Relay variable power optical system and a microscope equipped with the optical system

The present invention provides a relay variable power optical system in a simple structure which is capable of suppressing a change of the position of the exit pupil on varying the power. To this end, the relay variable power optical system is provided with a front lens group G0 for condensing a light from a primary image, a variable power lens system (G1 to G3) for receiving the light from the front lens group G0, and performing zooming and a rear lens group G4 for forming the secondary image by condensing the light from the variable power lens system. When the zooming is performed from the high magnification end to the low magnification end, a distance between the first lens group G1 and the second lens group G2 and a distance between the second lens group G2 and the third lens group G3 are changed. The the second lens group G2 satisfies predetermined magnification conditions with respect to an axial ray from an axial object point of the primary image imaged on the secondary image and a chief ray from a position of an entrance pupil of the relay variable power optical system imaged at a position of the exit pupil.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a relay variable power optical system and 
a microscope equipped with the optical system, and particularly, to a 
relay variable power optical system for forming a secondary image based on 
the light from a primary image in the microscope. 
2. Related Background Art 
As a microscope apparatus or as an inspecting or a measuring apparatus 
using a microscope, an apparatus is conventionally known in which the 
light sent from the primary image by an objective lens is re-imaged as a 
secondary image onto a focal plane of an eyepiece lens, an image plane of 
a TV camera, or the like, through a relay optical system. 
If, for example, a relay system of an optical system such as a microscope 
is to be adapted as a zoom lens in a simple structure, it becomes 
difficult to maintain the relationship between an entrance pupil and an 
exit pupil of the relay optical system to be substantially constant while 
maintaining the positional relationship between the primary image and the 
secondary image. More specifically, when a specific lens within the relay 
optical system is positively moved along the direction of the optical axis 
in order to change an image magnification while maintaining the positional 
relationship between the primary image and the secondary image, the 
position of the exit pupil of the optical system is widely changed with 
the movement of this lens. For this reason, when the secondary image which 
is formed by the relay optical system is observed in an enlarged manner by 
use of an eyepiece lens or the like, the position of an eye point is 
changed following a change of the image magnification. As a result, a part 
of the observation light may be vignetted (or eclipsed) to deteriorate an 
observed image, or the positions of the eyes must be displaced whenever 
the image magnification is changed, whereby it becomes very troublesome to 
observe the image. 
When two dichroic mirrors or the like are provided between the relay 
optical system and the secondary image formed by the optical system so as 
to form three secondary images for respective wavelengths and the images 
are detected by use of a TV camera of a three-tube type which has three 
image elements provided at the respective positions of the secondary 
images, if an inclination or a telecentricity of a chief ray entering into 
the above-mentioned two dichroic mirrors is changed due to the movement of 
the exit pupil of the relay optical system, wavelength separation 
characteristics of the two dichroic mirrors are changed, and colors become 
unfavorably uneven around the image photoelectrically detected. 
SUMMARY OF THE INVENTION 
The present invention was conceived taking the problems mentioned above 
into consideration and an object of the invention is to provide a relay 
variable power optical system in a simple structure which is capable of 
suppressing a change of the position of the exit pupil caused by a 
zooming, and a microscope equipped with the optical system. 
In order to achieve the above object, there is provided, according to a 
first aspect of the present invention, a relay variable power optical 
system which forms a secondary image based on a light from a primary 
image, and which comprises: a front lens group which condenses the light 
from the primary image, a variable power lens system which zooms the 
secondary image upon receiving the light from the front lens group, and a 
rear lens group which forms the secondary image by condensing the light 
from the variable power lens system; 
wherein the variable power lens system has a first lens group having a 
positive refracting power, a second lens group having a negative 
refracting power, and a third lens group having a positive refracting 
power, in the named order from the primary image side; 
wherein a distance between the first lens group and the second lens group 
and a distance between the second lens group and the third lens group are 
changed when the zooming is performed from the high magnification end to 
the low magnification end; and 
further wherein, when an axial ray from an axial object point of the 
primary image is imaged on the secondary image through the relay variable 
power optical system, the magnification of the second lens group at the 
high magnification end with respect to the axial ray is .beta.2H and the 
magnification of the second lens group at the low magnification end with 
respect to the axial ray is .beta.2L and, when a chief ray from the 
position of the entrance pupil of the relay variable power optical system 
is imaged at the position of the exit pupil of the relay variable power 
optical system through the relay variable power optical system, the 
magnification of the second lens group at the high magnification end with 
respect to the chief ray is .beta.'2H and the magnification of the second 
lens group at the low magnification end with respect to the chief ray is 
.beta.'2L, the following conditions are satisfied: 
EQU -1&lt;.beta.2L and .beta.2H&lt;-1, 
and 
EQU 1&lt;.beta.'2L and .beta.'2H&lt;1. 
According to a preferred embodiment of the first aspect of the present 
invention, when a zoom ratio of the relay variable power optical system is 
Z, the following conditions are satisfied: 
EQU -1.25&lt;.beta.2L.multidot.Z.sup.1/2 &lt;-0.8, 
and 
EQU 0.8&lt;.beta.'2L.multidot..beta.'2H&lt;1.25. 
