an optical comparator in which images of a master component and a sample component are inspected by comparison of the images that are projected in a moving , abutting , merging , mirror image , a limited area of the components being viewed in a scanning illumination at a controlled rate for full viewing coverage . the components are held in a sliding tray with means for rapidly changing the component to be inspected , whie maintaining precise alignment . a closely directed light source and efficient cooling device permits prolonged operation of the apparatus , and instant access to mark defective portions of the component is provided without interrupting viewing . the location of each defective portion is marked on a reference chart for use in a viewer which provides a composite image of the chart and component in proper registration for easy identification of the faults .