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 D40X'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 D40X vs. Canon EOS 400D (Digital Rebel XTi) vs. Olympus E-410
Nikon's approach to high ISO noise on the D40X is pretty much the same as ever, mostly chroma noise reduction with very little luminance noise reduction. This leads to a lack of digital-looking chroma blobs while maintaining as much detail as possible (little luminance smearing here). Obviously this does mean that 'flat areas' can look noisier than the competition but 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 1600 than the Nikon or Olympus. Luminance noise graphThe graphs below demonstrate that the D40X's ten megapixel sensor with its smaller pixel pitch is naturally noisier than the D40, that said we're really talking about fractional differences between the two. The ISO 3200 option, indicated on the D40X as 'HI 1' is quite noisy and should really only be used in extreme situations.
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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