Abstract: Disclosed is method of adjusting a microscope aperture to obtain the highest possible defect detection rate for a particular type of target. According to the method, an operator obtains an image of a calibration target and visually analyzes the image for defects. The operator then uses a defect detection process to analyze the image to obtain another set of defect information. This second set of defect information is compared with the visually obtained defect information to determine the accuracy of the defect detection performed by the defect detection process: a perfect match indicates 100% accurate defect detection. The operator then changes the aperture diameter and repeats the process to obtain a second set of defect information. This second set of defect information is, like the first set, compared with the visually obtained defect information. This process is repeated as many times as are necessary to determine which aperture diameter results in the highest defect detection rate.