Also, according to a second aspect of the present invention, there is 
provided a microscope which comprises an objective optical system which 
condenses a light from an observed object to form a primary image of the 
observed object, a relay variable power optical system which forms a 
secondary image based on the light from the primary image formed by the 
objective optical system, and an observation unit which observes the 
secondary image, which microscope is characterized in that: 
the relay variable power optical system is provided with a front lens group 
which condenses the light from the primary image, a variable power lens 
system which zooms the secondary image upon receiving the light from the 
front lens group, and a rear lens group which forms the secondary image by 
condensing the light from the variable power lens system; 
the variable power lens system is provided with a first lens group having a 
positive refracting power, a second lens group having a negative 
refracting power, and a third lens group having a positive refracting 
power, in the named order from the primary image side; 
a distance between the first lens group and the second lens group and a 
distance between the second lens group and the third lens group are 
changed when the zooming is performed from the high magnification end to 
the low magnification end; and 
wherein, when an axial ray from an axial object point of the primary image 
is imaged on the secondary image through the relay variable power optical 
system, the magnification of the second lens group at the high 
magnification end with respect to the axial ray is .beta.2H and the 
magnification of the second lens group at the low magnification end with 
respect to the axial ray is .beta.2L and, when a chief ray from the 
position of the entrance pupil of the relay variable power optical system 
is imaged at the position of the exit pupil of the relay variable power 
optical system through the relay variable power optical system, the 
magnification of the second lens group at the high magnification end with 
respect to the chief ray is .beta.'2H and the magnification of the second 
lens group at the low magnification end with respect to the chief ray is 
.beta.'2L, the following conditions are satisfied: 
EQU -1&lt;.beta.2L and .beta.2H&lt;-1, 
and 
EQU 1&lt;.beta.'2L and .beta.'2H&lt;1. 
According to a preferred embodiment of the second aspect of the present 
invention, the observation unit has an eyepiece optical system for 
observing the secondary image in an enlarged manner. Or, the observation 
unit has a photoelectric converting element for image-detecting the 
secondary image, and an image display system for displaying the secondary 
image based on an output signal from the photoelectric converting element.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 is a drawing for explaining the basic structure of a relay variable 
power optical system according to the present invention. 
The relay variable power optical system in FIG. 1 is an optical system for 
forming a secondary image on a focal plane of an eyepiece lens based on a 
light from a primary image which is formed, for example, by an objective 
lens of a microscope. This relay variable power optical system is 
constituted by a collimate lens group G0 having a positive refracting 
power, a first lens group G1 having a positive refracting power, a second 
lens group G2 having a negative refracting power, a third lens group G3 
having a positive refracting power, and an imaging lens group G4 having a 
positive refracting power, in the named order from the primary image side. 
Here, the collimate lens group G0 constitutes a front lens group for 
condensing a light from the primary image. Also, the first to third lens 
groups G1 to G3 constitute a variable power lens system for zooming a 
secondary image by receiving the light from the front lens group G0, and a 
distance between the first lens group G1 and the second lens group G2 and 
a distance between the second lens group G2 and the third lens group G3 
are changed when the zooming is performed. Further, the imaging lens group 
G4 constitutes a rear lens group for forming a secondary image by 
condensing the light from the variable power lens system G1 to G3. 
Note that a ray indicated by a broken line in FIG. 1 shows how a chief ray 
from the position of an entrance pupil of the relay variable power optical 
system is imaged at the position of an exit pupil of the relay variable 
power optical system through the relay variable power optical system. In 
other words, the ray indicated by the broken line shows a conjugate 
relation between the pupils of the relay variable power optical system by 
an imaging relation of the chief ray. 
Also, a ray indicated by a solid line in FIG. 1 shows how an axial ray from 
an axial objective point of the primary image is imaged on the secondary 
image through the relay variable power optical system. In other words, the 
ray indicated by the solid line shows a conjugate relation between the 
images of the relay variable power optical system by an imaging relation 
of the ray from the axial objective point of the primary image. 
Hereinafter, a magnification of the second lens group G2 with respect to an 
axial ray when the axial ray from the axial objective point of the primary 
image is imaged on the secondary image through the relay variable power 
optical system in the present invention is called "the magnification of 
the second lens group G2 in the image conjugate". Also, the axial ray when 
the axial ray from the axial objective point of the primary image is 
imaged on the secondary image through the relay variable power optical 
system is called "the ray related to the image conjugate". 
On the other hand, the magnification of the second lens group G2 with 
respect to a chief ray when the chief ray from the entrance pupil position 
of the relay variable power optical system is imaged on the exit pupil 
position of the relay variable power optical system through the relay 
variable power optical system is called "the magnification of the second 
lens group G2 in the pupil conjugate". Also, the chief ray when the chief 
ray from the entrance pupil position of the relay variable power optical 
system is imaged on the exit pupil position of the relay variable power 
optical system through the relay variable power optical system is called 
"the ray related to the pupil conjugate". 
As described above, the variable power lens system of the present invention 
is a zoom lens which has a first lens group G1 having a positive 
refracting power, a second lens group G2 having a negative refracting 
power, and a third lens group G3 having a positive refracting power, in 
the named order from the primary image side. The zoom lens consisting of 
three lens groups having positive, negative, and positive refracting 
powers performs a zooming operation by changing the magnification of the 
second lens group G2 in the image conjugate. Therefore, a change of the 
magnification of the second lens group G2 in the image conjugate caused by 
the zooming is an important factor in designing the relay variable power 
optical system of the present invention. Also, a change of the 
magnification of the second lens group G2 in the pupil conjugate has the 
greatest influence on a change of the conjugate relation between the 
pupils caused by the zooming. 
According to the present invention, the following Conditions (1) and (2) 
are satisfied: 
EQU -1&lt;.beta.2L and .beta.2H&lt;-1 (1), 
and 
EQU 1&lt;.beta.'2L and .beta.'2H&lt;1 (2), 
where .beta.2H is the magnification of the second lens group G2 in the 
image conjugate at the high magnification end; .beta.'2L is the 
magnification of the second lens group G2 in the image conjugate at the 
low magnification end; .beta.2H is the magnification of the second lens 
group G2 in the pupil conjugate at the high magnification end; and 
.beta.'2L is the magnification of the second lens group G2 in the pupil 
conjugate at the low magnification end. 
FIGS. 2A to 2C are drawings showing the rays related to the image conjugate 
at the low magnification end, in a middle magnification state, and at the 
high magnification end in the variable power lens system of FIG. 1. The 
magnification .beta.2L of the second lens group G2 in the image conjugate 
at the low magnification end in FIG. 2A is larger than -1, the 
magnification .beta.2M of the second lens group G2 in the image conjugate 
in the middle magnification state in FIG. 2B is equal to -1, and the 
magnification .beta.2H of the second lens group G2 in the image conjugate 
at the high magnification end in FIG. 2C is smaller than -1. That is, when 
the Condition (1) is satisfied, the middle magnification state in which 
the magnification of the second lens group G2 in the image conjugate is 
equal to -1 inevitably exists. 
The Condition (1) stipulates a condition for realizing a small-sized relay 
variable power optical system capable of zooming (variable power) of a low 
magnification. 
In the Condition (1), when the condition -1&lt;.beta.2L is not satisfied, the 
magnification of the relay variable power optical system is shifted to the 
high magnification side, so that it is difficult to make the magnification 
lower. On the other hand, when the condition .beta.2H&lt;-1 is not satisfied 
in the Condition (1), it becomes easier to make the magnification lower. 
However, an amount of movement caused by a variable power of the variable 
power lens groups (the first lens group G1 and the third lens group G3) 
becomes large, so that the size of the relay variable power optical system 
is increased. 
Also, according to the present invention, it is desirable to satisfy the 
following Condition (3), in order to position the zoom arrangement 
satisfying .beta.2M=-1 between the high magnification end and the low 
magnification end: 
EQU -1.25&lt;.beta.2L.multidot.Z.sup.1/2 &lt;-0.8 (3), 
where Z is a variable power ratio (zoom ratio) of the relay variable power 
optical system. 
FIGS. 3A to 3C are drawings showing the rays related to the pupil conjugate 
at the low magnification end, in a middle magnification state, and at the 
high magnification end in the variable power lens system of FIG. 1. The 
magnification .beta.'2L of the second lens group G2 in the pupil conjugate 
at the low magnification end in FIG. 3A is larger than 1, the 
magnification .beta.'2M of the second lens group G2 in the pupil conjugate 
in the middle magnification state in FIG. 3B is equal to 1, and the 
magnification .beta.'2H of the second lens group G2 in the pupil conjugate 
at the high magnification end in FIG. 3C is smaller than 1. That is, when 
the Condition (2) is satisfied, the middle magnification state in which 
the magnification of the second lens group G2 in the pupil conjugate is 
equal to 1 inevitably exists. 
The Condition (2) stipulates a condition for suppressing a change in the 
conjugate relation between the pupils caused by the zooming. As stated 
before, it is the second lens group G2 that has the most important effect 
on the conjugate relation between the pupils. Therefore, if the 
magnification of the second lens group G2 in the pupil conjugate is set to 
be around 1 for the entire variable power region, a change in the 
conjugate relation between the pupils with varying power can be reduced. 
When the condition -1&lt;.beta.'2L is not satisfied in the Condition (2), the 
magnification of the second lens group G2 in the pupil conjugate is 
smaller than 1 for the entire variable power region, so that a change in 
the conjugate relation between the pupils with varying power becomes 
large. 
On the other hand, when the condition .beta.'2H&lt;1 is not satisfied in the 
Condition (2), the magnification of the second lens group G2 in the pupil 
conjugate is larger than 1 for the entire variable power region, so that a 
change with varying the conjugate relation between the pupils in power 
becomes large. 
Also, according to the present invention, it is desirable to satisfy the 
following Condition (4) in order to balance a magnification of the second 
lens group G2 in the pupil conjugate at the low magnification end and that 
at the high magnification end: 
EQU 0.8&lt;.beta.'2L.multidot..beta.'2H&lt;1.25 (4). 
By satisfy the Condition (4), it is possible to further reduce a change in 
the conjugate relation between the pupils with varying power by balancing 
the magnification .beta.'2L of the second lens group G2 in the pupil 
conjugate at the low magnification end and the magnification .beta.'2H of 
the second lens group G2 in the pupil conjugate at the high magnification 
end. 
Embodiments of the present invention will be described below with reference 
to the attached drawings. 
FIGS. 4A to 4C are drawings for schematically showing the structure of a 
relay variable power optical system according to a first embodiment of the 
present invention. FIG. 4A shows the low magnification end, FIG. 4B a 
middle magnification state in which the magnification .beta.2M of the 
second lens group G2 in the image conjugate becomes -1, and FIG. 4C the 
high magnification end, respectively. The solid lines in FIGS. 4A to 4C 
respectively indicate the ray related to the image conjugate between the 
primary image and the secondary image, and the broken lines in FIG. 4A to 
4C the ray related to the pupil conjugate between the entrance pupil and 
the exit pupil, respectively. 
The relay variable power optical system in FIGS. 4A to 4C is an optical 
system for forming the secondary image on a focal plane of an eyepiece 
lens, an image plane of a TV camera, or the like, based on the light from 
the primary image formed by an objective lens or the like. The optical 
system is constituted by a collimate lens group G0 having a positive 
refracting power, a first lens group G1 having a positive refracting 
power, a second lens group G2 having a negative refracting power, a third 
lens group G3 having a positive refracting power, and an imaging lens 
group G4. 
Here, the collimate lens group G0 converts rays from the primary image into 
collimated rays. The first to third lens groups G1 to G3 constitute an 
afocal variable power lens system. The first lens group G1 and the third 
lens group G3 are moved along the optical axis when a zooming is 
performed. Further, the imaging lens group G4 forms the secondary image 
based on the collimated rays which are zoomed through the variable power 
lens system G1 to G3. Note that the relay variable power optical system in 
FIGS. 4A to 4C is an optical system which is telecentric on the object 
side, the entrance pupil of which is positioned at infinity. 
Specific values for the first embodiment are listed in the following Table 
(1). In Table (1), F0 to F4 denote the focal lengths of the lens groups G0 
to G4, respectively. Also, D0 to D5 respectively denote a distance along 
the optical axis between the primary image and the position of the 
principal point of the collimate lens group G0, a distance along the 
optical axis between the position of the principal point of the collimate 
lens group G0 and the position of the principal point of the first lens 
group G1, a distance along the optical axis between the position of the 
principal point of the first lens group G1 and the position of the 
principal point of the second lens group G2, a distance along the optical 
axis between the position of the principal point of the second lens group 
G2 and the position of the principal point of the third lens group G3, a 
distance along the optical axis between the position of the principal 
point of the third lens group G3 and the position of the principal point 
of the imaging lens group G4, and a distance along the optical axis 
between the position of the principal point of the imaging lens group G4 
and the secondary image. Further, .beta. denotes a magnification of the 
relay variable power optical system, Z a variable power ratio of the relay 
variable power optical system, ENTP an entrance pupil distance (a distance 
from the primary image to the entrance pupil along the optical axis), and 
EXTP an exit pupil distance (a distance from the secondary image to the 
exit pupil along the optical axis), respectively. 
TABLE 1 
______________________________________ 
F0 = 100 
F1 = 60 
F2 = -20 
F3 = 60 
F4 = 150 
Z = 2 
(Low magnification end) .beta. = -1 
D0 = 100 .beta. 2L = -0.667 
D1 = 83 .beta.'2L = 1.21 
D2 = 10 ENTP = .infin. 
D3 = 26.67 EXTP = .infin. 
D4 = 114 
D5 = 150 
(Middle magnification state) .beta. = -1.5 
D0 = 100 .beta. 2M = 1 
D1 = 73 .beta.'2M = 0.945 
D2 = 20 ENTP = .infin. 
D3 = 20 EXTP = 7200 
D4 = 120.67 
D5 = 150 
(High magnification end) .beta. = -2 
D0 = 100 .beta. 2H = -1.33 
D1 = 68 .beta.'2H = 0.836 
D2 = 25 ENTP = .infin. 
D3 = 13.33 EXTP = .infin. 
D4 = 127.34 
D5 = 150 
(Condition corresponding values) 
(3) .beta. 2L .multidot. Z.sup.1/2 = -0.943 
(4) .beta.'2L .multidot. .beta.'2H = 1.012 
______________________________________ 
Referring to Table (1), the exit pupil distance EXTP is .infin. at the low 
magnification end, 7200 in the middle magnification state, and .infin. at 
the high magnification end. That is, in the first embodiment, it is 
clearly seen that a change of the position of the exit pupil caused by the 
variable power can be suppressed to be very small with respect to the 
entrance pupil at infinity. Therefore, if the relay variable power optical 
system of the first embodiment is applied, for example, to a microscope, 
it is possible not only to reduce the size of an optical system of the 
microscope, but also to suppress a fluctuation of the eye point position 
for observing the secondary image by the eyes through an eyepiece optical 
system. As a result, it becomes easier to observe the secondary image. 
FIGS. 5A to 5C are drawings for schematically showing the structure of a 
relay variable power optical system according to a second embodiment of 
the present invention. FIG. 5A shows the low magnification end, FIG. 5B a 
middle magnification state in which the magnification .beta.2M of the 
second lens group G2 in the image conjugate is equal to -1, and FIG. 5C 
the high magnification end, respectively. The solid lines in FIGS. 5A to 
5C respectively indicate the ray related to the image conjugate between 
the primary image and the secondary image, and the broken lines in FIGS. 
5A to 5C the ray related to the pupil conjugate between the entrance pupil 
and the exit pupil, respectively. 
The relay variable power optical system in FIGS. 5A to 5C is an optical 
system for forming the secondary image on a focal plane of an eyepiece 
lens, an image plane of a TV camera, or the like, based on the light from 
the primary image formed by an objective lens or the like. The optical 
system is constituted by a collimate lens group G0 having a positive 
refracting power, a first lens group G1 having a positive refracting 
power, a second lens group G2 having a negative refracting power, a third 
lens group G3 having a positive refracting power, and an imaging lens 
group G4. 
Here, the collimate lens group G0 converts rays from the primary image into 
collimated rays. The first to third lens groups G1 to G3 constitute an 
afocal variable power lens system. The second lens group G2 and the third 
lens group G3 are moved along the optical axis when the zooming is 
performed. Further, the imaging lens group G4 forms the secondary image 
based on the collimated rays which are zoomed through the variable power 
lens system G1 to G3. Note that the relay variable power optical system in 
FIGS. 5A to 5C is an optical system which is telecentric on the object 
side, and the entrance pupil of which is positioned at infinity. 
