Improvements in connection with Photographic Dark Slides for Preventing a Second Exposure by Accident.
Year: 1889

page_text: Date of Application, 2nd Oct., 1889
Complete Specification Left, 28th June, 1890-Accepted, 2nd Aug., 1890
PROVISIONAL SPECIFICATION.
Improvements in connection with Photographic Dark Slides for
Preventing a Second Exposure by Accident.
I, GEORGE RENWICK, of 20, Station Street, Burton-on-Trent, Staffordshire,
Photographer, do hereby declare the nature of this invention to be as follows:-
:―
This invention consists of the herein described improvements in connection with
photographic dark slides by which the operator can tell whether the plate has been
exposed or not, and which will prevent the dark slide shutter being accidentally with-
drawn to expose the plate a second time.
For the purposes of my invention I provide a lever catch which is pivoted near one
end to a base plate fixed to the dark slide frame near the open end of the rabbet in
which the shutter fits. A suitable spring acts upon this lever catch and forces its
free end towards the shutter so that it will engage with a projection on the shutter
and thus lock the shutter in its closed position. This projection may be the end of
the tongue on the shutter which fits in the rabbet. Fixed to the shutter adjacent to
the free end of the lever-catch is a peg or hook and on the said lever catch, and pre-
ferably at or near the free end thereof, is a projection corresponding with the said pin
or. hook.
The parts above described operate as follows:-When an unexposed plate is in the
dark slide frame the operator, just before closing the shutter, pushes the lever-catch
sideways so that when the slide is pushed home the pin or hook on the shutter will
come into contact with the said projection on the lever and prevent the lever engaging
with the shutter, thus leaving the shutter free to be withdrawn to expose the plate.
On withdrawing the shutter to expose the plate, the said pin or hook on the shutter,
being withdrawn from the projection on the lever, allows the lever to spring against
the shutter so that when the plate has been exposed and the shutter again pushed home
the said projection on the lever will be free of the pin or hook on the shutter and the
lever-catch will engage with and lock the shutter. As the shutter cannot be with-
drawn without the operator first pushing the lever-catch sideways to unlock it from
the shutter, the operator knows that the plate has been exposed and its accidental
exposure a second time is thus prevented.
Dated this 27th day of September 1889
CHARLES BOSWORTH KETLEY,
Agent for the Applicant.
COMPLETE SPECIFICATION.
Improvements in connection with Photographic Dark Slides for
Preventing a Second Exposure by Accident.
I, GEORGE RENWICK, of 20, Station Street, Burton-on-Trent, Staffordshire,
Photographer, 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 :-
This invention consists of the herein described improvements in connection with
photographic dark slides by which the operator can tell whether the plate has been
exposed or not, and which will prevent the dark slide shutter being accidentally
withdrawn to expose the plate a second time.
On the accompanying drawing
my
Figs. 1, 2 and 3 represent the upper part of a double dark slide with invention
applied so as to illustrate the operation of my invention;
Fio 4 is a plan

page_text: Fig. 7 is a plan of the same open;
Fig. 8 is a perspective view of another part of the same as hereinafter described.
The same letters of reference indicate the same parts in all the Figures of the
drawing.
The dark slide frame is marked A and the dark slide shutters are marked respec-
tively B1, B2. Each of these shutters is represented as furnished with my invention
but in order to facilitate the description of the same I will refer to my invention as
applied to the shutter B' only.
C
For the purposes of my invention I provide a lever catch c which is pivoted at d to
a base plate e fixed to the dark slide frame A near the open end of the rabbet a in
which the shutter B fits. A spring facts upon this lever catch e and forces its end c¹-
towards the shutter B₁ so that when the shutter is closed it will be locked (see Fig. 3)
by the end engaging with a projection on the shutter B¹. This projection may be
and by preference is, as shown on the drawing, the end of the tongue on the shutter
which fits in the rabbet a¹. This end of the tongue is protected by a plate
which
is fixed to the shutter and is also formed as a peg or hook, which I call a release pin,
at g' so as to engage with a corresponding projection e² at the extreme end of the
lever catch c and hold the catch away from the shutter B before the plate has been
exposed. The other end of the lever c projects beyond the plate e for setting the
lever as hereinafter described.
The parts above described operate as follows:- When an unexposed plate is in the
dark slide frame A the operator, just before closing the shutter B corresponding with
the said plate, pushes the lever catch c sideways against the spring so that when the
slide B is pushed home the projection c² on the lever will come into contact with
the release pin g' on the shutter and prevent the part e¹ of the lever engaging with
the shutter (see Fig. 1) thus leaving the shutter B free to be withdrawn to expose
the plate. On withdrawing the shutter B₁ to expose the plate, the release pin yl
on the shutter, being thereby withdrawn from the projection c³ on the lever, allows
the lever c to spring against the shutter B (see Fig. 2) so that when the plate has
been exposed and the shutter B again pushed home (see Fig. 3) the projection on
the lever will be free of the release pin g¹ on the shutter and the part c' of the lever-
catch will spring over the plate g and thus lock the shutter B.
As the shutter B₁ cannot be withdrawn without the operator first pushing the lever-
catch c sideways to unlock it from the shutter, the operator knows that the plate has
been exposed and its accidental exposure a second time is thus prevented.
The base e may bear the distinguishing figure or letter which is usually placed on
the frame.
That part of the release pin g' against which the end 2 of the spring catch bears
is by preference notched at for the end to engage with so as to prevent the
shutter falling out of the frame if it should be loose in the rabbett and turned upside
down.
It will be evident that my invention is applicable either to single or double dark
slides.
The accompanying drawing illustrates what I consider to be the best way for carry-
ing my said invention into effect but it is to be understood that my said invention is
not limited to the precise details herein described and illustrated.
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 :-
-
The improvements in connection with photographic dark slides for preventing a
second exposure by accident arranged and operating substantially as and for the
purposes hereinbefore described and illustrated by the accompanying drawing.
Dated this 27th day of June 1890.
CHARLES BUSWORTH KETLEY,
Agent for the Applicant.