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Sony Alpha SLT-A33 vs Canon EOS 550D / Rebel T2i High ISO Noise (auto contrast and DR modes disabled)
The image above was taken with the Sony Alpha SLT-A33 at 100 ISO using the camera's metered exposure of 0.8 seconds and the lens set to 22mm f8; the original Large Fine JPEG measured 3.93MB. As found on our outdoor tests, the Canon EOS 550D / T2i metered a slightly longer exposure under the same conditions – in this case, one second at f8 and 100 ISO. While we matched the image brightness in our outdoor results, we've opted to show what each camera captures given exactly the same exposures below. As such we applied -0.3EV compensation to the Canon to match the exposures of the Sony. As you'll see below, the resulting images from the Canon are a little darker, implying a slightly lower sensitivity than the Sony at the same quoted ISO values. We'd say the Sony enjoys one quarter to one third of an EV greater sensitivity – not bad considering the fixed translucent mirror prevents all the light from striking the sensor. As always, the crops are taken from the area marked with a red square and reproduced here at 100%. The Canon crops show a slightly smaller area due to the camera's higher resolution: 18 Megapixels versus 14.2 on the Sony. Looking at the crops below, the most obvious differences are the Canon being slightly darker (due to a lower actual sensitivity) and opting for a warmer white balance than the Sony. Looking beyond these differences, both cameras share similarly clean images at 100 ISO and similar degrees of real-life detail, despite the 4 Megapixel difference. As explained on the previous page, the Canon sensor is held back by the basic EF-S 18-55mm IS kit lens, and fitting something better will allow it to resolve finer detail – but even then the difference in resolved detail between the two cameras isn't particularly significant. At 200 ISO there's very minor evidence of noise textures developing in the backgrounds of each crop, but this is serious pixel-peeping and to all intents and purposes both cameras remain clean at this point. Likewise at 400 ISO, where the textures have become a little more obvious, but again with no real detriment to the images as a whole. With the sensitivity increased to 800 ISO, both cameras are beginning to suffer a little with increased noise artefacts and a slight decrease in saturation. Despite this though, both images remain fairly respectable and very usable. 1600 ISO is where the noise becomes really obvious on both samples with graininess across the image, a further reduction in saturation and the finest details ironed-out by noise reduction. This story worsens as the sensitivity increases with 3200 and 6400 ISO only really suitable for small reproductions and 12,800 ISO best-avoided unless you're really stuck. The interesting thing about this comparison is the similarity between the two models in terms of resolved detail, noise levels and artefacts. Throughout their sensitivity ranges the crops actually look quite similar. Of course there's the small differences in brightness and white balance mentioned at the start, but match these and they're quite close in overall style and noise characteristics. So anyone hoping for lower noise levels from a sensor with four fewer Megapixels may be a little disappointed, although as mentioned earlier, we found the A33 was approximately one quarter to one third of an EV more sensitive than the Canon EOS 550D / T2i at the same quoted sensitivities – which isn't bad considering the translucent mirror prevents some of the light from striking the sensors. Equally, anyone expecting the 18 Megapixels of the Canon to resolve significantly more detail than the 14 Megapixel Sony will also be let down, unless they're willing to invest in a superior lens. This is where the story would end for most cameras, but the SLT-A33 boasts a number of additional modes designed to lower noise or increase the dynamic range by automatically combining a number of shots in-camera. These modes are what make the SLT-A33 and similar Sony cameras so special, so we're giving them the recognition they deserve by devoting a whole page of results to each. We'll start by taking a closer look at the Sony Alpha SLT-A33's Handheld Twilight mode. Alternatively if you've already seen enough, head on over to our Sony Alpha SLT-A33 Sample Images Gallery for more examples across its sensitivity range, or head straight over to our verdict!
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