| 摘要 |
PURPOSE:To facilitate focus adjusting operation and to improve the accuracy of the setting of the best focus position by providing the focus adjusting mechanism of a projection lens system and an automatic adjusting mechanism which measures the distance between a projection lens and a screen with an invisible light beam and adjust the focus of the projection lens system to the best focus position automatically. CONSTITUTION:An infrared-ray emission part 107 emits infrared rays, which are received by an infrared-ray photodetection part 106 to measure the distance between the projection lens and screen; and a driving signal for an automatic focus motor 101 is generated by an AF, CONT, IC 102 according to the distance to drive the motor, thereby moving forth or back the projection lens 103. The distance between the projection lens and screen is adjusted automatically to the focal length of the projection lens and light which is modulated by an optical modulation block 104 according to video information is enlarged and projected by the projection lens 103 to form a sharp image on the screen 108. Consequently, the operability and accuracy of the focus adjustment are improved drastically. |
