| 摘要 |
PURPOSE:To make small the unit in size, by forming imagewise on the photodetector and decreasing the distance between the photodetector and the converging lens, through the provision of optical element consisting of the combination of convex or concave lenses in the optical path of reflection beam. CONSTITUTION:The incident beam 2 through the converging lens 4 forms the focus on a point on the recording disc outside the optical axis (m) and the reflection beam 5 passes through the coverging lens 4 and the convex lens 8 inserted in the optical path. The image point P1 without the convex lens 8a moves to P2. To extend the diameter of the spot of the point P2, when the light beam passes through the convex lens 8b, the image point moves to P3 and spot is produced on the photodetector 6. Although the sensitivity of focus is kept constant with the insertion of the lens systems 8a, 8b, since the distance l1 is reduced, the unit is made small in size. |
