A novel fibre optic illuminator with a spatially variable output light intensity distribution was built. By the aid of a semitransparent mirror and lens optics, this light distribution was projected onto the object to be imaged directly from the direction of observation. It was found that very homogeneous intensity distributions can be achieved in the image plane of the camera by compensating the cosine-fourth law of the camera optics. This allows for a constant, position independent threshold setting for digitizing the image. We will report on very favourable results obtained for the illumination of hybrid circuit boards and wafer surfaces. The influence of object size, surface quality (diffuse or highly reflective) and polarized light will be discussed.
E Switzerland Morger,
"A Novel Fibre Optic Illuminator for Machine Vision", Proc. SPIE 0654, Automatic Optical Inspection, (17 November 1986); doi: 10.1117/12.938284; https://doi.org/10.1117/12.938284