Zoom finder

A zoom finder has first to third lens groups sequentially arranged from an object side to an eye pupil side and performs a zooming operation by fixing the first and third lens groups and moving the second lens group. The first lens group is constructed by a positive single lens. The second lens group is constructed by a negative single lens. The third lens group has a positive combinational focal length and is constructed by a negative single lens arranged on the object side and a positive single lens arranged on the eye pupil side. A frame system of the zoom finder is formed by an eye pupil side lens face of the negative single lens of the third lens group and the positive single lens of the third lens group. Radii R.sub.1 and R.sub.2 of curvature of lens faces of the first lens group on the object and eye pupil sides satisfy the following condition. EQU 0.8<R.sub.1 /.vertline.R.sub.2 .vertline.<1.2 (I) At least one lens face of the first lens group is constructed by an aspherical surface.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a zoom finder and can be utilized in 
finders of a lens shutter camera and a video camera. 
2. Description of the Related Art 
Various kinds of zoom finders used in a lens shutter camera are generally 
known. Recently, the lens shutter camera has been very compact in a high 
zoom ratio. Therefore, it is difficult to provide a high zoom ratio and 
compactness with respect to a general zoom finder. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide a novel zoom 
finder in which an entire length of the zoom finder can be effectively 
reduced a high zoom ratio can be obtained, and aberrations can be 
preferably corrected. 
To achieve the above object, in the present invention, a zoom finder has 
first to third lens groups sequentially arranged from an object side to an 
eye pupil side and performs a zooming operation by fixing the first and 
third lens groups and moving the second lens group. 
The zoom finder having each of first to fourth structures of the present 
invention is constructed as follows by four lenses in three lens groups as 
shown in FIG. 1. 
The first lens group is constructed by a positive single lens L1. The 
second lens group is constructed by a negative single lens L2. 
The third lens group has a positive combinational focal length and is 
constructed by a negative single lens L3 arranged on the object side and a 
positive single lens L4 arranged on the eye pupil side. A frame system of 
the zoom finder is formed by an eye pupil side lens face of the negative 
single lens L3 and the positive single lens L4. Namely, the frame is 
formed on an object side face of the lens L4. An image of this frame 
reflected on a half mirror formed on the eye pupil side face of the lens 
L3 is enlarged and observed by the lens L4. 
In the zoom finder having the first structure, radii R.sub.1 and R.sub.2 of 
curvature of lens faces of the positive single lens L1 of the first lens 
group on the object and eye pupil sides satisfy the following condition. 
EQU 0.8&lt;R.sub.1 /.vertline.R.sub.2 .vertline.&lt;1.2 (1-I) 
At least one lens face of the first lens group is constructed by an 
aspherical surface. 
In the zoom finder having the second structure, a focal length f.sub.3N of 
the negative single lens L3 of the third lens group and a radius R.sub.6 
of curvature of the eye pupil side lens face of the negative single lens 
L3 in the first structure satisfy the following condition. 
EQU 0.15&lt;.vertline.f.sub.3N .vertline./R.sub.6 &lt;0.2 (1-II) 
In the zoom finder having the first or second structure, the positive 
single lens L1 of the first lens group is constructed by a biconvex lens 
in accordance with the third structure of the present invention. The 
negative single lens L2 of the second lens group is constructed by a 
biconcave lens in the third structure. The negative single lens L3 of the 
third lens group is constructed by a biconcave lens in the third 
structure. The positive single lens L4 of the third lens group is 
constructed by a flat convex lens in the third structure. In this case, 
each of second, fourth, fifth, sixth and eighth lens faces of the zoom 
finder counted from the object side is constructed by an aspherical 
surface in accordance with the fourth structure of the present invention. 
The zoom finder having each of fifth to ninth structures of the present 
invention is constructed as follows by five lenses in three lens groups as 
shown in FIG. 6. 
A first lens group is constructed by a positive single lens L10. A second 
lens group is constructed by a negative single lens L20. 
A third lens group has a positive combinational focal length and is 
constructed by a negative single lens L30, a positive single lens L40 and 
a positive single lens L50 sequentially arranged from an object side to an 
eye pupil side. 
