Improvements in Photographic Coloured Screens.
Year: 1896

page_text: COMPLETE SPECIFICATION.
Improvements in Photographic Coloured Screens.
I, JAMES WILLIAM MCDONOUGH, of Manhattan Building, Chicago, Cook
County, Illinois, United States of America, Gentleman, 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 object of my invention is to make a new and improved adjustable regulating
screen for use with a camera in taking photographs, by which the quantity of the
different colored rays of light which pass from the object to be photographed to
the sensitive plate may be regulated in relation to each other, determinate up the
nature of the light existing at the time the photograph is taken. While it is
intended for use in taking all kinds of photographs, it is more particularly intended
by me for use in taking photographs in colors. My invention will be more fully
understood from a detailed description in connection with the drawings, as
hereinafter explained.
My improved screen may be placed either before or behind the lens of the
camera; or, if preferred, it may be placed in a slot between the two glasses
constituting the lens. It places in the hands of a photographer means by which
he can regulate the color values of different light passing from the object to be
photographed to the negative plate.
Sensitive plates used in taking photographs differ in their actinic properties in
accordance with different sensitizing processes. With most sensitive plates the
more refrangible rays, such as violets and blues, act very rapidly, and the less
refrangible rays, such as reds and yellows, act very slowly. In fact, the ratios
vary to a large extent. It is also well understood as a fact that in different
localities there are more or less alterations of the actinic values in light. Pure
sunlight, for example, is different from subdued light or artificial light. On a
bright, sunny day the red and yellow colors in the light are in larger proportions
than on cloudy days, while the blue and violet colors are in smaller proportions.
If we look, for example, at a landscape on a dull day through a piece of orange
or yellow colored glass, which suppresses the blue rays, the landscape will appear
to be illuminated with sunshine, thus showing that there is an excess of red and
yellow light on a bright day. Different parts of the sky are differently
illuminated, the position of the sun altering the values of the colors. Accepting
vermilion red, emerald green and ultramarine blue as representing the three
fundamental colors of light, it is important to provide means for altering the
amount or value of each separate color that falls upon the negative plate after its
passage from the object to be photographed.
In the drawings,
Figure 1 represents a side elevation of a plate formed of a very thin piece of
clear mica, celluloid, or other suitable transparent material, the surface of which
is covered with a thin and very transparent substance-as, for instance, a lemon
yellow;
Fig. 2 represents a side elevation of a piece of mica, or other suitable material,
covered with a thin coating of, say, lemon yellow substance, and attached to a
piece of metal as a part of a moving mechanism;
Fig. 3 represents a side elevation of a piece of mica, or other suitable material,

page_text: covered, say, with a thin coating of orange substance and attached to a piece of
metal as a part of a moving mechanism;
Fig. 4 shows a section, taken in line 4-4 of Fig. 3;
Fig. 5 shows a side elevation of a receptacle having a movable double eccentric
ring and a pair of movable pieces like that shown in Fig. 2, arranged on one of its
sides or faces;
Fig. 6 shows a similar receptacle having a movable eccentric ring and a pair
of movable pieces like those shown in Fig. 3, arranged on its opposite sides or face;
Fig. 7 shows a side elevation of a completed screen containing my improvements;
Fig. 8 represents an edge elevation of the screen shown in Fig. 7; and
Fig. 9 shows a vertical section of the screen taken in line 9-9 of Fig. 7, arranged
in place on the outer end of the tube of a lens.
In making my improved screen, I make a plate, A, of a sheet of thin mica,
celluloid, or other suitable transparent material, covered with a light lemon yellow
colored substance, which I represent by the parallel lines and which is intended
to absorb the excess of action of the blue rays. If I employ a deeper shade of
yellow, it would absorb all the blue rays, which is not desired. If preferred,
however, the color on the plate, A, may be entirely omitted, in which case the
plate itself may be dispensed with. When the clor is omitted or the plate itself
dispensed with, however, a deeper shade of color should be used on the parts
hereinafter described. This plate admits the passage of red and green rays, and
a small proportion of the blue rays. I then make a pair of movable plates, B,
like those represented in Fig. 2, with preferably an opening, B', in the form of
a half ellipse in each. This plate is strengthened and supported by a metal holding
piece, b, and is provided with a spring, It is also provided with a hole, 62, to
enable the piece to be pivotally mounted, as hereinafter explained. The piece, B,
is intended to be covered or coated with a light lemon colored substance, repre-
sented by the parallel lines shown on it. I then make a pair of movable pieces, C,
preferably provided with a balf elliptical opening, C', in each, made larger than
the opening B'. These pieces are also supported and strengthened by a metal
holding piece, c, provided with a spring, c', and with a hole, c, to enable the piece
to be movably mounted, as hereinafter explained. I then make a receptacle, D,
formed of a ring, not entirely complete, with side pieces extending inwardly and
provided with an annular opening at their centers. These side pieces may be made
integral with the ring, so as to form part of it, or be fastened to the ring by
screws, as shown in Figs. 7, 8 and 9 of the drawings. I arrange on the side
pieces a scale, D', represented by various numerals, as shown in Fig. 7, and provide
the pieces with outwardly extending flanges, D2, shown in Figs. 8 and 9, to enable
the receptacle to be slipped over the outer end of a tube, H, of a lens, G, as
shown in Fig. 9, and receive a cap (not shown) to exclude the light. Within
this receptacle I arrange two movable rings, E and F, provided with handles, E
and F', to enable them to be turned or slipped around in the receptacle. These
handles are provided with points or verniers, so that they can be adjusted at any
point desired on the indicating scale.
Within the receptacle I arrauge at one side double eccentrics, e, and at the other
double eccentrics, f, constituting, respectively, parts of the rings, E and F, so as
to turn with them. I then pivot to the sides of the receptacle, D, by means of
pins, d, on one side of the plate, A, a pair of movable plates, B, and on the other
a pair of movable plates, C. The springs, b, on the plates, B, and on the
plates, C, rest against pins, d', extending inward from the sides of the plates, D,
so that as the rings, E and F, are moved in one direction or the other, the
plates, B and C, will be moved by the tension of the springs in or out, thus
increasing or diminishing the opening, B', on one side of the plate A, and the
opening, C', on the other side of the plate A, as may be desired. In Figs. 5, 6
and 7, the openings formed by these plates are shown. In Fig. 5 an elliptical
opening, B1, appears, formed by the half elliptical openings, B', of the plates B. In
Fig. 6 an elliptical opening, C', appears formed by the half elliptical openings, C¹,

