Improvements in Photographic Camera Shutters.
Year: 1892

page_text: Date of Application, 24th May. 1892
Complete Specification Left, 24th Feb., 1893-Accepted, 25th Mar., 1893
PROVISIONAL SPECIFICATION.
Improvements in Photographic Camera Shutters.
We, CONRAD BECK, of 68 Cornhill, London, E.C., Optician, and JOSEPH
THACHER CLARKE, of Boston, Massachusetts, a citizen of the United States, at
present residing at 3 College Road, Harrow, Middlesex, Architect, do hereby
declare the nature of this invention to be as follows:-
Our invention relates to photographic shutters of the type described in Clarke's
Specification No. 20852 of 1890, in which the movable plate or shutter, revolving
in one direction only, is of a circular shape, with a single exposure aperture, the
size of this aperture being increased or diminished by a secondary or auxiliary
semicircular fan or stop attached to the face of the main shutter disc in such wise
as to obscure a greater or less portion of the aperture thereof. With an auxiliary.
stop of this nature the exposure aperture in the shutter disc may be varied from
the narrowest radial slit to a concentric zone extending to a length of one hundred
and eighty degrees.
In shutters of this type the exposure aperture, whether narrow or wide, has
hitherto been so arranged as to pass immediately in front of the lens on the shutter
being set in action: the auxiliary stop, i.e. the semicircular obscuring plate attached
to the main shutter, being moved, in the act of increasing the aperture, in a
direction contrary to that in which the shutter disc is revolved.
It has been found in practice that this arrangement does not give the greatest
possible latitude of exposure, inasmuch as the shutter disc, when released, revolves
with a gradually accelerating motion. Thus the narrowest available slit, being
immediately adjacent to the lens aperture, was passed in front of the lens at a
slower speed than was any portion of the zone situated at greater distance from
the lens. It is obvious that the result of this acceleration has been to decrease
the variability and range of the effective photographic exposure, which was thus
not directly proportionate to the aperture displayed in the shutter disc by pushing
aside the auxiliary stop from the zone.
not
Our present invention not only obviates this disadvantage, but profits by that
very acceleration in the rate of travel which has been observed in the movement
of the circular shutter disc. We obtain this advantage by so constructing the
auxilia y semicircular obscuring plate, that it is moved, in the act of increasing
the aperture, in the same direction as that in which the shutter disc revolves.
Accori ing to this arrangement the narrowest available slit is situated
immediately adjoining the lens aperture, but at a distance of one hundred and
eighty degrees therefrom. In other words, all that portion of the aperture zone
which is obscured by the auxiliary stop has to be passed across the lens before any
light is admitted. Thus the largest possible aperture is passed across the lens at
the slowest average speed, whilst the narrowest aperture is passed across the lens
at the most rapid speed. By this method of constructing the obscuring plate that
acceleration in the motion of the shutter disc which has hitherto been a drawback
is rendered actually advantageous.
As no
The change in the operation of the obscuring plate involved in our present
invention naturally leads to certain alterations in the details of the shutter.
time exposure is possible without the introduction of an entirely independent
detent, the secondary or retaining click, with its lifting apparatus, described in the
before mentioned Specification No. 20852 of 1890, is omitted. It has, furthermore,
been found economical and otherwise advantageous to replace the screw cap
attachment which was at first employed for the purpose of holding the obscuring
plate against the shutter disc by a light spring clip of thin metal affixed to and

page_text: revolving with the shutter disc, and capable of exercising sufficient pressure upon
the two plates to prevent their relative position from being unintentionally
altered.
Dated this 27th day of May 1892
CONRAD BECK.
JOSEPH THACHER CLARKE.
COMPLETE SPECIFICATION.
Improvements in Photographic Camera Shutters.
We, CONRAD BECK, Optician, of 68 Cornhill, London, Middlesex, and JOSEPH
THACHER CLARKE, Architect, of Boston, Massachusetts, at present residing at
3 College Road, Harrow, Middlesex, do hereby declare the nature of this invention
and in what manner the same is to be performed, to be particularly described and
ascertained in and by the following statement:—
Our invention relates to photographic shutters of the type described in Clarke's
Specification No. 20852 of 1890, in which the rotary plate or shutter is provided
with a single concentric exposure aperture, the effective size of which can be
increased or diminished by a secondary or auxiliary semicircular fan or stop
adjustable upon the face of the main shutter plate in such wise as to obscure a
greater or less portion of the aperture thereof. With an auxiliary stop of this
kind the exposure aperture in the shutter disc may be varied from the narrowest
radial slit to a concentric zone extending to a length of 180°.
In shutters of this type the exposure aperture, whether narrow or wide, has
hitherto been so arranged as to pass immediately in front of the lens on the shutter
being set in action: the auxiliary stop, i.e. the obscuring device attached to the
main shutter plate, being moved, in the act of increasing the aperture, in a
direction contrary to that in which the shutter disc revolves while making an
exposure.
It has been found in practice that this arrangement does not give the greatest
obtainable latitude of exposure, inasmuch as the shutter disc, when released,
revolves with a gradually accelerating motion. Thus the narrowest available slit,
being immediately adjacent to the lens aperture, was hitherto passed in front of
the lens at a slower speed than was any portion of the zone situated at greater
distance from the lens. It is evident that the result of this acceleration has been
to decrease the variability and range of the actual photographic exposure, which
was thus not directly proportionate to the aperture displayed in the shutter disc by
pushing aside the auxiliary stop from the zone.
Our present invention not only obviates this disadvantage, but profits by that
very acceleration in the rate of travel which has been observed in the movement
of the circular shutter disc. We obtain this advantage by so constructing the
auxiliary semicircular obscuring stop that it is moved, in the act of increasing the
aperture, in the same direction as that in which the shutter disc revolves.
According to this arrangement the narrowest available slit is situated, not imme-
diately adjoining the lens aperture, but at a distance of 180° therefrom. In other
words, all that portion of the aperture zone which is obscured by the auxiliary
stop has to be passed across the lens before any light is admitted thereto. Thus
the largest possible aperture is passed across the lens at the slowest average speed,
while the narrowest aperture is passed across the lens at the most rapid speed. By
this method of constructing the obscuring plate that acceleration in the motion of
the shutter disc which has hitherto been a drawback, is rendered actually
advantageous.
In order that our invention may be fully and clearly understood, we will now
particularly describe, with reference to the appended drawings, our improved
shutter plate and obscuring stop, as carried into practical execution.
Figure 1 is a view of a shutter constructed according to our invention, the front

