| 摘要 |
PURPOSE:To accurately observe a material to be measured on the upper surface of a board by providing a light transmission part in contact with the opening of a focusing optical system at a planar light source for emitting an illumination light toward the material. CONSTITUTION:Part (a) of a light emitted from a planar light source 9 is directly emitted perpendicularly or substantially perpendicularly to a mark 12. Part (b) of the light emitted to a vertical reflection surface 5 is emitted to the mark 12 at a large angle near a right angle. Part C1 of a light reflected on a reflection surface 6 is transmitted through a light transmission element 8, and emitted to the mark 12 at a considerably large angle. Further, part C2 of the light reflected on the surface 6 is emitted to the surface of the element 8, secondarily reflected on a reflection surface 7, then transmitted through the element 8, and emitted to the mark 12 at a small angle. |