Specific values for the second embodiment are listed in the following Table 
(2). In Table (2), F0 to F4 denote the focal lengths of the lens groups G0 
to G4, respectively. Also, D0 to D5 respectively denote a distance along 
the optical axis between the primary image and the position of the 
principal point of the collimate lens group G0, a distance along the 
optical axis between the position of the principal point of the collimate 
lens group G0 and the position of the principal point of the first lens 
group G1, a distance along the optical axis between the position of the 
principal point of the first lens group G1 and the position of the 
principal point of the second lens group G2, a distance along the optical 
axis between the position of the principal point of the second lens group 
G2 and the position of the principal point of the third lens group G3, a 
distance along the optical axis between the position of the principal 
point of the third lens group G3 and the position of the principal point 
of the imaging lens group G4, and a distance along the optical axis 
between the position of the principal point of the imaging lens group G4 
and the secondary image. Further, .beta. denotes a magnification of the 
relay variable power optical system, Z a variable power ratio of the relay 
variable power optical system, ENTP an entrance pupil distance (a distance 
from the primary image to the entrance pupil along the optical axis), and 
EXTP an exit pupil distance (a distance from the secondary image to the 
exit pupil along the optical axis), respectively. 
TABLE 2 
______________________________________ 
F0 = 100 
F1 = 60 
F2 = -20 
F3 = 60 
F4 = 175 
Z = 3 
(Low magnification end) .beta. -1 
D0 = 100 .beta. 2L = -0.571 
D1 = 83 .beta.'2L = 1.74 
D2 = 5 ENTP = .infin. 
D3 = 28.57 EXTP = .infin. 
D4 = 156 
D5 = 175 
(Middle magnification state) .beta. = -1.73 
D0 = 100 .beta. 2M = -1 
D1 = 83 .beta.'2M = 0.761 
D2 = 20 ENTP = .infin. 
D3 = 20 EXTP = 1900 
D4 = 149.57 
D5 = 175 
(High magnification end) .beta. = -3 
D0 = 100 .beta. 2H = -1.71 
D1 = 83 .beta.'2H = 0.576 
D2 = 28.33 ENTP = .infin. 
D3 = 5.71 EXTP = .infin. 
D4 = 155.52 
D5 = 175 
(Condition corresponding values) 
(3) .beta. 2L .multidot. Z.sup.1/2 = -0.989 
(4) .beta.'2L .multidot. .beta.2H = 1.002 
______________________________________ 
Referring to Table (2), the exit pupil distance EXTR is o at the low 
magnification end, 1900 in the middle magnification state, and co at the 
high magnification end. That is, in the second embodiment, it is clearly 
seen that a change of the position of the exit pupil caused by the 
variable power can be suppressed to be very small with respect to the 
entrance pupil at infinity. Therefore, if the relay variable power optical 
system of the second embodiment is applied, for example, to a microscope, 
it is possible not only to reduce the size of an optical system of the 
microscope, but also to suppress a fluctuation of the eye point position 
for observing the secondary image by the eyes through the eyepiece optical 
system. As a result, it becomes easier to observe the secondary image. 
FIGS. 6A to 6C are drawings for schematically showing the structure of a 
microscope according to a third embodiment of the present invention. The 
microscope of the third embodiment is a microscope of a type for observing 
an object by the eyes, which is provided with the relay variable power 
optical system of the first embodiment. 
FIG. 6A shows the low magnification end, FIG. 6B a middle magnification 
state in which the magnification .beta.2M of the second lens group G2 in 
the image conjugate is equal to -1, and FIG. 6C the high magnification 
end, respectively. The solid lines in FIGS. 6A to 6C respectively indicate 
the ray related to the image conjugate between the primary image and the 
secondary image, and the broken lines in FIG. 6A to 6C the ray related to 
the pupil conjugate between the entrance pupil and the exit pupil, 
respectively. 
The microscope in FIGS. 6A to 6C is provided with an illumination system IS 
for illuminating a sample 1 which is an object to be observed. An 
illumination light emitted from the illumination system IS is reflected by 
a half mirror HM and then illuminates the sample 1 through a first 
objective lens Gob. Light from the sample 1 which is positioned on the 
focal plane on the object side of the first objective lens Gob (on the 
sample side) is collimated through the first objective lens Gob, and 
enters the half mirror HM through an aperture stop 2 which is positioned 
on the focal plane on the image side of the first objective lens Gob (on 
the half mirror side). The light passing through the half mirror HM is 
condensed by a second objective lens Gt and, after being reflected by a 
mirror M1, forms a primary image of the sample 1. 
As stated above, the first objective lens Gob and the second objective lens 
Gt constitute an objective optical system for condensing light from the 
sample 1 which is an observed object so as to form a primary image of the 
object. Then, the position of the aperture stop 2 is the position of the 
exit pupil of the first objective lens Gob and the position of the 
entrance pupil of a compound system (Gt, G0 to G4) of the relay variable 
power optical system and the second objective lens. 
The light from the primary image is condensed by the relay variable power 
optical system (G0 to G4) and, after being reflected by a mirror M2, forms 
a secondary image of the sample 1. The light from the secondary image is 
collimated through an eyepiece lens Ge to reach an eye point EP of the 
observer. Thus, the observer can observe the secondary image of the sample 
1 in an enlarged manner through the eyepiece lens Ge. 
