ISO / Sensitivity accuracyIn a new addition to our reviews we are now measuring the actual sensitivity of each indicated ISO sensitivity. This is achieved using the same shots as are used to measure ISO noise levels, we simply compare the exposure for each shot to the metered light level (using Sekonic L-358), middle gray matched. We estimate the accuracy of these results to be +/- 1/6 EV. Just like almost every Nikon digital SLR past the D60's indicated ISO sensitivities exactly match the camera's actual sensitivity across the range (from ISO 100 to 3200).
ISO Sensitivity / Noise levelsISO equivalence on a digital camera is the ability to increase the sensitivity of the sensor. The 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 1.4 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 D60 vs. Canon EOS 400D (Digital Rebel XTi) vs. Olympus E-410
Nikon's approach to high ISO noise on the D60 is pretty much the same as ever, mostly chroma noise reduction with only a small amount of luminance noise reduction. This leads to a lack of digital-looking chroma blobs while maintaining as much detail as possible (little luminance smearing here). Although this means there is a little visible noise, this noise at least has a film-like grain rather than digital artifacts. Compared to the other cameras there's very little to choose although the EOS 400D does maintain more detail at ISO 800 and above than the Nikon or Olympus. There doesn't appear to be a huge difference in the processing used by the D60's 'Expeed' processor, though the output does look subtly different viewed this close (it's a little softer and chroma noise is a little less intrusive). The slightly soft appearance of the D60's default output (compared to the Canon, for example) is down to a combination of stronger (or at least more visible) noise reduction and conservative sharpening, and if you sharpen the results there's little difference between the D60 and the EOS 400D at all at anything under ISO 800 (try it yourself). Luminance noise graphAs the graphs show there's not a huge difference between the D60 and its predecessor at lower ISO settings, but you can see the slight difference in the way the Expeed processing deals with noise as you move up the range. In truth you can't see these differences in real world images. Canon's CMOS sensor is the clear winner here (Olympus - as the crops above show - is simply blurring away noise at higher ISO settings), but there's not a huge difference in the ISO 100-400 region.
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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