METHOD FOR ILLUMINATING LIGHT VISUAL FIELD AND DARK VISUAL FIELD

PURPOSE:To obtain the merits of both the illumination of light visual field and the illumination of dark visual field by which not only the defect of a surface but also the defect of a bottom part can be caught by radiating light to a boundary between the light visual field and the dark,visual field, that is, in such a way that an illuminating angle is a specified angle against a direction perpendicular to the upper surface of a processed substance. CONSTITUTION:The light 1 from a light source irradiates a substance to be illuminated 2 within a range from 5 deg. to 15 deg., and obtained reflected light 3 is allowed to get to the peripheral part of a lens 4 for photographing. In such a case, when the illuminating angle is set within 5 deg., the illumination of light visual field that the reflected light 3 irradiating the substance 2 directly enters the lens 4 is attained, whereby the defect of the bottom part is caught but the defect of the surface is not caught because it is not distinguished from a normal part. On the contrary, when it is set to >=15 deg., the illumination of dark visual field that the reflected light 3 irradiating the substance 2 does not directly enter the lens 4 is attained, whereby the defect of the surface is caught but the defect of the bottom part is not caught because it is hidden. Therefore, not only the defect of the surface but also the defect of the bottom part are caught by setting the illuminating angle to 5-15 deg..