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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. (Note that noise values indicated on the graphs here can not be compared to those in other reviews). Room temperature is approximately 22°C (~72°F), simulated daylight lighting.

Nikon D90 vs. Pentax K20D vs. Canon EOS 450D vs. Nikon D80

  • Nikon D90: Nikkor 50 mm F1.8 lens, Manual exposure, Manual WB, Active D-Lighting Off
    Default Parameters (Standard), High ISO NR (Default: Normal), JPEG Large / Fine

  • Pentax K20D: Pentax FA 50 mm F1.4 lens, Aperture Priority, Manual WB,
    Default Parameters (Bright), JPEG Large / Fine

  • Canon 450D: Canon 50 mm F1.4 lens, Aperture Priority, Manual WB,
    Default Parameters (Standard), JPEG Large / Fine

  • Nikon D80: Nikkor 50 mm F1.4 lens, Manual exposure, Manual WB,
    Default Parameters (Normal), High ISO NR (Normal), JPEG Large / Fine

Nikon D90
ISO 100
(L1.0)

Pentax K20D
ISO 100
Canon EOS 450D
ISO 100
Nikon D80
ISO 100

Nikon D90
ISO 200
Pentax K20D
ISO 200
Canon EOS 450D
ISO 200
Nikon D80
ISO 200

Nikon D90
ISO 400
Pentax K20D
ISO 400
Canon EOS 450D
ISO 400
Nikon D80
ISO 400

Nikon D90
ISO 800
Pentax K20D
ISO 800
Canon EOS 450D
ISO 800
Nikon D80
ISO 800

Nikon D90
ISO 1600
Pentax K20D
ISO 1600
Canon EOS 450D
ISO 1600
Nikon D80
ISO 1600

Nikon D90
ISO 3200
Pentax K20D
ISO 3200
Canon EOS 450D
n/a
Nikon D80
ISO 3200

Nikon D90
ISO 6400
(Hi 1.0)
Pentax K20D
ISO 6400
(ext)
Canon EOS 450D
n/a
Nikon D80
n/a

Up to ISO 400 all four cameras are virtually indistinguishable, with each retaining almost the same level of detail that they produce at their base ISO settings. It's not until ISO 800 that the differences start to appear, with the Nikon and Canon showing increasing attempts to control noise and producing relatively low noise images as a result. The D90 does a very convincing job of surpressing noise without destroying too much detail - its performance is essentially identical to the class-leading 450D all the way up to ISO 1600.

Unlike the 450D, the D90 is willing to try its hand at ISO 3200 and even offer a boosted 6400 equivalent mode. These results are less impressive, with the 3200 setting finally secumbing to noise reduction blurring and the 6400 equivalent showing a delightful combination of noise, noise reduction smearing and substantially reduced contrast. That said, ISO 6400 is extremely challenging for a camera with an APS-C sized sensor so even these noisy, smudgy, low-contrast results are amongst the better we've seen. It's a setting that may sometimes allow you to get the shot you're after, but we'd tend to use it only as a last resort.

* These results are with the cameras in their default modes, all four offer some control over the amount of noise reduction used at higher ISO settings. We assess the D90's on the next page.

Noise graphs

Note that we normally show both gray and black results on the same graph, comparing four cameras this became too difficult to read hence we have two separate graphs, one for the gray patch (middle gray) and one for the black patch (shadows).

Luminance noise graph (gray patch)

The D90's noise rises fairly gradually as sensitivity increases. Comparing this plot to the Canon 450D we can see it has been kept to similar levels. In fact, if you look back to the 450D review, you'll see the noise levels are very much in line with the Sony A700 (as reviewed), and the Olympus E-3. This suggests that some sort of consensus has been reached about how much noise customers at this level will tolerate and default noise reduction is tuned to achieve that result.

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

Luminance noise graph (black patch)

In the black (shadow region), tests, the D90 again very closely tracks the behavior of the Canon, with noise kept down to a very similar level, right up to ISO 800. Our dynamic range tests will show whether these low levels are archieved by simply clipping near-black noise (and detail), to black.

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

Chroma (color) noise graph

Chroma noise is where the D90 diverges most from the competition. At their default settings both the 450D and the K20D allow a lot more chroma noise to appear, though both have options to combat it. Instead, Nikon has made the decision to keep Chroma noise down without sacrificing too much detail or contrast until its highest ISO settings.

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

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