Viewfinder optical system

A viewfinder optical system has a relay optical system and an eyepiece optical system. The relay optical system has a first, a second, and a third relay lens. The eyepiece optical system has a first and a second eyepiece lens. The first eyepiece lens, which is disposed closest to a secondary-image plane formed by the relay optical system has an aspherical surface on its secondary-image plane side.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a viewfinder optical system, and 
particularly to a viewfinder optical system provided with a relay optical 
system for use in a single-lens reflex camera or other. 
2. Description of the Prior Art 
In the viewfinder optical system of a typical single-lens reflex camera, a 
pentaprism is used as an inverting optical system. However, with the 
pentaprism, it is difficult to construct a high-magnification viewfinder 
having a sufficiently long eyepoint distance. By contrast, if a relay 
optical system is used as an inverting optical system, it is possible to 
construct a high-magnification viewfinder having a sufficiently long 
eyepoint distance. 
However, a viewfinder optical system provided with the relay optical system 
has the disadvantage of being unable to achieve satisfactory matching of 
the pupils. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a viewfinder optical 
system that offers satisfactory matching of pupils despite being provided 
with a relay optical system. 
To achieve the above object, according to one aspect of the present 
invention, a viewfinder optical system is constituted of, from an object 
side to a pupil side, a relay lens system which forms an intermediate 
image on an intermediate image plane and has a first lens element disposed 
closest to the intermediate image plane, and a second lens element 
disposed on the pupil side of the intermediate image plane. Here, at least 
one aspherical surface is provided either on said first lens element or 
said second lens element. 
Alternatively, according to another aspect of the present invention, a 
viewfinder optical system is constituted of, from an object side to a 
pupil side, a relay lens system which forms an intermediate image on an 
intermediate image plane and has a first lens element disposed closest to 
the intermediate image plane, and an eyepiece lens system which projects 
the intermediate image on the pupil and has a second lens element disposed 
closest to the intermediate image plane. Here, at least one aspherical 
surface is provided either on said first lens element or said second lens 
element. 
According to still another aspect of the present invention, in either of 
the above viewfinder optical systems, aspherical surfaces are provided on 
both said first lens element and said second lens element.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Hereinafter, viewfinder optical systems embodying the present invention 
will be described with reference to the drawings. FIGS. 1 to 4 are optical 
path diagrams of the viewfinder optical systems of the first to fourth 
embodiments, respectively. In the first to fourth embodiments, a relay 
optical system for re-imaging a primary image formed on a focal plane I1 
onto a secondary-image plane I2 is constituted of a first relay lens G1 
composed of a biconvex lens element, a second relay lens G2 composed of a 
biconcave lens element, an aperture diaphragm, and a third relay lens G3 
composed of a biconvex lens element. The focal plane I1 is a primary-image 
plane on which an image is formed by an objective lens (not shown in the 
figures), and at the focal plane I1 is disposed a focusing screen. 
The first embodiment is provided with a positive-positive type eyepiece 
optical system. Specifically, the eyepiece optical system for directing 
light from the above secondary-image plane I2 to the pupil E has, from the 
secondary-image plane I2 side, a first eyepiece lens G4 and a second 
eyepiece lens G5, each composed of a biconvex lens element. The second 
embodiment is provided with a positive-positive-negative type eyepiece 
optical system. Specifically, the eyepiece optical system for directing 
light from the above secondary-image plane I2 to the pupil E has, from the 
secondary-image plane I2 side, a first eyepiece lens G4 and a second 
eyepiece lens G5, each composed of a biconvex lens element, and a third 
eyepiece lens G6 composed of a negative meniscus lens element with its 
concave surface facing toward the secondary-image plane I2 side. The third 
and fourth embodiments are provided with a positive-negative-positive type 
eyepiece optical system. Specifically, the eyepiece optical system for 
directing light from the above secondary-image plane I2 to the pupil E 
has, from the secondary-image plane I2 side, a first eyepiece lens G4 
composed of a biconvex lens element, a second eyepiece lens G5 composed of 
a negative meniscus lens element with its concave surface facing toward 
the pupil E side (with its convex surface facing toward the 
secondary-image plane I2 side), and a third eyepiece lens G6 composed of a 
biconvex lens element. 
