Abstract: An automatic focus adjusting system for a surface inspection microscope including a sheet setting stage, a microscope for observing a sheet surface set on the stage, a television camera for picking up an image observed by the microscope and a focus adjusting system. The system irradiates the back or front of an optically transparent sheet set on the stage creating an image on the front surface of the sheet. The image's contrast varies depending on the inner physical structure of the sheet. The television camera's video signals are processed by a focus evaluation circuit. The image contrast of the sheet's front surface image generates a contrast frequency allowing the focus evaluation circuit to calculate the focus evaluation degree. The system automatically adjusts the stage and compares the present focus evaluation degree with the prior focus evaluation degree.

Abstract: A surface inspection apparatus having a microscope and a television camera is disclosed. The inspection apparatus samples a signal portion from a horizontal scanning portions of the video signal produced by the television camera, compares the instantaneous voltages of a filtered signal of said sampled portion removing low-frequency components with a reference voltage, counts the number of pulses constituted from the high level portions of said filtered signal higher than said reference voltage sequentially moves the focal point of the microscope step by step relative to the object surface, compares the present pulse count with the previous pulse count thereof at just prior step of the moving of the focal point, and decides the focal point in the position corresponding to the maximum number of pulses to control the moving of the focal point for correctly setting the focal point in said corresponding position.