| 摘要 |
Light from a light source (58) is shaped into a linear parallel light beam by a lens (59) and directed to a beam splitter (60). A half of the incident light is reflected off the beam splitter (60) and made to vertically fall on a linear area on the surface of an optical disc (65), and the other half is transmitted through the beam splitter (60) and made to obliquely fall on the linear area on the surface of the optical disc (65). The amount of light vertically falling on the surface of the optical disc (65) is detected by a first camera (62). The incident light beam and the reflected light beam are both vertical to the surface of the optical disc (65). Consequently, even if there is a large defect on the surface, the first camera (62) generates no virtual image, thereby enabling accurate measurement of the defect size.
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