US3688675A

US3688675A - Shutter mechanism in a camera

Info

Publication number: US3688675A
Application number: US887664A
Authority: US
Inventors: Keizo Yamashita; Junichi Yokozato; Hideaki Yamamoto
Original assignee: Zenza Bronica Industries Inc
Current assignee: Zenza Bronica Industries Inc
Priority date: 1968-12-28
Filing date: 1969-12-23
Publication date: 1972-09-05
Anticipated expiration: 1989-09-05
Also published as: DE1965161A1; DE1965161B2

Abstract

A film winding and focal plane shutter cocking mechanism includes a safety gear that has an annular rib secured to one face. A cut out in the rib is engaged by an end of a lever which is moved by a sliding bar when the shutter actuating button is depressed. An interlocking mechanism which is operated by the safety gear prevents movement of the sliding bar again until the film winding and shutter cocking mechanism has been manually actuated to prevent double exposure.

Description

United- States Patent Yamashita et al.

[54] SHUTTER MECHANISM IN A' CAMERA [72] inventors: Keizo Yamashita; Junichi Yokozato; Hideaki Yamamoto, all of Tokyo,

Japan [73] Assignee: Zenza Bronica Kogyo Kabushiki Kaidm, Tokyo, Japan [22] Filed:' Dec. 23, 1969 I 1 Appl. No.2 887,664

[30] Foreign Application Priority Data Dec. 28, 1968 Japan ..43/96097 [52] US. Cl. ..95/57, 95/31 FL [51] Int. Cl ..G03b 9/34 [58] Field of Search.....95/l0 C, 53 E, 53 EA, 53 EB,

95/57, 31 AC, 31 FL [56] References Cited UNITED STATES'PATEN'IS I 2,961,934 11/1960 Hashimoto ..;....9s/57 Sept. 5, 1972 Otani et a1. ..95/10 3,437,026 8/1969 Espig ..95/ 10 X 3,437,027 4/ 1969 Straub ..95/10 X 3,498,195 3/1970 Ono ..95/57 835,127 11/1906 Borsum ..95/57 Burgarella ..95/10 C X Primary Examiner-Samuel S. Matthews Assistant Examiner-Michael L. Gellner Attorney-Michael S. Striker [57] 1 ABSTRACT A film winding and focal plane shutter cocking mechanism includes a safety gear that has an annular rib secured to one face. A cut out in the rib is engaged by an end of a lever which is moved by a sliding bar when the shutter actuating button is depressed. An interlocking mechanism which is operated by the safety gear prevents movement of the sliding bar again until the film windingfand shutter cocking mechanism has been manually actuated to prevent double exposure.

5 10 Drawing Figures tuating mechanism associated therewith comes into play for attaining the high-speed-shutter speeds.

A further object of the present invention is to provide a shutter mechanism wherein the mechanical contact between the shaft associated with the front shutter screen and the hollow shaft or drum'associated with the rear shutter screen is eliminated for attaining a positive and accurate shutter speed even in the case of the slowspeed shutter. I I

A still further object of the present invention is to provide a shutter mechanism which may be used advantag'eously with an electronic synchronization device.

A still further object of the present invention is to provide a shutter mechanism provided with a shutter button safety means whereby the shutter actuating mechanism does not come into play before completion of the film-winding shutter-tensioning operations. I

These and other objects of the invention will be described in the following detailed description and the accompanying drawing showing preferred embodiments of the present invention.

In the drawing;

FIG. 1 is a perspective view showing the construction of the shutter mechanism according to the present invention; I v

FIG. his a plan view of a gear operatively connected with the front leading shutter screen;

FIG. 2b is a plan view of a gear operatively connected with the rear trailing shutter screen;

screen 1 is tensioned by

belts

6, 6 secured to the bracket arm 5 and coiled about

rolls

7, 7 mounted on a shaft 4 serving simultaneously for guiding the rear shutter screen 2. The latter is coiled about a shaft 9 and tensioned by

belts

11, 11 secured to a further arm carrying the free end of the rear shutterscreen 2, and wound on a drum 8 by way of

guide wheels

12,12 mounted coaxially with the drum 3. Said drum 8 houses a coil spring, not shown, and is urged normally to rotate clockwise under the recoiling force of the spring in the same wayas already described with reference to front 7 shutter screen 1.

- metal 21 denotes a projection secured to the upper sur- FIG. '3 is a block diagram of an control circuit for controlling the actuation of the rear shutter screen;

FIG. 4 is a chart illustrating the performance characteristics of the circuit of FIG. 3;

FIG. 5 is a plan view showing an alternative construction of part of the rear shutter screen actuating device;

FIG. 6 is an enlarged view of the shafts associated with the front and rear shutter screen;

FIG. 7 is a perspective view of the substantial parts of the safety device associated with shutter actuation button;

.FIG. 8 is a plan view showing the safety device as shown in FIG. 7, the device being shown in the operative position when the shutter actuation button is depressed manually; and

FIG. 9 is a plan view showing the safety device as shown in FIG. 7, the device being shown in the operative position wherein the shutter actuation button is released from manual pressure.

Referring now to FIG. 1, a front shutter screen 1 is coiled at one end about a winding drum 3, and secured at the other end to a arm 5. The drum 3 houses a coil spring, not shown, and is urged normally to rotate clockwise under the recoiling force of the spring. Said face of said gear 20 for cooperation with a detent member 22 secured to the reverse side of said gear 14. Numeral 23 denotes a substantially L-shaped latch member pivotally mounted at 24 so that the one end thereof may be engaged normally with said projection 21. Numeral 26 denotes an iron armature secured to the other end of the latch member 23 and adapted to be attracted towards the electromagnet 27 against the action of spring 28 when the electromagnet 27 is energized. Numeral 29 denotes a bent connecting lever pivoted at 30 and having a projection 29a engageable with the other end of the latch member 16. The connecting lever 29 is formed with a raised part 29b adapted for cooperation with a mirror drive unit 31.

The arrangement is such that when the mirror (not shown in the drawing) is raised upwardly by the mirror drive unit 31 the raised part 29b of lever 29 is pressed by the mirror drive unit 31 so as to turn the connecting lever 29 clockwise.

Switch S is associated with a release lever 32, and switch S is associated with one end of the lever 29. Switch 8;, is associated with one end of a lever 34 pivoted intermediate its ends and engaged at the other end with a projection 33 on the gear 14. Switch 8., comprises a leaf spring engageable with a pin 36 mounted on the gear 20.

When the release lever 32 is depressed so as to close the switch 8,, it actuates the mirror drive unit 31 which in turn depresses the projection 29b on the connecting lever 29. Switch S is used for slow shutter operation to charge a desired voltage in the time constant circuit including R,, C,, so as not to open a transistorized control circuit for the rear shutter screen after the release lever has released the switch 8,.

Switch S is opened at the moment when the front shutter screen 1 starts to move, because of disengagement of the contacting end 17 of the latch member 16, by depressing the release lever 32 which operates to turn the connecting lever 29 and resulting rotation of gear 13 in counterclockwise direction.

The switch S is opened when both shutter screens have finished their movements.

FIG. 3 shows a transistorized control circuit for the rear shutter screen whereby the latter may be actuated after the lapse of a certain time interval from the time of actuation of the front shutter screen 1. Condenser C, is connected to the gate of transistor T, and the above mentioned switch S, is connected in parallel with the condenser C, which is charged through a variable resistor R, when the switch S, is opened. Resistor R, is mechanically connected with the shutter dial 37, as suggested by a dotted line in FIG. 3.

Condenser C, is connected in series with the resistor R, and the charging time of the condenser C, may be varied by adjusting the resistor R, to a desired value.

