Reducing the physical size of a camera, even if the total number of pixels is maintained, inevitably reduces the quality of the images because of two fundamental properties of light itself. This technical article looks at diffraction, usually explained by considering light as waves. A future article will look at photon noise, explained by considering light as particles.
A simple rule-of-thumb is established for determining the “diffraction limited f-number” by relating this to pixel pitch on the sensor.
The earlier, pre-digital, criterion for diffraction limited aperture (based on required print sharpness) is revisited and considered to be still valid – perhaps with a little sharpening.