Improvements in Color Photography.
Year: 1889

page_text: COMPLETE SPECIFICATION.
Improvements in Color Photography.
I, ANTOINE HIPPOLYTE CROS, of 5 bis Rue du Cirque, Paris, in the Republic of
France, Physician, 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 present invention has for its object the carrying into effect by means of new.
processes the principles discovered and made known by Mr. Charles Cros in his
studies on color photography.
These processes consist essentially in the arrangement of an apparatus capable of
taking at one time three superposable pictures and permitting, with the modifications
hereafter mentioned, the reconstruction of the complete picture of the objects
reproduced with their natural colors by the conveyance of the three separate
elementary pictures upon a common surface.
The annexed drawings shew the apparatus which accomplishes this object.
Figure 1 shews an elevation of the whole in perspective, sufficient to show the
exterior.
Figure 2 shews a plan following a horizontal section line taken under the shutter
of the box.
A is the frame of the dark chamber, it is mounted upon a base A². The dark
chamber is in two parts; the upper part fixed to the base carries the object glass B
which is put in focus by means of the button b; the lower moveable part is fixed to
the other by means of bellows slides working in grooves in two lateral rails a a
between which is an intermediate rack a¹; a spring stop engages in this rack to fix
the moveable part after it has been put in place.
This moveable portion has at the back (instead of one sensitive plate with its frame
and accessories) three vertical surfaces of the same size, arranged in the same way
and intended to undergo the same treatment. These surfaces are placed in three
different planes C, C, C, all three parallel to the front and arranged in regular steps
obliquely from left to right and from front to back.
In the interior of the dark chamber a glass wheel D is arranged as shewn in
Figure 2 and separately at Figure 3, it is mounted by its centre on a bronze boss
carrying trunnions which turn freely on bearings fixed to the sides of a split bar A¹
arranged at the bottom of the chamber so as only to show half of the wheel in the
interior. The plane of the wheel makes with the outer lateral side, from back to
front and from left to right an angle of 45°. It is put into movement by means of a
wound up cord as for spinning a top or in any other manner.
A plane mirror E is placed parallel and opposite to the visible portion of the other
wheel D.
The axis of the object glass B meets the wheel directly on the right side of its
centre at the half of its radius.
Then as is shewn at Figure 3 the wheel is divided into four sectors two of which
each occupy of the circle and having their apexes opposite are tinned or silvered
and the two others each occupying of the circle and opposite in the same way are
transparent or cut out. The reason for this arrangement will be seen further on.
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page_text: The three surfaces C, C1, C2, are each provided with three plates as is shown in
Figures 1 and 4, that is to say on the outside with the sensitive plate i, which is
introduced there with its frame from the top at the moment of operating; also with a
coloured glass plate and on the inner side with a shutter 2. To facilitate the
simultaneous lifting up of the shutters, they are connected together at the top by a
sliding bar !.
The surface C receives an orange coloured glass, the surface C₁ a green and the
surface a violet glass.
The chamber
exterior light.
or frame, in which everything is enclosed is protected from the
Thus mounted the apparatus is ready for use. The object glass is covered, the
interior shutters of the three frames aro raised and the wheel put into motion by
pulling the cord.
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During this time the model has been focussed, and after the usual "don't move
the object glass is uncovered. When the exposure is considered sufficient, the
object glass is closed as well as the frames which are taken away to develope.
Negatavies resulting from the action of yellow red and blue light are thus
obtained.
During this operation the rays of light coming from the object glass have followed
the three paths marked out in Figure 2 in consequence of the three successive
positions taken by the sectors of the operative portion of the wheel in the course of
its rotation from left to right.
These positions and the successive directions of the rays are more clearly shown in
Figures 5. 6 and 7. The wheel being mounted in the dark chamber so that the
centre of each of these sectors places itself upon the principal axis of the object glass
making with this axis an angle of 45° the first position on Figure 5 brings on the
line of this axis a transparent sector which permits the ray to strike directly upon
the glass C, the second position Figure 6 brings on the same line a reflecting sector
which sends the ray to the mirror E and from this to the left of the wheel which
presents a transparent sector across which the ray strikes the glass C₁, then the third
position Figure 7 opposes two reflecting sectors to the ray and finally directs it upon
the glass . It will be seen that the breaks resulting from the reflections causes
these rays to take exactly the same path in the three positions but by reason of the
progressive absorbtion of the light the orange has been put on to C, the green to C¹
and the violet to C2. The rotation of the wheel therefore alternately cuts off the
three sensitive plates and distributes the light to them in a rapid intermitting or it
may be in a quasi continuous manner. I will add that the direction of the rotation
above stated in order to explain the manner in which the described effects take place
is not essential and the wheel may be indifferently revolved in the one or the other
direction, the result being the same namely two rays to each glass at each revolution
of the wheel.
The three pictures thus obtained are not reversed because the light is not reflected in
one of the pictures and it is twice and four times reflected in the two others.
This same apparatus may with some modifications serve to control the results
obtained.
To do this it suffices to replace the object glass with a lens and to place three
colourless positives obtained from the negatives previously mentioned upon the three
surfaces C. CC2 for example that intended to be reproduced in blue upon the orange
glass at C, that intended for the red upon the green glass at C and that intended for
the yellow upon the violet glass at C, arranging them suitably and by giving them
equal light (for example by means of light reflected on a white wall). The three
pictures will then be seen through the lens confounded into one on putting the wheel
into motion and showing upon one apparent plane the natural colouring of the object
reproduced.
In order that the register of the three elementary pictures may be accurately
brought about three plane mirrors may be placed beyond the surfaces C C¹ C² and
fixed to their bases and inclined upon these and upon the horizontal plane at 45° and

page_text: that the three elementary pictures be brought to register upon one horizontal
transparent glass that is slidden in grooves above the three oblique mirrors which
have just been spoken of. Thus it will be seen that the three colorless pictures taken,
one with orange light, another with red light and a third with green light are seen
in rapid succession by the observer looking into the instrument through the lens ;
consequently the pictures appear superposed and as each picture is seen through its
appropriate tinted glass the combined picture appears in approximately its natural
colors. This trimonoscope offers great advantages over the apparatus of the same
kind heretofore proposed.
I reserve to myself the right of modifying the details of the described apparatus as
experience may render necessary and according to need.
I will not enter here into the details relating to the different treatments usual in
photographic operations which are indispensable to complete the above described
Invention these operations being already known and carried out in a more or less
satisfactory manner and may be adapted to the described process.
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 means and apparatus above described and illustrated by the annexed
drawings to be used for and in connection with the production of colored photographic
pictures.
2. The use in color photography of a rotating reflector substantially as described
to obtain simultaneously three or other number of images and receiving such images
on sensitive surfaces under conditions such that each surface may be affected by rays
of a different color.
Dated this 30th day of May 1889