Depth of focus analysis of optical systems using tunable aperture stops with a moderate level of absorption

The size of the aperture stop of a lens is a major parameter to define, e.g., the depth of focus of an optical imaging system. In conventional systems, totally absorbing apertures are generally assumed. Their optical performance can be easily described by a geometric ray model. We propose an extended model to estimate the depth of focus with respect to a nontotally absorbing circular aperture, which may correspond to new concepts for tunable apertures, in particular for micro-optical systems. We present specifications to analyze and optimize the performance of those systems and verify the theoretical model by experimental depth of focus measurements with a partly transparent aperture.