US2821103A - Micro-photometry - Google Patents

Description

Jan. 28, T958 G. c. F. BLET 2,821,103

MICRO-PHOTOMETRY Filed oct. 27, 195s fw S 59/ H IS AT TORN EYS United States Patent O MICRO-pHoroMETRY Georges Charles Frdric Blet, Paris, France, assignor to Centre National de la Recherche Scientifique, Paris, France, a corporation of France Application October 27, 1953, Serial No. 388,627

Claims priority, application France October 30, 1952 Claims. (Cl. 88-14) lt is often necessary to plot the microphotometric curve for a variable density coating, such as a photographic paper positive or a chromatographic recording, for example, or to check the condition of a surface or the authenticity of a document of some kind.

Micro-photographic devices are known, comprising a light source and a photo-electric cell placed on either side of the document, the light passing therethrough. To make the document translucent, it is dipped into a fatty substance, which action in most cases results in a destruction of thel document; the analysis has a very reduced fineness which is limited by more or less pronounced faults in the texture of the support.

Devices are also known using photo-electric cells receiving the light diffused by the document to be examined, which offer, in particular, a much attenuated sensitivity due to the low intensity of the diffused light and to the inertia inherent to the cells.

An object of the present invention is to obviate these various drawbacks and, especially, to allow, in a very simple manner, the micro-photometric analysis by direct readings, or by continuous or discontinuous recordings, of all documents, without any alteration or destruction of said documents, The invention concerns a microphotometry process consisting in picking up and distributing in a homogeneous manner almost all the light diffused by the document, which then acts on a sensitive receiving element.

The invention also concerns a device for the application of this process.

According to the process of the invention, through an integrating sphere provided with an analysis Slot, possibly adjustable and placed as close as possible to the document to be examined, a region-image of a light source is formed onto the document, by means of an optical system, which image acts as a secondary light source, whereby the incident rays are reilected on themselves, and almost all the light diffused by the document enters, through the analysis slot, the integrating sphere, inside which the lighting is uniform and inside which, after undergoing multiple diffusions, it acts on a sensitive receiving element, arranged at any point in the sphere and connected with a measuring or recording device, after an amplification of the current if necessary.

Using an integrating sphere, inside which the lighting is uniform and placing it almost tangentially to the document, makes it possible to pick up almost all of the light diffused by the illuminated area, which thus acts in its entirety on the sensitive receiving element, regardless of its position inside the integrating sphere.

The integrating sphere may be made of any suitable metal, copper, iron sheet, aluminum, etc.; its inner surface is made so as to have a maximum diffusion power; this result is obtained by any suitable means. The inner surface may, for instance, be coated with a layer of magnesia, or with a matt coating with a base of white cellulose paint, or any diffusion coating adhering suitably "ice to the material constituting the sphere, or again, it may be subjected to an anodic surface treatment or a treatment similar to parkerizing.

As the optical system makes it possible to form an image of the light source on the document to be examined and transforms the latter into a secondary light source of which the surface diffused light alone is picked up, there becomes possible to examine all documents with no necessity of making them translucent, by any preliminary dipping into fatty substances or otherwise; thus, the action of the latter on the document and support being eliminated, remarkable results are obtained, both as regards the sharpness of curves, for instance and the fineness of analysis, the document, finally remaining unchanged, the influence of the support structure being eliminated.

The invention makes it possible, finally, by the use of light filters and sensitive receiving elements, to carry out a microphotometric analysis at all wave lengths, thus making its utilization particularly valuable for chromatography.

When eltecting a continuous recording of the variations caused by the surface of a document, and transmitted by the photoelectric cell, it is convenient to adjust the unwinding of the recording film to a speed which is a known multiple of the speed of displacement of the document in front of the analysis slot of the integrating sphere. This makes it possible to determine rapidly and without any risk of error, the interesting points on the document, from a simple reading and comparison of the recording.

For a better understanding of the invention and of various additional details, advantages and characteristics thereof, reference is made to the following description of an embodiment thereof taken in conjunction with the accompanying drawings wherein:

Figure l is a side elevation in the from of a diagrammatic cross section taken along the axis of the said embodiment;

Figure 2 is a view, taken as indicated by the arrows 2A-2A, of certain details of the embodiment of Figure l; and

Figure 3 is a view in perspective of the embodiment of Figure l.

The device comprises essentially a light source 1, consisting, for example, of a lamp having a rectilinear lament, placed inside a lightbox 2, a passage 5 connecting the light box 2 with the integrating sphere 7; the passage 5 is provided with a slot 4 illustrated in Figure l as a block. This slot 4 has a section adjustable by any suitable means, for example, of the type generally used for the entrance slots of spectrographs. Usually the section of the entrance slot of a spectrograph is adjustable in length and width. The length and width of the slot section of a spectrograph may be symmetrically controlled by two devices of which the first thereof (Figure 2) is comprised of a screw 21 with two different pitches 23 and 24 respectively driving two nuts 25, 26 closer to or apart from each other when an adjusting knob 22 for the screw is turned in opposite directions. The nuts 2S, 26 carry shields 27, 28 which define slot S and make it narrower or wider in a first dimension. A second similar device (not shown) lies across axis XY in perpendif' -is metallic, for instance, and coated inside with a diffusing material such as magnesia, comprises the sensitive receiving element 10, consisting of a sensitive photo-electric cell and an analysis slot 8, arranged as close as possible and lparallel to the document to be examined. This arrangement of the sphere 7 and slot 8 is such that, practically, all of the diffused light be picked up by the slot 8, i. e. that the solid angle be substantially equal to 2.

