Viewfinder optical system

A viewfinder optical system has a relay lens system and an eyepiece optical system. The relay lens system refocuses a primary image as a secondary image. The relay lens system consists of a single lens element which has a surface having optical power of diffraction. The eyepiece optical system magnifies the secondary image and has a surface having optical power of diffraction.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a viewfinder optical system for a camera. 
2. Description of the Prior Art 
In general, single-lens-reflex cameras utilize relay-type viewfinder 
optical systems. Conventional relay-type viewfinder optical systems are 
composed of a number of lenses, and this has prevented the reduction of 
the weight, size, and cost of such viewfinder optical systems. These 
inconveniences can be overcome by reducing the number of constituent lens 
elements. 
However, the reduction of the number of lens elements and the use of 
plastic lenses make it more difficult to correct aberration 
satisfactorily. In particular, chromatic aberration, which can be 
corrected only with a combination of lenses made of materials having 
different dispersion, is difficult to correct with a reduced number of 
lens elements or with plastic lenses. In addition, since there are only 
few kinds of plastic that can be used satisfactorily as lenses, it is not 
possible to freely select plastic materials having different dispersions 
for the correction of chromatic aberration. Accordingly, it is difficult 
to use plastic lenses for all the lens elements constituting an optical 
system. 
On the other hand, lens-shutter cameras and digital cameras employ 
Kepler-type real-image viewfinder optical systems. Some conventionally 
known Kepler-type real-image viewfinder optical systems include an 
objective lens and an eyepiece lens, and correct chromatic aberration by 
the use of a diffracting optical surface. For example, U.S. Pat. No. 
5,044,706 proposes a viewfinder optical system in which a binary 
diffraction grating is provided only in the objective lens, and U.S. Pat. 
No. 5,446,588 proposes a viewfinder optical system in which a diffracting 
optical element is provided only in the eyepiece lens. 
The optical performance of a Kepler-type real-image viewfinder optical 
system is evaluated by evaluating its total optical performance including 
that of the objective lens and that of the eyepiece lens. Accordingly, for 
example, the axial chromatic aberration occurring in the objective lens is 
added together with that occurring in the eyepiece lens for evaluation. In 
addition, when the objective lens is a zoom lens system, the objective 
lens needs to be designed such that chromatic aberration is properly 
corrected over the entire zoom range. 
In the viewfinder optical system proposed in U.S. Pat. No. 5,044,706, since 
a diffracting optical surface is provided only in the objective lens, the 
chromatic aberration occurring in the eyepiece lens needs to be corrected 
by the use of negative lenses in the eyepiece lens. Accordingly, this 
viewfinder optical system inevitably requires more lens elements because 
of the extra negative lens elements used in combination. 
On the other hand, in the viewfinder optical system proposed in U.S. Pat. 
No. 5,446,588, a diffracting optical surface is provided only in the 
eyepiece lens, and the optical performance of the optical system is 
evaluated by evaluating only the optical performance of the eyepiece lens. 
Accordingly, to achieve proper correction of chromatic aberration over the 
entire system, this viewfinder optical system needs to be provided with 
additional negative lenses for correcting the chromatic aberration 
occurring in the objective lens. This inevitably increases the number of 
lens elements. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a viewfinder optical 
system that can correct chromatic aberration properly with a reduced 
number of lens elements. 
Another object of the present invention is to provide a viewfinder optical 
system that can correct chromatic aberration properly with a reduced 
number of lens elements and with plastic lenses alone. 
Still another object of the present invention is to provide a Kepler-type 
real-image viewfinder optical system that can correct chromatic aberration 
properly with a reduced number of lens elements. 
A further object of the present invention is to provide a Kepler-type 
real-image viewfinder optical system having a zoom function in which 
chromatic aberration is properly corrected over the entire zoom range with 
a reduced number of lens elements. 
To achieve the above objects, according to one aspect of the present 
invention, a viewfinder optical system is constituted of a relay lens 
system for refocusing a primary image as a secondary image and including 
at least one surface having optical power of diffraction; and an eyepiece 
optical system for magnifying the secondary image and including at least 
one surface having optical power of diffraction. 
According to another aspect of the present invention, a Kepler-type 
viewfinder optical system is constituted of an objective lens system for 
focusing rays from an object as an intermediate image and including at 
least one surface having optical power of diffraction; and an eyepiece 
optical system for magnifying the intermediate image and including at 
least one surface having optical power of diffraction. 
According to still another aspect of the present invention, in a viewfinder 
optical system consisting of a plurality of lenses whose material is 
plastic, at least one of the lenses includes at least one surface having 
optical power of diffraction.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Hereinafter, embodiments of the viewfinder optical system according to the 
present invention will be described with reference to the drawings. 
FIGS. 3, 5, 7, and 9 show the lens construction and optical paths (the 
order of diffraction on diffracting optical surfaces: +1) of the 
viewfinder optical systems of a first to a fourth embodiment, 
respectively, of the present invention. In FIGS. 3, 5, 7, and 9, Si (i=0, 
1, 2, 3, . . . ) represents the i-th surface from the primary image I1 
plane (SO), Gi (i=1, 2, 3) represents the i-th lens element from the 
primary image I1. A surface Si marked with an asterisk (*) is an 
aspherical surface, and a surface Si marked with [DOE] is a surface where 
a diffracting optical surface is formed on a refracting optical surface. 
The primary image I1 is a focal plane of a taking lens (not shown). The 
viewfinder optical systems of the first, second, and fourth embodiments 
are each constituted of, from the primary image I1 side, a relay lens LR, 
a condenser lens LC, and an eyepiece lens LE, each lens being composed of 
a single lens element. The viewfinder optical system of the third 
embodiment is constituted of, from the primary image I1 side, two relay 
lenses LR, and an eyepiece lens LE. Each of the first to fourth 
embodiments is composed exclusively of plastic lenses having positive 
power, and includes a minimal number (three in total) of lenses. 
The relay lens LR forms a secondary image I2 by refocusing the primary 
image I1. The condenser lens LC condenses the light beam exiting from the 
relay lens LR and directs it to the eyepiece lens LE. The eyepiece lens LE 
magnifies the secondary image I2 formed by the relay lens LR. The thus 
magnified image I2 is observed by an observer's eye E. 
In the first embodiment, the relay lens LR is composed of a plano-convex 
lens element G1 (having aspherical surfaces on its both surfaces S1 and 
S2, and having a diffracting optical surface on its image I1 side surface 
S1) with its convex surface facing toward the pupil E side. The condenser 
lens LC is composed of a positive biconvex lens element G2 (having an 
aspherical surface on its image I1 side surface S3). The eyepiece lens LE 
is composed of a positive biconvex lens element G3 (having a diffracting 
optical surface formed on an aspherical surface on its image I1 side 
surface S5). All the three lens elements G1 to G3 are plastic lenses made 
of PMMA (polymethyl methacrylate). 
In the second embodiment, the relay lens LR is composed of a plano-convex 
lens element G1 (having aspherical surfaces on its both surfaces S1 and 
S2, and having a diffracting optical surface on its pupil E side surface 
S2) with its convex surface facing toward the pupil E side. The condenser 
lens LC is composed of a positive meniscus lens element G2 (having a 
diffracting optical surface formed on an aspherical surface on its image 
I1 side surface S3) with its convex surface facing toward the pupil E 
side. The eyepiece lens LE is composed of a positive biconvex lens element 
G3 (having an aspherical surface on its pupil E side surface S6). All the 
three lens elements G1 to G3 are plastic lenses made of PMMA. 
In the third embodiment, the relay lens LR is composed of a negative 
meniscus lens element G1 (having an aspherical surface on its image I1 
side surface S1) with its concave surface facing toward the image I1 side, 
and a positive biconvex lens element G2 (having aspherical surfaces on its 
both surfaces S3 and S4, and having a diffracting optical surface on its 
pupil E side surface S4). The eyepiece lens LE is composed of a positive 
biconvex lens element G3 (having aspherical surfaces on its both surfaces 
S5 and S6, and having a diffracting optical surface on its pupil E side 
surface S6). All the three lens elements G1 to G3 are plastic lenses made 
of PMMA. 
