New or Improved Apparatus for Viewing Stereoscopic Pictures.
Year: 1895

page_text: Date of Application, 30th Jan., 1895
Complete Specification Left, 30th Oct., 1895-Accepted, 18th Jan., 1896
Y
[Communicated from abroad by PAUL MOESSARD, of 58 Rue de Vaugirard,
Paris, France, Gentleman.]
New or Improved Apparatus for Viewing Stereoscopic Pictures.
I, ERNEST DE PASS, of 78 Fleet Street in the City of London, Fellow of the
Chartered Institute of Patent Agents, do hereby declare the nature of this
invention to be as follows:-
This invention relates to new or improved apparatus for viewing stereoscopic
pictures, the object being to enable persons assembled in a lecture room, or theatre,
to see from their places with all the appearance of relief, ordinary stereoscopic
pictures projected by a lantern, or lanterns, on a white screen, or otherwise
exhibited by known means, so that every one can see them at the same time, instead
of each one having to look at them separately as when looking through an ordinary
stereoscope.
For this purpose, each person is provided with a special glass, either binocular,
or single, by looking through which the two pictures can be caused to blend as
they do in a stereoscope, so giving the required effect.
An advantage of this means of viewing stereoscopic pictures is, that they can be
placed one above the other, instead of side by side, and can consequently be made
of considerably greater length.
The special binocular or twin glasses (called by the inventor" stereo-jumelle ")
for viewing the steroscopic pictures, are provided with two similar prisms, or with
mirrors, for causing the pictures seen by the two eyes to blend together. The
prisms whose faces may be inclined at about 10° to each other, are held in tubes
suitably connected by double rings. They are provided with means, such as
teeth, or slotted arms, for rotating them simultaneously in opposite directions
through 90°, so as to suit for pictures placed side by side, and to cause the pictures
to blend properly.
If the pictures are placed one above the other, then one of the
prisms requires to be turned upside down, or end for end, to facilitate which it may
be mounted in a ring capable of turning in its place with a certain amount of
friction through 180°.
If mirrors are employed instead of prisms, they are arranged in pairs in front of
each eye, one of each pair being arranged to move or partially rotate.
The mirrors are so arranged that the image of the picture is seen after being
doubly reflected. When the pictures are arranged side by side, the mirrors are
upright and one pair is inclined towards the other pair. When the pictures are
superposed, the mirrors are inclined to the horizontal. In the latter case, a single
long mirror may be employed in combination with two short movable ones to give
the double reflection.
The special single glass (termed by the inventor "sterco-monocle ") is provided
with only one pair of mirrors, and is intended to be applied to one eye only, so that
while this eye sees a virtual image of one of the two stereoscopic pictures, the
naked eye sees the other picture directly, the two images blending and giving the
stereoscopic effect.
To prevent the same eye seeing both the pictures, the glasses are provided with
screens or stops for blocking out the picture which it is not desired to see, thereby
confining the view of each eye to its respective picture to avoid confusion.

page_text: When using mirrors, these may be made small enough to only reflect one picture,
thus obviating the screens or stops.
The prisms give clear, bright images if their angle is sufficiently acute, but
cannot be used very close to the screen, or picture, whereas the mirrors are not
open to this objection.
The glasses may be provided with any suitable means for magnifying the
images.
Dated this 30th dow of In 1905
New or Improved Apparatus for Viewing Stereoscopic Pictures.
I, ERNEST DE PASS, of 78, Fleet Street, in the City of London, Fellow of the
Chartered Institute of Patent Agents, 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, reference being had
to the accompanying drawings and to the letters and figures inarked thereon, that
is to say :-
This invention relates to a special optical instrument termed twin or binocular
stereoglass ("stereojumelle"), or in a simplified form single stereoglass ("stereo-
monocle"), and intended to allow of stereoscopic images of any size and nature,
whether transparent, mounted on card, or projected upon a white screen, by known
methods, being seen with all the appearance of relief.
In this latter case, everyone assembled in a theatre, or in a lecture room, can see
in relief, from their places, by aid of the apparatus images produced by a lantern
projector.
The stereoscope, as is known, is based upon the principle of binocular vision.
