Improvements in or relating to the Regulation of Photographic Shutters.
Year: 1892

page_text: Date of Application, 1st Nov., 1892
Complete Specification Left, 4th Jan., 1893-Accepted, 4th Feb., 1893
PROVISIONAL SPECIFICATION.
Improvements in or relating to the Regulation of Photographic
Shutters.
I, 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:-
:-
My invention relates to photographic shutters of that class in which the duration
of the exposure is governed by a pneumatic piston and cylinder, acting as a brake
of variable effect.
Hitherto the differentiation in the action of such pneumatic brakes has been
attained in two ways: either by varying, by means of a tap or of a movable cap
valve, the orifice through which the compressed air is permitted to escape from the
cylinder; or by so shifting the position of the piston arm in relation to the
working parts of the shutter that the leverage exercised by the shutter spring upon
the piston is changed, and the length of the piston travel is thereby altered.
My invention has for its purpose to provide an improved pneumatic shutter in
which the requisite differentiation of the brake is effected in a third and novel
manner. While dispensing with the valve for regulating the outflow of air from
the cylinder, and while leaving the leverage between the shutter spring and the
piston unchanged, and the length of play of the piston unaltered,
obtain the
variable speeds of my pneumatic brake by sliding the air-compressing chamber or
cylinder to and fro along the axis of the piston rod in such wise that the piston is
caused to plunge to a greater or less depth into the cylinder, the retarding effect
of which is thus restricted to a longer or shorter part of the travel of the piston.
In this movement of the air-compressing chamber, relative to a piston of fixed
travel, lies the gist of my invention.
The movable air-compressing chamber, or sliding cylinder, being provided with
no variable outlet, is preferably made to fit the piston somewhat loosely, so that
the air compressed therein by the movement of the piston may gradually escape
between its inner walls and the sides of the piston. In the event of the leakage
thus provided between the piston and the cylinder being found insufficient, a
further outlet may be provided by piercing one or more small apertures in the
walls of the cylinder. These apertures may be so arranged as to gradually cut off
the outflow, and consequently to increase the resistance of the air remaining in the
cylinder, as the piston passes them on its travel.
The air compressing chamber may be constructed as a plain cylinder closed at
its base, like a stopped organ pipe, so arranged as to slide along the line of play of
the piston, permitting this to move, at the one extreme, both forwards and back-
wards without entering it, and thus without compressing the air within it, or, at
the other extreme, to traverse its entire course within the closed cylinder, under
oneumatic restraint. Or, while arranged to slide in the manner indicated, the
ir-compressing chamber may be made with a slightly conical bore, so as to
gradually alter the amount of air leakage between its walls and the sides of the
iston as this latter is caused to penetrate more or less deeply within it. Such a
lightly conical bore will render the pneumatic retardation more
or less

page_text: appreciable, according as the piston travels along a more or less constricted portion
of the bore.
In either case it is preferred (although the principle of the invention is in
no wise dependent hereupon) to make the air-compressing chamber greater in
length than the travel of the piston, cutting out longitudinal slots or otherwise
perforating all that portion of the tube through which the piston travels when
the cylinder is so withdrawn as to exercise the least possible restraining effect.
Through these slots or perforations the air, displaced by the movement of the
piston, finds free escape, and hence exercises no retarding influence. The rails
formed by the strips remaining between the slots may serve as guides for the
piston during that portion of its travel in which it does not enter the unperforated
portion of the air-compressing chamber.
The piston may be connected with, and receive its motion from, any portion of
the shutter worked by the shutter spring. Thus, if the shutter plate be of that
type which performs an entire revolution for each exposure, the piston may work
upon a cam or excentric, the position of which in relation to the centre of revolu-
tion will determine the play, forwards and backwards, of the piston. If, on the
other hand, the shutter be of a type moving to and fro across the lens aperture, the
piston may be advantageously made to work in a slot in the shutter plate, or be
connected therewith in any other convenient manner. The piston can, if preferred
be directly connected with the operating spring of the shutter plate, as is well
understood. In shutters of the type last mentioned the piston will be moved back-
wards, i.e. away from the air-compressing chamber, by the act of winding the
shutter spring, and will differentiate the length of the photographic exposure only
during its forward travel.
The adjustment of the air-compressing chamber, for the purpose of setting the
speed of the shutter, may be performed in any convenient manner: either by direct
action of the fingers upon the cylinder itself, or, as in the case of hand cameras with
closed fronts, by means of an intervening lever or other shifting device. A scale,
indicating the speed to which the shutter is set, may be engraved, or otherwise
marked, either in connection with the cylinder or with the moving lever.