In the fourth embodiment, the relay lens LR is composed of a positive 
meniscus lens element G1 (having aspherical surfaces on its both surfaces 
S1 and S2, and having a diffracting optical surface on its image I1 side 
surface S1) with its convex surface facing toward the pupil E side. The 
condenser lens LC is composed of a positive biconvex lens element G2 
(having an aspherical surface on its image I1 side surface S3). The 
eyepiece lens LE is composed of a positive biconvex lens element G3 
(having a diffracting optical surface formed on an aspherical surface on 
its image I1 side surface S5). The first lens element G1 is a plastic lens 
made of amorphous polyolefin-based resin, and the second and third lens 
elements G2 and G3 are plastic lenses made of PMMA. 
The viewfinder optical systems of the first to fourth embodiments are all 
characterized in that at least one diffracting optical surface having 
positive power is provided between the position PE conjugate to the pupil 
E and the secondary image I2, and also between the secondary image I2 and 
the pupil E. Specifically, in the first, third, and fourth embodiments, a 
diffracting optical surface having positive power is provided in each of 
the relay lens LR and the eyepiece lens LE, and, in the second embodiment, 
a diffracting optical surface having positive power is provided in each of 
the relay lens LR and the condenser lens LC. Moreover, the viewfinder 
optical systems of the first to fourth embodiments are characterized also 
in that they are composed exclusively of plastic lenses. That is, all of 
the first to fourth embodiments are provided with diffracting optical 
elements made of plastic (diffracting/refracting hybrid lenses made of 
plastic) in which a diffracting optical surface is formed on a refracting 
optical surface. A description will be given below as to how the 
diffracting optical surfaces are arranged. 
FIG. 1 shows the paraxial power arrangement of a typical relay viewfinder 
optical system. In this figure, the primary image I1 (corresponding, here, 
to the object plane) and the pupil E are illustrated in reversed positions 
in order to make it easier to follow the paths of light-rays (an ideal 
marginal ray MR and an ideal principal ray PR). The pupil E corresponds to 
the position of an observer's eye, and is usually substantially conjugate 
to the relay lens LR. The condenser lens LC is disposed in the vicinity of 
the focal point of the eyepiece lens LE, and serves to focus the pupil E 
on the position of the relay lens LR. 
There are two types of chromatic aberration: axial chromatic aberration and 
lateral chromatic aberration. Assume that the coefficient of axial 
chromatic aberration is L, the coefficient of lateral chromatic aberration 
is T, the eyepiece lens LE is a first lens, the condenser lens LC is a 
second lens, and the relay lens LR is a third lens. Then, the total of 
each type of chromatic aberration occurring on the refracting optical 
surfaces of the i-th lens (here, i=1, 2, or 3) is expressed by formulae 
(A) and (B) below: 
##EQU1## 
where .phi.i: the power of the refracting optical surfaces of the i-th 
lens; 
.nu.i: the Abbe number of the refracting optical surfaces of the i-th lens; 
hi: the height at which the ideal marginal ray MR crosses the i-th lens; 
hi#: the height at which the ideal principal ray PR crosses the i-th lens. 
Both the power .phi.i and the Abbe number .nu.i of the refracting optical 
surfaces of the i-th lens are positive (.phi.i&gt;0, .nu.i&gt;0). The height hi 
at which the ideal marginal ray MR crosses the i-th lens and the height 
hi# at which the ideal principal ray PR crosses the i-th lens change their 
sign as shown in Table 1. 
As for axial chromatic aberration, since both hi.sup.2 and .phi.i/.nu.i of 
both the eyepiece lens LE and the relay lens LR are positive (h1.sup.2, 
h3.sup.2 &gt;0; .phi.1/.nu.1, .phi.3/.nu.3&gt;0), the axial chromatic aberration 
occurring in the eyepiece lens LE and that occurring in the relay lens LR 
are added together. On the other hand, since h2 of the condenser lens LC 
is zero, the refracting optical surfaces of the condenser lens LC do not 
affect the coefficient L of axial chromatic aberration. Accordingly, the 
coefficient L of axial chromatic aberration is always positive (L&gt;0). This 
indicates that axial chromatic aberration cannot be corrected with a 
combination of single convex lenses alone. As for lateral chromatic 
aberration, since h2 of the condenser lens LC and h3# of the relay lens LR 
are both zero (h2=h3#=0), lateral chromatic aberration occurs only in the 
eyepiece lens LE, to the degree represented by the term 
h1.multidot.h1#(.phi.1/.nu.1). 
When the relay viewfinder optical system includes diffracting optical 
surfaces, the axial chromatic aberration and lateral chromatic aberration 
occurring on the diffracting optical surface of the i-th lens are 
respectively added to those expressed by formulae (A) and (B). 
Accordingly, the total of each type of chromatic aberration occurring on 
the refracting and diffracting optical surfaces constituting the relay 
viewfinder optical system are expressed by formulae (C) and (D) below: 
##EQU2## 
where .phi.i': the power of the diffracting optical surface of the i-th 
lens; 
.nu.i': the Abbe number of the diffracting optical surface of the i-th 
lens. 
The Abbe number .nu.' of a diffracting optical surface is defined by 
formula (E) below. From formula (E), it is understood that a diffracting 
optical surface has a remarkably large negative dispersion (i.e. a 
remarkably small Abbe number) of .nu.'=-3.45. 
EQU .nu.'=.lambda.d/(.lambda.F-.lambda.C) (E) 
where 
.lambda.d: the wavelength of d-lines (=588 nm); 
.lambda.F: the wavelength of F-lines (=486 nm); 
.lambda.C: the wavelength of C-lines (=656 nm). 
When the power .phi.i' of the diffracting optical surface of the i-th lens 
is positive (.phi.i&gt;0), the term .phi.i'/.nu.i' in formulae (C) and (D) is 
negative (.phi.i'/.nu.i'&lt;0). This means that the diffracting optical 
surface has optical power that tends to correct both types of chromatic 
aberration occurring on the refracting optical surfaces. Accordingly, in 
order to reduce both the coefficient L of axial chromatic aberration and 
the coefficient T of lateral chromatic aberration, it is necessary to 
provide each of the lens units having optical power (i.e. the eyepiece 
lens LE, the condenser lens LC, and the relay lens LR) with a diffracting 
optical surface so that the term {(.phi.i/.nu.i)+(.phi.i'/.nu.i')} in 
formulae (C) and (D) becomes equal to zero. However, with regard to the 
condenser lens LC, since both h2.sup.2 and h2.multidot.h2# are zero (h2=0, 
hence h2.sup.2 =h2.multidot.h2#=0), the refracting optical surfaces of the 
condenser lens LC affect neither the coefficient L of axial chromatic 
aberration nor the coefficient T of lateral chromatic aberration. 
Therefore, in order to correct both axial chromatic aberration and lateral 
chromatic aberration, at least one of the eyepiece lens LE and the relay 
lens LR needs to be provided with a diffracting optical surface. FIG. 2 
shows the chromatic aberration occurring on the refracting and diffracting 
surfaces of the relay viewfinder optical system (FIG. 1), as observed at 
some particular positions therein, together with "+", "0", or "-" 
indications for the values of hi, hi#, and other parameters. 
As described above, both axial chromatic aberration and lateral chromatic 
aberration can be corrected properly by correcting the chromatic 
aberration occurring on the refracting optical surfaces with the 
diffracting optical surfaces. This helps reduce the number of lens 
elements constituting the viewfinder optical system, and thus reduce its 
weight, size, and cost. 
