more pixels are better!

The weather is indeed lousy, so I have dug out the SNRs at ISO800 for 1% and 10% reflectance from DxO's database. The upshot is that in a multiple regression analysis pixel pitch explains about twice as much of the variation in low light SNR as when the camera was introduced (NB: NOT "when the sensor was designed", which I don't have), but both factors together explain much more than either alone.

The first thing to say is that this analysis is complicated by Nikon's shift to CMOS sensors, which produced a step change (the CMOS cameras have the ):

Camera Date Pixel Pitch SNR, ISO800, 1% SNR, ISO800, 10%

D70 Jan04 7.8 10dB 26dB
D80 Sep06 6.1 8dB 24dB
D40 Nov06 7.8 15dB 27dB
D40x Mar07 6.1 11dB 24dB
D300* Aug07 5.4 14dB 27dB
D3* Aug07 8.4 21dB 34dB
D90* Aug08 5.5 17dB 27dB

When thinking about the effects of pixel pitch vs technical progress, note that the two and a half years the D80 had over the D70 did not compensate for the smaller pixels, but the D40 only two months younger than the D80 but with the same pixel pitch as the D70, has + - two stops less noise in low light than either the D70 or the D80.

Whether better SNR in low light comes from bigger pixels or newer sensor designs, as a rule of thumb the lower the light the bigger the improvement. At 10% reflectance the D80 is "only" one stop worse than the D90, but at 1% it is 3 stops worse, and the D90 is a stop better than the D300 at 1% but the same at 10%. Among Canon designs the 10D (February 03, 7.2 micron pixels) had SNR at ISO800 of 26dB at 10% reflectance and 11dB at 1%, while the 50D (August 08, 4.7 micron pixels) also has SNR of 26dB at ISO800 and 10% reflectance but 15dB at ISO800 and 1% reflectance (more than 1 stop over the 10D).

If low light performance is important to you, is the D40 a bargain or what?