US2179717A

US2179717A - Automatic photographic shutter

Info

Publication number: US2179717A
Authority: US
Publication date: 1939-11-14
Anticipated expiration: 1956-11-14

Description

Nov. 14, 1 939. N. v. FEDOTOFF.

AUTOMATIC PHOTOGRAPHIC SHUTTER Filed Dec. 2, 1937 INVENTOR ATTOR'NEY Patented Nov. 14, 1939 UNITED STATES PATENT OFFICE AUTOMATIC PHOTOGRAPHIC' SHUTTER Nicholas V. Fedotofi, Lynbrook, N. Y. Application December 2, 1937, Serial No. 177,757

4 Claims.

This invention relates to photographic shutters and particularly to such shutters in which the time of exposure is automatically controlled by the intensity of the light upon the object photographed.

The object of this invention is to provide a shutter capable of giving accurate exposures over a wide range of illumination intensities, and of giving extremely short exposures when required. This application is a contlnuation-in-part of my copending application Serial No. 137,938, filed April 20, 1937.

This object is carried out in accordance with this invention by the provision of a pair of curtains one of which starts the exposure and the second of which terminates the exposure. A delay means responsive to the light intensity controls the time of closing of the shutter by the second curtain in such a manner that the inertia of moving parts is eliminated as a factor in the undesirable prolonging of exposures, thus making, extremely short exposurespossible.

For a better understanding of the invention, together with other and further objects thereof and advantages achieved thereby, reference may be had to the following description taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

In the accompanying drawing, the figure is a circuit diagram illustrating a shutter control system embodying the present invention.

The system here illustrated comprises a control circuit including the windings of electromagnets 10 and H having movable armatures, indicated at [a and Ila, respectively, and connected in parallel in a series circuit including a suitable source of voltage, as, for example, a battery I2, and a manual control switch S.

For the purpose of preventing undue sparking and determining the period of operation of the magnets, a condenser l3 and resistor [3a are connected across the winding of the magnet Ill, and a condenser l4 and resistor Ma are similarly connected across the winding of the magnet H.

In order to control the period of operation of the magnet H, there is provided time-control means preferably comprising a plurality of condensers l5--23, inclusive, adapted to be selectively connected in parallel with the condenser H by way of suitable leads 24 and 25, an adjustable member 26 having a contacting arm 21, and contacts l5w-23a individually connected to condensers l523, respectively. The member 26 may be pivotally movable, as indicated, to a position with its arm 21 adjacent one or more contacts l5a23a and also adjustable to cause its arm 21 to make and break contact with those contacts l5a.-23a adjacent to which it has been moved.

For the purpose of effecting pivotal movement 5 of the member 26 to effect a time control in accordance with the value of illumination at a given source, indicated, for example, by the arrow A, there is provided a photoelectric cell P of a suitable type which may be connected, as shown, in circuit with'the winding of an electric magnet 28 having a movable armature 29. Where types of photoelectric cells are employed which require operating voltages and amplifiers, these may, of

course, be employed in a conventional manner.

The armature 29 is suitably connected to the member 26 and, being movable when the magnet 28 is energized by the photocell to an extent determined by the value of illumination at the, source A, serves to move the arm 21 relative to the contacts l5a23a, that is, to bring the arm to a position adjacent one or more of these contacts.

In order to complete the connection of one or more of the condensers 85-23 across the condenser l4, after the member has been adjusted by the armature 29 to a position corresponding to the value of illumination of the object A, an electric magnet 30 is provided, which has an 7 adjustable armature 3i operably connected to 3 the member 26 for adjustment thereof to move the arm 21 into and out of contact with the contacts l5a-23a adjacent to which it has previously been moved. The winding of the magnet 30 is connected, in a series circuit including the battery l2 and acontrol switch S2. The switch S2 is operably connected to a second armature 32 of the magnet II to be actuated thereby.

