Description Consider two monochromatic point sources, which are very far from a thin lens.
The wavelength of the light from each source is and the angular separation of the sources is . The diameter and focal length of the lens are, respectively, D and f . In this module there is an observation screen in the back focal plane of the lens, and the irradiance in this plane, call it , is calculated and depicted on the screen. Calculations Let us assume that the point sources are symmetrically position in angle about the optical axis of the lens.