page_text: of the case to which it is attached being omitted for the purpose of displaying the
entire surface of the disc.
Figure 2 is a section of the same shutter on the broken line z, Fig. 1.
In these two illustrations the shutter is represented as working in front of the
lens, the obscuring stop being adjustable through the lens aperture in the front of
the case.
The shutter mechanism is supported upon the shutter board or compartment 1,
which is perforated to receive the lens mount 2 and the casing for the shutter
spring 3. The shutter spring itself may be of either of the forms described in
the before mentioned Letters Patent No. 20852 of 1890, or of any of the various
patterns of such impelling devices as are suitable for a circular shutter revolving in
one direction only which are in every day usage and familiar to those skilled in
the art. We wish it to be understood that this shutter spring, together with the
method of winding or setting it, forms no part of our present invention. In the
appended drawings its details are not shown. If it be desired to wind the shutter
spring by means of a knob or button projecting from the front of the case, the
spindle to which such knob or button is attached may extend through the circular
apertures 4 and 5 which are pierced for this purpose in the shutter plates and in
the front casing of the camera.
The rotary shutter plate 6, which may be directly connected with the impelling
spring, is formed of a disc of thin sheet metal, and is centered or mounted within
the end of the spring casing 3. In this shutter plate 6 is pierced a single
exposure aperture 7, extending throughout a concentric zone of 180°. The width
of this zone, in a radial direction, is somewhat greater than the clear aperture of
the lens mount 2.
In order to vary the effective size of the aperture 7 in the shutter plate 6 a
secondary or auxiliary solid stop or fan 8 is attached to the face of the shutter
plate in such wise as to cover more or less of the exposure aperture 7. This
attachment is carried into effect by fitting the obscuring stop 8 over the concentric
ring or boss 9 of the shutter plate 6, and by screwing or otherwise firmly
attaching to said ring or boss 9 a spring catch or clip 10 which presses upon the
face of the obscuring stop 8 and holds this so closely in contact with the shutter
plate 6 as to prevent these pieces from being unintentionally shifted in their
relative position. In order to still further decrease the possibility of the obscuring
stop 8 being shifted upon the face of the shutter plate 6, the spring clip 10 is
provided with a pin 11 which enters into the apertures 12, 12, concentrically pierced
in the obscuring stop 8 at such distances as may be calculated to correspond with
exposures of definite ratio. The actual duration of the exposure which will be
effected when the spring clip 10 is engaged at any particular point is designated by
numerals which are concentrically engraved or otherwise marked upon the surface
of the obscuring stop 8. One of these numerals will, when the pin 11 is engaged in one
of the apertures 12, 12, be visible through the circular inspection hole 13 which is
pierced in the spring clip 10.
When it is desired to alter the duration of the exposure the position of the
obscuring stop 8 upou the face of the shutter plate 6 may be altered by pressure of
the finger upon the protuberances or bosses 14, 14, which are stamped up from the
body of the metal for the purpose of providing a convenient hold. The shutter
plate 6 is prevented from moving backwards during this operation by the check
spring 15.
In accordance with the leading principle of our invention, as has been above set
forth, the obscuring stop 8 will be moved, in the act of increasing the aperture,
in the same direction as that in which the shutter disc revolves while making an
exposure: namely in the direction of the arrow A drawn in broken lines in Fig. 1.
On the other hand the effective exposure aperture will be decreased by moving the
obscuring stop 8 in the contrary direction.
This direction of movement of the obscuring plate involves, as compared with
that illustrated and described in the beforementioned Letters Patent No. 20,852

