Improvements in Binoculars, Telescopes, and other Optical Instru- ments in which it is desired to Obtain a Rectified Image.
Year: 1898

page_text: Date of Application, 28th Apr., 1898
Complete Specification Left, 30th Jan., 1899-Accepted, 4th Mar., 1899
Improvements in Binoculars, Telescopes, and other Optical Instru-
ments in which it is desired to Obtain a Rectified Image.
I, HENRI LOUIS HUET, of 114, Rue du Temple, Paris, France, Optician, do hereby
declare the nature of this invention to be as follows:
-
This invention relates to a tetrahedron or pyramidal block of optical glass where-
by images viewed therethrough are reversed and which is applicable to all kinds
of optical instruments and particularly to monocular and binocular telescopes
whereby the field is much more luminous and defined than those with prisms
heretofore used, by reason of the fact that the reversal of the image enables an
astronomical eyepiece to be substituted for a terrestrial eyepiece. It is to be
understood that the word "glass" is intended to include all kinds of transparent
materials used in optical instruments.
My invention will be described with reference to the accompanying drawings in
which Figure 1 shews a vertical and a horizontal projection of the tetrahedron.
Figure 2 shews similar projections of two tetrahedrons combined. Figure 3 shews
a similar view of two tetrahedrons combined in a different position to those of
Figure 2. Figure 4 shews a face view partly in section of a binocular glass hav-
ing two tetrahedrons arranged according to my invention. Figure 5 is an objective
end view of the binocular, one side of the casing being in section. Figure 6 is an
evepiece end view of the binocular, one half of the case being in section on line 1-2
Figure 4. Figure 7 is a side view of one half of the binocular with its cover
removed. Figure 8 is a plan view of the removable cover separately. Figure 9
represents an elevation, plan, and end view of one of the tetrahedrons, and Figure 10
shews how it differs in form from the tetrahedron represented in the diagrams
Figures 1, 2 and 3. The same letters denote like parts in all the figures.
Referring to Figure 1 of the drawings the glass block is constructed in the fol-
lowing manner:-
LT being the ground line, a rectangular isosceles triangle represented by MNS,
MNS and situated in a plane towards the front constitutes one of the faces:
along the sides S M. S¹ M¹ on the one hand and S N, S¹ N¹ on the other extend
two planes S P M, S P¹ M¹ and S P N. S¹ P¹ N¹ each making an angle of 45°
with the face S M N. S¹ M¹ N¹ and situated on the same side of said face: these
two planes will form two other faces and the horizontal plane the fourth face of a
tetrahedron represented in horizontal projection by S M N P and in vertical
projection by S¹ M¹NI P¹.
This solid being made of flint or other glass or other refracting substance, if we
consider in the first place the passage through such a block of a ray (0.0. 01)
perpendicular to the vertical plane and consequently to the face S M. N. SI MINI
it will be seen that this rav making an angle of 45° with the plane S M P will
he reflected on said plane in a direction perpendicular to its original direction.
Consequently after this reflection the ray will be in the front plane 001. Its

page_text: horizontal projection will therefore be 0 0¹ and its vertical projection the per-
pendicular a ob₁ to the vertical projections S₁ M¹ of the arris S M. The ray is then
reflected upon the face M N P which is in the horizontal plane and this reflection
will again be at a right angle and it will be projected of true dimensions vertically
since it has been seen that the ray was in a front plane and that the same is the case
for the reflected ray. Owing to the symmetrical arrangement the same effects are
produced on the face S₁ P₁ N', S P N as on the face SM P, S M P and the
ray will pass out perpendicularly to the vertical plane, that is to say parallel to
its direction before entering the glass block.
If now we consider two planes perpendicular to each other and to the vertical
plane and directed the one parallel and the other perpendicular to S₁ M¹ the con-
struction shews that after being reflected successively upon the face S MP, SM P¹,
then upon face M N P and lastly upon the face SP N, S P N¹, these planes are
still on their exit from the block perpendicular to each other and to the vertical
plane and that the direction of each of them on exit is perpendicular to the direc-
tion they had on entering.