In the first embodiment, the focal plane I1 side surface of the second 
relay lens G2, the secondary-image plane I2 side surface of the third 
relay lens G3, the secondary-image plane I2 side surface of the first 
eyepiece lens G4, and the secondary-image plane I2 side surface of the 
second eyepiece lens G5 are aspherical surfaces. In the second embodiment, 
the focal plane I1 side surface of the second relay lens G2, the 
secondary-image plane I2 side surface of the third relay lens G3, the 
secondary-image plane I2 side surface of the first eyepiece lens G4, the 
secondary-image plane I2 side surface of the second eyepiece lens G5, and 
the secondary-image plane I2 side surface of the third eyepiece lens G6 
are aspherical surfaces. In the third and fourth embodiments, the focal 
plane I1 side surface of the second relay lens G2, and the pupil E side 
surface of the first eyepiece lens G4 are aspherical surfaces. 
As described above, in a viewfinder optical system of a typical single-lens 
reflex camera, a pentaprism is used as an inverting optical system, and 
this makes it difficult to construct a high-magnification viewfinder 
having a sufficiently long eyepoint distance. By contrast, in the first to 
fourth embodiments, as described above, a relay optical system of a 
positive-negative-positive triplet type is used as an inverting optical 
system, and accordingly it is possible to construct a high-magnification 
viewfinder having a sufficiently long eyepoint distance. 
The above-mentioned eyepoint distance refers to that distance from the rear 
end of the eyepiece optical system to the pupil (eye) of an observer (to 
the eyepoint) at which the field of view in the viewfinder can be viewed 
without being eclipsed. Too short an eyepoint distance is inconvenient 
because, for example, an observer wearing glasses cannot view the entire 
field of view. This inconvenience is overcome by making the eyepoint 
distance longer, but, even in that case, the viewfinder optical system 
needs to be so constructed that light from the entire field of view 
reaches the pupil of an observer (placed at the position of the design 
pupil E). 
As shown in FIGS. 1 to 4, in a construction where a relay optical system G1 
to G3 is used as an inverting optical system, a light beam is restricted 
by an aperture diaphragm A disposed within the relay optical system G1 to 
G3. Accordingly, the exit pupil of the relay optical system G1 to G3 
coincides with the entrance pupil of the eyepiece optical system G4 to G6, 
or G4 and G5. Moreover, the exit pupil of the eyepiece optical system G4 
to G6, or G4 and G5, coincides with the design pupil E (the pupil of an 
observer). Therefore, to ensure that light from the entire field of view 
reaches the pupil of an observer without being eclipsed, much attention 
needs to be paid to the conjugate relationship between the pupils. 
However, in general, as the magnification of the viewfinder becomes 
higher, the deviation between the axial pupil position (for a light beam 
from the center of the field of view) and the off-axial pupil position 
(for a light beam from the periphery of the field of view) becomes greater 
(generally called the spherical aberration of the pupil). This deviation 
in the pupil positions inconveniently causes the central region of the 
field of view to appear bright but the peripheral region of the field of 
view to appear dim and shadowed. 
To eliminate the above deviation in the pupil positions (i.e. to obtain 
better matching of pupils), in the first to fourth embodiments, the lens 
element disposed closest to the secondary-image plane I2 is provided with 
at least one aspherical surface. Specifically, within the eyepiece optical 
system, the eyepiece lens that is disposed closest to the secondary-image 
plane I2, i.e. the first eyepiece lens G4, which serves also as a 
condenser lens, is provided with at least one aspherical surface. The use 
of an aspherical surface here permits the entrance pupil to match with the 
exit pupil (which usually is the pupil of an observer). Thus, it is 
possible to suppress the spherical aberration of the pupil. To obtain 
still better matching of pupils, the above aspherical surface is so shaped 
as to have decreasing curvatures from the center to the edge. 
FIGS. 9A and 9B are optical path diagrams of the fourth embodiment 
(dioptric power: -0.99998 diopters, viewfinder magnification: -2.57883). 
FIG. 9A shows the optical path of a light beam from an image height of 
Y'=14.5 mm, and FIG. 9B shows the optical path of a light beam from an 
image height of Y'=5 mm. In both FIGS. 9A and 9B, an off-axial light beam 
and an axial light beam (a light beam at the center of the field of view) 
pass through the same position on a plane at the design pupil E. That is, 
pupils are coincident. Under this condition, even if an observer moves the 
eyes up and down (in a direction perpendicular to the optical axis AX), no 
off-axial light beam is eclipsed, and accordingly it is possible to view 
the entire field of view. 
