Device for separating a beam of white light into a plurality of

Details Device for separating a beam of white light into a plurality of Device for separating a beam of white light into a plurality of

1990-03-23

1992-06-02

Nelms, David C.

Radiant energy

Photocells; circuits and apparatus

Optical or pre-photocell system

25022723, 356405, G01J 350

Patent

active

051189267

DESCRIPTION:

BRIEF SUMMARY
The invention relates to a device for separating a beam of white light into a plurality of elementary beams of specific color; it is concerned more particularly with a device of the type in question for the printing and development of photographic proofs and more especially in order, by means of a single light source, to feed on the one hand the densitometer and on the other hand the assembly for color analysis or even contrast analysis.
In other words, the invention involves separating a composite beam of white light into a series of elementary beams of particular wavelength segments, for the purpose of analyzing this white light into these various components.
French Patent Application 87.14,229 filed by the Applicant on Oct. 9, 1987 provides a device of the type in question which makes use of a plurality of optical fibers and of a scanning system. This solution remains complex in mechanical terms, makes it possible only with difficulty to obtain a uniform acquisition of the zone to be scanned, this resulting in non-uniformity in the measurement, and finally weakens the transmitted signal.
Japanese Patent JP-A-6,010,223 describes a device for separating a beam of white light into three components likewise of white light. These three components are converted into electrical signals by means of photosensitive sensors, after having passed through color filters for blue, green and red respectively, this being for the purpose of an analysis in terms of chromatic definition. It emerges that the use of such a device does not make it possible to obtain a sufficient output as regards the transmission of light flux for specific wavelengths to obtain a sufficiently accurate chromatic definition or analysis required for the printing of photographic proofs in high-quality color.
The invention overcomes these disadvantages. It aims at a device of the type in question which is simple to produce and reliable and in which the light transmitted in the various wavelength segments is uniform and easy to measure for purposes of analysis and of which the quantity in the various wavelength segments is sufficient for a given initial quantity of light.
This device for separating a beam of white light into a plurality of elementary beams of particular color, which is integrated in a chromatic analyzer for the printing of color photographs, comprises collecting the directed beam of white light, in order to transmit it to an optical system in the form of a beam emerging from the said optical sensor;
This device is defined in that the optical system consists of a plurality of dichroic filters of complementary color which are parallel and which are inclined relative to the optical axis of the emerging beam, each filter making it possible to reflect the quantity of light corresponding to the color of this filter and to transmit the light in the other colors.
In other words, the invention involves first calibrating the directed beam of white light to an optical system formed from complementary dichroic filters reflecting the light in their particular color, and then transmitting this specific wavelength band to photosensitive sensors converting this light signal into an electrical signal which is amplified and processed in the appropriate way.
Advantageously, in practice:
the dichroic filters are three in number and are used as half-mirrors, each associated with a complementary filter intended for eliminating the spurious components of the reflected part beam and for correcting this beam;
the optical sensor consists of a flexible optical fiber, that is to say of a bundle of parallel glass multifilaments, the endpiece of which forms a calibrated aperture;
the mirrors are inclined at 45.degree. relative to the optical axis obtained from the optical sensor;
each photosensitive sensor consists of a photodiode, a phototransistor or the like and is associated with a logarithmic amplifier making it possible to obtain an electrical output signal proportional to the optical density to be measured;
the analog, hence logarithmic electrical signals

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patent: 4223216 (1980-09-01), Quick et al.
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patent: 4517456 (1985-05-01), Halsall et al.
patent: 4776702 (1988-10-01), Yamaba
patent: 4909633 (1990-03-01), Okui et al.

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