Light Transmitted by Very Small Pinholes

Abstract

When an optical system is illuminated by a pinhole of unresolvable size, light flux is lost by diffraction at the pinhole if the usual conditions for full-cone illumination are satisfied. Formulas are given for this loss and it is shown that for a pinhole small enough to appear as a true point source an illuminating cone of three or more times the angle of the cone accepted by the optical system must be used to avoid substantial light loss. Experimental confirmation is given.