Linked from
The 17 pages that link to Optical resolution, each with the reason it gives.
DiffractionRelated: Diffraction limits how finely an optical system can resolve objects.
Image resolutionRelated: A sensor's pixel grid cannot recover detail the optics fail to resolve.
Airy diskRelated: The disk’s size limits how closely two point sources can be distinguished.
Image scannerRelated: It sets the detail the scanner can capture before software interpolation.