Two photographs, two perspectives of the object, are taken at the same instant
from two points of view situated on the same level but at a distance apart about
equal to that between the eyes. If by any means or device one is enabled to see
with each eye only that one of the images which corresponds to it, and to cause
these two isolated images to coincide, a striking illusion is obtained. The objects
separate, become isolated, and appear to be enveloped in atmosphere, the planes
become disengaged and space themselves out, and everything becomes animated,
nature lives again with a marvellous intensity of life.
In the ordinary stereoscope the two pictures are placed side by side so that the
corresponding points are separated by about 8 centimetres. Two lenticular prisms
through which one looks serve to bring the images one upon the other, and the
effect is produced.
With this method, the images cannot exceed 8 centimetres at the side. To be
able to get as much as possible into these restricted limits, it is necessary to
considerably reduce the scale, to give to the figures a rediculously small size, and
to sacrifice several interesting details.
Furthermore, the stereoscope can only be looked through by a single observer
at a time. This is a solitary and selfish pleasure which one's nearest neighbour
cannot share.
With the twin stereoglass these inconveniences are obviated; the views
projected upon a screen are seen in relief simultaneously by all the spectators
in the room, and the exchange of impressions perceived in common increases
considerably the value thereof. These views can, moreover, as stated further on,
be extended in width as far as the screen will allow. Indeed, the dimension of the

page_text: details only depends upon the resources at one's disposal to make the projections of
the length of the room, on the power of the lantern, etc.
And in order that the invention may be readily understood, I will describe the
same with reference to the accompanying drawings, in which:
Figs. 1, 2 and 3 shew respectively, in elevation, in plan, and in section through
the axis of one of the tubes, a twin stereo-glass having prisms.
Fig. 4 shews a modification of the arrangement for ensuring solidarity of the
movements of rotation of the prisms.
Fig. 5 shews the relative position of two juxtaposed images.
Fig. 6 is a diagram showing the two extreme relative positions that the prisms
can assume in the case of two juxtaposed images.
Figs. 7, 8, and 9 show the relative positions of the diaphragms, corresponding to
the different cases hereinafter explained.
Fig. 10 shows the relative position of two superposed images.
Fig. 11 is a diagram showing the two extreme relative positions which the prisms
can assume in the case of two superposed images.
Figs. 12 and 13 show respectively, in elevation, and in plan, a twin stereo-glass
having mirrors.
Figs. 14 and 15 show a modification of construction of the twin stereo-glass with
mirrors, in the case of superposed images.
Figs. 16 and 17 shew respectively in transverse section and in front view a single
stereo-glass having a mirror.
DESCRIPTION OF THE APPARATUS.
The twin stereo-glass is provided either with prisms, or with mirrors. The
modification with mirrors has the advantage of lending itself to a more simple and
less costly combination, that is to say, the single stereoglass, which is only the twin
stereoglass cut in two.
In the first case, modification with prisms, the twin stereoglass consists essentially
of two like prisms in crown glass, the plane faces of which incline towards each
other at an angle of about 10°. These prisms A, B, C, D; E, F, G, H; (Fig. 1)
are mounted side by side, at a distance, equal to the normal separation of the two
eyes, in two parallel tubes of wood, or metal, which are connected by one or two
double rings I, J, K, L, in which they can turn through a right angle with but
little friction. The tubes are caused to rotate simultaneously either by means of
gearing (Figs. 1 and 2) or by means of a stud sliding in the fixed piece M, N,
and common to both tubes (Fig. 4) or by any suitable arrangement by which
the prisms turn always together and in a contrary direction through an equal
angle.
According to the initial arrangement of the prisms, either juxtaposed images, as
usual, or crossed images, or superposed images can, with this apparatus, be view
stereoscopically.
Jam CAST LUXTAPOSED IMAGES (FIC 5).
In this case the prisms have their edge parallel and facing each other when in
one of the extreme positions, as shown at A, B; E, F; (Fig. 1, and Fig. 6); in
the other extreme position they would form a prolongation of each other; and
in the intermediate position they would make a variable angle. When the prisms
are turned, the images perceived by each eye appear to move in the opposite
direction with a conical movement around their real position. They therefore
appear to separate or to come together laterally; at a given moment they coincide
In this case the prisms have their edge parallel and facing each other when in
one of the extreme positions, as shown at A, B; E, F; (Fig. 1, and Fig. 6); in
the other extreme position they would form a prolongation of each other; and
in the intermediate position they would make a variable angle. When the prisms
are turned, the images perceived by each eye appear to move in the opposite
direction with a conical movement around their real position. They therefore
appear to separate or to come together laterally; at a given moment they coincide
This favourable position of the prisms vari
and the relief is obtained.
size of the image and the distance from the spectator.
