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.
Canon EOS 500D vs. Nikon D5000 vs. Olympus E-620 vs Canon EOS 450D
- 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
- Canon EOS 450D: Canon 50 mm F1.4 lens, Aperture Priority, Manual WB,
Default Parameters (Standard PS), JPEG Large / Fine
|Canon EOS 500D||Nikon D5000||Olympus E-620||Canon EOS 450D|
From a noise and NR point of view there's very little difference in real terms between any of these cameras up to ISO 400. At ISO800 the first hints of chroma noise start to appear on all cameras apart from the D5000 which, in typical Nikon fashion, is heavy on the chroma noise but allows some luminance grain to creep in.
At higher sensitivities the Nikon produces a cleaner image (notably less chroma noise) than the 500D while in terms of detail retention both cameras are more or less on par (the 500D has more detail to start with, and is visibly better at ISO 1600, after which point it all gets evened out by noise and NR). The Olympus follows at quite a distance behind the leading duo with visibly more noise and detail blurring.
Looking at the EOS 500D compared to the EOS 450D at ISO 1600 it's good to see that the extra pixels haven't had a significant impact on the higher ISO capabilities of the sensor. Having said that the 500D is not significantly better than its predecessor in the noise department either although admittedly you can still keep shooting with the new model when the light gets too dark for the 450D's ISO 1600.
Note: like all Olympus SLRs the E-620 offers four levels of noise reduction; these samples are taken with the default 'STD' setting, which tends to produce rather soft results at higher ISOs. If you're prepared to live with more visible noise you can retain more detail and get sharper looking output. We'll look at the E-620's various noise reduction options in more depth in our forthcoming review.
In numerical terms the 500D cannot quite keep up with the Nikon at higher ISOs and also measures slightly higher chroma and gray luminance noise levels than its predecessor.
|Canon EOS 500D|
Finally let's take a look a the 500D's RAW output next to the competition. Removing any in-camera noise reduction and processing the images using Adobe Camera Raw (V5.4 Beta 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 500D's more tightly packed sensor produces visible and measurably larger amounts of both luminance and chroma noise than the Nikon and, surprisingly, also the EOS 450D. In fact, while the Nikon arguably produces the cleanest high ISO RAW image in this test, the 450D follows very closely in its tailwind. When looking at these RAW crops and corresponding JPEG samples above it becomes clear that on the pixel-dense 500D sensor Canon has not been able to keep RAW noise levels down to 450D levels but does a pretty good job in limiting the impact of this on its JPEG output by using improved noise reduction algorithms.
|Canon EOS 500D RAW||Nikon D5000 RAW||Olympus E-620 RAW||Canon EOS 450D RAW|
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 500D's sensor produces the highest levels of Chroma noise but can more or less keep up with the Olympus and the 450D in terms of black and gray luminance noise.
|Canon EOS 500D|