Shutter Mechanisms

Kershaw

Blinds

The blinds are a simple arrangement of two half-blinds linked by tapes. The tapes are wound on a separate spindle at the top of the camera, that spindle and the spindle carrying the top blind are usually geared together, pulling out the speed-setting knob disengages the tape spindle so that it can be rotated separately.

Mirror Mechanism

The mirror has a very unusual action that was the subject of Kershaw's 1904 patent. The mirror box is a self-contained unit that is not fixed to the camera, in fact it will slide out if a plate at the bottom of the camera is removed. The edge of the mirror is pin-jointed to an arm at the mirror's centre. The arm is pivoted and constrains the pin to move in a curved slot. The arm is connected via a link to the mirror setting lever (on the outside of the camera) pulling the setting lever down pulls the arm down which causes the pin to move around its curved slot.¹

The top rear edge of the mirror is attached to an inner frame pivoted at the bottom of the mirror box, as the pin moves in its slot its top edge moves backwards pivoting the inner frame, as the pin moves further in the curved slot the top of the mirror is brought back. Pulling the setting lever down also extends a large spring which, when released, pulls up the mirror. On the other side of the camera the mirror is guided in a slot in the same way, connected to the arm is a dashpot to smooth the mirror action.

As the shutter was not self-capping the mirror box had to be made light-tight when the mirror was lowered. A baffle hinges upwards to connect to the lower edge of the mirror, it is raised by a linkage that connects the two arms of the mirror pin.

This design was intended to allow shorter focus lenses to be used. As the mirror pivots and moves back as it rises the edge nearest the lens moves nearly vertically until near the end of its travel when it moves forward to cover the focusing screen. The question has to be asked, did it work? Well, to some extent, at its introduction lens apertures were smaller, f6.8 or possibly f4.5 being the norm for a reflex, these had a significantly smaller diameter than later and faster lenses, so with early lenses there was less obstruction and the mirror movement was a benefit.

Shutter Mechanism

The mechanism is a very simple affair. It is built onto a metal plate that an be removed from the camera leaving the blind spindles still in place. A large wheel is turned to wind the shutter, this moves a second gear wheel which rotates both the spindle to which the tapes are wound and the upper blind spindle. A large pawl acting on the second wheel prevents it running backwards. Pushing the release lever frees the pawl and the shutter unwinds. When set to T, a lever is moved that is struck by the release lever causing the end of the lever to move into the mechanism where it meets a tooth on the underside of the main wheel. This corresponds to the blinds being fully open, they are held in this position until the release lever is again pressed. On later shutters (from 1928) there are settings for both B and T and a more complicated means of holding the blinds.

Videx

The Videx used a simple shutter where the blinds are linked by tapes. The tapes are wound on their own roller placed just below the upper-blind roller. The winding knob winds the upper blind and the tape roller which is geared to it. Unusually, to change the speed the winding knob is pulled out and turned, this turns the upper blind which pulls more tape on to its roller or frees tape, the tape roller is under tension and winds up any free tape. The speeds are shown on a dial, on the opposite side of the camera, which is moved when the upper-blind roller is rotated, the dial also carries a stop that prevents further winding. The shutter can only be wound when the mirror is lowered, the speeds can only be changed when the shutter is wound. When the camera release is pressed the mirror is pulled up and a hook lifts the pawl engaging the lower-blind ratchet allowing the blinds to run down.

Minex

The Minex, of 1909, has two independent blinds mounted on separate sets of rollers. The aperture is formed by delaying the movement of the second blind.²

There are four versions of the shutter as fitted to the Minex camera (it was also sold separately for attachment to other cameras):

• First version, this corresponds to the patent description and illustrations in very early advertisements. It was very quickly replaced by the second version, certainly within a year. It has a separate I&B, T switch.
• Second version, the I&B, T switch is removed on this version, the settings are made directly on the speed dial, thus one control knob sets the full range of speeds including B and T, tensions the shutter and lowers the mirror. The speeds are selected by lifting and turning the knob so that a pin engages different holes. The control knob has a solid top, external studs are at 6 and 5 o'clock.
• Third version, this appeared before 1914. The control knob is retained by a slotted nut rather than being screwed to the shaft, external studs at 5 and 3 o'clock.
• Fourth version, the I&B, T selector returns but with a different mechanism to the first version. The control knob is retained by a slotted nut, no external studs. This change took place in 1926.

The illustrations and description below are for the box form cameras, the Folding model is generally similar but differs in detail. In each illustration the shutter is not tensioned.

Details of Second type

To tension the shutter the control knob (above and attached to the wheel I) is turned clockwise, this rotates the pinions PU and PL (via the intermediate gear P) which wind up the shutter blinds onto the upper rollers. P is prevented from running back by the ratchet A. The rotation of I causes J to rotate anti-clockwise, the pin MP acts on the lever M which turns down and re-sets the mirror. The mirror is locked in place by a spring catch.

The camera is fired by a release knob (or pneumatic connection) on the other side of the camera to the shutter mechanism. When the release is depressed the mirror is unlocked and free to rise. It is the movement of the mirror that fires the shutter. The mirror is attached to the lever N, as it rises N is displaced along with the links that pull on lever B, this raises the ratchet A allowing the lower blind to unwind (pulled by the spring in the roller at the bottom of the shutter) and for PL to rotate. The rotation of PL is transmitted via the upper part of P to the upper wheel of I (IU) which in turn rotates. At this stage the lower blind is uncovering the focal plane.

