Optical observation instrument with fiber optic image stabilizer

An optical observation instrument including on the one hand a mounting in which are mounted a convergent objective lens and a convergent eyepiece and on the other hand a disc formed of optical fibers arranged so as to reverse the image given by the objective lens and connected to the mounting by way of an articulation and held in a stable position, the front face of this disc being substantially at the focus of this objective lens.

SUMMARY OF THE INVENTION 
The present invention relates to an optical observation instrument which 
gives of a remote object an upright and stable image in spite of the 
disturbing movements which it undergoes. 
Observation carried out by means of an instrument having powerful 
enlargement is disturbed by the movements which this instrument undergoes. 
These movements may come from vibrations of mechanical origin when the 
instrument is mounted on a land, sea or air vehicle. These movements may 
also come from the observer's own movements if the latter is holding the 
instrument in the hand. 
A system for stabilization of observation comprises an optical system which 
deflects the light beams and is connected to a control system which 
remains relatively motionless in space either because of its own inertia 
or because of a gyroscopic effect. The beam emerging from this deflecting 
optical system remains motionless with respect to the eyepiece. The 
incident beam shifts with respect to the eyepiece but the deflecting 
optical system is displaced by the control system so as to compensate for 
the displacement of the eyepiece. The deflecting optical system is 
arranged at a suitable point on the optical path. 
Instruments exist in which in front of the eyepiece an optical system is 
located which is subordinated to a system of control for deflecting the 
light beams so as to keep them fixed with respect to the eyepiece. This 
optical system is in certain cases formed by a mirror which can pivot 
about an articulation. The angular position of the mirror is determined by 
a gyroscope which provides a reference direction, the connection between 
the mirror and the gyroscope being ensured by a system of levers which 
transmit the angles with a ratio of 1/2. These instruments are relatively 
complicated. The optical system arranged in front of the eyepiece may in 
certain cases be formed by a system of prisms having variable angles. 
Other instruments exist in which the optical system which deflects the 
light beams forms part of the optical system for observation. As 
previously, the deflecting optical system is manipulated so as to maintain 
the stability of the image. The deflecting optical system stabilized in 
space may be a lens movable perpendicularly to the optical axis. The 
deflecting optical system may be formed by a system of mirrors subject to 
a pendular device. The instruments of this category are compact and 
simple. Hence they are cheap and light and consequently portable by hand. 
The corrections which they can cause are, however, limited because of 
optical defects (geometrical aberrations or chromatism or lack of sharp 
focus) which increase with the movement of the deflecting optical system. 
The instrument in accordance with the invention ensures erecting of the 
image given by the objective and provides a stable image. This stability 
is obtained without secondary optical defects. It is simply achieved and 
the instrument is compact. 
The instrument in accordance with the invention includes on the one hand a 
mounting in which are mounted a convergent objective lens and a convergent 
eyepiece and on the other hand an optical member which is connected to the 
mounting by way of an articulation and is held in a stable position and it 
is characterized by the fact that this optical member consists of a disc 
formed of optical fibers arranged so as to reverse the image given by the 
objective and the front face of which is substantially at the focus of 
this objective. 
In accordance with another characteristic of the invention the articulation 
of the disc is about a point and the disc has a front face and a rear face 
which are spherical and centered upon the center of this articulation. 
In accordance with another characteristic of the invention, the center of 
articulation is located in front of the disc at a distance substantially 
equal to half the difference between the focal length of the objective and 
the thickness of this disc. 
The invention will now be described in greater detail by referring to 
embodiments given by way of examples and represented by the attached 
drawings.

