Topic: Point Spread Function

The Point Spread Function is a transference function, present in every optical instrument.

The true nature of this isrealted to the physical properties of the electromagnetic waves.
Whenever an electromagnetic plane wave faces an obstacle suffers what we call diffraction. Diffraction of a plane wave occurs always and the approximation where $\lambda << d$ results in no diffraction effect is not enough for describing the phenomenom in the focal plane of an optical telescope.