Extending down through IU is a pin. The position of the pin is determined when setting a shutter speed on the control knob, when the knob is lifted, turned and dropped back the pin on its underside engages a hole. The angular distance of the hole/pin from the neutral point determines the slit width of the blinds. As the wheel IU rotates the cam on the speed dial meets the pin TP and pushes it away, this causes lever T to move downwards. The end of T is in contact with pins EP, as T moves it in turn moves EP and the lever E. The other end of E is holding the upper blind in place by a stud on the lower wheel of P. Moving E frees the upper blind. However the lower wheel IL is still being locked by the lever G so the upper blind cannot move. As the wheel IU continues its rotation the pin meets a stud on the lower wheel IL and causes IL to rotate (the pin is locked in place by a flat spring on the face of IL). At this point the cam on the speed dial meets the pin GP, pushes it aside, and unlocks the wheel IL, thus the upper blind is free to follow the lower blind across the focal plane.

As they move the two wheels IU and IL and locked together so the slit width is fixed (mechanically) throughout its travel. But as the lower blind reaches the end of its journey the upper blind still has some distance to travel, as the wheel IU rotates it separates from IL (it runs a short distance up the threaded spindle to which it is screwed) this frees IL and the upper blind can finish its movement.

When the release is depressed, as well as freeing the mirror the movement is transmitted via a rod that runs the width of the camera and via several levers to the levers T and G, as the shutter is released lever T is raised and G is moved to lock the wheel IL in preparation for meeting the cam of the speed dial (instantaneous speeds) or lock the blind movement in the case of 'T' and 'B' settings.

When tensioning the shutter the control knob is turned, this rotates the upper wheel IU which winds the lower blind, fixed to this wheel is a pin, after a short distance of travel (to close the blinds) the upper pin meets the pin fixed to the lower wheel which causes the wheel IL to rotate and wind the upper blind.

Actually there are two pins on the speed dial the one referred to above is the pin that controls the timing. There is also a small registration pin under the cam that engages the holes that can be seen around the outside of the speed dial. The larger pin drops into holes on the shutter wheel IU but for fast speeds the holes are close together and join to form a slot, the small registration pin matches a hole for each speed and so locks the larger pin at a certain position in the slot.

An early example of the version 2 shutter has two setting pins, MP. Presumably this was a fail safe device. On later examples the second pin has been cut away leaving a steel piece set in the brass wheel. (A large batch of wheels must have been made before the change).

Details of Third type

In this version the Lever T is located at the side of the wheel I instead of below. The main difference is in the shutter wheel I. The locking spring on the lower wheel is replaced by a short stud, the speed dial pin is able to ride upwards when meeting the stud and lock in place when it drops back. To free itself when completing its travel the upper wheel moves up the ramp IR (see illustration of fourth type). The wheel IU is held in place by a coiled spring in the control knob which pushes IU into contact with IL.

The lower blind is released in a similar way to the earlier version.

Once the speed dial pin has locked with the lower wheel the pin GP is moved out of the way by the speed dial cam allowing the upper blind to move. When set to 'B' the speed dial is raised very slightly, as a result the speed dial cam moves the pin TP when it passes rather than passing through the slot in TP. This takes place at the start of the exposure so that the upper blind is not held at P, it is though, still held by G which is released when pressure is removed from the shutter release.

Details of Fourth type

The shutter operates similarly to the third type but with simplifications and a few rearrangements. The most noticeable change is that a lever R (which has an external setting stud) now selects the I&B, T setting this brings the lever C into play which acts on the blinds gear wheel P. Movement of the upper blind is triggered when the speed dial pin locks with the lower wheel and meets the cam on the end of lever D and pushes the lever aside, previously the lever D was locking the wheel IL and preventing the upper blind from moving.

In the illustration the upper setting wheel has been removed to show the pins on the lower wheel.

Ensign Focal-plane

A very simple focal-plane shutter mechanism was used on Ensign cameras before the first world war. It was produced in many different forms and was also used on Ensign roller-blind shutters from about 1910.

Blinds

The lower blind is linked by friction to tapes joined to the top blind, the tapes wind onto a roller at the bottom of the camera next to the roller for the lower blind. The slit width is adjusted by continuing to wind the shutter once the lower blind has reached the top, which pulls through the extra length of tape required. At the end of the exposure the tape roller can pull the excess tape through the friction grip to close the aperture making the shutter self-capping.

The blinds are wound by turning a large winding wheel anti-clockwise, the wheel is locked by a pawl which prevents the mechanism running backwards when winding and once it is set. To release the shutter the pawl is moved clear of the wheel.

Setting the shutter

Exposure settings are made on a dial situated above the winding wheel and fixed to the same shaft, the dial contains a pin on its underside, a ring, drilled with holes representing different shutter speeds, surrounds the dial and can be depressed and moved to engage the pin in different position, the ring is engraved with the shutter speeds. On the underside of the ring is a plate carrying a lug. On setting the dial/ring to a particular speed the position of the lug has changed relative to the winding wheel. When the shutter is wound the winding wheel is eventually stopped when the lug comes into contact with a pin fixed to the camera. In this way the speed setting on the ring/dial affects the rotation of the winding wheel and so the amount of tape that is wound.

