How does the D3 achieve such high ISO?

Started Feb 17, 2008 | Discussions thread
ejmartin Veteran Member • Posts: 6,274
Re: Who doesn't get it

DSPographer wrote:

Sensor noise for Canon and and Nikon D-SLR cameras comes from the
photosite pre-amplifier not from dark leakage (dark leakage is
negligible for exposures faster than 1s). This means that sensor
noise is independant of photosite area so bigger photosites are more
sensitive.

With respect to read noise, I was making an empirical observation.

Aas an extereme example, the Panasonic FZ50 has 2µ pixels and a read noise of 2.3 electrons at ISO 100. The Canon 1D3 has 7.2µ pixels and a read noise of 23 electrons at ISO 100. It takes 13 FZ50 pixels to make the same collection area as the 1D3; combining their noise as independent fluctuations would yield an aggregate read noise of less than 9 electrons, less than half that of the 1D3. The 40D has read noise of 17 electrons at ISO 100. Scaling by the pixel size, 7.2/5.7, to refer this noise to a per area basis, this is slightly less than the 1D3's read noise on a per area basis.

I haven't looked at the data for a wide variety of cameras, but there is somewhat of a trend for low ISO read noise to vary with pixel size. For high ISO, I agree that there seems to be something of a wall at about 4 electrons of read noise at ISO 1600 that seems to be independent of pixel size for the last couple of generations of 1-series cameras.

So there will be a deteriment to smaller pixels in shadow noise for high ISO; for midtones and highlights where photon noise dominates, there is no penalty within a wide range of pixel sizes, as the example of the 40D vs 1D3 shows -- they collect the same amount of light per unit area of sensor, while the 40D has 60% higher pixel density. Thus photon noise at fixed spatial frequency (lines per mm) is the same for these two cameras.

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