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To compare noise levels under real-life conditions we shot this scene with the Sony Alpha DSLR-A550 and Nikon D90 within a few moments of each other using each of their ISO settings. Each camera was fitted with its respective kit lens (see details below) and adjusted to deliver the same vertical field of view. The images were taken in Aperture Priority at f8 with Auto White Balance

The image above was taken with the Sony Alpha A550 at a sensitivity of 200 ISO and the kit lens set to 22mm f8; the original L:14 JPEG file measured 4.18MB. High ISO Noise Reduction was set to the default Normal settings for the A550 and D90 respectively. The Sony’s D-Range Optimizer and Nikon’s Active D-Lighting were both disabled for this test as they can artificially increase noise levels. The crops are taken from the area marked with the red rectangle near the centre of the frame, and presented here at 100%.

Note in order to achieve the same image brightness in the examples below, the Nikon D90 employed exposures roughly half that of the A550. At 200 ISO f8, the A550’s exposure was 1.3 seconds, while the D90’s was 0.62 seconds. This difference remained consistent up to the high-end of the scale, with the A550’s exposure at 3200 ISO f8 being 1/15 and the D90 being 1/30. This implies the D90 is more sensitive when both cameras are set to the same ISO values.

Both cameras share a base sensitivity of 200 ISO, although the D90 offers an extended lower setting equivalent to 100 ISO. With both cameras set to 200 ISO, you’ll notice the A550’s images are lacking the crispness of those from the D90 – this is mostly down to image processing defaults though and if desired, you can make the Sony punchier, or the D90 softer as desired. Both models are unsurprisingly delivering clean, detailed images at this point.

At 400 ISO, pixel-peepers may notice a very fine smattering of noise in darker areas of both images, but it’s really nothing to worry about – both models again remain clean and detailed.

With the sensitivity increased to 800 ISO, there’s a minor increase in noise artefacts, but again both cameras are delivering good-looking and very usable results.

At 1600 ISO though the Sony A550 appears to be suffering a little more than the D90, with more aggressive noise reduction softening fine details for a patchier-looking result. In isolation it’s still pretty good, but the D90 has the edge at this point on.

With the sensitivity increased to 3200 ISO the A550 takes a greater turn for the worse with visible noise artefacts, softening and a decrease in saturation – again it’s not terrible by any means, but again most would prefer the D90’s output.

At 6400 ISO, the A550’s image quality deteriorates further and while the D90 has also become quite noisy, its JPEG contains finer details. The D90 bows-out at this point, leaving the A550 to offer its top speed of 12,800 ISO. It’s looking pretty bad at this point though and you’d only really use it for emergency situations. But do check out our gallery section where you’ll see another sample a notch down at 6400 ISO, which looks fairly respectable.

So overall the A550 and D90 are pretty much neck-in-neck up to 800 ISO, but at 1600 ISO and above the Nikon enjoys the edge, especially at the highest sensitivities. As seen on the previous page we wouldn’t say the A550’s extra two Megapixels over the D90 have allowed it to resolve or record any additional real-life detail.

But the important point is the performance you see below is easily the best yet from a cropped-frame Sony DSLR. The imaging pipeline of the D90 (also shared by the D5000 and D300s) is one of the best around for a cropped sensor, and for the Sony to keep-up with it for much of its range is no mean feat. The new CMOS sensor employed by the A550 is certainly delivering the goods and we just wish there was a low or disabled option for noise reduction on its JPEGs; presumably we’ll have to wait for a revitalised A700 series for that.

So a very respectable performance from the Sony A550 here and we hope to compare it against the lower resolution A500 in the future. Now head-on over to our Sony A550 sample images gallery to see more examples across its sensitivity range along with a continuous shooting sequence.

Sony Alpha DSLR-A550 with Sony DT 18-55mm SAM		Nikon D90 with Nikkor DX 18-105mm VR
100 ISO not available		L1.0 (100 ISO)
200 ISO		200 ISO
400 ISO		400 ISO
800 ISO		800 ISO
1600 ISO		1600 ISO
3200 ISO		3200 ISO
6400 ISO		H1.0 (6400 ISO)
12800 ISO		12800 ISO not available