A dynamic reflective spatial attenuator for use in an optical inspection apparatus. The attenuator takes the form of a two-dimensional micro-mechanical reflective array that, in the first operative position of a mirror element, reflects the desired scattered light toward a detector and, in the second operative position of a mirror element, reflects undesired scattered light into a light dump. The mirror array's fast response and flexibility allows for changes during mid-scan to increase the defect's or contaminant's signal relative to the substrate surface's signal.