Resistor R is connected to the source of transistor T,. The transistors T, and T are connected to each other in such a way that the transistor T is made conductive and the transistor T, is made non-conductive when the potential difference at the two terminals of the condenser C, is equal to a certain value Vgs. The abovementioned electromagnet 27 is connected to the collector of transistor T Switch S, is connected in series with the electric source E and the switch S, which in turn is connected in parallel with the switch S The operation of the shutter mechanism so far shown and described is as follows:

FIG. 1 shows the shutter mechanism in the operative position and the shutter wherein a film is wound and the shutter is charged for photographing. In the operative position shown in FIGS. 1,, 2a and 2b, switches S,

v and S, are open, while switches S, and S, are closed.

When the release lever 32 is depressed, switch S, is closed. As the switch S is still in the on position, transistors T, and T are in the cut-off state. Transistor T, is, however, forwardly biased through the resistor R,, so that the electromagnet 27 is energized and the armature 26 is attracted magnetically towards the electromagnet 27 together with the latch member 23. The foremost part 25 of the latch member 23 abuts against projection 21 on the gear 20 and the latter is positively locked against rotation.

With the further depression of the release lever 32, the mirrordrive unit 31 comes into play and the mirror, not shown, starts to retreat from the light passage.

When the mirror has been completely retracted from the light passage, the mirror drive unit 31 masses against the raised part 29b on the connecting lever 29 which is moved in the direction of the arrow in FIG. 1 clockwise against the force of a spring so that the end of lever 29 closes the switch 8,. As the switch S is connected in parallel with the switch S, associated with the release lever 32, the electromagnet 27 is energized with the abovementioned clockwise rotation of the lever 29, while the latch member 16 engaging with the pin 29a is turned counterclockwise, so that the front shutter screen 1 is now actuated by means of pinion 13. With the actuation of the front shutter screen 1, detent member 22 on the gear 14 is moved away from projection 21 on the gear 20. At this time, the projection 21 is still engaged by the foremost part 25 of the latch member 23 and gear 20 thus prevented to rotate, so that the rear shutter screen will not be actuated.

With the start of rotation of gear 14, the projection 33 mounted on the latter is moved away from engagement with the lever 34 associated with the switch S and the lever 34 is rotated pivotally clockwise for opening switch 8,, so that the condenser C,in the transistorized control circuit of FIG. 3 is charged. with the current supplied from the current source E by way of the variable resistor R When the potential difference between the terminals of condenser C, is equal to Vgs, transistor T, is made conductive and transistor T, is made non-conductive, so that the electromagnet 27 is now deenergized.

As the capacity of condenser C, and the potential E of the current source remain unchanged and the value Vgs is constant, the charging time of condenser is decided by the change in the resistance of the variable resistor R,. FIG. 4 shows the relation between the changing voltage and charging time of the condenser C, with the variable resistor R, adjusted to r, and r As will be seen from FIG. 4, when the variable resistor R,, is adjusted to r,, condenser C, is charged to Vgs at 1,. When the variable resistor R, is adjusted to r,, then the condenser C, is charged to Vgs at t,. g

It will be seen from FIG. 4 that by adjusting the ohmic resistance of the variable resistor R,, on the shutter speed dial, the shutter time may be set to the desired value. 1

When the electromagnet 27 is deenergized, the latch member 23 is rotated counterclockwise under the force of the spring 28 and caused to move away from the projection 21 on the gear 20, so that the latter is urged to rotate counterclockwise and the rear shutter screen 2 actuated by means of pinion 19. Upon closure of the shutter, the projection 36 mounted on the gear 20 comes into abutting contact with the switch S, so that the latter is opened and current from the current source E is no longer supplied to the control circuit for the rear shutter screen. The above-mentioned shutter operation cycle may be repeated in the same way as described above.

As will be apparent from the foregoing, the energization time of the electromagnet 27 forming part of the rear screen actuating mechanism may be adjusted as desired by the on-off performance of the switch means S, to S, associated with the release lever and the mirror drive unit as well as the front shutter screen, so that the operation of the shutter mechanism may be made positive and accurate as compared with the conventional mechanical control device.

The various shutter speeds may he graduated as desired on the shutter speed dial in accordance with the position on the variable resistor R,, so that the shutter time adjustment may be attained in a highly simple manner. The shutter mechanism as disclosed in the present application may be advantageously employed as a focal plane shutter which may be mounted on a large-sized, medium or small-sized camera.