In the first to fourth embodiments, as shown in FIGS. 3, 5, 7, and 9, the 
relay lens LR is disposed behind the position PE conjugate to the pupil E, 
and the condenser lens LC and the eyepiece lens LE (only the eyepiece lens 
LE in the third embodiment) are disposed behind the secondary image 12. 
Accordingly, as seen from FIG. 2, the axial chromatic aberration occurring 
on the refracting optical surfaces is positive, and the lateral chromatic 
aberration occurring on the refracting optical surfaces is slightly 
positive. In the first, third, and fourth embodiments, since the 
diffracting optical surface in the eyepiece lens LE has positive power, it 
is possible to correct the positive axial chromatic aberration occurring 
on the refracting optical surfaces with the negative axial chromatic 
aberration occurring on the diffracting optical surface in the eyepiece 
lens LE. In the second embodiment, since the diffracting optical surface 
in the condenser lens LC has positive power, it is possible to correct the 
positive axial chromatic aberration occurring on the refracting optical 
surfaces with the negative axial chromatic aberration occurring on the 
diffracting optical surface in the eyepiece lens LE. 
However, the above diffracting optical surfaces cause negative lateral 
chromatic aberration as well. To correct this, in the first to fourth 
embodiments, a diffracting optical surface having positive power is used 
in the relay lens LR. This causes positive lateral chromatic aberration in 
the relay lens LR, and thus helps keep the chromatic aberration over the 
entire system well-balanced. In this way, by the use of two diffracting 
optical surfaces having positive power, it is possible to keep the 
chromatic aberration over the entire system well-balanced. 
It is preferable that, as in the first to fourth embodiments, the 
diffracting optical surface be formed on a refracting optical surface 
having an aspherical shape. The power of the diffracting optical surface 
offers some of the effects that are obtained by the use of an aspherical 
surface, but, as long as the diffracting optical surface is formed on a 
refracting optical surface (base surface) that is a spherical surface, it 
is impossible to eliminate chromatic spherical aberration and chromatic 
coma. If the diffracting optical surface is formed on an aspherical 
surface, it is possible to correct basic spherical aberration with the 
aspherical surface, and to correct chromatic aberration with the 
diffracting optical surface formed thereon. In addition, it is possible to 
shape the aspherical surface and the diffracting optical surface at the 
same time by, for example, machining. This leads to the reduction of 
production time, and to the improvement of production accuracy. 
In the first, third, and fourth embodiments, it is preferable that 
condition (1) below be satisfied: 
##EQU3## 
where .phi.Rd: the optical power of diffraction of the diffracting optical 
surface included in the relay lens; 
.phi.Rt: the composite optical power of diffraction and refraction of the 
diffracting and refracting optical surfaces included in the relay lens; 
.phi.Ed: the optical power of diffraction of the diffracting optical 
surface included in the eyepiece lens; 
.phi.Et: the composite optical power of diffraction and refraction of the 
diffracting and refracting optical surfaces included in the eyepiece lens. 
If the diffracting optical surfaces provided in the relay lens LR and the 
eyepiece lens LE satisfy condition (1), it is possible to obtain 
satisfactory aberration characteristics. If the upper or lower limit of 
condition (1) is exceeded, it is not possible to keep axial chromatic 
aberration and lateral chromatic aberration well-balanced, and thus it is 
not possible to obtain desired optical performance. 
In the second embodiment, it is preferable that condition (2) below be 
satisfied: 
##EQU4## 
where .phi.Rd: the optical power of diffraction of the diffracting optical 
surface included in the relay lens; 
.phi.Rt: the composite optical power of diffraction and refraction of the 
diffracting and refracting optical surfaces included in the relay lens; 
.phi.Cd: the optical power of diffraction of the diffracting optical 
surface included in the condenser lens; 
.phi.Ct: the composite optical power of diffraction and refraction of the 
diffracting and refracting optical surfaces included in the condenser 
lens. 
If the diffracting optical surfaces provided in the relay lens LR and the 
condenser lens LC satisfy condition (2), it is possible to obtain 
satisfactory aberration characteristics. If the upper or lower limit of 
condition (2) is exceeded, it is not possible to keep axial chromatic 
aberration and lateral chromatic aberration well-balanced, and thus it is 
not possible to obtain desired optical performance. 
Next, a description will be given below as to why the use of a diffracting 
optical surface makes it possible to compose a viewfinder optical system 
exclusively of plastic lenses, as in the above described embodiments. In 
conventional optical systems, chromatic aberration is corrected with a 
combination of a lens having negative power and a small Abbe number .nu.d 
(i.e. having strong dispersion) and a lens having positive power and a 
large Abbe number .nu.d (i.e. having weak dispersion). Accordingly, to 
correct chromatic aberration properly, it is necessary to select lens 
materials having appropriate Abbe numbers .nu.d from various materials 
having widely varying Abbe numbers .nu.d. However, since there are only 
few kinds of plastic that can be used as optical materials, it is not 
possible to freely select materials having appropriate Abbe numbers .nu.d 
for plastic lenses. Nevertheless, since a diffracting optical surface has, 
as described earlier, remarkably large negative dispersion (.nu.'=-3.45), 
it is possible to control chromatic aberration freely by the use of a 
diffracting optical surface even if it has only small power. Accordingly, 
the use of a diffracting optical surface eliminates the need to use a 
combination of lenses having widely different dispersion, and thus makes 
it possible to compose an optical system exclusively of plastic lenses. 
It is preferable that the plastic lenses be made of PMMA or amorphous 
polyolefin-based resin. Since both PMMA and amorphous polyolefin-based 
resin have a large Abbe number .nu.d, their use helps reduce the 
above-noted term .phi.i/.nu.i. Accordingly, a diffracting optical surface 
formed on a lens made of such materials can effectively correct chromatic 
aberration over the entire spectrum of light. In addition, these materials 
have other properties that make them suitable for use in optical systems; 
for example, PMMA is easy to mold, and amorphous polyolefin-based resin 
suffers little from moisture absorption. 
Moreover, where chromatic aberration is corrected by the use of a 
diffracting optical surface as in the above described embodiments, it is 
possible to compose the entire optical system exclusively with lenses 
having positive power, and thus it is possible to compose the optical 
system with a minimal number of lens elements. A description will be given 
below as to how chromatic aberration is corrected by the use of a 
diffracting optical surface. In the following description, it is assumed 
that a refracting optical surface having positive power and a diffracting 
optical surface having positive power are used to correct chromatic 
aberration. 
FIG. 11 is a chart schematically showing the relation between the power 
.phi. of a lens and the wavelength .lambda., for lenses A and B made of 
materials having different Abbe numbers. Of these 10 two lenses, lens A is 
made of a material having a larger Abbe number .nu.d (having weaker 
dispersion), and lens B is made of a material having a smaller Abbe number 
.nu.d (having stronger dispersion). Although lenses A and B have spherical 
surfaces of the same radius of curvature as their refractive optical 
surfaces, the power of the refractive optical surfaces of lenses A and B 
vary in different ways with the wavelength .lambda. because of the 
difference of their Abbe numbers, as indicated by the dash-dot lines A1 
and B1 (FIG. 11), respectively. 
Now, assume that diffracting optical surfaces having the 20 same positive 
power are individually formed on the refracting optical surfaces of lenses 
A and B so that the refracting optical surfaces are combined with 
diffracting optical surfaces. Then, since the diffracting optical surfaces 
have a negative Abbe number .nu.', their power vary as indicated by the 
dash-dot-dot line C1 (FIG. 11) with the wavelength .lambda.. When the 
power is set to be equal for g-lines and c-lines (i.e. when chromatic 
aberration is corrected), the composite power of the refracting and 
diffracting surfaces of lenses A and B vary as indicated by the solid 
lines A2 and B2 (FIG. 11) with the wavelength .lambda.. 
