Abstract: According to a process for regulating the amount of copying light in a closed control loop of a photographic color photocopier equipped with color filters, the copying light influenced by the color filters is selectively measured in the primary colors, red, green and blue. A deviation resulting from the comparison of the real values with predeterminable set values is subdivided into a color deviation and a brightness deviation. The color deviation is compensated by regulating the color filters, whereas the brightness deviation is converted into a correction factor for the lighting time, so that for each primary color the product of the light intensity real value by the effective lighting time is constant and identical to the product of the light intensity set value by the lighting time set value.

Abstract: A method for determining the exposure time in photographic copying includes measuring the light intensity at different measuring points of the projected picture of the original to be copied for an initial copying light intensity, and forming a mean value of the light intensity values measured at such points; the exposure time for a current copying light intensity is determined by modifying the aforementioned mean value with a proportional action factor corresponding to the ratio of the light intensity value measured at a selected one of the measuring points for the current copying light intensity relative to the light intensity value measured at the same point for the initial copying light intensity.

Abstract: This invention relates to a process and a device for adjusting a photographic color enlarging or copying apparatus. By means of the measuring device that uses copying light of the enlarging apparatus to be adjusted as the measuring light, the color densities of a test copy made of a test original and of a reference copy which represents a satisfactory picture reproduction of the test original are measured selectively in the colors red, green and blue and are compared with one another. Corresponding to an existing deviation, adjusting control means at the enlarging apparatus that color-selectively influence the amount of copying light are readjusted until the deviation is balanced, and another test copy is made with the new exposure conditions and is measured.

Abstract: In a circuit for the control of exposure time with photographic enlarging equipment with variable enlargement ratio, and with a device for determining light quantity, a light sensitive electric transducer is provided a fixed distance to the negative plane of the enlarging equipment. Means for generating a signal representing the enlargement ratio, in the form of a potentiometer, modifies the signal derived from the device for determining light quantity to thereby produce a signal representative of the proper change of exposure time for a selected enlargement ratio. The circuit incorporates function generators to modify the signal from the light sensitive electric transducers to allow for the correction of the failure of the reciprocity law.

Abstract: In a photometric circuit a reference current is supplied into the input of the logarithmic amplifier at the same time the signal compensating the error originating in the photocell is supplied to the circuit. The reference current corresponds to the current which would occur in the photocell for the lowest measurable intensity of illumination. A sum-and-difference amplifier has one of its inputs supplied by the output of the logarithmic amplifier and its second input is supplied by a reference voltage. The control loop contains a storage capacitor connected after the sum-and-difference amplifier and an impedance converter connected after the storage capacitor. The compensating and reference currents are controlled by switches synchronized with a light chopper mounted in front of the photocell.

Abstract: Three measuring channels in a photographic color printing and enlarging apparatus are utilized for determining the filter values of the primary colors. The exposure time is determined by adjusting and reading the amplification factor of an amplifier which amplifies the signal of a light-voltage transducer containing a photoelectric element, which obtains its input from a measurement of each of the three primary color components in the printing light. The light-sensitive element of the photoelectric element has a characteristic curve which is linearly related to the intensity of illumination and it is preferably a photodiode. The light impinging on the photodiode is modulated by an electromechanical light-chopping device and the measuring signal is controlled by a zero-regulator. The light-sensitive element, the zero-regulated device, the light-chopping device and filter controlling device are miniaturized and fitted into a light-measuring probe.