Diffraction Images of Circular Self-Radiant Disks

The diffraction image formed by an Airy-type objective when the object is a circular, uniformly self-radiant disk is found to exhibit the phenomenon of a secondary Airy disk when the radius of the object is near 1.2 Airy units. The time-averaged irradiance in the diffraction image is presented for radii up to 4 Airy units. A separate expression for the irradiance at the geometrical radius in the image shows that as the object becomes very large the value of this irradiance approaches one-half that at the center of the image.