SYSTEME OPTIQUE ALLONGE AVEC LENTILLES EN FORME DE BATONNETS

ELONGATED ROD LENS OPTICAL SYSTEM

Abrégé anglais

Abstract of the Disclosure
An optical system for conveying an optical image
having two first biconvex rod lenses arranged end to end on a
common optical axis in spaced relationship, and between said
first rod lenses but not in contact with them a pair of second
rod lenses also arranged end to end on the same axis, the
adjacent ends of the second rod lenses being concave and de-
fining a biconvex cavity which can contain a fluid whereby a
fluid lens is formed, the system being substantially sym-
metrical about a median plane through a biconvex cavity and the
modulus of the reciprocal of the radius of curvature of the
fluid lens being less than or equal to the modulus of the
difference between the reciprocal of the radius of curvature
of the convex surfaces of the first rod lenses adjacent to the
second rod lenses and the reciprocal of the radius of curvature
of the convex surfaces of the second rod lenses adjacent to the
first rod lenses.

Revendications

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. An optical system for conveying an optical image
having two first biconvex rod lenses arranged end to end on a
common optical axis in spaced relationship, and between said
first rod lenses but not in contact with them a pair of second
rod lenses also arranged end to end on the same axis, the
adjacent ends of the second rod lenses being concave and
defining a biconvex cavity which contains a fluid whereby a
fluid lens is formed, the system being substantially symmet-
rical about a median plane through the biconvex cavity and
the modulus of the reciprocal of the radius of curvature of
each surface of the fluid lens being less than or equal to
the modulus of the difference between the reciprocal of the
radius of curvature of each of the convex surfaces of the
first rod lenses adjacent to the second rod lenses and the
reciprocal of the radius of curvature of each of the convex
surfaces of the second rod lenses adjacent to the first rod
lenses.
2. An optical system according to claim 1 in which
the axial length of each of the pair of second rod lenses is
greater than 0,8 times the numerical value of the radius of
curvature of each surface of the fluid lens.
3. An optical system according to claim 1 in which
meniscus lens elements are arranged one in each space between
first and second rod lenses.
4. An optical system according to claim 3 in which
at least one of said meniscus lens elements is attached to an
end of one of said rod lenses, the refractive index of the
meniscus lens element being higher than that of the rod lens to

which it is attached.
5. An optical system according to claim 1 in which
the refractive index of the second rod lenses is not greater
than 1.55.
6. An optical system according to claim 1 in which
the fluid of the fluid lens is air.
7. An optical system according to claim 1 in which
the fluid of the fluid lens is water.
8. An optical system according to claim 1 in which
any spaces axially between the first and second rod lens is
filled with air.
9. An optical system according to claim 7 in which
any spaces axially between the first and second rod lenses
are filled with water.
10. An optical system, according to claim 1, for
use in an endoscope.

Description

~(~S843f~
This invention relates to optical systems and relates
particularly to optical systems for relaying an optical image
along a long, relatively narrow tube-like opticaliinstrument,
such as an endoscope.
When an optical image is relayed by a series of posi
tive lenses, errors of field curvature and astigmatism may occur.
One method of relaying an optical image along a tube is disclosed
in UK Patent No. 954,629 in which at least two rod lenses are
used to convey an image. Such a method can be used in an instru-
ment to view a useful field withaacceptably small astigmatismand image curvature, and is particularly described in the speci-
fication with referencs to a cystoscope. If this system is used
for a laparoscope, in which wider angles of view and higher aper-
tures are employed the aberrations may not be corrected adequately,
especially if a photographic record is required.
According to the invention, an optical system for
conveying an optical image comprises two first biconvex rod lenses
arranged end to end on a common optical axis in spaced relation-
ship and between said first rod lenses but not in contact with
them a pair of second rod lenses also arranged end to end on the
same axis, the adjacent ends of the second rod lenses being
concave and defining a biconvex cavity which can contain a 1uid
whereby a fluid lens is formed, the system being substantially
; symmetrical about a median plane through the biconvex cavity and
the modulus of the reciprocal of the radius of curvature of each
surface of the fluid lens being less than or equal to the modulus
of the difference between the reciprocal of the radius of curva ;-
ture of each of the convex surfaces of the first rod lenses
adjace~t~to the second rod lenses and the reciprocal of the
radius of curvature of each of the convex surfaces of the second
rod lenses adjacent to the first rod lemses.

