Patent GB-499052-A (GB)
Title: Improvements in or relating to photographic copying apparatus with photometric control
IPC: G01J1/12
Filed: 1937-08-30
Abstract: 499,052. Photometric apparatus. BIGGLESTON, H., LEGGETT, J. J., and BIGGLESTON, D. H., (trading as ELECTRIC STREET LIGHTING APPARATUS CO.), and WILMAN, D. Aug. 30, 1937, Nos. 23701/37, 13856/38, and 17226/38. [Classes 97 (i) and 98 (i)] Apparatus by which the light intensity at any part of an area of non- uniform intensity can be compared with a standard comprises a photometric member divided into a large number of small translucent portions each adjacent to a small opaque or reflecting portion, the opaque parts receiving light from the area under examination and the translucent parts being illuminated by a standard source, or vice versa. The apparatus may be used for example for measuring the densities of different parts of photographs, or for measuring the brightnesses of different parts of an illuminated area such as a road surface. Fig. 1 shows a simple form for use as a density grader for photographic transparencies, in which the photograph 2 is laid on a support 1 and is illuminated by a lamp 3. The photometric member 4, in which the photograph is viewed by reflection, consists of a mirror having a large number of translucent lines 6, 7, Fig. 2, by which it is divided into reflecting parts 5 and adjacent translucent parts. The translucent parts 6, 7 are illuminated by a lamp 8 and the illuminated lines are balanced with the image of any desired part of the photograph by adjustment of one of the lamps. Lightdiffusing sheets 9, 10 are preferably arranged below the support 1 and behind the member 4. A common light source, which may be a lamp or a diffusely illuminated surface, may be employed for the photograph and the photometric member. Fig. 7 shows a combined negative grader and printing apparatus, with means for indicating the correct grade of printing paper to be used. A cabinet 50 contains the lamp 51 for illuminating the negative, and adjustable shutters 54 for controlling the illumination. The negative is laid on an opal glass plate 59 over an aperture 58, and a backing plate 60 is connected by leaf springs 61 to a lever arm 62 so that it can be moved into a vertical position for photometric grading of the negative or into a horizontal position for printing. The transparent lines of the photometric surface 89 are illuminated from the rear by light from the lamp 51 passing through an aperture 65 covered by opal glass 66, and reflected by a mirror 87 on to an opal glass plate 88 inclined to the surface 89. The light passing through the aperture 65 is controlled by a slidable apertured shutter 67 operated by a knob 69 on a spindle 70 having a pinion 71 gearing with a rack 72 on the edge of an index plate 73, which carries a strip 74 pivoted at its lower end to a link 76 the free end of which engages in a slot 78 in a lever 79 pivoted at 80 and engaging at its other end with a pin 82 on the shutter 67. A pin 83 on the link 76 engages in a slot 84 in a fixed plate 85, the shape of the slot being such that the movement of the shutter relative to that of the strip 74 is logarithmic. The plate 73 has an aperture 90 across which extends an index wire 91, and behind the plate is a fixed photometric scale member 92 illuminated by a lamp 93. To indicate the grade of paper to be used, a plate 95 between the plate 73 and scale 92 is movable in guides 96 and has at its upper end a member 97 engaging the plate 73 so that the latter in its upward movement carries the plate 95 with it. The plate 95 can be held in its uppermost position by a brake member 99 on a spring 98, and the brake can be released by an inclined surface 100 on a slidable member 101 connected to the lever 62, the arrangement being such that the brake is released when the backing plate 60 is closed. The plate 95 has windows 109, 110, 111 of different colours, and, when raised by the plate 73 to obtain photometric balance on the most transparent parts of the negative, is held in this position and remains stationary when the plate 73 is lowered to obtain balance on the densest part of the negative. In the latter position the window across which the wire 91 extends is determined by the travel of the plate 73 between its extreme positions and thus the colour of the window gives an indication of the correct paper to be used. After the photometric measurement has been made with the plate 60 raised, printing can be effected with the plate closed. Fig. 8 shows an instrument for measuring the brightnesses at different parts of an illuminated road surface. Light from a selected part of the road is received by a lens 42 and is reflected by a mirror 43 to the photometric member 44 comprising a lined reflector as already described, the reflected rays from the mirror 44 being received by lens 45 and eyepiece 46. Light from a lamp 48 passes through controlling means 49 to a diffusing surface 47 to illuminate the transparent lines of the reflector 44. To measure the brightness of any part of the road the controlling device 49 is adjusted until the illuminated lines disappear against the image of that part of the road. Equal brightness lines can be traced by the use of a pantograph the tracing pointer of which can be caused to traverse the mirror 44 or an image thereof while the pencil &c. traverses a chart.