Improved Stereoscopic Telemeter.
Year: 1893

page_text: Date of Application, 11th Sept., 1893-Accepted, 14th July, 1894
COMPLETE SPECIFICATION.
Improved Stereoscopic Telemeter.
I, HECTOR ALEXANDER DE GROUSILLIERS, of No. 24 Englische Strasse,
Charlottenburg, near Berlin, in the Empire of Germany, Engineer and Chemist,
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 :-
In viewing a landscape through a binocle or double telescope, the observer has
an immediate perception of the relative depth, or the more or less distant situation,
of the objects standing one behind the other; and this is owing to the fact that
the real images produced by the object-glasses of the two telescopes in their focal
planes are not quite identical, but present parallactic differences in the location of
corresponding points of the images within the focal planes. If A, B, C, . . . N,
be objects situated at different distances from the observer and appearing nearly
in the same direction,-i.e., in close proximity to each other in the optical fields of
the two telescopes, say at the points A1, B1, N₁, of one field, and at the
points A2, B, N, of the other field-the linear distances A₁, B₁, A₁, C₁, ..
A₁, N₁, in the one field of view will differ from the linear distances of the correspond-
ing pairs of points A., B., A., C,... A., N., in the other field of view, in proportion
to the distance existing between the centres of projection of the two images, or in
other words, the distance between the two object-glasses.
The extent of these parallactic differences may generally be determined, according
to well-known rules, in the following manner:
Assuming A1, A2, to be the points at which, in both fields of view, an infinitely
distant object A is depicted, and N1, N,, to be the points at which is depicted an
object N, situated at a finite distance E from the observer; the difference between
the linear distances A., Ng, and A₁, N₁, i.e., the parallactic difference between the
image of the one object, situated at an infinite distance, and the other object, placed
at the finite distance E, will be:
The quantity A, in the case of an ordinary double telescope, is determined by
the distance of the eyes of the observer. Where, however, the object-glasses of
the double telescope are separated from each other further than usual by means of
mirrors or reflecting prisms-in accordance with the principle on which the
construction of the telestereoscope is based-A may be made to represent any
desired multiple of such distance of the eyes.
In a terrestrial telescope, so far as the real images are concerned which appear
efore the eye-pieces proper of the instrument, f should denote the equivalent focal
lengths of the entire optical systems by which those images are produced, ie., the

page_text: focal lengths of the object lenses combined with the intermediate image-inverting
lenses.
The said parallactic differences between the real images produced by the two
object-glasses, are independent of the particular part of the field of view in which
the objects to be compared may appear, as well as of the lateral distance existing
between such objects. These differences are made visible on an enlarged scale to
the eyes of the observer, through the eye-pieces of the telescopes, acting as
magnifying glasses; and, in viewing a landscape with various objects situated at
unequal distances from the instrument, the observer is enabled to perceive those
differences, as differences of depth within the stereoscopic picture resulting from
the combination of the two images of the landscape in binocular vision. Now,
exactly the same principle will apply to the production of a stereoscopic picture of
artificial objects of unequal depth by binocular vision.
Let a transparent glass plate be placed within the ocular field of each telescope,
and a series of marks (dots, lines, or the like) made on each plate in a direction
parallel to the junction line of the axes of the two telescopes; we will call the
marks in one field of view a, b₁ n₁, and the marks in the other field, uq
ს. . .
...ng. The lineary distances a₁ b₁, a₁ €1, ...a n₁, between the marks of
one ocular plate may be arbitrarily chosen; as to the distances between the corre-
sponding marks of the other plate, a, b, a, ca a, no, we will suppose them
to be so proportioned that the differences a, b,a₁ b₁, a₂ ca₁₁
are equal, respectively to the following quantities:
.
a, na ni
76g4
A being, as before, the distance between the two object-glasses of the double
telescope, and the focal length of the picture-producing set of lenses. Let,
furthermore, the position of the plates in the two fields be so adjusted, that, if the
picture of an object situated at a very long (infinite) distance, be projected in
one field at the point or mark a₁, it coincides at the same time with the mark as in
the other field. The two groups of marks a₁, b₁, c₁, ,—a2, ს, ვი
will then form correct stereographs of a group of artificial objects a, b,
n, which (no matter how combined or arranged) are situated at the
distances, eb, ec, en from the spot occupied by the observer; and
uniting the two fields in binocular vision through the two oculars, a stereoscopic
picture of the said objects a, b, c, n, must appear to the observer. The
observer at which the said objects appear
C, . .
.
distances eb, ec,
en from the
are given by the equation :
and are therefore known, provided that the respective values of the differences a, b,
-a b₁, as ca c₁
which the groups of marks are supposed to present,
are known also.
'
...
Supposing now that a landscape is viewed through the double telescope,
which comprises natural or real objects A, B, N situated at unknown
distances E, EB, Ex there will be projected into the image of this
landscape the image of the group of artificial objects a, b,
•
a
. n situated at
known distances; and, therefore, by comparing the positions of the former, in the
different planes of the panorama, to the positions of the latter, the unknown distances
at which the real objects A, B N are situated from the observer, may
readily be estimated by means of the known distances at which the artificial
objects a, b, . . . n are located.
Upon the principle above set forth is based a novel method of estimating distances,

