| 摘要 |
PURPOSE:To correct automatically a focal variation caused by a temperature variation, which a projection lens has essentially, by using a spacer member which has been formed by an organic high polymer material, etc. having a high expansion coefficient. CONSTITUTION:When a temperature rises, a spacer member made of a high expansion coefficient material expands, and its length stretches. A pressing force generated by an expansion of a spacer member 15 is pretty larger than a pressing force of a pressurized spring 17, therefore, a lens holder 13 is pushed aside against a pressure of the pressurized spring 17, and an interval between the lens holder 13 and a fitting plate 14 is widened by a very small quantity. Accordingly, an interval between a projection lens 11, and a face plate EP of a CRT is also opened by a very small quantity. On the contrary, when a temperature falls, the spacer member 15 contracts, and in this case, by a pressing force of the pressurized spring 17, the lens holder 13 is pushed aside to the CRT side. In this way, an out-of-focus on a screen caused by a variation of a focal distance of the projection lens 11, which follows a temperature variation is corrected automatically. |
