This project was inspired by an interest in observational astronomy. Its goal is to demonstrate important concepts and techniques of astronomical observation through simple laboratory experiments.

In astronomy, one often works with light from "point sources." These are simply sources of light, like stars, with negligible dimensions compared to their distance from us. A key concept in all types of optical imaging is the point spread function, or PSF, which is the image of a point source created by the optical system. In theory, the PSF of a point source is a point image, but aberrations and diffraction make this impossible to achieve in practice. Aberrations can be eliminated with perfect optics that are perfectly aligned, but diffraction cannot be eliminated, only reduced. As a consequence of diffraction, the PSF for light passed through a circular aperture is an "Airy pattern," a central disk of light surrounded by concentric rings. The size of the pattern is inversely dependent on the aperture; a larger telescope has less diffraction.

Our initial experiment consisted of determining the PSF of a simulated star by imaging it with a consumer camera, the Sony Mavica FD73, at 10X zoom setting. The "star" was created by illuminating a 100 micron pinhole with red light from a HeNe laser. With the camera placed 9.5 m from the pinhole the angular diameter of the "star" is 2.2 arcseconds. While this is still considerably larger than the largest actual star (Betelgeuse, 0.05 arcsec), it is sufficiently small for this experiment.

The figures below show the observed PSF as an expanded image and as a plot of pixel intensity values. The size of each pixel is 5.6x5.6 microns. The PSF is quite symmetric, and only about 2.5 times the estimated diameter of the Airy disk. We can conclude that the optics of the camera are excellent, and its imaging capability is close to the diffraction limit.

In the future we hope to use these results to explore spectroscopy of a simulated star by illuminating the pinhole with light from a spectral lamp and imaging this through a diffraction grating.