US3680024A

US3680024A - Light responsive and measuring device

Info

Publication number: US3680024A
Application number: US18399A
Authority: US
Inventors: Kenichi Tashiro; Hirokazu Tanaka
Original assignee: Stanley Electric Co Ltd
Current assignee: Stanley Electric Co Ltd
Priority date: 1970-02-27
Filing date: 1970-02-27
Publication date: 1972-07-25
Anticipated expiration: 1989-07-25

Abstract

A photosensitive device includes an insulator base on which are located inner, outer and intermediate space electrodes which delineate concentric circular or noncircular areas which are occupied by a photoconductive material engaging opposing edges of the electrodes along their lengths. One or more of the electrodes may be open across their lengths, the openings being occupied by photoconductive material connecting adjacent areas. One or more of the electrodes may be provided with spaced parallel legs interdigitated by legs of another of the electrode.

Description

United States Patent Tashiro et a1.

[451 July 25, 1972 LIGHT RESPONSIVE AND MEASURING DEVICE lnventors: Kenichi Tashiro; l-lirokazu Tanaka, both of Tokyo-to, Japan Assignee: Stanley Denki Kabushiki Kaisha, Tokyoto, Japan Filed: Feb. 27, 1970 Appl.No.: 18,399

Related 0.8. Application Data Division of Ser. No. 376,477, June 19, 1964, Pat. No. 3,521,962.

US. Cl ..338/l7, 338/15 Int. Cl ..H0lc 7/08 Field of Search 338/15, l7, l8, 19; 356/222; 250/209 [56] References Cited UNITED STATES PATENTS 3,013,232 12/1961 Lubin ..338/15 X Primary Examiner-Benjamin A. Borchelt Assistant Examiner-R. Kinberg Attorney-Stanley Wolder [5 7] ABSTRACT 8 Claims, 23 Drawing Figures LIGHT RESPONSIVE AND MEASURING DEVICE The present application is a divisional application of copending patent application Ser. No. 376,477 filed June 19, 1964, now US. Pat. No. 3,52l,962.

The present invention relates generally to improvements in light responsive and light measuring devices and it relates particularly to a light measuring system which is compensated to provide a desirable response characteristic for different and widely varying light conditions and is highly suitable for photographic purposes.

In the accompanying drawings which illustrate preferred embodiments of the present invention:

FIG. 1 is a circuit diagram of a conventional arrangement utilizing photocurrent generating devices such as selenium photocells, etc.;

FIG. 2 is a circuit diagram of a conventional compensated light measuring arrangement employing a light receiving photoconductive element made of cadmium sulfide or the like;

FIG. 3 is a graph showing a characteristic resistance variation of a photoconductive light measuring element in response to brightness variation;

FIG. 4 is a graph showing the measured current characteristic relative to photographic geometric series light amount,

which characteristic corresponds to the characteristic shown in FIG. 3;

FIG. 5 is a graph showing the pointer deflection angle characteristic of the measured light value indicating ammeter;

FIGS. 6 and 7 are circuit diagrams of embodiments of arrangements according to the present invention;

FIG. 8 is a graph showing the characteristic of the pointer deflection angle of the indicating ammeter of the arrangement of the present invention in response to brightness variation;

FIGS. 9 and 10 show examples of the light receiving structures of the arrangement according to the present invention;

FIG. 11 is a graph showing the brightness resistance characteristic of the resistor of the arrangement according to the present invention;

FIG. 12 is a graph showing the resistance-current characteristic of the arrangement according to the present invention;

FIG. 13 is a graph showing the measurement characteristic of the arrangement according to the present invention indicating the pointer deflection in response to photographic geometric series light amount;

FIG. 14 is a front view of the light receiving portion of the photoconductor utilized in the arrangement of the present invention;

FIG. 15 is a front view showing a modified form of the light receiving portion as shown in FIG. 14, the structure being arranged in a square shape;

FIGS. 16 and 17 are other modified examples of the light receiving portion of the photoconductor;

FIG. 18 is a graph showing the ideal photoconductive characteristic for arithmetical series indication of the light measuring arrangement and the general characteristic of the photoconductor of the arrangement according to the present invention;

FIG. 19 is a graph showing the measured value indication error characteristic of the arrangement of the present invention;

FIG. 20 is an example of the measuring circuit arrangement for reducing the indication error as far as possible; and

FIGS. 21, 22 and 23 show examples of the photoconductor structures to be utilized in the circuit as shown in FIG. 20.

