An Improved Method of Actuating Photographic Shutters.
Year: 1890

page_text: Date of Application, 7th May. 1890
Complete Specification Left. 5th Feb., 1891-Accepted. 21st Mar., 1891
PROVISIONAL SPECIFICATION.
An Improved Method of Actuating Photographic Shutters.
I, WILLIAM GAGE TWEEDY, of No. 8, Athenæum Terrace, Plymouth, in the
County of Devon, Tutor, do hereby declare the nature of this invention to be as
follows:-
The sliding part of a photographie drop-shutter, held in position by friction has
a cord of a suitable length attached to its lower edge. At the other end of the
cord is a small weight. The weight is lifted in the hand and dropped. The fall
causes the string to snatch down the shutter, thus uncovering the lens opening
more quickly than if the shutter merely dropped from rest with its own weight.
The upper part of the shutter similarly covers the opening more quickly. Hence
for a given total duration of exposure, a longer opening, or space between the upper
and lower parts of the shutter may be used and a smaller proportion of the whole
time is lost in uncovering and covering the lens opening, thus increasing the
efficiency of the exposure.
AL.... 1200
WILLIAM GAGE TWEEDY.
COMPLETE SPECIFICATION.
An Improved Method of Actuating Photographic Shutters,
1, WILLIAM GAGE TWEEDY. of No. 8, Athenæum Terrace, Plymouth, in the
County of Devon, Tutor, 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 :-
The common photographic drop-shutter consists of a flat slide (hereinafter called
"the screen") running in vertical grooves or guides on a base-board, and having
an aperture about its centre. This is arranged in connection with the lens of a
camera so that when the screen is raised to the top of its run, light is prevented
from passing through the lens, the screen being held in this position by a catch.
On releasing the catch the screen falls from rest, and light passes through the
lens during the time the aperture is falling across the lens, and is again shut off by
the upper part of the screen. The screen is prevented from falling too far by a
stop.
My improvement consists first in substituting for the catch a friction-spring just
strong enough to support the weight of the screen, and actuating the screen by the
impact of a falling weight (hereinafter called "the bob ") attached to it by a cord
(hereinafter called "the tape").
By allowing the bob to fall a definite distance, the screen is caused to start with
a definite velocity (as is shewn in treatises on physics), and by means of graduations
on the tape the length of the drop can be regulated so as to cause the aperture in
the screen to pass over the centre of the lens in a definite time (hereinafter called
"the exposure") varying from long to short according as the drop is short or long.
These times are marked against the corresponding graduations on the tape
which is shortened or lengthened by winding it in or out of a metal case forming
the bob.
These munduations are found by calculation from the formula

page_text: If then we put 1 sec. on the tape at such spot as will allow the hob to
fall 1947 feet before it snatches down the lower sereen (so uncovering the lens) and
allow the lower screen to fall 1-053 feet before it snatches down the upper screen,
we shall give 1 second exposure.
In this construction, one end of the tape is fixed to the upper screen, and there is
a clip on the lower screen by which it can be attached to the tape at any point, the
whole length of the tape being constant, and the bob attached to its lower end.
The tape is graduated by means of calculations from the formula (ƒ) in the manner
just described.
In all cases the instrument is to be operated by holding the bob against some
fixed point from which it can fall the required distance before it brings the tape
tant, and thus by impact through the tape snatches down the screen from the hold of
the friction spring. The upper screen (in the case when the screen consists of two
parts) is similarly snatched from the hold of its own friction-spring and is prevented
from falling too far by a suitable stop or stops.
In the drawing, which shows this last form of instrument, the letters U and L
denote the upper and lower screens running freely in guides RR, R, on the top
and sides of the baseboard B, in which is the hole A by which the instrument is
fitted on the hood of the lens of the camera.
The lower edge of U rests on the upper edge of L in the same plane, and the
chinck between them is covered by the clamp C, which projects at the ends
over R, R, and serves by coming against the stops S, S, to prevent U from falling
out of the guides when snatched down after the exposure. Under C, but on the
outer face of U is fixed at E the upper end of the tape T which passes down
through the clip D and the cleat F.
At the lower edge of L and at the back is a small clamp C, which serves to
strengthen L and also to hinder light from filing its way up between Land B.
Under C, is the lower friction-spring (, which retains L in place before the
exposure. Similarly U is kept supported by its spring G
K is the bob in the form of the common spring-tape measure case, which
contains T.
In use, the instrument is fixed on the hood of the lens, the whole of T is drawn
out of K, and L is slid along T till the arrow points to the exposure required, (it
is shown at 100 or 1th of a second). H is then turned so as to tighten D on T,
L is pushed up between R, R₁ till it is held by G₁, and K is held with M
against Sa
On letting K fall. it snatches down L and after 1 second U is also snatched down,
thus completing the exposure.
Fig. 1. is the front elevation.
Fig. 2. a vertical section on the line d-d.
Fig. 3. is the side elevation.
Fig. 4. is a horizontal section on a―a.
Fig. 5. is a portion of the upper corner to show Ga.
Fig. 6. is a horizontal section on b—.
Fig. 7. is a horizontal section on c―c.
Fig. 8. is elevation of tape holder from front.
Fig. 9. is elevation of tape holder from side.
The same letters refer to the same parts in all the figures.
Having now particularly described and ascertained the nature of my said
invention, and in what manner the same is to be performed, I declare that what
I claim is
(1) A photographic drop-shutter with a fixed aperture in its screen, actuated by
the impact through a graduated tape of a bob falling a variable distance: Said
screen being held in place before exposure by a friction spring.
(2) A photographic drop-shutter with a variable graduated aperture in its screen

page_text: actuated by the impact through a tape, of a bob falling a fixed distance: Said
screen being held in place before exposure by a friction spring.
(3) A photographic drop-shutter having two screen connected together vertically
by one or more flexible cords or tapes of fixed length; the lower screen actuated by
impact through a graduated tape, of a hob falling a variable distance: Said
sereens being held in place before exposure each by its own friction spring.
the
(4) A photographic drop-shutter having two-creens connected together vertically
by one or more flexible graduated tapes of variable length: the lower screen
nctuated by the impact through a tape, of a bob falling a fixed distance: Said
screens being held in place before exposure cach by its own friction >pring.
(5) A photographic drop-shutter having two sereeus connected together vertically
and to a bob, by one and the same graduated tape of fixed length: the lower screen
being clipped or made fast to the tape at varialde points and actuated by the impact
through the lower part of the tape, of the hol talling a variable distance. The
upper serven in turn is netuated by the impact, through the upper part of the tape,
of the lower screen filling the distance allowed by said upper part or remainder of
the tape: Said sereens being held in place before exposure each by its own friction
>pring.
Dated this 4th day of February 1801.
WILLIAM GAGE TWEEDY.