Patent GB-594067-A (GB)
Title: Improvements in or relating to photographic cameras
IPC: G03B39/02
Filed: 1943-09-07
Abstract: 594,067. Photographic cameras. MARLEY, W. G. Sept. 7, 1943, No. 14641. [Class 98 (i)] Apparatus for taking a series of photographs at intervals of the order of a fraction of a milli-second, as in the investigation of explosions or of sparking at the contacts of electric switchgear, comprises a number of fixed camera elements, and a common, continuously moving shutter member provided with a series of exposureeffecting means in a closed path, the number and spacing of which in relation to the number and spacing of the camera elements being such that every camera element is exposed once in turn in less than one complete circuit of the shutter member, provision also being made to ensure that each element is exposed only once during one cycle of operation of the apparatus, notwithstanding that, because of its high speed, the shutter must be run for a longer time than is necessary for making all the exposures. The shutter may be opaque, with apertures or windows at the desired locations. As shown, the apparatus comprises a base 1 supporting a panel 2 provided with a ring of objectives 18 which may be pin-holes or lenses of glass or synthetic resin, behind which is an annular exposure chamber 6, formed by rings 4, 5 on the panel 2 and an annular closure plate 7 rotatable about its centre as on rollers 8. Annular flanges 9, 10 in the chamber support the margins of a lightsensitive film in a single cylindrical turn, which may be loaded into the chamber through a slot therein, from a cassette detachably mounted on the outside of the chamber, by turning the plate 7 after passing the leading end of the film round a guide roller and securing it to a slotted, spring-braked roller on the plate. A rewinding knob is provided on the cassette. Behind each objective 18 is an adjustablytilted specular reflector 20 to reflect the rays from the objective radially upon the film. On the front of panel 2 are mounted first an annular occulting plate 23 capable of a limited rotation in its seating under the action of tangential tension springs 27, and in front thereof an exchangeable fixed annular diaphragm plate 28, both plates having as many apertures spaced around them as there are objectives, and the apertures in plate 28 being in alignment with the objectives. In front of this assembly is an exchangeable, high-speed shutter disc 30 carried by a shaft 32 extending along the common axis of the annular system and driven continuously as by an electric motor 33, at a speed of, e.g. 6000 r.p.m. which is recorded by a tachometer 35. The plate 23 is held by a catch in position occulting the objectives when its actuating springs are under tension, and its rotation when released from the catch is limited by stops to an angle which is just sufficient to allow each of its apertures to pass completely across the corresponding-aperture in the diaphragm plate 28. The shutter disc 30 has spaced around it a number of exposure apertures which is prime with respect to the number of objectives ; in the simplest case the numbers differ by unity : and the size of each aperture is such that there will be little or no overlap between successive exposures. The design of the parts is such that, although the shutter is continuously rotated, each objective is uncovered once only as the occulting plate makes its limited rotation. If the object to be photographed is an event which has to be initiated, the initiation may be effected by the means for releasing the catch holding the occulting plate ; thus, if the event is an explosion, this plate may carry on its periphery a short rack gearing with a segment on which are mounted an arm held in the starting position by a latch, and also a wing adapted, when the arm is released from the latch as by an electromagnetic device, to engage a pair of contacts in the firing circuit at the desired moment. The electromagnet of the releasing device may be wound with resistance wire so that on excitation its field will build up rapidly. Associated with the releasing means there may be another device, preferably electromagnetic coupled with a spring brake, designed to arrest the occulting plate in its non-occulting position when this is desired. Provision may be made in both devices for reducing risk of burning out the windings of the electromagnets. When the object is not self-illuminated, a synchronized flash of high intensity may be provided for making the exposures.