Sony Alpha SLT-A33
Sony SLT-A33 High ISO Noise Reduction
The Sony SLT-A33 offers only two high ISO noise reduction settings: Auto and Weak, with Auto being the default. The A33 user manual does not say at what ISO noise reduction kicks in, so we've included crops starting from the base ISO of 100. We've also included crops from the new Multi-frame Noise Reduction mode, which shoots a burst of six images with a single press of the shutter button and combines them in-camera to average out a lot of noise.
See for yourself how the noise reduction works under daylight-balanced lighting. Click on any of the crops below to see the corresponding full-sized image.
The above crops show the effects of the Sony A33's two high ISO noise reduction settings, plus Multi-frame Noise Reduction under our studio HMI lighting we use to simulate daylight. As you can see, the "Weak" setting does result in more chroma noise than the Auto, but it also smudges the detail in the red fabric at higher ISOs. (You can really see a difference at ISO 1,600 and above.) Multi-frame Noise Reduction takes a burst of 6 shots and combines them to average out noise. This new mode is similar to Hand-held Twilight, but gives you control over ISO and exposure mode (PASM). It produces some very clean, detailed images and also extends the available ISO settings to 25,600, but requires the use of a tripod at slower shutter speeds, so similar results can be obtained by simply shooting at a lower ISO with longer exposures if you're already using a tripod.
Let's see how the Sony A33 compares the Canon T1i, Nikon D5000 and Sony A560, which are similarly priced.
Here, we can see the Sony A33 is competitive in terms of noise performance in this group, at least in its JPEGs. The 12.3-megapixel Nikon D5000 still has the edge overall, especially when it comes to rendering the red leaf pattern at higher ISOs, though that's no surprise considering its larger photosites. Compared to the Canon T1i, the A33's images exhibit lower luminance and chrominance noise, and the Sony also doesn't smudge the red leaf pattern nearly as much as the Canon at higher ISOs, but the output from the Sonys is a bit softer overall. To our eyes, the A560 does slightly better than the Sony A33 in terms of noise, even though they share the same sensor. This is likely because the translucent mirror in front of the A33's imager is reducing the amount of light striking the sensor (by some 30% or about 1/2 f-stop). The Sony A33's sensor gain has probably been increased to compensate, resulting in slightly higher noise levels under the same conditions. That's just a theory, though. We'll know better once we can examine the A33's RAW files with a raw converter that doesn't apply noise reduction (dcraw).
Note that the last set of crops here were taken with Sony's new Multi-frame Noise Reduction feature, so noise levels are vastly lower than they would be if the cameras supported ISO 25,600 in the standard single-capture mode.
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Note: For details, test results, and analysis of the many tests done with this camera, please click on the tabs at the beginning of the review or below.