Improvements in Binocular Telescopes.
Year: 1894

page_text: Improvements in Binocular Telescopes.
I, JAMES YATE JOHNSON of 47 Lincoln's Inn Fields in the County of Middlesex
Gentleman do hereby declare the nature of this invention (which has been com-
municated to me from abroad by the Firm of Carl Zeiss of Carl-Zeiss Strasse Jena in
the Grand Duchy of Saxe Weimar in the Empire of Germany) 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 this invention is to enable two telescopes to be combined together
to form a binocular glass in a more advantageous or convenient form than it is
possible to obtain with two tubes arranged side by side and parallel with one
another in the manner heretofore practised.
According to this invention the direction of sight in each of the telescopes is at
right angles with the axis of the tube this result being obtained by twice deflecting
the rays
of light at an angle of 90 degrees, by means of two reflecting prisms, one
of which is combined with the object glass, the other having its principal or
diagonal side parallel with that of the first and being combined with the eye piece
of the telescope. Two such telescopes thus constructed are connected together at
the ends provided with the eye pieces by a hinge or joint, or combination of joints,
enabling the two telescopes to be rotated or turned relatively to one another, after
the mauner of the legs of a pair of compasses in a plane at right angles to the
direction of sight.
:
And in order that this invention may be fully understood, I shall now proceed
more particularly to describe the same and for that purpose I refer to the
accompanying drawings.
Figures 1 and 2 represent in views at right angles to each other, a portion of a
binocular telescope constructed according to this invention.
This instrument is constructed with two telescopes A and B, provided with object
glasses L with apertures at right angles to the length of the tubes. The object
glass of the telescope A. is omitted from the drawing, it being arranged in precisely
the same way as herein after described with regard to that of the telescope B. In
front of the object glass L of each telescope there is provided a right angled
isosceles reflecting prism M (which may be cemented to the object glass L so as to
form one piece therewith) whereby the optical axis at the objective end of the tube
is deflected at an angle of 90 degrees. A second similar prism N, whose principal
or diagonal side is parallel with that of the prism M is inserted near to, and in
front of, the eye piece O of each telescope, that is to say, between the eye piece
and a combination of lenses R, provided for the purpose of erecting the inverted
image, so that by again deflecting the optical axis at an angle of 90 degrees,
the said axis at the ocular end of the tube is directed parallel with that of the
entering rays, at the objective end of the tube, but at right angles with the axis
of the tube itself.
The prism N in both telescopes is preferably contained in a rectangular metal
case P, attached to the ends of the tubes A and B to which cases the eye
pieces O are respectively attached.
By means of the said cases P the two tubes are connected with the limbs of a
joint or hinge G, in such a manner that the axes of the two eye pieces O are
exactly parallel with the axis of rotation of the joint so that both tubes can be
moved similarly to the legs of a pair of compasses in a plane at right angles to the
axis of the joint and to the direction of sight and can be adjusted at different angles

page_text: of divergence as represented by the dotted lines at A' and Aº in Figure 2 for
example.
The position of the pin of the joint relatively to the axes of the eye pieces of
both telescopes is so regulated that firstly both tubes can be shut or folded together
so as to be parallel, or nearly so, with one another, the tube A being placed by the
side of the tube B, as represented by the dotted lines at A' Figure 2. and secondly
that by opening or separating the two limbs or members of the instrument they can
be placed in either of two positions in which the distance between the axes of the
eye pieces can be adjusted from about 58 to 72 millimetres, so as to suit the
.distance between the eyes of any observer in either of the two positions, namely,
firstly when the two tubes are opened out or caused to diverge at an angle of
about 30 degrees (as represented in dotted lines A° Figure 2, corresponding with
the medium distance of 65 millimetres between the eyes) and secondly when the
two tubes are placed in a straight or approximately straight line with one another
as represented by full lines in the drawing.
This improved construction of binocular telescopes compared with the instruments
heretofore employed is productive of the following advantages, namely:
-
(a) The binocular telescope is much more easily handled, this being of special
importance when the instrument is of large size. This applies to both positions of
the tubes (A and A° Figure 2) as in both cases the centre of gravity of the
instrument remains quite near to the head of the person using it. The use is the
most convenient in the position of small divergence of the tube (A° Figure 2)
because in this case the tubes when turned downwards by the observer form very
convenient handles by which it can be held up to the eyes.
(b) In the position of small divergence (A° Figure 2) the improved binocular
glass enables observations to be taken from behind a wall or rampart (even when
the latter projects above the head of the observer) by holding the tubes projecting
upwards. In this position the receiving aperture of the object glass is situated at
a height above the eyes of the observer equal to nearly the entire length of the
tubes.
(c) The adjustment in the position represented by full lines at A Figure 2. in
which the receiving apertures of the object glasses are separated by a distance
equal to about twice the length of the tube in the direction of a connecting line
drawn between the two eye pieces, affords a corresponding augmentation of the
depth of perspective. The arrangement of the binocular telescope as described
thus enables the principles of construction and action of the Helmholtz tele-stereo-
scope to be applied in a convenient form to a portable telescope.
Without prejudice to the advantages hereinbefore specified the arrangement of
the binocular glass illustrated in the drawing may be modified in various ways
without changing the principles of construction with regard to the arrangement of
the optical parts as well as with regard to the mechanical connection of the tubes.
With regard to the arrangement of the optical parts it is to be observed in the
first place that all kinds of telescopes presenting images in the erect or natural
position may be employed, comprising in addition to telescopes with terrestrial eye
pieces as in the example. illustrated, Galilean telescopes and telescopes in which
the erection of the image is effected by means of any suitable combination of prisms,
without the aid of the intermediate lens system usually provided with terrestrial
eye-pieces.
Apart from the different types of construction of the connected telescopes the
arrangement of the two deflecting prisms employed to produce the double deflection
of the optical axis may be modified in various ways provided that one deflection
takes place near the object glass whilst the other deflection (by which the optical
axis is caused to take a direction parallel with that of the axis of the receiving
aperture) takes place near the eye piece. Consequently the prism M in place of
being placed in front of the object glass L as represented in the drawing may with
equal advantage be situated behind the object glass and the prism N in place of
being close to the collecting lens of the eye piece O, may be placed farther from