A frame system of the zoom finder is constructed by a half mirror formed on 
an eye pupil side lens face of the positive single lens L40 and a frame 
formed on an object side lens face of the positive single lens L50. 
Namely, the frame is formed on the object side face of the single lens 
L50. An image of this frame reflected on the half mirror formed on the eye 
pupil side face of the lens L40 is enlarged and observed by the lens L50. 
In the zoom finder having the sixth structure, a focal length f.sub.3N (&lt;0) 
of the negative single lens L30 of the third lens group, a focal length 
f.sub.3P ' of the positive single lens L40, and a distance d.sub.12 
between a rear principal point of the negative single lens L30 and a front 
principal point of the positive single lens L40 satisfy the following 
conditions. 
EQU .vertline.f.sub.3N .vertline./f.sub.3P '&lt;0.5 (2-I) 
and 
EQU d.sub.12 /f.sub.3P '&lt;0.1 
In the zoom finder having the seventh structure, the focal length f.sub.3N 
of the negative single lens L30 and a combinational focal length F.sub.3 
of the third lens group in the fifth or sixth structure satisfy the 
following condition. 
EQU 0.08&lt;.vertline.f.sub.3N .vertline./F.sub.3 &lt;0.1 (2-II) 
In the zoom finder having the seventh structure, the positive single lens 
L10, the negative single lens L20, the negative single lens L30 of the 
third lens group, the positive single lens L40, and the positive single 
lens L50 in the eighth structure are respectively constructed by a 
biconvex lens, a biconcave lens, a biconcave lens, a positive meniscus 
lens having a convex face on the object side, and a flat convex lens. In 
this case, in accordance with the ninth structure, each of second, fourth, 
fifth, eighth and tenth lens faces of the zoom finder counted from the 
object side is constructed by an aspherical surface. 
As mentioned above, in the zoom finder of the present invention, the 
zooming operation is performed by fixing the first and third lens groups 
and moving the second lens group. When the zooming operation is performed 
from a low magnification to a high magnification, the second lens groups 
L2 and L20 are displaced from the object side to the eye pupil side. 
FIG. 2 is a view showing the arrangement of principal points at a time of 
the low magnification in the zoom finder having each of the first to 
fourth structures. FIG. 2 concretely relates to Embodiment 1 described 
later. 
A distance between principal points of the lenses L1 and L2 must be first 
reduced to make compact the zoom finder having each of the first to fourth 
structures and composed of four lenses in three lens groups by reducing an 
entire length of this zoom lens. If a shape of the lens L1 is flat and 
convex, the principal point of the lens L1 is located on the eye pupil 
side. Accordingly, the distance between the principal points of the lenses 
L1 and L2 can be minimized, but aberrations are increased. 
When the above condition (1-I) is satisfied, curvatures of the object side 
lens face and the eye pupil side lens face of the lens L1 are 
approximately equal to each other. Accordingly, the entire length of the 
zoom finder can be reduced by effectively correcting the aberrations 
without greatly increasing the distance between the principal points of 
the lenses L1 and L2. 
The aberrations can be more preferably corrected by setting at least one 
face of the single lens L1 to an aspherical surface. 
As shown in FIG. 2, a principal point of the third lens group is located on 
the eye pupil side with respect to a principal point of the positive 
single lens L4 of the third lens group. To reduce the entire length of the 
zoom finder, it is preferable to increase a distance S between a position 
of the principal point of the third lens group and a position of the 
principal point of the lens L4 so that the lenses L3 and L4 constituting 
the third lens group are located on the object side as much as possible so 
as not to prevent the lens L2 from being moved onto the eye pupil side at 
a high magnification time. 
F.sub.3 is set to a combinational focal length of the third lens group. 
Reference numeral d is set to a distance between the principal points of 
the lenses L3 and L4. f.sub.3P is set to a focal length of the positive 
single lens L4 of the third lens group. In this case, the above distance S 
is represented by the following formula (1). 
