Patent GB-872866-A (GB)
Title: Method and apparatus for making wide angle pictures
IPC: G03B37/02
Filed: 1957-09-06
Abstract: 872,866. Wide-angle cameras. CALDWELL, F. A., and BRUMMER, R. S. Sept. 6, 1957 [Sept. 6, 1956], No. 28254/57. Classes 97(1) and 98(1) A method of making wide-angle motion pictures up to 160 degrees or more on a film, includes the steps of continuously moving the film at a constant speed through a cylindrically curved path, projecting a slit of light constituting a fractional part of an image of the scene to be recorded on a concave portion of the film, and moving the slit of light along the cylindrically curved path at a constant angular velocity higher than that of the film to project the remaining fractional parts of the scene on to the film, so that the fractional part of the image appearing on the film at any instant of time is moving with a linear speed equal to that of the film, and repeating the last mentioned step at equally spaced time intervals, whereby a series of images are produced on the film. As shown, a cinematograph camera comprises a curved film gate 10 supported on a block 24 slidable in the direction of the arrow for the insertion of the film in the gate. Supported on the front of the camera housing 25 is a rotatable cylindrical canister 12 having opposed, longitudinal slits 13, 14 which allow passage of light on to the film, and containing an objective lens 15, the back nodal point n of which moves in a curved path on rotation of the lens. On rotation of the canister the successive strips of the film 11 which become adjacent the slit 14 are exposed in turn with result that, in one sweep of the canister 12, the whole of the field of view subtending a wide angle at the lens is recorded on the film 11. The film 11 moves in the gate during exposure, the rate of movement of the film being arranged so that the right-hand side of a frame is exposed at the right-hand end of the gate 10 and the left-hand end of a frame at the left-hand end of the gate 10, the gate being of greater length than the length F of the film. Expressions are derived in the specification relating the various dimensions and velocities required for optimum performance. To block light from the film when the canister rotates back to the starting position, a rod 19 attached to the canister is formed with a slit adjacent the slit 14 in the position shown in Fig. 9. When the slit 14 reaches the left-hand position 26, the rod 19 is rotated through 90 degrees relative to the canister by means of a Maltese cross follower attached to the pin engaging a fixed cam 21 and studs 22, 23 so that for the return motion of the canister the slit 14 is closed; the rod 19 is rotated through a further 90 degrees at the right-hand position 26 to re-align its slit with the slit 14. The film is fed by conventional means comprising a toothed driving wheel 28 and various friction reducing rollers. The canisterhousing junction is made light-tight by pieces of felt at 26, or alternatively a rotating felt cylinder is provided to reduce friction; for large canister slits, rollers may be provided for each of them such that slits in the rollers are brought into register with the canister slits when light passage is required, and are rotated through 90 degrees by cams to produce light blocking; in this way friction is reduced by presenting a continuous curved surface to the light excluding means at 26. For covering image fields subtending angles greater than 160 degrees, a modification (Fig. 15) comprises two coaxial canisters 52, 57 with single slits 53, 58 and containing mirrors 54, 56. As the canisters rotate together, strips of the image field pass successively through the slit 58 and are reflected at 56 through a fixed objective 55-coaxial with the canisters and having its back nodal point at n-on to the mirror 54 and through the slit 53 on to corresponding successive strips of the film in the gate 10, no blocking means being necessary for the return motion of the canisters. In an elaboration of this embodiment, the gate 10 may be driven with the film to reduce friction. The Specification also describes an arrangement using intermittent film feed Figs. 1 and 2 (not shown).