D3 sensor efficiency

Started Nov 18, 2007 | Discussions thread
OP ejmartin Veteran Member • Posts: 6,274
Measurement improvement

OK, I went back and did a somewhat more thorough job of analyzing available raw data. My previous methodology had somewhat overestimated the noise, leading to an underestimate of the efficiency of the D3 sensor. Before I was measuring the std dev of small uniform patches. This time, I used the difference of the two green subarrays of the sensor's Bayer array to calculate the noise, which should be more immune to subtle tonal gradients which were a systematic error in the initial measurement using standard deviations of small patches; this technique is much more robust since overall tonal gradients cancel between the two subarrays. I analyzed raw files found on the net from four different D3 bodies, at least one of which is a production model; they were all remarkably consistent with one another.

The result: the D3 collects 15.4 electrons per 12-bit raw level at ISO 200, or about 63,000 electrons at raw saturation for this ISO (and about 18% better than my initial rough measurement). This is to be compared with the 1Dmk3, which collects 10.2 electrons/12-bit raw level at this ISO, or a little over 39,000 electrons at raw saturation. The D3 collects about 50% more photons per pixel assuming that the calibration of ISO gain between the two cameras is comparable. Since S/N ratio goes as the square root of the photoelectron count, the D3 has about a 1/4 stop advantage over the 1Dmk3 at the pixel level in midtones and highlights at a given ISO; the two are about equal in shadows, since read noise is about the same.

If we compare the efficiency per unit of sensor area, however, the advantage largely disappears: The D3 is only about 5% less noisy for given sensor area (as for instance you would find by shooting the two at the same focal length; the D3 would just have a larger field of view).
--
emil
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http://theory.uchicago.edu/~ejm/pix/20d/

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