Search Images Maps Play YouTube News Gmail Drive More »
Sign in
Screen reader users: click this link for accessible mode. Accessible mode has the same essential features but works better with your reader.

Patents

  1. Advanced Patent Search
Publication numberUS3673415 A
Publication typeGrant
Publication dateJun 27, 1972
Filing dateNov 4, 1970
Priority dateNov 8, 1969
Also published asDE2054751A1
Publication numberUS 3673415 A, US 3673415A, US-A-3673415, US3673415 A, US3673415A
InventorsTakahata Hisatoshi, Yoshimura Hirofumi
Original AssigneeYashica Co Ltd
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Shutter operating circuit having means to close shutter when light is insufficient
US 3673415 A
Abstract
In a shutter operating circuit comprising a shutter time determining circuit including a photo-electromotive element, and a high input impedance transistor; means to initiate the operation of the shutter time determining circuit; a shutter control circuit controlled by the shutter time determining circuit; and a source of supply connected to said two circuits, there are provided a series circuit connected across the source and including serially connected resistor and capacitor, and a switching transistor with its base electrode connected to the juncture between the resistor and the capacitor, the series circuit acting to trigger the switching transistor to operate the shutter control circuit when the shutter time determining circuit fails to operate after elapse of a predetermined interval after the operation of the initiating means.
Images(1)
Previous page
Next page
Claims  available in
Description  (OCR text may contain errors)

United States Patent Yoshimura et a].

[ 1 June 27, 1972 l/l969 Mori et al. ..95/l0CT 12/1969 Fuwa et a1 ..250/2l2 X Primary Examiner-James W. Lawrence [72] inventors: Hirof'umi Yoshimura, Okaya; Hisatoshi Ass[s,ammmine, 1- Grigsby fakaham, shlmosuwa'Mach" both of AttameyChittick, Pfund, Birch, Samuels & Gauthier apan I [73] Assignee: Yashica Company Limited, Tokyo, Japan [57] ABSTRACT [22 Fil d; No 4 1970 in a shutter operating circuit comprising a shutter time determining circuit including a photo-electromotive element, and a [2n Appl' 86653 high input impedance transistor; means to initiate the operation of the shutter time determining circuit; a shutter control 30 F i Application priority Data circuit controlled by the shutter time determining circuit; and a source of supply connected to said two circuits, there are NOV. 8, 1969 Japan ..44/105631 p i a Series circuit Connected across the Source and cluding serially connected resistor and capacitor, and a if zs switching transistor with its base electrode connected to the E g 0 juncture between the resistor and the capacitor, the series ciro arc cuit acting to trigger the switching transistor to operate the shutter control circuit when the shutter time determining cir- [56] References Cited cuit fails to operate after elapse of a predetermined interval U D STATES PATENTS after the operation of the initiating means.

3,326,103 6/1967 Topaz ..95/l0 CT 4 Claims, 1 Drawing Figure --L SHUTTER TIME DETERMINING CIRCUIT I 6? 8 RI}? EH3? 4 P O SHUTTER Y CONTROL S2 l CIRCUIT TR-2 TR-l R2 E 2R5 Cl VR I PKTENTEDJUHZT I972 3673.415

A B SHUTTER TIME DETERMINING CIRCUIT Mr RI gm? SHUTTER L CONTROL {S2 CIRCUIT INVENTOR S HIROFUM I YOSHIMURA HISA'IOSHI TAKAHATA SHUTTER OPERATING CIRCUIT HAVING MEANS TO CLOSE SHU'I'IER WHEN LIGHT IS INSUI FICIENT BACKGROUND OF THE INVENTION This invention relates to a shutter operating circuit for cameras, and more particularly to a shutter operating circuit employing a photo-electromotive element.

1 An electric shutter operating circuit functions to determine a proper shutter time in accordance with the brightness of an object to be photographed, but the prior shutter. operating circuit is defective in that it operates to continuously maintain the shutter in the opened condition when the object is very dark. In the prior art shutter operating circuit utilizing a photoconductive element as means for determining the shutter time, for the purpose of eliminating this difirculty, a high resistance resistor is connected in parallel with the photoconductive element so as to establish a definite time constant by a capacitor and the resistance valve of the resistor m manifested thereby when the photoconductive element manifests an extremely high resistance whereby to close the shutter after it has been opened for a definite interval of time. Such idea has been disclosed in, for example, specifications of the US. Pat. Nos. 3,326,103 and 3,422,738.

