| 摘要 |
A curved reflector of electro-magnetic radiation formed of an elastic, imperforate reflective membrane utilizes a partial vacuum to provide the curvature to the membrane. The device for controlling the evacuation of the housing can be supported within the reflector housing in an adjustable manner to set the control device at a location corresponding to a predetermined deflection of the membrane below a reference plane, and thereby, to permit the focal length of the reflector to be varied. The control device can comprise a membrane contact surface surrounding an orifice which controls, with the interior surface of the membrane, fluid communication between the housing interior and the evacuation mechanism. Other control devices include an electrical limit switch, a light source and sensor, a capacitor or inductor sensing arrangement and a magnetic field sensing arrangement. The membrane can be releasably coupled to the housing via springs to facilitate replacement thereof.
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