Method and apparatus for optically inspecting a mold for manufacturing ophthalmic lenses for possible mold defects

Abstract

A method for optically inspecting a mold () for manufacturing ophthalmic lenses such as contact lenses for possible mold defects, including: generating a set of images of the mold () for different azimuthal illumination angles (ϕ) using an illumination system () and an imaging system (), the latter being aligned such that its focal plane cuts through the mold () at a specific axial position along a center axis of the mold (); generating a focal plane image by averaging pixelwise over the set of images after having masked out in each image those regions that include direct specular reflections from the mold (); repeating the previous steps for one or a plurality of different axial positions of the focal plane such as to generate a plurality of different focal plane images; identifying one or more image features in the plurality of focal plane images indicative for a possible mold defect; determining for each identified image feature in which focal plane image the identified image feature appears sharpest; generating for each identified image feature a respective image section out of the respective sharpest focal plane containing the image feature; and generating a composed dark field image of the mold () by composing the respective image sections for each identified image feature, thus enabling to determine as to whether the possible defects of the mold () still allow the mold () to be used.