When the photoconductive element or the time constant determining element is a passive element, the high resistance element connected in parallel therewith operates as desired whereas when the time constant determining element comprises a photo-electromotive element it is impossible to close the shutter with the prior shutter operating circuit utilizing a parallel connected high resistance element.

In. the accompanying drawing blocks A and B show a conventional shutter operating circuit utilizing a photo-electromotive element. 'More particularly, A represents a shutter time determining-circuit while block B a well known shutter control circuit. Since the construction of the shutter control circuit contained in block B is well known in the art, the detail thereof has been omitted fromthe drawing a source E is connected to the shutter operating circuit through a switch 8,. The shutter time determining circuit A comprises a photoelectromotive element P which generates an electromotive force when it is irradiated with light andcooperates with a capacitor C to form a serially connected time constant circuit. A switch S connected in parallel with capacitor C is arranged to be opened concurrently with the operation of a shutter release. There is'provided a semiconductor element TR-l a field efiect transistor for example, having a high input impedance characteristic. The source electrode of the field effect transistor TR-l is connected to the negative pole of the source E through a variable resistor VRwhereas the drain electrode to the positive pole of the source through a variable resistor R,, a bleeder circuit comprising a resistor R and a variable resistor R is connected between the positive pole of the source E and the source electrode, and the juncture between these resistors is connected to one side of the photoelectromotive element P. The gate electrode of the field effect transistor TR-l is connected to the juncture between the element P and capacitor C In the circuit constructed as above described, in order to eliminate the effect of the dark current upon the switching time it is necessary to decrease the negative bias impressed upon the photo-electromotive element P, for example a solar cell, thus decreasing the dark current. The presently available solar cell having a high signal-to-noise ratio has a very small output, moreover there is a limit for the signal-to-noise ratio and the internal resistance of the solar cell is very high, for example more than several thousand megohms. It is impossible to prevent permanent opening of the shutter even when a high resistance resistor is connected in parallel with the photo-electromotive element.

SUMMARY OF THE INVENTION It is the principal object of this invention to obviate aforementioned defects.

More specific object of this invention is to provide a novel shutter operating circuit which can positively close the shutter of a camera even when the brightness of an object is not sufficiently high.

According to this invention, in a shutter operating circuit comprising a shutter time determining circuit including a photo-electromotive element and a high input impedance transistor; means to initiate the operation of the shutter time determining circuit; a shutter control circuit. controlled by the shutter time determining circuit; and a source of supply connected to two circuits described above, there are provided a series circuit including a resistor and a capacitor which is connected across the source and a switching transistor with its base electrode connected to the juncture between the resistor and the capacitor, the series circuit acting to trigger the switching transistor to operate the shutter control circuit when the shutter time determining circuit fails to operate after elapse of a predetermined interval after the operation of the initiating means.

BRIEF DESCRIPTION OF THE DRAWING The invention can be more fully understood from the following detailed description taken in conjunction with the accompanying drawing in which a single FIGURE shows a block diagram of one example of the shutter operating circuit embodying this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT According to this invention, a series circuit including a resistor R and a capacitor C is connected across E source through switch S and the juncture between resistor R and capacitor C is connected to the base electrode a switching transistor TR-2. The emitter electrode of this transistor is connected to the negative pole of source E through a potentiometer resistor R whereas the collector electrode of transistor TR-2 is connected to the drain electrode of the field effect transistor TR-l.