During exposure the winding wheel rotates clockwise and the blind unwinds pulled down by the tension roller. On instantaneous settings the movement of the winding wheel during exposure is not impeded.

B and T

When set to B, pin A on the winding wheel has moved as far as it can and has rotated lever C across the winding wheel, the tail end of lever C has also been displaced. Plate B has moved downwards. On release, the winding wheel rotates clockwise and releases the blinds, movement is stopped when pin B meets the face of lever C. Lever C would rotate out of the path of pin B but the tail end of lever C is prevented from moving by the curved end of the release lever which has moved upwards. The intermediate lever has come into contact with the springy end of plate B and is trapped by a hook on the underside of the plate, this leaves the release pawl in the open position. On freeing the release knob the release lever moves down allowing lever C to rotate out of the path of pin B and the winding wheel to continues its travel. At the end of the exposure pin A lifts plate B upwards and is then held.

The T setting is similar to B except that the winding wheel does not travel so far when being set, as a result plate B is not displaced. When the shutter is fired the intermediate lever is not held by plate B and, as pressure is removed from the release knob, can move back allowing the release pawl to engage and hold the winding wheel.

The shutter comes in many versions with differences in detail, the version described above is from an Ensign Reflex. One drawback is that the shutter speed has to be set before winding.

Several patents are mentioned in connection with the shutter. The main ones are BP 27461/1910 by G.F. Prout, H. Holmes and Houghtons Ltd. which covers tensioning and releasing the shutter and BP 15548/1908 by F.P. Whitehead and W.F. Giles, which has a very similar mechanism and was also used on the T-P Unit shutter. BP 16353/1906 by T.T. Hora is sometimes included. Patent BP 27461/1910 itself mentions BP 12105/1909 by H.G. Chessher (Tella Camera Co.), this patent includes mounting the tape roller inside the blind roller which was used in the Roller-blind form of the Ensign shutter.³

Unit - Whitehead and Giles

An unusual self-capping arrangement was developed by F.P. Whitehead and W.F. Giles, it was sold by Thornton-Pickard as the Unit and was also used on other cameras.⁴

Early examples of the shutter which was sold by T-P from about 1910 had a tension selector cog on the left-hand side (when in use) and slit-width selector set on a dial on the right-hand side. The combination of tension and slit was looked up on an attached table which gave the speed. From 1912 the tension setting was no longer used and the speed was set directly on the dial. The Unit was replaced by the Ruby shutter on T-P cameras from 1913.

As with the later Ruby shutter the Unit is in a chassis that can be slotted into the camera body allowing all of the precision work to be contained within the shutter itself.

Blinds

The shutter consists of two blinds wound on separate sets of rollers. When un-tensioned blind 1, which is fixed to a lower roller by tapes, has its leading edge at the bottom of the camera. Blind 2 (which is nearer the focal plane) is the capping blind, its leading edge is at the top of the camera and covers the image area. Blind 2 is fixed to an upper roller by tapes and is pulled onto its upper roller by a spring in that roller.

Tensioning the shutter

When the shutter is tensioned, by rotating the setting wheel K anti-clockwise, blind 1 is pulled to the top of the camera, this winds up the spring in its lower roller, C. The degree to which it is wound onto the upper roller (which gives the slit-width) is determined by the speed set on the setting ring. The pinion wheel, E, at this point does not engage C.

Releasing

When the release arm H is pressed the pinion wheel E is moved to engage both of the lower rollers C and D. The pawl M is then moved clear of the setting wheel K allowing K to rotate and the blinds to un-wind. Blind 2 drops to the bottom of the camera followed by blind 1 (the blinds move together but there is a gap produced by the tapes of blind 1), both movements being due to the spring in roller C which is strong enough to overcome the pull of the spring in the upper roller of blind 2.

When blind 1 has reached the end of its travel the connection between the rollers is broken this allows blind 2 to be pulled up by the spring in its top roller. Blind 2 now covers the image area when the shutter is next tensioned.

B setting

The setting wheel K is rotated to its full extent when the pin N moves the lever P across the face of the setting wheel. The end of P is held by a pin P7 on a spring plate. On exposure the wheel K rotates (clockwise), the pin O comes into contact with the lever P and is held, this corresponds to the blinds being fully open, when the release lever is freed the capping blind, 2, is pulled back to its top roller as normal.

The setting ring found on late versions is the same as was used on the Ruby shutter.

Ruby

The Ruby shutter replaced the earlier Unit shutter on Thornton-Pickard cameras. It was a self-capping model with two independent blinds, the slit was produced by varying the tape length. The mechanism is simple and rugged and consequently in many cases still works. In the description below the slightly odd numbering ties in with the patent drawings. The illustrations are of an early Ruby Reflex.⁵

Tensioning the shutter

The two setting wheels B, B1, are locked together during the first part of the setting movement, that is, until the lower blind is fully wound and the adjustment of the exposure slit is obtained by further winding the setting wheel B to draw more tape onto the upper roller. The wheel B operates pinion Z which winds blind a, B1 operates z1 which winds blind a1.

