Sony Alpha A900

Noise Reduction (6.68)

Noise reduction processing didn’t kick in until ISO 800, at which point it provided a substantial improvement over results with noise reduction turned off. The difference between the effects of the three settings, though, was quite small.

The noise trends among individual color channels and luma noise (the noise in gray areas of the photo) are consistent, though noise in the red channel is clearly more a problem for the A900, while yellow and green are better controlled. More on how we test noise.

The Sony A900 is a middle-of-the-pack performer when it comes to image noise. We found that with the noise reduction system turned off, the A900 started off well at ISO 200, with only the noise-busting Nikon D700 posting better figures, but as ISO settings increased, noise rose more quickly than the other cameras in our test group until, at ISO 3200, only the Canon 50D produced higher image noise. The noise reduction system is effective, keeping average color noise below 1% through ISO 1600 at maximum level, but not as effective as the system found in the other cameras: the A900 displayed the highest average color noise levels among the tested cameras across the ISO range when all were set to their maximum noise reduction settings.

Image noise is to digital photography what film grain was in the old days — spots and dots most noticeable in areas of flat color, caused in this case by random electrical activity in the image capture process. To test how well each camera keeps this phenomenon under control, we shoot the X-Rite color chart under bright 3000 lux illumination, at each official ISO setting (low-light noise performance is measured separately, along with low-light color reproduction, in our Long Exposure testing). When there are multiple high ISO noise reduction levels, we shoot at each. For the Sony A900, this means four sets of data, one with noise reduction off and then three at different noise reduction settings.

All of our test cameras followed roughly the same progression when tested with noise reduction off, though the Sony image noise rose slightly faster than the Nikon D90 at the extremes of the ISO range.

We noted above that the noise reduction system had no signficant effect until we passed ISO 800, which accounts for the Sony’s notably higher noise levels at that point compared to the other cameras in our group.

The overall noise score for the Sony A900 puts it behind all but the Canon 50D, though the differences among the scores aren’t high enough to be very significant.

ISO Options

Available ISO settings range from ISO 100 to 6400, all at full resolution, a more modest range than some competing cameras. Both the Canon 5D Mark II and Nikon D700, for example, offer extended-range ISO settings out to 25,600.

Sony doesn’t follow the Canon / Nikon route of clearly labeling ISOs that produce less-than-optimal results with non-standard naming conventions (dubbing extended-range settings as L for Low or H for high and leaving ISO numbering off). Sony numbers the complete range but highlights ISOs below 200 and above 3200 with rules above and below in the menu screen. The manual says, ‘The available luminosity limits for an image (dynamic range) are a little narrower in the range less than ISO 200. When ISO 3200 or higher is selected, the range is treated as an expanded range and the noise is more noticeable.’ As shown in the actual-size image crops below, we don’t see a major drop-off in dynamic range below 200, but there’s no question image noise explodes when we pass the ISO 3200 mark, and has already jumped upward long before we get to that point.

When set to Auto ISO, you can set a limit to the acceptable ISO range. Five settings are available: 200-400, 200-800, 200-1600, 400-800 and 400-1600.

ISO Comparisons
Sony Alpha A900	Canon EOS 5D Mark II	Canon EOS 50D	Nikon D90	Nikon D700
ISO Low
ISO 100	ISO 100	ISO 100	ISO 200
ISO 100	ISO 100	ISO 100	ISO 200
Sony Alpha A900	Canon EOS 5D Mark II	Canon EOS 50D	Nikon D90	Nikon D700
ISO 200
Sony Alpha A900	Canon EOS 5D Mark II	Canon EOS 50D	Nikon D90	Nikon D700
ISO 400
Sony Alpha A900	Canon EOS 5D Mark II	Canon EOS 50D	Nikon D90	Nikon D700
ISO 800
Sony Alpha A900	Canon EOS 5D Mark II	Canon EOS 50D	Nikon D90	Nikon D700
ISO 1600
Sony Alpha A900	Canon EOS 5D Mark II	Canon EOS 50D	Nikon D90	Nikon D700
ISO 3200
Sony Alpha A900	Canon EOS 5D Mark II	Canon EOS 50D	Nikon D90	Nikon D700
ISO 6400
Sony Alpha A900	Canon EOS 5D Mark II	Canon EOS 50D	Nikon D90	Nikon D700
ISO 12800
Sony Alpha A900	Canon EOS 5D Mark II	Canon EOS 50D	Nikon D90	Nikon D700
ISO 25600
Sony Alpha A900	Canon EOS 5D Mark II	Canon EOS 50D	Nikon D90	Nikon D700

NOTE: The images above are not used in our testing or scoring, but are included here to show real-world examples of the differences between cameras at the various ISO settings.