Patent GB-630266-A (GB)
Title: Improvements in photographic sensitometers
IPC: G01J1/12
Filed: 1946-12-23
Abstract: 630,266. Photographic sensitometers. GENERAL ANILINE & FILM CORPORATION. Dec. 23, 1946, No. 37749. Convention date, Jan. 8. [Classes 98 (i) and 98 (ii)] A sensitometer for effecting test exposures of multilayer colour film having a light-tight chamber, a light source and an exposure aperture, is characterized in that a filter member is provided having a plurality of sections, each corresponding in size to the picture area of the film to be tested and progressively varying in colour and density, the filter being placed between the light source and the film under test, a support for a test film including a frame for registering it under the filter sections, the film being movable through the frame, another support for an unexposed film including a frame for registering it under the test film, the unexposed film being movable therethrough, and shutter means to admit light from the source for exposing the unexposed film after passing through the filter and the film under test. As shown, a cuboidal casing 10 encloses a cylinder 12, which surrounds a bracket carrying a number of lamps 13. The voltage applied to the lamps is regulated to control or maintain their colour temperature. The cylinder is supported and rotated by a shaft fast with one end plate and driven by a synchronous motor, and has an adjustable longitudinal slot 30. The end remote from the shaft is supported on rollers 20. Air is blown through the cylinder and casing 10 for cooling. An elongated aperture 38 in the wall 37 is provided with a ground glass diffusing screen 39, a shutter plate 40, and a diaphragm plate 47. The shutter plate closes the aperture, but may be raised by solenoids 43, and returned by springs or by gravity. The diaphragm plate 47 is adjusted by a rack 48 and pinion 49 to vary the aperture width. The bottom wall 11 of the casing 10 is extended and carries guideways 33 for a frame 32 connected to the front of the casing 10 by bellows 35 and carrying in an aperture 52 a filter 54 having a number of sections, each the size of a frame of the film to be tested, which vary progressively in colour and density. The frame 32 may also support a filter 53 to correct the response of a second, unexposed, film. The film F under test is threaded through the aperture in front of the filters, and is adjusted so that the frames register with the sections of the filter 54. An unexposed film F<SP>1</SP> is threaded from a light-tight magazine through a recess in a carrier 58, hinged at 57 to the frame 32, to a second light-tight magazine. When the carrier 58 is in the closed position (full lines) a plunger-operated pad 69 presses the films F and F<SP>1</SP> together against the filter 54. In the open position (broken lines) the pad is retracted and the film F<SP>1</SP> protected from light by a curtain 64 carried by rollers, which has an aperture brought into register with the recess in the carrier when in closed position. This curtain may be omitted if the instrument is used in a dark room. In operation, the pad 69 is retracted, the curtain 64 closes the recess, and carrier 58 is swung to open position. The film F is then adjusted to bring the frames to be tested into registration with the filter sections. Since the shutter 40 is closed, this operation is performed by light from a lamp 80 reflected by a mirror 81 ; on completion the lamp is extinguished and the mirror drawn out of the light path. The carrier 58 is then closed and fastened by a latch 59, the curtain 64 moved to open the recess, and the pad 69 advanced to press the films against the filter. The circuit energizing the solenoids actuating the shutter plate 40 contains a relay with normally open contacts. The coil circuit of the relay includes a resitance limiting the current to a value insufficient to actuate the relay, but sufficient to hold it on when the contacts close. The resistance is short-circuited when a master switch and a switch momentarily closed by a cam on the cylinder at each revolution are both closed. When the motor driving the cylinder has run up to speed, the master switch is closed, and the next operation of the camcontrolled switch short-circuits the resistance and operates the relay, energizing the solenoids and opening the shutter at the moment when the slot 30 in the cylinder approaches the slot 38 in the casing 10. The shutter remains open until the slot 30 has passed the slot 38, when another switch is momentarily opened by the cam, opening the relay circuit to close the shutter. The master switch must be reopened before the first cam-controlled switch closes again. The film F<SP>1</SP> is moved on for a fresh trial, for which a different portion of the film F may be selected, or the filters 53, 54 may be replaced by filters of similar type but different colours or densities. The exposure time may be varied by altering the width of the cylinder slot 30, and the light intensity by moving the frame 32 towards or away from the casing 10 along the guides 33, or by varying the width of slot 38 by moving diaphragm plate 47. The Specification as open to inspection under Sect. 91, states that the opening movement of the carrier 58 may bring the mirror 81 into operative position and light the lamp 80, the closing movement withdrawing the mirror and extinguishing the lamp ; and that movement of the curtain 64 may be so controlled that it may open only when the carrier 58 is in closed position, or may be opened by the closing action. This subject-matter does not appear in the Specification as accepted.