Comparison of the solid line A2 with the solid line B2 shows that, even if 
the power is equal for g-lines and c-lines, the power for light rays other 
than g-lines and c-lines still varies with the wavelength .lambda.. For 
example, for d-lines, the deviation .alpha. of the composite power of the 
refracting and diffracting optical surfaces of lens A is smaller than the 
deviation .alpha.+.beta. of the composite power of the refracting and 
diffracting optical surfaces of lens B. This means that, even when 
diffracting optical surfaces having the same power is combined with 
refracting optical surfaces having the same radius of curvature, better 
correction of chromatic aberration can be achieved on the whole with a 
refracting optical surface made of a material having a larger Abbe number 
.nu.d. 
Where chromatic aberration is corrected by the use of a diffracting optical 
surface as in the above described embodiments, it is preferable to use a 
material having an Abbe number larger than 50 as the lens material. By 
composing an optical system exclusively of lenses made of plastic having 
an Abbe number larger than 50, it is possible to reduce the deviations of 
the power for d-lines, g-lines, and c-lines, and thus to improve the 
chromatic aberration characteristics of the entire optical system even if 
it is constituted of positive lenses alone. In this way, it is possible to 
compose the optical system with a minimal number of lens elements. 
Tables 2 to 5 list the construction data of the viewfinder optical systems 
of the first to fourth embodiments (FIGS. 3, 5, 7, and 9), respectively. 
In the construction data of tables 2 to 5, Si (i=0, 1, 2, 3, . . . ) 
represents the i-th surface from the focal plane S0 side (i.e. from the 
primary image I1 side), ri (i=0, 1, 2, 3, . . . ) represents the radius of 
curvature of the i-th surface from the focal plane S0 side, di (i=0, 1, 2, 
3, . . . ) represents the i-th axial distance from the focal plane S0 
side, and Ni (i=1, 2, . . . ) and .nu.i (i=1, 2, . . . ) respectively 
represent the index of refraction (Nd) and the Abbe number (.nu.d), for 
d-lines, of the i-th lens Gi (i=1, 2, 3) from the focal plane S0 side. 
In the construction data of the first to fourth embodiments, a surface Si 
marked with an asterisk (*) is an aspherical surface. The shape of an 
aspherical surface is defined by formula (AS) below: 
##EQU5## 
where X: the displacement from the reference plane of the optical axis 
direction; 
Y: the height in a direction perpendicular to the optical axis; 
C: the paraxial curvature; 
K: the conic coefficient; 
Ai: the aspherical coefficient of the i-th degree. 
In the construction data of the first to fourth embodiments, a surface Si 
marked with [DOE] is a surface where a diffracting optical surface is 
formed on a refracting optical surface. The pitch of a diffracting optical 
surface is determined by its phase shape, which is defined by formula (DS) 
below: 
##EQU6## 
where .phi.(H): the phase function of the diffracting optical surface; 
Ci: the phase function coefficient of the diffracting optical surface of 
the 2i-th order; 
H: the height in a direction perpendicular to the optical axis; 
.lambda.O: the design reference wavelength (=546.07.times.10.sup.-6 mm). 
Table 6 lists the value corresponding to conditions (1) and (2) 
{.vertline.(.phi.Rd/.phi.Rt)-(.phi.Ed/.phi.Et).vertline., 
.vertline.(.phi.Rd/.phi.Rt)-(.phi.Cd/.phi.Ct).vertline.} and related 
values (.phi.Rd, .phi.Rt, .phi.Ed, .phi.Et, .phi.Cd, .phi.Ct) as observed 
in each embodiment. 
FIGS. 4A to 4C, 6A to 6C, 8A to 8C, and 10A to 10C are aberration diagrams 
showing the aberration observed in the first to fourth embodiments, 
respectively (the order of diffraction of the diffracting optical 
surfaces: +1). In these aberration diagrams, a broken line represents 
aberration for c-lines (wavelength: .lambda.c=656.3 nm), a solid line 
represents aberration for e-lines (wavelength: .lambda.e=546.1 nm), and a 
dash-dot line represents aberration for g-lines (wavelength: 
.lambda.g=435.8 nm). In these aberration diagrams, aberration is plotted 
in millimeters and on the assumption that the entire system forms an 
imaging optical system having at the pupil E position an ideal lens with a 
focal length of f.sub.id =20. Spherical aberration is plotted in relation 
to h/h0, which is the radius h of the pupil E standardized by its maximum 
effective diameter h0, and astigmatism and distortion are plotted in 
relation to half the angle of view .omega..degree.. Moreover, in these 
aberration diagrams, S1 to S3 indicate astigmatism on the sagittal plane, 
and M1 to M3 indicate astigmatism on the meridional plane. 
As described above, according to the present invention, it is possible to 
have a viewfinder optical system that can correct chromatic aberration 
properly with a reduced number of lens elements. In other words, since 
both axial chromatic aberration and lateral chromatic aberration are 
corrected properly by diffracting optical surfaces as described above, it 
is possible to greatly reduce the number of lens elements. As a result, it 
is possible to reduce the weight, size, and cost of viewfinder optical 
systems. 
Moreover, according to the present invention, the use of at least one 
diffracting optical surface in an optical system makes it possible to 
realize an optical system that, despite being composed exclusively of 
plastic lenses, achieves proper correction of both axial chromatic 
aberration and lateral chromatic aberration. Furthermore, since both types 
of chromatic aberration are corrected properly by such a diffracting 
optical surface, it is possible to greatly reduce the number of lens 
elements constituting an optical system, and thus it is possible to reduce 
the weight, size, and cost of the optical system. Moreover, since an 
optical system can be composed exclusively of plastic lenses, it is 
possible to further reduce the weight of the optical system. In addition, 
since plastic lenses can be produced by molding, diffracting optical 
surfaces can be massproduced at low cost. 
FIG. 12 shows the paraxial power arrangement of a typical Kepler-type 
real-image viewfinder optical system. In FIG. 12, the light ray passing 
through the center of the pupil he is the ideal principal ray PL, and the 
light ray passing through the pupil he perpendicularly thereto is the 
ideal marginal ray ML. In this optical system, an objective lens tg forms 
an image of an object in the vicinity of a condenser lens co, and the thus 
formed image is then magnified by an eyepiece lens se so that the image is 
observed from the position of the pupil he behind the eyepiece lens se. 
As mentioned in formulas (A) through (E) of the first and second 
embodiments, it is understood that a diffracting optical surface has a 
remarkably small negative Abbe number equivalent value of .nu.'=-3.45. 
Since normal lenses having only refracting optical surfaces have an Abbe 
number (representing their dispersion) ranging from 20-80, combined use of 
refracting and diffracting optical surfaces allows the positive term 
.phi.i/.nu.i to be canceled out by the negative term .phi.i'/.nu.i'. This 
means that the chromatic aberration occurring on the refracting optical 
surfaces can be corrected with the diffracting optical surfaces. 
When a diffracting optical surface is provided only in the eyepiece lens 
se, the chromatic aberration occurring in the eyepiece lens se is 
corrected, but the chromatic aberration occurring in the objective lens tg 
remains uncorrected. When a diffracting optical surface is provided only 
in the objective lens tg, the chromatic aberration occurring in the 
objective lens tg is corrected, but the chromatic aberration occurring in 
the eyepiece lens se remains uncorrected. The viewfinder optical systems 
of the fifth and sixth embodiments, which will be presented later, are 
characterized in that a diffracting optical surface is provided both in 
the objective lens tg and in the eyepiece lens se. When a diffracting 
optical surface is provided both in the objective lens tg and in the 
eyepiece lens se, the chromatic aberration occurring in each of the lenses 
tg and se can be individually corrected by the diffracting optical surface 
provided in each lens, and thus it is possible to correct chromatic 
aberration properly over the entire viewfinder optical system. 
