Sony Alpha A550

Noise Reduction (6.47)

Unlike most SLRs, which offer the option to turn high-ISO noise reduction off entirely to preserve the maximum level of image detail, the A550 offers only two choices here: high, which emphasizes image quality and normal, which prioritizes shooting speed). (Panasonic also prohibits turning high ISO noise reduction off entirely, though they do offer five levels to choose from). Given Sony’s take it or take a little less of it attitude, the question becomes ‘How well do the A550 photos capture fine image detail after the noise reduction system gets done with them?’ In our sample photos taken at high ISOs, we found the camera ramped up sharpening substantially as ISOs increased, producing images that do deliver fine detail, albeit in a field of colorful speckles.

The difference in processing kicks in at ISO 1600 and the higher setting does offer a small improvement at ISO 1600 and 3200, where the noise levels are still low enough to offer usable results.

We break out the levels for the component parts of image noise: red, green, blue, yellow and chroma (gray). If the noise in one channel spikes over the others it can cause a problem even when the overall noise level is relatively low. In this case, though, they are all grouped tightly together. More on how we test noise.

Image noise results were about average for a decent digital SLR. We don’t see a huge variation in this category, with the exception of the smaller-sensor Four Thirds and Micro Four Thirds models, which take a hit in the image noise category.

To test image noise levels, we shoot the ColorChecker chart under bright 3000 lux studio illumination, at all standard ISO levels and all available high-ISO noise reduction settings. (Low-light performance is tested separately). We use Imatest software to analyze the image noise levels under each test condition.

ISO Options

Available settings range from ISO 200 to an unusually high ISO 12800. There is also an Auto ISO setting, which is the only available mode when shooting in Auto or scene modes. Auto ISO is limited to the ISO 100-1600 range.

Focus Performance

The A550 uses a 9-point autofocus system when shooting with the viewfinder, with eight line sensors and a cross-hair sensor in the middle. There are two focus modes, Single-shot and Continuous, plus an automatic mode that lets the camera make the call.

By default, the camera uses an Eye-Start AF system when shooting with the optical viewfinder. Holding the camera up to your eye automatically starts the autofocus system, which then continues to adjust focus as you move the camera. If you’re used to holding the shutter button halfway to autofocus, this alternative approach takes some getting used to. It can potentially shave a second or so off your ready-to-shoot time. At the same time, having the camera start autofocusing on its own threw off our tried-and-true shooting rhythm, and we found that as we held the camera between shots, we frequently triggered the autofocus as the viewfinder moved close to our body. Full credit to Sony for providing the option, but we went into the Custom menu and turned it off.

In well-lit settings, the autofocus speed was very good, but moving into low-light situations we ran into trouble. First problem: the system uses the flash as an autofocus assist instead of a dedicated AF assist lamp, blasting two blinding staccato bursts of light — so much for candid shots in a dark room. Second problem: even with the autofocus assist, the camera failed to achieve a proper focus too often in night shooting situations.

There are three focus area options: Wide, Spot, and Local.

The local focus area option is unnecessarily tricky to use because of the poor viewfinder display as you select a focus point. It blinks briefly while you hold the directional pad down, but that’s hard to see, and there’s no indication afterward to show which of the nine points you’ve selected until you see the point blink red to confirm focus. Also challenging is moving the pad diagonally to select the corner points. All in all, it’s a clumsy system.

Long Exposure (9.30)

Our long exposure test weighs two component factors, image noise and color accuracy. The Sony A550 did well when it came to noise and less well on color accuracy (which makes sense, since even under ideal conditions its color reproduction isn’t great). Overall, this produced a decent but not exceptional score.

The long exposure test procedure involves shooting the X-Rite ColorChecker chart under subdued lighting, at shutter speeds ranging from 1 second to 30 seconds, with any long exposure noise reduction system set both on and off. The resulting test images are run through Imatest to determine image noise levels and color accuracy. More on how we test long exposure.

Color error remained nearly constant, at a relatively high level, across all tested shutter speeds, and saturation ran about 108% across the board. Long exposure noise reduction had no effect on the results.

The image noise levels didn’t vary much with shutter speed either, remaining at under 1% throughout. The long exposure noise reduction system had little effect here either, which is a result we often see — in fact, it’s not uncommon for long exposure noise reduction to make matters worse. The concept is to have the camera take a second exposure with the shutter closed, analyze the noisy areas in this dark exposure and then mathematically remove these spots from the original shot. However, since the overwhelming majority of image noise is random, this approach rarely produces much improvement and, what’s more, doubles the time before you can take another shot.

The two stragglers in our comparison group, the Olympus and Panasonic, have something in common: they both use smaller Four Thirds / Micro Four Thirds sensors, which are subject to higher image noise than the larger APS-C format sensors found in the other three cameras. The Sony didn’t match the performance of the Canon Rebel T1i or Nikon D5000, but it’s not far behind.