On winding the external knob C on the shaft c in an anti-clockwise direction, the rear wheel B, controlling the upper blind a, is rotated and carries with it the wheel B1, controlling the lower blind a1, by means of a pivoted catch D which engages a pin d extending from the wheel B through a concentric slot d1 in the wheel B1. The knob is wound until the catch D is disengaged from the pin d by a fixed projection L. At this point the wheel B1 and blind a1 are held wound by the release lever F engaging a notch between the two setting wheels. The knob C is again rotated to further wind the blind a, during this operation the pin d travels in the slot d1. The face of the wheel B is provided with a series of notches, e, which are engaged to hold the wheel B by a spring pawl E projecting through the wheel B1. The notches correspond to the exposure slits. On a ring between the shutter mechanism and the knob C are a second series of notches, X, corresponding to e, the notch (and so the required slit width and exposure) can be selected by turning the ring, the movement of the knob C is limited by the setting (the patent shows the notches X on the wheel B1).

Releasing

On releasing the shutter lever F, both blinds run down together until the pin e2 rides upon the slope of a stop-plate G, thereby retracting the pawl E from the wheel B. The wheel B1 is stopped by the edge g on the plate G, the wheel B continues to run down to close the slit until the pin d again comes to the end of the slot d1, and is re-locked to the wheel B1 by the spring catch D.

B setting

For Bulb exposures, the winding of wheel B is continued until the pin d reaches the other end of the slot d1 where it engages in, and rocks the spring catch H, so that on actuating the lever k the lever F is also operated, releasing the shutter which runs down until the catch H is arrested, by the lever K at the open aperture. The exposure is completed by releasing the lever k which frees H, and the parts return to their initial position.

N&G Reflex

This shutter was developed by Arthur Newman for use on Newman & Guardia Reflex cameras - the Self-Focusing Reflex of 1902 and the Square Reflector of 1904. It is built into a chassis as a self-contained unit, on the Square Reflector it attached to the very rear of the camera after the revolving back mechanism. On the Self-Focusing Reflex it fitted into the body of the camera but could be simply unclipped and removed for cleaning or adjustment.

This separation from the mirror movement and shutter/mirror release required some difficult connection arrangements. The shutter release was on the camera body, it had first to trip the mirror and then release the shutter. The mirror had also to be lowered before the shutter was wound as it was not self-capping. The result is an ingenious design occupying little space but also one that is unsuccessful; it would be more suited to a precision instrument than a camera that had to stand up to hard use. Another drawback, one disliked by many photographers, was the very small winding wheel requiring several turns to set the shutter.

The illustrations are of a shutter fitted to a Self-Focusing Reflex, the description is based on the patent specification.⁶

Blinds

There are two blinds wound on separate sets of rollers, each has a fixed aperture, the exposure slit is formed by the displacement of one blind relative to the other. Blind 1 is the inner blind wound on the bottom spring roller 5 and attached to the upper roller 6, blind 2 is wound on the bottom spring roller 7 and attached to the upper roller 8. The blind displacement (slit width) is achieved by continuing to wind roller 8 after blind 1 has been fully wound.

Setting the Blinds

The rollers 6, 8 are geared together by wheels 12, 11 and 10, 9. The intermediate wheels 10, 11 are mounted on a shaft 13 and are pressed together by a spring, 16, forming a friction clutch. The further winding of roller 8 is permitted by the wheel 11 slipping on the wheel 10. The pin 23 and the wheel 10 are rigidly fixed on the shaft 13. The clutch-sleeves 19, 20 and 21 rotate on shaft 13 and enclose the spring 16. The clutch-parts have their ends shaped into a single tooth such that after an amount of angular movement of one sleeve the teeth meet and the clutch-sleeves turn in unison. After completing a revolution, pin 23 turns the clutch-sleeve 19. After two revolutions, the sleeve 20 is turned by the sleeve 19, and finally, after four revolutions the sleeve 21 comes in contact with the pin 29 on the loose wheel 11. The movement of the wheel 11 with regard to the wheel 10 is therefore limited to four revolutions. The displacement of the roller 8 with regard to the roller 6 is shown by the indicating-disc 32.

Release Mechanism

The roller 6 carries a disc with a notch 47 and is geared to the disc 51 having a notch 52. The catch-levers 30, 36 have pairs of projections 53, 55 and 54, 56, which engage simultaneously with the notches 47, 52. The roller 6 and disc 51 are so geared together that the notches are only brought into position for engagement when the shutter has made its full movement, for instance after the roller 6 has made four and a half turns and the disc 51 one and half turns. To hold the roller 6 during the winding of the shutter, the lever 36a engages with the ratchet wheel 36b. The lever 36a is disengaged simultaneously with the catch-lever 36. The catch-levers 30, 36 are operated by the mechanism for moving the mirror. When the mirror is lowered, a bar from the mirror disengages the catch 30, and the shutter is free to be wound. On raising the mirror the bar is drawn back which releases the catch 36 and makes the exposure.

The engagement sequence is:

• After exposure. Lever 30 engages 47 and 52. Levers 36, 36a lifted clear.
• Mirror set. Lever 30 lifted clear. Lever 36a engages 36b. Lever 36 pushed against 51.
• Shutter wound. Lever 36 engages 47 and 52.
• Shutter released. Lever 36, 36a lifted clear. Lever 30 pushed against 51.

Square Reflector

On the Square Reflector the shutter is separated from the mirror/release by the revolving back. A pivoted spring lever inside the shutter housing operates on the levers 30, 36, a bar, H, attached to the mirror setting lever, G, passes through the revolving back and pushes on the lever. When the mirror is raised the bar extends into the shutter housing, thus preventing the revolving back from turning. When the mirror is lowered the bar is withdrawn allowing the revolving back to move. The lever 36a can move to engage the ratchet wheel 36b and lever 30 is moved clear allowing the shutter to be wound. When the shutter is released the bar moves into the shutter housing freeing levers 36, 36a allowing the blinds to move.

The shutter is slightly different to the Self-Focusing Reflex, the spring 16 is on a separate spindle allowing the clutch sleeves to be reduced in size.

The release and mirror controls are straightforward. Rotating the lever G tensions a large coiled spring situated beneath it, a lever E is also rotated. E is loosely connected to the edge of the mirror, rotating E lowers the mirror. At the end of the movement E is locked in place by the edge A1 of the rocking plate A. Pressing the release button L which is behind the area A2 rocks the plate A, lowers A1 and frees the lever E. The mirror now rises.

The shutter release bar H has a connecting rod attached to it terminating near the mirror setting lever G, as the mirror is set pressure on the connecting rod is removed and H is pushed clear of the shutter area. When the mirror is raised, at the end of the exposure, a plate attached to the coiled spring pushes the connecting rod and H into the shutter housing.

The T setting is interesting, it works on the release controls rather than within the shutter. A small catch, M, near the release button, L, is moved down, the mirror is lowered and the shutter wound so that the image area is completely uncovered. When the release is pressed the mirror rises, exposing the image, but the bar does not move into the shutter which would close the blinds. A second operation of the release is needed to move the bar into the shutter housing and operate the shutter. Moving the plate M lowers the plate D on the inside of the camera. C sits on top of D and is also lowered slightly, The result is that the lever E is caught a fraction before its normal completion, first by the edge C2 and then by the edge C1, the coiled spring below the setting lever G does not unwind completely and so does not hit the connecting rod of H.

K is a connection from the alternative release on the other side of the camera. J is a connection to the alternative position of the revolving back. Note the curved track of the mirror, this guides the front edge of the hinged section of the mirror after it has hinged down.

N&G Two-Shutter Reflex

This camera is based on the Square Reflector but has in addition to the focal-plane shutter a two-blade return shutter mounted between the lens. When the front shutter is used the operations are:

• Open the shutter once the mirror is lowered.
• On release, close the shutter then raise the mirror.
• Fire the shutter.

The setting/raising of the mirror and the linkages to the focal-plane shutter and revolving back are the same as in the Square Reflector and are described above. A switch on the side of the camera sets which shutter is to be used. When the front shutter is used the focal-plane has to be manually opened, as do the front blades when the rear shutter is used.

The major part of the front shutter controls is in the body of the camera, from there, a single transmission bar is used to operate the front shutter. The bar moves both clockwise and anti-clockwise to make the settings, it is also telescopic for bellows extension.

The first illustration shows the camera in the untensioned state, mirror raised, and set for front shutter use. The setting for front or focal-plane shutter is by a stud near the mirror setting handle, G, this moves a plate, 2, inside the camera. One arm of 2 engages one of two notches on the end of plate 1. Plate 1 lies next to 7 which is connected to and follows the mirror movement. Hooks at each end of 7 engage the shaped end of the sliding plate 8 and the bar 4. The other end of 4 connects to lever 9 which rotates the transmission bar 10. Moving 2 also pushes the end of bar 4 to the left or right so that, when the front shutter is used, it can meet the hooks on 7, 2 also moves the connecting rod 11 which disengages the connection to the focal-plane shutter.

When set for Front shutter use

Moving 2 draws the connecting rod 11 and the attached lever H away from the focal plane and prevents the focal-plane shutter from firing. The upper notch of 1 is engaged by the arm of 2. The mirror is in the up position and plate 7 is at the top of the camera. Lowering the mirror brings 7 down in an arcuate course. The upper end of 7 moves 4 and 8 down. Attached to the end of 4 is the lever 9 which rotates away from the camera body, this rotates the bar 10 which hinges a pallet near the lens box back which opens the blades. The movement of 4 depresses the end of lever 12 and brings the other end of 12 immediately under the release stud 6.

On release, initial pressure moves the transmission the bar 10 to close the blades. Stud 6 depresses lever 12 which raises 4 (a spring on top of 4 was pushing it down) this frees 4 from the end of 7 and allows 10 to rotate towards the camera body which closes the front blades. Plate 4 moves upwards, as a result of the rotation of 9, with its far end now in front of 7. Lever 9 is now resting on the raised, bevelled, section of 8. Further depression of the release knob frees 7 (by the ordinary Square Reflector mechanism) which now travels towards the top of the camera. Near the end of its travel it meets the end of 8 and slides 8 upwards, this allows lever 9 to drop further and rotate the bar 10, the pallet hinges forward and operates the blades of the front shutter.

When set for Focal-plane use

Plate 2 moves rod 11 so that the attached lever H connects to the focal-plane shutter and moves lever 4 slightly to the right so that it is not in contact with plate 7.

Front Shutter

The front shutter is a two-blade return type with pneumatic regulation similar to the model fitted to the Postcard Sibyl. It fits into a 'lens box' and is completely removable allowing other lenses to be fitted to the camera, the shutter will also function when removed from the camera. The illustration shows the shutter removed from the lens box.

The shutter is controlled by a pallet which is moved by the transmission bar, the pallet hinges backwards to open the blades and forward to close the blades and then make the exposure. The pallet fits into a fork, 26, at the edge of the shutter. As 26 moves backwards the lever 27 engages a hole in a spring attached to the blades, 27 moves towards the top of the camera thereby opening the blades. This is the focusing position. The shutter is now tensioned by moving the arm 23 upwards until it is locked by the spring plate 30. When the body release is pressed the pallet hinges forward, this lifts 27 clear of the hole in the spring plate and the blades close. Continuing pressure on the body release brings the pallet further forward resulting in the arm 29 depressing 30, this frees the rod to which 23 is attached. 23 is pulled down by a spring attached to the top of the rod and fixed to the bottom of the shutter, its progress is retarded by the pneumatic delay cylinder. As 23 descends it meets the stud 21 and rotates it anti-clockwise which opens the shutter blades for the exposure. Further descent brings it into contact with the stud 24 (21 and 24 sit on the same lever) which is rotated clockwise to close the blades.

When the focal-plane shutter is used the blades are manually opened by moving the lever 22.

At the top of the shutter is a sliding plate 20, this has settings for 'Mirror', B or T and I. Normally the mirror setting is used, selecting the other settings allows the shutter to operate independently of the camera. A plate (not shown in the illustration) fits along the top of the shutter and carries a release button and cable release socket, these operate on plate 28 which moves 30 to release the blades.

N&G Folding Reflex

The shutter developed for the N&G Folding Reflex was also used, in a modified form, on the Dallmeyer Speed and Baby Speed Reflex cameras.

In its original form, as fitted to the Folding Reflex, the shutter mechanism is split into two halves situated each side of the camera. On the left, when in use, is the shutter/mirror release and controls for B, T and I, on the right is the timing and shutter setting wheels.

The description that follows is largely taken from the patent specification.⁷

Shutter Blinds

The shutter comprises two blinds one, 43, with an aperture 47 is wound on a spring roller 46 and the central part 45 of an upper roller. The other blind is wound on a spring roller 48 with tapes 44 wound on rollers 49 and 50 adjacent to, and on the same spindle as, the upper roller. When the blind 44 has been fully unwound from the spindle 48 the aperture blind 43 can be further wound on the roller 45 to an adjustable extent forming a slit of predetermined size. On running down for an exposure when the blind 44 is fully re-wound on the roller 48 the blind 43 continues to wind on the spring roller 46 to close the slit. This is allowed by the clutch arrangement in the upper roller where the part 45 can rotate while the rollers 49, 50 remain stationary.

Mirror Setting

The mirror is mounted on the axis 21 which contains a coiled spring tending to raise the mirror. The mirror is lowered by hand and held in place by moving arm 30, the arm has a series of projections (31, 32, 33) on the underside, the projection 31 is held by catch 34 on arm 35 when 30 is lowered. Lowering the arm 30 also moves pawl 80 to engage the gear wheel 66. Without lowering the mirror the shutter cannot be wound.

The arm 35 is connected with a release and timing lever 36 which has a catch 94 that engages one of the projections 31, 32, 33 depending on the shutter setting of B, T, I. The mirror pivot 21 also operates linkages whereby, when the mirror rises for an exposure, the link 29 engages the pawl 80, which holds the shutter in the set position, freeing the gear wheel 66.

B T I Setting

The setting of B, T, I is made by moving the pin 42 and the sliding plate 140. The edge of the plate has shoulders - 98, 99, 100 - which limit the angular movement of the arm 36.

For instantaneous exposures pin 42 is moved to the I setting (lowest) which brings shoulder 100 opposite the projection 41 on the lever 36. When the release lever, 37, is pressed the arm 30 and mirror are released, arm 30 rises, the shoulder 100 limits the movement of lever 36 and keeps the catch 94 free of the projections 31, 32, 33. The arm 29 then releases the shutter pawl 80.

For Time exposures pin 42 is moved to T (middle position) which brings shoulder 99 opposite the projection 41 so that on operating the release 37 the catch 94 on the lever 36 engages the projection 32 on the arm 30 and on the return of the release 37 the catch 94 engages the projection 33. The corresponding movement of the arm 29 is to release the shutter pawl 80 but to be held in the path of a projection 96 on the gear wheel 66, arresting the shutter in the open position until the release 37 is again actuated to release the mirror from the catch 33.

For Bulb exposures pin 42 is set in the B position, bringing the stop 98 into position to arrest the projection 41. On operating the release 37 the catch 94 arrests the projection 31 on the arm 30 and the corresponding movement of the arm 29 is to release the shutter pawl 80 and engage the projection 96 holding the shutter open as long as the release 37 is held.