EQU S=(F.sub.3 .multidot.d/f.sub.3P)-d (1) 
A focal length f.sub.3N of the negative single lens L3 of the third lens 
group is provided by the following formula (2). 
EQU f.sub.3N =F.sub.3 (d-f.sub.3P)/(F.sub.3 -f.sub.3P) (2) 
When the above formula (2) is differentiated with respect to f.sub.3P, the 
following formula (3) is obtained. 
EQU df.sub.3N /df.sub.3P =F.sub.3 (d-F.sub.3)/(F.sub.3 -f.sub.3P).sup.2( 3) 
Since d&lt;F.sub.3 is set, the right-hand side of the formula (3) is negative. 
Accordingly, it should be understood from the formula (3) that f.sub.3N is 
decreased (df.sub.3N &lt;0) if f.sub.3P is increased (df.sub.3P &gt;0). 
With reference to the formula (1), it should be understood that f.sub.3P is 
preferably decreased and refracting power of the lens L4 is therefore 
increased to increase the above distance S. However, as mentioned above, 
when f.sub.3P is decreased, f.sub.3N is increased so that negative 
refracting power of the lens L3 is increased. 
In the zoom finder of the present invention, the frame system as an albada 
section is formed by the eye pupil side face of the lens L3 and the lens 
L4 as mentioned above. Accordingly, the radius R.sub.6 of curvature of the 
eye pupil side lens face of the lens L3 is necessarily determined if the 
focal length f.sub.3P of the lens L4, the lens face distance D.sub.6 
between the lenses L3 and L4 on an optical axis of the zoom finder in FIG. 
1, and a central thickness D.sub.7 of the lens L4 in FIG. 1 are 
determined. 
As mentioned above, when f.sub.3P is reduced to increase the distance S, it 
is necessary to increase the refracting power of the lens L3. However, the 
radius R.sub.6 of curvature of the eye pupil side lens face of the lens L3 
must be set to be large to a certain extent for formation of the frame. 
Therefore, curvature of the object side lens face of the lens L3 must be 
set to be large to increase the negative refracting power of the lens L3. 
In such a situation, it is desirable to satisfy the above condition (1-II) 
so as to preferably correct aberrations while effects provided by the 
reduction in entire length of the zoom finder and a high zoom ratio are 
held. 
When the ratio .vertline.f.sub.3N .vertline./R.sub.6 in the condition 
(1-II) exceeds an upper limit thereof, no effects of the reduction in 
entire length of the zoom finder can be sufficiently obtained. In contrast 
to this, when the ratio .vertline.f.sub.3N .vertline./R.sub.6 in the 
condition (1-II) exceeds a lower limit thereof, a displacing region of the 
lens L2 is limited by the lens L3. Accordingly, it is difficult to obtain 
a high zoom ratio and preferably correct the aberrations. 
As shown in Embodiments described later, the entire length of the zoom 
finder can be set to be equal to or shorter than 29 mm and the zoom ratio 
can be set to be equal to or greater than 1.8 by satisfying both the 
conditions (1-I) and (1-II). 
As explained above, curvature of the object side lens face of the negative 
lens of the third lens group is necessarily very large in the zoom finder 
having each of the first to fourth structures. 
When the zoom finder is constructed by three lens groups having positive, 
negative and positive refracting powers from the object side to the eye 
pupil side, a light beam from the second lens group is incident to a lens 
face or the third lens group on a most object side at an incident angle 
large with respect to the optical axis of the zoom finder. Therefore, when 
curvature of the most object side lens face of the third lens group is 
large as in the zoom finder having each of the first to fourth structures, 
large aberrations shown by the inclination of an image tend to be caused. 
To avoid such aberrations, it is necessary to satisfy the above conditions 
(1-I) and (1-II). 
The entire zoom finder having the fifth structure is constructed by three 
lens groups having positive, negative and positive refracting powers. The 
third lens group is constructed by a negative single lens L30, a positive 
single lens L40 and a positive single lens L50 sequentially arranged from 
an object side to an eye pupil side. Further, a half mirror is arranged on 
an eye pupil side face of the positive single lens L40. 
