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. As we have seen in previous reviews the Nikon cameras are right on the spot for ISO accuracy and the Canon cameras are about a third more sensitive than indicated (ISO 100 is more like ISO 125).
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. Boosted sensitivitiesFor the EOS 30D the ISO 3200 setting is only accessible once the 'ISO expansion' custom function has been enabled and is indicated by the camera as 'H', hence outside the recommended sensitivity range. The same is true for the Nikon D200, its ISO 3200 accessed as HI+1.0. We have indicated boosted sensitivities with a double asterisk '**' suffix. Canon EOS 30D vs. Nikon D200 vs. Canon EOS 5D
Apart from the obvious resolution difference the EOS 30D and EOS 5D produced fairly similar levels of visible noise and also limited softening at ISO 1600 and 3200. The Nikon D200 exhibits more noise above ISO 800 and pretty heavy noise reduction effect at ISO 3200. The D200's noise reduction seems to take care of chroma (color) noise better than Canon giving noise a more film like monochromatic appearance. However on balance it's clear that the EOS 30D comes away with a more usable image (compared to the D200) at ISO 1600 and 3200. Luminance noise graphOur new luminance noise graph shows noise levels in both the middle gray and black patches. As noted above luminance noise levels between these three cameras is pretty similar up to ISO 800, after this the Nikon's noise reduction system can no longer contain the noise. The other difference is shadow noise (the dotted line) which is higher.
Indicated ISO sensitivity is on the horizontal axis of this graph, standard deviation of luminosity on the vertical axis. Luminance noise graph magnified (Canon only)The graph below represents the same data as above (except for the removal of the D200) but on a standard deviation scale of 0 to 5 instead of 0 to 10, this makes it easier to see the limited difference between the Canon cameras. As you can see any question that the EOS 30D is using a different sensor / image pipeline than the EOS 20D can be quickly quashed with a single glance at this virtual identical result.
Indicated ISO sensitivity is on the horizontal axis of this graph, standard deviation of luminosity on the vertical axis. Chroma (color) noise graphIn addition to measuring luminance noise we now also measure chroma (color) noise. As you can see the D200's more 'film like' monochromatic noise appearance keeps chroma (color) noise to a minimum.
Indicated ISO sensitivity is on the horizontal axis of this graph, standard deviation of each of the red, green and blue channels are on the vertical axis. |
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