Patent GB-417285-A (GB)
Title: Improvements in photographic telescope finders having a converging objective part
IPC: B62L5/10
Filed: 1933-11-17
Abstract: 417,285. View - finders. ZEISS, C., [Firm of], Carl - Zeiss-Strasse, Jena, Germany. Nov. 17, 1933, No. 32049. Convention date, Nov. 19, 1932. [Classes 97 (i) and 98 (i).] In a telescopic view-finder having a converging objective part, a converging ocular part, and a device for indicating the image field, the field of view produced by the finder is made to correspond to the field imaged in a photographic camera at different focusing distances and/or focal lengths of the camera objective by varying that part of the optical members lying before the telescopic image plane as regards quality and/or position relatively to that part of the optical members lying behind the image plane. In the form shown in Fig. 1, 9 is an image field diaphragm in the telescopic image plane, 8 a prism system, 11 an ocular focused on the image plane, 10 a collective lens, and 6 an objective lens of which the mount 5 is axially movable, graduations 7 enabling the objective 6 to be set in accordance with the focusing distance of the camera objective. In a modification, Fig. 3, the mount 16 of the objective 19 is movable in an inclined bore 14 so that the objective 19 simultaneously with its axial movement moves towards or away from the axis of the camera objective thus bringing the field of view in the finder into correspondence with that in the camera as regards both variation of focusing distance and parallax between the images in the camera and finder. In a further modification in which the finder is adapted for use with camera objectives of different focal length, a disc carrying a number of objective systems for alternative use is rotatably mounted in front of the image plane of the finder. Each objective system comprises a front lens and a collective lens. Slight rotation of the disc in accordance with graduations thereon moves the objective system for the time being in front of the telescopic image plane towards or away from the camera objective thus providing a correction for parallax. As shown in Fig. 15, the disc 29 may be rotatably mounted on a threaded spindle 52 so that the objective system 30, 31 simultaneously with its movement towards or away from the camera objective for parallax correction in accordance with graduations 34 is moved axially to correct for varying focusing distances of the camera objective. In a further modification in which a rotatably mounted disc carries a number of single objective lenses for alternative use, the collective lens being fixed, the simultaneous rotation and axial movement of the disc as described with reference to Fig. 15 is achieved by a groove in the cylindrical edge of the disc having a number of helical parts and co-operating with a fixed pin. Fig. 8 shows a still further modification in which an objective tube 37 carrying two reversely equal converging lenses 38, 39 is changeable with another or may be reversed in its support 4, image fields corresponding to those of camera objectives of different focal length being obtained by providing differently apertured diaphragms 40, 41 at the ends of the tube 37. The slide 3 by which the finder is attached to the camera may be inserted in its guide in reversed position so that the ocular 12 becomes the objective. This reversal together with the reversal of the tube 37 provides four different image fields in the finder. A pair of inverted figures are so marked on the plane surfaces of each lens 38, 39 that only one figure appears erect and laterally correct for each adjustment of the finder and indicates the focal length of the camera lens to which the adjustment corresponds. In a further modification, in which the objective tube may be reversed in its mounting and the finder so attached to the camera that the ocular may serve as an objective the optical axis of the telescope is deflected by a prism, the axis of the ocular being at right angles to that of the objective.