Improvements relating to Photographic Dark Slides and Cameras for Process Work.
Year: 1897

page_text: Date of Application, 25th Jan., 1897-Accepted, 11th Sept., 1897
COMPLETE SPECIFICATION.
Improvements relating to Photographic Dark Slides and Cameras for
Process Work.
We, ANDREW WYBRANT PENROSE, Wholesale Chemist of 8 and 8a Upper Baker
Street, London, W.C., and WILLIAM GAMBLE, Journalist, of 8 and 8A Upper
Street, London, W.C., 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 in the improvements relating to photographic dark slides
or cameras for Process work hereinafter described.
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(1) The screen adjustment. Whereas it is necessary for carrying out the
photographic process known as Half-tone to place in front of the sensitive plate
a glass plate ruled with lines, or impressed with a stipple, or any like pattern
consisting of alternate opaque and transparent spaces, and called a screen":
and that it is further necessary that this screen should be in a frame or carrier
which can be adjusted at different distances from the sensitive plate and parallel
to it, (the sensitive plate remaining fixed), we can accomplish this movement
in either one of the two following ways:
(a) In the dark slide. As there is insufficient extension in the dark slide for
the use of slides or guides, parallel with the axis of the camera we make use of
oblique parallel slots and guide pins.
Thus we place at suitable distances in the sides of the movable frame or carrier
which holds the screen, projecting pegs or pins, and we cut inclined slots in a
suitable longitudinally guided rectangular strip of wood, metal, ebonite or like
material, these slots corresponding to the position of the pins or pegs so that when
a pair of such strips are suitably placed in the dark slide the pins or pegs will
be in the slots, and further when such strips are raised or lowered by means of a
rack and pinion, the frame or carrier to which the pins or pegs are fixed must
move to and fro to the extent allowed by the slots, the movement being in a
horizontal plane.
The measurement of the separation of this moving screen carrier from the
sensitive plate can be indicated by a pointer extending through a slot to the
outside of the camera and registering on a divided scale.
Obviously the order of the arrangement may be reversed the pins being inserted
in the moving strip and the slotted strip being attached to the side of the carrier.
The accompanying drawing (Sheet 1) substantially illustrates our invention.
Fig. 1 is a sectional view showing the pins or pegs marked A A A and the
inclined slots B B B: the rectangular moving strip C C: and the rack and
pinion D.
Fig. 2 is a similar view in which the travelling frame or carrier E E is shown
having been thrust forward by the movement of the strip thrusting the pins
along the slots.
Figure 3 is an exterior elevation in which the pointer F and indicating scale G
are shown, the pointer being a continuation of one of the pegs.