page_text: which essentially differs from any of the methods heretofore adopted in this
particular, that it utilizes the direct immediate perception of the depth-dimension
in stereoscopic vision.
The improved method may be carried out in practice in two different ways,
which, though identical in principle, involve the employment of different means of
measurement.
One arrangement may be carried out by placing groups of marks; such as above
referred to, within the two fields of view, in the shape of scales, the lines of which
represent exact stereographs of a series of objects extending on either a straight or
curved line, at irregular or regular distances-say at 100 metres from line to line.
Owing to the binocular combination of the images of these scales, there will
therefore be projected into the image of the landscape viewed, the image of a
series of optical distance-marks extending downwards in a more or less oblique
direction towards the line of vision, the distance of each mark from the observer
being immediately ascertainable by the numbers with which the scales are provided.
To determine, therefore, the distance of a given object in the landscape viewed, it
is only necessary to turn or direct the telescope so as to bring the object sighted
near to the stereoscopic image of the distance scale. Taking, then, any fractions
of the degrees of the scale duly into account, the position or depth of the object
may be ascertained by observing the point of the scale with which it coincides, or
which (on the telescope being slightly turned in the horizontal plane) it appears to
intersect.
Scales representing correct stereographs of such series of distance-marks in
regular succession or gradation may be produced in accordance with the formulæ
given above, either by photography, or by engraving series of lines with a diamond
on glass plates by means of a suitable dividing mechanism.
In the other form of apparatus, the marks introduced into the field of view of
the double telescope may be so arranged that, when viewed stereoscopically, instead
of (as in the arrangement just described) showing a number of objects situated at
different distances, simultaneously and in juxtaposition, they present to the view
the image of one object only, which appears to move in succession to different
points, each situated at a different, though predetermined, distance. If only one
mark be brought into each ocular field-say a diamond-cut line in a transparent
glass-plate, or simply a thread-and if arrangements be made to enable the mark
of one field to be shifted by means of a screw or other adjusting mechanism in a
uniform manner and to a measurable extent, parallel to the line of junction of the
eye-pieces, while the mark of the other field retains its position unaltered near the
centre of such field, the gradual displacement of the movable mark and the binocular
junction of the two images will present to the view an object appearing uniformly
to move nearer to, or farther away from, the observer. In one position of the mark
or thread the stereoscopic image will appear to be situated at an infinite distance,
viz., when an infinitely distant real object, while it is projected by the object-glass
of one telescope to the stationary mark or thread, is at the same time made exactly
to coincide with the movable mark or thread by the other object-glass.
Supposing now that the latter mark or thread is moved from this position (which
we take to be the zero position) a certain length 8; the apparent distance e from
the observer of the artificial object perceived stereoscopically may be worked out
by the following equations :-
50 and, given the values of A and f, and the extent of displacement & of the mark being
known, the distance e may easily be determined.
The unknown distance E of a natural object in a landscape viewed through the
binocle is next determined by finding the position of the movable mark (displaced
to the extent 8) at which the artificial object, stereoscopically viewed, appears in

