Diffraction is explored in detail in Making Sharp Images.
This series is with the 16-megapixel Nikon D4 and the Zeiss 100mm f/2 Makro-Planar, a world-class lens.
Stopping down too far begins to degrade contrast at first, then starts destroying resolution. Diffraction doesn’t care which camera is used or its sensor resolution, but a high-resolution sensor suffers more in terms of per-pixel quality, because diffraction blurs the resolved spot size more relative to the size of the sensor photosites, “spilling over” a single photosite, reducing the contrast and then the resolved detail.
With the Nikon D4, the pixel area is more than twice as large as on the Nikon D800, and thus diffraction is less of an issue (per pixel) on the D4.
Article continues for subscribers...
diglloyd Advanced Photography includes hundreds of pages of exclusive coverage and high resolution, Retina-grade example pictures detailing Canon and Nikon DSLR bodies and their lenses, with in-depth analysis of sharpness and contrast, color, bokeh, vignetting, distortion, MTF, and flare. Also included is a wealth of in-context technique and workflow insight. Since 2006, diglloyd Advanced Photography is the authoritative review and on-line reference for discerning Canon and Nikon shooters. Subscriptions cost $ per year.