An
optical aberration is a departure of the performance of an
optical system from the predictions of
paraxial optics. In an imaging system, it occurs when
light from one point of an object does not converge into (or does not diverge from) a single point after transmission through the system. Aberrations occur because the simple paraxial theory is not a completely accurate model of the effect of an optical system on light, rather than due to flaws in the optical elements.