It is preferable that diffracting optical surfaces be introduced to the 
objective lens tg and the eyepiece lens se by providing each of these 
lenses tg and se with a diffracting optical element that has a diffracting 
optical surface formed on a refracting optical surface (i.e. a 
diffracting/refracting hybrid lens). This is because the use of such 
hybrid lenses not only makes it possible to correct the chromatic 
aberration occurring on the refracting optical surfaces by the use of the 
diffracting optical surface, but also eliminates the need to use 
additional optical elements (e.g. negative lenses) for chromatic 
aberration correction. Thus, as compared with the optical system where 
chromatic aberration is corrected by the use of negative lenses in the 
objective lens tg or in the eyepiece lens se, it is possible to reduce the 
number of the lens elements. 
In a typical Kepler-type real-image viewfinder optical system, a 
field-of-view mask (field-of-view frame) is provided on the image plane of 
the objective lens tg to limit the field of view. Improper correction of 
chromatic aberration within the eyepiece lens se directly affects the 
image formed on the field-of-view mask, with the result that the 
field-of-view mask appears colored. However, in the viewfinder optical 
systems of the fifth and sixth embodiments, presented later, since the 
chromatic aberration occurring in the eyepiece lens se is corrected by the 
diffracting optical surface provided in the eyepiece lens se, such 
coloring of the field-of-view mask never occurs. 
It is preferable that the eyepiece lens se is composed of a positive single 
lens. By composing the eyepiece lens se of a single lens, it is possible 
to reduce the number of lens elements and simplify the construction of the 
viewfinder optical system. 
When the viewfinder optical systems of the fifth and sixth embodiments, 
presented later, are further provided with a zoom function, it is 
preferable that a zoom lens system is used as the objective lens tg, and 
that a diffracting optical surface is provided in the lens unit that is 
moved to achieve zooming. FIGS. 13A and 13B show the paraxial power 
arrangement of a viewfinder optical system whose objective lens tg is a 
zoom lens system, with FIG. 13A illustrating the wide-angle state and FIG. 
13B illustrating the telephoto state. Here, the objective lens tg is 
constructed as a typical zoom lens system consisting, from the object 
side, a first lens unit g1 having negative power and a second lens unit g2 
having positive power. The second lens unit g2 is a variator that mainly 
serves to control zooming, and the first lens unit g1 is a compensator 
that serves to adjust the position of the image plane. 
From FIGS. 13A and 13B, it will be understood that, with the movement of 
the second lens unit g2 that has the longer distance to move, the heights 
h and h' significantly vary in the second lens unit g2. This means that 
the degree of chromatic aberration significantly varies during zooming. 
Accordingly, if a diffracting optical surface is provided in the lens 
units g1 and g2 that are moved for zooming, it is possible to reduce the 
variation of chromatic aberration during zooming. That is, in a viewfinder 
optical system whose objective lens tg is a two-unit zoom lens system 
consisting of negative and positive lens units, it is possible to correct 
chromatic aberration properly over the entire zoom range if a diffracting 
optical surface is provided at least in the first lens unit g1 or in the 
second lens unit g2. 
In a viewfinder optical system whose objective lens tg is a zoom lens 
system and in which a diffracting optical surface is provided in the lens 
unit that is moved to achieve zooming, it is preferable that condition (3) 
below be satisfied: 
##EQU7## 
where .phi.OD: the optical power of diffraction of the diffracting optical 
surface included in the objective lens; 
.phi.O: the composite optical power of diffraction and refraction of the 
diffracting and refracting optical surfaces included in the objective 
lens; 
.phi.ED: the optical power of diffraction of the diffracting optical 
surface included in the eyepiece lens; 
.phi.E: the composite optical power of diffraction and refraction of the 
diffracting and refracting optical surfaces included in the eyepiece lens. 
In condition (3), .phi.OD/.phi.O represents the amount of chromatic 
aberration corrected by the diffracting optical surface in the objective 
lens tg, and .phi.ED/.phi.E represents the amount of chromatic aberration 
corrected by the diffracting optical surface in the eyepiece lens se. 
Condition (3) defines the balance of chromatic aberration corrected in the 
objective lens tg and in the eyepiece lens se. When condition (3) is 
satisfied, it is possible to achieve well-balanced correction of chromatic 
aberration in the objective lens tg and in the eyepiece lens se. If the 
lower limit of condition (3) is exceeded, chromatic aberration is 
undercorrected in the objective lens tg. If the upper limit of condition 
(3) is exceeded, chromatic aberration is undercorrected in the eyepiece 
lens se. 
FIGS. 14 and 15 show the lens construction and optical paths of the 
viewfinder optical systems of a fifth and a sixth embodiment, 
respectively, of the present invention, at their wide-angle end [W]. In 
FIGS. 14 and 15, arrows m1 and m2 indicate the movement of the first and 
second lens units g1 and g2, respectively, during zooming from the 
wide-angle end [W] to the telephoto end [T] 
Tables 7 and 8 list the construction data of the viewfinder optical systems 
of the fifth and sixth embodiments (FIGS. 14 and 15), respectively. 
In the construction data of tables 7 and 8, Si (i=1, 2, . . . ) represents 
the i-th surface from the object side, ri (i=1, 2, . . . ) represents the 
radius of curvature of the i-th surface Si from the object side, and di 
(i=1, 2, . . . ) represents the i-th axial distance from the object side. 
For axial distances that vary with zooming (variable distances), two 
values are listed, which are, from the left, the surface-to-surface 
distances between the related lens units at the wide-angle end [W] and at 
the telephoto end [T]. Moreover, Ni (i=1, 2, . . . ) represents the index 
of refraction (Ne) for e-lines of the i-th lens element from the object 
side, and .nu.i (i=1, 2, . . . ) represents the Abbe number (.nu.d) for 
d-lines of the i-th lens element from the object side. The symbol of an 
optical element is given on the right side of its Abbe number. Listed 
together with the construction data are the viewfinder magnification 
.beta., the value corresponding to condition (3) 
{.vertline..phi.OD.multidot..phi.E/(.phi.O.multidot..phi.ED).vertline.}, 
and the values related thereto (.phi.O, .phi.OD, .phi.E, .phi.ED) at the 
wide-angle end [W] and at the telephoto end [T]. 
In the construction data of the fifth and sixth embodiments, a surface Si 
marked with [DOE] is a surface where a diffracting optical surface is 
formed on a refracting optical surface, and a surface S1 marked with an 
asterisk (*) is an aspherical surface. The shape of an aspherical surface 
is defined by formula (AS) below: 
##EQU8## 
where Y: the displacement from the reference plane of the optical axis 
direction; 
X: the height in a direction perpendicular to the optical axis; 
C: the paraxial curvature; 
.epsilon.: the quadric surface parameter; 
Ai: the aspherical coefficient of the i-th degree. 
FIGS. 16A to 16C show the aberration observed at the wide-angle end of the 
fifth embodiment; FIGS. 17A to 17C show the aberration observed at the 
telephoto end of the fifth embodiment. FIGS. 18A to 18C show the 
aberration observed at the wide-angle end of the sixth embodiment; FIGS. 
19A to 19C show the aberration observed at the telephoto end of the sixth 
embodiment. Of these aberration diagrams, FIGS. 16A, 17A, 18A, and 19A 
show astigmatism, FIGS. 16B, 17B, 18B, and 19B show distortion, and FIGS. 
16C, 17C, 18C, and 19C show lateral chromatic aberration. In all of these 
aberration diagrams, it is assumed that the object distance is 3 m. In 
these aberration diagrams, aberration for light of different wavelengths 
(design wavelengths: e-lines, c-lines, and g-lines) is plotted with 
different types of line. Specifically, if FIG. 16A is taken as an example, 
the solid line 11 represents tangential aberration for e-lines, the 
short-dash line 12 represents sagittal aberration for e-lines, the 
dash-dot line 13 represents tangential aberration for c-lines, the 
long-dash line 14 represents sagittal aberration for c-lines, the dotted 
line 15 represents tangential aberration for g-lines, and the dash-dot-dot 
line 16 represents sagittal aberration for g-lines. Note that this 
distinction between the types of lines for light of different wavelengths 
is used also in similar aberration diagrams presented here and later, that 
is, in FIGS. 17A to 17C, 18A to 18C, and 19A to 19C. For astigmatism, the 
dioptric power (in diopters) is taken along the vertical axis; for 
distortion, the percentage of distortion is taken along the vertical axis; 
for lateral chromatic aberration, the angle with respect to the optical 
axis (in radians) is taken along the vertical axis. In all of these 
aberration diagrams, the angle of incidence (in radians) on the pupil 
plane is taken along the horizontal axis. 
