Changeable magnification inverted galilean finder

A changeable magnification inverted Galilean finder includes, in succession from the object side, an objective lens group having a negative refractive power, and an eyepiece of positive refractive power disposed at a predetermined distance from the objective lens group. The objective lens group has a first objective lens for low magnification and a second objective lens for high magnification. The first objective lens for low magnification has a first negative lens component having a predetermined negative refractive power. The second objective lens for high magnification has a negative refractive power smaller than the refractive power of the first objective lens for low magnification, and has a second negative lens component and a positive lens component added on the object side of the second negative lens component. A low magnification state in which the objective lens for low magnification is disposed on the same optic axis as that of the eyepiece and a high magnification state in which the objective lens for high magnification is disposed on the same optic axis as that of the eyepiece are selectively constructed.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a finder used in a camera or the like, and 
particularly to a changeable magnification inverted Galilean finder. 
2. Description of the Prior Art 
In a focal length change-over type camera, it is desired that with a change 
of the angle of view of the photo-taking lens, a photographing range 
display be changed in the finder. In a camera containing an inverted 
Galilean finder therein, changing the size of the field frame and changing 
the magnification of the finder are two known techniques for changing the 
photographing range display. For changing the size of the field frame, 
there is known, for example, a method of providing an illuminating window 
type bright frame and moving the bright frame to thereby vary the apparent 
size of the frame, but this method has a disadvantage that if the angle of 
view becomes narrow, the apparent field of the field frame becomes small 
and it becomes difficult to look through the field frame. In contrast, in 
a system for changing the magnification of the finder, it is possible to 
make the apparent field of the photographing range constant so that a 
finder observation more approximate to the actual photographing picture 
plane becomes possible. This system is thus superior to changing the size 
of the field frame. 
As the method of changing the magnification, the focal length of a negative 
lens as an objective lens may be varied and an afocal state may be kept 
between the negative lens and an eyepiece of positive refractive power. 
More specifically, there is known a method in which, as shown in FIGS. 1A 
and 1B of the accompanying drawings, a negative lens L2 is replaced with a 
negative lens L1 having a different focal length, or a method in which, as 
shown in FIGS. 2A and 2B of the accompanying drawings, a negative lens L4 
is removed from the optical path and a negative lens L1 is moved toward 
the observation side to thereby effect the change of the magnification to 
a high magnification. FIGS. 1A and 2A show the low magnification state, 
i.e., the wide angle side, and FIGS. 1B and 2B show the high magnification 
state, i.e., the telephoto side. These methods are methods of changing the 
magnification by positioning a negative lens onto or of the optic axis, 
but these methods have a disadvantage that the amounts of displacement S1 
and S2 of the negative lens in the direction of the optic axis during a 
change between high magnification and great, so that magnification are 
great and it is difficult to provide sufficient space on the eyepiece side 
and therefore, the construction of the finder is liable to become bulky. 
In a finder for a camera, it is desirable to set the full length of the 
finder to a value equal to or shorter than the thickness of the body of 
the camera and in practice, the full length of the finder is desirably of 
the order of 30-40 mm. Particularly, in the latest finders, it is desired 
that numerous types of information such as the field frame, the range 
finding frame, the photographing distance display and the propriety of 
exposure amount be displayed at the same time and therefore, it has become 
necessary to add space-consuming members such as an Albada system and a 
half-mirror for the illuminating window type bright frame. However, where 
the amount of displacement of the negative lens for magnification change 
on the optic axis is great, the space in which optical members for various 
information displays are disposed becomes smaller and thus, design 
limitations have become more severe and sufficient information displays 
have been difficult. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to eliminate the above-noted 
disadvantages peculiar to the prior art and to provide a changeable 
magnification inverted Galilean finder in which the amount of decrease in 
the eyepiece side space resulting from the magnification change of the 
inverted Galilean finder is small and accordingly advantageous compact 
finders have become possible while providing large effective space in the 
finder, thereby enabling numerous information displays to be accomplished 
in the field of view of the finder. 
To achieve such an object of the present invention, in an inverted Galilean 
finder having an objective lens having a negative refractive power and an 
eyepiece having a positive refractive power disposed on the emergent light 
side of the objective lens at a predetermined distance therefrom, 
change-over is effected between a low magnification state using an 
objective lens for low magnification having a predetermined negative 
refractive power and a high magnification state using an objective lens 
for high magnification having a negative refractive power considerably 
weaker than said predetermined negative refractive power. The objective 
lens for high magnification is constituted, in succession from the object 
side, by a positive lens and a negative lens disposed at a predetermined 
distance therefrom. In the high magnification state, the light beam from 
an object to be photographed is first converged by the positive lens in 
the objective lens for high magnification, and then is diverged by the 
negative lens, whereby the principal point for the objective lens for high 
magnification having a negative refractive power lies on the eyepiece side 
and thus, even in the high magnification state, a space larger than in the 
prior art is secured between the objective lens and the eyepiece.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In a changeable magnification inverted Galilean finder according to the 
present invention, as shown in FIGS. 3A and 3B, a negative lens Lb as an 
objective lens in a low magnification state and an objective lens Lo for 
high magnification having a positive lens La and a negative lens Lc in 
succession from the object side are interchangeably provided, and by 
interchanging the negative lens Lb with the objective lens Lo for high 
magnification, a high magnification state is achieved. More particularly, 
a lens group Lb having a negative refractive power as an objective lens 
and a lens group Le having a positive refractive power as an eyepiece 
disposed at a predetermined distance from the lens group Lb are provided 
in succession from the object side, and further, an objective lens Lo for 
high magnification interchangeable with the negative lens group Lb as an 
objective lens for low magnification is constituted by a positive lens La 
and a negative lens Lc in succession from the object side, and by 
interchanging the negative lens Lb with the objective lens for high 
magnification, the change to a high magnification state is made possible. 
In the construction of the present invention shown in FIGS. 3A and 3B, it 
is possible that the negative lens Lb as the objective lens for low 
magnification and the negative lens Lc in the objective lens for high 
magnification are provided by the same lens. In such case, the negative 
lens Lb as the objective lens for low magnification can be used also as 
the negative lens Lc of the objective lens for high magnification. That 
is, as shown in FIG. 4A (a low magnification state) and FIG. 4B (a high 
magnification state), during the change-over from the low magnification 
state to the high magnification state, the negative lens Lb as the 
objective lens for low magnification is moved toward the eyepiece Le and 
the positive lens La is inserted into the object side of this negative 
lens Lb. Where the objective lens for low magnification is constituted by 
a plurality of negative lenses, the design may be such that only some of 
the negative lenses are moved toward the eyepiece. In other words, the 
lens group Lb having a negative refractive power as the objective lens and 
the lens group Le having a positive refractive power as the eyepiece 
disposed at a predetermined distance from the lens group Lb are provided 
in succession from the object side, and by moving at least one negative 
lens in the negative lens group Lb toward the eyepiece and inserting the 
positive lens La onto the optic axis on the object side of the moved 
negative lens Lb, the change to a higher magnification is accomplished. 
The geometro-optical basic construction of the changeable magnification 
inverted Galilean finder according to the present invention will 
hereinafter be described in detail. 
FIG. 5 is a geometro-optical construction view showing the popular high 
magnification state according to the prior art, FIG. 6 is a 
geometrooptical construction view showing the low magnification state of 
the inverted Galilean finder according to the present invention, and FIG. 
7 is a geometrooptical construction view showing the high magnification 
state of the inverted Galilean finder according to the present invention. 
In the changeable magnification inverted Galilean finder of the present 
invention, it is to be understood that the state of FIG. 6 is the low 
magnification state and the state of FIG. 7 is the high magnification 
state. In the high magnification state in the present invention, the 
objective lens Lo for high magnification is formed by a composite system 
of the positive lens La and the negative lens Lc, and it has substantially 
the same function as the objective lens Lo in the popular high 
magnification state shown in FIG. 5. 
Assuming that the finder magnification in the popular high magnification 
state (i.e., the telephoto side) shown in FIG. 5 is .beta.1, the focal 
length of the objective lens Lo is fo, the focal length of the eyepiece is 
fe, the distance between the principal points of the objective lens Lo and 
the eyepiece Le is dl and the finder is a completely afocal system, then 
the following relations are established: 
EQU .beta.1=-fo/fe (1) 
EQU d1=fe+fo (2) 
Next, assuming that the finder magnification on the low magnification side 
(the wide angle side in FIG. 6 is .beta.2, the focal length of the 
negative lens Lb as the objective lens is fb, the focal length of the 
eyepiece Le is fe, which is the same as the focal length on the high 
magnification side, and the distance between the principal points of the 
objective lens Lb and the eyepiece Le is d2, then the following relations 
are established: 
EQU .beta.2=-fb/fe (3) 
where .beta.1&gt;.beta.2 
EQU d2=fe+fb (4) 
If equations (3) and (4) are solved, 
##EQU1## 
Comparing the present invention with the prior art shown in FIGS. 1A and 
1B, it can be considered that the negative lens L1 as the objective lens 
in the high magnification state (FIG. 1B) has the focal length fo, the 
negative lens L2 as the objective lens in the low magnification state 
(FIG. 1A) has the focal length fb and the positive lens L3 as the eyepiece 
has the focal length fe. The amount of displacement of the negative lens 
L2 and the negative lens L1 for magnification change is S1. 
In such an example of the prior art, when the spacing between the objective 
lens and the eyepiece in the high magnification state and the spacing 
between the objective lens and the eyepiece in the low magnification state 
are d1 and d2, respectively, 
d2&gt;d1 
and therefore, the full length of the finder is prescribed by the value of 
d2 and usually, the dimension thereof is a value approximate to the 
thickness of the camera body. By substituting equations (1) and (6) into 
equation (2), the value of d1 is found as 
##EQU2## 
By substituting equation (6) into equation (1), the value of the focal 
length fo of the objective lens Lo for high magnification is found as 
##EQU3## 
Generally, the amount of displacement of the negative lens Lo as the 
objective lens for high magnification and the negative lens Lb as the 
objective lens for low magnification in the direction of the optic axis 
may be roughly shown as the amount of d2-d1 if the position of the 
eyepiece fe is constant. From equation (7), 
##EQU4## 
If d2, .beta.1 and .beta.2 are given as the conditions of the finder, the 
lens arrangements in the low magnification state and the high 
magnification state are determined in accordance with equations (5), (6), 
(7), (8) and (9). 
Accordingly, an amount of distance of the order of that defined by equation 
(9) becomes necessary as the amount of displacement S1 of the negative 
lens according to the conventional systems of FIGS. 1A, 1B, 2A and 2B. In 
the prior art of FIGS. 1A and 1B, the amount of displacement S1 from the 
negative lens L2 to the negative lens L1 is S1=d2-d1, and in the prior art 
of FIGS. 2A and 2B, the amount of displacement S2 of the negative lens L1 
is S2.noteq.d2-d1 when the lenses L1 and L4 are near each other. 
Equation (9) may be deformed into 
##EQU5## 
and if the magnification ratio .beta.1/.beta.2 of the finder is a constant 
value, as the value of .beta.2 is made smaller, the value of d2-d1 becomes 
smaller, because (.beta.1/.beta.2)&gt;1 and 0&lt;.beta.2&lt;1. 
Conversely, if the value of d2-d1 is limited to less than a certain value, 
the upper limit of .beta.2 will be prescribed, and this is the reason why 
only finders having a small value of .beta.2 and accordingly a small 
apparent field have heretofore been provided. Equation (9') means that if 
the value of the magnification ratio .beta.1/.beta.2 of the finder becomes 
greater, the amount of displacement d2-d1 of the negative lens is 
increased, and if the magnification ratio .beta.1/.beta.2 of the finder is 
made greater by the magnification changing system of the prior art, the 
requirement for making the value of .beta.2 even smaller is increased and 
the apparent field unavoidably becomes smaller. 
The present invention can secure a large effective space within the finder 
while keeping the same magnification .beta.2 on the high magnification 
side, not by the conventional arrangement of FIG. 5 but by the arrangement 
of FIG. 7. 