It is obvious that the principle of my invention may be retained although the
relative positions of cylinder and piston be so reversed that the former is connected
with some moving portion of the shutter and the latter adjusted by sliding along
the line of travel.
One of the notable advantages of my improved pneumatic shutter is that, even
in protracted exposures, the lens aperture is opened (and in the case of shutters of
the before mentioned circular type is likewise closed) with the maximum rapidity
of the shutter. This is due to the fact that the piston is permitted to commence
(and in shutters of the circular type likewise to terminate) its movement without
restraint from the pneumatic brake, the retarding effect of which is not brought
into action until after the shutter has been passed aside from the lens aperture by
the unrestrained force of the shutter spring. The character of the photographic
exposure is hereby greatly improved.
Dated this First day of November 1892.
COMPLETE SPECIFICATION.
Improvements in or relating to the Regulation of Photographic
Shutters:
I, JOSEPH THACHER CLARKE, Architect, of Boston, Massachusetts, United
States of America, but 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:―
My invention relates to photographic shutters of that class in which the duration

page_text: of the exposure is governed by a pneumatic cylinder and piston, acting as a brake
of variable effect.
Hitherto the differentiation in the retarding action of such pneumatic brakes
has been brought about in two ways: either by varying, by means of a tap, or of a
cap valve, an orifice at the end of the cylinder through which the air is allowed to
escape with greater or less freedom; or by so shifting the position of the piston
arm in relation to the working parts of the shutter that the leverage exercised by
the shutter spring upon the piston is changed, and the length of the piston stroke
thereby altered.
In both of these methods the effective air-compressing and retarding action of
the brake must remain constant and invariable throughout its operation. The
result of this is that the movement of the piston, whether it be comparatively fast
or comparatively slow, will be uniform in speed, throughout its course. Thus the
restraining effect of these pneumatic brakes can not be utilized to differentiate
between the various portions of the travel of the shutter itself, and, in particular,
can not serve to prolong the period during which the lens aperture remains open,
without in like manner slowing down the opening and closing of the lens aperture
by the cover plate of the shutter.
My invention has for its purpose to provide an improved pneumatic shutter in
which the variable effect of the brake is obtained in a third and novel manner,
permitting a differentiation to be thereby introduced between the various portions
of the travel of the shutter itself.
While employing no tap or valve for opening more or less widely that orifice
through which the compressed air is allowed to escape from the cylinder,-and
while leaving the leverage between the shutter spring and the piston unchanged,
and the length of play of the piston unaltered,-I obtain the various speeds of my
brake by employing a loosely fitting or, as it is generally termed, a "leaky
piston, and by so altering the effective length of the air-compressing chamber that
this piston performs a longer or a shorter part of its stroke under pneumatic
restraint,-
,-a larger or smaller fraction of the movement of the shutter, during the
act of exposure, being thus subjected to the retarding influence exercised by the
column of enclosed air. The said variation in the effective length of the air-
compressing chamber I carry into practical execution by altering the position of
the cylinder (or, if the cylinder be not a complete air-compressing chamber in
itself, then by altering the position of that complementary adjunct which enables
it to act as such) relative to the travel of the piston. In this adjustment of the
air-compressing chamber, in such wise that the piston is caused to plunge to a
greater or less depth into the closed portion of the cylinder, lies the gist of my
invention.
By means of a pneumatic brake.constructed in accordance with my invention the
air-compressing chamber may be caused to exercise its retarding effect only during
that portion of the travel of the shutter plate which takes place while the lens is
entirely uncovered. Thus the lens aperture may, even in protracted exposures, be
opened and closed with the maximum rapidity of the shutter. The practical
advantages of photographic exposures made under these conditions will be explained
hereinafter.
In order that my invention may be clearly and fully understood, and that the
advantages attending its use may be made apparent, I will now particularly describe,
with reference to the appended drawings, various modes or manners in which it may
be carried into effect.