FIGS. 10A and 10B are optical path diagrams of the fourth embodiment with 
its aspherical surfaces replaced with spherical surfaces (dioptric power: 
-0.99998 diopters, viewfinder magnification: -2.57883). FIG. 10A shows the 
optical path of a light beam from an image height of Y'=14.5 mm, and FIG. 
10B shows the optical path of a light beam from an image height of Y'=5 
mm. Here, as shown in FIG. 10B, pupils are coincident for an off-axial 
light beam from a low image height such as Y'=5 mm, but, as shown in FIG. 
10A, pupils are not coincident for an off-axial light beam from a high 
image height such as Y'=14.5 mm. For this reason, when the center of the 
pupil of an observer is located away from the optical axis AX in a 
direction perpendicular thereto, the region from the center of the field 
of view up to an image height of Y'=5 mm can be viewed without problem, 
but off-axial beams from an image height of Y'=14.5 mm are eclipsed and 
cannot be sighted. This causes the peripheral region of the field of view 
to appear dim and shadowed. 
In the first to fourth embodiments, the pupil is designed to have a 
diameter of 6 mm (see the construction data of the first to fourth 
embodiments below). As the pupil has a larger diameter, it causes larger 
spherical aberration. This additional spherical aberration can be 
effectively corrected by replacing part of the lenses disposed near the 
aperture diaphragm A with aspherical lenses. Specifically, in the first to 
fourth embodiments, the second and third relay lenses G2 and G3 are the 
ones disposed near the aperture diaphragm A. Accordingly, here, at least 
the front-side (focal plane I1 side) surface of the second relay lens G2 
is made aspherical to correct the spherical aberration. In this way, 
providing at least one aspherical surface in the relay optical system as 
well as in the eyepiece optical system not only helps to achieve better 
matching of pupils, but also allows the reduction of spherical aberration. 
Moreover, in the first to fourth embodiments, the above relay optical 
system has a positive-negative-positive triplet construction. This makes 
it possible to correct the spherical aberration more effectively. 
Moreover, in the first to fourth embodiments, the first eyepiece lens G4 is 
so designed as to function also as a condenser lens disposed away from the 
secondary-image plane I2. This contributes to the improvement of image 
surface quality (to the reduction of curvature of field, i.e. variation of 
the view distance in accordance with the image height). This feature will 
be described in more detail below. 
Generally, when an optical system having a strong positive power such as a 
relay optical system is combined with another optical system having a 
strong positive power such as an eyepiece optical system, it is necessary 
to use a condenser lens (which also has a strong positive power) to make 
pupils coincide. This is because, when no condenser lens is arranged, the 
peripheral region of the image plane is eclipsed and becomes dim. The 
condenser lens for making pupils coincide is usually disposed near the 
image plane. This is because, near the image plane, the condenser lens 
does not much affect imaging performance, and its effective diameter can 
be reduced to a minimum. 
Moreover, in general, to reduce the size of a viewfinder optical system in 
which a relay optical system is used as an inverting optical system, it is 
necessary to shorten the total length of the viewfinder optical system. To 
shorten the total length of the viewfinder optical system, it is at the 
same time necessary to shorten also the conjugate distance of the pupils 
of the eyepiece (the entrance and exit pupils). Furthermore, to shorten 
the conjugate distance of the pupils, it is necessary to increase the 
power of the condenser lens. As a result, all of the optical systems 
constituting the viewfinder optical system (i.e. the relay optical system, 
condenser lens, and eyepiece optical system) are each given a strong 
positive power. As the power of a viewfinder optical system becomes 
stronger in the positive direction, its Petzval sum becomes greater in the 
positive direction, and this degenerates image plane quality. In short, an 
attempt to reduce an increasing astigmatic difference inevitably results 
in an increase in curvature of field, and thus results in an inclination 
of the image plane. 