page_text: of the plate C. In Fig. 7 circular openings appear caused' by the movement of
the plates B and C, sufficiently toward each other to change the elliptical openings
into the circular openings.
In the use of the screen, if it is desired that a small quantity of blue rays shall
he admitted from the object to be photographed to the negative plate, the
pieces, B', should be moved toward each other, so as to diminish the space in the
plate, A, through which the rays of light pass; while, if a larger quantity of blue
rays be desired, the pieces, B, may be moved from each other. If a small quantity
of green rays be desired, the pieces, C, may be moved toward each other;
while, if a larger quantity be desired, they may be moved from each other,
thus presenting less obstruction to the passage of the green rays. The red
rays pass through the entire circular opening in the screen, as they pass through
all of the plates used in the formation of the screen. If, now, the day on
which it is desired to use the screen be bright, the handles, E', should be moved
opposite that numeral in the scale that will admit the desired quantity of blue
rays; while if the day be dull, it should be moved opposite a numeral which
will permit the less quantity of blue rays to pass through the screen. In the same
manner, if it be desired to admit a larger or smaller quantity of the green rays, the
handles, F, should be moved backward or forward until they register with the
numeral on the scale at which the desired quantity of green rays will be permitted
to pass through the screen.
covers
In practice these handles may be readily adjusted to obtain equal action of
the three colors passing from the object to the sensitive plate. The openings
assume a size to admit the desired quantity of the different kinds of rays,
according to the position of the handles. The orange regulating screen
the margin of the lens, the opening of the screen allowing the passage of the blue
rays the center, and the green the intermediate space. This arrangement gives a
more coincident focus for the separate colors, as the different circles of colored
substances act in the nature of diaphragms or "stops" through means of which the
openings for the passage of blue and green rays are smallar than that for the
passage of the red rays, in consequence of which the focus of the blue and
green rays is lengthened to coincide with that of the red; and the position of this
screen near the lens 'causes a diffusion of the different colors and makes the different
circles and lines unobservable when the picture is forined upon the sensitive plate.
If preferred, different thicknesses of mica may be employed to subserve the focussing
of the different colored rays.
When this screen is placed near the sensitive plate, the different circles of
light will be impressed upon the plate, together with all markings, thus defeating
the object. Other shades and tints, and even colours, may be used in this
combination; but those described have seemed to me to give the best results.
As already intimated, these regulating screens are particularly valuable for use in
connection with my multi-colored screens formed in fine alternating lines or dots in
primary colors, which are placed in close contact with the sensitive plate. A
white object placed in the view may be used to form a spot in the picture where
comparison may be made to determine exact equal colored impressions upon the
negative.
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. The method of making a negative by regulating the quantity of blue and
green rays of light that pass from an object to be photographed to the sensitive
plate, which consists in adjusting the size of the openings through which they pass
to the sensitive plate, in relation to each other, determinate upon the nature of the
light existing at the time the photograph is taken.
2. A compound regulating screen composed of two or more transparent plates
uniformly tinted with different tints or colors, and adapted to be placed near the

page_text: lens of a photographic camera, whereby the rays of light from an object to be
photographed pass through such screen before reaching the sensitive plate.
3. A compound regulating screen composed of two or more transparent plates
uniformly tinted with different tints or colors, arranged nearly in the same plane
and adapted to be placed near the lens of a camera, whereby the rays of light from
an object to be photographed pass through such screen before reaching the
sensitive plate.
4. A compound regulating screen composed of two or more transparent plates
uniformly covered with different tints or colors, arranged in nearly the same plane
so as to be movable in relation to each other, and adapted to be placed near the
lens of a camera, whereby the rays of light from an object to be photographed pass
through such screen before reaching the sensitive plate.
5. A compound regulating screen composed of two or more transparent plates of
different tints or colors, arranged to be movable in relation to each other, and
adapted to be placed near the lens of a camera, combined with means for adjusting
the plates in relation to each other, whereby the area of each color may be easily
adjusted to different conditions of light.
6. A compound regulating screen composed of two or more transparent plates of
different tints or colors, arranged to be movable in relation to each other, and
adapted to be placed near the lens of a camera, combined with indicating scales
and means for adjusting the area of the different colors in relation to each
other, whereby they may be easily and certainly adjusted to different conditions
of light.
7. A compound regulating screen composed of two or more transparent plates of
different tints or colors, adapted to be placed near the lens of a photographic
camera, and having the part of the screen for regulating the quantity of the red
and green rays surrounding the margin of the lens opening, and the part permitting
the passage of the blue rays over the center of the lens opening, and the part
permitting the passage of the green rays and regulating the passage of the blue
rays intermediate the margin and the center.
Dated this 23rd day of June 1896.
HASELTINE, LAKE & Co.,
45 Southampton Buildings, London, W.C., Agents for the Applicant.