Photographic shutter of the focal-plane type

The shutter comprises a first and a second blind (47, 48) extending in parallel planes close to each other and wound on at least one roller (6, 9) on each side of the exposure window, which blinds each have an edge (55, 56) which edges define a shutter slit (5) between them. The roller of the first blind is driven by a first pinion (7) which is rigidly coupled to a drive mechanism (31). In accordance with the invention the shutter comprises a second pinion (11) which is rotationally coupled to the first pinion, and a third pinion (14) which is coaxial with the second pinion and which is driven by the second pinion via an angular-positioning device (59) which drives the roller (9) of the second blind; the shutter also comprises tension means (49, 52, 53) which maintain each blind in its respective plane. In this way an accurately variable width of the shutter slit can be obtained. The shutter is used in cameras for aerial or marine surveillance.

The invention relates to a photographic shutter of the focal-plane type, 
comprising a first and a second blind which extend in parallel planes 
close to each other and which are each partly wound on at least one drive 
roller which is situated on one side and on the other side of the exposure 
window respectively and which is mounted, for rotation on a chassis, which 
blinds each comprise at least one edge which is movable across the 
exposure window in such a way that a shutter slit is formed between said 
edges, the roller of the first blind being driven directly by a first 
pinion which is rotatably coupled to a drive mechanism mounted on said 
chassis. 
The focal-plane shutter in accordance with the invention may be used in all 
types of photographic cameras, which may be normal commercially available 
cameras or more specialized cameras such as those used for aerial or 
marine surveillance. 
Shutters comprising two blinds are known, for example from French Patent 
Application No. 2.439.413. This prior-art shutter has the advantage that 
for a constant travelling speed v(t) of each blind it provides a slit 
width d and thus an exposure time T which can be adjusted, the following 
relationship being valid: 
EQU d=vT (1) 
This is an improvement in comparison with certain cameras comprising a 
single blind with a fixed slit width, in which the exposure time is varied 
by replacing the blind by another blind having a slit of a different 
width, or in comparison with conventional commercially available cameras 
having a shutter blind without slit which upon its release returns to its 
closed position after a predetermined time. This last-mentioned method 
does not provide a wide exposure-time control range in contradistinction 
to the method employing shutters with two blinds. On the other hand, in 
the case of a shutter comprising one or more blinds whose shutter slit 
travels across the image to be exposed and whose exposure time T complies 
with the above equation (1), it is attempted to make the parameters d and 
v constant as a function of time, so as to obtain a constant exposure time 
T during the translational movement of the blind(s). This is difficult to 
accomplish when high speeds v are required because of the inevitable 
acceleration and deceleration of the shutter parts to be rotated or 
translated. One solution to this technical problem is to make the 
instantaneous values of the parameters d and v proportional by various 
known means, i.e. to ensure that the following relationship is valid 
during operation of the shutter: 
EQU d(t)=K v(t) (2) 
K being a constant in first approximation. Nevertheless, it is difficult to 
ensure that such a relationship is complied with precisely. The shutter 
comprising two blinds described in French Patent Specification No. 
2.439.413 has two disadvantages: the movements of the two blinds are 
independent, whereas their speeds v(t), which vary as a function of time, 
are substantially equal. It follows that for a great slit width this width 
varies during the translational movement of the slit, which variation may 
change even to a different extent for each of the blinds. On the other 
hand, for very small slit widths of the order of 1 to 2 mm, i.e. very 
short exposure times, the accuracy of the system deteriorates because of 
the high relative error to which the width d is the subject. 
In principle, it is the object of the invention to provide a shutter whose 
slit width is accurately variable, whilst permitting high speeds of 
operation. 
This object is achieved and the drawbacks of the prior art are mitigated or 
eliminated when the photographic shutter defined in the opening paragraph 
is characterized by a mechanical connection between said drive rollers 
such that at any instant a relative position of the blinds can be obtained 
which defines a shutter slit of predetermined width, said blinds being 
tensioned permanently, which shutter, for this purpose, comprises a second 
pinion which is mounted for rotation on said chassis which second pinion 
is arranged opposite the first pinion on the other side of the exposure 
window and is rotatably coupled to said first pinion, a third pinion which 
is coaxial with the second pinion and which is driven by said second 
pinion via an angular-positioning device which is independent of the 
simultaneous rotary movements of the second and the third pinion, said 
third pinion driving said drive roller of said second blind with the same 
speed of rotation as the drive roller of the first blind, and tension 
means which maintain each blind in its respective plane. The basic idea of 
the invention is to interlock the translational movements of the two 
blinds, preferably by mechanical means, in such a way that the slit width 
can have, for example, a fixed value or varies in accordance with a 
predetermined function while the blinds travel across the image to be 
exposed. 
In a preferred embodiment said tension means comprise, for the first blind, 
a third drive roller which is mounted for rotation on the chassis and 
which is rotated by said second pinion and, for the second blind, a fourth 
roller which is mounted for rotation on the chassis near said drive 
mechanism and which is driven by a tension band which is wound around the 
rollers carrying the second blind with winding directions opposite to 
those of the second blind, and said first and second blinds each have a 
rectangular aperture which is capable of exposing the entire format, one 
of the small sides of said aperture forming an edge of the shutter slit. 
In another preferred embodiment, which is compatible with the foregoing 
embodiment, said drive mechanism is a helical spring with non-adjoining 
turns, which spring may be loaded in torsion in both directions of 
rotation, the shutter being characterized in that the angular positioning 
device comprises a combination of a first and a second concentrically 
arranged drum, which drums are mounted for rotation on said chassis, a 
spindle, and at least one limb, which first drum is rigidly connected to 
said second pinion and which second drum is rigidly connected to said 
third pinion, said spindle being coaxial with said second and third 
pinions in which it can slide freely, said limb being mounted for rotation 
so that it cannot be translated on said spindle inside said drums and 
engaging a first and a second curved slot formed in the walls of the first 
and the second drum, respectively, which slots are curved oppositely, the 
angular displacement between said second and third pinions being a 
function of the translational position of said spindle along its axis. 
Another preferred embodiment of the invention, which is compatible with the 
preceding embodiments, is characterized in that said second drum is longer 
than said first drum and its slot extends further than said first drum in 
accordance with a generatrix of the cylinder formed by the drum in such a 
way that for a range of values corresponding to a deep insertion of said 
spindle in the drums said limb is disengaged from said first slot so that 
the two drums are not coupled to each other. 
This last-mentioned embodiment enables exposures to be made by means of 
only one of the two blinds, so that no shutter slit is formed and the 
image format remaining exposed throughout the selected exposure time.

In the various Figures elements having the same functions bear the same 
reference numerals. 
In FIGS. 1 to 3 the chassis which carries the various parts of the shutter 
is not shown for the sake of clarity. The shutter shown in FIG. 1 
comprises a first blind 1 and a second blind 2 which extend substantially 
in the same plane or in parallel planes close to each other and each 
comprise an edge, 3 and 4 respectively, which can move across the exposure 
window (not shown) in such a way that a shutter slit 5 having a width d is 
formed between the edges 3 and 4. Each blind is partly wound on a drive 
roller, which rollers are each situated on one side of the exposure 
window, the blind 1 being wound on a roller 6 which is driven directly by 
a first pinion 7, which is rotated by a drive mechanism 8 which is rigidly 
connected to the chassis, and the shutter 2 is wound on a roller 9. In 
accordance with the invention the two blinds are mechanically interlocked 
permanently, i.e. no matter whether the shutter is operative or 
inoperative, and the width of the slit 5 can be varied at any instant, the 
blinds 1 and 2 remaining always taut. Inoorder to achieve this, the 
shutter firstly comprises a second pinion 11, which is arranged opposite 
the first pinion 7 on the other side of the exposure window and which is 
rotatably coupled to said first pinion, for example by means of a pinion 
12, which is rigidly connected to the pinion 7, and a gear rack 13; the 
shutter also comprises a third pinion 14 which is coaxial with the pinion 
11 and which is driven by the latter via an angular-positioning device 15 
which is independent of the simultaneous rotary movement of the pinions 11 
and 14; finally, the shutter comprises tension means which ensure that 
each shutter remains taut in its plane. 
In a manner, not shown, the gear rack 13 can be translated on rollers which 
are provided with flat-bottom grooves and which are mounted for rotation 
on the chassis, the two toothed end portions of the gear rack being in 
engagement with the pinions 11 and 12. The angular-positioning device 15 
comprises two cylindrical drums, of which the drum 16 is rigidly connected 
to the pinion 11 and of which the drum 17 is rigidly connected to the 
pinion 14. In each drum wall a curved slot 18, 19 is formed, for example, 
a helical slot with opposite curvatures. During assembly of the shutter 
the drums are inserted one into the other so that they can rotate freely 
in each other, for example in the same way as a sleeve bearing or by means 
of roller bearings, and the pinion 14 is then in mesh with the drive 
pinion 21 of the roller 9. After assembly the pinions 11 and 14 as well as 
the drums 16 and 17 have a common axis 22. The assembly comprising the 
elements 11, 14, 16 and 17 is supported on the chassis by means of two 
bearings, not shown, one bearing at the location of the pinion 11 and one 
bearing at the end of the drum 17 which is remote from the pinion 14. The 
journal of the pinion 11 has a bore for the passage of a spindle 23 which 
has an axis 22. The spindle 23 can perform free translational and 
rotational movements inside the drums and a member 24, which is located 
inside the drums and which comprises at least one limb 25, is mounted on 
said spindle so that it can rotate but cannot be translated (for example 
by means of a bearing whose inner race is clamped on the spindle 23). The 
limb 25 engages in the slots 18 and 19. Preferably, the 
angular-positioning device described in the foregoing comprises two 
further slots such as 18 and 19 and comprises a further limb such as 25, 
which elements are disposed mirror-symmetrically relative to the axis 22 
in order to balance the mechanical stresses occurring during operation of 
the device. Alternatively, there may be provided 2 times three slots and 
three limbs which are disposed at 120.degree. from each other around the 
axis 22. 
When the limbs, such as 25, are simultaneously in engagement with the slots 
such as 18 and 19 a translation of the spindle 23 gives rise to a 
corresponding angular displacement between the pinions 11 and 14, thus 
establishing a special geometrical relationship between the respective 
points of the slots such as 18 and 19 which are situated in one plane 
perpendicular to the axis 22 by means of the limbs such as 25, said 
angular displacement having the same predetermined value, whilst the 
pinions 11 and 14 which are rotatably coupled to each other via the limbs 
25 rotate until they are stopped, i.e. during exposure or between two 
exposures. If x is the variable which represents the displacement of the 
spindle 23 along the axis 22, this results in a continuous function d(x) 
for the slit width which can be varied as desired independently of the 
movement and the translational positions of the blinds 1 and 2, provided 
that the reduction ratios between the motor pinion 7 and each of the drive 
rollers 6 and 9 is the same by choosing a suitable construction. A shaft 
in rotary position between the pinions 11 and 14 therefore results in a 
corresponding proportional variation of the width d of the slit, which can 
thus be made very small. It is to be noted that once the slit width has 
been adjusted by the translational position of the spindle 23 as indicated 
by the double arrow 16 it is irrelevant for the control of the slit as 
described in the foregoing whether the spindle 23 is rotated (through 
friction inside the pinion 11) or is maintained stationary in that it 
slides over a part of the chassis, so that no rotation is possible, 
because the member 24 is mounted for rotation around the spindle 23. 
Preferably, the spindle 23 cannot rotate relative to the chassis and its 
translational position (arrow 26) is defined by means of a threaded bush 
which is mounted for rotation on the chassis, for example by means of a 
bearing and which is fitted onto a threaded end portion of the spindle 23. 
