| 摘要 |
PURPOSE:To use a plastic lens for an optical system by adopting a TTL system in which a projecting optical system and a focusing optical system are common. CONSTITUTION:An image reproduced on a liquid crystal panel 1 is projected on a screen 4 by an illuminating system 2 and the projecting optical system 3. A part of light beam from the picture reproduced on the screen 4 pass through the projecting optical system 3 again and return to the liquid crystal panel 1. The part of the light beam i5 made incident on a focusing state detecting device 6 through a reflecting mirror 7 arranged between the projecting optical system 3 and the liquid crystal panel 1. Relation among the projecting optical system 3, the liquid crystal panel, and the screen 4 is constituted in a state where the luminous flux introduced in the focusing state detecting device 6 is to be the luminous flux on the peripheral part of the liquid crystal panel 1 among the luminous fluxes guided from the liquid crystal panel 1 to the screen 4. Thus, even through the focal length of the projecting optical system 3 is changed by temperature change, the liquid crystal panel 1 can, 5 held in the focusing state with respect to the screen 4. |
