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ISO Sensitivity / Noise levels

ISO 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 (ie. 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 K2000 vs. Canon EOS 1000D vs. Sony DSLR-A200 vs. Olympus E420

  • Pentax K2000: Pentax FA 50 mm F1.4 lens, Manual exposure, Manual WB,
    Default Parameters (Bright), High ISO NR Off (default), JPEG Large / Best

  • Canon EOS 1000D: Canon 50 mm F1.4 lens, Manual exposure, Manual WB,
    Default Parameters (Standard), High ISO NR Off (default), JPEG Large / Fine
     
  • Sony DSLR-A200: Minolta 50 mm F1.4 lens, Manual exposure, Manual WB,
    Default Parameters (Standard), High ISO NR Off (default), JPEG Large / Fine
     
  • Olympus E-420: Olympus 50 mm F2.0 Macro lens, Aperture Priority, Manual WB,
    Default Parameters (Normal), High ISO NR (Normal), JPEG Large / Fine
Pentax K2000
ISO 100
Canon EOS 1000D
ISO 100
Sony DSLR A200
ISO 100
Olympus E420
ISO 100

Pentax K2000
ISO 200
Canon EOS 1000D
ISO 200
Sony DSLR A200
ISO 200
Olympus E420
ISO 200

Pentax K2000
ISO 400
Canon EOS 1000D
ISO 400
Sony DSLR A200
ISO 400
Olympus E420
ISO 400

Pentax K2000
ISO 800
Canon EOS 1000D
ISO 800
Sony DSLR A200
ISO 800
Olympus E420
ISO 800

Pentax K2000
ISO 1600
Canon EOS 1000D
ISO 1600
Sony DSLR A200
ISO 1600
Olympus E420
ISO 1600

Pentax K2000
ISO 3200

Canon EOS 1000D
N/A

Sony DSLR A200
ISO 3200
Olympus E420
N/A

The Pentax takes a rather different approach to image processing, compared to its peers - its slightly clumsy sharpening and high contrast at its default settings means its ISO 100 image really stands out, while the other three manufacturers have essentially chosen to make their images look the same. This different way of working extends to noise reduction, with the K2000 doing very little to surpress either chroma or luminance noise. And this isn't the lunacy it might sound like. Although the chroma noise starts to become obvious in the gray patch from ISO 800 upwards, it isn't particuarly visible in the detailed crop, so is unlikely to be a problem in most real-world shots.

The luminance noise is also allowed fairly free rein, compared to the K2000's peers, and the effect is not at all unpleasant. The ISO 1600 image may be a bit more 'gritty' than the other cameras here, but it gives the impression of being more detailed (though the high default level of sharpening isn't particuarly helping). The ISO 3200 is such a poor result after an otherwise promising performance that it resembles nothing so much as an England batting collapse. And, in common with that slightly colloquial idiom, it's exactly what we should have learned to expect by now - this is ISO 3200, after all.

Luminance noise graph (gray)

Indicated ISO sensitivity is on the horizontal axis of this graph, standard deviation of luminosity on the vertical axis.

Luminance noise graph (black)

Indicated ISO sensitivity is on the horizontal axis of this graph, standard deviation of luminosity on the vertical axis.

Chroma (color) noise graph

Indicated ISO sensitivity is on the horizontal axis of this graph, standard deviation of color on the vertical axis.

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