IMPROVEMENTS IN APPARATUS FOR CONTROLLING THE EXPOSURE IN PHOTOGRAPHIC OPERATIONS
Year: 1880

page_text: LETTERS PATENT to John Chadwick and William Isaac Chadwick, both of
Manchester, in the County of Lancaster, Engineers, for an Invention of
"IMPROVEMENTS IN APPARATUS FOR CONTROLLING THE EXPOSURE IN
PHOTOGRAPHIC OPERATIONS."
PROVISIONAL SPECIFICATION left by the said John Chadwick and William
Isaac Chadwick at the Office of the Commissioners of Patents on the 11th
March 1880.
JOHN CHADWICK and WILLIAM ISAAC CHADWICK, both of Manchester, in the
County of Lancaster, Engineers. "IMPROVEMENTS IN APPARATUS FOR CONTROLLING
THE EXPOSURE IN PHOTOGRAPHIC OPERATIONS."
Our Invention relates to photographic apparatus employed in the obtaining of
so called "instantaneous" photographs, and consist in an improved method of
exposing and covering the lens aperture of the camera with sufficient rapidity, and
also of regulating the duration of exposure. The apparatus consists of a disc or
frame fixed or mounted in front of the lens, the said disc or frame having an
aperture opposite to the lens. A shutter consisting of two segments of a circle or
otherwise suitably shaped is centred on the disc, so as to revolve in front of and at
times obscure the said opening, two spring stops or catches being arranged at
different parts of the periphery of the shutter to catch and retain it in position
when covering the lens aperture. An adjustable spring is employed to shoot the
shutter round upon its centre when in operation. This-latter-spring-is-bent-or-
compressed against a pin or abutment on a disc, which can be adjusted so as to
increase the tension of the spring and consequently the rapidity of the movement
of the shutter, or the abutment may be otherwise arranged to be adjustable. In
order to release the spring catch, which retains the shutter with its blind part in
front of the lens, I prefer to employ hydraulic pressure as the incompressibility of
water renders it a more efficient agent for instantaneously transmitting. pressure
from a distance than air.
I connect the instrument by means of a tube with an india rubber ball or other
collapsible reservoir, or with a cylinder or chamber fitted with a piston or diaphragm