For the fifth and sixth embodiments, as seen from their construction data, 
the aberration occurring on the diffracting optical surfaces is evaluated 
by the use of the Sweatt model. The Sweatt model refers to a method of 
performing optical calculations on diffracting optical surfaces in a 
simplified way. According to the Sweatt model, calculations on diffracting 
optical surfaces can be performed in a similar way as ordinary 
calculations in geometrical optics, simply by using an extremely large 
index of refraction in relation to a given wavelength. Here, each type of 
aberration is calculated on the assumption that the index of refraction 
for e-lines is 10001.00000. 
In both of the fifth and sixth embodiments, the objective lens tg is 
constituted of a first lens unit g1 having negative power, a second lens 
unit g2 having positive power, and a third lens unit g3 having positive 
power. Zooming is performed by moving the first and second lens units g1 
and g2 as indicated by arrows m1 and m2, respectively. The third lens unit 
g3 is formed as one unit together with a prism having a reversing 
function. The condenser lens co is formed as one unit together with a 
reversing prism p on the entrance surface thereof. Behind the reversing 
prism p, the eyepiece lens se composed of a single lens is disposed. 
In the fifth embodiment, diffracting optical surfaces are provided on the 
pupil he side surface of the second lens unit g2, which has the longer 
distance to move, and on the pupil he side surface of the eyepiece lens 
se. In the sixth embodiment, diffracting optical surfaces are provided on 
the pupil he side surface of the first lens unit g1 and on the pupil he 
side surface of the eyepiece lens se. By providing a diffracting optical 
surface both in the objective lens tg and in the eyepiece lens se, it is 
possible to correct the chromatic aberration occurring in each of the 
lenses tg and se by the use of the diffracting optical surface provided in 
each lens. As a result, as seen from the aberration diagrams in FIGS. 16A 
to 16C, 17A to 17C, 18A to 18C, and 19A to 19C, well-balanced correction 
of both axial chromatic aberration and lateral chromatic aberration can be 
achieved both at the wide-angle end and at the telephoto end. It is to be 
noted that the diffracting optical surfaces may be provided on either of 
the object side or pupil he side surface of the lenses, though they are 
provided on the pupil he side surface of the lenses in the fifth and sixth 
embodiments. 
As described above, according to the present invention, since a diffracting 
optical surface is provided both in the objective lens and in the eyepiece 
lens, it is possible to realize a viewfinder optical system that achieves 
proper correction of chromatic aberration with a reduced number of lens 
elements. That is, since the chromatic aberration occurring in each of the 
lenses is individually corrected properly by the diffracting optical 
surface provided in each lens, it is possible to reduce the number of lens 
elements as compared with conventional viewfinder optical systems, and 
thus it is possible to reduce the weight, size, and cost of a viewfinder 
optical system. 
Moreover, depending on the way that the present invention is implemented, 
it is also possible to reduce the number of lens elements and simplify the 
construction of the viewfinder optical system if the eyepiece lens is 
composed of a positive single lens, to correct chromatic aberration 
properly over the entire zoom range if a diffracting optical surface is 
provided in the lens unit that is moved to achieve zooming, and to achieve 
well-balanced correction of chromatic aberration in the objective lens and 
in the eyepiece lens if above-noted condition (3) is satisfied. 
FIGS. 20A to 20D are enlarged cross-sectional views of examples of 
diffracting optical surfaces as used in the embodiments of the present 
invention. In the example in FIG. 20A, a diffracting optical surface is 
composed by forming a resin layer 2 having a saw-toothed cross section on 
a glass substrate 1 having a predetermined curvature. In the example in 
FIG. 20B, which is a modified type of the example in FIG. 20A, a 
diffracting optical surface is composed by forming a resin layer 2' having 
a step-like cross section on a glass substrate 1 having a predetermined 
curvature. Of course, the pitch of the pattern formed by these resin 
layers is determined in accordance with the optical power of diffraction 
required on those surfaces. 
In the examples in FIGS. 20A and 20B, there exists a border surface between 
the resin layer 2 or 2' and the glass substrate 1. However, by making the 
index of refraction of the resin layer 2 or 2' substantially the same as 
that of the glass substrate 1, the existence of the border surface can be 
ignored from the optical viewpoint. Even then, although the border surface 
between the resin layer 2 or 2' and the glass substrate 1 is optically 
non-existent, a light ray incident on this optically functioning surface 
is affected both by the optical power of diffraction resulting from the 
saw-toothed shape of the resin layer and by the optical power of 
refraction resulting from the curvature that the surface as a whole has. 
Accordingly, even if this optically functioning surface has only one 
surface physically, this surface is regarded, from the optical viewpoint, 
as having optical power of both diffraction and refraction. 
In the diffracting optical surfaces in FIGS. 20A and 20B, the resin layer 2 
or 2' can be produced by first applying optical resin to the surface of 
the glass substrate 1, and then either molding it with a mold prepared 
beforehand or cutting the optical resin layer directly with a laser beam 
or the like. 
FIGS. 20C and 20D show further examples of diffracting optical surfaces, 
corresponding to the examples in FIGS. 20A and 20B, respectively. In the 
examples in FIGS. 20C and 20D, the saw-toothed or step-like portion that 
exerts optical power of diffraction and the portion corresponding to the 
glass substrate of the first two examples are formed as one seamless 
optical element offering an optically functioning surface. 
The examples in FIGS. 20C and 20D, unlike those in FIGS. 20A and 20B, do 
not have any smooth surface as is found in normal lenses exerting optical 
power of refraction. However, also here, even if this optically 
functioning surface has only one surface physically, this surface is 
regarded, from the optical viewpoint, as having optical power of both 
diffraction and refraction. 
The diffracting optical surfaces in FIGS. 20A and 20B can be produced, for 
example, by molding resin or the like with a mold prepared beforehand. 
TABLE 1 
______________________________________ 
h1 h2 h3 h1.SIGMA. 
h2.SIGMA. 
h3.SIGMA. 
______________________________________ 
Sign Positive 
0 Negative 
Positive 
Positive 
0 
______________________________________ 
__________________________________________________________________________ 
&lt;&lt; Embodiment 1 &gt;&gt; 
__________________________________________________________________________ 
Radius of 
Axial Index of 
Abbe 
Surface 
Curvature 
Distance 
Refraction 
Number 
__________________________________________________________________________ 
S0 r0 = .infin. (Focal Plane) 
d0 = 57.072 
S1*[DOE] 
r1 = .infin. 