The dimensions of the slot 4 are preferably about ten to ltwelve times smaller than those of the slot 8.

The document to be examined, 9, is placed on a conventional device allowing an examination of all areas. This device may take the form, for example, of two drums 12 and 13 of which the former is mounted on a lshaft 16 and the latter on a shaft 17. The document 9 to be analyzed is fastened in a loop around these drums to be moved thereby past the analysis sloty 8 as the shaft 16 is driven by a motor (not shown).

Within the scope of the invention, the adjustable slot 4 and the analysis slot 8 may be replaced by diaphragms or any other conventional device having the same function.

The sensitive receiving element 10 may consist of any sensitive photo-electric cell, the current generated being amplified if necessary. Thus the output of the photoelectric cell may be amplified by an amplifier interposed between the photoelectric cell and a registering device 21. This registering device may be a conventional indicating galvanometer. If a record is desired, the galvanometer 21 may be provided with a recording pen (not shown) adapted to inscribe a trace on a. recording medium as, say, a registering band 30 fastened in a loop around the drums 14 and 15, these drums being respectively mounted on the shafts 16, 17. With the registering band so arranged, the band will move past galvanometer 21 at the same speed as the movement of document 9 past analysis slot 8, the displacement of the hand in recording thus being a known multiple of displacement of the document in front of the analysis slot.

It is possible to simplify the optical arrangement, which forms the image of the light source on the document to be examined, by omitting the convergent system 3 and suitably adjusting the diaphragm or slot 4 so that the image be formed on the document.

In case it is desired to carry out an analysis for a predetermined region of the spectrum, suitable colour filters are interposed at 11. As a means for interposing separate color filters, there may be provided a disk 18 perforated with holes bearing filters F, the disk being rotatable around a shaft 19. Such a disk may be provided with one hole deprived of a filter, so as to cause the beam to pass directly to the document. The filters may be colored in case a colored document is studied. For instance, when a more or less colored blue band is to he studied, filters may be used of a complementary orange color in order to enhance the sensitivity.

It must be stated that the document can be either a printed or coated paper, or any surface material coated or not, various portions of which can be disposed parallel and close to the analysis slot.

What I claim is:

1. An apparatus for surveying the conditions of surface of bodies capable of diffusing light, comprising a symmetrical casing having its axis perpendicular to said surface, the end of the casing which is towards said surface being substantially fully spherical and having an inner diffusing surface, in said spherical part a first slot parallel and as close as possible to the surface, a light sensitive receiver fixed on the inside wall of said spherical part, at the other end of the casing and inside thereof a source of light centered on the axis of the casing, an adjustable slot uniformly illuminated by the source of light perpendicular to the axis of the casing between the source 'of'light'and the spherical part of the casing, an optical device between the slot and the surface for concentrating the images of said adjustable slot on the surface through the first slot, and a measuring device connected to the light sensitive receiver.

2. An apparatus for surveying the conditions of surface of bodies capable of diffusing light, comprising a symmetrical casing having its axis perpendicular to said surface, the end of the casing which is towards said surface being substantially fully spherical and having an inner diffusing surface, in said spherical part a first slot parallel and as close as possible to the surface, a light sensitive receiver fixed on the inside wall of said spherical part, at the other end of the casing and inside thereof a source of light centered on the axis of the casing, an adjustable slot uniformly illuminated by the source of light perpendicular to the axis of the casing between the source of light and the spherical part of the casing, an optical device between the slot and the surface for concentrating the images of said adjustable slot on the surface through the first slot, and a registering device connected to the light sensitive receiver.

3. An apparatus for surveying the conditions of surface of bodies capable of diffusing light, comprising a symmetrical casing having its axis perpendicular to said surface, the end of the casing which is towards said surface being substantially fully spherical and having an inner diffusing surface, in said spherical part a` first slot parallel and as close as possible to the surface, a light sensitive receiver fixed on the inside wall of said spherical part, at the other end of the casing and inside thereof a source of light centered on the axis of the casing, an adjustable slot uniformly illuminated by the source of light perpendicular to the axis of the casing between the source of light and the spherical part of the casing, an optical device between the slot and the surface for-concentrating the images of said adjustable slot on the surface through the first slot, a measuring device connected to the light sensitive receivers, and a registering device connected to the measuring device.