Figures & 2 are elevations and Figure 3 is a section on line Fig. 1 of a
shutter regulated in accordance with my invention. In pneumatic brakes of this
particular design the air-compressing chamber consists of a single piece; this, being
the simplest form, may be regarded as best adapted to exemplify and explain that
method of pneumatic regulation which constitutes my invention. Figures 1 & 3
show the shutter plate 1 at rest in its normal position, covering the lens aperture 2,
and show the air-compressing chamber 3 so adjusted as to exercise the least possible

page_text: restraining effect upon the piston 4, the brake thus being so set as to give the shortest
possible exposure. The shutter plate 1 revolves together with an axis 5, performing
for each exposure one entire revolution of 360° in the direction indicated by the
arrow a a, and receiving its motion from an impelling spring acting upon the
axis 5. This impelling spring, together with the detent and set-off of the shutter,
may be arranged according to any of the various methods well-known to those
skilled in the art. The piston 4 is connected by a link 6 with a pin 7, placed
excentrically upon the shutter plate 1: the amount of this excentricity being equal
to one half of the travel determined upon for the piston 4, namely the distance
between the dotted lines b & c. The link 6 is connected with the piston 4 by means
of a pin 8, and works freely at both ends. Thus the piston 4 is moved from 6 to c
and back again, towards and from the air-compressing chamber 9, by the revolution
of the shutter plate 1, the amount of this travel of the piston being, as before
explained, equal to the diameter of the circle of revolution d of the pin 7. In a
brake of this form the cylinder 3 may be considered to consist of two parts, cach
of which has a distinct function. The first of these is the air-compressing
chamber 9, which is terminated at one end by the closed base of the cylinder 10,
comparable to a stopped organ pipe, and is limited at the other end by the edge of
the aperture 11. The degree of pneumatic restraint to which the shutter is
subjected will depend upon the comparative length of that portion of the travel of
the piston which is performed within this air-compressing chamber. The secondary
portion of the cylinder 3 is formed by those strips or rails 12 which remain between
the apertures 11 & 13 and serve as guides for the support of the piston 4. The
cylinder 3 is held in position by upright bearers 14 which slide along a guide
rod 15. The adjustment of the cylinder upon this guide rod may be effected in
any convenient manner, as for instance by the direct pressure of the fingers upon
the bearers, or, if the shutter be enclosed in a hand camera, by any suitable form of
setting device, such as a screw or a lever, which may be operated by hand from the
outside of the camera case. When the cylinder 3 is adjusted in the position
in which it is represented in Fig. 1 the piston 4 will perform the whole of its
stroke from 6 to c without traversing any part of the enclosed air-compressing
chamber 9, and, in consequence, entirely free from pneumatic restraint.
air displaced by the piston will escape freely through the aperture 11, and the
brake will exercise no appreciable retarding effect upon the movement of the shutter
plate 1. When, however, the cylinder 3 is moved along towards the piston 4 in
the direction of the arrow e, Fig. 1, the stroke of the piston, being of fixed
length, will be performed in greater part within the air-compressing chamber 9,
and the degree of restraint thus exercised upon the piston 4 will determine the
retarding effect of the pneumatic brake.
The
In Figure 2 the same shutter and the same air-compressing chamber are repre-
sented in different positions, and in a different adjustment. The shutter plate 1 is
shown at that point which it will occupy when one half of its revolution has been
performed, the lens aperture 2 being thereby opened so as to allow light to gain
access to the sensitized surface within the camera. The cylinder 3 is shown as
adjusted in such wise that the greatest possible part of the stroke of the piston 4
will take place within the enclosed air-compressing chamber 9, or, in other words,
in that position in which the brake will exercise the greatest possible retarding
influence upon the movement of the shutter plate 1.
It is obvious that the principle of my invention may be retained although the
relative positions of the cylinder 3 and piston 4 be so reversed that the former is
connected with some moving part of the shutter, while the latter is adjusted by
sliding along the line of stroke.
When the available space is cramped, or when the facilities for adjustment render
it desirable to construct the movable parts of the regulating brake of the smallest
possible dimensions, the air-compressing chamber may be formed of two separate
parts, a guide or inner cylinder extending along the entire course traversed by the
piston, this guide or inner cylinder being rigidly fixed in one position, and being

page_text: provided with one or more apertures which, when not closed by a separate movable
occluding jacket) are sufficiently large to allow the unrestrained escape of the air
throughout the entire length traversed by the piston. In order to create, in a
brake of this form, an air-compressing chamber of variable length, the occluding
jacket must be so moved in relation to the fixed guide or inner cylinder that the
aperture or apertures in this latter are closed progressively or successively, com-
mencing with that which extends farthest from the piston end of the cylinder:
the length of the enclosed column of air being thus, in effect, lengthened or
shortened.
Figure 4 shows an air-compressing chamber and piston of this form. The
piston 16, travelling from the dotted line to the dotted line 9, plays within the
open guide or inner cylinder 17, which is closed at its base. The aperture 18 in
the side of this inner cylinder may be closed to a greater or less extent by moving
the cylindrical occluding jacket 19 in the direction of the arrow h, a portion of the
inner cylinder 17 being thereby transformed into an effective air-compressing
chamber, having the functions above explained.
