Sony SLT-A55 Digital Camera Review$899.99
Looking at the individual color channels, we found that the same pattern was consistent, so there is no one color that is adding more to the noise. Only the luminance channel was slightly higher than the others, but not significantly so. More on how we test noise.
The SLT-A55 offers a very impressive ISO range, going from 100 up to 12800, all at the full resolution of the camera. If you really need to push it further, the SLT-A55 offers a special ISO expansion mode that takes 6 shots for each shutter press and combining the images together to form a single image. This can widen the effective ISO range to 100 to an incredible 25600. However, moving objects can confuse the camera: see our Sample Photos for an example. All of the images below were shot in the standard, single shot mode.
Shooting in low light often involves using long exposures, and long exposures mean more time for electronic noise to gather in the sensor. This means noisy images, so we test how well the camera deals with this by shooting a number of images at different shutter speeds and examining the noise in them using Imatest. We found that the SLT-A55 had some issues here: although the colors in log exposure images were pretty constant, the noise in images with exposure times of more than 1 second was significant. We also found that enabling the long exposure noise reduction didn't make that much difference: in some cases, it seemed to make things a little worse. More on how we test long exposure.
When we look at the noise in images (see the chart below), we see that the noise in images rises as the exposure time increases, rising from 1.05 per cent to about 1.24 per cent at 30 seconds. The long exposure noise reduction didn't make much difference, and at some speeds it seemed to make things slightly worse.
Compared to other SLRs, the SLT-A55 didn't fare well: many other SLRs have lower, or more consistent, noise with long exposure levels. So, the SLT-A55 earns a lower noise score than all of our comparison cameras.
Video: Low Light Sensitivity
The SLT-A55V needed 11 lux of light to hit 50 IRE on our waveform monitor. In a strange coincidence, this was the same amount of light required by the other three cameras we compared it to. This makes it rather simple to compare the A55V's low light sensitivity to the competition.