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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 ISOs. 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.

Sony DSLR-A380 vs. Canon EOS 500D vs. Nikon D5000 vs. Olympus E-620

  • Sony DSLR-A380: Sony 50 mm F1.4 lens, Manual exposure, Manual WB,
    Default Parameters (Standard), High ISO NR Off (default), JPEG Large / Fine

  • Canon EOS 500D: Canon 50 mm F1.4 lens, Aperture Priority, Manual WB,
    Default Parameters (Standard PS), High ISO NR (Default; Standard), JPEG Large / Fine
     
  • Nikon D5000: Nikkor 50 mm F1.4G lens, Aperture Priority, Manual WB, ADL off
    Default Parameters (Normal), High ISO NR (Default; Norm) JPEG Large / Fine
     
  • Olympus E-620: Olympus 50 mm F2.0 Macro lens, Aperture Priority, Manual WB,
    Default Parameters (Normal), High ISO NR (Normal), JPEG Large / Fine
  Sony DSLR-A380 Canon EOS 500D Nikon D5000 Olympus E-620
ISO 100
ISO 200
ISO 400
ISO 800
ISO 1600
ISO 3200

Up to ISO 400 the noise and noise reduction differences between these cameras is fairly small but they become more obvious once the sensitivity goes up higher. At ISO 800 the Sony shows visibly more chroma noise than the competitors in this comparison. There are also first signs of relatively heavy-handed noise reduction. While on the Nikon and Canon noise shows in a fairly fine-grained format on the Sony, and to a lesser degree on the Olympus, noise reduction blurring leads to the appearance of fairly intrusive 'pixel blobs'.

At higher sensitivities the Nikon produces the cleanest image (notably less chroma noise) among the contenders followed by the EOS 500D. Both these cameras' noise reduction algorithms concentrate on battling the chroma noise first and are much less heavy-handed on the less intrusive, more grainy luminance noise. The Olympus and Sony follow at quite a distance behind the leading duo with visibly more intrusive 'noise blobs' and detail blurring.

Noise graphs

In numerical terms the A380 is pretty much in line with the competition but you can see that at ISO 800 chroma noise levels are highest on the Sony. The following drop at ISO 1600 is due to noise reduction kicking in. On the samples above we can see that this strategy leads to high levels of detail blurring at higher ISOs.

  Sony DSLR-A380
Chroma
Black
Gray
Indicated ISO sensitivity is on the horizontal axis of this graph, standard deviation of luminosity on the vertical axis.

RAW noise

Finally let's take a look at the A380'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 reduced to a minimum the A380's relatively tightly packed sensor produces visibly and measurably larger amounts of noise at almost all sensitivities than the competition. In fact, we had to change the scale of the graphs below in order to show the Sony's results at ISO 3200. The Nikon D5000 delivers the cleanest results by a margin. Interestingly, while the EOS 500D produces less RAW noise than the A380 the difference is not massive. However, the Canon produces much more pleasant JPEG results which goes to show the difference a well-balanced approach to noise reduction can make.

Please note that on the A380, like on previous Sony DSLRs, the noise reduction setting actually has an impact on the RAW file. With NR set to on noise reduction is applied to the RAW file which means a RAW file taken with NR enabled will create different results to one that was taken with NR disabled.

  Sony DSLR-A380 Canon EOS 500D RAW Nikon D5000 RAW Olympus E-620 RAW
ISO 100
ISO 200
ISO 400
ISO 800
ISO 1600
ISO 3200

Raw Noise graphs

The graphs below confirm what we can see in the sample crops. The Nikon leads the pack with lower RAW noise levels than the competition. The A380 produces the highest noise levels pretty much from base ISO upwards.

  Sony DSLR-A380
Chroma
Black
Gray
Indicated ISO sensitivity is on the horizontal axis of this graph, standard deviation of luminosity on the vertical axis.
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