Aberrations
What are aberrations
and where do they come from?
In an idealized optical system, the paraxial approximation holds and the frequency of light is unimportant for its propagation through the system. In a real system, this is not true, as there are marginal rays and the frequency of light has an impact on its transmission through a system. The difference between the ideal system and a real system, is known as the aberration.
Aberrations can be classified into two types: