US3547022A

US3547022A - Exposure control for photographic apparatus

Info

Publication number: US3547022A
Application number: US777315A
Authority: US
Inventors: Rudolf Baron; Kurt Thate
Original assignee: Agfa Gevaert AG
Current assignee: Agfa Gevaert AG
Priority date: 1967-11-30
Filing date: 1968-11-20
Publication date: 1970-12-15
Anticipated expiration: 1987-12-15
Also published as: DE1597090A1

Description

United States Patent EXPOSURE CONTROL FOR PHOTOGRAPHIC APPARATUS 10 Claims, 2 Drawing Figs.

US. Cl 95/64, 95/10; 352/141 Int. Cl G03b 7/08, G03b 19/18 Field of Search 95/ 10C, 64,

Primary Examiner-John M. Horan Assistant Examiner-Joseph F. Peters, Jr. Attorney-Michael S. Striker ABSTRACT: An exposure control for photographic cameras wherein the armatures of two moving iron instruments are mounted on a common shaft which carries a diaphragm blade. A control switch is actuated by the shutter release trigger to first connect the winding of one instrument in circuit with an energy source whereby the corresponding armature moves the blade to a starting position. On further actuation of the trigger, the control switch connects the winding of the other instrument in circuit with the energy source and with a photosensitive resistor so that the position of the blade is changed and the blade defines an aperture whose size is a function of scene brightness.

PATENTEDUECISIQYC I 354 022 INVENTOR.

RU DOLF BARON KURT THATE EXPOSURE CONTROL FOR PHOTOGRAPIIIC APPARATUS BACKGROUND OF THE INVENTION The present invention relates to improvements in exposure controls for photographic apparatus. More particularly, the invention relates to improvements in exposure controls of the type wherein the size of the aperture defined by the blade'or blades of a diaphragm is a function of scene brightness.

It is already known to adjust a multibladediaphra'gm in dependency on the intensity of scene light. In certain types of such conventional exposure controls, an armature moves the blade or blades in dependency on the strength of currents flowing through a winding, and the strength of such currents is a function of scene brightness because the winding is in circuit with a photoelectric receiver, e.g., with a photosensitive resistor. The ends of blades carry permanent magnets which cooperate with the roof-shaped core of an electromagnet. The winding of the electromagnet is connected in parallel with a photosensitive resistor and the first mentioned winding is in circuit with a battery. If the voltage of the battery drops after extended use, the magnitude of forces which act on the blades as a function of scene brightness decreases; however, the restoring force of the electromagnet which is installed between the permanent magnets also decreases to thus compensate for the drop in battery potential and to prevent inaccuracies in adjustment of the diaphragm.

A drawback of the just described conventional exposure control is that it is prone to malfunction and that it is quite complicated and hence expensive. The permanent magnets contribute significantly to the initial cost, especially because they must be shaped with a high degree of precision. Moreover, care must be taken during assembly to prevent contamination of permanent magnets with ferromagnetic particles of dust or other foreign matter.

SUMMARY OF THE INVENTION An object of the present invention is to provide a rugged, simple and relatively inexpensive exposure control which exhibits all important advantages of the aforedescribed conventional exposure control.

Another object of the invention is to provide a novel electric circuitry for the exposure control and to provide the exposure control with a novel instrument which effects displacements of one or more diaphragm blades to optimum positions for making exposures under various circumstances.

A further object of the invention is to provide an exposure control which can be incorporated in still cameras or in motion picture cameras and which is also suited for use in single lens reflex cameras.

The improved exposure control comprises diaphragm blade means, rotary carrier means operatively connected with the blade means to move the latter between a'plurality of positions including a starting position and to thus furnish a range of aperture sizes, a pair of moving iron instruments each including core means, winding means and armature means with the armature means of both instruments affixed to the carrier means, a first electric circuit including one of the winding means, a second electric circuit including the other winding means and a photosensitive receiver which is exposed to scene light, and control means movable between a first position in which it completes the first circuit whereby the corresponding armature means moves the blade means to starting position, and a second position to thereby complete the second circuit whereby the corresponding armature means moves the blade means to a position in which the aperture size is a function of scene brightness.

The exposure contro'l further comprises a source of electrical energy, preferably a single source which is connected in the first and second circuits in the first and second positions of the control means. Such control means may comprise an electric switch which is actuatableby the shutter release trigger.

LII

The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved exposure control itself, however, both as to its construction and its mode of operation, together with additional features and advantages thereof, will be best understood upon perusal of the following detailed description of a specific embodiment with reference to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is an exploded perspective and partly diagrammatic view of an exposure control which embodies the invention; and

FIG. 2 is a similar exploded perspective view of a detail in the exposure control of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 illustrates an exposure control which comprises a composite moving iron instrument 1 which includes two identical instruments numbered 2 and 3. The instrument 2 comprises a core 4, a winding 5 and a turnable armature 6; the instrument 3 comprises a core 7, a winding 8 and a turnable armature 9. The armatures 6 and 9 are affixed to a common rotary carrier 10 here shown as a shaft having smaller-diameter end portions 11 and 12 which are received in bores l3, 14 respectively provided in supporting

brackets

15 and 16. A screw 17 connects the lower end portions of the instruments 2 and 3, and two additional screws l8, 19 are provided to fix the

brackets

15, 16 to each other. The screws 18, 19 extend through openings provided in the cores 4 and 7. Distancing

members

22, 23, 24 are interposed between the cores 4 and 7. The shaft 10 is connected with a diaphragm blade 40 having a substantially horn-shaped recess 41. The blade 40 cooperates with a fixed blade 43 which is installed in front and overlies a portion of the objective 42. The

blades

40, 43 can define a range of aperture sizes in that the blade 40 can move with the shaft 10 between a plurality of angular positions including a starting position or end position which corresponds to an aperture of maximum size.

