable shots out of ten. At even lower shutter speeds all images are blurred or very blurred.
Hand-held, with SteadyShot on (18-55 mm kit lens, 82.5 mm equiv. FOV)
With the activated SteadyShot system we get a pretty significant improvement. We get 100% sharp shots down to 1/30th sec and at 1/8 sec we still get 100% usable shots (60% sharp). Even at a shutter speed as slow as 1/2 sec 40% of all images would still be good enough for at least smaller prints. The system gives you a 2-3 EV advantage across all shutter speeds which is pretty much in line with the results from Sony's SteadyShot system that we've seen in previous reviews. Especially at slow shutter speeds your chances of getting a sharp shot increase dramatically.
Autofocus speed / accuracy
Sony's 'Fast AF Live View' as it is found in the Alpha 390 brought phase-detection in live view mode to the market, but the A33 and A55 take things even further. A new 15-point AF module is Sony's most advanced yet, and in day-to-day use with static subjects AF is very fast and very accurate. Unfortunately, where the A55's AF system falls down is when it is tasked with focusing on fast-moving subjects.
On paper, the SLT A55 should be an ideal tool for shooting fast action. It can shoot at 10fps with continuous autofocus. The A55 also has a trick up its sleeve that even the Canon EOS-1D Mark IV cannot match - because its mirror is fixed, the AF sensor can operate full-time, without interruption. This should ensure more accurate continuous AF performance, since the camera is constantly being fed data with which to make the necessary calculations.
That's the theory, but unfortunately it isn't born out in practice. We have found that when presented with fast moving subjects (we shot a range of subjects, including cyclists on a track), focus accuracy is far from 100%. In 10fps mode it is clear that the A55's AF system is simply unable to predict subject position accurately when presented with fast-moving subjects at relatively close range, and in a typical sequence of images of cyclists on a track, whilst the zone of focus shifts from frame to frame, it is almost always slightly behind the intended subject.
Even when it finds its mark, the A55's auto exposure/ISO system (which is set by default and cannot be adjusted in 10fps mode with continuous AF enabled) appears to be using a simple 1/focal length calculation to determine the ideal shutter speed. This is fine for eliminating camera shake but is not always fast enough to freeze fast-moving action (which is what many people will be trying to do with 10fps bursts).
In our shooting, we've found that in good light, at the long end of a 70-400mm lens, the A55 will aim for as low an ISO sensitivity setting as possible - typically sets a shutter speed of no higher than 1/500sec. This is fine for static subjects, but not always fast enough to ensure sharp images of a fast-moving cyclist or soccer player, even if the AF is accurate.
If you want to take control over exposure but still shoot fast bursts it is necessary either to switch to single-servo AF or leave the dedicated 10fps setting and select continuous shooting (6fps or 3fps) in one of the other exposure modes.
We have found that in aperture and shutter priority modes, assuming we can keep the shutter speeds high enough, shooting at 6fps our hit rate of sharp images increases dramatically. However, as far as focusing is concerned, when faced with fast-moving targets the A55 has the same problem as it does in 10fps mode, and seems consistently to lag slightly behind the action. The conclusion has to be that for everyday use, the A55's AF is perfectly capable, and very good for its class, but in a demanding shooting situation where efficient predictive AF is called for, i.e. when tackling sports and action photography, it cannot always keep up.
Aug 12, 2013
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