| 摘要 |
PURPOSE:To enhance the accuracy of punching position of a center hole of mold for high density recording original record discs by providing an automatic focusing means to an optical microscope which observes over the turntable disposed with a holing tooling. CONSTITUTION:At the time of reproducing a large volume of records from a high density recording original record disc, a mold for the original record disc is made and this is placed on a turntable which is disposed at its center with a holing tooling and while the signal tracks of the mold is being observed by the use of an optical microscope provided with an automatic focusing device, the central holing of the mold is performed. The automatic focusing device detects the capacity between the metal disc 5 at the lens end and the mold surface, detects the change in the capacity with frequencies and drives a lens 9 with a voice coil type driver. Hence, the signal tracks may be observed at a high magnification without taking deep the focal depth of the lens and therefore the accuracy of the center hole may be considerably increased. |
