Patent GB-705051-A (GB)
Title: Improvements in and relating to the exposure of cinematograph films
IPC: H04N3/40
Filed: 1948-01-30
Abstract: 705,051. Kinematograph cameras. VINTEN, C. Jan. 18, 1949 [Jan. 30, 1948], No. 2845/48. Class 97(1) [Also in Groups XL(a) and XL(b)] A method of cinematography wherein each frame of a sensitized film is successively exposed to succeeding images of the scene or picture being photographed, has the light of at least one of the images directed upon a luminescent screen to which the film frame is exposed. The method is used in a cinematographic camera comprising at least one luminescent screen upon which light of one of the images can be directed in order to excite thereon a luminescent reproduction of the image, to which reproduction a film frame can be exposed, and means for the simultaneous exposure of one film frame to the image excited on the fluorescent screen, and another film frame to a succeeding image of the scene or picture. In the arrangement shown in Fig. 1 a rotating reflecting disc 3 such as described in Specifications 597,269 and 638,238 is interposed between the objective 1 and the direct exposure aperture 2 of the film gate. The film 4 is moved intermittently through the gate upwardly and light from the reflector 3 is directed upwardly to a reflecting prism 5 positioned in front of another exposure aperture 6 so spaced from the aperture 2 that adjacent frames of the film 4 register simultaneously with the two apertures. The aperture 6 has a fluorescent screen 7 on to which the prism 5 directs the reflected light, thereby exciting the emulsive coating thereon which has short time period afterglow characteristics. The rear of the upper aperture 6 is closed by a shutter 8 which shields the film 4 from exposure to the fluorescent emission from the screen 7 during the exciting period, light being prevented from reaching the direct exposure aperture during this period by the rotating reflector 3. During this period the film is nowhere exposed to light and can be moved in normal manner. When the film is again at rest the reflector 3 exposes the film to directly incident light at the aperture 2 and simultaneously, by connections not shown, the shutter 8 of the aperture 6 is withdrawn, exposing the film to the light image emitted by the fluorescent screen 7 which during this period does not receive light from the rotating reflector 3. After this exposure period the apertures 2 and 6 are closed again by the reflector 3 and shutter 8 and the film is again stepped forward and the screen 7 re-exposed to light from the reflector 3 and prism 5. The film is advanced by one frame at each movement and in the arrangement shown the film is moved upwardly so that each frame is exposed first to directly incident light and thereafter to fluorescent emission, the two images being superimposed. If it is desired to move the film downwardly the fluorescent screen is located beneath the direct exposure aperture. In the modification shown in Fig. 2 the rotatable reflector and reflecting prism are omitted and the fluorescent screen is carried on a frame (not shown) slidable between positions above and in front of the aperture 2. A shutter 8 is movable to shield the film 4 both at the aperture 2 and at a position above it, or at the upper position alone. In its lower position the shutter 8 closes the direct exposure aperture 2 and (the next upper film frame being then also shuttered) the film is advanced. During this time the screen 7 is in the aperture 2 and is exposed to light from the objective 1. When the film is again at rest the screen 7 and shutter 8 are raised to the upper position (thereby exposing a film frame at the aperture 2 to directly incident light) and after the screen 7 has come to rest in the upper position the shutter 8 is further withdrawn exposing the film frame at the upper position to fluorescent emission from the screen 7. After a suitable exposure time the shutter 8 is closed over the screen 7, the screen 7 and shutter 8 moved down to close the aperture 2 and the cycle repeated. The features of the constructions shown in Figs. 1 and 2 are combined in the construction shown in Fig. 3 in which two film exposure apertures 2 and 9, two reflecting prisms 10 and 11 and two intergeared rotatable reflecting discs 3 and 3a having their edges cut away are provided. In any of the arrangements colour filters may be inserted in any of the paths along which light is directed in order to record selected colour images. The Provisional Specification refers also to a modification of the construction shown in Fig. 3 for use in colour cinematography in which three separate films are exposed at three different apertures provided with differently colour sensitive fluorescent screens and corresponding filters. The fluorescent materials on the screens can have different intensities of emission. A modified form of camera for recording colour pictures on two or three films is shown in Figs. 4 and 5 in which a rotatable reflecting disc 3 is located behind the camera objective 1 with its reflecting plane at 45 degrees to the objective axis and arranged to reflect light downwardly to the film gate 12. The disc 3 is cut away as shown in Fig. 5 so that during part of each rotation light from the objective 1 passes directly to the film gate 13 and during another part of the rotation is reflected to the film gate 12. Suitable colour filters 19 are provided at each gate and the gate 13 accommodates one film while the gate 12 accommodates one film or two superimposed films. A claw 14 intermittently engages and moves all the films simultaneously. The gates may be provided with film register pins. The disc 3 carries a curved mirror or reflecting surface 15 disposed at right angles to the reflecting surface 3 and forming a cylindrical flange which is sufficiently wide to screen both gates 12 and 13 from light through the camera objective during the intermittent advances of the film and which, during rest periods, reflects light uwards where it forms an image upon a ground glass screen 16 or passes through lenses 17, prism 18 and an eye-piece of a view-finder located on the top of the camera, as described in Specification 597,269. The film gates accommodate fluorescent screens or gate pads with fluorescent screens and oscillatory shutters are provided between the screens and the films for intermittent operation. The fluorescent materials are preferably selected to be most sensitive to light of the colour transmitted by their associated filters and may be arranged to modify the spectral distribution. Appropriate gearing is provided to ensure proper movements of the films in relation to the movement of disc 3. A camera for photographing television images displayed on the screen of a C.R.T. is shown in Fig. 6, which is an adaptation of Fig. 3, and comprises two rotatable reflectors 3, 3a located in front of the C.R.T. 29 and synchronously rotated so that images of the television image are alternately reflected to opposite sides of the tube axis, where they fall on fluorescent screens 30, 31. The emissions of the screens 30, 31 are photographed on the film 4 by optical systems 24, 25 and shutters 26, 27. The timing of the reflectors 3, 3a and shutters 26, 27 is arranged so that while one television image is being scanned upon the tube screen the shutters 26, 27 are both closed and the film 4 can be stepped forward one frame by the claw 28. During this time the television image is reflected on to one of the fluorescent screens 30, 31 having long afterglow characteristics, e.g. screen 31. Upon termination of the scanning of this television image the reflector involved passes out of immediate operation and the other reflector directs an image of the television image to the other fluorescent screen, e.g. screen 30, which thus receives an image of the succeeding interlaced television tracing. During this tracing the shutters 26, 27 are open and adjacent film frames are exposed respectively to the afterglow image of the former tracing on the screen 31 and the image of the interlaced tracing newly excited on the screen 30. When the interlaced tracing is completed the shutters 26, 27 close and the cycle is repeated. If desired the longer afterglow screen 31 may be formed of more sensitive fluorescent materials whereby the initial brightness of the image excited thereon is greater than that on the screen 30 so that the decayed image on the screen 31, as exposed to the film, may be comparable in brightness with the image newly excited on the screen 30 to which the film is simultaneously exposed.