In the high magnification state of FIG. 7, it is to be understood that the 
focal lengths of the positive lens La and the negative lens Lc 
constituting the objective lens are fa and fc, respectively, and these 
positive lens La and negative lens Lc are disposed with the 
inter-principal point spacing d4. It is also to be understood that the 
composite focal length of the objective lens is fo and the interprincipal 
point spacing between the positive lens La and the eyepiece Le is d3. To 
change over from the low magnification state of FIG. 6 to the high 
magnification state of FIG. 7, the negative lens Lb as the objective lens 
for low magnification is removed from the optical path and instead, the 
objective lens Lo having the positive lens La and the negative lens Lc 
disposed with the inter-principal point spacing d4 is inserted into the 
optical path. Comparing the high magnification state of FIG. 5 in the 
prior art with the high magnification state of FIG. 7 by the present 
invention, it is clear that the space d5 at the eyepiece Le side of the 
negative lens Lc for changing the high magnification state into 
geometrically the same high magnification condition is substantially 
greater than d1. 
In the construction of the high magnification state by the present 
invention shown in FIG. 7, when the distance between the object side focus 
Fe of the eyepiece Le and the negative lens Lc is a, 
##EQU6## 
This may be rearranged into 
##EQU7## 
Also, from the imaging relation with respect to the negative lens Lc, 
##EQU8## 
If the above equation is rearranged with respect to fc and equation (10) 
is substituted thereinto, fc will be found as 
##EQU9## 
And 
EQU d3=fe-a+d4 (12). 
The difference between the amount of displacement of the negative lens 
according to the prior art and the amount of displacement of the negative 
lens according to the present invention, i.e., the distance b between the 
position of the negative lens Lo in the high magnification state by the 
conventional magnification changing system shown in FIG. 5 and the 
position of the negative lens Lo in the high magnification state by the 
magnification changing system of the present invention shown in FIG. 7, is 
expressed as 
EQU b=-fo-a (13). 
Solving a from equations (11) and (12), since a&gt;0, 
##EQU10## 
When the spacing d3 between the positive lens La added in the high 
magnification state and the eyepiece is given by the above equation in 
addition to the spacing d2 between the objective lens Lb and the eyepiece 
Le in the low magnification state, the magnification .beta.1 in the high 
magnification state and the magnification .beta.2 in the low magnification 
state, fb, fe, d1, fo and d2-d1 are successively determined by equations 
(5) to (9), and a is determined by equation (14) for any negative value 
fc. Further, fa is determined by equation (10) and the value of b is 
determined by equation (13). The amount of decrease .DELTA. in the space 
on the eyepiece side in the finder by the interchange of the objective 
lens for magnification change is found as 
EQU .DELTA.=a-1.vertline.fb.vertline.. 
By substituting equation (14) into equation (12), the on-axis spacing d4 
between the positive lens La and the negative lens Lc is found as 
##EQU11## 
By substituting equation (13) into equation (10), the following is 
obtained: 
##EQU12## 
In order that with fo&lt;0 and fa&gt;0 as the premise, the amount of decrease 
.DELTA. in the space on the eyepiece side of the negative lens Lc 
according to the present invention may be smaller relative to the amount 
of displacement of the negative lens according to the prior art, b can be 
b&gt;0 and for that purpose, it is necessary from equation (10') that d4&gt;0. 
That is, in equation (15), it is necessary that the numerator of the right 
side be positive. 
The condition for which the numerator of the right side of equation (15) is 
positive is a case where 
(i) fe-d3&lt;0 or 
(ii) fe-d3.gtoreq.0 and moreover 4fc(fo+fe-d3)&gt;0. 
fc&lt;0 and from equation (12), 
fo+fe=d1 
and hence, in order that 
EQU 4fc(fo+fe-d3)=4fc(d1-d3)&gt;0, 
it is necessary that d1&lt;d3. 
That is, in order that the amount of displacement of the negative lens Lb 
according to the present invention may be smaller than the amount of 
displacement of the negative lens according to the prior art, d1 may be 
d1&lt;d3. 
Generally, d1 is also d2&gt;d1 and therefore, a case where d2=d3, that is, the 
full length of the finder in the high magnification state and the full 
length of the finder in the low magnification state are the same, can be 
realized. Also, d2&lt;d3 is possible and therefore, by providing the positive 
lens La projectedly on the front face of the finder, it is also possible 
to change the magnification to the high magnification. According to the 
system of the present invention, it is also possible to provide 
EQU .beta.1.gtoreq.1 
on the high magnification side, that is, to provide one-to-one 
magnification or enlargement. Further, the present invention has a 
positive lens as the objective lens in the high magnification state, and 
this is advantageous in correcting negative distortion which is liable to 
occur in the inverted Galilean finder. 