Speed Setting

The speed of the shutter is controlled by a setting knob which positions a notched disc 73, freely mounted on the axis of wheel 64 and held by a spring catch 76. The disc 73 has a pin 74 extending into a slot 72 of a plate 69 which is also freely mounted on the same shaft as 64 and itself carries a pin 70. This pin is normally adjacent to a pin 71 on the pinion wheel 64.

On rotating the winding knob (sited above pinion 66) and the pinion 66, the blinds of the shutter are wound by rotation of the winding pinion 201 via gear wheel 64, 201 is directly connected to the spindle carrying 45, 49 and 50. After one revolution of the wheel 64, the pin 71 engages the pin 70 on the plate 69. The blinds are further wound to the extent allowed by the slot 72 and until rotation is stopped by the pin 74 on the setting disc 73. The purpose of the floating plate 69 is that when set to T or B the wheel 71 needs to rotate more than 360 degrees, the slot 72 allows this extra movement. When the shutter unwinds the projection 96 on wheel 66 moves a plate 200 upwards which frees the notched wheel 73.

When used on the Dallmeyer cameras the B, T, I settings were moved to the same area as the shutter setting wheels.

Leica

The Leica shutter is a very simple mechanism built with a minimum of parts. It consists of two blinds with the slit formed by a time delay. The leading blind is mounted on a spring roller with the tapes of the following blind mounted on an adjacent spring roller. The following blind is attached to a large take-up drum with the tapes of the leading blind attached to drums at either end. On pressing the release button the leading blind is released and unwinds through a distance equal to that of the slit, the following blind is then released and the blinds move together across the focal plane.⁸

The detail of the shutter changed over its long life, the illustrations are of a Leica I of 1928.

There are two gear trains deployed in the shutter. The first transmits the movement of the film-advance knob to the top of the sprocket drum. The second, at the bottom of the camera, transmits the rotation of the sprocket drum to the take-up drums of the blinds. The timing device sits on top of the take-up drums.

Setting the Shutter

The film is advanced, and the shutter wound, by turning a knob situated above spindle 200. This motion is transferred to the wheel 203 at the top of the sprocket drum 204 on spindle 30. Spindle 30 is loosely coupled to the lower gear train: as 30 rotates a pin, 102, drives pin 103 which is mounted on a disc above gear wheel 26. Thus motion is transferred to the lower gear train, finally gear wheel 25 rotates causing spindle 1 and the drums 2 and 3 on which the tapes for the leading blind are wound to rotate. The drum 7, on which the following blind is wound is loosely coupled to drum 2 and also rotates. Both blinds are wound onto their take-up drums and the springs in rollers 21 and 24 are tensioned. A coiled spring in the winding knob prevents backward movement of the mechanism (a pawl was used in early models). A pin on the underside of wheel 25 limits rotation and so stops the winding motion.

Shutter Release

On pressing the release button, 32, spindle 30 moves downwards and displaces a leaf spring 29. The two pins 102 and 103 are also disengaged freeing the lower gear train and so the blinds are free to move. As the leaf spring 29 is lowered so rod 31 is pushed down, the top of 31 carries a catch 33 which is also lowered. At this point the leading blind is free and travelling across the focal-plane. The second blind is being held. Drum 7 carrying the following blind is connected by a short rod to the timing mechanism and arm 10 in the mechanism. Arm 10 is trying to rotate but is held by catch 33. As spindle 1 rotates (as a result of the leading blind moving) the arm 15 carrying pin 17 will move catch 33 and free arm 10 allowing it to rotate and the following blind to move across the focal-plane. Arm 15 is attached to the external speed dial and can be lifted and positioned by locating pin 16 in holes drilled in plate 12, the hole selected determines the exposure. The loose connection between the take-up drums 7 and 2 consists of a connecting rod working in an arcuate slot, this allows enough free movement of 7 to continue its travel at the end of the exposure to cap the blinds.

Film Re-wind

The sprocket drum must be able to move freely and rotate backwards when the film is re-wound and therefor has to be decoupled from the top and bottom gear train. This is accomplished by moving a small lever on the top of the camera, below the lever is a cam which acts on a spindle, 101, and lowers it. At the top of 101 is a gear within the train connecting the film-advance knob to the sprocket drum, this is displaced and so decouples the sprocket drum from the upper gear train, the bottom of spindle 101 acts on a disc on spindle 30 sited above gear wheel 26, this is displaced separating the two pins 102 and 103 and so freeing the sprocket drum from the lower gear train.

Sibyl

Original, Ordinary 2 ½" x 3 ½"

Spring powered sector with pneumatic regulation. When introduced in 1906 these were very simple but well made shutters. The sector moves across the lens at uniform speed in alternate directions and can be tensioned in either position. The shutter is particularly quiet in operation.

The main spring fits over a spindle on the setting sector, its two ends are both at the bottom of the spindle and project forming arms that lie each side of a shaped projection. The shutter is tensioned when an external lever moves one of the arms through a short arc. As the arm is moved the setting sector is held by the release lever. Pressing the release lever frees the sector allowing it to rotate and relax the spring, as the sector rotates links force the blade across the lens opening.

The speeds are set by moving an external lever which moves the speed setting rod which adjusts the flow of air to and from the pneumatic cylinder. A 'B' setting is possible by a short depress of the release when the shutter is set to a slow speed. The setting sector is caught by the release lever at its middle notch.