FIG. 5 shows the detailed construction of the latch member 23 and the projection 21 on the gear 20 associated with the latch member 23. As will be seen from FIG. 5, the foremost engaging part 25 of the latch member 23 is cut obliquely at an acute angle a with respect to the tangential direction of the gear 20. In the similar way, the projection 21' on the gear 20 is cut obliquely at the same angle and so as to form an inclined surface 21 contactable with the obliquely cut foremost part 25 of the latch member 23.

When the electromagnet 27 is energized, and the foremost engaging part of the latch member 23 engages with the correspondingly inclined meeting surface 21' on the projection 21, the rear shutter screen 2 cannot be actuated. At this time, a component P is acting tangentially and a component 0 is acting radially on the foremost part 25 of the latch member 23. When the electromagnet 27 is deenergized after a certain time interval following the actuation of the front shutter screen, the latch member 23 is pivoted about shaft 24 under the recoiling force of the spring 28. In this way, the foremost part 25 of the member 23 is moved away from engagement with the inclined meeting surface 21' formed on the projection 21.- Thus, the gear 6 is urged to rotate and the rear shutter diaphragm 2 is now set into motion.

As will be seen from FIG. 5, the said inclined face 21' on the projection 21 abuts with pressure on the foremost engaging part 25 of the latch member 23. As long as the projection 21 engages with the foremost engaging part 25 of the latchmember 23, the component Q acts for releasing the latter from its engagement with the projection 21. When the electromagnet 27 is deenergized, the component 0 acts in such a way that the latch member '23 may be readily set into rotation as if the spring 28 were not provided and the rear shutter screen may be actuated in synchronism with the deenergization of the electromagnet 27.

FIG. 6 shows a detailed construction of the guide shaft 4 for rear screen 2 and

rollers

7, 7 mounted on the guide shaft 4. In FIG. 6, the bearing means 38, 38 are formed integral with

tubular parts

39, 39,. and the hollow shaft 4 formed into a drum 4a is rotatably mounted on the

tubular parts

39, 39 through the bearing means, not shown. A spindle 4b is passed through the hollow inside space of the guide shaft 4 and secured at either endsto the

rolls

7, 7. The said spindle 4b abuts on the inner peripheral faces 39b,39b of the tubular parts 39,

39. Pinion 13 is secured to the extreme leftward part of the spindle 4b.

When the shutter is released,

belts

6, 6 are reeled out with rotation of the

rolls

7, 7 secured to the spindle 4b, which is rotated axially in sliding contact with the outer

peripheral faces

39a, 39a of the bearing means 38, 38. As will be realized from FIG. 6, there is no direct mechanical contact between the spindle 4b and the drum 40 so that actuation of the front and rear screens may not be adversely affected by the frictional contact of the moving parts associated therewith and the shutter speed fluctuations may be positively avoided. The number of component parts may also be reduced and the camera may be miniaturized.

In FIGS. 7-9, there is shown a shutter safety device whereby fool-proof operation of the shutter mechanism may be attained. Numeral 40 denotes a sliding bar for pressing the shutter button and numeral 41 is a gear 41 meshing with a gear 43 connected to 'an operating handle adapted for filmwindin g and shutter-cocking operation. An annular rib 44 is formed on the upper surface of the gear 43 concentrically therewith and cut out at 45 for interlocking with the end 46 of trifurcated lever 46 pivotally mounted at 47. The end 46" of the lever 46 is associated with a spring 48 which acts for turning the lever 46 about pivot 47 in such a way that the end 46' is moved away from engagement with the cut-out part 45 of the rib 44. The end 46" of the lever 46 engages with the foremost part of the abovementioned sliding bar 40. An 'L-shaped lever 49 is pivotally mounted at 51 and is urged to rotate counterclockwise under the force of spring 52., into abutting contact with a projection 50 on the abovementioned sliding bar 40. An L-shaped detent'lever 53 is formed with a stop pin 54 which may be engaged by the slanted end edge49' or the hook surface 49" of the lever 49. The foremost part of the arm 53a of the detent lever 53 is arranged so as to abut the end part of the upright flange 40' mounted on sliding bar 40 or to slide on the lateral surface of the flange 40'. The other arm 53b of lever 53 is so arranged and designed so as to abut a stop pin 57 mounted on the camera housing under the force of spring 56, while the foremost part 53'b thereof rests on the rib 44. v