In accordance with such a fifth structure, no half mirror is formed on an 
eye pupil side face of the negative single lens L30 as a most object side 
lens of the third lens group. Therefore, the required refracting power of 
this single lens L30 can be allocated to curvatures of both lens faces of 
this single lens L30. Thus, the curvature of an object side lens face of 
the single lens L30 can be set to be reduced in comparison with the zoom 
finder constructed by four lenses in three lens groups in each of the 
first to fourth structures. Accordingly, it is possible to effectively 
restrain an image face from being inclined without satisfying the above 
conditions (1-I) and (1-II). Further, since the curvature of the object 
side lens face of the negative single lens L30 is reduced, it is easy to 
secure a space for moving the negative single lens L20 of the second lens 
group in a zooming operation at a high magnification time. 
FIG. 7a is a view showing the arrangement of principal points at a low 
magnification time in the zoom finder of the present invention. FIG. 7b is 
a view showing the arrangement of principal points of the third lens 
group. As shown in FIG. 7b, a distance between principal points is set to 
be positive in an eye pupil direction with a black circle as a starting 
point. FIGS. 7a and 7b concretely relate to Embodiment 4 described later. 
In the following description, f.sub.12 is set to a combinational focal 
length of a negative single lens L30 and a positive single lens L40 of the 
third lens group. Further, as described before, f.sub.3N (&lt;0) is set to a 
focal length of the single lens L30, and f.sub.3P ' is set to a focal 
length of the positive single lens L40. d.sub.12 is set to a distance 
between a rear principal point of the negative single lens L30 and a front 
principal point of the positive single lens L40. In this case, the 
combinational focal length f.sub.12 is provided by the following formula 
(4) using the focal lengths f.sub.3N and f.sub.3P ' and the distance 
d.sub.12. 
EQU f.sub.12 =f.sub.3N .multidot.f.sub.3P '/(f.sub.3N +f.sub.3P '-d.sub.12)(4) 
The combinational focal length f.sub.12 is negative in a range in which the 
condition (2-I) in the sixth structure of the present invention is 
satisfied. In this range, as shown in FIG. 7b, a combined rear principal 
point is located by a length S.sub.1 on an object side of the zoom finder 
from the rear principal point of the positive single lens L40. In this 
case, the length S.sub.1 is provided as follows. 
EQU S.sub.1 =f.sub.3P '.multidot.d.sub.12 /(f.sub.3N +f.sub.3P '-d.sub.12) 
At this time, d.sub.12 is small in accordance with the condition (2-I) so 
that the front and rear principal points at the combinational focal length 
f.sub.12 are approximately in conformity with each other. 
Therefore, a distance d shown in FIG. 7b can be increased by the length 
S.sub.1 in comparison with a case in which the third lens group is 
constructed by two lenses having negative and positive refracting powers. 
Therefore, an entire length of the zoom finder can be further reduced as 
follows. 
Namely, as shown in FIG. 7b, it is necessary to increase a distance S in 
position between a front principal point of the third lens group and the 
front principal point of the positive single lens L40 to reduce the entire 
length of the zoom finder by five lenses in three lens groups in the fifth 
structure of the present invention. The distance S is provided by the 
following formula (5) using the above combinational focal length F.sub.3 
of the third lens group, the distance d and a focal length f.sub.3P " of 
the positive single lens L50 of the third lens group. 
EQU S=(F.sub.3 .multidot.d/f.sub.3P ")-d(&gt;0) (5) 
When this formula (5) is differentiated with respect to the distance d, the 
following formula is obtained. 
EQU dS/dd=(F.sub.3 /f.sub.3P ")-1(&gt;0) 
Accordingly, if the distance d is increased as mentioned above in 
accordance with the above condition (2-I), the distance S is increased so 
that the entire length of the zoom finder can be reduced. Thus, it is 
possible to obtain effects according to the lens construction of the fifth 
structure of the present invention. 
When the third lens group is constructed by two lenses having negative and 
positive refracting powers as in the zoom finder having each of the first 
to fourth structures, a distance between these two lenses of the third 
lens group is increased by increasing the distance d so that no entire 
length of the zoom finder is necessarily reduced. 
