| 摘要 |
PURPOSE:To simplify the structure of the device and to miniaturized the device. CONSTITUTION:A photosensor 32 is provided between the liquid crystal cells ES1 and ES3 of a liquid crystal panel 16 of the front surface projection type display device which irradiates a screen 20 with the projecting light 22 from a light source 10 via a projecting lens 18 and displays a projected image 26 on the screen 20. The reflected light via the projecting lens 18 from the projected image 26 is received by this photosensor 32 and the focus is adjusted by moving the projecting lens 18 until the quantity of the received light is minimized. For example, a projecting lens moving mechanism 34 is so controlled by a control circuit 38 as to minimize the quantity of the light received by the photosensor 32. The light source for projection is commonly usable as the light source for focus adjustment in such a manner and, therefore, the need for optical systems for emission and receipt of IR rays independent from the optical system for projection is eliminated. |