It is comparatively simple to carry out exposure value measurement and automatic exposure setting in accordance with such measured value under normal photographic conditions. Under counter-light photographic conditions, however, the application of such average illumination measurement methods as under normal light condition result in under-exposure. Such defective results are apparent not only in photography in which the light image sensitizes the emulsion but also in television camera operation where the image is electrically transduced.

In order to automatically compensate such excessive indication or setting of the light measurement means which is inevitably produced under counter-light or back lighting photographing conditions, that is where the subject is highly illuminated by light from the rear of the subject relative to the camera it has been proposed and practiced to some extent to utilize a circuit which is essentially shown in FIG. I as a light measurement compensating arrangement comprising photocurrent generating element such as selenium photocell. In this arrangement, two selenium photocells S, and S of different light receiving areas are provided. The photocell S of large light receiving area is connected to an indicating meter M in the same manner as in the normal reflection measurement method, while the photocell S of small light receiving area has a large light receiving angle of the incident ray measurement method. In order to compensate the indication accuracy when intense direct light rays impinge, with the photocells connected in different polarity from each other, resistors R and R of suitably selected values are respectively provided in series connection so that under-exposure due to excessive meter indication under counter-light conditions can be avoided.

It is clear that such system cannot be applied to the arrangement utilizing photoconductive elements such as cadmium sulfide, cadmium selenide, etc. When a photoconductor is utilized as a light receiving element for indicating photographic exposure value, the situation is different from that of other meters such as illuminometers. That is, the indicated value must correspond to light intensity variation of geometric series with the common ratio of 2 whereby each doubling of the light intensity provides a unit increment increase in the indicated value or measurement, so that compensation of the light response is highly difficult. The brightness resistance characteristic of the conventional photoconductor consisting of cadmium sulfide, cadmium selenide, etc. is as shown by the curve A of FIG. 3. In connection with this characteristic it can be said that in response to brightness variation in the manner of geometric series, the resistance value also varies in the manner of geometric series, the two variations being in logarithmic relation with each other. Therefore, when an ammeter is used which is provided with uniform magnetic field or with a very slightly compensated magnetic field which is almost uniform, the indicating pointer deflection angle variation in response to brightness geometric series variation is also in the manner of geometric series, so that the scale graduation is not uniformly spaced and wide brightness range indication cannot be made within a certain pointer deflection range.

In order to compensate for such phenomenon it has been common practice to provide a compensating circuit as shown in FIG. 2 in which a fixed resistor R which does not change its value in response to brightness variation is connected in parallel with a photoconductor PC to define a shunt. Accordingly, when the brightness is low, the current intensity (power source: battery B) through the ammeter is increased, and when brightness is high the current intensity which of necessity increases is suppressed by a resistor R in series connection. This resulted in a slight advantage in indication effect, but the current variation in response to geometric series variation of v brightness is still such as shown in FIG. 4 which is not satisfactory. According to such compensated circuit characteristic, if the ammeter M is suitably compensated so as to have a deflection angle characteristic such as shown by the solid line of FIG. 5. the indication scale can be of course graduated by proportional uniform spacing in response to geometric series variation of received light brightness. However, such compensation of the ammeter M is technically difiicult.

If a uniform magnetic field ammeter is utilized having a deflection angle characteristic as shown by the dotted line of FIG. 5, for the aforementioned reason the scale graduation is not uniformly spaced so that measurement accuracy changes with illumination ranges and reading of indicated value becomes very troublesome and human error is apt to be caused in reading.

;-,l ine"curve of FIG. is connected to the photoconductor without circuit compensation, it may be considered that approximately uniformly spaced scale graduation be obtained. According to this method, however, the measurement range becomes extremely narrow and measurement cannot be performed for a wide range of brightness variation.

The object of the present invention is to automatically compensate the excessive indication of the light measuring device or automatic setting operation of the camera in response to such indication so that excellent effect can be obtained in the resulting photograph.

Another object of the present invention is to provide a light measuring arrangement comprising light receiving photoconductor elements, such as of cadmium sulfide, cadmium selenide, etc., having a measurement range corresponding to broad brightness variation and having almost, uniformly spaced indicating deflection angle scale graduation in relation to variation of received light brightness in the manner of geometric series with the common ratio of 2.

A further object of the present invention is to provide novel light receiving elements adapted for attaining the above objectsof the present invention more effectively.

