JP2000227551A - Lens optical system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lens optical system made compact in the aspect of aberration by effectively using a diffraction grating. SOLUTION: This lens optical system is provided with a 1st group Gr1 having positive power, a 2nd group Gr2 having negative power, a 3rd group Gr3 having positive power and a 4th group Gr4 having positive power in turn from an object side. By changing an interval between the 1st and the 2nd groups Gr1 and Gr2 and an interval between the 3rd and the 4th groups Gr3 and Gr4, a zooming action is executed. The group Gr3 is provided with a joined lens and the joined lens is provided with the diffraction grating at a boundary surface (r14#). The curvature of the boundary surface (r14#) is different from those of the incident surface and the emitting surface (r13 and r15*) of the joined lens.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a lens optical system, and more particularly, to a lens optical system using a lens having a diffraction grating.

[0002]

2. Description of the Related Art A lens optical system (for example, an imaging optical system such as a zoom lens, and an observation optical system such as a finder optical system) used for an optical device (for example, a digital camera, a video camera, a silver halide camera) is made compact. It is effective to use a diffraction grating for aberration correction. Specifically, a diffractive optical surface that is constituted by a diffraction grating formed on a surface of an optical element or a boundary surface of a medium, and realizes a lens function by its diffractive effect may be used. A zoom lens having a diffractive lens is disclosed in
It is proposed in JP-A-48757 and JP-A-10-161022. The former is a positive / negative / positive / positive four-component type zoom lens, and has a diffractive lens in the second or third group. On the other hand, the latter is a negative / positive two-component type zoom lens, and has a diffractive lens in the second group. However, in any case, it cannot be said that the diffraction grating contributes sufficiently effectively to downsizing.

When the diffraction grating used has a blazed shape, the diffraction efficiency at a specific wavelength (that is, the design wavelength of the diffraction grating) is 100%, but the diffraction efficiency at a different wavelength does not reach 100%. . This is because phase matching occurs with respect to the height of the diffraction grating for light having a design wavelength, but phase mismatch occurs for light having a wavelength other than the design wavelength. Examples in which a diffraction grating is provided at the interface between two different optical materials in order to match the phase of light even at a wavelength other than the design wavelength are disclosed in Japanese Patent Application Laid-Open No. Hei 9-123321 and US Pat. , 73
4,502. If this diffraction grating is used, the diffraction efficiency becomes 100% even at wavelengths other than the design wavelength,
The diffraction efficiency can be increased in a wide wavelength range.

[0004]

However, the light beam obliquely incident on the blazed shape is affected by the diffraction by the blazed wall portion even at the strictly designed wavelength.
The diffraction efficiency will not reach 100%. In particular, when the diffraction grating height is large due to having a diffraction grating at the interface between the two materials, or when the height of the blazed wall is relatively large (that is, the diffraction grating height) because the diffraction grating interval is small. In this case, the effect of the blazed wall portion is large, so that the diffraction efficiency is greatly reduced. Further, when a diffraction grating is used for the lens system, it is inevitable that light rays are obliquely incident in a blazed shape due to the angle of view, which causes a problem of reduction in diffraction efficiency.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and a first object is to provide a lens optical system which has been made compact in terms of aberration by effectively using a diffraction grating. Is to provide. A second object is to provide a lens optical system using a diffraction grating so that the diffraction efficiency of obliquely incident light does not decrease.

[0006]

In order to achieve the first object, a lens optical system according to a first aspect of the present invention includes, in order from an object side, a first unit having a positive power and a first unit having a negative power. A second group, a third group having a positive power, and a fourth group having a positive or negative power, wherein the first group and the second group
A lens optical system that performs zooming by changing an interval between groups and an interval between the third group and the fourth group, wherein the third group has a cemented lens, and The lens has a diffraction grating at a boundary surface, and a curvature of the boundary surface is different from a curvature of an entrance surface and an exit surface of the cemented lens.

In order to achieve the first object, a lens optical system according to a second aspect of the present invention is characterized in that, in the configuration of the first aspect, the diffraction grating satisfies the following conditional expression. 0.02 <φDOE / φgr3 <0.1 where φDOE: lens power by the diffraction grating, φgr3: power of the third lens unit.

To achieve the first object, a lens optical system according to a third aspect of the present invention is characterized in that, in the configuration of the first or second aspect, the diffraction grating satisfies the following conditional expression. I do. 0.05 <tW / fW <0.4, where tW is the distance between the upper surface of the diffraction grating and the aperture at the wide-angle end on the air-equivalent axis, and fW is the focal length of the entire zoom system at the wide-angle end.

In order to achieve the first object, a lens optical system according to a fourth aspect of the present invention is characterized in that, in the configuration of the first or second aspect, the following conditional expression is satisfied. | Y'max / PZ | <0.4 where Y'max: maximum image height, PZ: distance from the image plane to the exit pupil position.

In order to achieve the second object, a lens optical system according to a fifth aspect of the present invention is a lens optical system having a diffraction grating lens on a boundary surface where two different optical materials are in close contact with each other, The diffraction grating satisfies the following conditional expression representing a blaze shape at an arbitrary height H in a direction perpendicular to the optical axis. | (H / d) tanθ | ≦ 0.045, where h is the height of the diffraction grating, d is the interval between the diffraction gratings, θ is the incident angle, and Ci is the phase coefficient, λ0 is the design wavelength, and d is the equation of the phase function Φ (H):

(Equation 2) The equation for the height H in the direction perpendicular to the optical axis is represented by: d (H) = − 2π / (dΦ / dH).

In order to achieve the second object, a lens optical system according to a sixth aspect of the present invention is a lens optical system having a diffraction grating lens on a boundary surface where two different optical materials are in close contact with each other, The diffraction grating satisfies the following conditional expression. 0.01 ≦ | {(h • φDOE • DDOE) / (2 • λ0)} • tan (ωmax) | ≦
0.06 where h: height of the diffraction grating, λ0: design wavelength, φDOE: lens power by the diffraction grating, DDOE: effective diameter of the lens by the diffraction grating, ωmax: maximum value of the half angle of view of the lens optical system.

In order to achieve the second object, a lens optical system according to a seventh aspect of the present invention is a lens optical system having a diffraction grating lens on a boundary surface where two different optical materials are in close contact with each other, The diffraction grating satisfies the following conditional expression. 0.005 ≦ | (h / dmin) · tan (ωmax) | ≦ 0.07, where h is the height of the diffraction grating, dmin is the minimum diffraction grating interval within the effective diameter range of the lens by the diffraction grating, and ωmax is the half-length of the lens optical system. The maximum value of the angle is

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a lens optical system embodying the present invention will be described with reference to the drawings. FIGS. 1, 3, 5, and 7 are lens configuration diagrams corresponding to the zoom lenses according to the first to fourth embodiments, respectively.
[W], middle (intermediate focal length state) [M], and lens arrangement at the telephoto end [T] are shown. Di (i =
(1,2,3, ...) is the air gap counted from the object side.
A variable interval that changes during zooming among the third axial upper surface intervals is shown. Also, ri (i = 1,
The surfaces marked with (2,3, ...) are the i-th surface counted from the object side (however, the final surface is the image surface (I)), and the surface marked with * is an aspheric surface. The surface marked with # in ri is the surface of the diffraction lens on which the diffraction grating is formed.

In the first and second embodiments, in order from the object side, a first lens unit (Gr1) having a positive power, a second lens unit (Gr2) having a negative power, and a positive lens unit having a positive power 3rd group (Gr3)
And a fourth group (Gr4) having a positive power. In the third embodiment,
A first group (Gr1) having a positive power, in order from the object side,
A second group having negative power (Gr2), a third group having positive power (Gr3), and a fourth group having positive power (Gr4);
And a fifth unit (Gr5) having negative power. In the fourth embodiment, in order from the object side, a first unit (Gr1) having positive power, a second unit (Gr2) having negative power, and a third unit (Gr3) having positive power And a fourth group (Gr4) having a negative power and a fifth group (Gr5) having a positive power.

Each of the embodiments is a zoom type having four components of positive, negative, positive and (positive or negative) having a diffraction grating in the third lens unit (Gr3), and includes a first lens unit (Gr1). The zooming is performed by changing the distance between the first lens unit and the second lens unit (Gr2), the distance between the third lens unit (Gr3) and the fourth lens unit (Gr4), and the like. The third group (Gr3) is located between the second group (Gr2) and the third group (Gr3).
An aperture (S) that zooms together is arranged, and a low-pass filter (LPF) is arranged closest to the image plane (I).

In the first embodiment (FIG. 1), each group is configured as follows in order from the object side. Group 1 (G
r1) is composed of a cemented lens composed of a negative meniscus lens concave on the image side and a biconvex positive lens, and a positive meniscus lens convex on the object side. The second group (Gr2) includes a negative meniscus lens concave on the image side, and a cemented lens including a biconcave negative lens and a biconvex positive lens. The third lens unit (Gr3) includes a cemented lens including a positive meniscus lens convex on the object side and a negative meniscus lens concave on the image side, and has a diffraction grating on the fourteenth surface (r14). .
The fourth unit (Gr4) includes a biconvex positive lens and a biconcave negative lens.

In the second embodiment (FIG. 3), each group is configured as follows in order from the object side. Group 1 (G
r1) includes a negative meniscus lens concave on the image side and a biconvex positive lens. The second group (Gr2) includes a negative meniscus lens concave on the image side, and a cemented lens including a biconcave negative lens and a positive meniscus lens convex on the object side, and has an eighth surface (r8 ) Has a diffraction grating. Third
The group (Gr3) is composed of a cemented lens composed of two positive meniscus lenses convex on the object side, and has a diffraction grating on the twelfth surface (r12). The fourth unit (Gr4) includes a biconvex positive lens and a negative meniscus lens concave on the image side.

In the third embodiment (FIG. 5), each group is configured as follows from the object side. Group 1 (G
r1) is composed of a cemented lens composed of a negative meniscus lens concave on the image side and a biconvex positive lens, and a positive meniscus lens convex on the object side. The second group (Gr2) includes a negative meniscus lens concave on the image side, and a cemented lens composed of a biconcave negative lens and a positive meniscus lens convex on the object side. The third lens unit (Gr3) includes a cemented lens including a positive meniscus lens convex on the object side and a negative meniscus lens concave on the image side, and has a diffraction grating on the fourteenth surface (r14). . The fourth unit (Gr4) includes a biconvex positive lens,
And a biconcave negative lens. 5th group (Gr5)
Is composed of a negative meniscus lens concave on the object side.

In the fourth embodiment (FIG. 7), each group is configured as follows from the object side. Group 1 (G
r1) is composed of a cemented lens composed of a negative meniscus lens concave on the image side and a biconvex positive lens, and a positive meniscus lens convex on the object side. The second group (Gr2) includes a negative meniscus lens concave on the image side, and a cemented lens composed of a biconcave negative lens and a positive meniscus lens convex on the object side. The third group (Gr3) includes a cemented lens composed of a biconvex positive lens and a biconcave negative lens, and has a diffraction grating on the fourteenth surface (r14). The fourth group (Gr4)
It is composed of a negative meniscus lens concave on the image side. Fifth
The group (Gr5) includes a biconvex positive lens and a biconcave negative lens.

In order to make a zoom type lens optical system having positive, negative, positive and (positive or negative) compact, a diffraction grating is used for the third lens unit (Gr3) as in the above embodiments. This is effective for aberration correction, and the third lens unit (Gr3) has a cemented lens, and the cemented lens has a boundary surface (that is,
It is desirable that a diffraction grating is provided at a boundary surface where two different optical materials are in close contact with each other, and the curvature of the boundary surface is different from the curvatures of the entrance surface and the exit surface of the cemented lens. These features will be described later in detail.

Next, as in each embodiment, the third lens unit (Gr3)
Is a zoom type with four components of positive, negative, positive and (positive or negative) having a diffraction grating, and the third group (Gr3) has a cemented lens, and the cemented lens is A description will be given of a desirable conditional expression that a lens optical system having the diffraction grating and having a curvature of a boundary surface of the cemented lens different from a curvature of an entrance surface and an exit surface of the cemented lens is satisfied. It is not necessary to satisfy all of the following conditional expressions at the same time, and if each conditional expression is satisfied independently, it is possible to achieve the corresponding operation and effect. Of course, it is needless to say that satisfying a plurality of conditional expressions is more desirable from the viewpoint of optical performance, compactness, and the like.

It is desirable that the diffraction grating satisfies the following conditional expression (1). 0.02 <φDOE / φgr3 <0.1 (1) where φDOE: lens power by the diffraction grating, φgr3: power of the third lens unit (Gr3).

Conditional expression (1) shows that the power φgr3 of the third lens unit (Gr3)
A desirable condition range of the ratio of the lens power φDOE by the diffraction grating to (including φDOE) is defined. By satisfying conditional expression (1), a compact lens optical system can be achieved. If the lower limit of conditional expression (1) is not reached, the effect of correcting the chromatic aberration of the diffractive lens cannot be obtained, so that the size of the lens optical system increases. Conditional expression (1)
Exceeds the upper limit, the astigmatism of the diffractive lens increases, and the size of the lens optical system increases to correct the astigmatism.

It is desirable that the diffraction grating satisfies the following conditional expression (2). By satisfying conditional expression (2), it is possible to achieve a lens optical system having good chromatic aberration. If the lower limit of conditional expression (2) is exceeded, the lens cannot be held. If the upper limit of conditional expression (2) is exceeded, axial chromatic aberration correction at the wide-angle end [W] will be insufficient. 0.05 <tW / fW <0.4 (2) where tW is the distance between the diffraction grating and the diaphragm (S) at the wide-angle end [W] on the air-equivalent axis, and fW is the zooming system at the wide-angle end [W]. The focal length,

It is desirable to satisfy the following conditional expression (3). By satisfying the conditional expression (3), when the image pickup device is used, the illuminance around the screen falls within a favorable range. | Y'max / PZ | <0.4 (3) where Y'max is the maximum image height, and PZ is the distance from the image plane (I) to the exit pupil position.

The conditional expression described below is a desirable conditional expression that a lens optical system having a lens using a diffraction grating at the boundary surface where two different optical materials are in close contact with each other as in the above embodiments. It is. Conditional expression mentioned above
As in (1) to (3), it is not necessary to satisfy all of the following conditional expressions at the same time.If each individual conditional expression is satisfied independently, it is possible to achieve the corresponding action and effect, and It is more desirable to satisfy a plurality of conditional expressions from the viewpoint of optical performance, diffraction efficiency, and the like.

The diffraction grating has an arbitrary height in the direction perpendicular to the optical axis.
It is desirable to satisfy the following conditional expression (4) representing the blaze shape at H. If the diffraction grating satisfies the conditional expression (4), the reduction in the diffraction efficiency of the obliquely incident light will not be a problem.
If the upper limit of conditional expression (4) is exceeded, the diffraction efficiency of the diffractive lens will be insufficient.

| (H / d) tan θ | ≦ 0.045 (4) where h: diffraction grating height, d: diffraction grating interval, θ: incident angle, Ci: phase coefficient, λ0: design wavelength, Where the diffraction grating interval d is the equation of the phase function Φ (H):

(Equation 3) The equation for the height H in the direction perpendicular to the optical axis is represented by: d (H) = − 2π / (dΦ / dH).

It is desirable that the diffraction grating satisfies the following conditional expression (5). If the diffraction grating satisfies conditional expression (5),
The reduction in the diffraction efficiency of obliquely incident light rays is of such a degree that no problem occurs. If the lower limit of conditional expression (5) is exceeded, the chromatic aberration correction effect of the diffractive lens will be insufficient. If the upper limit of conditional expression (5) is exceeded, the diffraction efficiency of the diffractive lens will be insufficient.

0.01 ≦ | {(h · φDOE · DDOE) / (2 · λ0)} · tan (ωmax) | ≦ 0.06 (5) where h: height of diffraction grating, λ0: design wavelength, φDOE: diffraction The lens power by the grating, DDOE: the effective diameter of the lens by the diffraction grating, ωmax: the maximum value of the half angle of view of the lens optical system.

It is desirable that the diffraction grating satisfies the following conditional expression (6). In the case of a general photographing lens, if the diffraction grating satisfies the conditional expression (6), the reduction in the diffraction efficiency of obliquely incident light rays will not be a problem. If the lower limit of conditional expression (6) is exceeded, the chromatic aberration correction effect of the diffractive lens will be insufficient. If the upper limit of conditional expression (6) is exceeded,
The diffraction efficiency of the diffraction lens becomes insufficient.

0.005 ≦ | (h / dmin) · tan (ωmax) | ≦ 0.07 (6) where h: height of the diffraction grating, dmin: minimum diffraction grating interval within the effective diameter range of the lens by the diffraction grating, ωmax : The maximum value of the half angle of view of the lens optical system.

Next, the diffraction efficiency when a light beam is obliquely incident on the diffraction grating used in each embodiment is calculated by the above-mentioned conditional expression.
This will be described in connection with (4) to (6). FIG. 12 is an enlarged view showing a state where light rays are obliquely incident on the blazed diffraction grating. FIG. 12A shows a case where the diffraction grating height h is low, which corresponds to a case where a diffraction grating is provided on the lens surface in contact with air. FIG. 12B shows a case where the diffraction grating height h is high, which corresponds to a case where a diffraction grating is provided at the boundary between two materials. In FIG. 12, a dotted line AX ′ is a straight line parallel to the optical axis (AX in FIG. 14) of the lens optical system, and a solid region D0 is a non-diffracted portion due to the diffraction grating height h.

FIG. 12 shows that the non-diffracted portion D0 increases as the diffraction grating height h increases. Also, it is expected that the non-diffracted portion D0 will increase due to the relatively large diffraction grating height h due to the small diffraction grating interval d. Further, when the incident angle θ increases, the non-diffracted portion D0 is expected to increase. Further, from the relationship of FIG. 12, the size of the non-diffracted portion D0 is (h /
d) It is understood that it is proportional to tan θ.

FIG. 13 is a graph showing the relationship between the grating pitch (d / λ0) and the diffraction efficiency. The curve in this graph shows the change in diffraction efficiency with respect to the grating spacing d when a light beam with a design wavelength λ0 = 587 nm is incident at an incident angle θ = 10 ° on a blazed grating having a grating height h = 17 μm. (Calculation result)
Is shown. Since it is known from experiments that the practical diffraction efficiency is required to be 0.9 or more, the region indicated by the arrow α1 in the graph of FIG. 13 is the practically necessary diffraction efficiency. Therefore, the condition range of the diffraction grating interval d indicated by the arrow α2 in FIG. 13 is determined from the diffraction efficiency required for practical use. From the obtained (h / d) tan θ, if the height h and the interval d of the diffraction grating of the blazed shape and the incident angle θ of the light beam incident on the diffraction grating are within the range of the conditional expression (4), practical use is possible. It can be seen that the required diffraction efficiency is obtained. │ (h / d) tanθ│ ≦ 0.045… (4)

Next, the diffraction grating interval d will be described. When the diffraction grating acts as a lens, Ci: phase coefficient, λ0:
When the design wavelength is used, the phase function Φ (H) of the diffraction grating is expressed by the following equation with respect to the height H from the optical axis:

(Equation 4) It is represented by

In particular, the power φDO of the lens by the diffraction grating
E is represented by the formula: φDOE = -2 · C1. The diffraction grating interval d is expressed by the following equation: d (H) = − 2π / (dΦ / dH) from the first derivative of the height H of the phase function Φ (H) in the direction perpendicular to the optical axis.

In a normal diffraction lens, since the phase coefficient C1 of i = 1 that determines the lens power is sufficiently large, the diffraction grating interval d (H) monotonically decreases with respect to the height H in the optical axis vertical direction below the effective diameter. I do. Therefore, when the phase coefficient Ci of i> 1 is small and ignored, and the effective diameter of the lens formed by the diffraction grating is DDOE, the minimum value dmin of the diffraction grating interval d (H) is expressed by the following equation (7).
It is represented by From this equation (7), the power φDOE of the diffractive lens is obtained.
It can be seen that the diffraction grating interval d (H) becomes smaller as is larger and as the effective diameter DDOE is larger. dmin = d (DDOE / 2) =-(2.lambda.0) / (2.C1.DDOE) = (2.lambda.0) / (. phi.DOE.DDOE) (7)

Next, the incident angle θ will be described. In the case of a lens optical system, as shown in FIG.
(In FIG. 14, AX is the optical axis of the lens optical system). Therefore, the maximum angle of view is the maximum incident angle. Strictly speaking, the incident angle θ with respect to the lens surface changes depending on the lens arrangement of the lens optical system, but even if the maximum value ωmax of the half angle of view ω is substituted for the incident angle θ in the conditional expression (4), It is possible to grasp the degree of the diffraction efficiency depending on the angle θ. Therefore, using the equation (7) for the conditional equation (4), and reviewing the constant values on the right side in accordance with these changes,
The following conditional expression (8) is obtained. | {(H • φDOE • DDOE) / (2 • λ0)} • tan (ωmax) | ≦ 0.06… (8)

[0040]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The construction of a lens optical system embodying the present invention will be described below with reference to construction data, aberration diagrams, and the like.
This will be described more specifically. In addition, the following Examples 1 to
Reference numeral 4 denotes a lens configuration diagram corresponding to the above-described first to fourth embodiments, respectively, and showing the first to fourth embodiments.
(FIG. 1, FIG. 3, FIG. 5, FIG. 7) show the corresponding lens configurations of Examples 1 to 4, respectively. Further, a comparative example (having no diffraction grating) with respect to Example 1 is also shown, and the lens configuration is shown in FIG.

In the construction data of Examples 1 to 4 and Comparative Example, ri (i = 1, 2, 3,...) Is the radius of curvature of the i-th surface counted from the object side, and di (i = 1, 2). (2,3, ...) indicates the i-th axial top surface distance counted from the object side, and Ni (i = 1,2,
3, ...), νi (i = 1,2,3, ...) indicate the refractive index (nd) and Abbe number (νd) of the i-th optical element counted from the object side for d-line. I have. In the construction data, the distance between the upper surfaces of the axes (variable distance) that changes during zooming is the wide-angle end.
(Short focal length end) [W]-Middle (intermediate focal length state) [M]-
This is the on-axis air gap between each group at the telephoto end (long focal length end) [T]. Focal length f, half angle of view ω (°) and F-number FNO of the entire system corresponding to each focal length state [W], [M], [T], and corresponding values of conditional expressions (1) to (3) Are also shown. Furthermore, the conditional expression
Table 1 shows corresponding values of (4), and Table 2 shows corresponding values of conditional expressions (5) and (6). Note that there is a range in the corresponding value of the conditional expression (4),
This is because the value of the diffraction grating interval d changes with the height H from the optical axis.

A surface with a * mark on the radius of curvature ri indicates a surface constituted by an aspherical surface, and is defined by the following equation (AS) representing the surface shape of the aspherical surface. Also, the surface marked with a # mark on the radius of curvature ri indicates that the surface is a diffraction lens surface on which a diffraction grating is formed, and is defined by the following formula (DS) that represents the phase shape of the pitch of the diffraction lens surface. Shall be.
The aspheric surface data of each aspheric surface and the diffraction surface data of each diffraction lens surface are shown together with other data.

Z (H) = (C0 · H ² ) / {1 + √ (1-C0 ² · H ² )} + (A · H ⁴ + B · H ⁶ + C · H ⁸ + D · H ¹⁰ )… (AS) where, in equation (AS), Z (H) is the displacement in the optical axis direction at the height H (based on the surface vertex), and H is the height from the optical axis (vertical to the optical axis). Height), C0: paraxial curvature, A, B, C, D: aspheric coefficient.

Φ (H) = (2π / λ0) · (C1 · H ² + C2 · H ⁴ + C3 · H ⁶ ) (DS) where Φ (H) is a phase function, H: height from the optical axis (height in the vertical direction of the optical axis), λ0: design wavelength, C1, C2, C3: phase coefficient.

[0045]

[Aspherical surface data of sixth surface (r6)] A = 1.98 × 10 ^-4 , B = 2.18 × 10 ^-5 , C = -5.66 × 10 ^-7 [Aspherical surface data of seventh surface (r7)] ^{] a = 9.23 × 10 -5,} B = 2.98 × 10 -5, C = 1.83 × 10 -6 [ aspheric data of the fifteenth surface (r15)] a = 1.59 × 10 -4, B = 3.82 × 10 - ⁵ , C = -8.18 × 10 ^-6 , D = 6.25
× 10 ^-7 [Aspherical surface data of the 18th surface (r18)] A = 1.60 × 10 ^-3 , B = -1.84 × 10 ^-4 , C = 2.09 × 10 ^-6 [Aspherical surface of the 19th surface (r19)] Data] A = 4.01 × 10 ^-3 , B = -7.71 × 10 ^-5 , C = 4.53 × 10 ^-6

[Diffraction Surface Data of Fourteenth Surface (r14)] C1 = -9.46 × 10 ^-4 , C2 = 2.73 × 10 ^-5

[Values Corresponding to Conditional Expressions] Conditional expression (1): φDOE / φgr3 = 0.042 Conditional expression (2): tW / fW = 0.16 Conditional expression (3) (at wide-angle end [W]): | Y′max / PZ | = 0.18 Conditional expression (3) (at telephoto end [T]): | Y'max / PZ | = 0.19

[0049]

[Aspherical surface data of third surface (r3)] A = -1.25 × 10 ^-4 , B = -1.06 × 10 ^-6 , C = -4.87 × 10 ^-8 [Aspherical surface data of sixth surface (r6)] Spherical data] A = -3.28 × 10 ^-4 , B = 6.87 × 10 ^-5 , C = -4.27 × 10 ^-6 [Aspheric data of the seventh surface (r7)] A = -4.26 × 10 ^-3 , B ^{= 2.75 × 10 -4, C =} -2.03 × 10 -5 [ eleventh surface (r11) aspherical ^{data] a = 8.72 × 10 -4,} B = -1.08 × 10 -4, C = 2.32 × 10 - ⁵ [Aspherical surface data of the thirteenth surface (r13)] A = 1.24 × 10 ^-3 , B = -7.98 × 10 ^-5 , C = 1.54 × 10 ^-5 , D = 1.02
× 10 ^-6 [Aspherical surface data of 14th surface (r14)] A = -4.03 × 10 ^-4 , B = -3.29 × 10 ^-5 , C = -3.90 × 10 ^-6 [16th surface (r16) Aspherical surface data] A = 1.96 × 10 ^-3 , B = 2.36 × 10 ^-5 , C = -2.19 × 10 ^-6 [Aspherical surface data of 17th surface (r17)] A = 5.41 × 10 ^-3 , B = 2.47 × 10 ^-4 , C = 1.09 × 10 ^-5

[Data of Diffraction Surface of Eighth Surface (r8)] C1 = 2.69 × 10 ⁻³ , C2 = −2.58 × 10 ⁻⁴ , C3 = −1.52 × 10 ^-5 [Diffraction Surface of Twelfth Surface (r12)] Data] C1 = -2.26 × 10 ^-3 , C2 = 3.48 × 10 ^-5 , C3 = 5.95 × 10 ^-6

[Values Corresponding to Conditional Expressions] Conditional expression (1): φDOE / φgr3 = 0.073 Conditional expression (2): tW / fW = 0.08 Conditional expression (3) (at wide-angle end [W]): | Y′max / PZ | = 0.17 Conditional expression (3) (at telephoto end [T]): | Y'max / PZ | = 0.19

[0053]

[Aspherical surface data of sixth surface (r6)] A = -1.03 × 10 ^-3 , B = 1.20 × 10 ^-4 , C = -2.65 × 10 ^-6 [Aspherical surface of seventh surface (r7)] Data] A = -1.02 × 10 ^-3 , B = 7.26 × 10 ^-5 , C = 6.52 × 10 ^-6 [Aspherical surface data of 15th surface (r15)] A = 2.18 × 10 ^-4 , B = 3.14 × 10 ^-5 , C = -6.47 × 10 ^-6 , D = 6.70
× 10 ^-7 [Aspherical surface data of 18th surface (r18)] A = 1.97 × 10 ^-3 , B = -2.51 × 10 ^-4 , C = 2.20 × 10 ^-6 [Aspherical surface of 19th surface (r19)] Data] A = 4.27 × 10 ^-3 , B = -1.41 × 10 ^-4 , C = 3.02 × 10 ^-6

[Diffraction Surface Data of Fourteenth Surface (r14)] C1 = −1.20 × 10 ⁻³ , C2 = 2.38 × 10 ⁻⁵

[Values for Conditional Expressions] Conditional expression (1): φDOE / φgr3 = 0.039 Conditional expression (2): tW / fW = 0.16 Conditional expression (3) (at wide-angle end [W]): | Y′max / PZ | = 0.17 Conditional expression (3) (at telephoto end [T]): | Y'max / PZ | = 0.19

[0057]

[Aspherical surface data of sixth surface (r6)] A = -3.69 × 10 ^-4 , B = 4.50 × 10 ^-5 , C = -9.55 × 10 ^-7 [Aspherical surface of seventh surface (r7)] Data] A = -4.32 × 10 ^-4 , B = 3.68 × 10 ^-5 , C = 1.77 × 10 ^-6 [Aspherical surface data of the 15th surface (r15)] A = 6.37 × 10 ^-4 , B = 2.58 × 10 ^-5 , C = -1.08 × 10 ^-5 , D = 9.99
× 10 ^-7 [Aspherical surface data of 17th surface (r17)] A = -3.92 × 10 ^-4 , B = 3.83 × 10 ^-5 , C = -1.29 × 10 ^-6 [Aspherical data of 20th surface (r20) Spherical data] A = 1.53 × 10 ^-3 , B = -1.49 × 10 ^-4 , C = 2.09 × 10 ^-6 [Aspherical data of the 21st surface (r21)] A = 4.22 × 10 ^-3 , B =- 4.32 × 10 ^-5 , C = 7.38 × 10 ^-6

[Diffraction Surface Data of Fourteenth Surface (r14)] C1 = -1.15 × 10 ^-3 , C2 = 4.13 × 10 ^-5

[Values for Conditional Expressions] Conditional expression (1): φDOE / φgr3 = 0.029 Conditional expression (2): tW / fW = 0.18 Conditional expression (3) (at wide-angle end [W]): | Y'max / PZ | = 0.17 Conditional expression (3) (at telephoto end [T]): | Y'max / PZ | = 0.19

[0061]

[Aspherical surface data of sixth surface (r6)] A = 7.67 × 10 ⁻⁴ , B = −1.15 × 10 ⁻⁵ , C = 8.18 × 10 ⁻⁸ [Aspherical surface data of seventh surface (r7)] ] A = 8.54 × 10 ^-4 , B = 1.62 × 10 ^-5 , C = 5.77 × 10 ^-7 [Aspheric data of the 16th surface (r16)] A = 9.53 × 10 ^-5 , B = 2.01 × 10 ^{− 5} , C = -4.61 × 10 ^-6 , D = 3.69
× 10 ^-7 [Aspherical surface data of the 19th surface (r19)] A = 1.66 × 10 ^-3 , B = -1.25 × 10 ^-4 , C = 1.37 × 10 ^-6 [Aspherical surface of the 20th surface (r20)] Data] A = 4.20 × 10 ^-3 , B = -2.46 × 10 ^-5 , C = 5.03 × 10 ^-6

[0063]

[Table 1]

[0064]

[Table 2]

The comparative example is a four-component zoom lens of positive / negative / positive / positive. The first lens unit (Gr1) has three lenses including a negative lens, a positive lens and a positive lens, and the second lens unit (Gr2) has a negative lens. The third lens unit (Gr3) has two lenses, a positive lens and a negative lens, and the fourth lens unit (Gr4) has two lenses, a positive lens and a negative lens.
It is composed of Table 3 shows the wide-angle end [W],
At the telephoto end [T], the chromatic aberration coefficient of the entire optical system and each group (G
r1 to Gr4) (here, LC: axial chromatic aberration coefficient, TC: chromatic aberration of magnification coefficient).

