achromatic doublet

Aberrations, a lecture in optics.

Optics series Lecture — I
Optical Aberrations
delivered on 24 – 1 – 2017 — all optics series lectures can be accessed here. 

This lecture has been delivered in one of the honors class that I am teaching this semester. You will do really well to read the linked article on Optical path and Fermat’s principle which is not not intended as a honors lecture.

Optical systems are studied under two assumptions:

a. Object points do not lie far away from the axis of the optical system.

b. Rays taking part in image formation make a small angle with the axis of the optical system.

The domain of optics where the above two assumptions are valid is called as Paraxial optics. Paraxial systems are highly idealized and in reality they do not perfectly represent the situation. The consequential errors in image reconstruction are known as aberrations.

The paraxial assumption can be represented by truncating at the first term of the polynomial expansion of the sine function by the Maclaurin series.