The release of these shutters is on the side of the shutter. On very early examples the shutter blade is unpainted, after a very short time the blade was painted black and was marked with a + and O sign, these indicate which way the setting lever is to move to set the shutter.

Ordinary quarter-plate

Spring powered sector with pneumatic regulation.

Similar to the shutter fitted to the smaller Ordinary model but the shutter spring now sits over the pivot point of the blade, the setting sector is also centred on pivot point. As a result the delay cylinder is angled upwards. This symmetric arrangement does away with the links that connected the spring to the blade and would have given more even travel of the blade in its two directions of movement. The spring itself is contained in a small housing on the face plate of the shutter.

The shutter release is now at the lower left of the face plate. A spring pushes the release lever upwards. Two buffers have been introduced to cushion the blade movement.

Special

The shutter fitted to the Special model is very similar to that fitted to the quarter-plate Ordinary. The blade has lost its top connecting strip and now consists of two circular lobes.

Baby, New Special, New Ideal

The improvement over the shutter fitted to the Special is the inclusion of a separate I, T, B selector. A sliding stud on the front is used to make the selection which moves a plate with shaped projections in line with the (internal) release lever. The release lever is lifted by the projections, to free the shutter, and additionally may be caught or slip over the projections depending on the setting. The release button on the face plate now moves a short lever which acts on the edge of the I, T, B lever which moves sideways.⁹

Excelsior, Vitesse

Two-blade pivoted return. Compared to earlier Sibyls the main spring has been considerably strengthened allowing a higher top speed and a different blade action. The I, B, T selection is much more positive than in other Sibyls and is more reliable. The shutter, though, is much noisier than other models.¹⁰

The blades are opened and closed by moving a small stud sited below the lens, a link connects the stud to a cam. A small pin on the link engages in a slot in the cam, rotation of the cam moves the pin and hence moves the shutter blades. The slot is shaped such that as the cam rotates the pin moves at first quickly, to open the blades, then slowly during the exposure and then quickly to close the blades. Above the cam is a 'trigger plate' that is held by the release levers, above the trigger plate is the main spring that powers the shutter.

When tensioned the trigger plate is held by the first (top) of the release levers, on depression of that release lever the main spring is free to unwind. A sliding I, B, T selector plate works in conjunction with the release levers. The external release button sits above and depresses the selector plate and so operates the levers. Each lever is pushed up at the left by a spring, the selector plate holds the levers down or frees them, the right hand ends of the levers interfere with the movement of the trigger plate as it tries to rotate. The photograph shows the I setting, moving the selector plate up gives B and then T. When the lever is moved to the B position the middle lever is depressed the other end is raised, when the shutter is released by the top lever the trigger plate rotates but is then held by the middle lever until pressure is removed from the release knob. When set to T the bottom lever rises, it was held down by the separate T plate, on release the trigger plate can rotate until it meets the end of the middle (B) lever where it is held until pressure is removed from the release button, it is then held by the lowest (T) lever until the release knob is again pressed. When set to I, the B and T levers are inoperative.

The exposure is determined by a pneumatic delay cylinder, this is connected to a 'speed selector plate', The speed selector plate is moved up and down by the speed dial on the front of the camera. When the shutter blades are open the trigger plate comes into contact with a stud on the speed selector plate and its movement is retarded whilst the pneumatic delay runs its course.

Post Card

Two-blade pivoted return. The shutter is set by raising a rod until a second notch on the rod catches in a fork which is the end of the release linkage. When the release is pressed the fork is lowered allowing the setting rod to drop, in doing so the release arm first moves the 'open stud' which opens the blades, the arm then moves the 'close stub'.

The I, B, T lever on the front plate moves a plate which determines the amount of depression of the release and release linkage. When set to I the movement of the fork is enough to free the setting rod. When set to T the depression is small, enough to free the rod but the fork can rise to catch and hold the rod at another notch. When set to B the depression is large, the rod is freed but is then caught when the top of the fork falls into a notch on the front of the rod.

De Luxe, Imperial

Two-blade pivoted return. This is an unusual shutter with two main springs that are used alternately.

With the setting bar in its lower position the lower spring is in compression. The upper setting arm is now moved to its upper position by moving an arm on the face plate, this compresses the upper spring. The shutter can now be released by depressing the release, the lower spring extends and operates the shutter blade by moving the setting bar upwards. The two blades are connected by two pivoted links which are moved by the setting bar, at the start and end of an exposure the links are in a V position, as they are moved into line the blades are forced apart.

N&S Patent

The Patent is a simple three-blade leaf shutter with pneumatic delay. It was introduced in 1912 or 1913 and based on the patent of A.S. Newman. It was originally called the Accurate, later the Perfect.¹¹

The shutter is set by moving a lever on the front plate which tensions a coiled spring. When the spring is tensioned a plate, underneath the spring, catches on the end of the release lever. Operating the external release shifts this lever and allows the spring to unwind. A short depress of the release when the shutter is set to a slow speed results in a second projection on the plate catching the release lever, this gives a B setting. When the blades are fully open a stud is momentarily held in a spring mechanism at the top of the shutter. The blades are operated by a pivoting plate having slots for pins attached to the blades, the plate is moved by the main spring. A dial on the front of the shutter sets the speed by moving the speed setting rod of the delay cylinder.

References & Notes