[0066]

[Table 3]

From the chromatic aberration coefficient values of the entire optical system of the comparative example, the axial chromatic aberration coefficient LC and the magnification chromatic aberration coefficient TC at the wide-angle end [W] are positively large, and the chromatic aberration coefficient TC at the telephoto end [T]. Is large negatively. Further, it is found that the degree of poor axial chromatic aberration at the wide angle end [W] with respect to the entire optical system is greater than the degree of poor lateral chromatic aberration at the wide angle end [W] and the telephoto end [T] with respect to the entire optical system. . Therefore, correcting axial chromatic aberration at the wide-angle end [W] is aberrationally effective.

On the other hand, the position where the axial chromatic aberration coefficient LC is large is near the stop (S), and the corresponding group position at the wide angle end [W] is the third group (Gr3). Therefore, the third group (Gr3)
It can be predicted that chromatic aberration correction can be effectively performed if the diffraction lens is disposed in the area. The third group (G
The lens configuration when a diffractive lens is used in r3) corresponds to the first embodiment. Table 4 shows the chromatic aberration coefficient of the entire optical system and each group (Gr1) at the wide-angle end [W] and the telephoto end [T] of the first embodiment.
To Gr4) are shown in the same manner as in Table 3. However, regarding the chromatic aberration coefficient generated in the third group (Gr3), the third group (Gr3)
3) The total chromatic aberration coefficient and the chromatic aberration coefficient generated by the diffractive lens are shown separately. From Table 4, it can be seen that the negative axial chromatic aberration coefficient LC generated by the diffraction lens of the third group (Gr3) improves the axial chromatic aberration coefficient LC of the entire optical system at the wide-angle end [W].

[0069]

[Table 4]

Next, the effects of astigmatism and Petzval when a diffractive lens is used will be discussed below. FIG.
Optical systems of three types of thin lenses shown in (c): (a) a positive / negative cemented lens, (b) a cemented surface is a diffractive lens surface
A positive / negative cemented lens composed of (broken line portion) and a positive single lens (c) having a diffractive lens surface (broken line portion) are considered as models. In the model (a), chromatic aberration correction is performed at the positive / negative junction, in the model (b), chromatic aberration correction is performed at the positive / negative junction and the diffraction lens surface, and in the model (c), chromatic aberration correction is performed only at the diffraction lens surface. Is performed. Since the degree of chromatic aberration correction by the diffractive lens has the relationship of (a) <(b) <(c), the lens power of the diffractive lens also has the relationship of (a) <(b) <(c).
Therefore, the lens power of the diffraction lens of the model (c) in which the degree of chromatic aberration correction by the diffraction lens is the largest is the largest.

The third group (Gr3) of the comparative example is composed of a positive lens and a negative lens. The glass type of the positive lens is relatively low in refractive index and low dispersion, and the glass type of the negative lens is relatively high in refractive index. rate·
High dispersion. Therefore, the cemented lenses of the models (a) and (b) also have a relatively low refractive index and low dispersion glass type of the positive lens.
The glass type of the negative lens has a relatively high refractive index and high dispersion. In the third lens unit (Gr3) of the first embodiment, the glass type of the positive lens has a relatively high refractive index and low dispersion, and the glass type of the negative lens has a relatively low refractive index and high dispersion. Therefore, as the cemented lens of the model (b), a positive lens made of a glass type having a relatively high refractive index and low dispersion and a negative lens made of a glass type having a relatively low refractive index and high dispersion are also examined. Table 5 shows the glass type data of each lens (however, nd: refractive index for d-line, νd:
Abbe number. ).

[0072]

[Table 5]

Table 6 shows the aberration coefficients of the entire optical system of each of the models (a) to (c) (provided that PT: Petzval coefficient,
AS: astigmatism coefficient). In the comparative example, the third group (Gr
3) is located behind the aperture (S), so each model (a) to
Similarly, assuming that (c) is located after the aperture (S),
Calculation of the aberration coefficient was performed. In calculating the aberration coefficient of each of the models (a) to (c), bending was given to minimize the spherical aberration coefficient of the entire optical system. From Table 6, it can be seen that the Petzval coefficient PT decreases as the lens power of the diffractive lens increases. Also, the astigmatism coefficient A
It can be seen that S increases as the lens power of the diffractive lens increases.

[0074]

[Table 6]

Table 7 shows the Petzval coefficient PT and the astigmatism coefficient AS of the comparative example and Example 1 {the optical system having a diffractive lens in the third group (Gr3)}. The two optical systems were designed to have the same lens performance. As can be seen from Table 7, the comparative example has a slightly positive astigmatism coefficient AS at the wide-angle end [W]. It is considered that the Petzval coefficient PT of the third lens unit (Gr3) is reduced due to the effect of the diffractive lens, so that there is a margin in aberration, and as a result, a zoom type having a small size is obtained.