Numeral 58 in the drawing denotes a release pin projecting from the shutter safety gear 41 inside of the annular rib 44, numeral 59 denotes a guide pin engaging in a slot 66 of and guiding the abovementioned sliding bar 40, numeral 61 denotes a movable stop associated with the film winding mechanism in such a way that the stop 61 is moved to the left when the'film is wound in a manner not forming part of the present invention, but it may beshifted to the position shown by chain-dotted line before the film is wound'up, so as to retard the movement of the trifurcated lever 46 and hence the operation of the shutter actuation mechanism.

In the above-described construction, when the handle 42 is turned manually for one or two revolutions of the gear 41, and the'film wound up, the annular rib 44 mounted on the gear 41 comes to a halt with the cutout part 45 thereof in facing relation with the end 46' of the trifurcated lever. 46 as shown in FIG. 7. The shutter button is then depressed, and the bar 40 associated therewith is moved towards the left and viewed in FIGS. 7-9 and urges the end 46" of the lever 46 towards the left in FIG. 7. As the movable stop 61 is shifted to the full-line position as shown in FIG. 7, the lever 46 is free to rotate about shaft 47, thus allowing for depression of the release button. The sliding bar 40 is free to move towards the left in FIG. 7 and the shutter mechanism comes into play, as will be seen by referring to FIG. 8 showing the operative position of the shutter mechanism depicted above. When the. shutter operation is brought to an end, shutter button is released from manual pressure. Then, the lever 46 is returned to the initial position under the force of spring 48, and the sliding bar 40 is also returned to the initial position. In this situation, the hook face 49" on the lever 49 is engaged with the stop pin 54 on the lever 53 so that the sliding bar 40 is locked and the shutter actuating mechanism does not come into play evenif the shutter button is depressed manually, as will be realized by referring to FIG. 9 showing the operative position of the shutter mechanism depicted above.

The movable stop 61, on the other hand, is shifted to the chain-dotted line in FIG. 7, as the film is not yet wound.

When the handle 42 is turned manually in the abovementioned way for film-winding and shutter-changing operation, the arm 53b of the L-shaped lever 53 is turned by the engagement thereof with the release pin 58 so that the foremost part of the arm 53a on the L- shaped lever 53 is disengaged from its abutting contact with the end part of the flange 40 on the sliding bar 40 and the lever 53 is restored to the position as shown in FIG. 7.

It will be appreciated from the foregoing description that the shutter mechanism does not come into play while the film is wound up, while the release button can not be depressed following the release operation, and the film-winding operation is prevented from its occurrence as long as the shutter button is depressed manually. Thus, the occasional errors in the operation of the shutter mechanism such as double exposure may be obviated in a positive manner. The shutter mechanism embodying the abovementioned feature may be fitted on the expensive camera adapted for use with a so-called removable film pack.

What is claimed is:

1. in a shutter mechanism for a camera, a combina-. tion comprising, a film winding and shutter cocking mechanism including a safety gear having a pair of opposite end faces and an annular rib coaxial with said gear secured to one of said end faces and provided with a radially extending. cutout; lever means movable between an active position in which one end of said lever means is engaged in said cutout and an inactive position; biasing means cooperating with said lever means andztending to maintain the latter in said inactive position; a sliding bar shiftable upon depression of a shutter button from a rest to an advanced position in which said sliding bar engages said lever means to move the latter against the force of said biasing means to said active position; interlocking means cooperating with said sliding bar during movement thereof from said rest to said advanced position and back to said rest position for preventing the latter to move again to said advanced position before operation of said film windingand shuttercocking mechanism; and means on said safety gear cooperating with said interlocking means for releasing said sliding bar during operation of said film winding and shutter cocking mechanism so that said sliding bar may again be moved from said rest to said advanced position thereof.

