| 摘要 |
PURPOSE:To quicken the check by receiving the 0th order diffracted light from a reflected light from a recording face, detecting respectively the light intensity of two regions split in the direction of the minor axis to obtain a sum signal and a difference signal of each detection signal, comparing the difference signal at a proper detection level so as to switch the detection level of the sum signal based on the result of discrimination. CONSTITUTION:The + or - 1st order diffracted lights 14, 15 of the reflected light from a recorded face 6 are shut by a slit 11 and only the 0th order diffracted light 13 is collected on a detector. Let output signals of cells 12-a, 12-b be va, vb respectively, then an adder 17 obtains a sum signal 18 of (va+vb). Further, a subtractor 19 obtains a subtraction signal 20 of (va-vb). A pit error B and a film error C are detected by providing a detection level of + or -v1 to the difference signal but no foreign material A in the base is detected. That is, it is possible to discriminate the foreign material in the base from an error of a recorded face, and the dropout detection compatible with a recording and reproducing optical system using a circular beam is attained by forming the dropout detection level for discriminating a foreign material in the base as + or -v2 and the dropout detection level for discriminating an error of the recorded face as + or -v3 (v2>v3>0). |
