# Original description of point sources and point spread functions

I already asked this question in the Astronomy community, but there it was recommended to me to also try my luck here.

I would like to know the original description of point sources and point spread functions. They are well-known concepts (in particular in astronomy e.g.), but every source that I could find so far that discusses them doesn't mention who actually discovered or came up with them.

The closest thing that I found for now is the work by Airy, who mathematically described the diffraction pattern generated by a perfect optical system. So I guess that is very close. However, according to the wiki article, the phenomenon was described by Herschel at least seven years prior. But that is just regarding the outer rings of the diffraction pattern. So I would guess astronomers must have been aware of the blob-like appearance of poin sources even earlier.

Partial answer to get things started.

Point sources were a natural concept for mathematicians pondering waves, and the Huygens construction for a spherical wavefront generated by a point source is an expanding spherical shell with each point on the surface being a new point source.

Image source: The Fact Factor's Application of Huygens Wave Theory of Light but probably cropped from somewhere else.

But I wonder if you are really interested in the development of theory not of point sources, but of apertures. Apodization and point spread function go hand-in-hand; in a well-focused and diffraction-limited optical system for example, they are essentially Fourier transforms of each other.

In modern times we apodize all kinds of things, outside of optics as well, cf. Is it "common practice in Fourier transform spectroscopy to multiply the measured interferogram by an apodizing function"? If so, why? in Chemistry SE.

In advanced optical systems pushing limits of resolution like deep-UV optical photolithography scanners, the pupil of the lenses can be fitted with both amplitude and phase apodization (as can the illumination systems for the mask)

All of this taken together suggests to me that the history of Fourier optics may yield some helpful resources.

• Thanks a lot! This is very interesting and a great start.
– mapf
Commented Mar 23, 2023 at 9:11