GB808395A - Variable focal length lens system for movie cameras - Google Patents

Abstract

808,395. Optical systems. EDNALITE OPTICAL CO. Inc. Nov. 5, 1956 [Dec. 6, 1955], No. 33761/56. Class 97(1) A zoom lens attachment for a photographic objective comprises a barrel in which are mounted two axially spaced converging lenses having between them a diverging lens of greater power than either of the converging lens, cam mechanism being provided to change the magnification by moving at least two of the lenses so that in one position the diverging lens is adjacent the front converging lens whereby the system forms an erect diminished visual image and in the opposite extreme position the diverging lens is adjacent the rear converging lens to form an erect enlarged virtual image, means also being provided for axial adjustment of the lens system to focus for different object distances. The cam mechanism may be coupled to a variable viewfinder attached to the barrel to produce simultaneous adjustment of the viewfinder field. As shown in Fig. 2 the zoom lens comprises a barrel 22 having a positive lens 16 secured thereto by a mount 15 screw threaded on to the barrel so as to be axially adjustable to move the lens 16 for focusing. Within the barrel is a sleeve 30 engaged by a pin 48 passing through a part-circumferential slot 28 in the barrel 22 and attached to a gear ring 47 rotatable on the barrel 22 by a handle 13. The rear converging lens 17 is carried by a mount 70 axially slidable within the sleeve 30 and having guide bars 72 projecting therefrom to increase the surface area bearing on the sleeve 30. The diverging lens 18 is similarly carried by a mount 80 having guide bars 81. The mounts 70, 80 respectively carry pins 26, 84 passing through curved slots 32, 33 in the sleeve 30 into a longitudinal groove 27 formed in the inner surface of the barrel 22. Rotation of gear 47 by handle 13 causes rotation of the sleeve 30 the slots 32, 33 of which cause the necessary axial movement of the lenses 17, 18 which are themselves prevented from rotating by the groove 27. A photographic objective 19 may be attached to the system. The viewfinder system, Fig. 4, which is attached to the barrel 22 of the zoom system by a bracket 12, comprises an objective 91 and an eyepiece 128, 129 fixed within a barrel 95 and a diverging lens 92 in a tubular mount 117 axially slidable within the barrel 95 having a pin 120 engaging an axial groove 98 thereon. Rotatably mounted on the outside of the barrel 95 is a drive ring 103 carrying a pin 104 passing through a part circumferential slot 97 in the barrel 95 and into a helical groove 118 on the tubular mount 117. Rotation of the ring 103 therefore causes axial movement of the lens 92 to vary the magnification and so the field of view of the viewfinder, this rotation being effected by a gear 133 engaging the gear 47 on the zoom lens and engaging gear teeth on the ring 103.