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Performance

Overall Performance

The SLT-A77 is a high-end enthusiast SLR and its performance, both in terms of ergonomics and general operational speed reflect this status. With some caveats (detailed further down this page) the A77 is a pleasantly fast, responsive camera in all of its shooting modes, not only its 'trademark' SLT high-speed continuous shooting functions.

Naturally though, when you talk about the A77's performance, you have to talk about its maximum framerate. One of the major selling points of the Sony Alpha SLT-A77 is its capture speed, made possible by its unique design. Fixed mirrors are nothing new, but what makes Sony's SLT cameras so interesting is the integration of a phase-detection AF sensor not in the base of the mirrorbox, but in the top, where a conventional DSLR's pentamirror/prism would be. Light reflected from the semi-transparent mirror feeds the AF sensor constantly, and the main imaging sensor takes care of the live view feed that you use for image composition.

Crucially, the fixed-mirror SLT design means that the A77 doesn't need to wait for its mirror to get out of the way before it can make an exposure, so frames can be captured at a maximum rate governed by the speed of the shutter mechanism. Ultimately, it is easier and cheaper to build a shutter which opens and closes 10 or 12 times per second than it is to make a mirror which has to be raised and lowered at the same rate. Those cameras which can manage it, like the Canon EOS-1D IV or the Nikon D3S, are very costly.

Because the AF sensor is constantly fed light reflected from the fixed mirror, the A77's phase-detection AF system can operate continuously, even during image capture (still and video). Theoretically, this should give the A77 a head start compared to more conventional DSLRs when it comes to shooting sports and action.

With the lens removed, we're looking straight down the A77's throat, at (or rather through) its semi-transparent mirror. The cluster of faint glass bead-like objects you can see in the centre of this view is the reflection of the A77's phase-detection AF array, which is positioned in the roof of the camera, above the mirror. The faint green rectangle in the centre of this view is the A77's exposed 24MP CMOS sensor. A newly developed 19-point AF array is recessed inside the roof of the A77's mirror box. In a significant improvement over the original A55, eleven of the 15 AF points are of the cross type (shown here in purple) for more accurate focus with large-aperture lenses.

Continuous Shooting and Buffering

The SLT-A77 has three continuous shooting modes, 'Lo','Hi' and 'Continuous Advance Priority AE'. In continuous 'Lo' mode the A77's nominal framerate is 3fps, which increases to 8fps in 'Hi' and 12fps in 'Continuous Advance Priority AE' mode.

The 'AE' in Continuous Advance Priority AE mode stands for 'automatic exposure'. Unlike continuous Lo and Hi, continuous advance priority AE can only be accessed via the exposure mode dial. As we saw in the A55, which offered a maximum framerate of 10fps in the same mode, there are some downsides to this maximum capture rate. In Continuous Advance Priority mode the A77 can still focus continuously, but in order to be able to do this, aperture is either fixed wide open, or limited to f/3.5 if the maximum aperture allows it. You can take full control over aperture in Continuous Advance Priority AE mode, but only if you select AF-A or manual focus. The reason for this limitation is the same reason why you cannot combine AF with manual aperture control in movie mode - at apertures smaller than f/5.6 the A77's AF system receives essentially no light, so cannot function.


Another disadvantage of the SLT system when it comes to fast shooting is that it isn't possible for the A77 to maintain a live view feed in its fastest 8fps and 12fps continuous capture modes. The viewfinder does not black out when shooting at these high framerates, but shows a sequence of still frames in real time. What this means is that at any given moment, you don't see the view through the camera's lens right now, but how it was a fraction of a second ago. This makes little or no difference if you're shooting slow-moving or static subjects, but it makes panning with fast-moving subjects very hard indeed, since you never know where they are - only where they were.

Continuous Advance Priority AE

Timing
JPEG Large/Fine
JPEG Large/Extra Fine
raw
raw+JPEG Fine
Frame rate 12.0 fps 12.0 fps 12.0 fps 12.0 fps
Number of frames 17 14 14 13
Buffer full rate 2.5 fps 1.5 fps 1.2 fps 0.9 fps
Write complete 8 sec 14 sec 12 sec 14 sec

Continuous Hi

Timing
JPEG Large/Fine
JPEG Large/Extra Fine
raw
raw+JPEG Fine
Frame rate 8.0 fps 8.0 fps 8.0 fps 8.0 fps
Number of frames 18 14 14 13
Buffer full rate 2.6 fps 1.0 fps 1.1 fps 1.0 fps
Write complete 6 sec 12 sec 12 sec 13 sec

Continuous Lo

Timing
JPEG Large/Fine
JPEG Large/Extra Fine
raw
raw+JPEG Fine
Frame rate 3.4 fps 3.2 fps 3.0 fps 3.0 fps
Number of frames 40 24 20 16
Buffer full rate 2.5 fps 1.1 fps 1.1 fps 0.9 fps
Write complete 9 sec 9 sec 13 sec 13 sec

All timings performed using a 16GB SanDisk Extreme Pro UHS-I SDHC card (45MB/s)

One of our biggest criticisms of the original SLT-A55 was its lengthy buffer times after shooting continuous bursts of images - up to around 50 seconds depending on the file type. As you can see, with our current UHS-I SDHC test memory card, the A77 turns in a much better performance, and write times do not exceed 14 seconds even when shooting continuous 12fps bursts of raw+JPEG files (something that we're fairly confident that you won't do very often).