Specific values for the third embodiment are listed in the following Table 
(3). In Table (3), Fob, Ft and Fe denote the focal lengths of the first 
objective lens Gob, the second objective lens Gt and the eyepiece lens Ge, 
respectively. Also, Do denotes a distance along the optical axis between 
the sample 1 and the position of the principal point of the first 
objective lens Gob, Dot a distance along the optical axis between the 
position of the principal point of the first objective lens Gob and the 
position of the principal point of the second objective lens Gt, Dt a 
distance along the optical axis between the position of the principal 
point of the second objective lens Gt and the primary image, D6 a distance 
along the optical axis between the secondary image and the position of the 
principal point of the eyepiece lens Ge, and De a distance along the 
optical axis between the position of the principal point of the eyepiece 
lens Ge and the eye point EP, respectively. 
Note that F0 to F4 denote the focal lengths of the lens groups G0 to G4, 
respectively, in the same way as in the first embodiment. Also, D0 to D5 
respectively denote a distance along the optical axis between the primary 
image and the position of the principal point of the collimate lens group 
G0, a distance along the optical axis between the position of the 
principal point of the collimate lens group G0 and the position of the 
principal point of the first lens group G1, a distance along the optical 
axis between the position of the principal point of the first lens group 
G1 and the position of the principal point of the second lens group G2, a 
distance along the optical axis between the position of the principal 
point of the second lens group G2 and the position of the principal point 
of the third lens group G3, a distance along the optical axis between the 
position of the principal point of the third lens group G3 and the 
position of the principal point of the imaging lens group G4, and a 
distance along the optical axis between the position of the principal 
point of the imaging lens group G4 and the secondary image. Further, 
.beta. denotes a magnification of the relay variable power optical system, 
Z a variable power ratio of the relay variable power optical system, ENTP 
an entrance pupil distance (a distance from the primary image to the 
entrance pupil along the optical axis), and EXTP an exit pupil distance (a 
distance from the secondary image to the exit pupil along the optical 
axis), respectively. 
TABLE 3 
______________________________________ 
Fob = 100 
Ft = 10 
Fe = 25 
Dob = 10 
Dot = 110 
Dt = 100 
D6 = 25 
F0 = 100 
F1 = 60 
F2 = -20 
F3 = 60 
F4 = 150 
Z = 2 
(Low magnification end) .beta. = -1 
D0 = 100 .beta. 2L = -0.667 
D1 = 83 .beta.'2L = 1.21 
D2 = 10 ENTP = .infin. 
D3 = 26.67 EXTP = .infin. 
D4 = 114 De = 25 
D5 = 150 
(Middle magnification state) .beta. = -1.5 
D0 = 100 .beta. 2M = -1 
D1 = 73 .beta.'2M = 0.945 
D2 = 20 ENTP = .infin. 
D3 = 20 EXTP = 7200 
D4 = 120.67 De = 24.9 
D5 = 150 
(High magnification end) .beta. = -2 
D0 = 100 .beta. 2H = -1.33 
D1 = 68 .beta.'2H = 0.836 
D2 = 25 ENTP = .infin. 
D3 = 13.33 EXTP = .infin. 
D4 = 127.34 De = 25 
D5 = 150 
(Condition corresponding values) 
(3) .beta. 2L .multidot. Z.sup.1/2 = -0.943 
(4) .beta.'2L .multidot. .beta.'2H = 1.012 
______________________________________ 
Referring to Table (3), the distance De from the position of the principal 
point of the eyepiece lens Ge to the eye point EP is 25 at the low 
magnification end, 24.9 in the middle magnification state, and 25 at the 
high magnification end. That is, in the microscope of the third 
embodiment, a change of the position of the eye point hardly occurs upon 
varying power. Therefore, it becomes easier to observe the secondary image 
by the eyes through the eyepiece lens, so as to improve the working 
efficiency . 
FIGS. 7A to 7C are drawings for schematically showing the structure of a 
first modification of the third embodiment of the present invention. 
The first modification has a similar structure to that of the third 
embodiment, except that an image observation by use of an image display, 
in addition to the observation by the eyes through an eyepiece lens, is 
possible in the first modification. That is, in the first modification, 
the relay variable power optical system of the first embodiment is applied 
to a microscope which is capable of the observation by the eyes and the 
image display. In FIGS. 7A to 7C, components having identical functions to 
those of the components in the third embodiment are given the same 
reference numerals and symbols as in FIGS. 6A to 6C. The first 
modification will be described below taking the difference from the third 
embodiment into consideration. 
In the first modification shown in FIGS. 7A to 7C, light passing through 
the relay variable power optical system (G0 to G4) enters a half mirror 
HM2. The light which is reflected by the half mirror HM2 forms a secondary 
image of a sample 1 on the front focal plane of the eyepiece lens Ge. On 
the other hand, the light passing through the half mirror HM2 forms a 
secondary image of the sample 1 on a detection plane of a photoelectric 
converting element such as a detector D. An output from the detector D 
which detects the secondary image is supplied to an image display unit 3 
such as a CRT. Thus, the image display unit 3 displays the secondary image 
of the sample 1 based on an output signal from the detector D. 
In this manner, in the first modification, the observer can observe the 
secondary image of the sample 1 by the eyes through the eyepiece lens Ge, 
and can also observe the secondary image of the sample 1 as a displayed 
image through the image display unit 3. 
FIGS. 8A to 8C are drawings for schematically showing the structure of a 
second modification of the third embodiment of the present invention. 
