Usually in optical imaging, we call the specimen under an optical microscope “object” and the image formed at the CCD detector “image.” e object can be thought as composing of points, which is dimensionless, or at innitely high detail. e image, on the contrary, can be seen as composed of so-called “point spread functions” (PSFs). ese PSFs are the result of diraction, which makes a dimensionless point to have a nite size. e resolution of a microscope system is limited by the fact that (1) as the PSFs are with a nite size and (2) when two PSFs get too close with each other simultaneously, the sum of them cannot be discerned.