GB639409A - Improvements in and relating to view finders for photographic apparatus - Google Patents

Abstract

639,409. View-finders. KALART CO., Inc. June 5, 1947, No. 14886. Convention date, Jan. 22. [A Specification was laid open to inspection under Sect. 91 of the Acts, June 5, 1947.] [Classes 97 (i) and 98 (i)] A collimating view-finder comprises a shortfocal length eye-piece having. an angle of field of at least 70 degrees and a substantially flat field which eye-piece is focused on a mask consisting of a plate of transparent material the surface of which facing the eye-piece is substantially opaque and has formed therein grooves which extend into the transparent material, serve to gather light incident on said transparent material and define a framed area. In one form, the eye-piece 2 and the mask 3 are supported in a housing 4, which, can be secured to a camera by ears 7, and the mask comprises a plate as of glass, the surface of which facing the object has been ground and the other surface of which has been given an opaque coating and has been cut or etched to form grooves 12-14, which are preferably V-shaped. Each of the grooves 12 to 14 defines an area equal to that of the image which would be formed in the camera by a lens having a particular focal length. Thus, if a lens of 90 mm. focal length is in use in the camera, the photographer looks through the eye-piece with one eye and the object seen with the other eye appears to be visually superimposed on images at infinity of the grooves 12 to 14 and the part of the object which appears to be bounded by the image of groove 14 is that part which the camera lens images on the film in the camera. The eyepiece may comprise two lenses, optical data for which are given in the Specification. The view-finder may be combined with a rangefinder as shown in Fig. 11 in which a mask 25 is disposed in the focal plane of an eye-piece 27 and between the mask and eye-piece a prism 35 and a negative lens 38 are positioned. The photographer on looking into the eyepiece 27 sees an image at infinity of the grooves 12 to 14 and two images of the object formed by light rays which are directed by a fixed prism 28 and a rotatable prism 29 on to a semitransparent mirror 33, a prism 34 and then on to the prism 35. By rotation of the prism 29, the two images of the object may be superimposed ; prism 29 may be coupled with the camera lens mount so that the lens is in focus when the two images of the object appear to be superimposed in the eye-piece 27.