2. A shutter mechanism for a camera comprising, in combination, a front screen and a rear screen; a release lever; a normally open switch associated with said release lever to be closed when said release lever is actuated; means cooperating with said release lever for starting operation of said front shutter screen upon actuation of said release lever; a current source; a transistorized control circuit for control of movement of said rear screen, said control circuit comprising a condenser, a normally open switch in parallel with said condenser-and associated with said front screen to be opened upon actuation of the latter, and an adjustable resistor in circuit with said condenser; an electromagnet connected to said control circuit so as to be deenergized after elapse of a charging time at which said condenser is charged to a predetermined potential, which charging time varies with the adjustment of said adjustable resistor; means cooperating with said electromagnet for starting operation of said rear screen upon deenergizing of said electromagnet; a film winding and shutter cocking mechanism including a safety gear, having a pair of opposite faces and an annular rib coaxial with said gear secured to one of said faces and provided with a radially extending cutout; lever means of said lever means is engaged in said cutout and an inactive position; biasing means cooperating with said lever means and tending to maintain the latter in said inactive position; a sliding bar shiftable upon depression of a shutter button from a rest to an advanced position in which said sliding bar engages said lever means to move the latter against the face of said biasing means to said active position; interlocking means cooperating with said sliding bar during movement thereof from said rest to said-advanced position and back to said rest position for preventing the latter to move again to said advanced position before operation of said film winding and shutter cocking mechanism; and means on said safety gear cooperating with said interlocking means for releasing said sliding bar during operation of said film winding and shutter cocking mechanism so that said sliding bar may again be moved from said rest to said advanced position thereof.

3. A shutter mechanism as defined in claim 2, and including a roll on which said rear screen is wound and pulling means tending to pull said rear screen off said roll, and said means cooperating with said electromagnet for starting operation of said rear screen comprising a rotary member to be driven by said roll, a projection fixed to said rotary member and havingan engaging face extending at an acute angle with respect to a plane including the axis of rotation of said rotary member and intersecting said face midway between said ends thereof, and a double-armed lever turnably about an' axis intermediate its ends and having at one end a face engaging said engaging face to thereby stop rotation of said rotary member and therewith actuation of said rear screen, an armature on the other end of said lever .and cooperating with said electromagnet, when the latter is energized, for holding said face on said one end of said lever in engagement with said engaging face, and spring means cooperating with said lever for turning the. same in a direction disengaging said face thereof from said engaging face upon deenergization of said magnet. j

4. A shutter mechanism as defined in claim 2, and including amirror drive actuated by said release lever, a second normally open switch connected in parallel with said first-mentioned normally open switch and together with the same connected in series with said current source, said second normally open switch being associated with said mirror drive and moved to the closed position upon actuation of said mirror drive.

5. A shutter mechanism as defined in claim 2, wherein said rear screen has a rear part wound about a wind up drum and a leading edge laterally spaced from a said drum, and including a guide drum for guiding said rear screen between said wind-up drum and said leading edge on the outer peripheral surface of said guide drum, a spindle extending axially through said guide drum spaced from the inner surface thereof, means mounting said spindle for rotation about its axis, bearing means mounting said guide drum on said spindle for rotation relative thereto, and a pair of rollers fixed to opposite ends of said spindle for rotation therewith, said front screen having a trailing edge and including a pair of spaced belts each connected at one end to said trailing end of said front screen and at the opposite end to a respective one of said rollers.

movable between an active position in which one end

Claims

1. In a shutter mechanism for a camera, a combination comprising, a film winding and shutter cocking mechanism including a safety gear having a pair of opposite end faces and an annular rib coaxial with said gear secured to one of said end faces and provided with a radially extending cutout; lever means movable between an active position in which one end of said lever means is engaged in said cutout and an inactive position; biasing means cooperating with said lever means and tending to maintain the latter in said inactive position; a sliding bar shiftable upon depression of a shutter button from a rest to an advanced position in which said sliding bar engages said lever means to move the latter against the force of said biasing means to said active position; interlocking means cooperating with said sliding bar during movement thereof from said rest to said advanced position and back to said rest position for preventing the latter to move again to said advanced position before operation of said film winding and shutter cocking mechanism; and means on said safety gear cooperating with said interlocking means for relEasing said sliding bar during operation of said film winding and shutter cocking mechanism so that said sliding bar may again be moved from said rest to said advanced position thereof.

