GB915118A - Newton viewfinder for a photographic camera - Google Patents

Abstract

915,118. Viewfrinders AGFA A.G. June 1, 1959 [June 18, 1958], No. 18636/59. Classes 97 (1) and 98 (1). An Albada-type Newton viewfinder for a camera comprises two negative objective lenses (one of these may be positive) and a positive eye lens as shown in Fig. 1, the rear concave surface R2 of the front negative lens being half-silvered and forming a virtual reflected image of the image field bounding marks 7 which are supported on preferably the rear concave surface R4 of the second negative lens. The optical separating distance l between the surfaces R2 and R4 should satisfy the condition where S<SP>1</SP> is the focal length of lens I. Lenses I and II may be conveniently of the same power, and lens II may be of such thickness as to practically fill the space between surfaces R2 and R4 with glass (thereby increasing the aperture of the system). To prevent corrosion of the metallized image field bounding marks, surface R4 may be bloomed; other surfaces may also be bloomed with advantage. Either or both of the lenses I and II may be axially and/or transversely adjustable for sharp focusing.