Back-of-the-envelope image resolution estimation using an aberrated Rayleigh criterion

In an optical imaging sensor (i.e., lens plus focal plane array), the critical output is the image itself, and quality of that image is a measure of the sensor's performance. Image quality is dependent on several terms such as the sensor-level point-spread function (PSF), sampling period, and signal-to-noise ratio. The sensor resolution is mainly dependent on the PSF, which is comprised of many aspects. Often, the resolution is determined by the diffraction-limited Rayleigh criterion; however, due to the blur contributions of the collecting optics wavefront errors, pixel size, etc., the sensor PSF is not often diffraction-limited. Here, we develop two simple back-of-the-envelope calculations that provide an estimate of a nondiffraction-limited imaging sensor PSF size based on the sensor-level required resolution. Moreover, an allocation based on this PSF size can be used to dole out an allotment to the various blur effects, e.g., wavefront error, during sensor-level design.