In this embodiment of the invention, the system is used to effect related controls of two photo- 0 electric shutters .or curtains 33 and, of, for example, a camera, not shown. The

curtains

33 and 34 are provided with suitable arm members 33a and 3401, respectively, which are operably connected to the armatures I00. and Ila of the magnets l0 and II, as shown, to be pivotally moved thereby. For the purpose of clarity of illustration, the curtains are illustrated as if spaced apart in the same plane. Actually, however, the curtains well overlap one another. so

Openings 33b and 341 are found in the upper and lower portions, respectively, of the

curtains

33 and 34, so that in the positions thereof which are indicated, and which will be assumed when the magnets in and H are deenergized, the

optical axis with reference to the object A, in.- dicated at 0), coincides with the center oi the opening 3%, but light is prevented from passing through the composite curtain structure by the upper solid portion or" the curtain 1. Moreover, both of the curtains are pivotally moved, by energiaation of their magnets, to upper positloris, so that the center of the opening coincides with the optical axis, the lower solid portics of the curtain 3?; will then prevent light from passing through the composite structure. Light will be permitted to pass through both curtains only when the curtain is in its lower osition arid the curtain 3d in upper: po .tion, that is, when the magnet magnet ll energized.

"in the operation of the system described, when the circuits of the magnets it and it are closed, current blows in their circuits increasing exponentially and actuating their armatures, and when their circuits are opened the current decays exponentially, releasing the armatures. The durations of the latter or the cycles oi opera tlon are affected by the lmpedances connected in circuit with the windings of the magnets, that is, the condensers and resistor in the embodiment shown. Since the greater the value or the ca pacitance in parallel with the magnet winding, the greater the eriod oi the current decay, a control is provided, by the provision the adjustable capacitance means including the condensers tile-23o, whereby a precise adjustment of the period of operation or" themagnct ll may be effected.

The general operation oi the system may be described considering the curtains and 3G to be applied to a camera to control its period oi exposure. The photoelectric cell P may be disposed opposite an object to be photographed. The illumination of this object, or a desired part thereof, according to the position of the cell, will then excite the cell and cause a flow of current through its circuit corresponding in value to the intensity of the energy radiated from, or value of illumination at, the object. The magnet 28, therefore, will be actuated to adjust its armature 2t and, hence, the member to a corresponding extent, thereby bringing the arm 22'! adjacent a member oi the contacts flat-23a corresponding to the value of the illumination. The switch S will then be closed completing the circuits of the windings of the magnets ill and H, which are thereupon energised with consequent movement of their armatures its and Mo to move both of the curtains and to their upper positions and, the armature 32 to close the switch S2, thereby completing the circuit of the magnet 3b. The latter action by movement of armature 3i and member 26 efiects contact be tween the arm 21 and as many of the contacts l5a2ta adjacent to which it has previously been moved by the photoelectric cell action.

When the operator is ready to expose the film, or take the picture, the switch S is simply released, thereby breaking the circuits oi the magnets l0 and *H. The magnet it is constructed and arranged to have a relatively short, or substantially instantaneous, period of operation and will thereupon release its armature Ho and, hence, bring the curtain 33 to its normal or lower position. Due to the time-control action of the circuit including the condenser it and such of 2 it deenergized and the the magnet ill, or, more particularly, of a duration corresponding to the illumination at the object Hence, the return movements of the armature lid and curtain 34 are correspondingly delayed with respect to those of the armature lilo and curtain 32 and the centers oi" both openings 33b and 3th coincide with the optical axis 0 so that the light rays are permitted to pass entirely through the curtain structure into the camera. At the end of this period the armature Ma and curtain 3d, of course, also assume their normal positions terminating the exposure.

will be appreciated that a wide range of periods of exposure and exceedingly precise ad-- justments may be obtained by the system 'described, dependent upon the number and size of the condensers fle -23.

