GB756001A - Focussing device for photographic cameras - Google Patents

Abstract

756,001. Photographic cameras; lens mounts. KIRCHHOFF, K. May 14, 1954 [May 16, 1953], No. 14135/54. Classes 97 (1) and 98 (1). A supplementary lens attachment for a photographic camera comprises, in a single housing 7, Fig. 1, two lenses capable of forming an afocal system and a range-finder coupled to one of the lenses, the coupled lens being adjustable along the optical axis of the objective. The objective 2 to which the attachment is secured is focused for an object at infinity and objects at finite distances may then be brought into focus by adjusting the range finger on them. Preferably, the lenses 9, 10 are of equal and opposite power so that the system is afocal when they are touching. The lens may consist of two entirely separate components forming a Galilean system or an inverted Galilean system for telephoto or wide angle effects respectively. As shown in Fig. 1, lens 10 is movable through screw-threaded engagement of mounting 16 with member 13 attached to housing 7. A member 18 secured to mounting 16 is provided with a knurled edge 19 and an eccentric cam track 23 on which pin 24 rides and tilts mirror 27 of a coincidence-type short home base range finder. A fixed half-silvered mirror 28 is provided. In another form clamping ring 3 can be changed to fit different cameras and a separate cam track member is provided which does not move axially with member 18. Stops are also provided to limit the rotation of mounting 16. In a similar form the base of the range finder is arranged horizontally. As shown in Fig. 9, objective 87 is coupled with lens 10 and forms a sharp image on ground-glass screen 78 when the camera is in focus. The focal length of objective 87 may be numerically equal to that of one of the lenses 9 or 10. When lens 9 is adjustable the motion imparted to objective 87 must be reversed.