In the zoom finder having each of the fifth and sixth structures, it is 
desirable to satisfy the condition (2-II) in accordance with the seventh 
structure of the present invention. 
When .vertline.f.sub.3N .vertline./F.sub.3 in the condition (2-II) exceeds 
an upper limit thereof, it is difficult to effectively reduce the entire 
length of the zoom finder. In contrast to this, when .vertline.f.sub.3N 
.vertline./F.sub.3 in the condition (2-II) exceeds a lower limit thereof, 
refracting powers of the two positive single lenses L40 and L50 of the 
third lens group are increased so that it is difficult to correct 
aberrations. In particular, in the case of the ninth lens structure, the 
positive single lens L40 is constructed by a positive meniscus lens having 
a convex face on the object side. Therefore, as refracting power of the 
negative single lens L30 is increased, it is difficult to secure a 
required lens edge thickness when refracting power of the single lens L40 
is increased. 
As shown in the following Embodiments, the entire length of the zoom finder 
can be set to be equal to or shorter than 30 mm and a zoom ratio can be 
set to be equal to or greater than 1.8 by satisfying both the conditions 
(2-I) and (2-II).

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The preferred embodiments of a zoom finder in the present invention will 
next be described in detail with reference to the accompanying drawings. 
Concrete Embodiments of the present invention will next be described. 
Embodiments 1 to 3 are embodiments of a zoom finder having each of first 
to fourth structures of the present invention. As shown in FIG. 1, R.sub.i 
(i=1 to 8) designates a radius of curvature of an i-th lens face counted 
from an object side of the zoom finder. D.sub.i (i=1 to 7) designates a 
distance between the i-th lens face and an (i+1)-th lens face on an 
optical axis of the zoom finder. D.sub.8 designates a distance between an 
eighth lens face as a final lens face counted from the object side and an 
eye pupil point position on the optical axis of the zoom finder. N.sub.j 
designates a refractive index of the material of a j-th lens counted from 
the object side with respect to line d. An entire length of the zoom 
finder is provided by adding D.sub.1 to D.sub.7 to each other. 
A Z-axis is set to be in conformity with the optical axis of the zoom 
finder. Y is set to a coordinate in a direction perpendicular to the 
optical axis of the zoom finder. In this case, an aspherical surface is 
obtained by rotating a curve represented by the following formula around 
the optical axis of the zoom finder. 
EQU Z=(Y.sup.2 /R)/[1+ {1-(1+K)Y.sup.2 /R.sup.2 }]+A.multidot.Y.sup.4 
+B.multidot.Y.sup.6 +C.multidot.Y.sup.8 
In this formula, K is a conical constant and A, B and C are respectively 
aspherical coefficients of fourth, sixth and eighth orders. A shape of the 
aspherical surface is specified by giving the conical constant K and the 
aspherical coefficients A, B and C. 
