I. Introduction
For a long time, the term “resolution” was related to optics and, in particular, to the diffraction limitation described by Rayleigh criterion. Optical apertures with finite dimensions feature point-spread functions of finite extension. The relation between the aperture size and the extension of the related point-spread function is governed by the Heisenberg uncertainty principle featuring any Fourier transform pair. The same applies to observation time windows of finite duration and the related spectral purity as well as band limited spectral data and the related temporal resolution.