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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 1.5 in this review). Click here for more information. Room temperature is approximately 22°C (~72°F), simulated daylight lighting. Pentax K-7 vs. Pentax K20D vs. Nikon D300 vs Canon EOS 50D
As usual in our ISO-noise comparisons the differences between the contenders are pretty marginal up to ISO 400. From ISO 800 onwards the cameras' varying noise characteristics become more visible. The K-7 and K20D show visibly more of both luminance and chroma noise than the Nikon and Canon. The D300 maintains a good balance between noise and image detail up to the highest sensitivities while the EOS 50D's approach to noise reduction is more heavy-handed and results in more blurring of fine detail than on the Nikon. Despite representing two different camera generations the K-7 and K20D produce near identical output up to ISO 800. From ISO 1600 upwards on the K-7 noise reduction kicks in whereas on the K20D noise reduction is switched off at default settings. While this naturally results in a larger amount of chroma noise on the K20D at higher sensitivities, the difference in luminance noise is fairly small. However, selecting the 'Weak' noise reduction setting on the K20D the differences pretty much disappear. At higher sensitivities it's obvious that Pentax is applying far less luminance noise reduction than Canon or Nikon. On the plus side this means that detail is retained and the results look visibly sharper; the downside is that noise is, inevitably, considerably more obvious. On balance, for viewing at normal magnifications (when color noise is still visible), the Canon and Nikon approach is preferable for JPEGs (though once you get to ISO 6400 none of them is that impressive). Noise graphsThe graphs below confirm what we have seen in the sample crops above. In numerical terms the K-7 teams up with its predecessor in being the noisiest camera in this group of four cameras. Up to ISO 400 the differences are manageable but then the gap opens up and measured noise on the Pentax duo goes pretty much through the roof.
RAW noiseFinally let's take a look a the K-7's RAW output next to the competition. Removing any in-camera noise reduction and processing the images using Adobe Camera Raw (V5.4 in this case, all NR set to 0) 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. In the RAW comparison the K-7 and K20D can easily keep up with the competition from Nikon and Canon. Surprisingly the older model K20D even outperforms its successor at higher sensitivities and produces slightly cleaner RAW files.
Raw Noise graphsThe graphs below confirm what we can see in the sample crops. The four cameras compared here produce similar amounts of noise at all ISO settings. The EOS 50D measures the largest amount of chroma noise and the K20D is producing the lowest RAW noise levels pretty much across the range.
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