______________________________________ 
Embodiment 1 
i R.sub.i D.sub.i j N.sub.j 
______________________________________ 
1 28.661 5.96 1 1.49154 
2 -26.150 variable 
3 -97.802 1.30 2 1.49154 
4 5.730 variable 
5 -5.130 1.30 3 1.49154 
6 58.000 6.30 
7 .infin. 2.63 4 1.49154 
8 -8.050 15.00 
______________________________________ 
Variable amounts 
zooming wide angle 
telescopic 
point end end 
______________________________________ 
magnification 0.317 0.578 
D.sub.2 0.4 7.05 
D.sub.4 10.75 4.1 
______________________________________ 
Aspherical Surfaces 
Second face 
K=-13.327, A=6.393.times.10.sup.-6, B=-1.118.times.10.sup.-8, C=0.00 
Fourth face 
K=-0.200, A=-1.622.times.10.sup.-4, B=3.234.times.10.sup.-6, C=0.00 
Fifth face 
K=-1.480, A=-4.540.times.10.sup.-4, B=-5.010.times.10.sup.-5, 
C=2.730.times.10.sup.-7 
Sixth face 
K=156.146, A=-1.199.times.10.sup.-4, B=-8.520.times.10.sup.-6, C=0.00 
Eighth face 
K=-2.968, A=-5.011.times.10.sup.-4, B=1.763.times.10.sup.-6, C.times.0.00 
Parametric values of conditional formula 
EQU R.sub.1 /.vertline.R.sub.2 .vertline.=1.1, .vertline.f.sub.3N 
.vertline./R.sub.6 =0.16 
entire length: 28.64, zoom ratio: 1.823 
______________________________________ 
Embodiment 2 
i R.sub.i D.sub.i j N.sub.j 
______________________________________ 
1 26.128 6.22 1 1.49154 
2 -26.217 variable 
3 -90.160 1.20 2 1.49154 
4 5.444 variable 
5 -5.268 1.30 3 1.49154 
6 57.285 6.30 
7 .infin. 2.80 4 1.49154 
8 -8.114 15.00 
______________________________________ 
Variable amounts 
zooming wide angle 
telescopic 
point end end 
______________________________________ 
magnification 0.317 0.58 
D.sub.2 0.4 6.76 
D.sub.4 10.46 4.1 
______________________________________ 
Aspherical Surfaces 
Second face 
K=-15.500, A=5.976.times.10.sup.-6, B=-1.143.times.10.sup.-8 
Fourth face 
K=-0.272, A=-1.465.times.10.sup.-4, B=4.533.times.10.sup.-6 
Fifth face 
K=-1.481, A=-4.420.times.10.sup.-4, B=-5.080.times.10.sup.-5 
Sixth face 
K=145.417, A=-1.289.times.10.sup.-4, B=-8.124.times.10.sup.-6 
Eighth face 
K=-2.982, A=-4.982.times.10.sup.-4, B=1.621.times.10.sup.-6 
Parametric values of conditional formula 
EQU R.sub.1 /.vertline.R.sub.2 .vertline.=1.0, .vertline.f.sub.3N 
.vertline./R.sub.6 =0.17 
entire length: 28.68, zoom ratio: 1.83 
______________________________________ 
Embodiment 3 
i R.sub.i D.sub.i j N.sub.j 
______________________________________ 
1 28.971 5.82 1 1.49154 
2 -27.320 variable 
3 -108.880 1.00 2 1.49154 
4 5.903 variable 
5 -5.428 1.30 3 1.49154 
6 52.086 6.30 
7 .infin. 3.00 4 1.49154 
8 -8.300 15.00 
______________________________________ 
Variable amounts 
zooming wide angle 
telescopic 
point end end 
______________________________________ 
magnification 0.317 0.58 
D.sub.2 0.4 7.35 
D.sub.4 11.1 4.15 
______________________________________ 
Aspherical surfaces 
Second face 
K=-14.857, A=3.945.times.10.sup.-6, B=-7.749.times.10.sup.-9 
Fourth face 
K=-0.254, A=-1.351.times.10.sup.-4, B=3.365.times.10.sup.-6 
Fifth face 
K=-2.296, A=-1.162.times.10.sup.-3, B=-2.948.times.10.sup.-5 
Sixth face 
K=109.798, A=-1.558.times.10.sup.-4, B=-6.191.times.10.sup.-6 
Eighth face 
K=-2.994, A=-4.890.times.10.sup.-4, B=1.983.times.10.sup.-6 
Parametric values of conditional formula 
EQU R.sub.1 /.vertline.R.sub.2 .vertline.=1.1, .vertline.f.sub.3N 
.vertline./R.sub.6 =0.19 
entire length: 28.92, zoom ratio: 1.83 
FIGS. 3a-3h, 4a-4h and 5a-5h respectively show aberrational diagrams of the 
zoom finder at a wide angle end (FIGS. 3a-3c), (FIGS. 4a-4c) and FIGS. 