page_text: the image or panorama to be situated at the same distance (or depth) as the real
object.
The second way of distance measurement according to the improved method may
further be modified as follows: Instead of displacing the mark or thread within
one ocular field, the marks are allowed to remain stationary in both fields; while
the real image of the external objects is micrometrically displaced within the field
of one eye-piece, in relation to the stationary mark of that field-just as it would
be displaced if the axis of one telescope were to turn so as to alter its direction in
relation to the axis of the other telescope.
In this case the stereoscopic object viewed through the binocle, will appear at a
constant distance from the observer, and this distance will be larger or smaller
according to the position of the marks in relation to the axes of the two eye-pieces;
while the displacement of the image of the landscape viewed, in the one ocular
field, will cause the object, sighted at the same time, to apparently advance towards,
or recede from, the observer, and on being so displaced to a certain extent it will
appear to lie in the same plane (or at the same depth) as the stereoscopic mark.
Now, if the displacement of the movable image is measured from that position
as the zero point, in which an infinitely distant external object is seen at the same
depth as the stereoscopic mark, the finite distance E of an object will be found from
the equation: E = A. f the extent of displacement & from the zero position
being that which is necessary to bring the object sighted to the same depth as the
stereoscopic mark.
'
The required displacement of the picture of the landscape in the one field of
view may be effected, to a measurable extent, by any change of position of the
parts of one of the telescopes, which is equivalent to an inclination imparted to
the axis of that telescope in relation to the axis of the other telescope, within the
plane in which both axes are situated. This is feasible, for example, by a micro-
metric displacement of the object-glass at right angles to its axis; or, in the case
of telestereoscopic instruments, by micrometrically turning one of the reflecting
prisms, deflecting the axis of the telescope at 90°; or by any other method of
micrometric measurement used in connection with distance-measuring devices.
In the accompanying drawings, a stereoscopic telemeter is shown by way of
example, and as an illustration of the foregoing observations, it being arranged
with eye-pieces which are adjustable by hand.
Fig. 1 is a plan thereof;
Fig. 2 a front view, partly broken away;
Fig. 3 is an end view of the instrument, including a side elevation of the
eye-piece; and
Fig. 4 is a horizontal section on line A-B, Fig. 2, through the eye-pieces and
their supporting plate.
In its optical arrangement, the instrument is not unlike a telestereoscope,
consisting of two ordinary terrestrial telescopes, the distance between the apertures
of immergence of the object lenses being about 70 centimetres.
The two tubes R¹, R, which carry the objectives Q', Q', and the reflecting
prisms P1, P, located in front of such objectives, are connected, in the form of
instrument shown, by a parallelopipedic casing G, H. Within this casing are
secured the prismatic reflectors p', p, while the front wall G of the casing carries
the eye-pieces o', o. In the front wall or plate G, as shown in the section, Fig. 4,
are fitted glass plates 1, 2, provided with stereoscopic scales such as have been
fully described above. The glass plate s' situated in front of the eye-piece o¹ is
stationary in the metal plate G, while the other glass plate & is carried by a slide
or carriage t, adjustable within small limits in its slide-way by means of a screw ;
so that one scale may at any time be properly adjusted in relation to the other.
The tubes R1, R2, are so regulated as regards their length, that the images of
distant objects projected by the object glasses of the telescopes fall exactly into
the planes of the scales. The observer bimself, however, is in a position, by

page_text: adjusting the eye-lenses, to regulate the scales in such a manner that, in binocular
sighting, he may perceive, at the same time, both the stereoscopic image of the
landscape viewed, and the stereoscopic image of a series of distance-marks,
projected into that image of the landscape, which marks will correspond to the
stereographs upon the plates s', 8ª.
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. An improved telemeter, consisting of a double telescope (which term includes-
telestereoscopes with an enlarged distance between the object-glasses) within the-
ocular fields of which scales are so arranged that, when viewed binocularly, they
present the image of a series of distance-marks extending downwards and situated.
at predetermined distances from the observer; the image of such series of marks.
being projected into the image or panorama of a landscape, as seen through the
double telescope, so that the distance of any object viewed may be immediately
read off the scale according to the point between any two marks of such scale to.
which the object can be made to correspond with regard to the visual depth.
2. A double telescope, or telestereoscope, within each ocular field of which, for
the purpose of estimating distances there is provided a mark (being simply a line.
or a thread) which is stationary in one ocular, but capable of displacement to a
measurable extent in the other, by means of a micrometrical instrument, the
arrangement being such, that, when a landscape is viewed binocularly, there
appears to be projected into the image of such landscape a distance-mark, the
distance of which, for the time being, is ascertainable by means of the micrometer,.
and which, on being compared with the depth occupied by the object viewed in
the panorama of the landscape, determines the distance between such object and
the observer.
3. In telemeters, in which the distance at which any given object is situated is
estimated by the micrometric measurement of its parallax through two telescopes
connected together, the arrangement for the simultaneous binocular viewing of the
object of which the distance is to be determined and of the sighting-marks of the
two telescopes so that the stereoscopic image of such marks may be compared with
the stereoscopic image of the object viewed, as regards their position at a greater
or less distance or depth.
Dated this 11th dor of Santambor 1902
ALLISON BROS.,
Agents for the Applicant..