Compare 3 top-end cameras:
Camera | Format | MPixel | Pixel Pitch |
Pentax K-5 | APS-C | 16Mp | 4.75 µm |
Canon 1D IV | APS-H | 15Mp | 5.7 µm |
Nikon D3x | FF | 24Mp | 5.9 µm |
DxOMark - Compare sensors
While the price difference is enormous, what is also noticeable is the relatively weak low ISO performance of the Canon (the 7D is similar).
The K-5 has the smallest pixel pitch. When the Screen tab (to compare sensel-to-sensel performance, regardless of Mp) is used in the DxO SNR 18% chart, the sensel performance is close for all three. If the Print tab is used (normalised to 8Mp output size so that the better noise performance of extra Mp are accounted for when producing a fixed size 8"x12" printout), the Nixon D3x, with its 24Mp, powers ahead. But SNR 18% is for the typical exposure level in a well exposed shot, so this is mid-tone noise.
When looking at the DR, where the saturation level is compared to the noise floor, the situation changes. Under the Screen tab, the K-5 sensel, although having the smallest sensel pitch, is the best performer at ISO400 and below, due to its new technology. The Nikon, under the Print tab, is now similar to K-5, due to more Mp. The Canon is superior to both from about ISO 2500 and above, but at low ISO, its DR performance collapses.
Roger Clark mentions how the
intrinsic read noise of the 1D IV at high ISO has set a new standard for performance: 1.7 electrons. With its full well (saturation) capacity of 55,6000 electrons per sensel, he works out the sensor's DR as:
Sensor dynamic range = 55600/1.7 = 32700 = 15.0 stops (log32700/log2).
But this in not the camera's low-ISO DR, because the read noise rises to 22.2 electrons @ ISO100 with the DR now: 55600/22.2 = 2504 = 11.3 stops. This is similar to DxO's DR value under the Screen tab: 11.46 stops @ ISO100 (indicated).
In his Conclusion, he states:
Dynamic range is still limited to a little over 11-stops, apparently by downstream electronics that must process the data extremely fast (at 10 frames per second; that is over 160 megapixels/second). I would like to see a camera option that used a slow 16-bit A/D converter and low noise amplifiers to deliver data with the full capability of the sensor, which is 15 stops. Even if it took 10 seconds to read out the sensor (longer readout times are used in scientific applications), there are situations where high dynamic range imaging would benefit. Clarkvision.com: Canon 1D Mark IV Sensor Analysis
Now compare the DR of 3 other Canon models, under the DxO Screen tab:
5D II
60D
7D
At the single sensel level, all these cameras' DR only reaches about 11 stops @ISO100. So I don't think Roger Clark's explanation of the relatively poor low ISO DR of the 1D IV is the reason.
DxOMark - Compare sensors
So it seems that Canon has made a design decision that 11 stops DR performance for a sensel is sufficient. Just don't go boosting your shadows too far with a Canon DSLR, if you've shot at a low ISO hoping to maximise performance.
Dan.
Last edited by dosdan; 12-29-2010 at 04:15 AM.