| 摘要 |
PURPOSE:To enable to control pressure of a projection optical system without providing particularly a gas supply source as system environment of the projection optical device by a method wherein the projection optical device is so constructed as to make the device to be enabled to control of itself space to be controlled in the projection optical system. CONSTITUTION:When driving of motor 9 is started, an MPU (microprocessor unit) reads a detection signal 3a, and the fact that pressure of the chamber 1f of a projection lens 1 reached an objective value or not is judged. When it is judged. When it is judged as the objective value is reached, driving of the motor 9 is stopped. While when expansion of a bellows pump 8 reaches an up range during cource of the building up characteristic of a variation of magnification, the MPU closes an electromagnetic valve 5, and after linkage of the chamber 1f and the pump 8 is checked, an electromagnetic valve 12 is opened to make the pump to be leaked to the air. Then the MPU examines sizes of the detection signal 3a of a pressure sensor 3 and the detection signal 17a of a pressure sensor 17, and at the case when 3a<=17a, the motor 9 is driven to compress the pump 8. While, at the case when 3a>=17a, the pump 8 is expanded. At a point in time when the pressure difference becomes to zero, the valve 5 is released.
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