Abstract

Image formation at out-of-focus planes has been the subject of several recent papers that explore the following issues: the focal shift effect, automatic focusing, understanding the properties of 3-D wave fields, and increasing the depth of focus. A simple way to analyze defocused imagery is to employ the Strehl (irradiance) ratio, which is defined as the ratio between the on-axis irradiance of the defocused point spread function (PSF), and the on-axis irradiance of the diffraction-limited PSF. Here, we apply the Strehl (irradiance) ratio to design a spatial filter that increases the depth of focus. We explain how the Strehl ratio, in the form of McCutchen's theorem, can be used to design a spatial filter to increase the depth of focus. We present computer simulated images to show the increment in focal depth.

© 1985 Optical Society of America