The means for actuating the spindle 23 are not shown in FIG. 1. For more 
details on the angular-positioning device reference is made to FIG. 5 and 
the corresponding part of the description. In order to ensure that the 
shutters remain taut and flat for all possible slit widths, there are 
provided tension means. In FIG. 1 these tension means comprise bands 27 of 
a thin elastic material which are disposed perpendicularly to the rollers 
6 and 9 near the shutter edges which are perpendicular to the edges 3 and 
4 of the slit. The ends of each of the four bands are secured to the 
shutters by a known means, one of the ends being situated very close to an 
edge of the slit and the other end being in a backward position relative 
to the opposite edge of the slit on the other shutter, which permits a 
large elongation of the elastic bands for all the desired slit widths. The 
bands are arranged in sets of two and they are arranged above each other 
on both sides of the shutters, for example symmetrically relative to the 
axis which indicates the centre of the slit, as shown in the Figure. The 
drive mechanism 8 comprises, for example, an electronically controlled 
electric motor which is mounted on the chassis, by means of which motor 
the desired speed characteristics and sequences for the shutter operation 
can be obtained, which operation can be obtained for either direction of 
travel of the slit 5 relative to the shutter window. Alternatively, the 
drive mechanism may comprise a helical spring, preferably having 
non-adjoining turns as shown in FIGS. 2 and 3, so that high torques and 
consequently high speeds can be obtained for the movable parts of the 
shutter. In this last-mentioned case a sequencing and energy supply 
mechanism must be used in conjunction with the drive mechanism for example 
as described with reference to FIGS. 2 and 3 hereinafter. It is to be 
noted that the drive rollers 6 and 9 provide a positive drive for the 
blinds 1 and 2 in both directions of rotation, such that the tension 
means, such as the bands 27 in FIG. 1, only have to overcome the inertia 
of the blinds, which is negligible relative to that of in particular the 
rotating parts, during the acceleration or deceleration phase by which 
each shutter release is attended. 
FIG. 2 shows an embodiment of the shutter in accordance with the invention 
in which the drive mechanism comprises helical spring have non-adjoining 
turns 31, in conjunction with a sequencing (release) and energy supply or 
take-off mechanism, and in which the blind-tension means differ from the 
elastic bands 27 in FIG. 1. In FIG. 2 the angular-positioning device is 
similar to that shown in FIG. 1 and operates in the same way, the drive 
pinion 21 of the roller 9 being shown symbolically against the pinion 24 
because the angular-positioning device is shown in an exploded view. One 
of the ends of the actuating spring 31 is secured to an annular member 32 
and its other end to the motor pinion 7. A gear rack 33 is driven by the 
pinion 12 or by a pinion 34 which is coupled to an electric motor, not 
shown, via an eccentric pin 35 which engages with a slight clearance in a 
slot 36 formed in the gear rack 33 and which extends substantially 
perpendicularly to said rack. The annular member 32, which is connected to 
one end of the spring, cooperates, via splines 37, with a spring-balancing 
member 38 which is fixed to the chassis. In a manner not shown the rollers 
6 and 9 and the pinions 12, 11 and 14 as well as the pinion 34, which 
comprises a non-return pawl 39, are supported by bearings mounted on the 
chassis, in the same way as in FIG. 1. The gear rack 33 is translated on 
rollers, not shown, having a flat-bottom groove for its guidance, on one 
side after gear rack being in contact with said rollers and the other side 
engaging with the pinions 11 and 12. 
In both directions indicated by the double arrow 41 the shutter operates 
with energy regeneration as explained hereinafter. The force exerted by 
the spring for a specific position of the assembly comprising the blinds 
and the slit between said blinds is controlled by means of the 
spring-balancing member, in such a way that when the pin 35 is disposed at 
one end of the slot 36, the gear rack being substantially in its centre 
position, the actuating spring is in the rest position. The spring 31, 
which has non-adjoining turns, may be loaded in both directions, i.e. in 
the direction in which the turns expand (which is accompanied by slight 
elongation) or in the direction in which the turns contract (which is 
accompanied by a slight reduction in length). The variation of the length 
of the spring is possible a result of the splines 37. For example, when 
the pin 35 is in its upper position the pinion 34 is rotated in the 
direction of the arrow 42 until the pin is situated in the centre of the 
slot 36. At this instant the spring is wound up to the maximum extent, the 
gear rack is situated at the extreme right in the Figure, and the slit 5 
is also disposed at the extreme right outside the camera format. After the 
passage of this extreme point of the pin the pinion 7 provides the drive 
under the influence of the spring, whilst for example a freewheel is 
provided for the pinion 34 in the direction of the arrow 42. During this 
very rapid movement of all the movable parts, the slit scans the image to 
be recorded and passes across the format in the other direction, the 
inertia of all the moving parts partly winding the spring in a direction 
opposite to that indicated in the foregoing. This winding of the spring is 
only partial because of the friction losses. The (oscillatory) return of 
the movable system to the rest position (spring not loaded) is prevented 
by the provision of the non-return pawl 39. The electric motor which 
rotates the pinion 34 may stopped during the rapid movement of the blind. 
