| 摘要 |
<p>955, 741. Photo-electric exposure control. A. C. COUTANT. Sept. 26, 1961 [Sept. 29, 1960], No. 34392/61. Heading G1A. [Also in Divisions G2 and G3] In an automatic control system for an astronomical telescope, photographic camera or cinematographic camera, an attenuating device is interposed between a lens and an observer's eye or a sensitive film and the position of the attenuating device is controlled so as to maintain a predetermined light intensity at the eye or on the film. As shown, Fig.2, a film 9 is exposed through a lens 6 and a rotatable sensitometric wedge 3 in the form of a disc is interposed in the light path to the film. A partially reflecting aluminised mirror 8 is positioned behind the wedge and reflects 20% of the total light passing through the wedge on to resistive type photo-cell 7 the output of which, through a reversing relay 10, controls the energization of a motor 4, coupled through a reducing gear to the wedge 3, to position the wedge so that the light intensity on the film 9 is maintained constant. In a modification, the back of the wedge 3 is aluminised and the plane of the wedge is tilted at 45 degrees, the aluminised surface of the wedge then acting as the mirror 8. In another modification, the mirror 8 is totally reflecting and is small in proportion to the light beam from the lens. In a further modification, Fig. 5, the system is applied to a single lens reflex camera. The light-beam from a lens 6 to a film 9 is interrupted by an inclined rotary shutter 11 having a reflective portion which directs the light from the lens 6 on to a partially transmissive mirror 8 and thence to a viewing lens 12. The light transmitted by the mirror 8 falls on a photocell 7 which controls the motor 4 as described for Fig. 2. A transistor amplifier can be used between the photo-cell and motor. An adjustable vignetted screen can be disposed in front of the photo-cell to compensate for film or shutter-speed.</p> |
