Patent GB-836876-A (GB)
Title: Improvements in or relating to optical systems
IPC: G02B15/14
Filed: 1956-03-26
Abstract: 836,876. Optical systems. WATSON & SONS Ltd., and HOPKINS, H. H. March 26, 1957 [March 26, 1956], No. 9421/56. Class 97(1) A zoom lens system comprises four co-axial lenses, the front lens being negative, the two middle lenses being positive, and the rear lens having a focal length longer than the numerical values of the focal lengths of each of the other three lenses, the focal length of the rear lens being negative if it is a simple lens or the sum of the focus of the components of the rear lens being negative if it is a compound lens, at least the two middle lens being axially movable relatively to each other and relatively to the other lenses, and means for moving the movable lenses axially with or without simultaneous axial movement of an image receiver according to a law such that the image formed by the system of an object at a fixed distance therefrom remains in focus while its size is changed by the system. As shown in Fig. 1 the front lens consists of components 31, 32, 33, the second lens of components 34, 35, 36, the third lens of components 37, 38, 39 and the rear lens of components 40 and 41. Fig. 1 shows the system ,in the position of long focal length. To change to short focal length the first two lenses are moved towards the diaphragm 25, the second lens moving more rapidly than the first, and the third and fourth lenses are also moved towards the diaphragm, the third lens more rapidly than the fourth, whilst the diaphragm is itself moved towards the image plane 26. Numerical data are given for one example of this objective. The mechanism for adjusting the lenses comprises a base 51, Figs. 5, 6 carrying bars 52 on which is slidable a carriage 53 having two pairs of bars 55, 56 relatively vertically displaced. The lenses 21, 23, 24 and the diaphragm 25 are supported respectively by carriages 77, 78, 79, 81 slidable on the bars 56 and having respectively cam followers 82, 83, 84, 85 engaging cams 73, 74, 75 and 67. The cam 67 is mounted on a shaft carrying a gear 66 engaging a rack 65 on a carrier 57 which supports the lens 22 and is slidable on the bars 55. Movement of the carrier 57 is effected by a nut 61 engaging lugs 59 on the carrier and screwed to a rod 63 supported on the carriage 53. Rotation of the rod 63 moves the carrier 57 and the lens 22, the carrier 57 rotating the gear 66 to drive the cam 67 directly and the cams 73, 74 and 75 through belts 69, 71, 72 and so adjust the other optical members. The diaphragm 25 has an operating arm 76 engaging a slot 102 in a pivotally adjustable arm 103 so that movement of the diaphragm automatically adjusts the aperture thereof. The gear 66 also carries a cam 68 engaging a follower 86, Fig. 9, on an arm pivoted to the base 51 and having a sliding pin 92 therein engaging a sliding block 93 on the carriage 53 and adjustable along guides 94 by a pivoted lever 95. This adjustment enables the cam 68 to adjust the whole optical system relation to the image plane to take account of different object-distances. Specifications 639,610, 639,611, 639,612. 646,409, 685,945, 713,024, 722,375 and 836,877 are referred to.