page_text: (b) In the Camera. Instead of placing the screen carrier and mechanism for
moving it in the dark slide we may fit it into the back of the camera, so that it
may be projected into the dark slide when the latter is in position and the
shutter drawn.
In adopting this plan of construction, we prefer to use instead of rack and pinion
a system of levers or toggle joints actuated by a lever on the outside of the camera
the said lever being shown in Fig. 4 Sheet 2. In order to ensure returning the
outside lever H to the same position after focussing and when the dark slide is
inserted we place an adjustable screw stop J so as to enable the operator to
maintain a constant distance. Figs. 5 and 6 on the same sheet show on a larger
scale different views of the screw stop.
:
The rising Front. Whereas it is desirable that the operator should have the
means of raising or lowering the lens carrying front, without having to change
his position when focussing at the back of the camera, we accomplish this object
by means of a rod passing from back to front placed centrally underneath the
camera. (See Fig. 7 Sheet 2.) At one end of this rod is a winch and at the
other end a bevel wheel actuating another bevel wheel to which is attached a
screw threaded to the rising front. The novelty of our invention consists in
making allowance for the back body K and the front body L moving indepen-
dently to and fro from the fixed central body M. We accomplish this by coring
the part of the rod marked N, so that the square rod marked O can slide into
By adjusting the lengths of the cored rod and the square rod the necessary
extension or contraction is obtained, without interfering with the usual movement
of the bodies.
it.
(3) The Roller Shutter. Whereas with photographic Dark Slides, constructed
on the roller shutter principle, it has been objected that it is not possible to remove
the shutter in order to test or clean the Dark Slide, the shutter in one of its
positions closing either the back or front opening of the slide; we have made the
following improvement in such slides, namely a roller shutter which will draw
right out. To accomplish this, we cut away the part of the bottom of the slide
marked P. P. Figs 8 and 8*, hitherto forming a stop, to continue to the outside
edge the grooves QQ Fig. 9, in which the shutter slides. Thus when the
shutter R, Fig. 10, is drawn beyond the part marked S S, Fig. 10, it is pulled
right out, and can be readily replaced by again inserting it into the groove.
order to avoid the shutter being accidentally withdrawn when not wanted, we
place a stop or a catch at the point marked T, Fig. 8.
In
(4) The door of Dark Slide. Whereas in wet collodion work metal catches on
the door of the dark slide get rusted or oxidised and break off and whereas it is
difficult to find their place when working in the subdued light of the dark room,
we avoid the necessity of any catches by constructing the recess for the door
so that when it is inserted it only has to be pushed upward a little way, into the
groove U Fig. 8, and when it falls "home" it drops into a groove U in the
bottom of the slide. To remove the door it is lifted upwards by the tag U
Figs. 8 and 8 and pulled outward.
5. The Plate Spring. Whereas it is a disadvantage to place, as hitherto, a
spring on the back lid or door of photographic dark slides to press the plate
forward, because when the plate is thin it is apt to bend or bulge in the centre
or to break, we make the following improvement to obviate these drawbacks:
We construct a metal bar extending across the dark slide, or across the carrier,
at a position corresponding to the top of the plate. This bar is swung at each
end on suitable brackets the pivoted ends of which have cams which press against
springs, so that the pressure can be thrown off or on by swinging the bar up or
down. Figs. 11 11*, Sheet 3, illustrate the arrangement in section and front view.
V V is the bar, W. W the pivot, X X the stops against which the sensitive plate
rests, Y Fig. 11* is the cam and Z the spring partly in section. The bar is covered
with indiarubber to protect it from the silver solution in wet collodion work.
When the plate is in position the bar is brought down and presses against the

page_text: plate. The lower edge of the plate is kept forward by bevelling the lower edge
of the dark slide or carrier, as illustrated in Figs. 12, 12.
6. Draining Trough. Whereas much injury to dark slides is occasioned in
wet Collodion work by the silver running over the front of the carrier, we cut
a groove forming a trough along the front of the carrier under the plate, as illus-
trated in Figs. 12 and 12 Sheet 3 at Z¹.
Having now particularly described and ascertained the nature of this inven-
tion and in what manner the same is to be performed we declare that what
we claim is :-
1. The Adjustment of the screen carrier by means of inclined slots with pins
or pegs travelling in them for securing a parallel movement to and from the
sensitive plate in dark slides or cameras carrying ruled screens or gratings for
working the half-tone process.
2. The adjustment of the screen carrier in a camera or dark slide by means of
levers and toggle joints governed by an exterior lever and a screw stop, for
regulating the end position of said exterior lever.
3. The combination of the rising front of an extensible camera with means for
vertically adjusting the same and a telescopic rod, extending under the camera
to the rear end thereof for the operation of said means of vertical adjustment
substantially as described.
4. The combination with a dark slide of a roller shutter which can be drawn
completely away from the dark slide in the way described.
5. A means of attaching the dark slide without metal catches, as described.
6. In a dark slide a spring operated bar for securing the plate substantially
as set forth to avoid the necessity for the usual spring on the door of the dark slide.
7. In a dark slide a draining trough slotted in the lower carrier substantially
as illustrated.
Noted this 25th day of Januar 1897
HERBERT HADDAN & Co.,
18 Buckingham Street, Strand, London, W.C.,
Agents to Applicants.