4. An apparatus for surveying the conditions of surface of bodies capabley of diffusing light, comprising a symmetrical casing having its axis perpendicular to said surface, the end of'the casing which is towards said surface being substantially fully spherical and having an inner diffusing surface, in said spherical part a first slot pai'- allel and as close as possible to the surface, a light sensitive' receiver fixed on the inside wall of said spherical part, at the other end of the casing and inside thereof centered on the axis of the casing, a first optical device perpendicular to the axis, an adjustable slot uniformly illuminated through the first optical device perpendicular to the axis between the first optical device and the spherical part of the casing and constituting a secondary source of. light, a second optical device between the slot and the surface for concentrating the images of said adjustable slot o n the surface through the first slot, and a measuring device connected to the light sensitive receiver.

5. An apparatus-for surveying the conditions of surface of bodies capable of diffusing light, comprising a symmetrical casing having its axis perpendicular to said surface, the end of the casing which is towards said surface being substantially fully spherical and having an inner diffusing surface, in said spherical part a first slot parallel and as close as possible to the surface, a light sensitive receiver fixed on the inside wall of said spherical part, at the other end of the casing and inside thereof a source of light centered on the yaxis of the casing, a first optical device perpendicular to the axis, an adjustable slot uniformally illuminated through the first optical device perpendicular to the axis between the first optical device and the spherical part of the casing and constituting a secondary source of light, a second optical device between the slot and the surface for concentrating the images of said adjustable slot on the surface through the first slot, and a registering device connected to the light sensitive receiver.

6. An apparatus for surveying the conditions of surface of bodies capable of diffusing light, comprising a symmetrical casing having its axis perpendicular to said surface, the end of the casing which is towards said surface being substantially fully spherical and having an inner diffusing surface, in said spherical part a first slot parallel and as close as possible to the surface, a light sensitive receiver fixed on the inside wall of said spherical part, at the other end of the casing and inside thereof a source of light centered on the axis of the casing, an adjustable slot uniformly illuminated by the source of light perpendicular to the axis of the casing between the source of light and the `spherical part of the casing, a chromatic filter perpendicular to the axis of the casing, an optical device between the filter and the surface for concentrating the image of said adjustable slot on the surface through the first slot, and a measuring device connected to the light sensitive receiver.

7. An apparatus for surveying the conditions of surface of bodies capable of diffusing light, comprising a symmetrical casing having its axis perpendicular to said surface, the end of the casing which is towards said surface being substantially fully spherical and having an inner diffusing surface, in said spherical part a first slot parallel and as close as possible to the surface, a light sensitive receiver xed on the inside wall of said spherical part, -at the other end of the casing and inside thereof a source of light centered on the axis of the casing, an adjustable slot uniformly illuminated by the source of light perpendicular to the axis of the casing between the source of light and the spherical part of the casing, a chromatic filter perpendicular to the axis of the casing, an optical device between the filter and the surface for concentrating the image of said adjustable slot on the surface through the first slot, and a registering device connected to the light sensitive receiver.

8. An apparatus for surveying the conditions of surface of bodies capable of diffusing light, comprising a symmetrical casing having its axis perpendicular to said surface, the end of the casing which is towards said surface being substantially fully spherical and having an inner diffusing surface, in said spherical part a first slot parallel and as close as possible to the surface, a photo-electric cell fixed on the inside wall of said spherical part, at the other end of the casing and inside thereof a source of light centered on the axis of the casing, an adjustable slot uniformly illuminated by the source of light perpendicular to the axis of the casing between the source of light and the spherical part of the casing, an optical device between the slot and the surface for concentrating the image of said adjustable slot on the surface through the first slot and a measuring device connected to the photo-electric cell.

9. An apparatus for surveying the conditions of surface of bodies capable of diffusing light, comprising a symmetrical casing having its axis perpendicular to said surface, the end of the casing which is towards said surface being substantially fully spherical and having an inner diffusing surface, in said spherical part a first slot parallel and as close as possible to the surface, a light sensitive receiver fixed on the inside wall of said spherical part, at the other end of the casing and inside thereof a source of light centered on the axis of the casing, an adjustable slot uniformly illuminated by the source of light perpendicular to the axis of the casing between the source of light and the spherical part of the casing, an optical device between the slot and the surface for concentrating the image of said adjustable slot on the surface through the first slot, a registering device connected to the light sensitive receiver, and means for moving in synchronism the surface and the registering device.

10. An apparatus for surveying the conditions of surface of bodies capable of diffusing light, comprising a symmetrical metallic casing having its axis perpendicular to said surface, the end of said casing which is towards said surface being substantially fully spherical and bearing on its inside wall a diffusing coating, in said spherical part a first slot parallel and as close as possible to the surface, a light sensitive receiver fixed on the inside wall of said spherical part, at the other end of the casing and inside thereof a source of light centered on the axis of the casing, an adjustable slot uniformly illuminated by the source of light perpendicular to the axis of the casing between the source of light and the spherical part of the casing, an optical device between the slot and the surface for concentrating the image of said adjustable slot on the surface through the first slot, and a measuring device connected to the light sensitive receiver.

References Cited in the le of this patent UNITED STATES PATENTS Tuttle et al Feb. 16, 1943 Schurcliff Apr. 18, 1944 OTHER REFERENCES

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