US 4,792,829 A · Light-exposure control unit

Abstract

An improved light-exposure control unit for a photographic printer offering minimized leakage problems, elimination of special precision capacitors and a range selecting circuit which eliminates masking of the photosensitive device used to detect variations in intensity of the light source. The improved control unit including operational amplifiers connected to the photosensitive device, which is mounted after the color filter but before the negative, sending a voltage adjustable according to the desired range and proportional to the amount of light impinging thereon, to an integrating amplifier with a variable input resistance adjusted accordingly to the desired density. The integrating amplifiers output is compared to a voltage derived from a precision reference source adjustable according to the settings made to magnification and speed-factor controls. The length of the exposure period is the time period required for the integrating amplifiers output to reach equality with this voltage and is controlled automatically by the amount of light impinging upon the photosensitive device, from the source, through the color filter.

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Claims17

Dependent claims

An improved exposure control unit for a photographic printer having a light source, an adjustable magnification factor, an adjustable lens aperature, an adjustable color filter, support means for the negative which is to be printed and support means for the material to be exposed, said exposure control unit improvements comprising:

(a) a photovoltaic cell mounted to receive color-filtered light from said source unchanged by said negative;
(b) circuit means in direct association with said photovoltaic cell for generating current within said photovoltaic cell and converting said current into an output voltage directly proportional to the intensity of the filtered light impinging upon said photovoltaic cell;
(c) first adjustable means for modifying the proportionality of said output voltage directly proportional to light intensity from said circuit means, said first adjustable means providing adjustment according to the range of said exposure control unit;
(d) a precision reference voltage source;
(e) second adjustable means providing a first variable multiple of said precision reference voltage, said second adjustable means providing adjustment according to the magnification factor of said photographic printer;
(f) voltage divider means associated to divide the output of said second adjustable means by a predetermined factor;
(g) third adjustable means in circuit association with the output of said voltage divider means for providing a second variable multiple of the divided voltage from said second adjustable means, said third adjustable means providing adjustment according to the speed factor of the sensitive material being exposed;
(h) integrating means providing a voltage ramp output representing the integral of its input current wherein the magnitude of said input current hence the slope of said voltage ramp output is manually variable by fourth adjustable means and automatically variable by a voltage representing light intensity from the output of said first adjustable means, said fourth adjustable means providing adjustment according to the desired density factor;
(i) comparator means in circuit association with the output of said integrating means and the output of said third adjustable means for terminating the exposure period, therefore said light source, when said output of said integrating means is equal to the output of said third adjustable means;
(j) momentary switch means for initiating or terminating said exposure period therefore said light source;
(k) first flip flop means for retaining the current status of said exposure control unit responsive to said momentary switch means and said comparator means output;
(l) means for creating pulses synchronous with the zero crossover region of the alternating power source energizing said exposure control unit;
(m) buffer amplifier means for energizing relay means in circuit association with said light source;
(n) second flip flop means responsive to said first flip flop means and to said pulses synchronous with said zero crossover region of said alternating power source, having complementary outputs for controlling said buffer amplifier means, and, switching means controlling the charging and discharging of a capacitor in circuit association with said integrating means.

11 more elements

Dependencies are inferred from the claim text.

Description3,844 words

Summary799 words

#1. Field of the Invention

#This invention relates to an improved exposure control unit which is used advantageously in the exposing of light-sensitive materials such as photographic film or paper, either monochrome or color.

#The improved control unit of the present invention may be used in the production of all types of photographs and particularly special purpose photographs, such as for advertising or other commercial or governmental purposes, where the photographs to be produced are not of the fixed magnifications ordinarily used in the exposing of photographic prints for the public.

Brief description of the drawings4 figures

#FIG. 1 is a simplified diagrammatic representation of a photographic enlarging system employing the automatic exposing device of the present invention;

#FIGS. 2a, 2b, 2c, and 2d when adjoined in sequence from left to right present a schematic circuit diagram of the control system and power supply for the exposing device;

#FIG. 3 is an equivalent circuit diagram for the decade resistance switching devices employed in the control system of the present invention;

Detailed description2,947 words

#Referring now to FIG. 1 there is shown diagrammatically a photographic enlarger system comprising a light source or lamp 10, a multi-color filter 12, a photographic negative 16, a focusing lens 17, and the printing material 18 contained in or supported by a housing 20, but no effort has been made to illustrate the structural mounting details since such means are well known.

#The multi-color filter is shown to include three different color filter elements 13, 14, and 15 which, in a typical case, will be cyan, magenta and yellow. Each of the color filter elements 13, 14, and 15 is also of varying density, increasing progressively in density from one marginal region to the other, and each filter element is separately adjustable, so by adjusting the filter elements 13, 14, and 15 a wide range of color filtration may be obtained. The lamp 10 and the multi-color filter 12 may, if desired, be a device known as a Chromega D. Lamphouse, a produce of Simmon Brothers, Inc. of New York State, embodying U.S. Pat. No. 3,027,801.

#In accordance with the present invention, a photodiode 45 is disposed with the housing 20, in a position to receive the filtered light from the light source 10. Preferably, the photodiode 45 is disposed within the housing 20 between the color filter 12 and the negative 16, but located to one side of the negative, in such position that the photodiode 45 is within the filtered light which is directed to the negative 16. Positioning the photodiode between the color filter and the negative, rather than between the negative and the printing paper, is deemed important, at least to the preferred embodiment of the present invention.

Light-exposure control unit

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Light-exposure control unit

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Abstract

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Claims17

Description3,844 words

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Classification2 codes

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Description3,844 words