| 摘要 |
PURPOSE:To enable measurement of a pattern area rate with about the same precision as a PS plate by a construction wherein a diffusing means of diffusedly reflecting an irradiation light to a lithographic plate to be measured and passing the same is disposed in front to a light source. CONSTITUTION:Lights from halogen lamps 2-1 to 2-n are applied to a lithographic plate 1 to be measured through a diffusing plate 4 and reflected lights enter a CCD camera 3. By passing through the diffusing plate 4, the lights from the lamps 2-1 to 2-n are reflected diffusedly to be averaged and then applied to the lithographic plate 1. In the case when a water-stopped lithographic plate is used as the plate 1, the lights reflected diffusedly to the averaged by passing through the diffusing plate 4 are applied onto the surface of the plate, and therefore it is eliminated that the reflected lights from the parts around the points of intersection with the optical axis lines L-1 to L-n of the lamps 2-1 to 2-n become strong. Consequently an output voltage value of the camera 3 shifts in a sphere of an upper limit voltage value or below, and precise measurement of a pattern area rate is performed on the basis of the output voltage value of the camera 3. |
