| 摘要 |
PURPOSE:To exercise focusing control by detecting a focus error without using any pinhole, etc., by controlling the movement of a condenser lens corresponding to a difference in oscillation output change among respective semiconductor light sources by returning projected beams from plural semiconductor light sources, shifted in the optical-axis direction, to the semiconductor light sources again. CONSTITUTION:Focusing semiconductor light sources 21a and 21b have light projection flanks shifted symmetrically from that of reading semiconductor light source 21c in the light-axis direction and spot light beams arriving from light sources 21a and 21b by way of condenser lens 4 and reflected by disk 7 are incident to light sources 21a and 21b. Through oscillations corresponding to the focusing state of lens 7, light sources 21a and 21b vary in light intensity and obtain the maximums respectively in focusing. In this maximum state, the output of differential amplifier 15 generating an output difference between photo detectors 23a and 23b detecting the light intensity values of light sourccs 21a and 21b is zero. Therefore, a focus error detection signal exercising feedback control over lens 7 in generated without using any pinhole hard to adjust from amplifier 15 and influenced by a temperature, etc., and a secure automatic focus adjustment can be made with a simple optical system. |
