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(Pocket-lint) - The Sony Alpha SLT-A33 adds to the storm of changing camera technologies. Inside the last year or so we’ve seen the likes of mirrorless "hybrid" Compact System Cameras - including the Sony NEX-3 and NEX-5 - unhinge a fair share of the DSLR market. And now, with the launch of Sony’s new "SLT" (Single Lens Translucent) Alpha A33, it looks as though the breadth of categories expands yet further. Does the A33 spell the beginning of the end for DSLR cameras…?

The 14.2-megapixel Sony A33 (the "little brother" of the simultaneously-released Sony Alpha SLT-A55) is modelled much like a DSLR, but with one major difference: the usual mirror has been made translucent. Without getting too technical, and certainly as the A33 is aimed at a broad audience from point-and-shooters to manual-control-tweakers, the differences on the inside do require a bit of explaining…

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A typical DSLR system bounces light from a mirror and through a pentaprism to enable a full-time preview via an optical viewfinder. The same light is also split and sent to an autofocus sensor to achieve phase-detection autofocus - the fastest form available. The mirror itself has to move out the way when a shot is fired so light can fall onto the sensor to capture the final image. As the Sony A33’s mirror is translucent there’s no need for any "slow" mechanical movement of the mirror whatsoever. The light can already pass through it and onto the sensor for a full-time live-view or electronic viewfinder preview and, crucially, the same light can also be simultaneously bounced to a 15-point AF sensor for full-time phase-detection autofocus - this means the A33 can boast a super-fast 7fps capture at full resolution and with continuous autofocus.

Compact System Cameras (CSC) or DSLR cameras set to Live View mode use a contrast-detection autofocus method on the image sensor itself that is much slower at achieving focus and will only continuously shoot in burst mode to a fixed-point of focus - issues that the A33 has fundamentally eradicated by allowing for phase-detection Live View for the very first time. And the A33 is jaw-droppingly fast; the kind of speed that would usually cost around an extra three grand in a top-of-the-line pro DSLR.

However, the caveat here is you’ll need good light and probably a better lens than the relatively slow 18-55mm F/3.5-5.6 kit lens provided to ensure a high enough shutter speed for crisp shots at every frame (though a top-end 1/4000th second shutter is pretty nippy and more than capable in the right circumstances). In use the 15 focus points are fairly centrally arranged, so don’t expect edge-to-edge AF control - it would have been nice to see a greater span across the sensor. Focus is fast though certain "flat" subjects can cause issues with non-focus. What’s surprisingly good is the kit lens’s ability to focus close to objects, whether at the wide angle 18mm or even full 55mm zoom, subjects can be crisply focused as close as 10cms from the lens.

Despite its benefits, the A33 system isn’t going to be for everyone: without the pentaprism there is no optical viewfinder, so an in-built 1.15 million-dot electronic viewfinder (EVF) stands in its place. While this may put off some prospective customers its quality is actually up there with the best current EVFs available: the resolution is quite reasonable, there is a full 100 per cent angle of view that’s desirable (and fairly uncommon in DSLR cameras of this class), superimposed visible AF points and focus confirmation, plus vertical and horizontal digital levels that almost hark back to 1980s arcade shoot-‘em-ups (I cite this as a good thing!) can be activated to assist with dead-pan shots. On paper most of these additional benefits far outweigh the drawbacks. Yet, saying that, the colour shift and occasional blur when panning don’t match up to the same optical viewfinder class.

Found below the EVF is also a 3-inch, 921k-dot 16:9 rear LCD screen which is detailed and resolute, and even has a tilt-angle capability to view from a variety of unusual angles or safely stow away, but the disproportionate widescreen ratio aligns itself more to video recording than stills capture.

Of course there are other benefits to be had for the inner workings of the camera. The A33’s 1080i/50 video mode is stunningly good, especially when considering the difficulty in controlling the majority of other CSCs and DSLR cameras on the market. The thing that sets the SLT-A33 apart from the competition is the ability for fast and continuous autofocus while recording - pan out from a closeup to a more distant subject and the focus glides steadily between the two, without over or under-focusing as so many other cameras do. The major qualm, however, is the lack of controls available that can cause issues - there’s no way to temporarily focus lock during recording, meaning it’s either all auto or otherwise entirely manual - and the kit lens isn’t especially smooth through the zoom which doesn’t bode well for video capture with manual focus. Although the kit lens is rather noisy when recording video there is a 3.5mm microphone port to connect external microphones for more professional recording. Do note, however, that the Sony/Minolta hotshoe differs from the "flat" ones found on the majority of other cameras.

Apart from the Electronic Viewfinder, the SLT-A33 is much like using a DSLR camera. The sensor is a 1.5x crop APS-C size and has Steady Shot Inside image stabilisation technology, as per other mid-range Sony models, and although the body is a little smaller without the pentaprism construction there’s still plenty to grip and hold onto: it’s not too small overall.

And just to add a bit of extra fun the A33 features fully automated shooting with written prompts to assist newcomers with what modes do, as well as including creative extra modes such as Sweep Panorama for real time panoramic shooting and D-Range Optimizer to "expose" for both shadow and highlight detail.

Given the A33’s translucent mirror, around 30 per cent less light than usual reaches the image sensor. Although that may sound like a lot, it only equates to around a third of a stop and, as digital sensors don’t have a base sensitivity in the same way as film of old did, it’s not a particularly big problem for the sensor to adjust the signal readout to compensate accordingly. Therefore a JPEG at ISO 100 is equally as exposed as any competitor camera’s ISO 100, and so on.

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Overall image quality is very good and doesn’t differ from what’s come to be expected from a Sony DSLR of similar ilk. Just because the mirror is different doesn’t mean that quality suffers and, despite less light reaching the sensor, it’s not of a consequence to results.

The APS HD CMOS sensor is the same resolution and size as that found in the Sony NEX-5 and the results could be seen as comparable also.

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Looking through shots from ISO 100-800 and the results are very good - with detail remaining intact and only a fairly low grain-like image noise. Even results from ISO 1600-3200 are excellent, though above this there is deterioration in sharpness and colour saturation given the noise reduction in play - though these shots are still usable. 

To recap

The Sony Alpha SLT-a33 is blisteringly fast in continuous AF, which extends superbly to 1080i/50 HD video capture with smooth focus transitions. The DSLR quality is there though the Electronic Viewfinder may put off more traditional users not looking for what’s essentially a very technologically-advanced, gadgety DSLR-like offering

Writing by William Perceval.