Patent GB-1036105-A (GB)
Title: Improvements in lens focussing systems and means for moving lens means of an opticalprojection system
Inventor: JEFFREE JOHN HENRY
IPC: G03B27/36
Filed: 1961-08-04
Abstract: 1,036,105. Lens focusing for enlargers. CAPS (RESEARCH) Ltd. Aug. 2, 1962 [Aug 4, 1961], No. 28502/61. Heading G2A. A lens focusing system has a first movable means carrying the lens system and arranged to move parallel to the optical axis, and a second movable means parallel to the said axis, so arranged that as the length of the light path is changed the said second means moves half that length, a coupling connecting said first and second means so that movement of the second means causes movement of the first means such that the focus is maintained. The invention is shown as applied to a micro-film enlarger, which comprises a main framework on which is mounted a pair of telescopically extending tubes 14,12 and 13, 11, inclined at about 30 degrees to the vertical. These carry at their upper end a hood 15 within which is a mirror inclined at 15 degrees to the horizontal, reflecting incident light on to a viewing or printing bed 17. A lamp 18, heat filter 20, gate and condenser lens 22, and magnifying lens system 23 are aligned on the optical axis. Between the gate and heat filter is a shutter (not shown). A main spine 24 is fixed to the framework parallel to the telescopic tubes, having side plates, 25, 26 supporting the lamp, the heat filter and the gate. A T-shaped beam 36 is mounted between the side plates, and is constrained by rollers 33, 34, 35 to move parallel to the optical axis. The upper end of the beam carries the lens 23. The lower end of the beam carries an adjustably spaced member 42 having a pair of pulleys 44. On the beam is slidably mounted a block 40 carrying a pair of pulleys 41. The distance between pulleys 41 and 44 in a direction perpendicular to the optical axis is made equal to the focal length of lens 23. Adjustment of screws 43 accordingly allow lenses of different focal lengths to be used. Secured to an arm 46 extending transversely between side plates 25, 26 are two metal tapes 47, which pass over pulleys 41 and 44, and are finally secured to member 42. As block 40 slides along beam 36, it is required that it shall move through half the distance by which the optical path is altered, and a device using a pair of different-sized pulleys (Fig. 2, not shown) is described for accomplishing this. An equation is given relating the distance between pulleys 41 and 44 to the focal length and magnification. Variation in the length of the optical path is effected by a motor 60 which is linked with the telescopic rods 13, 14, to cause them to extend or retract. Corresponding movement of beam 36 and block 40 follows, to maintain the lens system in focus. Arm 46 is connected by a jointed spindle 70 to a knob 79, rotation of which moves the arm along the optical axis and hence provides a further focusing adjustment, for light of different wave-length ranges. A fixed degree of such adjustment can be provided automatically by a solenoid-operated sector gear 80 (Fig. 4, not shown) driving a gear wheel 74 on spindle 70, to change the focus setting for white light to that for ultra-violet light.