d1 = 5.903 
N1 = 1.4914 
v1 = 57.82 . . . G1 
S2* r2 = -9.015 
d2 = 27.742 
S3* r3 = 34.892 
d3 = 4.250 
N2 = 1.4914 
v2 = 57.82 . . . G2 
S4 r4 = -21.485 
d4 = 16.000 
S5*[DOE] 
r5 = 169.332 
d5 = 4.000 
N3 = 1.4914 
v3 = 57.82 . . . G3 
S6 r6 = -15.655 
d6 = 17.000 
S7 r7 = .infin. (Pupil E) 
__________________________________________________________________________ 
&lt;Aspherical Coefficients&gt; 
__________________________________________________________________________ 
[Surface] 
[K] [A4] [A6] [A8] [A10] 
__________________________________________________________________________ 
S1 0.00 -2.68 .times. 10-4 
-8.88 .times. 10.sup.-6 
1.02 .times. 10.sup.-7 
-8.32 .times. 10.sup.-9 
S2 1.75 .times. 10.sup.-1 
6.18 .times. 10.sup.-6 
-1.93 .times. 10.sup.-7 
-4.16 .times. 10.sup.-8 
-3.28 .times. 10.sup.-10 
S3 1.51 .times. 10.sup.-1 
-2.50 .times. 10.sup.-5 
-4.52 .times. 10.sup.-7 
1.00 .times. 10.sup.-9 
0.00 
S5 -9.53 .times. 10.sup.3 
-6.21 .times. 10.sup.-5 
-1.48 .times. 10.sup.-7 
7.42 .times. 10.sup.-9 
-6.31 .times. 10.sup.-11 
__________________________________________________________________________ 
&lt;Phase Function Coefficients of Diffracting Optical Surfaces&gt; 
__________________________________________________________________________ 
[Surface] 
[C1] [C2] [C3] [C4] 
__________________________________________________________________________ 
S1 -2.18 .times. 10.sup.-3 
1.36 .times. 10.sup.-6 
4.72 .times. 10.sup.-7 
-3.30 .times. 10.sup.-8 
S5 -1.10 .times. 10.sup.-3 
-1.68 .times. 10.sup.-5 
3.76 .times. 10.sup.-7 
-2.20 .times. 10.sup.-9 
__________________________________________________________________________ 
__________________________________________________________________________ 
&lt;&lt; Embodiment 2 &gt;&gt; 
__________________________________________________________________________ 
Radius of 
Axial Index of 
Abbe 
Surface 
Curvature 
Distance 
Refraction 
Number 
__________________________________________________________________________ 
S0 r0 = .infin. (Focal Plane) 
d0 = 51.177 
S1* r1 = .infin. 
d1 = 7.000 
N1 = 1.4914 
v1 = 57.82 . . . G1 
S2*[DOE] 
r2 = -7.929 
d2 = 26.629 
S3*[DOE] 
r3 = -91.927 
d3 = 4.000 
N2 = 1.4914 
v2 = 57.82 . . . G2 
S4 r4 = -17.477 
d4 = 10.852 
S5 r5 = 33.759 
d5 = 3.800 
N3 = 1.4914 
v3 = 57.82 . . . G3 
S6* r6 = -19.640 
d6 = 18.000 
S7 r7 = .infin. (Pupil E) 
__________________________________________________________________________ 
&lt;Aspherical Coefficients&gt; 
__________________________________________________________________________ 
[Surface] 
[K] [A4] [A6] [A8] [A10] 
__________________________________________________________________________ 
S1 0.00 -6.76 .times. 10.sup.-4 
8.40 .times. 10.sup.-7 
-5.00 .times. 10.sup.-7 
-2.51 .times. 10.sup.-8 
S2 7.70 .times. 10.sup.-2 
-9.94 .times. 10.sup.-7 
-1.09 .times. 10.sup.-6 
-3.12 .times. 10.sup.-8 
-8.72 .times. 10.sup.-10 
S3 -5.54 .times. 10 
3.56 .times. 10.sup.-5 
4.84 .times. 10.sup.-7 
-2.35 .times. 10.sup.-8 
1.72 .times. 10.sup.-10 
S6 -2.28 .times. 10 
6.07 .times. 10.sup.-6 
-2.21 .times. 10.sup.-7 
7.16 .times. 10.sup.-10 
0.00 
__________________________________________________________________________ 
&lt;Phase Function Coefficients of Diffracting Optical Surfaces&gt; 
__________________________________________________________________________ 
[Surface] 
[C1] [C2] [C3] [C4] 
__________________________________________________________________________ 
S2 -2.64 .times. 10.sup.-3 
5.59 .times. 10.sup.-6 
2.21 .times. 10.sup.-7 
0.00 
S3 -4.46 .times. 10.sup.-3 
0.00 0.00 0.00 
__________________________________________________________________________ 
__________________________________________________________________________ 
&lt;&lt; Embodiment 3 &gt;&gt; 
__________________________________________________________________________ 
Radius of 
Axial Index of 
Abbe 
Surface 
Curvature 
Distance 
Refraction 
Number 
__________________________________________________________________________ 
S0 r0 = .infin. (Focal Plane) 
d0 = 38.816 
S1* r1 = -16.496 
d1 = 3.000 
N1 = 1.4914 
v1 = 57.82 . . . G1 
S2 r2 = -27.623 
d2 = 3.321 
S3* r3 = 17.074 
d3 = 5.500 
N2 = 1.4914 
v2 = 57.82 . . . G2 
S4*[DOE] 
r4 = -9.476 
d4 = 33.946 
S5* r5 = 22.538 
d5 = 5.500 
N3 = 1.4914 
v3 = 57.82 . . . G3 
S6*[DOE] 
r6 = -16.262 
d6 = 18.000 
S7 r7 = .infin. (Pupil E) 
__________________________________________________________________________ 
&lt;Aspherical Coefficients&gt; 
__________________________________________________________________________ 
[Surface] 
[K] [A4] [A6] [A8] [A10] 
__________________________________________________________________________ 
S1 2.98 -9.52 .times. 10.sup.-1 
-2.13 .times. 10.sup.-5 
2.12 .times. 10.sup.-6 
-1.57 .times. 10.sup.-7 
S3 -1.13 .times. 10 
-1.51 .times. 10.sup.-5 
-5.70 .times. 10.sup.-7 
-1.60 .times. 10.sup.-8 
1.29 .times. 10.sup.-10 
S4 -1.45 .times. 10.sup.-1 
4.42 .times. 10.sup.-5 
6.83 .times. 10.sup.-7 
1.10 .times. 10.sup.-9 
-9.39 .times. 10.sup.-11 
S5 -6.54 -1.17 .times. 10.sup.-5 
-4.89 .times. 10.sup.-7 
-8.88 .times. 10.sup.-9 
-1.62 .times. 10.sup.-10 
S6 5.98 .times. 10.sup.-2 
-2.42 .times. 10.sup.-6 
-1.14 .times. 10.sup.-7 
-4.00 .times. 10.sup.-9 
4.28 .times. 10.sup.-13 
__________________________________________________________________________ 
&lt;Phase Function Coefficients of Diffracting Optical Surfaces&gt; 
__________________________________________________________________________ 
[Surface] 
[C1] [C2] [C3] [C4] 
__________________________________________________________________________ 
S4 -2.28 .times. 10.sup.-3 
3.52 .times. 10.sup.-7 
-7.86 .times. 10.sup.-8 
-2.98 .times. 10.sup.-9 
S6 -1.65 .times. 10.sup.-3 
8.18 .times. 10.sup.-6 
3.90 .times. 10.sup.-8 
-6.73 .times. 10.sup.-9 
__________________________________________________________________________ 
__________________________________________________________________________ 
&lt;&lt; Embodiment 4 &gt;&gt; 
__________________________________________________________________________ 
Radius of 
Axial Index of 
Abbe 
Surface 
Curvature 
Distance 
Refraction 
Number 
__________________________________________________________________________ 
S0 r0 = .infin. (Focal Plane) 
d0 = 56.723 
S1*[DOE] 
r1 = -118.605 
d1 = 5.969 
N1 = 1.5251 
v1 = 56.38 . . . G1 
S2* r2 = -9.011 
d2 = 28.058 
S3* r3 = 34.892 
d3 = 4.250 
N2 = 1.4914 
v2 = 57.82 . . . G2 
S4 r4 = -21.485 
d4 = 16.000 
S5*[DOE] 
r5 = 193.963 
d5 = 4.000 
N3 = 1.4914 
v3 = 57.82 . . . G3 
S6 r6 = -15.514 
d6 = 17.000 
S7 r7 = .infin. (Pupil E) 
__________________________________________________________________________ 
&lt;Aspherical Coefficients&gt; 
__________________________________________________________________________ 
[Surface] 
[K] [A4] [A6] [A8] [A10] 
__________________________________________________________________________ 
S1 -9.69 .times. 10.sup.2 
-3.17 .times. 10.sup.-6 
-1.08 .times. 10.sup.-5 
2.18 .times. 10.sup.-7 
-1.13 .times. 10.sup.-8 
S2 1.52 .times. 10.sup.-1 
4.12 .times. 10.sup.-6 
-4.46 .times. 10.sup.-7 
-4.71 .times. 10.sup.-8 
8.59 .times. 10.sup.-11 
S3 1.51 .times. 10.sup.-1 
-2.50 .times. 10.sup.-5 
-4.52 .times. 10.sup.-7 
1.00 .times. 10.sup.-9 
0.00 
S5 -1.55 .times. 10.sup.4 
-6.28 .times. 10.sup.-5 
-2.37 .times. 10.sup.-7 
8.44 .times. 10.sup.-9 
-6.68 .times. 10.sup.-11 
__________________________________________________________________________ 
&lt;Phase Function Coefficients of Diffracting Optical Surfaces&gt; 
__________________________________________________________________________ 
[Surface] 
[C1] [C2] [C3] [C4] 
__________________________________________________________________________ 
S1 -2.32 .times. 10.sup.-3 
-1.94 .times. 10.sup.-7 
1.12 .times. 10.sup.-6 
-7.72 .times. 10.sup.-8 
S5 -1.05 .times. 10.sup.-3 
-1.89 .times. 10.sup.-5 
4.31 .times. 10.sup.-7 
-2.67 .times. 10.sup.-9 
__________________________________________________________________________ 
______________________________________ 
Emb. 1 Emb. 2 Emb. 3 Emb. 4 
______________________________________ 
.phi.Rd 0.00436 0.00528 0.00456 
0.00464 
.phi.Rt 0.0581 0.0675 0.0785 0.0582 
.phi.Ed 0.0022 -- 0.00331 
0.0021 
.phi.Et 0.0469 -- 0.0528 0.0468 
.phi.Cd -- 0.00893 -- -- 
.phi.Ct -- 0.0547 -- -- 
.vertline.(.phi.Rd/.phi.Rt)- 
0.028 -- 0.0045 0.035 
(.phi.Ed/.phi.Et).vertline. 
