OPTICAL INFORMATION READER

摘要

PURPOSE:To attain focus control with high accuracy by allowing a condenser lens placed between a beam deflector and a photodetector to condense a beam and placing a light shielding substance formed by coating one side of a light transmitting medium having >=1.0 refractive index with a light beam opaque medium on the focused position to increase the difference of luminous amount of the photodetector with a short optical length and a focal point shift. CONSTITUTION:A beam condensing lens 7 is placed at a position of the front side of the photodetector 6, and the beam is condensed at a position of the front side of the photodetector by the lens 7. The beam shielding substance 9 made of a substance transparent to the beam having >=1.0 refractive index and formed with the beam shielding film on a part of the one side and having a prescribed thickness is provided to the beam condensing point 8. Since the beam shielding substance is arranged at the light condensing position of the condenser lens, the minimum beam diameter of the condenser lens is decreased to a value correspnding to a fraction of conventional values, the luminous amount difference is increased for the photodetector with respect to a minute focal point shift, and the focus control of a minute amount is attained.