(5a-5c), a telescopic end (FIGS. 3d-3f), (FIGS. 4d-4f), and (FIGS. 5d-5f) 
and a finder frame (FIGS. 3g-3h), (FIGS. 4g-4h) and (FIGS. 5g-5h) with 
respect to Embodiments 1 to 3. FIGS. (3a, 3d, 3g), FIGS. (4a, 4d, 4g) and 
FIGS. (5a, 5d, 5g) illustrate spherical aberration diagrams; FIGS. (3b, 
3e, 3h), FIGS. (4b, 4e, 4h) and FIGS. (5b, 5e, 5h) illustrate astigmatism 
diagrams; and FIGS. (3c, 3f), FIGS. (4c, 4f) and FIGS. (5c, 5f) illustrate 
distortional aberration diagrams. .omega. designates a half field angle. 
.omega.' designates an angle formed between an optical axis of the zoom 
finder and a principal ray incident to a lens L1 at a field angle .omega. 
when this principal ray is emitted from a lens L4. In astigmatic diagrams, 
reference numerals S and M respectively designate sagittal and meridional 
rays. In each of the Embodiments 1 to 3, aberrations are preferably 
corrected and an entire length of the zoom finder can be set to be equal 
to or shorter than 29 mm. Further, a zoom ratio of the zoom finder can be 
set to be equal to or greater than 1.8. 
The following Embodiments 4 and 5 are concrete embodiments of a zoom finder 
having each of fifth to ninth structures. 
As shown in FIG. 6, R.sub.i (i=1 to 10) designates a radius of curvature of 
an i-th lens face counted from an object side of the zoom finder. D.sub.i 
(i=1 to 9) designates a distance between the i-th lens face and an 
(i+1)-th lens face on an optical axis of the zoom finder. D.sub.10 
designates a distance between a tenth lens face as a final lens face 
counted from the object side and an eye pupil point position on the 
optical axis of the zoom finder. N.sub.j designates a refractive index of 
the material of a j-th lens counted from the object side with respect to 
line d. An entire length of the zoom finder is provided by adding D.sub.1 
to D.sub.9 to each other. 
Similar to the Embodiments 1 to 3, the shape of an aspherical surface is 
specified by giving the conical constant K and the aspherical coefficients 
A, B and C. 
______________________________________ 
Embodiment 4 
i R.sub.i D.sub.i j N.sub.j 
______________________________________ 
1 25.319 5.64 1 1.49154 
2 -32.608 variable 
3 -119.108 1.30 2 1.49154 
4 5.859 variable 
5 -8.577 1.00 3 1.49154 
6 6.039 0.91 
7 7.941 1.30 4 1.49154 
8 33.593 6.60 
9 .infin. 2.30 5 1.49154 
10 -9.530 15.00 
______________________________________ 
Variable amounts 
zooming wide angle intermediate 
telescopic 
point end focal length 
end 
______________________________________ 
magnification 
0.317 0.421 0.58 
D.sub.2 0.4 3.86 7.32 
D.sub.4 10.52 7.06 3.6 
______________________________________ 
Aspherical Surfaces 
Second face 
K=-22.014, A=8.454.times.10.sup.-6, B=-1.813.times.10.sup.-8 
Fourth face 
K=-0.962, A=2.662.times.10.sup.-4, B=1.355.times.10.sup.-5 
Fifth face 
K=-2.687, A=-3.88.times.10.sup.-5, B=-1.134.times.10.sup.-5 
Eighth face 
K=1.458, A=-4.679.times.10.sup.-5, B=-1.639.times.10.sup.-6 
Tenth face 
K=-2.996, A=-3.314.times.10.sup.-4, B=-2.15.times.10.sup.-7 
Parametric values of conditional formula 
EQU .vertline.f.sub.3N .vertline./f.sub.3P '=0.3, d.sub.12 /f.sub.3P '=0.04, 
.vertline.f.sub.3N .vertline./F.sub.3 =0.088 
entire length: 29.97, zoom ratio: 1.83 
______________________________________ 
Embodiment 5 
i R.sub.i D.sub.i j N.sub.j 
______________________________________ 
1 23.634 5.76 1 1.49154 
2 -34.101 variable 
3 -127.010 1.20 2 1.49154 
4 5.679 variable 
5 -8.711 1.00 3 1.49154 
6 6.375 0.90 
7 8.408 1.30 4 1.49154 
8 33.701 6.60 