The advantage of the use of the two movable shutter curtains is that a very wide range of exposure periods is possible down to a very small fraction of a second. The reason why extremely short exposures are possible is that the inertia of the shutter mechanism is eliminated as a factor prolonging exposure, which inertia would be a factor if only a single curtain were moved to the opening position and then dropped back again. The reason the effect of inertia ls eliminateol is that the exposure does not start when curtain (it is moved to the exposure axis, but instead, starts only when curtain 33 drops bacl: to the axis after curtain 3 is opened. Curtain can be dropped baclz from the axis a much smaller traction of a second after curtain 33 drops down to the axis than could curtain 34 itself be dropped be. :1 after its original. opening.

For example, if both curtains be made of the same size and weight, as shown, and if there were no delay means at all delaying the return of the second curtain, both curtains would snap to normal at the same time, resulting in no exposure at all, even though. each individual curtain mechanism possesses inertia. By reason ot'thls ability of both curtains to start moving at the same time, it follows that the application of a small degree oi'delay will produce a correspondingly small exposure which can be made as small as desired down to zero exposure. If there were only one curtain it would be impossible to make th exposure zero or nearly zero.

While the particular system embodying the invention, which has been described, includes two actuating circuits for effecting two related control actions, it will, of course, be appreciated that other systems embodying the invention may be utilized which include only one actuating circuit with time-control means therefor. Moreover, while a specific electric circuit arrangement including adjustable capacitance means has been described, it will be understood that various other equivalent arrangements will be readily epparent to those skilled in the art, where, for example, adjustable impedance means of other types are utilized in efiecting the time control.

While there have been described what are at present considered to be the preferred embodiments of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. An automatic photographic shutter having an optical axis along which the exposure to an object is made, comprising two movable curtains one of which is normally in an unobstructing position with reference to the optical axis and the other normally positioned to obstruct the axis so that the shutter is closed, relay means for operating the curtains, switch means for connect ing the relays with an electrical source to move the first mentioned curtain to an obstructing position and the second mentioned to an unoh structing position, with reference to the axis, and then disconnecting said relays, means for returning the first curtain to its unobstructing position after said relays are disconnected to start the exposure, an electrical delay circuit set into operation atthe start oi the exposure, said delay circuit comprising electrical reactance connected with the relay which operates the second. curtain for holding the latter relay energized for a period of time after said disconnection, reactance-varying means operated by a photoelectric cell which is subjected to the light on the object for varying said reactance according to the intensity of said light, and means for moving said second curtain to'its normally obstructing position at the end of said time period to terminate the exposure.

2. An automatic photographic shutter having an optical axis along which they xposure to an object is made, comprising two movable curtains one of which is normally in an unohstructing position with reference to the optical axis and the second is normally positioned to obstruct the axis so the shutter is closed, an operating device for setting the curtain in an ole- Miran structing position and the second curtain in object, for determining the duration or said time in accordance with the intensity of said light, and means for moving said second curtain to its normal obstructing position at the end oi said time period to terminate the exposure.

An automatic photographic shutter having an optical axis along which the exposure to an object is made, comprising two movable curtains eachproviding an aperture, said apertures being not both aligned with said optical axis in the norinal unexposed position, an operating device for moving both of said curtains to align their apertures with the axis to start the exposure, delay mechanism operating during the exposure for holding the second curtain in the aligned position for a period of time after the alignment of the aperture of the first curtain, said delay mecha nism comprising a photoelectric cell subjected to the light on the object, for determining the duration of said time in accordance with the intensity of said light, and means for moving said second curtain to its normal misaligned position at the end or said time period to terminate the exposure.

i. An automatic photographic shutter having an optical axis along which the exposure to an object is made, comprising two movable curtains, mechanism for moving the first of said curtains to an obstructing position and the second curtain.

} to an unobstructing position with reference to the axis, an operating device for moving the first curtain to an unobstructing position to start the exposure, delay mechanism operating during the exposure for holding the second curtain in the iniobstructing position for a period of time after the movement of the first curtain. to the unobstructing position, said delay mechanism comprising a photoelectric cell subjected to the light on the object for determining the duration of said time accordance with the intensity of said light, and mechanism for moving said sec= ond curtain to the obstructing position with reil erence to said axis at the end of said time period to terminate the exposure.

NICHQLAS "v"; FFDOTQFF.