In the arrangement of the present invention as shown in FIGS. 6 and 7, for the above purpose, in the circuit comprising a power source battery 1 and an ammeter or sensitive current meter 2 there are inserted

photoconductors

3, 4 in series connection as light receiving elements, and a resistor is connected in parallel with one of or each of more than two of such photoconductors. In the example as shown in FIG. 6, a single resistor 6 is connected in parallel with the photoconductor 3 to define a shunt, and in another example as shown in FIG. 7 three

photoconductors

3, 4 and 5 are connected in series with each other and resistors 6and 7 are connected in series with

photoconductors

3 and 4 respectively. In practice variable resistors may be utilized for such resistors so as to be adjustable upon inspection of the operation of the arrangement. Another resistor 8 is provided for compensating the indicated value.

If it is assumed that in the circuit as shown in FIG. 6 the photoconductor 4 has a fixed resistance value independent of the brightness, then the resultant resistance due to the photoconductor 3 and the resistor 6 in parallel connection is smaller than the resistance which would appear if the photoconductor 3 alone is inserted in the circuit, so that the current flowing into the ammeter is more intense. The rate of decrease of this resistance is. large when the brightness is low and small when the brightness is high. Accordingly, on the as sumption that the resistance value of the photoconductor 4 is constant, the resistance variation is shown by the curve of FIG. 3.

If two or more photoconductors are connected in series with each other as shown in the example of the present invention shown in FIG. 7, the photoconductor 5 varies its resistance valuein response to received light brightness. This resistance change is great when the brightness is low and small when the brightness is high so that the resultant resistance variation is such as shown by the curve C of FIG. 3. In this case the current flowing through the ammeter is approximately proportional to the logarithmic variation of the brightness. Accordingly, a uniform magnetic field ammeter or an ammeter compensated so as to have approximately uniform magnetic field is utilized, the characteristic curve is such as shown by the curve a of FIG. 8. The characteristic curve a in this case does not produce any compensating function in a counter-light photographing. However, as shown in FIGS. 9 and 10, by making the light receiving angle of the photoconductor 4 smaller than that of the photoconductor 3, the resistance value variation of the photoconductor 4 is made substantially duller than that of the photoconductor 3, and further, impinging of harmful rays outside the image angle is prevented. As a result, the circuit resistance value at the high brightness side of the curve C of FIG. 3 is increased.

Thus, when light measurement is made with high brightness that is proper to a counter-light photographing, the ammeter deflection is decreased as shown in the characteristic curve a of FIG. 8 so that exposure value according to lightmeasurement indication is increased, and, in automatic setting cameras, the diaphragm aperture or exposure time can be increased. Since such compensation and operation amount may be increased with the height of brightness, the compensation or the resulting operation may be automatically carried out in accordance with the brightness difference between the object to be photographed and the counter-light. As a result, excellent effect is obtained which is adapted for the actual purpose of the photographing.

In such arrangement of the present invention, the lowest brightness current flow due to the circuit resistance resulting from the photoconductor and the resistor in parallel connection is not under the influence of a resistor of constant value and in series connection, but under the influence of the circuit resistance resulting from the photoconductor and the resistor connected in parallel therewith both of which receive light rays of the same brightness. On the other hand, under high brightness condition the current flowing into the ammeter is suppressed not by a constant value resistor in series connection but by complex suppressive action in accordance with the received light brightness. Accordingly, the general characteristic curve indicating the correlation between the resistance value outside the ammeter 2 and the brightness is such as shown by FIG. 11. As a result, by making the light rays-imp inge on each of the photoconductors provided as light receiving elements, it is possible to obtain a current characteristic as shown in FIG. 12. By connecting a uniform magnetic field ammeter 2 the ammeter pointer may be made to deflect in pro-' portion to the geometric series variation of the received light brightness (for example, light valueindication). Further, since this arrangement can be applied to wide' brightness range, if this arrangement is applied to an automatic exposure value setting camera, the action is effectively related to the diaphragm aperture or exposure time setting device; and when this arrangement is applied to a reading exposure meter which is a separate single light measuring device, the scale graduation can be uniformly spaced and of multi-stage system so that the reading of scale is made easyand partialaccuracy change can be avoided. r

The novel structure of thelight receiving element to be utilized in the arrangement according to the present invention is of such electrode arrangement that over the whole light receiving face arranged on a base there are provided several light receiving bandsranging from the central portion to the peripheral portion of the face, said bands being able to receive light rays separately or selectively in several combined groups. 7

Detailed description is given herebelow in conjunction with each of the illustrated examples.