The comparative length of the pneumatic brake may be still further decreased
by the adoption of the form shown in Figure 5, Figure 6 being a section thereof
on the dotted line y Fig. 5. The guide or inner cylinder 20, closed at its base, is
pierced along its side by four slots, 21, 22, 23, and 24, of different lengths. These
openings may be successively shut by moving the occluding jacket 25 in the
direction of the arrow k. The traverse of the piston takes place between the
dotted lines l and m. When the occluding jacket 25 is so pushed aside that all
four of the slots pierced in the inner cylinder are opened, the piston will perform,
its travel between 1 and m without being subjected to any pneumatic restraint.
When the slot 21, only, is closed by the jacket 25, that portion of the brake which
is comprised between the dotted lines m and n will alone constitute an effective air-
compressing chamber, and that part of the piston stroke which is performed
between these lines will alone be subjected to pneumatic restraint. Similarly, the
occlusion of the other slots 22, 23 and 24 will extend the length of the column of
enclosed air to the dotted lines o, p and q. Thus the movement of a shutter con-
trolled by a brake of this form will be limited to five definite degrees of speed. A.
limitation of this kind is occasionally desirable, in order that the length of photo-
graphic exposures may be restricted to predetermined fractions of a second, or
other units of time.
The same result may be obtained with an inner cylinder and occluding jacket
having the arrangement of parts shown in Figure 7. The apertures 26, 27, 28, 29
& 30 in the guide or inner cylinder 31, closed at its base, are pierced in a straight
line, and may be successively closed by moving, in the direction of the arrowr, the
occluding jacket 32, which is formed with a fore edge of spiral outline. Or the
same apertures 26, 27, 28, 29 & 30 in the inner cylinder 31 Fig. 7 may be closed
by an occluding jacket having a stepped fore edge, such as that shown in Figure 8.
Each one-sixth of a revolution of either of these occluding jackets, in the direction
of the arrows r and s respectively, will close the before mentioned apertures in
regular sequence, commencing at the base of the air-compressing chamber.
In all the forms of air-compressing chambers hitherto described the effective
action of the adjustment will be precisely the same, having as. its result the
variation of the length of the column of air which is traversed by a piston of fixed
stroke.
In all these forms, furthermore, the air-compressing chamber, preferably of
cylindrical section, is made to fit the piston somewhat loosely, so that the air
enclosed therein by the forward movement of the piston may escape between the
inner walls of the air-compressing chamber and the sides of the piston itself. Or,
if it be preferred, the air-compressing chamber may be made with a slightly conical
bore, so as to gradually alter the amount of leakage between its walls and the sides
of the piston, as this latter penetrates more or less deeply within it. Such a slightly
conical bore will render the pneumatic retardation more or less appreciable,

page_text: according as the piston travels along a more or less constricted portion of the air-
compressing chamber.
When the air-compressing chamber is formed of one single piece, as shown in
Figures 1, 2, & 3, additional outlets for the enclosed air may, if it be desired to
increase the leakage, be provided by piercing one or more small apertures in the
walls of the cylinder. These apertures may be so arranged along the sides of
the cylinder, in a line parallel to the travel of the piston, that the outflow of air
through them is cut off, and the resistance of the air remaining in the cylinder
consequently increased, as the piston passes them on its forward stroke. Such
apertures are, however, not essential, and form no part of my present invention."
In Figures 1, 2 & 3 I have shown my improved pneumatic brake as working in
connection with a shutter of circular type. It will, however, be obvious to those
skilled in the art that pneumatic brakes working on this principle may readily be
applied to shutters of any of the various forms which are now in usage. If, for
instance, the shutter be of a type moving to and fro across the lens aperture, the
piston may advantageously be connected with a slot in the shutter plate, or be
connected therewith in any other convenient manner. The piston may, if preferred,
be directly connected with the operating spring of the shutter plate, as is well
anderstood. In shutters of the type last mentioned the piston will be moved
backwards, i.e. away from the air-compressing chamber, by the act of winding the
shutter spring, and will differentiate the length of the photographic exposure only
during its forward travel.
A scale, indicating the speed to which the shutter is set, may be engraved or
otherwise marked, either in connection with the air-compressing chamber or in
connection with any device, such as a screw or a lever, which is introduced to adjust
the same..
