D3 sensor efficiency

Started Nov 18, 2007 | Discussions thread
cpw Regular Member • Posts: 313
Re: Measurement improvement

ejmartin wrote:

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.

Hello Emil,

That's awesome! That takes care of the nonuniformities. Also, turning this around, you now have data both with and without the nonuniformites, and so have a pretty good idea how the D3's CMOS sensor is doing in this regard in keeping the nonuniformities down.

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

So, assuming that the D3 and 1Dmk3 have similar efficiencies, and so if we extrapolate a little and compare the D3's pixel area to that of the 5D/1Dmk2 (which got to about 80,000 e- fullwell, from PIXmantra above and at Roger's website), maybe the D3 will go higher than this. It would be interesting to see in future measurements.

Take care,

Chris

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