The second modification has a similar structure to that of the third 
embodiment, except that secondary images of three colors are formed by two 
dichroic mirrors, and these secondary images of three colors are combined 
and displayed as a color image in the second modification. That is, in the 
second modification, the relay variable power optical system of the first 
embodiment is applied to a microscope which is capable of image 
observation by use of a TV camera of a three tube type. In FIGS. 8A to 8C, 
components having the identical functions to those of components in the 
third embodiment are given the same reference numerals and symbols as in 
FIGS. 6A to 6C. The second modification will be described below taking the 
difference from the third embodiment into consideration. 
In the second modification shown in FIGS. 8A to 8C, light passing through 
the relay variable power optical system (G0 to G4) enters a first dichroic 
mirror DM1. The first dichroic mirror DM12 has a characteristic of 
reflecting, for example, light of color R (red) and passing other light 
through. Therefore, the light reflected by the first dichroic mirror DM12 
forms a secondary image of red color on an image plane of an image element 
D1. 
The light passed through the first dichroic mirror DM12 enters a second 
dichroic-mirror DM2. The dichroic mirror DM2 has a characteristic of 
reflecting light having a specific color such as B (blue) and passing 
another color such as G (green). Therefore, the light reflected by the 
second dichroic mirror DM2 forms a secondary image of blue color on an 
image plane of an image element D3. On the other hand, the light passing 
through the second dichroic mirror DM2 forms a secondary image of green 
color on an image plane of an image element D2. 
The image elements D1 to D3 photoelectrically detect secondary images of 
three colors, and outputs of three colors therefrom are supplied to the 
image display unit 3 such as a CRT. Thus, the image display unit 3 
displays the secondary image of the sample 1 as a color image on the basis 
of the output signals from the image elements D1 to D3. 
In this manner, in the microscope of the second modification, the secondary 
image of the sample 1 can be observed as a color image by use of a TV 
camera of a three tube type. In this case, since the position of the exit 
pupil of the relay variable power optical system hardly fluctuates at the 
time of zooming, the inclination or the telecentricity of the chief ray 
which enters the two dichroic mirrors DM12 and DM2 hardly changes. 
Therefore, according to the microscope of the second modification, it is 
possible to obtain an excellent color image without generating uneven 
colors around the image which is detected photoelectrically. 
FIGS. 9A through 9C are drawings schematically showing the structure of the 
relay variable power optical system according to a fourth embodiment of 
the present invention. 
FIG. 9A shows the lens arrangement at a low magnification end 
(.beta.=-1.0), FIG. 9B shows the lens arrangement at a middle 
magnification state (.beta.=-1.5) in which the magnification .beta.2M of 
the second lens group G2 in the image conjugate becomes -1.0, and FIG. 9C 
shows the lens arrangement at a high magnification end (.beta.=-2.0), 
respectively. 
For example, the relay variable power optical system in FIGS. 9A through 9C 
is an optical system for forming the secondary image on a focal plane of 
an eyepiece lens based on light from a primary image formed by an 
objective lens of a microscope or the like. 
The optical system is constituted by a collimate lens group G0 having a 
positive refracting power, a first lens group G1 having a positive 
refracting power, a second lens group G2 having a negative refracting 
power, a third lens group G3 having a positive refracting power, and a 
fourth lens group G4 having a positive refracting power in the named order 
from the primary image side. 
Here, the collimate lens group G0 converts rays from the primary image into 
substantially collimated rays. The first to third lens groups G1 to G3 
constitute a substantially afocal variable power lens system. The first 
and third lens groups G1 and G3 are moved along the optical axis, whereby 
a gap d2 between the first lens group G1 and the second lens group G2, and 
a gap d3 between the second lens group G2 and the third lens group G3 are 
changed during the zooming operation. 
The imaging lens group G4 forms the secondary image by converging the 
substantially collimated rays from the variable power lens groups G1 to 
G3. The relay variable power optical system in FIGS. 9A to 9C is an 
optical system which is telecentric on the object side (the primary image 
side), the entrance pupil of which is positioned at infinity. 
Table 4 shows specific values of the fourth embodiment. Under "Total 
Specific Values," F0 to F4 represent the focal lengths of the lens groups 
G0 to G4, respectively, d0 represents an air gap along the optical axis 
between the primary image and the collimate lens G0, d1 represents an air 
gap along the optical axis between the collimate lens group G0 and first 
lens group G1, d2 represents an air gap between the first lens group G1 
and the second lens group G2, d3 represents an air gap between the second 
lens group G2 and the third lens group G3, d4 represents an air gap 
between the third lens group G3 and the imaging lens group G4, and Bf 
represents an air gap along the optical axis (back focus) between the 
imaging lens group G4 and the secondary image. Further, .beta. represents 
a magnification of the relay variable power optical system, F NO 
represents an F number of the relay variable power optical system, Z 
represents a zoom ratio of the relay variable power optical system, ENTP 
represents a distance of the entrance pupil (an air gap along the optical 
axis from the primary image to the entrance pupil), EXTP represents a 
distance of the exit pupil (an air gap along the optical axis from the 
secondary image to the exit pupil). 
Under "Lens Specific Values," the first column includes lens surface 
numbers, r in the second column represents a radius of curvature of lens 
surface, d in the third column represents a lens surface separation 
wherein d1 to d4 are changed during the zooming operation, n in the fourth 
column represents a refractive index for the d-line (.lambda.=587.6 nm), a 
blank in the fourth column represents air (i.e. n=1.00000), and .nu. in 
the fifth column represents an Abbe's number. Table 4 also includes values 
relating to magnification of the second lens group (including values for 
each of conditions (1) and (2)) and values for each of conditions (3) and 
(4). 