.vertline.(.phi.Rd/.phi.Rt)- 
-- 0.085 -- -- 
(.phi.Cd/.phi.Ct).vertline. 
______________________________________ 
__________________________________________________________________________ 
&lt;&lt; Embodiment 5 &gt;&gt; 
.beta. = 0.44 .about. 1.0 
__________________________________________________________________________ 
Radius of 
Axial Index of Abbe 
Surface 
Curvature 
Distance 
Refraction 
Number 
__________________________________________________________________________ 
S1* r1 = -12.218 
d1 = 1.000 
N1 = 1.49329 
v1 = 57.82 . . . g1 
S2* r2 = 22.796 
d2 = 12.12 .about. 1.92 
S3* r3 = 9.953 
d3 = 2.800 
N2 = 1.49329 
v2 = 57.82 . . . g2 
S4 r4 = -12.11460 
d4 = 0.000 
N3 = 10001.00000 
v3 = -3.45 
S5[DOE] 
r5 = -12.1145474 
d5 = 0.78 .about. 9.34 
S6 r6 = 40.000 
d6 = 16.000 
N4 = 1.58752 
v4 = 30.36 . . . g3 
S7 r7 = .infin. 
d7 = 3.000 
S8 r8 = 17.489 
d8 = 12.300 
N5 = 1.58752 
v5 = 30.36 . . . p 
S9 r9 = .infin. 
d9 = 8.980 
S10* r10 = 19.205 
d10 = 3.000 
N6 = 1.49329 
v6 = 57.82 . . . se 
S11 r11 = -16.94522 
d11 = 0.000 
N7 = 10001.00000 
v7 = -3.45 
S12[DOE] 
r12 = -16.9451069 
__________________________________________________________________________ 
&lt;Aspherical Coefficients&gt; 
__________________________________________________________________________ 
S1 : .epsilon. = 1.00, A4 = -6.23 .times. 10.sup.-4, A6 = -2.04 .times. 
10.sup.-6 
S2 : .epsilon. = 1.00, A4 = -7.00 .times. 10.sup.-4, A6 = 2.80 .times. 
10.sup.-6 
S3 : .epsilon. = 1.00, A4 = -5.13 .times. 10.sup.-4, A6 = 1.00 .times. 
10.sup.-6 
S10: .epsilon. = 1.00, A4 = -1.05 .times. 10.sup.-4, A6 = 2.00 .times. 
10.sup.-7 
__________________________________________________________________________ 
&lt;Value Corresponding to Condition (3) and Related Values&gt; 
__________________________________________________________________________ 
.phi.O = 0.09, .phi.OD = 0.0038, .phi.E = 0.0548, .phi.ED = 0.0015, 
.vertline..phi.OD .multidot. .phi.E/(.phi.O .multidot. ED) .vertline. = 
1.56 
__________________________________________________________________________ 
__________________________________________________________________________ 
&lt;&lt; Embodiment 6 &gt;&gt; 
.beta. = 0.41 .about. 0.93 
__________________________________________________________________________ 
Radius of 
Axial Index of Abbe 
Surface 
Curvature 
Distance 
Refraction 
Number 
__________________________________________________________________________ 
S1* r1 = -28.382 
d1 = 1.000 
N1 = 1.58752 
v1 = 30.36 . . . g1 
S2* r2 = 15.12500 
d2 = 0.000 
N2 = 10001.00000 
v2 = -3.45 
S3[DOE]* 
r3 = 15.1249540 
d3 = 12.12 .about. 1.87 
S4* r4 = 10.815 
d4 = 2.800 
N3 = 1.49329 
v3 = 57.82 . . . g2 
S5 r5 = -10.141 
d5 = 0.78 .about. 9.34 
S6 r6 = 40.000 
d6 = 16.000 
N4 = 1.58752 
v4 = 30.35 . . . g3 
S7 r7 = .infin. 
d7 = 3.000 
S8 r8 = 17.489 
d8 = 20.000 
N5 = 1.58752 
v5 = 30.36 . . . p 
S9 r9 = .infin. 
d9 = 4.930 
S10* r10 = 19.205 
d10 = 3.000 
N6 = 1.49329 
v6 = 57.82 . . . se 
S11 r11 = 21.24076 
d11 = 0.000 
N7 = 10001.00000 
v7 = -3.45 
S12[DOE] 
r12 = -21.2406234 
__________________________________________________________________________ 
&lt;Aspherical Coefficients&gt; 
__________________________________________________________________________ 
S1 : .epsilon. = 1.00, A4 = -6.23 .times. 10.sup.-4, A6 = -2.04 .times. 
10.sup.-6 
S2 : .epsilon. = 1.00, A4 = -7.00 .times. 10.sup.-4, A6 = 2.80 .times. 
10.sup.-6 
S3 : .epsilon. = 1.00, A4 = -7.00 .times. 10.sup.-4, A6 = 2.80 .times. 
10.sup.-6 
S4 : .epsilon. = 1.00, A4 = -5.13 .times. 10.sup.-4, A6 = 1.00 .times. 
10.sup.-6 
S10: .epsilon. = 1.00, A4 = -1.05 .times. 10.sup.-4, A6 = 2.00 .times. 
10.sup.-7 
__________________________________________________________________________ 
&lt;Value Corresponding to Condition (3) and Related Values&gt; 
__________________________________________________________________________ 
.phi.O = -0.0621, .phi.OD = 0.002, .phi.E = 0.0505, .phi.ED = 0.003, 
.vertline..phi.OD .multidot. .phi.E/(.phi.O .multidot. .phi.ED) 
.vertline. = 0.54 
__________________________________________________________________________