You said you "haven't heard anything so confusing in a long time". I'm afraid you are, confused that is, and you also managed to get this thread off-topic. Oh well, what's new.
Erik's three camera models do have virtually similar physical sensor sizes but with quite different sensel pitches. The sensel pitch has shrunk with each generation, but with that, the on-sensor resolution has increased (assuming the same lens performance and similar AA-filter characteristics).
As do mine, Bart. I've been quite clear all along that my comparisons relate to equal size sensors with a different pixel pitch. No confusion on my part, old chap.
Whenever a DSLR manufacturer significantly raises the pixel count of its latest model we seem to get the same old concerns about diffraction, raised again and again. Will the extra pixels serve any purpose when the camera is used above F5.6 or F8? Is there a cut-off point at a particular F stop, beyond which no further resolution can be gleaned however large the ouput size?
Erik's graph demostrates that even a camera with the very high pixel density of the SLT-A77, which is equivalent to a 55mp full-frame sensor of the same pixel density, can show a resolution edge at all apertures up to, and including F16
, compared with a camera of half the pixel count, such as the Alpha 700. The graph also shows that F22 is the point where no further resolution benefits are to be had from the 24mp A77, compared with Alpha 700.
Now you are quite right to point out, Bart, that the differences in pixel densities between the 12.25mp Alpha 700 and the 24.3mp ALT-A77, are greater than the differences between the Canon 40D and 50D. In the case of the two Sony cameras, one has double the pixel count of the other. In the case of the two Canon cameras, one has only 50% greater pixel-count than the other.
One should therefore not presume from Erik's graph that a sensor with a lower pixel density than the A77, such as the Canon 50D, equivalent to a 38 or 39mp full frame, will also show a resolution edge at F16. And indeed I haven't presumed that. I carried out my own tests back in September 2008, and discovered for myself that even a camera with a modest 50% increase in pixel count over another of fairly similar pixel density to the Alpha 700, will show a very slight resolution edge at F16. (Alpha 700 roughly equivalent to 28mp full-frame; 40D roughly equivalent to 25.6mp. That's close enough).
The question that now remains, will a camera such as the D800 with 3x the pixel count of a D3 show any resolution advantage whatsoever at F32? I doubt it, but I'm fairly confident that the D800 will show a very slight advantage at F22, and a more significant advantage at F16, compared with the D3.
Enjoy your Dutch Herring, Bart.