Alternatively, it may rotate permanently, its number of resolutions 
determining the exposure rhythm and the shutter slit scanning consecutive 
images alternately in the one and the other direction. In a preferred 
embodiment the pinion 34 may be supported by a bearing which is rigidly 
connected to the chassis and the electric motor, which is not coupled to 
said pinion, comprises a shaft provided with a cam which during every half 
revolution of the pinion 34 moves the pin 35 to its extreme position in 
the lateral direction. This variant is preferred because a dead time 
occurs between two consecutive movements of the blind, during which the 
motor is not loaded by the shutter mechanism, which enables it to be used 
for other functions, such as advancing the film relative to the exposure 
window for the next exposure. In this way a symmetrically operating device 
is obtained in which most part of the energy produced by the spring is 
recovered by the spring itself, so that the electric motor only has to 
deliver a small amount of energy in order to tension the spring to the 
maximum extent. The principal advantages of this method of driving the 
blinds are: a high speed of the blinds is obtained of the order of a few 
metres per second, a low power consumption and, for each exposure, a range 
of substantially constant speed during the travel of the slit across the 
format to be exposed. 
In FIG. 2 the tension means comprise two elastic belts 42 and 43, 
preferably of circular cross-section, which are arranged in suitable 
grooves in the rollers 6 and 9 and which form close loops, the ends of the 
belts being attached to the edges 3 and 4 of the slit 5 so as to pull said 
edges towards each other. In order to reinforce the edges of the slit and 
a satisfactory attachment, these edges are the edges of the blinds (not 
visible in FIG. 2) are clamped in metal portions 44 and 45 (for example 
sections). Preferably, the metal portions 44 and 45 project from the 
blinds on both sides to provide free ends for attaching the belts 42 and 
43, which suitably comprise helical springs of very small diameter. At its 
end each spring is provided with a wire or string 46 which extends through 
one of the metal portions and which is attached to the other metal 
portion. In order to prevent a return torque being exerted on the metal 
portions 44 and 45, which would affect the accuracy of the slit width d, 
the strings 46 must extend in the plane of the blinds 1 and 2, as far as 
this is possible. It is to be noted that in the embodiment shown in FIG. 2 
the distance between the drive rollers 6 and 9 is greater than in the 
embodiment shown in FIG. 1. This is because the blind-tension means in 
FIG. 2 cannot be wound around the rollers 6 and 9 in contradistinction to 
the situation shown in FIG. 1; therefore, it is necessary that after each 
exposure the shutter slit is closed or is at least situated well outside 
the exposure format in order to preclude fogging of the film. The spaced 
arrangement of the rollers in FIG. 2 ensures that the film is protected 
against the penetration of stray-light through the shutter slit 5. 
The embodiment shown in FIG. 3 comprises the same energy recovery and 
release mechanism as the embodiment in FIG. 2. However, the blind-tension 
means and the angularpositioning device differ from those shown in FIGS. 1 
and 2. In the present case the blinds are not juxtaposed but are 
superimposed so that a first or upper blind 47 is obtained and a second or 
lower blind 48, which are arranged in parallel with each other with a 
clearance of approximately 1 mm underneath the upper blind in the Figure. 