~1~5~3436
Preferably the axial length of each of the second pair
of rod lenses is greater than 0.8 times the numerical value of
the radius of curvature of each surface of the fluid lens.
To provide further correction of any optical errors,
and more particularly the chromatic aberration, meniscus lens
elements may be arranged one in each space between the first and
second rod lenses and each meniscus lens element may be attached
either to an end of a first rod lens or to an end of a second
lens, the meniscus lens elements haviny a higher refractive
index than the lenses to which they are attached. The
refractive index of the second rod lenses should be not
greater than 1.55.
The fluid comprising the fluid lens may, for example,
be air or water and the fluid may also fill any spaces axially
between the first and second rod lenses.
The curvature of the fluid lens in relation to the
curvature of the adjacent convex surfaces of the first and second
rod lenses can be expressed in mathematical terms as follows:
/ C5 / -~~~~~~ / C3 - C4 /
C3 being the curvature ( = 1 ) of the convex
radius
surface of the first rod lens adjacent to the second rod lens, C4
being curvature of the convex surface of the second rod lens
adjacent the first rod lens and C5 being the curvature of each
surface of the fluid lens.
The customary cartesian convention for the sign of
curvature of a surface is that the sign is positive if the centre
of curvature is to the right of the surface and negative if the
centre of curvature is to the left of the surface.
One or more systems according to the invention may be
used to relay an image along a tube-like optical instrument such
as an endoscope.
.~ . , -. ~ . .

~058a~36
The invention ~ill ngw be described by way of example
with reference to the drawings filed herewith in which:
Figure 1 illustrates in section one form of optical
system according to the invention.
Figure 2 illustrates in section an alternative form of
optical system~ and figure 3 illustrates diagrammatically use of
the system shown in Figure 1 in an endoscope.
In figure 1, two first biconvex rod lenses 10, 11 each
have attached at one end a negative meniscus element 12, 13
respectively. Between lenses 10, 11 are two second rod lenses
14, 15 the adjacent faces of which 16, 17 are partially concave
and which define a biconvex air lens 18. The meniscus elements
12, 13 are separate axially from the second rod lenses, 14, 15
by air gaps 19, 20.
The full specification of the optical system shown in
Figure 1 is given in Table I below:
'

1~5843~i
Table I
. . .
Radius Axlal thick- Reiractive Dlspersion
mm ness mm index
.... .~ .. _ _ _
12.7~2
Rod lens 10 28,179 1.5168 64~17
and meniscus - 5.36
element 12 1.248 1.68893 31.18
- 9.528
. _ _ _ _ .. __ ,. .. __
Air gap 19 0.312 ,_ 0
Rod lens 145.870
4.075 4.327 1.5168 64.17
~ __._ - _
Air lens 18 0.512 1 0
. , _ , ~... , ___
Rod lens 15- 4.075
- 5.~70 4.327 1.5168 64.17
~ __ _ _ . _
Air Gap 20 0.312 1 0
_ 9.5-2~-- _ _ __
Meniscus 1.248 1~68893 31.18
element 135.369
and rod lens 1] 28.179 1.5168 64.17
-12.752 _ _ _ _ _
_

105~436
In Figure 2, two first rod lenses 22, 23 are arranged
with two second rod lenses 24, 25 between them, the lenses 24,
25 each havin~ a convex surface, which surfaces define a bi-
convex air lens 26. To the lenses 24, 25 are attached meniscus
elements 27, 28 respectively.
In Figure 3 an endoscope 29 comprises a tube contain-
ing at one end a negative lens 31 and biconvex lenses 32, 33
forming an objective lens system. The endoscope contains typical-
ly five of the optical systems shown in Figure 1 or Figure 2
although only two are shown ir detail, as references 10 to 15,
and also contains eyepiece lenses 34, 35. The lenses are spaced
in the tube by annular spacers (not shown). Such an endoscope
may have an angle of field equal to 70.
In general an optical system according to the invention
is suitable for use when an image is to be relayed along a tube
of diameter much less than its length. In a typical case the
diameter would be less than lOmm, and the length would be substan-
tially greater than the diameter, for example, by a factor of ten
or more. The system is applicable to any endoscopes, such as,
for example, cystoscopes and bronchoscopes.
. -~