| 摘要 |
PURPOSE:To decrease the crossing speed at a just focus position with a simple constitution and to perform secure automatic focusing operation by fitting focus iron pieces to the flank of the cylindrical part of an objective lens holder. CONSTITUTION:The focus iron pieces 19 and 20 which generate focus-directional force to the objective holder 6 are fitted on the flank of the cylindrical part of the holder 6 and normally positioned in a magnetic gap. When the iron pieces 19 and 20 are in the magnetic gap, no force operates on the iron pieces 19 and 20 in very direction, but when the lens 14 approaches to the just forcus position and moves out of the gap, attractive force which attracts the lens back into the gap operates on the iron pieces 19 and 20. This attractive force serves as braking force to decrease the crossing speed of the lens at the just focus position, so that the automatic focusing operation is performed securely without any failure. |
