| 摘要 |
PURPOSE:To improve stability and accuracy in the measurement of pattern area rate in a light room by an apparatus wherein a spherical interference filter selectively transmissible for only the light of laser wavelength is provided in front of a photo detector for detecting the intensity of the reflected light from a printed plate. CONSTITUTION:An interference filter 11 having a characteristic as shown by a curve A is provided in front of a light receiving part 10 of a photo detector 7 to make only the light of laser wavelength transmissible therethrough. The interference filter is shaped into the spherical form which has a radius (r) with the light receiving surface being as the origin. This permits the reflected light to enter the interference filter at a nearly right angle even when a laser spot is scanned over a printed plate from one end to the other end, whereby a shift amount of the spherical characteristic can be restrained to the minimun and the intensity of the reflected laser beam can be made uniform all over the surface of the printed plate. Thus, only the light near the laser wavelength is allowed to pass through the filter and enter the light receiving part 10 without suffering significant influence from the external light, so that the measurement may be always carried out with stability and high accuracy. |