Improvement of the above-mentioned image plane quality can be most 
effectively achieved by optimizing power arrangement. In the first to 
fourth embodiments, the first eyepiece lens G4 also functions as a 
condenser lens disposed away from the secondary-image plane I2. This 
efficient power arrangement contributes to the improvement of image plane 
quality. Specifically, in the first to fourth embodiments, the condenser 
lens is disposed away from the secondary-image plane I2, so that it also 
functions as a part of the eyepiece optical system (i.e. as the first 
eyepiece lens G4). This efficient power arrangement reduces the Petzval 
sum, and thus alleviates the curvature of field, with the result that the 
image plane has less of a tendency to inclination. In addition, since the 
first eyepiece lens G4 that is disposed closest to the secondary-image 
plane I2 is disposed at a predetermined distance away from the 
secondary-image plane I2, even if the first eyepiece lens G4 collects 
pieces of dust on its lens surfaces, they do not hinder the observation. 
Furthermore, selecting glass materials having the most suitable refractive 
indices is effective in the improvement of image plane quality. 
Specifically, selecting a glass material having a high refractive index 
for convex lenses and selecting a glass material having a low refractive 
index for concave lenses is effective, and is especially so with lenses 
having strong powers. In the first to fourth embodiments where the first 
eyepiece lens G4 has the strongest power, it is desirable that the first 
eyepiece lens G4 be made of high-refractive-index glass such as LaC8 or 
Nb1F (manufactured by HOYA). Note that the first eyepiece lens G4, which 
is realized as an aspherical lens so that satisfactory matching of pupils 
is obtained, may be made of plastics, with which aspherical surfaces can 
be formed at low cost, because it is at present difficult to form 
aspherical surfaces on glass pieces at low cost. 
In addition to image plane quality, chromatic aberration needs to be taken 
into consideration. As is well-known, to correct chromatic aberration 
properly, it is desirable to select low-dispersion glass for convex lenses 
and high-dispersion glass for concave lenses. 
Moreover, to realize a compact viewfinder optical system having a high 
magnification, the first to fourth embodiments satisfy the following 
conditions (1) and (2): 
(1) the relay magnification is in the range from -0.3.times. to 
-0.5.times.; 
(2) the absolute value of the ratio of the focal length of the eyepiece 
optical system (the lens system on the downstream side of the 
secondary-image plane I2) to the focal length of the entire viewfinder 
optical system is in the range from 0.3 to 0.5. 
Hereinafter, the viewfinder optical systems of the above described 
embodiments of the present invention will be presented more specifically, 
with their construction data at a dioptric power of -1 diopter, aspherical 
surface data, aberration diagrams, and other data. 
In the construction data of each embodiment, Si (i=0, 1, 2, 3, . . . ) 
represents the i-th surface from the focal plane S0. In the construction 
data of each embodiment are listed the curvature radius of the surface Si, 
the axial distance between the surfaces Si and Si+1, the radius of the 
i-th lens from the focal plane S0 (or the radius of the pupil E), the 
refractive index (Ne) for e-lines of the i-th lens from the focal plane 
S0, the Abbe number (.nu.d) for d-lines of the i-th lens from the focal 
plane S0, and the name of each optical element or other. 
Moreover, a surface Si marked with an asterisk (*) is an aspherical 
surface. The shape of an aspherical surface is defined by formula (A) 
below: 
EQU X=C.multidot.Y.sup.2 /{1+1-.epsilon..multidot.C.sup.2 
.multidot.Y.sup.2).sup.1/2 }+A4.multidot.Y.sup.4 +A6.multidot.Y.sup.6 
+A8.multidot.Y.sup.8 (A) 
where 
X: displacement from the reference surface of the optical axis; 
Y: height in the direction perpendicular to the optical axis; 
C: paraxial curvature; 
.epsilon.: quadric surface parameter; 
A4, A6, A8: aspherical coefficients of the fourth, sixth, and eighth 
orders. 
Table 5 below lists the focal length of the entire viewfinder optical 
system, the focal length of the eyepiece optical system, the relay 
magnification, and the viewfinder magnification at a dioptric power of -1 
diopter. 