DETAILED DESCRIPTION 
The instruments represented in FIGS. 1 and 2 comprise a convergent 
objective lens 1 and a convergent eyepiece 3. This objective lens and this 
eyepiece are mounted in a mounting 4. The optical axis 7 passes through 
the optical centers of the objective lens and the eyepiece. The eyepiece 3 
is mounted in a tube 41 which can slide along the optical axis. This 
eyepiece might be replaced by a binocular. 
An optical member 2 is arranged between the objective lens and the 
eyepiece. This optical member consists of an image transmission disc, 
known in itself. This disc is composed of optical fibers and forms a front 
face 21 facing the objective lens and the incident light and a rear face 
22 facing the eyepiece 3. The disc consists of a large number of optical 
fibers of small dimensions consisting each of a core of high refractive 
index surrounded by a sheath of lower refractive index. These fibers are 
combined so as to form a compact assembly. Each optical fiber has one end 
terminating at the front face 21 and one end terminating at the rear face 
22, the light being transmitted from the face 21 towards the face 22. The 
fibers are spiralled so that each fiber has one of its ends substantially 
symmetrical with the other end with respect to the center C of the disc. 
The disc provides on the rear face 22 an image reversed with respect to 
the incident image arriving on the front input face 21. The disc 2 is 
mounted so that the image plane of the objective lens coincides 
substantially with the input face 21 or else so that this face is 
substantially at the image focus of this objective lens. The objective 
lens 1 forms of a remote object a real image which is reversed and located 
in its image focal plane and on the input face 21 of the optical disc. The 
disc yields from this reversed image an upright image. This image is 
observed through the eyepiece 3 which acts as a magnifying glass and 
yields an enlarged upright virtual image. Fine adjustment is effected by 
movement of the eyepiece 3. It will of course be advantageous if the rear 
face 22 of the disc coincides substantially with the object focal plane of 
the eyepiece, the instrument then being afocal. 
The disc 2 is joined to the mounting by way of an articulation which gives 
it two degrees of freedom while holding it substantially fixed along the 
optical axis 7. The disc can pivot with respect to the mounting about the 
point 6 located on the optical axis of the instrument between the front 
face of this disc and the objective lens. This articulation is preferably 
an articulation of the gimbal type. For this purpose the bearer frame 51 
integral with the disc is joined by an articulation on the axis 61 to a 
frame 63 which is in turn joined by an articulation on the axis 62 to the 
mounting 4, the axis 62 being perpendicular to the axis 61. 
The mass of the disc 2 is balanced with respect to the point of 
articulation 6 by means of a balance mass 52. The disc can thus remain in 
a fixed position. 
The axis passing through the center C of the disc and the center of 
articulation 6 is fixed in Galilean space by suitable means in spite of 
the movement of the instrument. 
In the embodiment as FIG. 1, the immobilization of the disc is ensured by 
the inertia of the mass of the disc and of the adjoining members. Friction 
due to the articulation must be low. 
In the embodiment as FIG. 2, the immobilization is ensured by a gyroscope 8 
mounted to be directly integral with the bearer frame 51. The image given 
by the objective lens is reflected by mirrors 91 and 92 integral with the 
mounting of the objective lens and located between the disc and the 
gyroscope. 
The front face 21 and the rear face 22 of the disc are spherical faces 
centered upon the center 6 of the articulation which is located in front 
of this face 21. 
Furthermore the objective lens exhibits a field curvature having 
substantially the same radius as that of the front face 21 of the disc. 
This curvature of course turns its concavity like the face 21 towards the 
front, that is to say, towards the incident light. The eyepiece exhibits a 
field curvature having substantially the same radius as that of the rear 
face 22 of the disc. This curvature of course turns its concavity towards 
the front, that is to say, towards the incident light. 
The center 6 of the articulation is located in front of the disc at a 
distance R which corresponds with the radius of the face 21 and which is 
substantially equal to half the difference between the focal length F of 
the objective and the central thickness E of this disc. F, R and E are 
hence connected by the relationship R=1/2(F-E). 
The operation of the instrument will now be explained. Let us suppose that 
the whole of the telescope (including the observer) turns about the point 
6, the axis of the optical disc remaining fixed. The axis of the telescope 
turns by an angle .alpha. and comes into the position 7'. 
The axis of the optical disc is maintained along the initial axis 7. The 
image I of a distant point--originally located on the optical axis--comes 
to I', at a distance h from the old optical axis such that h=(F-R) tan 
.alpha.. The image point I corresponds at the output from the optical disc 
with the image point A located on the axis 7. The image point I' 
corresponds at the output from the optical disc with the image point A'. 
This point A' is located at a distance h from the axis 7 and from the 
point A because the point A' is substantially symmetrical with I' with 
respect to the center of the optical disc. The point of intersection of 
the axis 7' with the output face of the disc is located with respect to 
the axis 7 at a distance (R+E) tan .alpha.. Now, as E is connected with F 
and R by the relationship E=F-2R, the distance of this point of 
intersection with respect to 7 will be (F-R) tan .alpha.. This point of 
intersection will be located at the same distance from the axis 7 as the 
image A' which is tantamount to saying that the image A' will be on the 
axis 7'. The image originally located on the optical axis 7 hence appears 
to the observer to be located on the new optical axis 7'. Hence the image 
remains stable. 
Of course without departing from the scope of the invention variants and 
improvements in detail may be conceived of and the use of equivalent means 
be envisaged.