1
It follows that if an object is represented by a b c d its image thrice reflected
on the three faces of the solid S M P, M N P, and SNP will be presented
as a b₁₁ c¹ d, that is to say so orientated that the object will appear to have
been rotated 90° about an axis perpendicular to its plane. If now in front of a
solid of this kind, be placed a second one as represented in Figures 2 and 3 the
image will naturally appear to have effected a second rotation of 90°, and if this
rotation be effected in the same direction as the first the two rotations will he
cumulative and the final effect of the six reflections effected by the two pyramids
will be to produce an image representing the object after a rotation of 180°. The
complete reversal of the image is thus obtained. In order that the two rotations
of 90° produced respectively by each of the tetrahedrons should be cumulative
so as to produce the complete reversal of the image, the two tetrahedrons must
be arranged as follows:-Supposing an observer to be placed in a line with S P, S¹ P
the head towards the apex S and looking towards the entering face S M N, let
the faces S M P, SNP, which are respectively to his left and right be styled left
and right faces. This definition being adopted it is necessary and sufficient in
order that the two rotations shall be cumulative that the entry of the light into
one or other tetrahedron shall be effected at faces of contrary name. Thus in
Figures 2 and 3 it will be seen that the entry of the light into the first tetrahedron
is effected at the left face and into the second tetrahedron at the right face.
I would here remark that it is not important that the two solids should have a
fixed orientation relatively to one another since the rectification is the result of
two rotations of 90° which each will always produce, whatever may be its position
with regard to the luminous rays.
2
In Figure 2 I have represented the path of the rays in the two solids when
the bases M, N, P₁, M, N, P, are parallel and horizontal, and in Figure 3. the path
of the same rays when the said bases are perpendicular to each other. In each
case it will be seen that the resulting image is absolutely orientated in the same
manner and in reality the same orientation of the image could be obtained by
inclining the two tetrahedrons relatively to each other at any angle provided that
their faces S, M, N₁, S, M, N₁ remain parallel to each other.
The stability of the orientation of the image and its absolute independence of
the respective orientations of the two tetrahedral elements are characteristic pro-
perties of the system, which are very important in practice as regards the facility. of
construction and regulation of optical instruments. In combinations of prisms for
rectifying the image hitherto known, such as those of Dowe, Porro, etc., the total
reversal being the result of two partial reversals in two directions perpendicular to
each other, effected separately by each of the prisms of the systems, it follows that
it is necessary that these two elements be placed exactly perpendicular to each
other in order to obtain a complete reversal. In the present case, on the contrary,
as has been before shewn, the two tetrahedrons may be orientated as may be de-

page_text: sired with great advantage as regards the form of the instrument. If in par-
ticular the position of the prisms represented in Figure 2 be chosen, that is to
say one in which the bases M, N, P, and M, N, P₂ are parallel, the instrument can
be made of flattened form which is particularly advantageous for binocular glasses
to be carried in the pocket.
The pencil of rays utilized in optical instruments being generally of circular
form, it is evident that the trihedral angles will not generally be utilized and
that the tetrahedron might be truncated. As ordinarily employed it would in
reality have the form represented in Figures 9 and 10 in which the trihedral angles
are all removed. If O (Figure 10) represents the area utilized for the entry of the
pencil of rays, O₁ will be that utilized for its exit.
This system of tetrahedrons may be applied in all cases in which it is required
to rectify reversed images and consequently to telescopes, binoculars for direct
vision, or photographic instruments, or to microscopes, etc. When applied to
binoculars it is necessary to place the object glasses out of the lines of collimation
of the eyepieces on account of the effects inherently produced by the system. The
displacement of the axis imposed by the optical combination itself, necessarily leads
to an augmentation of the relief or stereoscopic effect inherent to binocular vision,
this augmentation resulting in this case, according to well known principles
defined by Helmholtz, from the greater spacing of the object glasses as compared
with that of the eyepieces.
For telescopes and binoculars in order to obtain upright images orientated
similarly to the objects themselves, it is only necessary to combine two of these
tetrahedrons with the ordinary optical elements of astronomical telescopes, i.c.
positive or negative object glasses and eyepieces. It is, moreover, evident that
the rectifying arrangement may be placed in any way relatively to the magning
element but the preferred mode consists in placing it between the object glass and
the eyepiece as shewn in Figure 4. The optical axis being returned upon itself
three times in parallel directions results in a considerable reduction of the length
of the instrument. The binocular may be constructed in any suitable manner as
regards the mounting and assemblage of the different parts but it is preferred
to employ the arrangement illustrated in Figures 4, 5, 6, 7, and 8, in which a b
are the two tetrahedrons constituting the essential part of my invention. These
optical combinations are mounted in a pair of body portions constructed of flat
cases c closed by sliding covers d (Figure 8) of which the two sides slide in
grooves (Figure 7). f f are the object glasses, gg are the eyepieces, and h
is a diaphragm. The two body portions are connected by telescopically adjustable
cross bars adjusted by means of pinions, rods i¹ carrying the eyepieces so as
to enable the observer to adjust the spacing of the eyepieces, by means of the
milled head, to suit his eyes; the focussing is effected by means of a second
milled head m. A binocular glass thus constructed is very convenient to handle
and the optical combinations contained are well protected from dust although
readily accessible by removing the covers d.
The following are further advantages:
(1) Facility of mounting and regulating as the reversed image is perfectly
stable and independent of the mutual orientation of the two elements of the
combination;
(2) The flattened form obtained by placing the tetrahedrons parallel instead of
being necessarily perpendicular to each other as in the Porro and other similar
arrangements;
(3) Greatly increased stereoscopic effect owing to the displacement of the axis
resulting from two successive cumulative displacements in the same plane whereas
the two displacements in the Porro combination are in two perpendicular planes and
the total displacement is only equal at the maximum to the length of the hypotenuse
of a right-angled triangle having for sides the lengths of the two partial displace-
ments;
(4) Considerable reduction in the length of the instrument.

page_text: It is to be understood that the details of the binocular described are only given
by way of example and may be varied without in any way affecting the invention
which as before explained is applicable not only to binocular glasses but also to all
kinds of telescopes and optical instruments such as microscopes and others in
which it is desired to rectify the image.
1000
Improvements in Binoculars, Telescopes, and other Optical Instru-
ments in which it is desired to Obtain a Rectified Image.
I, HENRI LOUIS HUET, of 114, Rue du Temple, l'aris, France, Optician, do hereby
declare the nature of this invention and in what manner the same is to be per-
formed, to be particularly described and ascertained in and by the following state-
ment:-
This invention relates to a tetrahedron or pyramidal block of optical glass where-
by images viewed therethrough are reversed and which is applicable to all kinds
of optical instruments and particularly to monocular and binocular telescopes
whereby the field is much more luminous and defined than those with prisms
heretofore used, by reason of the fact that the reversal of the image enables an
astronomical eyepiece to be substituted for a terrestrial eyepiece. It is to be
understood that the word "glass" is intended to include all kinds of transparent
materials used in optical instruments.
My invention will be described with reference to the drawings accompanying
my Provisional Specification in which Figure 1 shews a vertical and a horizontal
projection of the tetrahedron. Figure 2 shews similar projections of two tetra-
hedrons combined. Figure 3 shews a similar view of two tetrahedrons combined in
a different position to those of Figure 2. Figure 4 shews a face view partly in
section of a binocular glass having two tetrahedrons arranged according to my
invention. Figure 5 is an objective end view of the binocular, one side of the
casing being in section. Figure 6 is an eyepiece end view of the binocular, one
half of the case being in section on line 1-2 Figure 4. Figure 7 is a side view of
one half of the binocular with its cover removed. Figure 8 is a plan view of the
removable cover separately. Figure 9 represents an elevation, plan, and end-view
of one of the tetrahedrons, and Figure 10 shews how it differs in form from the
tetrahedron represented in the diagrams Figures 1, 2 and 3. The same letters of
reference denote like parts in all the figures.
Reterring to Figure 1 of the drawings the glass block is constructed in the
following manner :-
LT being the ground line, a rectangular isosceles triangle represented by MNS,
MNS and situated in a plane towards the front constitutes one of the faces;
along the sides S M, S¹ M¹ on the one hand and S N, S¹ N¹ on the other extend
two planes S P M, S P¹ M and S P N, S' P¹ N¹ each making an angle of 45°
with the face S M N, S¹ M' N¹ and situated on the same side of said face; these
two planes will form two other faces and the horizontal plane the fourth face of a
tetrahedron represented in horizontal projection by S M N P and in vertical pro-
jection by S¹ M¹ N¹ P¹.
This solid being made of flint or other glass or other refracting material, if we
consider in the first place the passage through such a block of a ray (00, 0¹)

page_text: perpendicular to the vertical plane and consequently to the face S M N, SM N',
it will be seen that this ray making an angle of 45° with the plane S M P will
be reflected on said plane in a direction perpendicular to its original direction.
Consequently after this reflection the ray will be in the front plane 0 0¹. Its
horizontal projection will therefore be 0 0¹ and its vertical projection the per-
pendicular a¹ o 6¹ to the vertical projection S¹ M³ of the arris S M. The ray is then
reflected upon the face MNP which is in the horizontal plane and this reflection will
again be at a right angle and will be projected of true dimensions vertically since it
has been seen that the ray was in a front plane and that the same is the case
for the reflected ray. Owing to the symmetrical arrangement the same effects are
produced on the face S¹ P¹ N¹, S P N as on the face S¹ M¹ P, S M P and the.
ray will pass out perpendicularly to the vertical plane, that is to say parallel to
the direction which it had before entering the glass block.
If now we consider two planes perpendicular to each other and to the vertical
plane and directed the one parallel and the other perpendicular to S¹ M¹ the con-
struction shews that after being reflected successively upon the face S M P, S¹ M¹ P¹,
then upon face M N P and lastly upon the face SP N, S¹ P¹ N¹, these planes are
still on their exit from the block perpendicular to each other and to the vertical
plane and that the direction of each of them on exit is perpendicular to the direc-
tion which it had on entering.
It follows that if an object is represented by a¹ b₁ e¹ d¹ its image thrice reflected
on the three faces of the solid S M P, M N P, and S N P will be presented
as a b c d that is to say so orientated that the object will appear to have
been rotated 90° about an axis perpendicular to its plane. If now in front of a
solid of this kind, be placed a second one as represented in Figures 2 and 3 the
image will naturally appear to have effected a second rotation of 90°, and if this
rotation be effected in the same direction as the first the two rotations will be
cumulative and the final effect of the six reflections effected by the two pyramids
will be to produce an image representing the object after a rotation of 180°. The
complete reversal of the image is thus obtained.
In order that the two rotations of 90° produced respectively by each of the
tetrahedrons should be cumulative so as to produce the complete reversal of the
image, the two tetrahedrons must be arranged as follows;-Supposing an observer
to be placed in a line with S P, S₁ P₁ the head towards the apex S and looking
towards the entering face S M N, let the faces S M P SNP, which are respectively
to his left and right be styled left and right faces. This definition being adopted
it is necessary and sufficient in order that the two rotations shall be cumulative that
the entry of the light into one or other tetrahedron shall be effected at faces of cou-
trary name. Thus in Figures 2 and 3 it will be seen that the entry of the light
into the first tetrahedron is effected at the left face and into the second tetrahedron
at the right face.
I would here remark that it is not important that the two solids should have a
fixed orientation relatively to one another since the rectification is the result of
two rotations of 90° which each will always produce, whatever may be its position
with regard to the luminous rays.
1
In Figure 2 I have represented the path of the rays in the two solids when
the bases M, N, P₁, M, N, P, are parallel and horizontal, and in Figure 3 the path
of the same rays when the said bases are perpendicular to each other. In each
case it will be seen that the resulting image is absolutely orientated in the same
manner and in reality the same orientation of the image could be obtained by
inclining the two tetrahedrons relatively to each other at any angle, provided that
heir faces S, M, N₁, S, M, N, remain parallel to each other.
The stability of the orientation of the image and its absolute independence of
the respective orientations of the two tetrahedral elements are characteristic pro-
perties of the system, which are very important in practice as regards the facility
of construction and regulation of optical instruments.
In combinations of prisms for rectifying the image hitherto known, such as those

page_text: of Dowe, Porro, te, the total reversal being the result of two partial reversals in
two directions perpendicular to each other, effected separately by each of the prisms
of the system, it follows that it is necessary that these two elements be placed
exactly perpendicular to each other in order to obtain a complete reversal. In
the present case, on the contrary, as has been before shewn, the two tetrahedrons
may be orientated as may be desired with great advantage as regards the form of
the instrument. If in particular the position of the prisms represented in Figure 2
be chosen, that is to say one in which the bases M, N, P, and M, N, P, are parallel,
the instrument can be made of flattened form which is particularly advantageous for
binocular glasses to be carried in the pocket.