TABLE 1 
______________________________________ 
&lt;&lt; Embodiment 1 &gt;&gt; 
______________________________________ 
&lt;Construction Data&gt; 
Curva- Axial Refrac- 
Sur- ture Dis- Lens tive Abbe 
face Radius tance Radius 
Index Number 
Name 
______________________________________ 
S0 .infin. Focal Plane I1 
48.2 
S1 11.196 
2.8 5 1.493 57.82 1st Relay 
Lens G1 
S2 -13.333 
0.4 
S3* -12.915 
1.0 4.3 1.626 24.01 2nd Relay 
Lens G2 
S4 11.413 
1.6 
S5 .infin. 3 Aperture Dia- 
phragm A 
5.4 
S6 20.221 
3.8 6.6 1.527 56.38 3rd Relay 
Lens G3 
S7* -9.898 
20.844 
S8 .infin. Secondary-image 
plane I2 
7.763 
S9* 23.984 
3.5 10 1.493 57.82 1st Eyepiece 
Lens G4 
S10 -28.571 
10.950 
S11* 31.844 
3.7 10 1.493 57.82 2nd Eyepiece 
Lens G5 
S12 -22.954 
18.0 
S13 .infin. 3 (Pupil Radius) 
Pupil E 
______________________________________ 
&lt;Aspherical Surface Data&gt; 
S3: .epsilon. = 1.908, A4 = -2.19 .times. 10.sup.-4, A6 = 5.37 .times. 
10.sup.-6 
S7: .epsilon. = 1.123, A4 = 1.73 .times. 10.sup.-4, A6 = 1.99 .times. 
10.sup.-6, A8 = -5.67 .times. 10.sup.-10 
S9: .epsilon. = -10.989 
S11: .epsilon. = -34.683, A4 = 7.11 .times. 10.sup.-5, A6 = -6.29 .times. 
10.sup.-7, 
A8 = 1.61 .times. 10.sup.-9 
______________________________________ 
TABLE 2 
______________________________________ 
&lt;&lt; Embodiment 2 &gt;&gt; 
______________________________________ 
&lt;Construction Data&gt; 
Curva- Axial Lens Refrac- 
Abbe 
Sur- ture Dis- Ra- tive Num- 
face Radius tance dius Index ber Name 
______________________________________ 
S0 .infin. Focal Plane I1 
48.2 
S1 11.1959 
2.8 5 1.493 57.82 
1st Relay 
Lens G1 
S2 -13.3333 
0.4 
S3* -12.915 
1 4.3 1.626 24.01 
2nd Relay 
Lens G2 
S4 11.4129 
1.6 
S5 .infin. 2.9 Aperture Dia- 
phragm A 
5.4 
S6 20.2211 
3.8 6.6 1.527 56.38 
3rd Relay 
Lens G3 
S7* -9.898 
20.8438 
S8 .infin. Secondary-image 
plane I2 
16.1543 
S9* 25.000 
6 11 1.527 56.38 
1st Eyepiece 
Lens G4 
S10 -28.5714 
6.80051 
S11* 48.662 
3.8 11 1.716 53.94 
2nd Eyepiece 
Lens G5 
S12 -26.3797 
2.84319 
S13* -21.182 
1 9.5 1.757 25.14 
3rd Eyepiece 
Lens G6 
S14 -134.573 
15 
S15 .infin. 3 (Pupil Radius) 
Pupil E 
______________________________________ 
&lt;Aspherical Surface Data&gt; 
S3: .epsilon. = 1.908, A4 = -2.19 .times. 10.sup.-4, A6 = 5.37 .times. 
10.sup.-6 
S7: .epsilon. = 1.123, A4 = 1.73 .times. 10.sup.-4, A6 = 1.99 .times. 
10.sup.-6, A8 = -5.67 .times. 10.sup.-10 
S9: .epsilon. = -0.727 
S11: .epsilon. = -84.865, A4 = 3.91 .times. 10.sup.-5, A6 = -6.06 .times. 
10.sup.-7, 
A8 = 1.21 .times. 10.sup.-9 
S13: .epsilon. = -1.619, A4 = -1.12 .times. 10.sup.-5, A6 = 2.29 .times. 
