more pixels are better!

I apologise if I have misunderstood what folk meant or quoted anything out of context.

Here is a link to the relationship between SNR and exposure: http://www.microscopyu.com/tutorials/java/digitalimaging/signaltonoise/index.html

Nikon allergic folk can find the same information on the Olympus site or on the original Florida State U site.

The key point the graphs make is that you need a lot of light to make sensors photon-noise limited, ie, to make it true that SNR is related to total sensor area, rather than to the size of individual photosites.

Improvements in sensor design are a factor, but DxO's data show that they have not been sufficient to outweigh the effects of increased pixel density: SNRs have been falling steadily over the last few years. From their graphs "normalised" to constant pixel pitch it is clear that SNRs have gone up 3-6 dB because of improved sensor design. That is nice - but it means that if the manufacturers had not increased pixel numbers we could have had 1-2 stops more ISO head room, instead of a nett effect of nothing which is what we got!

It should, however, be noted that DxO's graphs of SNR vs date are all at 18% reflectance, which is quite a lot of light - roughly, the centre of the histogram. Noise is not such a big deal at the centre of the histogram, and the question is what has happened down the left hand end. If the weather here stays miserable I will re-plot the SNR vs date graphs using SNRs for low light and post the results.