page_text: under the controlof the operator. By compressing this ball or reservoir or acting
upon the said piston or diaphragm the liquid pressure acts upon a diaphragm or
piston at the end of the connecting tube, and moves the spring catch clear of the
stop on the shutter, which is then impelled by the hereinbefore referred to spring
round upon its centre until the lens opening is again obscured, when the shutter is
caught and retained by the second spring catch, the blank space between the shutter
segments having meanwhile allowed the lens to become momentarily exposed to the
daylight.
I provide the moving shutter with a spring clip to hold paper or card cut to a
suitable form when it is advisable to give one part of the plate less exposure than
another, or I otherwise adapt suitable additions to the shutter with the same
object. The herein before referred to apparatus may be applied to cameras having
a double lens, as, for example, in instruments employed in obtaining stereoscopic
photographs.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said John Chadwick and William Isaac Chadwick in the Great Seal
Patent Office on the 11th September 1880.
"
JOHN CHADWICK and WILLIAM ISAAC CHADWICK, both of Manchester, in the
County of Lancaster, Engineers. IMPROVEMENTS IN APPARATUS FOR CONTROLLING
THE EXPOSURE IN PHOTOGRAPHIC OPERATIONS."
Our Invention relates to apparatus employed in obtaining so called "instan-
taneous" photographs, and consists in improved means of controlling and regulating
the duration of the exposure. The apparatus consists of a rotary shutter centred
on a fixed disc so as to revolve in front of the lens aperture. The shutter is a
plate composed of two sector shaped portions, which balance each other on the
centre and alternately obscure the lens aperture, the exposure taking place during
the intervening interval. The shutter is rotated by the impulse of a spring, which
is bent or compressed against an abutment made adjustable to enable the tension
of the spring and consequently the rapidity of the movement of the shutter to be
regulated to lengthen or shorten the exposure at will. The fixed disc on which
the shutter rotates has an opening fitting on or in the lens tube, and is provided
with two spring catches, one of which retains the shutter when set for use, and the
other prevents it rebounding after the exposure. The first catch is acted on to
release the shutter and effect the exposure by a diaphragm on the end of a tube, to
which is attached an indiarubber bulb or its equivalent within reach of the
operator, the bulb and tube being preferably filled with water. The shutter when
thus released from the catch is impelled round upon its centre, thereby momentarily
uncovering and again obscuring the lens aperture, the shutter being then caught
and retained by the second catch. A stop is provided to hold the shutter in a
position to leave the lens uncovered whilst focussing.
The herein before referred to apparatus may be applied to cameras having a
double lens, as, for example, in instruments employed in obtaining stereoscopic
photographs.
In the accompanying Drawings Figure 1 is a front elevation of the apparatus
with the shutter in the position for focussing the picture; Figure 2 is a front
elevation, and Figure 3 a vertical section, the shutter being "set" before exposure;
Figure 4 is a front elevation after exposure; Figure 5 is a rear elevation of the
apparatus.
A is the fixed disc upon which the shutter rotates. It has a peripheral flange a
to protect the shutter, and an opening A' surrounded at back by a flange that
screws either into the end of the lens tube, or into a split tube fitting onto the lens
tube; B is the shutter consisting of a plate in the form of two sectors b, b¹,
symmetrically placed with regard to the centre 6, upon which the shutter rotates;
C is a spring fixed in a clip c upon the part b of the shutter, and D) is the stop
against which the spring abuts, as shown in Figures 2 and 3. The stop D consists
of a screw stud secured by a binding nut in a slotted plate d fixed on the flange a
of the disc A, so that by moving the stop D along the slot the spring C will be
bent more or less against it. The spring catch for retaining the shutter in the "set"
position, shown in Figures 2 and 3, consists of a lever E pivotted at e, and provided
with a nib e¹ that engages with a stud e³ on the shutter, it being pressed inwards
by a spring e³ at the tail end.
F is a stop against which the part b of the shutter strikes when it arrives in front
of the lens (the part b' passing clear of the stop), and G is the spring catch to
O prevent any recoil of the shutter. The catch ( is fixed on the flange a, and its
nib g passes through a slot in the flange and engages with a stud g' on the shutter
immediately the latter arrives at the position shown in Figure 4; H is a small
bolt sliding in a slotted plate h fixed to the disc A, and engaging in a grooved

page_text: stud h on the shutter to hold the latter in the position shown in Figure 1;
I, I, are spring clips on the shutter to hold a paper or other mask, cut to a suitable
form when desired to give one part of the plate less exposure than another; K is
the diaphragm tied over the mouth of a tubular piece, to which is attached a
flexible tube provided with an indiarubber bulb. The diaphragm K is in contact
with the tail end of lever E, and when inflated oscillates it so as to withdraw
catch e¹ clear of the stud e², as shown in dotted lines, Figure 2.
Having described the nature of the said Invention and the manner of performing
the same, we declare that what we claim as the Invention to be protected by the
_hereinbefore in part recited Letters Patent is,-
1st. A shutter for covering and uncovering the lens of a photographic camera
mounted to rotate on a centre in front of the lens, substantially as shown and
described.
2nd. A rotary shutter for covering and uncovering the lens of a photographic
camera consisting of two sector shaped portions, which balance one another on the
centre and alternately cover the lens, substantially as shown and described.
3rd. The combination of the rotary photographic shutter, the spring for
impelling the shutter, and the adjustable abutment for the said spring, substantially
as and for the purpose shown and described.
4th. The combination with the rotary photographic shutter B of the spring C,
its abutment D, and of the spring catch E for retaining the shutter, substantially
as shown and described.
5th. The combination with the rotary spring impelled photographic shutter,
and the stop F of the spring catch G for preventing recoil of the shutter,
substantially as shown and described.
In witness whereof, we, the said John Chadwick and William Isaac Chadwick,
have hereunto set our hands and seals, this Ninth day of July, in the
year of our Lord One thousand eight hundred and eighty.
JOHN CHADWICK.
(L.S.)
WILLIAM ISAAC CHADWICK. (L.S.)