Resistor R and capacitor C comprises a time constant circuit that determines an instant at which switching transistor TR-2 becomes conductive, the time constant being determined by a preset interval between the opening of the shutter caused by a release button and an instant at which the shutter should be closed. The time constant is determined by the product of the resistance of resistor R and the capacitance of capacitor C In operation, switch S is closed. Concurrently with the operation of the shutter release, short circuiting switch S is opened. The output current from the photo-electromotive element P commences to charge capacitor C Where the light impinging upon the photo-electromotive element P is extremely weak so that the voltage across capacitor C does not build up to a valve suflicient to turn ON transistor TR-l, this transistor will not be rendered conductive by the capacitor voltage so that the shutter will be maintained in the opened state. However, according to this invention, capacitor C is charged by source E through switch S, and resistor R to a voltage sufficient to render conductive transistor TR-2 during the predetermined interval. As a result, transistor TR-2 controls the shutter control circuit B as if the field effect transistor TR-1 were rendered conductive, thus closing the shutter.

In accordance with another embodiment of this invention, the interval which is determined by the resistor R and the capacitor C, can be made variable. An example of this construction is provided, as shown in the drawing by connecting another resistor R through a switch S across the resistor R When the switch S, is closed, the time constant obtained by the resultant resistance of the resistor parallel circuit and the capacitor C becomes decreased and therefore said interval becomes short. Such a shutter operating circuit as this embodiment is useful for an automatic shutter camera for use with photoflash device.

Thus, this invention provides a new and improved shutter control circuit which assures desired shutter opening period under adverse light conditions.

It will be clear that the invention is not limited to the particular embodiment illustrated and that many changes and modifications will occur to one skilled in the art within the true scope and spirit of the invention as defined in the ap pended claims.

What is claimed is:

1. In a shutter operating circuit comprising a shutter time determining circuit including a photo-electromotive element and a high input impedance transistor; means to initiate the operation of said shutter time determining circuit; a shutter control circuit controlled by said shutter time determining circuit; and a source of supply connected to said two circuits, the improvement which comprises a series circuit connected across said source and including serially connected a first resistor and capacitor and a switching transistor with its base electrode connected to the juncture between said resistor and capacitor, said series circuit acting to trigger said switching transistor to operate said shutter control circuit when said shutter time determining circuit fails to operate after elapse of a predetermined interval after the operation of said initiating means.

2. The shutter operating circuit according to claim 1 wherein said photo-electromotive circuit is connected in series with a capacitor which is normally short circuit by a switch which is opened when a shutter release is operated so that when an object to be photographed has sufficient light, said photo-electromotive element charges said capacitor within a predetermined interval to trigger said high input impedance transistor.

3. The shutter operating circuit according to claim 1 wherein said first resistor is a variable resistor.

4. The shutter operating circuit according to claim 1 is further provided with the second resistor connectable across said first resistor of said series circuit and a switch adapted to connect said second resistor in parallel with said first resistor.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US3326103 *Dec 9, 1964Jun 20, 1967Polaroid CorpAuxiliary shutter timing mechanism
US3422738 *Jul 13, 1965Jan 21, 1969Citizen Watch Co LtdAutomatic exposure flash camera
US3485152 *Mar 1, 1967Dec 23, 1969Ricoh KkPhotographic camera incorporating a battery charger
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3769886 *Jul 27, 1972Nov 6, 1973Asahi Optical Co LtdShutter operating mechanism having an automatic exposure time control means for photographic camera
US3849786 *Dec 8, 1972Nov 19, 1974Minolta Camera KkLight integrating type light detector circuit with photovoltaic cell
US3864565 *Sep 13, 1973Feb 4, 1975Asahi Optical Co LtdLight amount integration means
US4037237 *Nov 12, 1975Jul 19, 1977Eastman Kodak CompanyExposure control apparatus
US4052726 *Jan 26, 1976Oct 4, 1977Eastman Kodak CompanyExposure control apparatus
US4190335 *Oct 13, 1977Feb 26, 1980Olympus Optical Company, Ltd.Shutter controlling aid means for use with camera
US4214825 *Oct 25, 1977Jul 29, 1980Olympus Optical Co., Ltd.Shutter control means with auto strobo for electrical shutter camera
US5175484 *May 16, 1990Dec 29, 1992Power Beat International, Ltd.Electrical power distribution
Classifications
U.S. Classification250/214.00P, 396/251, 250/214.0SG
International ClassificationG03B7/083, G03B7/08
Cooperative ClassificationG03B7/083
European ClassificationG03B7/083