In the foregoing description, the negative lens Lb as the objective lens 
for low magnification and the negative lens Lc in the objective lens for 
high magnification have been described as different lenses, but where, as 
previously described, the negative lens Lb for low magnification is used 
also as the negative lens for high magnification, fc=fb may be placed in 
the foregoing equations and of course, just the same construction can be 
realized. In such case, if the high magnification state of FIG. 5 
according to the prior art is compared with the high magnification state 
of FIG. 7 according to the present invention, it will be clear that the 
amount of displacement of the negative lens in the direction of the optic 
axis for changing the magnification to the geomerically identical high 
magnification condition is reduced from the heretofore required (d2-d1) to 
d4. 
In the foregoing description, the finder system has been described as a 
completely afocal optical arrangement, but with the actual finder, it is 
sometimes the case that the finder is not made into a completely afocal 
system but a predetermined visibility correction is applied. This 
visibility correction can of course be easily achieved by moving the 
eyepiece Le toward the object side or the observation side by an amount 
corresponding to the predetermined visibility. 
The geometro-optical basic construction of the present invention has been 
described above in detail. Since the position of the principal point of 
the eyepiece or the objective lens is variable by the specific lens 
construction, the lens shape, the lens thickness, etc., the values of said 
d1, d2 and d3 are not always coincident with the full length of the 
finder. However, according to the above-described principle of the present 
invention, it is clear that as compared with the prior art, the amount of 
decrease in the space on the eyepiece side in the finder is smaller during 
the change of the magnification to the high magnification. With the finder 
of a camera, it is often the case that various optical members such as a 
half-mirror for providing an illuminating window type bright frame and a 
lens having a half-transmitting mirror surface for providing an Albada 
finder are added on the optic axis, but these members may be considered to 
be a part of the objective lens or the eyepiece. 
Specific numerical values will now be shown as embodiments of the 
changeable magnification finder according to the present invention. 
In first to third embodiments of the present invention, as shown in FIGS. 8 
to 10, respectively, magnification change is accomplished by interchanging 
the negative lens Lb as the objective lens for low magnification with the 
positive lens La and the negative lens Lc as the objective lens for high 
magnification. 
Also, fourth to sixth embodiments of the present invention, as shown in 
FIGS. 11 to 13, respectively, are ones in which the negative lens Lb as 
the objective lens for low magnification is used also as the negative lens 
in the objective lens for high magnification and, in these embodiments, 
the negative lens Lb is moved on the optic axis for magnification change 
and in the high magnification state, the positive lens La is inserted or 
added on the object side of this negative lens Lb. 
The numerical data of the respective embodiments will be shown in the 
tables below and will be described. 
In the tables below: 
.beta.1: finder magnification in the high magnification state 
.beta.2: finder magnification in the low magnification state 
d2: distance between the negative lens Lb as the objective lens in the low 
magnification state and the eyepiece Le 
d3: distance between the positive lens La forming the objective lens in the 
high magnification state and the eyepiece Le 
d4: distance between the positive lens La and the negative lens forming the 
objective lens for high magnification 
d1: distance between the negative lens Lo equivalent to the high 
magnification objective lens in the high magnification state (which lens 
Lo corresponds to the objective lens for high magnification in the prior 
art) and the eyepiece Le 
fa: focal length of the positive lens forming the objective lens for high 
magnification 
fb: focal length of the negative lens forming the objective lens for low 
magnification 
fc: focal length of the negative lens forming the objective lens for high 
magnification 
fe: focal length of the eyepiece 
fo: composite focal length of the objective lens for high magnification in 
the high magnification state 
a: distance between the object side focus of the eyepiece and the negative 
lens forming the objective lens for high magnification in the high 
magnification state 
b: distance between the negative lens Lo equivalent to the high 
magnification objective lens in the high magnification state (which lens 
Lo corresponds to the objective lens for high magnification in the prior 
art) and the negative lens forming the objective lens for high 
magnification 
TABLE 1 
______________________________________ 
(First Embodiment) 
d2 = 38.5, d3 = 35, .beta.2 = 0.4x, (.beta.1/.beta.2) = 1.6 
______________________________________ 
By equation (5), fb = -25.667 
By equation (6), fe = 64.167, .beta.1 = 0.64 
By equation (1), fo = -41.067 
fc = -30.0 
By equation (14), a = 38.451 
By equation (15), d4 = 9.284 
By equation (10), fa = 145.744 
By equation (2), d1 = 23.100 
By equation (13), b = 2.616 
______________________________________ 
The optical path of the first embodiment in the high magnification state is 
shown in FIG. 8. In the upper portion of this Figure, the objective lens 
Lb for low magnification is shown at an on-axis position to be 
interchanged. In this case, relative to the low magnification state, in 
the high magnification, the eyepiece side space decreases by 
.DELTA.=12.784, but the eyepiece side space in the finder can be enlarged 
by 2.616 as compared with the magnification change by the conventional 
system, thereby accomplishing the magnification change to the high 
magnification. 
