Patent GB-200098-A (GB)
Title: Apparatus for taking time exposures of moving objects
IPC: G03B15/00
Filed: 1923-06-28
Abstract: 200,098. Aero Survey Corporation, (Assignees of Cooke, H. L.). June 28, 1922, [Convention date]. Angle-measuring instruments.-A camera and fighting-device for taking photographs of objects in motion relatively thereto, especially applicable to photography from aircraft, and which permits the employment of wide-angle lenses, is of the kind provided with mechanism for eliminating relative motion between the image of the landscape and the member on which the image is produced, and is characterized by (1) a gyrostatic mounting for rendering the camera independent of small irregularities in the flight of the aircraft (2) supports for a strip of sensitized medium, which are independent of the gyrostat system, so that the movement of the medium through the camera will not disturb the centre of the gyrostat system, and (3) means for producing relative motion between the objective and sensitive medium in which the motion is interrupted at intervals and the parts are restored after each interruption to a given initial position. The compensating means is adapted to furnish courseindicating data to the pilot. In the form shown in Figs. 2 and 3, the camera 14, carrying a level filled with viscous liquid, is carried by a frame 8 turning on fore and aft trunnions 9 in a gimbal frame 5 trunnioned at 6 in a frame 4 rotatably mounted on a ring 1 secured to the floor 3 of an aircraft. Screws 40, 41 provide means for adjusting the frictional forces on the trunnion bearings 6, 9. On an extension of the frame 8 is mounted a high-speed motor 12 driving a gyrostat wheel 13. The centre of mass of the frame 5 and moving system supported by the trunnions 9 is at the intersection of the trunnion axes 6-6, 9-9. In the camera back 14b, Fig. 6, is a slidable, non-rotatable rod 15, mounted parallel to the trunnion axis 9-9, and rigidly connected to a film support 25 the surface of which is maintained normal to the camera axis. Surrounding the rod 15 is a single-turn screw cam 21, incapable of longitudinal movement, and driven by worm gearing from a motor 22. A pin 23 on the rod 15 is pressed against the cam surface by a spring 19, so that as the cam rotates, the rod 15 and the attached film support 25 are displaced at constant speed to the left, and then snap back to the right, the cycle of movement being repeated continuously so long as the motor 22 is kept running. A switch controls the speed of this motor, and an indicator 100 shows the motor speed and the number of reciprocations of the rod 15. The sensitive film 34 is carried on reels 30a, Fig. 3, in boxes 30 on the frame 4, and passes therefrom to the camera back 14b through bellows 32, which will not impose any appreciable angular constraint upon the gyrostat system when the aircraft is flying comparatively steadily. The film support 25 has film guiding grooves 13, Fig. 12, and is provided with a known device, such as a valve-controlled suction back 150, to cause the part of the film in engagement with it to participate in its reciprocation. The reels 30a may be manually or automatically wound to advance the film after each exposure, and means such as is well known in kinematographic apparatus is provided for maintaining sufficient slack in the film on both sides to allow for its reciprocating motion. A telescope 34, rigidly attached to the camera 14 and its supporting frame 8, and having an object glass of the same focal length as the camera objective 14<d>, tis slotted at 37a to receive transversely at the focal plane of the object glass a bracket 37 carrying cross-wires 38, and passing through a lighttight slot in the camera, wherein it is rigidly attached to one end of the film support 25, so that it participates in the reciprocation of this member. Apertures 50, 51 are provided in the floor 3 of the aircraft beneath the camera and telescope objectives, and a wind-plough surrounds the aperture 50. Clamping means 42 is provided to lock the frames 5 and 8 to the frame 4, as when the aircraft is banking. In operation, the camera is rotated on the ring 1 until the relative motion of the ground, as seen through the telescope 34, is parallel to the fore and aft cross-wires. The motor 22 is then started, and its speed adjusted until the cross-wires share the steady speed of the ground image in the telescope. The ground image on the sensitive film will then be stationary, and an exposure may be made by manually operating the shutter 14<h>, Fig. 6, care being taken to choose an instant when the cross-wires are in the middle of their forward travel, to avoid the danger of the film snapping back during exposure. If a colour filter is employed, it is incorporated as a unit with the camera lens to avoid loss of light in the oblique rays. The mean position of the camera axis relative to the film during exposure is indicated for photogrammetric purposes by a frame 75, Fig. 10, mounted in front of and close to the film 34, and carrying indicator marks 56, 57 the shadows of which are reproduced on the film. The pilot may adjust his line of flight to any desired magnetic bearing if (1) the camera operator maintains the angular position of the apparatus so that there is no motion, parallel to the transverse gimbal axis 6-6, of the telescopic ground image relative to the cross-wires, and (2) the angular displacement of the axis 9-9, as indicated by a pointer on the ring 1 working over a scale on the frame 4 is communicated to the pilot, or automatically transferred to his compass : this angular displacement is the angle between the line of flight relative to the ground, and the fore and aft axis of the aircraft. The indicator 100 may be calibrated to give (1) the ground-speed of the aircraft, and (2) the ground distance travelled by the aircraft, if a standard height be chosen for navigation. Thus, if the aircraft is steered on a given course, and camera exposures are made at intervals of a chosen number of reciprocations of the rod 15, evenly-spaced photographs may be taken covering a given tract of land in predetermined manner. A modified form of camera is described in which the film is fixed in relation to the camera, and the camera objective is caused to execute a reciprocating movement of the kind hereinbefore described to compensate for the apparent movement of the ground. In this construction (1) the camera is not rotatably mounted as a whole, the direction of relative motion of the objective being adjusted by causing the objective to partake of two independently adjustable component motions at rightangles to each other, and (2) the cross-wires of the telescope are fixed, and the object glass is caused to move in unison with the camera objective. Either form of camera may be adapted to take sensitive plates instead of a film, the suction back being then dispensed with.