The exposure control further comprises two electric circuits one of which includes the winding 5 of the moving iron instrument 2, a variable resistor 26 and a first contact 30a forming part of a control switch 30. The other electric circuit comprises the winding 8, a photosensitive receiver 27 which is exposed to scene light, a second variable resistor 28 and a second contact 30b of the control switch 30. The two circuits comprise a common source 25 of electrical energy. The control switch 30 comprises a third contact 300 which can connect the energy source 25 in circuit with an electric motor 29; the latter is used to operate the film transporting mechanism. For example, and if the exposure control of FIG. 1 is embodied in a motion picture camera, the motor 29 can drive the customary claw pulldown, not shown. The control switch 30 is actuated by the shutter release trigger 50.

THE OPERATION When the user decides to depress the trigger 50, the control switch 30 is moved to a first position in which the contact 30a completes the circuit including the variable resistor 26, winding 5 and energy source 25. The armature 6 is then caused to turn the shaft 10 whereby the latter moves the blade 40 to the aforementioned starting position in which the blade 40 cooperates with the fixed blade 43 to define therewith an aperture of maximum size, i.e., the blade 40 ispivoted in a counterclockwise direction so that it does not overlie any part of the objective 42. In view of such movability of the blade 40 to starting position, the exposure control of the present invention can be used with advantage in single lens reflex cameras.

As the user continues to depress the trigger 50, the control switch 30 moves to a second position in which the contact 3% completes the circuit including the variable resistor 28, photosensitive receiver 27, winding 8 and energy source 25',

the contact 30c simultaneously completes the circuit including the energy source 25 and motor 29. A magnetic field which develops in the instrument 3 opposes that produced by the instrument 2. Thus, the armature 9 causes the shaft 10 to turn counter to the direction in which the shaft turns in response to completion of the circuit including the winding 5. The resulting position of the blade 40 is a function of scene brightness as determined by the photosensitive receiver 27, and the aperture size is also a function of scene brightness.

1f the potential of the energy source 25 decreases, for example, due to extended use of the photographic apparatus, the magnetic fields produced by the instruments 2 and 3 are weakened to the same extent so that such drop in potential does not result in improper adjustment of the diaphragm.

In order to facilitate the assembly of the moving iron instruments 2 and 3, they preferably comprise cores which are assembled of several sections. As shown in FIG. 2, the core 4 of the instrument 2 comprises two halves 4a, 4b which respectively comprise

tonguelike sections

51, 52 and 53 54. The sections 51, 53 form a pair and have complementary inclined edge faces which abut against each other when the sections are inserted into the winding 5 from opposite ends as indicated by arrows A and B. The same applies for the

sections

52, 54. In this way, the core .4 can completely fill the interior of the winding 5 to enhance the magnetic efficiency of the instrument 2. The core 7 of the instrument 3 is assembled in similar fashion.

As shown in FIG. 1, the instruments 2, 3 are angularly offset with reference to each other as considered in the direction of rotation of the shaft 10. It is also desirableto arrange the instruments 2, 3 in such a way that the armature 6 tends to turn the shaft in a first direction when the winding 5 is energized and that the armature 9 tends to turn the shaft 10 in the opposite direction in response to energization ofthe winding 8.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features which fairly constitute essential characteristics of the generic and specific aspects of our contribution to the art.

We claim:

1. An exposure control for photographic apparatus, comprising diaphragm blade means; rotary carrier means operatively connected with said blade means to move the latter between a plurality of positions including a starting position to thus furnish a range of aperture sizes; a pair of moving iron instruments each including core means, winding means and armature means with both said armature means'atfixed to said carrier means; a first electric circuit including one of said winding means; a second electric circuit including photosensitive received means exposed to scene light and the other of said winding means; and control means movable between a first position to thereby complete said first circuit whereby the corresponding armature means moves said blade means to said starting position, and a second position to thereby complete said second circuit whereby the corresponding armature means moves said blade means to a position in which the aperture size is a function of scene brightness.

2. An exposure control as defined in claim 1, further comprising a source of electrical energy which is connected in said first circuit in the first position of said control means and in said second circuit in the second position of said control means.

3. An exposure control as defined in claim 1, wherein one of said instruments is angularly offset with reference to the other instrument as considered in the direction of rotation of said carrier means.

4. An exposure control as defined in claim 1, wherein said winding means are arranged to effect angular movements of corresponding armature means in opposite directions.

5. An exposure control as defined in claim 1, wherein each of said core means comprises a plurality of iriterfitted sections. 6. An exposure control as defined in claim 5, wherein said sections comprise pairs of tongues having complementary inclined edge faces.

7. An exposure control as defined in claim 1, further comprising means for securing said core means to each other.

8. An exposure control as defined in claim 1. further comprising distancing means interposed between said core means.

9. An exposure control as defined in claim 1, wherein said control means comprises an electric switch and further comprising trigger means operative to move said switch between said first and second positions.

10. An exposure control as defined in claim 1, further comprising motor means arranged to operate the film transporting mechanism of the photographic apparatus in response to movement of said control means to second position.