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ISO Sensitivity / Noise levelsISO equivalence on a digital camera is the ability to increase the sensitivity of the sensor. This works by turning up the "volume" (gain) on the sensor's signal amplifiers (remember the sensor is an analogue device). By amplifying the signal you also amplify the noise which becomes more visible at higher ISO's. Many modern cameras also employ noise reduction and / or sharpness reduction at higher sensitivities.To measure noise levels we take a sequence of images of a GretagMacBeth ColorChecker chart (controlled artificial daylight lighting). The exposure is matched to the ISO (i.e. ISO 200, 1/200 sec for consistency of exposure between cameras). The image sequence is run through our own proprietary noise measurement tool (version 1.6 in this review). Click here for more information. Room temperature is approximately 22°C (~72°F), simulated daylight lighting. Canon EOS 7D vs. Canon EOS 50D vs. Nikon D300s vs. Pentax K-7
It will come as no surprise to discover that there's no huge difference between the strategies being used by the two big camera makers - they are both trying to reduce noise to similar levels. Pentax, meanwhile has allowed more noise to remian in its images (at the default noise reduction setting), with the result that the images look more noisy but also appear more detailed. The D300S fares very well against the Canon 50D and, although the 50D's images are of higher nominal resolution (pixel count), they don't appear any more detailed than the Nikon's. The EOS 7D however, is not just capturing but also retaining more detail than the Nikon. The difference is extremely small but, given the noise measurements are so similar at the individual pixel level, the higher resolution 7D would also trump the Nikon in terms of overall image noise. The D300S results remain amongst the best we've seen for an APS-C camera, with remarkably usable JPEGs even at high ISOs (and lets not forget that ISO 3200 is a very high sensitivity, regardless of how much further the boundaries are currently being pushed). Noise graphsThe graphs below confirm what we have seen in the sample crops above - both Canon and Nikon appear to have decided what is an acceptable level of noise and tuned their noise reduction accordingly. The key thing is that, up to ISO 1600, this does not require the destruction of too much detail (things get a bit smoothed and mushy beyond that point).
RAW noiseFinally let's take a look a the D300's RAW output next to the competition. Removing any in-camera noise reduction and processing the images using Adobe Camera Raw gives us the nearest thing to a 'level playing field' for assessing the relative noise levels of the four cameras' sensors. With noise reduction turned off we get a more accurate idea of how noisy these sensors are and the image looks slightly different to what we've seen above in the JPEG section of this page. There's not a significant difference between any of these cameras - if anything, the most telling thing is how similarly the sensors of three different manufacturers perform.
Raw Noise graphsUsing a common raw converter makes clear that much of the difference between the cameras' performances in JPEG are, unsurprisingly, down to decisions made by the manufacturers about noise reduction levels. In RAW, these differences are removed from the equation, giving a better impression of what the sensors are doing. As you can see, there's very little to choose between them visually - the Nikon and Pentax perform better in numerical terms at lower ISOs, at the pixel level, but are overtaken by the 7D at the really high ISO settings, comparing on the whole-image level, you'd be hard pressed to spot any advantage.
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