page_text: this lens and nearer to the eye glass of the eye piece being arranged between the
collecting lens and the eyeglass or behind the latter on the outer side of the eye
glass according as it is desired to employ a longer or shorter mounting for the
eye-piece.
It is evident that the reflecting prisms employed in the arrangement hereinbefore
described may be replaced by plane mirrors inclined at an angle of 45 degrees with
the axes of the tubes, but this arrangement is not so advantageous.
With regard to the mechanical connection of the two telescopes by means of a
joint or hinge, the essential point is simply to enable the two tubes to move like
the legs of a pair of compasses in a plane at right angles to the axes of the eye
pieces, and whilst retaining the parallelism of the lines of sight to enable the
distance between the eyepieces to be accurately adjusted to the distance between
the eyes of the observer, and it is desirable that this should be arranged so that it
can be done in distances of at least one degree of divergence of the axes of the
tubes. It is of little importance that the two tubes be symmetrically arranged
relatively to the axis of rotation so as to be in all their positions invariably
symmetrical with the line connecting the two eye pieces (as represented in the
drawing) and the same remark applies to the connection of the joint by a single
pin. With equal advantage to a symmetrically arranged joint, a joint may be
employed whose axis is unsymmetrical relatively to the axes of the eye pieces of
the two telescopes and whose limbs are of unequal length and form correspondingly
unequal angles with the axes of the tubes. An arrangement of this description
may be employed for example in order that when the eye pieces are adjusted to the
medium distance between the eyes one tube may be in an approximately horizontal
position whilst the other tube is in a vertical position extending downwards so as
to form a convenient handle for supporting the instrument when in use. In like
manner it may be advantageous in some cases notwithstanding the greater difficulty
of the mechanical construction to employ in place of one hinge with a single pin, a
combination of joints with two or more parallel axes for the purpose of enabling
large telescopes to be folded up in the most compact form possible for travelling or
for the purpose of obtaining a greater variety of positions of the two tubes with a
distance between the eye pieces corresponding to the distance between the eyes
than it is possible to obtain with one single joint.
Having now particularly described and ascertained the nature of the said inven-
tion and in what manner the same is to be performed I declare that what I
claim is :-
1. In a binocular telescope constructed with two telescopes presenting images in
the erect or natural position and having the optical axes of the objective or object
glass apertures, and of the ocular or eye piece apertures parallel with one another
and at right angles to the optical axis of the tube of the telescope, a joint or joints
whose axis is or axes are parallel with the parts of the optical axes situated in the
direction of sight the said joint connecting together the two telescopes at the eye
piece ends and enabling the binocular telescope to be folded up and opened out in
the same way as the limbs of a pair of compasses substantially as hereinbefore
described with reference to the accompanying drawings.
2. The arrangement and combination of parts constituting the binocular
telescope, substantially as herein before described and illustrated in the accom-
panying drawings.
Dated this 17th day of March 1894.
JOHNSONS & WILLCOX,
Agents.