9 .infin. 2.50 5 1.49154 
10 -9.585 15.00 
______________________________________ 
Variable amounts 
zooming wide angle intermediate 
telescopic 
point end focal length 
end 
______________________________________ 
magnification 
0.317 0.421 0.58 
D.sub.2 0.4 3.77 7.14 
D.sub.4 10.34 6.97 3.6 
______________________________________ 
Aspherical Surfaces 
Second face 
K=-25.833, A=8.874.times.10.sup.-6, B=-1.841.times.10.sup.-8 
Fourth face 
K=-0.832, A=2.114.times.10.sup.-4, B=1.453.times.10.sup.-5 
Fifth face 
K=-3.296, A=-7.385.times.10.sup.-5, B=-1.22.times.10.sup.-5 
Eighth face 
K=1.115, A=-4.718.times.10.sup.-5, B=-1.654.times.10.sup.-6 
Tenth face 
K=-3.046, A=-3.345.times.10.sup.-4, B=2.869.times.10.sup.-7 
Parametric values of conditional formula 
EQU .vertline.f.sub.3N .vertline./f.sub.3P '=0.3, d.sub.12 /f.sub.3P '=0.04, 
.vertline.f.sub.3N .vertline./F.sub.3 =0.094 
entire length: 30, zoom ratio: 1.83 
FIGS. 8a-8f show aberrational diagrams of the zoom finder at a wide angle 
end (FIGS. 8a-8e) and an intermediate focal length in a mean state (FIGS. 
8d-8f) with respect to Embodiment 4. FIGS. (8a, 8d) illustrate spherical 
aberration diagrams; FIGS. (8b, 8e) illustrate astigmatism diagrams; and 
FIGS. (8c, 8f) illustrate distortional aberration diagrams. FIGS. 9a-9e 
show aberrational diagrams of the zoom finder at a telescopic end (FIGS. 
9a-9c) and a finder frame (FIGS. 9d-9e) with respect to Embodiment 4. 
FIGS. (9a, 9d) illustrate spherical aberration diagrams; FIGS. (9b, 9e) 
illustrate astigmatism diagrams; and FIG. 9c illustrates a distortional 
aberration diagram. FIGS. 10a-10c show aberrational diagrams of the zoom 
finder at a wide angle end and an intermediate focal length in a mean 
state (FIGS. 10d-10f) with respect to Embodiment 5. FIGS. (10a, 10d) 
illustrate spherical aberration diagrams; FIGS. (10b, 10e) illustrate 
astigmatism diagrams; and FIGS. 10c, 10f) illustrate distortional 
aberration diagrams. FIGS. 11a-11e show aberrational diagrams of the zoom 
finder at a telescopic end (FIGS. 11a-11c) and a finder frame (FIGS 
11d-11e) with respect to Embodiment 5. FIGS. (11a, 11d) illustrate 
spherical aberration diagrams; FIGS. (11b, 11e) illustrate astigmatism 
diagrams; and FIG. 11c illustrates a distortional aberration diagram. 
.omega. designates a half field angle. .omega.' designates an angle formed 
between an optical axis of the zoom finder and a principal ray incident to 
a lens L10 at a field angle .omega. when this principal ray is emitted 
from a lens L50. In astigmatic diagrams, reference numerals S and M 
respectively designate sagittal and meridional rays and in the spherical 
aberration diagrams reference letter SC designates a sine condition. In 
each of the Embodiments 4 and 5, aberrations are preferably corrected and 
an entire length of the zoom finder can be set to be equal to or shorter 
than 30 mm. Further, a zoom ratio of the zoom finder can be set to be 
equal to or greater than 1.8. 
As mentioned above, the entire length of a novel zoom finder having each of 
first to ninth structures of the present invention is short and this zoom 
finder has a high zoom ratio. Further, aberrations of the zoom finder are 
preferably corrected. 
Many widely different embodiments of the present invention may be 
constructed without departing from the spirit and scope of the present 
invention. It should be understood that the present invention is not 
limited to the specific embodiments described in the specification, except 
as defined in the appended claims.