TABLE 2 
______________________________________ 
(Second Embodiment) 
d2 = d3 = 38.5, .beta.2 = 0.4x, (.beta.1/.beta.2) = 1.6 
______________________________________ 
By equation (5), fb = -25.667 
By equation (6), fe = 64.167, .beta.1 = 0.64 
By equation (1), fo = -41.067, 
fc = fb = -25.667 
By equation (14), a = 36.497 
By equation (15), d4 = 10.830 
By equation (10), fa = 97.321 
By equation (2), d1 = 23.100 
By equation (13), b = 4.570 
______________________________________ 
The optical path of the second embodiment in the high magnification state 
is shown in FIG. 9. In this case, relative to the low magnification state, 
in the high magnification state, the eyepiece side space decreases by 
.DELTA.=10.830, but the eyepiece side space in the finder can be enlarged 
by 4.57 as compared with the magnification change by the conventional 
system, thereby accomplishing the magnification change to the high 
magnification. Thus, even if d2=d3, a changeable magnification finder can 
be realized as in the previous embodiment. If the full length on the low 
magnification side is the full length of the finder, it is desired that 
d3.ltoreq.d2, but by equation (14), as the numerical value of d3 is 
greater, the value of becomes smaller and accordingly, by equation (13), 
the value of b becomes greater and therefore, when d2=d3, that is, in the 
high magnification state, the finder will become most compact if the 
positive lens is disposed at the same position as the objective lens in 
the low magnification state. Further, in the present embodiment, the focal 
length of the negative lens Lb as the objective lens for low magnification 
is equal to the focal length of the negative lens Lc forming the objective 
lens for high magnification and therefore, these lenses can be 
manufactured as a common lens and this is advantageous. 
TABLE 3 
______________________________________ 
(Third Embodiment) 
d2 = d3 = 40, .beta.2 = 0.5x, (.beta.1/.beta.2) = 2.2 
______________________________________ 
By equation (5), fb = -40.0 
By equation (6), fe = 80.0, .beta.1 = 1.1 
By equation (1), fo = -88.0 
fc = -30.0 
By equation (14), a = 62.895 
By equation (15), d4 = 22.895 
By equation (10), fa = 80.253 
By equation (2), d1 = -8.0 
By equation (13), b = 25.105 
______________________________________ 
The optical path of the third embodiment is schemically shown in FIG. 10. 
Again in this embodiment, d2=d3, but .beta.1 is a considerably high 
magnification and moreover, the magnification ratio is as great as 2.2, 
and enlargement observation is possible in the high magnation state of 
.beta.1=1.1. It should be noted that d1=-8.0 means that in the high 
magnification state of the conventional system, a negative lens having a 
focal length fo=-88.0 is further disposed on the observation side of the 
eyepiece, that is, this system is a Galelian type telephoto optical 
system. Thus, according to the present invention, telephoto observation 
becomes possible simply by interchanging the lens on the object side of 
the eyepiece. 
TABLE 4 
______________________________________ 
(Fourth Embodiment) 
d2 = 38.5, d3 = 35, .beta.2 = 0.4x, (.beta.1/.beta.2) = 1.6 
______________________________________ 
By equation (5), fb = -25.667 
By equation (6), fe = 64.167, .beta.1 = 0.64 
By equation (1), fo = -41.067 
By equation (14), a = 37.346 
By equation (15), d4 = 8.179 
By equation (10), fa = 90.268 
By equation (2), d1 = 23.100 
______________________________________ 
The optical path of the fourth embodiment is schematically shown in FIG. 