2. A shutter mechanism for a camera comprising, in combination, a front screen and a rear screen; a release lever; a normally open switch associated with said release lever to be closed when said release lever is actuated; means cooperating with said release lever for starting operation of said front shutter screen upon actuation of said release lever; a current source; a transistorized control circuit for control of movement of said rear screen, said control circuit comprising a condenser, a normally open switch in parallel with said condenser and associated with said front screen to be opened upon actuation of the latter, and an adjustable resistor in circuit with said condenser; an electromagnet connected to said control circuit so as to be de-energized after elapse of a charging time at which said condenser is charged to a predetermined potential, which charging time varies with the adjustment of said adjustable resistor; means cooperating with said electromagnet for starting operation of said rear screen upon deenergizing of said electromagnet; a film winding and shutter cocking mechanism including a safety gear, having a pair of opposite faces and an annular rib coaxial with said gear secured to one of said faces and provided with a radially extending cutout; lever means movable between an active position in which one end of said lever means is engaged in said cutout and an inactive position; biasing means cooperating with said lever means and tending to maintain the latter in said inactive position; a sliding bar shiftable upon depression of a shutter button from a rest to an advanced position in which said sliding bar engages said lever means to move the latter against the face of said biasing means to said active position; interlocking means cooperating with said sliding bar during movement thereof from said rest to said advanced position and back to said rest position for preventing the latter to move again to said advanced position before operation of said film winding and shutter cocking mechanism; and means on said safety gear cooperating with said interlocking means for releasing said sliding bar during operation of said film winding and shutter cocking mechanism so that said sliding bar may again be moved from said rest to said advanced position thereof.

3. A shutter mechanism as defined in claim 2, and including a roll on which said rear screen is wound and pulling means tending to pull said rear screen off said roll, and said means cooperating with said electromagnet for starting operation of said rear screen comprising a rotary member to be driven by said roll, a projection fixed to said rotary member and having an engaging face extending at an acute angle with respect to a plane including the axis of rotation of said rotary member and intersecting said face midway between said ends thereof, and a double-armed lever turnably about an axis intermediate its ends and having at one end a face engaging said engaging face to thereby stop rotation of said rotary member and therewith actuation of said rear screen, an armature on the other end of said lever and cooperating with said electromagnet, when the latter is energized, for holding said face on said one end of said lever in engagement with said engaging face, and spring means cooperating with said lever for turning the same in a direction disengaging said face thereof from said engaging face upon deenergization of said magnet.

4. A shutter mechanism as defined in claim 2, and including a mirror drive actuated by said release lever, a second normally open switch connected in parallel with said first-mentioned normally open switch and together with the same connected in series with said current source, said second normally open switch being associated with said mirror drive and moved to the closed position upon actuation of said miRror drive.

5. A shutter mechanism as defined in claim 2, wherein said rear screen has a rear part wound about a wind up drum and a leading edge laterally spaced from said drum, and including a guide drum for guiding said rear screen between said wind-up drum and said leading edge on the outer peripheral surface of said guide drum, a spindle extending axially through said guide drum spaced from the inner surface thereof, means mounting said spindle for rotation about its axis, bearing means mounting said guide drum on said spindle for rotation relative thereto, and a pair of rollers fixed to opposite ends of said spindle for rotation therewith, said front screen having a trailing edge and including a pair of spaced belts each connected at one end to said trailing end of said front screen and at the opposite end to a respective one of said rollers.