GB2101755A - Focal plane camera shutter - Google Patents

Abstract

A focal plane shutter comprises two lightweight shutter blades which move rectilinearly in succession to open and close an exposure aperture, one exposure being effected by movement of the blades to the left (from the cocked right hand position shown) and the next exposure being effected by movement of the blades to the right in the reverse order. Blades 1 and 2 move successively to the left under the action of springs 1 and 2 by the successive release of latches 1 and 2, and are latched by latches 4 and 3. The blades are then cocked in the left hand position by shifting cocking levers 1 and 2 to the left (compressing springs 3 and 4) by means of cams 1 and 2, enabling shutter release by successive movement to the right of blades 2 and 1. The blades move rapidly across the aperture with very low inertia. <IMAGE>

Description

SPECIFICATION Focal plane camera shutter This invention relates to focal plane shutters for cameras; particularly (but not necessarily solely) a focal plane shutter consisting of two thin opaque plates being arranged to perform mutually parallel motion by means of guidance in slots in order to open and close an exposure aperture.

According to one aspect of the invention there is provided a focal plane shutter comprising two shutter blades, means to apply an accelerating impulse to one said shutter blade to give said one blade momentum such that it moves across an exposure aperture to open the exposure aperture and means to apply an accelerating impulse to the other shutter blade to give said other blade momentum such that it moves across the exposure aperture to reclose the exposure aperture.

According to another aspect of the invention there is provided a focal plane shutter for a camera comprising a base plate having an exposure aperture therein, two thin, opaque shutter blades, two cam-operated or link-operated cocking levers, four compression springs and four shutter blade latches, the focal plane shutter being characterised in that each shutter blade is free to 'fly' across the exposure aperture after receiving an impulse from its related spring and in that subsequent exposure of the exposure aperture is made by returning the thin, opaque shutter blade to its original position.

Referring to the drawings by way of example, two successive exposures may be made by sending the blades from left to right for the first exposure and then from right to left for the second exposure, across the exposure aperture--see diagrams A through E of the drawings for a right to left exposure sequence.

The following provides a description of a preferred embodiment of this invention and is to be read in conjunction with the accompanying drawings in which: Diagram A shown a focal plane shutter with both blades in the cocked state on the righthand ("RH") side of the base-plate; Diagram B shows blade 1 released and approximately halfway across the exposure aperture; Diagram C shows blade 2 released after a timed interval and taking the same path across the exposure aperture as blade 1; Diagram D shows both blades 1 and 2 latched on the opposite side of the exposure aperture; Diagram E shows the cocking levers moved to the right to compress the left-hand ("LH") springs (3 and 4) and decompress springs 1 and 2 thus re-cocking the mechanism for the next exposure (i.e. from Left to Right).

The exposure aperture exposure sequence commences with the various components as shown in diagram A or diagram E. The following description assumes commencement at diagram A.

When latch 1 is released, spring 1 being in a compressed state imparts an accelerating impulse to blade 1, which is initially at rest with respect to the base-plate. The accelerating impulse ceases upon spring 1 having extended a predetermined amount (corresponding to a predetermined displacement of blade 1) after which the blade 1 proceeds under its own momentum across the exposure aperture towards latch 4 and spring 4 (diagram B), opening the aperture.

After a timed interval (effectively the exposure time) latch 2 is released and spring 2 (being initially compressed) imparts an accelerating impulse to blade 2 (which is initially at rest, like blade 1) lasting until spring 2 has extended a predetermined amount like spring 1, after which the blade 2 proceeds under its own momentum across the exposure aperture towards latch 3 and spring 3 (diagram C).

It is preferred for springs 1 to 4 to be indentical with identical extensions to give identical accelerating impulses and for blades 1 and 2 to have identical inertia so that the characteristics of motion (acceleration, velocity and displacement) of blades 1 and 2 are identical, that is to say, each blade has an identical velocity vupon having moved a given distance x (for all values of vand x) after having been respectively unlatched.

Although it is preferrea for the accelerating impulse to have ceased before the respective blade reaches the position at which opening or reclosure respectively of the aperture commences (so that the respective blade travels across the aperture entirely under its own momentum) this is not essential. Each blade may still be accelerating under the effect of its respective spring impulse when it commences crossing the aperture.

On completion of crossing the exposure aperture shutter blade 1 is held by latch 4 to stop it returning. Likewise shutter blade 2 is held by latch 3 (see diagram D).

Rotation of cams 1 and 2 then move cocking levers 1 and 2 to compress springs 3 and 4 against shutter blades 2 and 1 respectively holding them securely against latches 3 and 4 respectively. The rotation of cams 1 and 2 also decompresses springs 2 and 1.

The shutter is then cocked ready for the next exposure in which instance shutter blade 2 is released prior to shutter blade 1.

The dimensions of shutter blades 1 and 2 are determined to allow a reasonable overlap on the exposure aperture to make it properly light-tight at the two cocked positions.

Very high acceleration is required for each blaA to reach the required high speed in a very short time and over a short distance, and so the mass (and hence the inertia) of each blade is as small as possible in order to minimise the acceleration force required. This also means than the deceleration force required to stop each blade after traversing the aperture is a minimum.

Assuming that the two blades have the same characteristics of motion) acceleration, velocity and displacement-see above) the gap between the two blades nevetheless only remains constant if both blades traverse the aperture under the same, constant, velocity.

This is most nearly achieved if each blade is entirely under its own momentum and moving neariy friction-free.

The opaque thin blades have a simple, geometric form uncomplicated by pivots associated with some conventional focal plane shutters and lend themselves therefore to ease of manufacture.

The cams 1 and 2 may be replaced by suitable links (not shown) to move the cocking levers.

Claims (8)

1. A focal plane shutter comprising two shutter blades, means to apply an accelerating impulse to one said shutter blade to give said one blade momentum such that it moves across an exposure aperture to open the exposure aperture and means to apply an accelerating impulse to the other shutter blade to give said other blade momentum such that it moves across the exposure aperture to reclose the exposure aperture.

2. A focal plane shutter os claimed in claim 1 wherein each impulse is terminated by the time that the respective blade commences to traverse the aperture.

3. A focal plane shutter as claimed in claim 1 or 2 wherein each blade is initially latched against a spring-bias which supplies the impulse when the blade is unlatched.

4. A focal plane shutter as claimed in claim 1, 2 or 3 wherein two blades are guided in a guideway means.

5. A focal plane shutter as claimed in claim 4 wherein the guideway means is in the form of slots.

6. A focal plane shutter as claimed in any preceding claim wherein the two blades are arranged to move along a substantially common path in a substantially common direction, the one leading the other.

7. A focal plane shutter as claimed in any preceding claim wherein the two blades reverse their respective directions of motion and exchange their respective aperture-opening and aperture-closing roles for successive exposures.

8. A focal plane shutter for a camera comprising a base plate having an exposure aperture therein, two thin, opaque shutter blades, two cam-operated or link operated cocking levers, four compression springs and four shutter blade latches, the focal plane shutter being characterised in that each shutter blade is free to 'fly' across the exposure aperture after receiving an impulse from its related spring and that subsequent exposure of the exposure aperture is made by returning the thin, opaque shutter blade to its original position i.e. an exposure may be made by sending the blade from left to right or from right to left across the exposure aperture.