Direct determination of f-number by using Ronchi test

A method to determine f-number for an imaging system is discussed. This method uses Ronchi test and is different in that the value of f-number of the system can be determined without depending on any particular parameters. Two different sizes of aperture for a common system were investigated and the corresponding f-numbers were compared with those calculated by a lens design software. In addition, the determined f-numbers are proved to be consistent with other values obtained in this study.