An optical inspection system with an improved illumination system. First lens region 10 includes a plurality of first projections 172. The copper diffusion barrier layer may be removed using a different technique. The head holders are formed to be movable parallel to a sub scanning direction, irrespective of the rotation angles thereof. Other filters may be used and a filter is selected based upon the noise and vibration measurements made by the analyzers 32, 34, 36, and 38. The present invention provides a coated tablet characterized in that an uncoated tablet containing a drug having a guanidino group has been coated with a polyvinyl alcohol for film coating which comprises polyvinyl alcohol, acrylic acid, and methyl methacrylate.