Each blind is tautened in its plane in that it is supported and driven by 
two rollers, disposed on both sides of the film format, which rollers 
constitute the tension means; the first blind 47 is driven by the roller 6 
and by a third roller 49 which is mounted for rotation on the chassis and 
which is rotated by the second pinion 11 via a pinion 51 which is 
rotatably coupled to the pinion 11, and the second blind 48 is driven by 
the second roller 9 and a fourth roller 52, which is mounted for rotation 
on the chassis near the drive mechanism and which is rotated via a tension 
band 53 which is wound around the second and fourth supporting rollers of 
the second blind 58 with winding directions opposite to those for the 
blind 48. During operation the rollers 49 and 52 have the same 
circumferential speed as the rollers 6 and 9. In the present embodiment 
the first and the second blinds each have an aperture, 57 and 58 
respectively, in the form of ractangular windows of the same height, each 
of which can exposure the entire format, one of the small sides 55, 56 of 
said windows forming an edge of the shutter slit. As a result of this 
arrangement each blind comprises two half blinds which are interconnected 
by straps 54. In the same way as in the embodiment shown in FIGS. 1 and 2 
the blinds 47 and 48 shown in FIG. 3 are preferably made of stainless 
steel or titanium having a thickness of approximately 25 microns. Their 
rigidity is such that they are resiliently loaded relative to the rollers 
on which they are arranged (with a different capacity of the rollers 6 and 
49 or 9 and 52), so that the blinds can always be taut even in the case of 
a variation of the diameter of the rollers owing to the different length 
of blind which they contain. It is to be noted that in FIG. 3 the edges 55 
and 56 of the shutter slit have been reversed relative to those shown in 
FIGS. 1 and 2, the edge 55 of the first blind 47 being situated at the 
side of the angular-positioning device and the edge 56 of the second blind 
being situated at the side of the drive mechanism. This reversal is 
allowed because each blind has an aperture. 
The angular-positioning device with the reference numeral 59 in FIG. 3 may 
be the same as that shown in FIGS. 1 and 2. However, owing to the special 
construction of the blinds, the blind drive and the blind-tension means as 
described in the foregoing, the angular-positioning device may be modified 
so as to enable time exposures by means of a suitable control. In the 
device 59 the first drum 60 carries the pinion 51 in addition to the 
pinion 11 and comprises one or more slots 70. The second drum 61 is longer 
than the drum 60 and the slot(s) 62 which guide(s) the limb(s) 25 
change(s) into a cylinder generatrix 61 towards the back of the Figure. 
This allows the lower blind 48 to be uncoupled, which happens when the 
limbs 25 are disengaged from the slots 70. In order to set the shutter to 
time exposures the shutter slit must be disposed as close as possible to 
the drive mechanism, the drums 60 and 61 still being interlocked by means 
of the limbs 25, in such a way that the aperture 57 of the lower blind 
exposes the entire format and the aperture 58 of the upper blind fully 
covers the latter. In this particular position, in which the pin 35 is 
situated substantially in its extremely left-hand position in the Figure, 
the limbs 25 are disengaged from the drum 60 by depressing of the spindle 
23. In order to ensure that the blind 48 is held in this last-mentioned 
position in a stable manner so that it is immune to shocks or vibrations, 
the member 24 is pushed towards the back by means of the spindle 23 so 
that it is pressed against the inner bearing ring, which is secured to the 
chassis and thus immobile, of the drum 61. Thus, the shutter can be 
operated to make exposures with an unlimited exposure time by means of the 
upper blind 47 only. This mode of operation resembles that of commercially 
available conventional cameras with a single shutter blind. In this 
special mode of operation one complete cycle of the drive mechanism is 
necessary (i.e. one full revolution of the pinion 34), so that the film 
must be advanced only once instead of twice during this cycle: before a 
time exposure the upper blind covers the entire format (the blind 47 being 
pulled completely to the left, see FIG. 4d). The exposure time begins when 
the shutter is released by means of the electric motor and the upper blind 
is pulled to the right after which the electric motor stops (in this 
last-mentioned position the entire format is exposed--see FIG. 4e). After 
an electronically obtained delay equal to the exposure time, the motor is 
re-energized and the blind 47 moves across the format in the reverse 
direction to its initial position where the motor is stopped for the 
second time (see FIG. 4d) in which position it remains until the next 
exposure is taken. From the position shown in FIG. 4d change-over 10 
instantaneous exposures is effected by pulling out the spindle 23, so that 
the drums 60 and 61 are interlocked again. In order to facilitate the 
insertion of the limbs 25 into the slots 70, said slots are suitably 
formed with a widened portion 63 at their open ends (FIG. 3). 
As will be described hereinafter with reference to FIG. 5, the spindle 23 
may be passed through the bearing of the drum 61 with a sliding fit and on 
the other side of said bearing it may actuate a potentiometer by means of 
a mechanism resembling the mechanism 59, the output voltage V of this 
potentiometer corresponding to the dimension d (or the exposure time T). 