TABLE 4 
______________________________________ 
(Total Specific Values) 
______________________________________ 
d0 = 99.8469 
Bf = 153.82 
F NO = 12 .about. 18 .about. 24 
.beta. = -1 .about. -1.5 .about. -2.0 
Z = 2 
F0 = 100 
F1 = 60 
F2 = -20 
F3 = 60 
F4 = 150 
______________________________________ 
(Lens Specific Values) 
r d n .upsilon. 
______________________________________ 
1 .infin. (d0) 
2 54.9409 2.50 1.62588 
35.70 
3 49.3103 4.50 1.49782 
82.52 G0 
4 -410.3620 
(d1) 
5 29.7051 2.50 1.49782 
82.52 
6 -32.9087 1.20 1.74950 
35.19 G1 
7 -98.5774 (d2) 
8 -30.1513 1.50 1.86074 
23.01 
9 -23.4016 1.00 1.52682 
51.35 
10 27.1479 1.50 G2 
11 -20.6531 1.00 1.61266 
44.41 
12 66.2867 1.50 1.86074 
23.01 
13 -84.9033 (d3) 
14 132.9663 3.00 1.49782 
82.52 
15 -21.7941 1.50 1.71736 
29.46 G3 
16 -31.2340 (d4) 
17 -76.3981 4.00 1.60311 
60.64 
18 -24.1012 1.50 1.74810 
52.30 G4 
19 -74.4595 0.20 
20 74.7940 3.00 1.51680 
64.10 
21 -165.8719 
(Bf) 
22 .infin. 
______________________________________ 
(Variable Parameters) 
.beta. -1.0 -1.5 -2.0 
______________________________________ 
d1 78.28 68.28 63.28 
d2 7.03 17.03 22.03 
d3 20.41 13.74 7.08 
d4 104.82 111.48 118.15 
ENTP .infin. .infin. .infin. 
EXTP .infin. 7200 .infin. 
______________________________________ 
(Low magnification end) .beta. = -1.0 
.beta.2L = -0.667 
.beta.'2L = 1.21 
(Middle magnification state) .beta. = -1.5 
.beta.2M = -1 
.beta.'2M = 0.945 
(High magnification end) .beta. = -2.0 
.beta.2H = -1.33 
.beta.'2H = 0.836 
(Condition Values) 
(3) .beta.2L .multidot. Z.sup.1/2 = -0.943 
(4) .beta.'2L .multidot. .beta.'2H = 1.012 
______________________________________ 
FIGS. 10A through 12F show aberrations of the relay variable power optical 
system having the lens specific values indicated in Table 4. 
FIGS. 10A through 10F are drawings showing aberrations in the fourth 
embodiment when the magnification of the variable power optical system is 
-1.0. FIG.10A shows the spherical aberration, FIG. 10B shows the 
astigmatism, FIG. 10C shows the distortion, FIG. 10D shows the comatic 
aberration at the image height 100% (Y=6), FIG. 10E shows the comatic 
aberration at the image height 67% (Y=4), and FIG. 10F shows the comatic 
aberration at the image height 0%. 
FIGS. 11A through 11F are drawings showing aberrations of the fourth 
embodiment when the magnification of the variable power optical system is 
-1.5. FIG. 11A shows the spherical aberration, FIG. 11B shows the 
astigmatism, FIG. 11C shows the distortion, FIG. 11D shows the comatic 
aberration at the image height 100% (Y=6), FIG. 11E shows the comatic 
aberration at the image height 67% (Y=4), and FIG. 11F shows the comatic 
aberration at the image height 0%. 
FIGS. 12A through 12F are drawings showing aberrations of the fourth 
embodiment when the magnification of the variable power optical system is 
-2.0. FIG. 12A shows the spherical aberration, FIG. 12B shows the 
astigmatism, FIG. 12C shows the distortion, FIG. 12D shows the comatic 
aberration at the image height 100% (Y=6), FIG. 12E shows the comatic 
aberration at the image height 67% (Y=4), and FIG. 12F shows the comatic 
aberration at the image height 0%. 
In each of the aberration diagrams, FNO represents an F number of the relay 
variable optical system, and Y represents an image height. Further, in the 
spherical aberration diagrams of FIGS. 10A, 11A, and 12A, the broken line 
represents the sine condition. 
In the astigmatism diagrams of FIGS. 10B, 11B, and 12B, the broken line 
represents a meridional image surface, and the solid line represents a 
saggital image surface. 
From the above-mentioned drawings of aberrations of FIGS. 10A through 12F, 
it is clearly seen that the relay variable power optical system of the 
fourth embodiment of the present invention has an excellent image 
formation performance. 
As described above, according to the present invention, it is possible to 
comparatively suppress a change in the position of the exit pupil of the 
relay zooming optical system caused by variable power without 
deteriorating the positional relationship between the primary image and 
the secondary image, in spite of the simple structure. Therefore, when the 
relay variable power optical system of the present invention is applied to 
a microscope, it is possible to reduce the size of an optical system of 
the microscope. Further, since a fluctuation of the position of an eye 
point can be suppressed when a secondary image is observed by the eyes 
through, for example, an eyepiece optical system, it becomes easier to 
observe the secondary image and to improve the working efficiency using a 
microscope or the like. In addition, when a secondary image which is 
formed by the relay variable power optical system is detected by using a 
TV camera of a three tube type, or the like, it is possible to obtain an 
excellent image without generating uneven colors around the 
photoelectrically-detected image.