In comparing the various forms of pneumatically controlled shutters which I
have described as embodying my invention, it will be observed that, even when the
restraining effect of the air-compressing chamber is increased to its maximum,
there still remains a certain fraction of the length of the piston travel (this part
of the travel occurring in brakes connected with shutters of the circular type both
at the beginning and at the end of the stroke) in which the piston moves outside
the limits of the air-compressing chamber, altogether without pneumatic restraint,
and consequently at its maximum speed. Owing to this fact the shutter plate
will always be moved away from (and in shutters of the circular type likewise
towards and across) the lens aperture at its maximum speed, thus covering and
uncovering the lens with the greatest rapidity of the shutter, and doing this even
though the brake be so adjusted that the entire exposure is protracted as much as
possible. This peculiarity of my method of shutter regulation, which in so far
as I am aware, has not been obtainable by any of the brakes hitherto known,—is of
noteworthy practical importance, inasmuch as the character of the photographic
exposure is thereby greatly improved. It is well known, and may be stated as an
axiom, that it is always desirable to permit the greatest possible quantity of light
to gain access to the lens during the shortest possible period of time. An illustration
of the improved action of my pneumatically regulated shutter in this regard will be
afforded by the following example. The movement of a body which is to be
photographed is, let it be assumed, sufficiently rapid to blur the image upon the
sensitive plate if the exposure be prolonged beyond some given period. In shutters
regulated by the brakes of uniform effect hitherto in usage, a considerable fraction
of this period will be occupied by the shutter plate, which moves at a uniform
rate of speed, in fully opening the lens, and the same fraction will be occupied in
the closing of the lens. In shutters of the circular type, such as that shown in
Figures 1 to 3, this fraction will amount to about one eighth of the total exposure;
in shutters of the "up and down" type this fraction may be as great as one third.
Thus the lens aperture will, during a total of at least one quarter of the entire
exposure, be more or less obscured by the shutter plate, and the light admitted
to the sensitive surface within the camera will be thereby proportionately diminished.

page_text: In a shutter regulated by my improved pneumatic brake, on the other hand, these
proportions will be incomparably more favorable. If, for instance, the maximum
rapidity of the shutter revolution be, say, one hundredth of a second, the time
during which the lens aperture will be more or less obscured by the shutter plate,
during the act of opening and closing, may be calculated, in accordance with the
above assumption, to be one four hundredth of a second. This small amount, as
before explained, will not be increased, even when the shutter is slowed down to
its maximum exposure, say one entire second or more. Thus the period of incomplete,
and consequently defective, exposure may be as small as one two hundredth part of
the total, or even less, in the place of one quarter of the total. The gain thus
effected may, of course, be, at the option of the photographer, applied either to
increase the quantity of light admitted to the sensitive surface, or to shorten the
total duration of the exposure, or, finally, if the quantity of light and duration
of exposure be left unaltered, to improve the definition by "stopping down" the
lens aperture by means of a diaphragin, as is well understood.
As I obtain the differentiation of my improved pneumatic shutter brake without
changing the leverage exercised by the impelling spring thereupon, or otherwise
altering the length of the stroke of the piston, and as I employ no valve, or, in
other words, as I dispense altogether with devices for varying the aperture through
which the compressed air can escape from the cylinder,--depending in this respect
solely upon the leak of a loosely fitting piston, it is obvious that the degree of
resistance which will be afforded by my pneumatic brake will depend directly and
entirely upon the length of that column of air enclosed in the cylinder which is com-
pressed by the stroke of the piston. In my brake the piston will perform a fraction
of its travel under pneumatic restraint, and the remainder altogether free therefrom;
the variability in its retarding effect depending upon the relative proportions of
these two fractions, as determined by the adjustment of the air-compressing chamber.
I believe myself to be the first to provide means for varying the length of a column
of air enclosed in an air-compressing chamber traversed by a piston of fixed stroke,
thereby affording a method of variable regulation which, when applied to a photo-
graphic shutter, causes this to move at a speed which is not uniform during the
course of each exposure.
Having now particularly described and ascertained the nature of my said inven-
tion, and in what manner the same is to be performed, I declare that I am
acquainted with the Specification of Newman No. 7156 of 1886; that I am
acquainted with the Specification of Bausch and Lomb No. 12442 of 1890; and
that I am acquainted with the Specification of Hill and Adams No. 12029 of 1892.
I desire it to be understood that I claim nothing which has been described in the
before mentioned Specifications. What I claim is:
1. In combination with a photographic shutter, a pneumatic regulating brake
consisting of a fixed air-compressing chamber with an occluding jacket adjustable
thereupon in such wise that the piston performs a longer or shorter part of its
stroke under pneumatic restraint, substantially as and for the purposes hereinbefore
Bet forth.
2. The several arrangements and combinations of parts constituting the pneumatic
regulating apparatus for photographic shutters consisting of a fixed air compressing
chamber with an occluding jacket adjustable thereupon as hereinbefore described
and illustrated in Figures 4, 5, 6, 7 and 8 of the accompanying drawings.
Dated this 4th day of January 1893.
JOSEPH THACHER CLARKE.