Patent ID: 8204298
Filing Date: 2012-06-19
Classification: G01N

Abstract:
1. A method of determining a desired axial location for placement of an imageable object in an inspection optical system defining an optical axis, comprising: placing an axially-translatable object within a field of view of the inspection optical system; axially translating the object sequentially to a plurality of axial locations along the optical axis; acquiring a plurality of images of the translated object, each of the plurality of images being associated with a respective axial location along the optical axis; determining a plurality of lateral-location-dependent figures of merit for the plurality of images using a processor, each of the plurality of lateral-location-dependent figures of merit being associated with a respective axial location along the optical axis; identifying a plurality of worst image quality values from the plurality of lateral-location-dependent figures of merit using the processor, each of the plurality of worst image quality values being associated with a respective axial location along the optical axis; determining a best worst image quality value from the plurality of worst image quality values; associating the best worst image quality value with a desired axial location along the optical axis, based on the associations between the worst image quality values and the axial locations along the optical axis; and selecting the desired axial location, wherein the desired axial location has a reduced variation in image quality across a field of view.