FIGS. 4a, b, c, d and e illustrate different stages of operation of the 
embodiment shown in FIG. 3, the mode of operation illustrated by means of 
FIGS. 4a, b and c being also possible with the embodiments shown in FIGS. 
1 and 2 which comprise a single drive roller per blind (6 and 9 
respectively). At the right of the Figures the corresponding position of 
the control spindle 35 in the slot 36 is shown. The format of the camera 
is indicated by the two dash-dot lines 65, the middle of the format being 
indicated by the dash-dot line 66. On each side of the format the drive 
rollers for the blinds are shown, 6 and 49 on one side and 9 and 51 on the 
other side. The line of attachment of the blinds to the rollers is 
symbolically represented by a point 67 on the circle representing each 
roller and the figure inside each circle indicates the number of turns of 
each blind around the rollers for a specific choice of the point of 
attachment of the blinds to the rollers, which choice is arbitrary with 
the proviso that a minimum take-up length is observed for each roller. In 
FIG. 4a a double arrow 68 indicates the control range attainable for the 
width d of the shutter slit, which may vary between, for example, d 
min=1.75 mm (T=1/3200 s) and d max=22.4 mm (T=1/250 s). In FIG. 4a an 
intermediate value di has been chosen for the slit width d. FIG. 4a shows 
the shutter position when the actuating spring 31 is not loaded and the 
spindle is situated at one of the ends of the slot 36. FIG. 4b shows the 
system for the same slit width di, pulled towards the left by means of the 
spindle 35 which is disposed in its extreme left-hand position, ready for 
release. Between the positions shown in FIGS. 4b and 4c the shutter is 
released, the shutter slit scanning the format from the left to the right 
with a substantially constant high speed, the shutter slit stops briefly 
at the right outside the format, during which the change to another 
exposure is effected, and subsequently proceeds with its movement to the 
right under the influence of the electric motor and the spindle 35 until 
it has reached the position shown in FIG. 4c. The next exposure 
corresponds to the passage from position 4c to position 4b, the operation 
being the reverse of the sequence described above. FIGS. 4d and 4e 
illustrate a time exposure. The starting position in which the drum 61 is 
disengaged is indicated in FIG. 4d, which position is the same as that 
shown in FIG. 4b. The change from position 4d to the position 4e proceeds 
as described for the passage from 4b to 4c for the upper blind. During 
this transition the lower blind 48 remains stationary so that in position 
4e the entire format is exposed. At the end of the exposure in position 4e 
the electric motor is reenergized and the blinds 47 and 48 return to 
position 4d (or 4b if the spindle 23 has been pulled). 
FIG. 5 shows how the angular-positioning device 59 of FIG. 3 may be 
constructed. To simplify the Figure certain parts are represented as a 
single part, although in practice they comprise a plurality of separate 
components, which is necessary for mounting them, the separate parts being 
fixed to each other by any known means after assembly. This is in 
particular so for the bearing supports. The chassis bears the reference 
numeral 71 and the various parts indicated by reference numerals in FIG. 3 
are also shown, namely the second pinion 11, the third pinion 14, the 
drums 60 and 61 with their slots 70 and 62 respectively, the spindle 23, 
the member 24 which carries the limb(s) 25, the gear rack 33 and the 
pinion 51. The drum 60 is mounted for rotation on the chassis by means of 
a bearing 72 and, on the opposite side, the drum 61 by means of a bearing 
73. The drum 61 is rotatable relative to the drum 60 via at least three 
rollers 64 whose spindles are supported by the drum 60. By means of a 
bearing 75 the member 24 is rotatable around a member 76, which is clamped 
on the spindle 23 and which is rigidly connected to a brake pad 77. A 
toothed end-portion of the gear rack 63 is enclosed between the pinion 11 
and a roller which has a flat-bottom groove 78 and which is mounted for 
rotation on a spindle 79 which is rigidly connected to the chassis. An end 
portion 81 of the spindle 23 is threaded and engages a threaded bush 82 
which is supported by the chassis via a sleeve bearing; when the bush 82 
is rotated this construction ensures that the spindle 23 is advanced or 
with-drawn and thus the assembly comprising the elements 24, 25, 75, 76, 
77 inside the drums 60 and 61, if rotation of the spindle 23 is inhibited. 
