Patent GB-508064-A (GB)
Title: Apparatus for determining the depth of focus of a photographic camera
IPC: G03B17/02
Filed: 1937-12-21
Abstract: 508,064. Photographic cameras. UFFRECHT, B. Dec. 21, 1937, No. 35318. [Class 98 (i)] A focus-adjusting device for a camera comprises four fixed slide guides I, II, III, IV, Fig. 1, forming a harmonic pencil in which slide four knobs P1, P2, P3, P4, the knob P1 adjusting the aperture and index scale of the diaphragm, the knob P2 actuating an index indicating the nearest plane of good definition, the knob P3 focusing the camera objective and actuating an index indicating the plane of sharp focus and the knob P4 actuating an index indicating the farthest plane of good definition, the knobs sliding in a fifth movable guide V, by which they are maintained in a straight line so that by adjusting any two of the knobs to the appropriate positions, the other two are automatically adjusted. The knobs PI, P4 comprise respectively slides 9, 10, Fig. 4, moved in guides 1, 4 by screws 11, 15, the screw 11 having a screw 12 engaging a gear 13 to rotate a shaft adjusting the diaphragm aperture and bearing an index 31, Fig. 12, and the screw 15 having a rack 16 to move a gear 17 to adjust an index 33 along a distance scale. The slides 9, 10 have pins 7, 8 engaging a slot in a bar 5, Fig. 6, comprising the line V, the bar slidably carrying a slide 18 which is guided in a slide 3 and engages a rack 23 rotating a gear 24 which focuses the objective through gearing 41, 42, 43, 44, Fig. 10, and adjusts an index 34. The knob P2 comprises a slide 20, Fig. 8, having a pin 26 engaging a slot 25 in the slide 18 and having a rack 29 actuating a gear 30 to move an index 35 over the distance scale. In addition to the distance scales, the camera front bears a revolvable dial 50 bearing exposure time indications and carried on a sleeve axle having a knob 52 carrying film speed indications, the sleeve being in frictional engagement with a shaft 57 connected by gearing to a knob 51 moving over a scale 59 corresponding to the readings of an exposure guide. Alternatively, the knob 51 may actuate an exposure meter viewed through an aperture 58. In operation, the dial 52 is first moved relatively to the shaft 57 according to the film speed, and the dial 51 is then rotated according to the light conditions, this rotation setting the dial 50. The screw 15 is then actuated to set the index 33 on the farthest point on which it is desired to focus, and the screw 11 is adjusted until the index 35 indicates the nearest distance desired, this latter operation automatically focusing the lens and setting the diaphragm to the appropriate aperture. The necessary exposure time is then indicated on the dial 50 by the index 31 connected to the diaphragm. For given exposure times the dial 50 is set as before, and the. screw 11 actuated to adjust the index 31 to the desired exposure time ; the screw 15 is then adjusted to focus the objective and to indicate the depth of focus obtained. To allow the diaphragm to be adjusted without focusing the camera as when larger enlargements are required, the gear 24, Fig. 10, is connected to the gear 41 by a pin 33 and slot 37, the pin being pressed against the end of the slot by a spring on the shaft 43. When the lens is held fixed by a suitable movable slot and the diaphragm adjusted, the pin 33 moves in the slot so that the lens remains stationary.