Ok the
This effect being obtained, three images are seen disposed horizontally; the
centre one alone is in relief, the two others, which are flat, proceed one from the left

page_text: 9.
2ND CASE. CROSSED IMAGES.
The prisms have their bases towards one of the extreme positions; the angles
are then according to C D, and G H, (Fig. 1).
The stereoscopic images must then be inverted, that intended for the left eye
being placed to the right, and on a level with the other, the movement of rotation
of the prisms being effected, as in the first case, the screens intended to block
out the multiple images being placed outside, and their vertical edges being
separated to a distance corresponding to the mean separation of the eyes
(Fig. 9).
In this
case,
3RD CASE. SUPERPOSED IMAGES.
the edges of the prisms are directed according to A B, E F (Fig. 4),
as Fig. 11, indicates for the two extreme positions. Then the stereoscopic images
seen by each eye appear to approach each other, or to recede from each other, in
rising or in descending during the rotation of the prisms. When these images
coincide the relief is obtained.
At that moment three images are perceived arranged vertically, the middle one
alone being in relief. In order to shut out the two others I again use two small
semicircular diaphragm screens (Fig. 7) fixed in front and as near as possible to the
prisms, and having their free edges R and S horizontal and as nearly as possible in
line with each other. In the superposed position (Fig. 10), the screen T corre-
sponds to the left eye and blocks out the lower image. Here again, the extent to
which it is necessary to turn, the prisms to bring about the coincidence of the
images and the effect of relief depends upon the size of the image and the distance
away of the spectator.
It will be seen on reference to Figs. 1, 2, 36 and 11, and to Figs. 7, 8, and 9,
that to pass from juxtaposed images to superposed images, or to crossed images, it
is only necessary to turn one or other of the prisms E F, G H, end for end, and to
turn the diaphragm screens in the contrary direction through 90° or 180°. The
same apparatus will then serve in both cases.
This end for end displacement of the prism may be obtained by the rotation of
a ring in which it is fitted, and which turns between two stops with considerable
friction through 180° in the tube of the twin stereoglass; it may also be obtained
by removing the prism from its frame and then replacing it therein in the contrary
direction, or by any other means. The rotation of the diaphragm screens, on
changing from one arrangement to the other, is also easily effected.
Each diaphragm is caused to turn by pushing in the one direction, or in the
other, the tail piece which projects from its periphery, (Figs. 7, 8 and 9).
In all these positions one of the diaphragms is free to slide in a groove, so as to
vary the position of its free edge and consequently to permit of accommodating the
sight either to the separation of the eyes of the spectator, or to the deviation
produced by the prisms. Advantage can be taken of this regulation to block out
or completely mask from each eye the part of the image which is only to be seen
by the other eye.
It has been stated that the deflection of the images and their superposition may
also be produced by means of plane mirrors instead of by prisms. Thus, referring
to Figs. 12 and 13 a and b are two reflecting mirrors, the faces of which are turned
towards each other. After double reflection upon these mirrors, the ray ca will be
deflected according to bd making, with its original direction, an angle double that

page_text: of the two mirrors. The eye at d will therefore see on the prolongation of d b.
The deflection will vary with the angle of the mirrors.
By placing in front of each eye a system of suitably arranged double mirrors,
one can therefore, as in the case of the prisms, cause images on the right and on
the left to travel so as to produce the coincidence thereof.
1ST AND 2ND CASES. JUXTAPOSED AND CROSSED IMAGES, FIG. 5.
The mirrors are vertical and movable about vertical axes (Figs. 12 and 13).
This mobility may be possessed by the four mirrors, but it is sufficient that any one
of them should turn while remaining vertical so that the regulation shall be possible.
Each eye d and g receives, after double reflection, the image which corresponds to
it; by an appropriate movement of the movable mirror the superposition is brought
about and the relief appears.
As with the prisms, three images are seen; the centre one alone is good. The
two others are eliminated by means of a central screen or by two lateral screens, or
by employing small sized mirrors so as only to contain the image corresponding to
one eye.
3RD CASE. SUPERPOSED IMAGES (FIG. 10).