Rotation is inhibited by means of a limb 83 which is fixed perpendicularly 
to the other end of the spindle 23 and which engages a straight slot 84 in 
the chassis. In order to obtain a sufficiently rapid movement of the 
spindle 23 the threaded end portion 81 may be provided with multiple 
thread. The bush 82 may be actuated manually or by means of an 
electronically controlled electric motor. It is even possible to vary the 
slit width d in accordance with any desired function of time during the 
shutter-release stage. In particular during the time interval in which the 
slit travels across the image to be recorded its speed v(t) is not 
entirely constant but, in particular if the drive mechanism is a spring, 
it increases from the beginning to the middle of this time interval and 
then decreases from the middle towards the end in accordance with a 
relationship which can be determined with a suitable accuracy by 
experiment. Thus, in accordance with the invention it is possible to 
impose a variation d(t) on the dimension d during said time interval, 
which variation is for example proportional to the variation v(t) (similar 
functions of time--see formula 2) in such a way that by virtue of fomula 
(1) a predetermined constant exposure time T is obtained during the entire 
time in which the slit travels across the image (the slit becomes wider 
when it has passed the centre line 66 of the format--FIG. 4). 
In FIG. 5 a dashed-line rectangle 80 symbolically represents the presence 
of further limbs 25 which cooperate with further slots 70, 62 formed in 
the drums 60 and 61. Preferably, the limbs 25 comprise rotary rings 85 to 
facilitate their movement in the slots. When the limbs 25 are disengaged 
from the slot 70 upon depression of the spindle 23 the drum 61 is no 
longer interlocked with the drum 60. A slight additional depression brings 
the braking disc 77 into contact with the bottom 92 of the drum 61, so 
that said drum is stopped because the disc 77 itself cannot rotate as a 
result of the presence of the limb 83. Alternatively, as described above 
with reference to FIG. 3, the braking disc may be rigidly connected to the 
member 24 and act against the surface 93 of the chassis, which surface 
extends substantially in the same plane as the surface 92. 
In a manner not shown the maximum depression of the spindle 23 mechanically 
actuates a mechanical or electro-mechanical control which serves to 
inhibit one of every two film-transport sequences during a complete cycle 
of operation of the driving mechanism, which precludes that during time 
exposures one half of the photosensitive surface of the film to be exposed 
is spoilt. 
In the right-hand part of FIG. 5 on the other side of the bearing 73 a 
mechanism is shown which is controlled by the translational position of 
the spindle 23, which mechanism is capable of converting the instantaneous 
value of the slit width d into an electrical value. This mechanism 
comprises a cylindrical sector 86 which is provided with a curved slot 87 
and which is mounted for rotation on the chassis by means of bearings 88. 
The limb 83 extends in the slot 87 and the sector 86 is provided with a 
pinion 89 mounted on the spindle 90 of a potentiometer. The translational 
movement of the limb 83 causes a rotation of the spindle 90 in accordance 
with the curvature of the slot 87. If V is the output voltage of the 
potentiometer 90 it is thus possible to obtain the required transfer 
function between the parameters d and V or T and V. The output signal of 
the potentiometer (the voltage V) may be used for indicating the exposure 
time value on a display and/or for recording purposes, or it may be used 
as a transducer output for controlling the film exposure in conjunction 
with an aperture control with a preset exposure time or with an exposure 
time which can be varied independently or together with the aperture. 
The principle advantages of the shutter described above are the following: 
alternate operation in the one or the other scanning direction, so that a 
rapid sequence of exposures can be made (up to ten exposures per second); 
if the drive mechanism is a spring energy recovery, which saves drive-motor 
energy (by means of a single spring); 
full control of the slit width both when stationary and during operation, 
which results in extremely small slits (down to 1 mm) and consequently 
vary short exposure times (variable and accurate exposure times up to 
1/4000 s); 
variation of the slit width is possible during the movement of the blinds; 
in the embodiment comprising four blind-drive rollers a simple control 
(same actuating button as for the slit width) of time exposures (night 
photography with flare); 
the blinds exert no or a small load on the rollers in a radial direction 
(as in certain cameras), so that the blinds can be made of light alloys 
and the rotary mass of the rollers can be low, which yields a gain in 
speed and saves energy.