| 摘要 |
PURPOSE:To correct automatically a focal variation caused by a temperature variation, which a projection lens has essentially, by interposing a temperature sensitive member made of a shape memory alloy, between the projection lens and a lens fitting plate. CONSTITUTION:A temperature sensitive member 15 is deformed by a pressing force of a bias spring 17, but when an ambient temperature rises, it is shifted in the shape returning direction, therefore, a lens holder 13 is pushed and moved in the left direction by an increase quantity of a size W against the pressing force of the bias spring 17. A projection lens 11 moves to the left side by an increase quantity of a size W, and an interval between the projection lens 11 and a face plate FP of a CRT increases by a very small quantity. In this way, an out-of-focus on a screen caused by an increase of a focal distance caused by a temperature rise is corrected, and a good image formation state can always be held. Next, when a temperature falls, the temperature sensitive member 15 is deformed by a pressing force of the bias spring 17 and the size W decreases. Accordingly, an out-of-focus on the screen caused by a reduction of a focal distance due to a temperature fall can be corrected. |