Because these figures are so much better than our experience of the A55, we also measured the A77's performance with a conventional class 10 SDHC card, to see what difference the faster memory card was making. 'A lot', is the answer. In JPEG Fine mode, with a class 10 SDHC card fitted, the A77's buffer drops by 3-5 frames depending on the shooting speed, and the write time, to allow the buffer to clear, increases dramatically. With a UHS-I card, In Continuous Advance Priority AE mode the A77 can squirt off 17 frames at 12fps before slowing, and the data takes 8 seconds to be written to the card. With a conventional class 10 SDHC card, the burst depth drops to 13 frames and the write time increases to a slightly tedious 17 seconds.

If you choose to shoot in raw+JPEG mode at the A77's fastest 'standard' framerate of 8fps, you're looking at a reduced burst depth (9 frames compared to 13) and a greatly increased write time of 38 seconds, before the camera's buffer is clear. The solution here is obvious but somewhat expensive - if you intend to use the 77's continuous shooting modes regularly, a UHS-I SDHC memory card would be a very smart investment.

Both of these images are 'keepers' from longer sequences shot at the A77's maximum standard framerate of 8fps. You shouldn't expect a 100% success rate in terms of composition and focus when shooting this quickly, but having hundreds of frames to choose from does at least allow you to cherry pick the standout shots.

For all of the A77's speed, it can't compete with dedicated press cameras like Canon's EOS 1D Mark IV or the Nikon D3S. This shouldn't come as any surprise at all. Despite its headline-grabbing high-speed shooting modes the A77 is much closer to competitors like Canon's EOS 7D and Nikon's D7000. Compared to these cameras, the A77 acquits itself very well indeed, although the trade-off of the A77's faster framerates is reduced burst depth. Both the 7D and D7000 can capture more images in a single burst, but at framerates slower than the A77's 8fps 'continuous hi' mode. This said, a continuous burst of 14 high-quality 24MP JPEG frames at 12fps is very good, even if most users might never go beyond playing with the function once or twice.

Autofocus speed / accuracy

The SLT-A77 uses an all-new 19-point AF system which Sony claims offers a significant upgrade over the A55's 15-point array. From the point of view of performance, the increased number of AF points is less interesting than the increased number of cross-type sensors. These detect contrast on both horizontal and vertical axes, which increases AF accuracy, especially in marginal lighting conditions.

It is very hard to make any definitive statements about the A77's AF performance compared to that of the A55 because there are so many variables involved, but like its predecessor the A77's AF system is very capable. In most shooting situations, its AF system is accurate and reliable, and with one of Sony's newer internal-focussing SSM lenses it is at least as quick and silent as we've come to expect from Canon's USM and Nikon's high-end AF-S systems.

We've had mixed luck when shooting fast action with the A77. We had the opportunity to do a fair amount of action photography during the shooting for this review and whilst we captured a lot of sharp, accurately focussed frames, we didn't enjoy anything approaching a 100% hit-rate. To be fair though, we didn't expect to.

It is clear that the new Object Tracking function works very well in some situations - namely when the subject is very easily distinguishable from its background and isn't moving too quickly - but it doesn't cope at all well when faced with fast, erratically-moving subjects, to the point where we consider it almost useless for action photography (except, perhaps, airplanes against a blue sky or watersports with an uncluttered background).

Apart from anything else, to get Object Tracking to work at all, you have to first carefully place a frame over your subject and 'lock' onto it. This is easier said than done when shooting in the dust and chaos of a high-intensity sports event, and even when we could get a 'lock' the AF frame tended to jump around so much that reliable tracking was simply impossible.

Frame 1
Frame 2
Frame 3
Frame 4
Frame 5
Frame 6
Frame 7
Frame 8
Frame 9
Frame 10
Frame 11

This sequence of images was shot in the A77's Continuous Advance Priority AE mode, with AF set to continuous and the central AF 'zone' activated. As you can see, out of a run of 11 images, only one (frame 5) is genuinely sharp, although several more are sharp enough given the A77's pixel count to be perfectly useable. This is an extreme example though - in general, with a little trial and error, our experience suggests that you can expect between 40-60% of frames will have part of the subject in focus with AF set to 'C'.

Overall, we feel pretty much the same about the A77's continuous AF performance as we did about the system in its predecessor the A55. Namely that it is perfectly capable most of the time, but in terms of its tracking abilities it can't quite keep up with the systems in competitors like Canon's EOS 7D and the Nikon D7000. No-one should be surprised that it isn't up to the task of keeping every frame in 12fps bursts (like the one shown above) reliably in focus. Like the A55, the A77's focussing system seemed to lag a little behind the action in much of our most challenging fast-action shooting, although experimentation with AF zones is essential depending on what you're shooting. In general, we got best results with AF set to the central zone (assuming we could keep our subject safely within this zone when panning).

In single-shot mode however - the mode in which the camera will be used most often - autofocus is solid, reliable and very accurate, even in marginal lighting conditions.

Image Stabilization

The A77's SteadyShot INSIDE sensor-based image stabilization system is the latest incarnation of a very well-established technology introduced by Konica-Minolta, long before Sony took over the brand and began making its own DSLRs. This is a long way of saying that it is tried and tested and in our time with the camera we have found it to be reliable and useful.

Sony claims that SteadyShot INSIDE offers a benefit of between 2 and 4 stops, and our testing backs this up. In normal use we would expect to reliably get around three stops (allowing you to shoot with a 100mm lens at around 1/30sec, for example, assuming only moderate camera shake). Naturally, it also works with every lens you can put onto the camera, including those which don't have optically-stabilized equivalents in the Canon and Nikon systems (such as wideangles and fast primes).

Battery life

Despite the amount of technology inside the A77, including full-time live view and sensor-based image stabilization, we are happy to report that in our experience with the camera battery life is in line with Sony's own measurements. This means greater than 400 images in normal use, including lengthy continuous shooting sequences, prolonged on-camera reviewing and editing, video shooting and plenty of swapping between the rear LCD and EVF.

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