I recently found this YouTube video in which the inventor of the CMOS image sensor (Dr. Eric Fossum) admits current pixels are smaller than the diffraction limit of green light and therefore higher pixel count does not really allow you to see the image better. The higher pixel count is just a marketing advantage. Look at section 38:00 to 45:28.
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I should note that Dr. Fossum says the diffraction limit of green light at f 2.8 is 4 microns and we now commonly can make sensors with 1.1 to 2.2 micron pixels and sensors with less than a micron pixel are coming soon. So each point of light as best as we can focus it now covers more than one pixel. Thus, once you make pixels smaller than the diffraction limit of your lens you really do not gain any increased resolution.
Here is my question: If the upcoming D400 is really 24 megapixels and the upcoming D800 is really 36 megapixels, will the size of those sensor pixels be so much lower than the diffraction limit of Nikon glass that the increased pixels won't really produce increased resolution? I know we will have to wait for production samples to test the resolution of the new cameras and it will depend upon the software processing the data from the sensor but I thought it interesting to see the inventor of the CMOS image sensor admit increased megapixels are more a marketing ploy than a real improvement in resolution.