The pencil of rays utilized in optical instruments being generally of circular
form, it is evident that the trihedral angles of the block will not generally be utilized
and that the tetrahedron might be truncated. As ordinarily employed it would be in
reality have the form. represented in Figures 9 and 10 in which the trihedral angles
are all removed. If 0 (Figure 10) represents the area utilized for the entry of the
pencil of rays, O₁ will be that utilized for its exit.
This system of tetrahedrons may be applied in all cases in which it is required
to rectify reversed images and consequently to telescopes, binoculars for direct
vision, or photographic instruments, or to microscopes, etc. When applied to
binoculars it is necessary to place the object glasses out of the lines of collimation
of the eyepieces on account of the effects inherently produced by the system. The
displacement of the axis imposed by the optical combination itself, necessarily leads
to an augmentation of the relief or stereoscopic effect inherent to binocular vision,
this augmentation resulting in this case, according to the well known principles
defined by Helmholtz, from the greater spacing of the object glasses as compared
with that of the eyepieces.
For telescopes and binoculars in order to obtain upright images orientated
similarly to the objects themselves, it is only necessary to combine two of these
tetrahedrons with the ordinary optical elements of astronomical telescopes, i.e.
positive or negative object glasses and eyepieces. It is, moreover, evident that
the rectifying arrangement may be placed in any way relatively to the magnifying
element but the preferred mode consists in placing it between the object glass and
the eyepiece as shewn in Figure 4. The optical axis being returned upon itself
three times in parallel directions, results in a considerable reduction of the length
of the instrument.
The binocular may be constructed in any suitable manner as regards the mount-
ing and assemblage of the different parts, but it is preferred to employ the arrange-
ment illustrated in Figures 4, 5, 6, 7 and 8, in which a bare the two tetrahedrons
constituting the essential part of my invention. These optical combinations are
mounted in a pair of body portions constructed of flat cases c closed by sliding
covers (Figure 8) of which the two sides slide in grooves e (Figure 7). ff are.
the object glasses, g g are the eyepieces, and h is a diaphragm. The two body
portions are connected by telescopic cross bars k k₁ adjusted by means of pinions,
rods carrying the eyepieces so as to enable the observer to adjust the spacing of
the eyepieces, by means of the milled head 1, to suit his eyes; the focusing is
effected by means of a second milled head m. A binocular glass thus constructed
is very convenient to handle and the optical combinations contained are well
protected from dust although readily accessible by removing the covers d.
The following are further advantages:-
(1) Facility of mounting and regulating as the reversed image is perfectly
stable and independent of the mutual orientation of the two elements of the
combination;
(2) The flattened form obtained by placing the tetrahedrons parallel instead of
being necessarily perpendicular to each other as in the Porro and other similar
arrangements;
(3) Greatly increased stereoscopic effect owing to the displacement of the axis re-
sulting from two successive cumulative displacements in the same plane whereas the

page_text: two displacements in the Porro combinations are in two perpendicular planes and the
total displacement is only equal at the maximum to the length of the hypotenuse
of a right-angled triangle having for sides the lengths of the two partial displace-
ments;
(4) Considerable reduction in the length of the instrument.
It is to be understood that the details of the binocular described are only given
by way of example and may be varied without in any way affecting the invention
which as before explained is applicable not only to binocular glasses but also to all
kinds of telescopes and optical instruments such as microscopes and others in
which it is desired to rectify the image.
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
18:-
1. In an optical instrument the use of the system of tetrahedron or pyramidal
block such as herein described with reference to Figures 1, 2, 9 and 10 under
such conditions that the incident ray is doubled back in a direction parallel to
itself as described.
2. In an optical instrument the combination of two tetrahedrons or pyramidal
blocks such as herein described, the tetrahedrons being combined for use in such
manner that the complete reversal of the image is thereby effected, as described.
3. A binocular provided with the herein described optical combination of tetra-
hedrons substantially as described with reference to Figures 4 to 8 of the drawings.
Dated this 28th day of January 1899.
A. M. & WM. CLARK,
Chartered Patent Agents, 53, Chancery Lane, London.