11. The upper portion of FIG. 11 shows the low magnification (wide angle) 
state, and the lower portion of FIG. 11 shows the high magnification 
(telephoto) state. In this case, by moving the negative lens Lb by 
.DELTA.=11.679 and adding the positive lens La on the object side thereof, 
there is constructed an inverted Galelian finder which is capable of being 
changed over to the high magnification while decreasing the amount of 
displacement of the negative lens by 3.721 as compared with the 
magnification change by the conventional system. 
TABLE 5 
______________________________________ 
(Fifth Embodiment) 
d2 = d3 = 38.5 .beta.2 = 0.4x, (.beta.1/.beta.2) = 1.6 
______________________________________ 
By equation (5), fb = -25.667 
By equation (6), fe = 64.167, .beta.1 = 0.64 
By equation (1), fo = -41.067 
By equation (14), a = 36.497 
By equation (15), d4 = 10.830 
By equation (10), fa = 97.321 
By equation (2), d1 = 23.100 
By equation (13), b = 4.570 
______________________________________ 
The optical path of the second embodiment is schematically shown in FIG. 
12. In this case, by moving the negative lens Lb by .DELTA.=10.83 and 
adding the positive lens La on the objective side thereof, there is 
constructed an inverted Galilean finder which is capable of being changed 
over to the high magnification while decreasing the amount of displacement 
of the negative lens by 4.570 as compared with the magnification change by 
the conventional system. Thus, even if d2=d3, a changeable magnification 
finder can be realized as in the previous embodiment. If the full length 
on the low magnification side is the full length of the finder, it is 
desired that d3.ltoreq.d2, but by equation (14), as the numerical value of 
d3 is greater, the value of a becomes smaller and accordingly, by equation 
(13), the value of b becomes greater and therefore, when d2=d3, that is, 
in the high magnification state, the finder will become most compact if 
the positive lens is disposed at the same position as the objective lens 
in the low magnification state. 
TABLE 6 
______________________________________ 
(Sixth Embodiment) 
d2 = d3 = 40, .beta.2 = 0.5x, (.beta.1/.beta.2) = 2.2 
______________________________________ 
By equation (5), fb = -40.0 
By equation (6), fe = 80.0, .beta.1 = 1.1 
By equation (1), fo = -88.0 
By equation (14), a = 68.166 
By equation (15), d4 = 28.166 
By equation (10), fa = 124.968 
By equation (2), d1 = -8.0 
By equation (13), b = 19.834 
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The optical path of the third embodiment is schematically shown in FIG. 13. 
In this case, by moving the negative lens Lb by .DELTA.=28.166 and adding 
the positive lens La on the object side thereof, there is constructed an 
inverted Galilean finder which is capable of being changed over to the 
high magnification while decreasing the amount of displacement of the 
negative lens by 19.834 as compared with the magnification change by the 
conventional system. Again in this embodiment, d2=d3, but .beta.1 is a 
considerably high magnification and the magnification ratio 
(.beta.1/.beta.2) is as great as (.beta.1/.beta.2)=2.2, and enlargement 
observation is possible in the high magnification state of .beta.1=1.1. It 
should be noted that d1=-8.0 means that in the high magnification state of 
the conventional system, the negative lens Lo having a focal length 
fo=-88.0 is further disposed on the observation side of the eyepiece, that 
is, the system is a Galelian type telephoto optical system. Thus, 
according to the present invention, the eyepiece is fixed and the lens is 
displaced and added on the object side thereof, whereby telephoto 
observation also becomes possible. 
As is apparent from the foregoing specific examples of the numerical 
values, according to the present invention, there is realized a changeable 
magnification inverted Galilean finder having a structure which secures a 
larger eyepiece side space in the finder than in the prior art during 
magnification change and yet is compact and capable of simply changing 
over the magnification. 
Also, according to the present invention, there is realized a changeable 
magnification inverted Galilean finder having a structure in which the 
amount of displacement of the negative lens in the direction of the optic 
axis is made considerably smaller than in the conventional system and yet 
which is compact and capable of simply changing over the magnification. 
Therefore, a sufficient space for containing optical members for effecting 
various displays can be secured in the field of view of the finder, and 
this leads to the provision of a changeable magnification inverted 
Galilean finder which is capable of effecting numerous information 
displays.