Patent GB-669411-A (GB)
Title: Improvements in or relating to photographic cameras and control apparatus therefor
Inventor: LINZELL LESLIE
IPC: G03B27/66
Filed: 1949-03-08
Abstract: 669,411. Producing photo-mechanical printing surfaces. PICTORIAL MACHINERY, Ltd. Feb. 28, 1950 (March 8, 1949], No. 6346/49. Class 98 (ii). In a camera for making photographs through a half-tone screen, apparatus for displaying readings of diaphragm apertures appropriate to camera extensions comprises the combination of a diaphragm aperture indicating device incorporating a scale bearing a range of direct readings of diaphragm apertures and a relatively movable index member for taking readings from the scale, a cameraextension measuring device, and means for connecting this device to the diaphragm indicating device, whereby alteration of the camera extension effects movement of the scale relative to the index so that the appropriate diaphragm aperture may be read off. As shown in Fig. 2, a shaft 17 is journalled in a base-plate 11, and a gear-wheel 22 fast on shaft 17 meshes with a gear-wheel 23 fast with a gear-wheel 26. A drum 28 loosely mounted on shaft 17 is fast with a gear-wheel 27 meshing with gear 26, and contains a spring 31 attached at one end to the drum and at the other to shaft 17. Base-plate 11 is fixed to the lens board of the camera (not shown) at eye level, so that shaft 17 is horizontal and perpendicular to the direction of movement of the lens board. A metal tape 33, coiled round drum 28 and anchored thereto, passes round a pulley 63 carried by the lens board and thence passes horizontally to the camera back to which it is secured. Movement of the lens board relatively to the back thus causes a rotation of the drum which is transmitted through reduction gearing to the shaft 17; tension in tape 33 being maintained by action of spring 31. A disc 34 carrying concentric scales of diaphragm apertures is normally clamped between a collar 36 fast on shaft 17 and a washer 43 by means of a nut 35, so that it turns with shaft 17, but may be adjusted by loosening nut 35. A disc 50 in which shaft 17 is journalled is fixed by screws 13 and spacers to the base-plate, and has an aperture 52. A disc 44 lies between discs 34, 50, and is spaced therefrom by washer 43 and by a friction washer-53, so that it normally remains stationary, but can be turned by hand to bring a pointer 61, Fig. 1, opposite any one of a number of marks 56, 57, 58, 59, 60 on the edge of disc 50, thus bringing one of a set of apertures 45, 46, 47, 48, 49 in disc 44 to the aperture 52. A different scale on disc 34 is visible through each aperture in disc 44. In use, the camera is focused for a degree of enlargement of unity, and disc 44 is turned so that its central aperture 47 is visible through aperture 52. Nut 35 is loosened and disc 34 is turned until the number on its middle scale visible through apertures 47, 52 indicates the appropriate diaphragm aperture as determined by the screen in use and its distance from the photographic plate. Nut 35 is then tightened, and as the camera extension is varied the appropriate stop can be read from the scale. Where lighter or denser negatives are required, disc 44 is turned so that the outer or inner scales of disc 34 are brought into use. Specification 487,688 is referred to.