Referring to FIG. 14,

electrodes

21, 22 and 23 are arranged on a base 25 which is, as is well known, made of quartz, ceramic, or other suitable insulating material. Between the electrodes there are provided bands of photoconductive resistors 26 composed of such photoconductive substance as cadmium sulfide, etc. The

electrodes

21, 22 and 23 are of the shape of arcs of concentric circles. The electrode 21 is of ring shape which in a part is cut apart and in another part connected by a band to the central electrode. The electrode 22 surrounding this electrode 21 is composed of two partially cutapart ring-shaped members and a ring-shaped member therebetween, these members being connected together by a connecting member. The inner partially cut apart ring-shaped portion of the electrode 22 is positioned inside the partially cut-apart ring-shaped portion of theelectrode 21. The outermost electrode 23 consists of a ring-shaped portion and a partially cut-apart ring-shaped portion, which latter portion is positioned inside the outer partially cut-apart ring-shaped portion of the electrode 22.

In a light receiving element of such structure, the portions between

electrodes

21 and 22 and between 22 and 23 act as independently separate light receiving bands. Accordingly, by

making the electrode 22 a two-way terminal and switching this electrode into a circuit with either

electrode

21 or 23, measurements may be made separately by the inner light receiving band and by the outer light receiving band so that the condition of illumination distribution or nonuniform illumination condition can be detected. Further, by connecting the two light receiving bands in series with each other with the electrode 22 acting as a two-way terminal, automatic exposure value compensation at the time of counter-light photographing can be carried out.

In FIG. 15, a square-shaped light receiving element is shown which is different from that shown in FIG. 14 only in that the electrode 21 is square-shaped, the electrode 22 consists of an enclosing square-frame-shaped portion and squarely bent two arm portions connected to aforementioned portion, and the electrode 23 consists of two squarely extending arms connected together and positioned between the

electrodes

21 and 22, the function and utility of this element being the same as that shown in FIG. 14. g

In the light receiving element as shown in FIG. 16 the

electrodes

21, 22, 23 and 24 are arranged in concentric circles. By attaching a lead to each of said

electrodes

21, 22, 23 and 24, the resistors 26 between the mutually adjacent electrodes may be utilized as separate light receiving bands. Further, it is possible to utilize the combined whole surface of the light receiving faces inside the electrode 22, inside the electrode 23, or inside the electrode 24. According to such manner of use, the light measuring angle range can be changed as shown in FIG. 10, so that every time the lens is changed and the photographic angle is changed, accurate measurement of the average illumination within the photographing angle can be effectively performed. Further with respect to a single photographing angle, the influence of outer harmful light rays on the accurate local illumination measurement of the object to be photographed can be detected, so that the operator can determine the most appropriate exposure condition with due consideration to elimination of such harmful influence. In FIG. angles 0,, Oand 0 indicate light measuring image angles corresponding to each of said light receiving bands respectively, and L indicates a condensing lens for controlling incident light rays.

In the example as shown in FIG. 17 the structure of the element of FIG. 16 is so arranged as to have a square configuration.

In each of the illustrated light receiving elements the photoconductive resistors 26 are shown ashaving approximately the same width. However, it is of course not absolutely necessary to arrange the electrodes with even spacings and the spacing can be changed so as to be adapted to different purposes.

As mentioned above, according to the light measuring arrangement of the present invention, the light measurement value compensation for accurate film exposure and indication of said light measurement value in the manner of arithmetical series can be carried out. In order to reduce the indication error, the following measure is taken.

The general characteristic of the photoconductor as utilized in the aforementioned light measuring arrangement is shown by the curve I, of FIG. 18. In this case, the error between the arithmetical series indication of the light measuring arrange ment in response to the geometrical series illumination variation of the object to be photographed is indicated by the solid line n of FIG. 19. The most important factor of the direct cause of this indication error is the photoconductive characteristic of the photoconductor. In order to obtain highly accurate light measurement indication, it is necessary to cause the photoconductive characteristic of the above light measuring arrangement to sufficiently approach the ideal characteristic curve for accurate arithmetical series indication (the solid line I of FIG. 18). In view of the deviation in high brightness range of photoconductive characteristic curve I of the above light measuring arrangement from the ideal characteristic curve I,

in FIG. 18, compensation of the high brightness range photoconductive characteristic of the light measuring arrangement is now considered.