10.sup.-7, 
A8 = -5.53 .times. 10.sup.-11 
______________________________________ 
TABLE 3 
______________________________________ 
&lt;&lt; Embodiment 3 &gt;&gt; 
______________________________________ 
&lt;Construction Data&gt; 
Curva- Axial Refrac- 
Sur- ture Dis- Lens tive Abbe 
face Radius tance Radius 
Index Number 
Name 
______________________________________ 
S0 .infin. Focal Plane I1 
48.2 
S1 8.367 
3.2 5 1.700 56.47 1st Relay 
Lens G1 
S2 -76.191 
1.3 
S3* -11.922 
1.0 5 1.588 30.36 2nd Relay 
Lens G2 
S4 6.470 
3.6 
S5 .infin. 2.7 Aperture Dia- 
phragm A 
0.0 
S6 35.739 
3.1 5.1 1.758 51.57 3rd Relay 
Lens G3 
S7 -10.981 
20.312 
S8 .infin. Secondary-image 
plane I2 
7.188 
S9 18.454 
7.2 11.5 1.527 56.38 1st Eyepiece 
Lens G4 
S10* -15.463 
11.000 
S11 111.686 
1.0 9.5 1.843 21.00 2nd Eyepiece 
Lens G5 
S12 19.943 
3.3 
S13 31.126 
3.8 9.5 1.758 51.57 3rd Eyepiece 
Lens G6 
S14 -31.126 
13.0 
S15 .infin. 3 (Pupil Radius) 
Pupil E 
______________________________________ 
&lt;Aspherical Surface Data&gt; 
S3: .epsilon. = 1.000, A4 = -1.45 .times. 10.sup.-4, A6 = 1.11 .times. 
10.sup.-5 
S10 : .epsilon. = 1.000, A4 = 9.70 .times. 10.sup.-5, A6 = 2.73 .times. 
10.sup.-7 
______________________________________ 
TABLE 4 
______________________________________ 
&lt;&lt; Embodiment 4 &gt;&gt; 
______________________________________ 
&lt;Construction Data&gt; 
Curva- Axial Refrac- 
Sur- ture Dis- Lens tive Abbe 
face Radius tance Radius 
Index Number 
Name 
______________________________________ 
S0 .infin. Focal Plane I1 
46.8 
S1 7.811 
3.4 5 1.716 53.94 1st Relay 
Lens G1 
S2 -30.333 
0.8 
S3* -10.315 
1.0 5 1.588 30.36 2nd Relay 
Lens G2 
S4 5.498 
0.8 
S5 .infin. 2.6 Aperture Dia- 
phragm A 
3.4 
S6 32.114 
2.8 5.1 1.716 53.94 3rd Relay 
Lens G3 
S7 -10.085 
18.259 
S8 .infin. Secondary-image 
plane I2 
9.141 
S9 16.952 
6.8 11.2 1.527 56.38 1st Eyepiece 
Lens G4 
S10* -17.045 
9.002 
S11 91.881 
1.0 9.5 1.843 21.00 2nd Eyepiece 
Lens G5 
S12 19.106 
4.4 
S13 25.007 
3.8 9.5 1.716 53.94 3rd Eyepiece 
Lens G6 
S14 -47.427 
15.0 
S15 .infin. 3.3 (Pupil Radius) 
Pupil E 
______________________________________ 
&lt;Aspherical Surface Data&gt; 
S3: .epsilon. = -0.600, A4 = -2.70 .times. 10.sup.-4, A6 = 1.32 .times. 
10.sup.-5 
S10: .epsilon. = -0.900, A4 = 6.10 .times. 10.sup.-5, A6 = 1.20 .times. 
10.sup.-7 
______________________________________ 
TABLE 5 
______________________________________ 
&lt;&lt; Focal Lengths and Magnifications &gt;&gt; 
Emb. 1 Emb. 2 Emb. 3 Emb. 4 
______________________________________ 
Focal Length of 
-53.78 -57.96 -46.90 -50.79 
the Entire System 
Focal Length of 
18.25 19.50 20.00 20.00 
the Eyepiece 
Optical System 
Relay -0.36 -0.36 -0.45 -0.42 
Magnification 
Viewfinder -2.49858 -2.48346 -2.81574 
-2.60329 
Magnification 
______________________________________ 
FIGS. 5A to 5C, 6A to 6C, 7A to 7C, and 8A to 8C show aberration in the 
first to fourth embodiments, respectively, at a dioptric power of -1 
diopter. FIGS. 5A to 8A show spherical aberration, FIGS. 5B to 8B show 
distortion, and FIG. 5C to 8C show astigmatism. In these aberration 
diagrams, a solid line (e) represents aberration for e-lines, a broken 
line (g) represents aberration for g-lines, and a broken line (DM) and a 
solid line (DS) represent astigmatism on the meridional and sagittal 
planes, respectively. Note that h represents the radius of the pupil E, 
and .omega. represents half the angle of view. 
As described above, according to the present invention, a viewfinder 
optical system provided with a relay optical system offers satisfactory 
matching of pupils, owing to an aspherical surface provided on a lens 
disposed nearest to the secondary-image plane.