page_text: of 1890, certain alterations in the details of the shutter set-off. A simple and
suitable form of set-off may be provided by the bar 16, sliding on the slots 17, from
which project. two pins 18 and 19, which engage alternately with a lobe or catch 20
projecting from the edge of the shutter plate 6. When the shutter plate 6 is in
its normal position, ready for an exposure, the upper pin 18 will be in engagement
with the lobe 20. On the set-off bar 17 being pushed up by means of a suitable
bolt 21, the lobe 20 will be released from its engagement with the upper pin 18,
and the shutter will revolve until the lobe 20 comes into engagement with the
lower pin 19, which will thus prevent the shutter from being carried further
around by its impetus than is necessary for one complete exposure.
When pressure
is applied by the finger to the set-off bolt 21 the sliding bar 16 is prevented by
the stop pin 22 from rising so far that the lower pin 19 is brought into contact
with the periphery of the shutter plate 6, friction upon which might stop or slow
down the rotation of the shutter. When the pressure is removed from the bolt 21
the bar 16 is returned to its normal position by the spring 23, and the shutter
completes its entire revolution, resuming its normal position with the lobe 20 in
engagement with the upper pin 18.
If it be desired to cause the shutter plate and the obscuring stop to work between
the combinations of the lens the arrangement of parts may be modified as shown
in the alternative section. illustrated in Figure 3.
The main points of difference between this section and that shown in the
preceding figure are those connected with the mechanism for adjusting the length
of the exposure which, of course, cannot be effected, in the case of a shutter
"working between the lenses, by the direct pressure of the fingers upon the face of
the obscuring stop. The attachment of the obscuring stop 24 to the shutter
plate 25 is provided by means of the spring clip 26, which is reduced in extent,
but which is in construction identical with that of the spring clip 10, Fig. 2. The
obscuring, stop 24 is, in this modification, itself provided with one or more projecting
pins or knobs, such as 27, which enter into a series of corresponding concentric
apertures or depressions, such as 28, stamped into the body of the shutter plate 25,
thus holding the two plates 24 and 25 so firmly together under the pressure of the
spring clip 26, that they are not liable to be unintentionally shifted in relative
position. The adjustment of the obscuring stop 24 may be effected from the
outside of the case by means of the connecting tube 29 which is rigidly attached
to the face of the obscuring stop 24, at a zone so far outside the spring clip 26
as not to interfere therewith during the process of adjusting the speed of the
shutter. This connecting tube 29 is provided, upon the outside of the case, with
a milled flange 30 which may be conveniently grasped by the fingers. By turning
this flange 30, the obscuring stop 24 can be shifted upon the face of the shutter
plate 25, and the effective exposure aperture be thus varied. A ring shaped
plate 31 is attached to the front of the casing 32, and is engraved with numerals
which, when the shutter is set, designate by their relation to an arrow engraved
upon the flange 30 the speed at which the shutter will work.
The remaining features of the alternative arrangement shown in the section
Fig. 3 are identical with those shown in the section Fig. 2 and the elevation
Fig. 1.
Experience has shown that, when constructed according to the principle of
our invention, the scope, or in other words the variability, of shutters of this type
is approximately doubled. If the width, in a concentric direction, of the smallest
available aperture be one-ninth of the width of the largest available aperture, and
the shutter were to perform its revolution at an absolutely uniform speed, it is
obvious that the duration of the longest exposure should be nine times that of the
shortest exposure.
In point of fact, however, it has been determined by experiment
that the gradually accelerating speed with which the shutter plate revolves
materially affects these proportions. Thus in shutters of this type which have
been in use prior to our invention the actual variation in the duration of the
exposures, under the above conditions, is found to be about one to six instead of

page_text: one to nine; while with shutter plates adjusted according to our invention, the
variation is found to be about one to twelve, instead of one to nine. These propor-
tions will depend somewhat upon the relative strength of the impelling spring
employed, but under all conditions an appreciable gain in respect to scope will be
obtained by the employment of an obscuring stop adjusted according to our
improved method.
Having now particularly described and ascertained the nature of our said inven-
tion, and in what manner the same is to be performed, we declare that what we
claim is :
1. In a photographic shutter of the type described the combination with a
shutter plate, such as 6 or 25, of an obscuring stop, such as 8 or 24, so adjustable
upon the face of the shutter plate that the effective aperture may be increased by
moving the obscuring stop in the direction traversed by the shutter plate while
making an exposure, and decreased by moving the obscuring stop in a direction
contrary to that traversed by the shutter plate while making an exposure, substan-
tially as and for the purposes hereinbefore set forth.
2. In a photographic shutter of the type described the combination with a
shutter plate, and an obscuring stop adjustable thereupon, of a spring clip, such
as 10 or 26, bearing upon and retaining the obscuring stop in such wise as to
prevent this stop from being unintentionally shifted from its position in relation to
the shutter plate, substantially as hereinbefore illustrated and described.
Dated this 24th day of February 1893.
CONRAD BECK.
JOSEPH THACHER CLARKE.