For such purpose, a photoconductive element S which is highly responsive in high brightness range is connected in parallel with the

photoconductors

3 and 4 connected in series with each other of the above light measuring arrangement, as shown in FIG. 20. With such novel arrangement, a general photoconductive characteristic curve as shown by the dotted line 1 of FIG. 18 is obtained, and the indication error is now shown by the curve n of FIG. 19.

The novel structure of the light receiving photoconductive element for such error compensating circuit is as follows:

Referring to FIG. 21, in the light receiving element there are provided a point electrode P at the center, another electrode P surrounding the electrode I in partially cut apart loops connected together, and still another electrode P also sur rounding the electrode P in partially cut apart loops connected together, said electrodes P and P being positioned in mutually opposed relation with their are shaped branch members arranged in mutually interposed relation. The spaces between electrodes P and P P and P and P and P are directly covered by a continuous band of photoconductor. In FIGS. 22 and 23 there are shown further modification of such structure. By suitably connecting the electrodes P P and P of the element, the circuit shown in FIG. 20 is readily constituted and aforementioned advantage is obtained.

As mentioned above, according to the arrangement of the present invention, accurate compensation of the characteristic of and the proper function of the photoconductor is carried out. Further, by suitably changing the numbers of the connected photoconductors and of the resistors in parallel connection, different kind of compensation may also be perfonned. By applying different structures of the above mentioned kinds to various photoconductive elements, building-in of the elements in the arrangement can be readily performed, and manufacture of the each element is carried out simultaneously and under the same condition and as a result sufficiently high measurement accuracy can be obtained by the elements placed under the same condition. Thus the arrangement of the present invention provides a great advantage.

While there have been described and illustrated preferred embodiments of the present invention it is apparent that numerous alterations, omissions and additions may be made without departing from the spirit thereof.

What is claimed is:

l. A photosensitive device comprising an insulating base, a plurality of spaced concentric bands of rectangular configuration of photoconductive material disposed on said base, anda plurality of concentric spaced conductor electrodes of rectangular configuration disposed on-said base and engaging opposite edges of said photoconductive bands.

2. A photosensitive device comprising a plurality of mutually spaced electrodes including an inner first electrode, an outer second electrode and an intermediate third electrode, and delineating a first inner area between said first and third electrodes and a second outer area between said second and third electrodes extending about said first area, and a photoconductive material disposed in said first and second areas and engaging the edges of opposing electrodes along the lengths thereo 3. The photosensitive device of claim 1 wherein said first and second areas are substantially concentric.

4. The photosensitive device of claim 3 wherein said areas v are of circular configuration.

5. The photosensitive device of claim 3 wherein said areas are of substantially rectangular configuration.

6. The photosensitive device of claim 2 wherein said intermediate electrode has an opening formed across the length thereof to provide a passageway between said first and second areas, said photoconductive material being disposed in said passageway and interconnecting said photoconductive material in said first and second areas.

trode and delineating with said second electrode a third area extending about said second area, and a photoconductive material disposed in said third area and engaging the opposing edges of said second and fourth electrodes.

Claims

1. A photosensitive device comprising an insulating base, a plurality of spaced concentric bands of rectangular configuration of photoconductive material disposed on said base, and a plurality of concentric spaced conductor electrodes of rectangular configuration disposed on said base and engaging opposite edges of said photoconductive bands.

2. A photosensitive device comprising a plurality of mutually spaced electrodes including an inner first electrode, an outer second electrode and an intermediate third electrode, and delineating a first inner area between said first and third electrodes and a second outer area between said second and third electrodes extending about said first area, and a photoconductive material disposed in said first and second areas and engaging the edges of opposing electrodes along the lengths thereof.

3. The photosensitive device of claim 1 wherein said first and second areas are substantially concentric.

4. The photosensitive device of claim 3 wherein said areas are of circular configuration.

7. The photosensitive device of claim 2 wherein at least one of said electrodes includes a pair of spaced opposite first legs and another of said electrodes includes a second leg disposed between and spaced from said first legs.

8. The photosensitive device of claim 2 including a fourth electrode disposed outside and spaced from said second electrode and delineating with said second electrode a third area extending about said second area, and a photoconductive material disposed in said third area and engaging the opposing edges of said second and fourth electrodes.