Fig. 1.

Optical resolution is defined as the smallest distance between two points on a specimen that can be distinguished as two separate entities. Assuming the blur introduced by the microscope to be Gaussian with a known standard deviation, the resolution is defined as a distance between points that equals at least one standard deviation. For distances smaller or equal one standard deviation, the observed pattern, i.e., sum of two Gaussian functions (green and blue) has an appearance of a pseudo-Gaussian with one maximum (magenta).