The mirrors are arranged in this case parallel to the horizontal, Figs. 14 and 15
and the movement of that one which is, or of those which are, movable, is effected
about a horizontal axis. Three mirrors are sufficient, as shown in Figs. 14 and 15.
One, i, which is the first to receive the rays, has a length of about 10 centimetres,
it sends the images upon the mirrors J, K, placed in front of each eye, and by the
rotation of the images of the like points and m are caused to blend or unite at n.
The two multiple images are shut out by screens or by reducing the mirrors J, K,
sufficiently.
SINGLE STEreoglass.
With mirrors, a different apparatus is necessary for each disposition of the
images, but if of the stereo twin glass the combination corresponding to one eye
only be taken, then one has a single stereo glass which consists simply of two plane
mirrors forming a variable angle (Figs. 16 and 17).
The image is looked at directly with the eye which corresponds thereto; and
by placing the single stereo glass in front of the other eye, the doubly reflected
second image is brought to coincide with the first, which is always possible.
The single stereo glass bas the advantage of being very simple, of small size, and
of being directly applicable to all possible cases and all arrangements of images.
It can be used with one or the other eye, at will.
DISPOSITION OR ARRANGEMENT OF THE PROJECTED IMPRESSIONS
OR IMAGES.
The stereoscopic images may be projected by two lanterns, or, by preference,
by one only:
The three arrangements provided for these images offer the following
advantages. The juxtaposed arrangement allows of the stereoscopic pictures in
common use being projected without alteration, or after reduction. The crossed
arrangement allows of images or impressions being projected such as are supplied
by stereo photographic cameras, without it being necessary to separate and invert
the two images; furthermore, it is brighter and renders easier the accomodation
of the eyes to the relief. The vertical arrangement (Fig. 10) necessitates an
alteration of the mounted stereoscopic pictures; but if dealing with views from
which the sky and ground can be omitted, it allows the whole of the screen to be
covered, and thereby increases the magnification. This arrangement even allows

page_text: of views taken stereoscopically with any camera, or panoramic cameras, being
employed, thereby avoiding any loss.
The twin stereoglass, and the single stereoglass, obviously permit, to be seen in
relief, stereoscopic views mounted upon card, or transparencies, enlarged or
reduced, and arranged horizontally or vertically. They can be used with magni-
fying glasses, with opera glasses, with telescopes, with microscopes, or with any
optical system to obtain a magnification.
Having now particularly described and ascertained the nature of this inven-
'tion and in what manner the same is to be performed, I declare that what I
claim is :-
1. The novel means for blending or uniting two stereoscopic images, whether
pasted on card, or projected on a screen, so as to produce the appearance of relief,
consisting of a binocular glass (called twin stereo glass-"stereojumelle ") in
which are either combined two refracting prisms turning in opposite directions
with a symmetrical movement in their own plane, or in which are combined four
plane mirrors grouped in pairs in front of each eye, one of which mirrors only is
necessarily movable about an axis parallel to the edges of the dihedral angles
formed by these mirrors, the object of this movement of the prisms, or of one
mirror, being to enable the observer always to bring into coincidence the two
stereoscopic images whatever may be his position in relation to these images,
substantially as described.
2. The apparatus, called single stereo glass-" stereomonocle," consisting of a
set of two movable small plane mirrors adapted to be placed in front of one or the
other eye in order to strictly bring about, in every possible case, the coincidence of
the direct image perceived by the naked eye, with the virtual image, doubly
reflected, perceived by the eye to which the apparatus is applied, substantially as
described.
3. The means for enabling stereoscopic images to be seen with the appearance
of relief, and without the use of coloured glasses, and from all parts of a room,
such images being disposed in any way, but preferably by placing them one above
the other, so that they can be extended lengthwise to cover the whole surface of
the screen, substantially as described.
4. The application of the means herein before described to any kind of stereo-
scopic views, photographic or otherwise, and enlarged or reduced, mounted,
transparent, or in projection, and of any size and relative position, and at any
distance from the eye of the observer.
5. The combinations of the arrangements or systems of twin stereo-glass, or of
single stereo-glass, with magnifying glasses, opera glasses, telescopes, microscopes,
or any optical apparatus intended for producing an enlargement of the stereoscopic
images viewed.
6. The new or improved apparatus for viewing stereoscopic pictures, sub-
stantially as herein before described with reference to the accompanying drawings.
Dated this 30th day of October 1895.
ERNEST DE PASS.