Improvements in Photographic Shutters and in the Method of Operating the same.
Year: 1896

page_text: Date of Application, 20th Feb., 1896-Accepted, 21st Mar., 1896
COMPLETE STECIFICATION.
Improvements in Photographic Shutters and in the Method of
Operating the same.
A. communication from abroad by NICOLAI HANSEN, of 6 Boulevard de Strasbourg,
Paris, France.
I, GEORGE CLEMENT DOWNING of 8 Quality Court, London W.C. Patent
Agent, do hereby declare the nature of my said 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 that class of photographic shutters in which thin plates
are arranged to slide in front of the object glass or lens, in order to govern the
period of exposure, the object of my invention being to vary such exposure to any
extent, as required by springs or variable tensions.
And in order that my said invention may be particularly described and
ascertained, reference is hereby made to the accompanying drawing, illustrating
one method of carrying out my invention, it being well understood that the shutter
illustrated is only one example of the various kinds of photographic shutters to
which the invention may be applied. The invention is applicable to the whole
class of such shutters in which plates are arranged to slide successively in front of
the object glass or lens.
In the drawing the shutter case is shown fitted with two rectilinear shutters A
and B sliding in the guides gg. The plate A is longer than, and is placed in front
of, the plate B. The plate A has an aperture h corresponding with the full aperture
of the lens. C is a spring, one end of which is attached to the plate A, and the
other end is carried round a drum E. D is another spring, one end of which is
attached to a raised flange m forming part of the plate B and the other end to the
drum F. k is an ordinary trigger which retains the plate A in the position shown,
the plate B being held back by the contact of the plate A with the flange m.
Any suitable device may be used for "setting" the plates or shutters, such as a
spring controlled rod and catch as shown.
The spring C is of a greater tensile strength than the spring D, the difference of
tension being regulated by means of the drums E and F. the duration of the
exposure being regulated by such difference.
On letting go the trigger the plate A is carried towards the disc E, the aperture
in the plate A then coinciding with the aperture in the camera. This motion of
the plate A is immediately followed by the plate B usually at a somewhat slower
rate of speed. The passage of the solid plate B, between the plate A and the lens
of the camera closes the aperture.
It will be understood that the duration of the exposure depends upon the relative
strength of the springs C and D, which can be regulated by winding or unwinding
the springs upon or around the drums C and F.
If preferred one drum only may be used instead of two, the difference of tension
being regulated by adjusting one spring only. Also the springs may be regulated
by screws, or other ordinary appliances instead of by the drums E and F.
It will thus be seen that if the springs be of equal tension the two plates A and B
would slide together at the same speed and consequently the aperture would not
be uncovered; and that the greater the difference between the tensions of the

page_text: springs (the spring D being usually less in tension than the spring C) the longer is
the aperture uncovered and the lens exposed to the rays of light.
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 what I
-claim is :-
1. In a photographic shutter, the application and use of two springs of different
tensions so arranged relatively to the plates or shutters as to cause variable
exposure according to the respective tensions of the springs, substantially as
.described.
2. In a photographic shutter, the combination of two shutters each fitted with a
separate spring, capable of being regulated in tension, so as to cause the shutters
to travel at variable speeds, substantially as and for the purposes hereinbefore
described.
Dated 20th Th
1000
GEORGE C. DOWNING.