Patent GB-836877-A (GB)
Title: Improvements in or relating to optical systems
IPC: G02B15/14
Filed: 1956-04-20
Abstract: 836,877. Optical lens systems; diaphragms. WATSON & SONS Ltd, W., and HOPKINS, H. H. April 16, 1957 [April 20, 1956], No. 12186/56. Class 97(1) A system comprises several coaxial lenses, means for moving one or more of the lenses to vary the effective focal length and according to a law such that the image position corresponding to a particular object position remains stationary at an image-receiving position during such variation of the focal length, and means for effecting relative movement between said lenses as a whole and image-receiving means at said image-receiving position (such movement being additional to the aforesaid movement of one or more of the lenses), according to a law such that the image position corresponding to another object position at a distance from the system different from the distance therefrom of the said particular object position is coincident with the position of the image-receiving means, and remains at that position during variation of the focal length, whereby the system may be focused for the said other object position instead of for the said particular object position. Preferably, the focusing of the system is continuously adjustable, so that the system may be focused on to any one of a continuous range of object positions. One embodiment of a lens system is shown in Fig. 1, and comprises relatively movable lenses 21, 22, 23, 24 and a movable stop 25, having a variable aperture, and an image receiving surface 26. Optical data for the system shown are given in the Specification, which also contains graphs illustrating the law of movements of the lenses. As shown in Fig. 1 of the Provisional Specification, movements are imparted to the lenses 21-24 by a mechanical arrangement comprising a base 51 carrying track rods 52, on which is slidably mounted a carriage 53 supporting two pairs of track rods 55, 56. On the track rods 55 is slidably mounted a carrier 57, which is movable by a handle 64 and on which is rigidly mounted a holder 58 containing the second lens 22. This carrier 57 is rigidly attached to a rack 65 engaging a gearwheel 66 on a shaft journalled in the main carriage 53. The shaft carries two cams 67. 68 and has driving connections with further cams 73. 74, 75 such that, when the carrier 57 moves along the rails all the cams rotate in unison. This causes axial movement of the lenses 21, 23, 24 and of the movable stop 25, slidably mounted on rails 56, in holders 77, 78, 79, 81 by means of pins 82, 83, 84, 85 spring-urged against the respective cams. As shown in Fig. 5 of the Provisional Specification, the main carriage 53 is spring-urged to maintain cam 68 in contact with the roller 86 on a pivoted arm 87, having a dovetail slide 89 carrying a block with a pin 92. This pin rotates in a second block 93 slidable between the rails 94, secured to the underside of the main carriage 53. to which is pivoted at 96 a focus-adjusting arm 95, having a longitudinal slot 98 embracing a pin 92. Manual adjustment of this arm 95 by an external knob 97 serves to move the pin 92 along the arm 87 and thus vary the amplitude of the movement of the main carriage 53, which is produced by rotation of the cam 68. The stop 25 is provided by an iris diaphragm having a control arm 76 engaged in a slot 102 in a pivoted lever 104, the inclination of which can be set to a desired value corresponding to the required relative aperture by a reference to a calibrated arcuate member 105. Movement of the stop along its track relative to the lever 103 causes the latter to act on the control arm 76 to vary the aperture of the stop and so maintain the relative aperture of the system substantially constant. Specification 836,876 is referred to.