[0076]

[Table 7]

From the above examination results, it can be seen that when a diffractive lens is used, the degree of compactness is determined by the balance between the chromatic aberration correction effect and the effects of Petzval and astigmatism. Then, as in the present embodiment, positive / negative / positive /
Third group (Gr.) Of zoom type with four components (positive or negative)
If a diffractive lens is used in 3), a compact optical system can be obtained due to the chromatic aberration correction effect.

FIG. 2, FIG. 4, FIG. 6, and FIG. 8 are aberration diagrams of Examples 1 to 4, and FIG. 10 is an aberration diagram of a comparative example. The wide-angle end [W], the middle [M], and the telephoto end [ T]. The aberration diagrams at each focal length state show [A] spherical aberration, [B] astigmatism, and [C] distortion in order from the left. In the spherical aberration diagram [A], the vertical axis is a value H / H0 in which the height of incidence H on the entrance pupil is normalized by its maximum height H0 (= 1) (that is, the relative height that cuts the entrance pupil plane). The horizontal axis represents the amount of displacement (mm) in the optical axis direction from the paraxial imaging position. Dashed line is C line
(Wavelength: λC = 656.3 nm), spherical aberration amount, solid line is d-line
(Wavelength: λd = 587.6 nm), the amount of spherical aberration, the dashed line is g
A spherical aberration amount with respect to a line (wavelength: λg = 435.8 nm) is shown. In the astigmatism diagram [B], the vertical axis represents the image height Y ′ (mm), and the horizontal axis represents the amount of displacement (mm) in the optical axis direction from the paraxial imaging position. The solid line X represents astigmatism on the sagittal surface, and the solid line Y represents astigmatism on the meridional surface. In the distortion diagram [C], the vertical axis is the image height Y ′ (mm), and the horizontal axis is the distortion amount (%).

[0079]

As described above, according to the first to fourth aspects of the present invention, since the diffraction grating is effectively used, the size of the lens optical system can be reduced in terms of aberration. According to the fifth to seventh aspects, a lens optical system using a diffraction grating can be realized so that the diffraction efficiency of obliquely incident light does not decrease.

[Brief description of the drawings]

FIG. 1 is a lens configuration diagram of a first embodiment (Example 1).

FIG. 2 is an aberration diagram of the first embodiment.

FIG. 3 is a lens configuration diagram of a second embodiment (Example 2).

FIG. 4 is an aberration diagram of the second embodiment.

FIG. 5 is a lens configuration diagram of a third embodiment (Example 3).

FIG. 6 is an aberration diagram of the third embodiment.

FIG. 7 is a lens configuration diagram of a fourth embodiment (Example 4).

FIG. 8 is an aberration diagram of the fourth embodiment.

FIG. 9 is a lens configuration diagram of a comparative example.

FIG. 10 is an aberration diagram of a comparative example.

FIG. 11 is a view for explaining the effects of astigmatism and Petzval when a diffractive lens is used.

FIG. 12 is a diagram for explaining the influence of the height of a diffraction grating when a light beam is obliquely incident on the blazed diffraction grating.

FIG. 13 is a graph showing a relationship between a diffraction grating interval and a diffraction efficiency at an incident angle of 10 °.

FIG. 14 is an optical path diagram for explaining an incident angle with respect to a lens optical system.

[Explanation of symbols]

 Gr1… First group Gr2… Second group Gr3… Third group Gr4… Fourth group Gr5… Fifth group S… Aperture LPF… Low pass filter

Continued on front page F-term (reference) 2H087 KA03 NA14 PA07 PA08 PA19 PA20 PB09 PB10 PB11 QA02 QA06 QA07 QA17 QA21 QA25 QA37 QA39 QA41 QA42 QA45 QA46 RA05 RA12 RA13 RA32 RA43 RA46 SA23 SA27 SA53 SA53 SA53 SA43 SA53 SA53 SA53 SA43 SA53 SA53 SA53 SA53 SA53 SA53 SA53 SA53 SA53 SA53 SA53 SA53 SA53 SA53 SA43 SA53 SA53 SA53 SA53 SA53 SA53 SA53 SA53 SA53 SA53 SA53 SA53 SA53 SA53 SA53 SA53 SA53 SA53 SA53 SA53 SA53 SA53 SA53 SA53 SA53 SA53 SA64 SA65 SA66 SA72 SA74 SA75 SA76 SB03 SB04 SB14 SB23 SB32 SB33 SB42 SB43

Claims (7)

[Claims] 1. A first group having a positive power, a second group having a negative power, a third group having a positive power, and a fourth group having a positive or negative power, in order from the object side. A lens optical system that performs zooming by changing an interval between the first group and the second group and an interval between the third group and the fourth group, A lens wherein the third group has a cemented lens, the cemented lens having a diffraction grating at a boundary surface, and a curvature of the boundary surface is different from a curvature of an entrance surface and an exit surface of the cemented lens. Optical system. 2. The lens optical system according to claim 1, wherein the diffraction grating satisfies the following conditional expression: 0.02 <φDOE / φgr3 <0.1, where φDOE: lens power by the diffraction grating, φgr3: third The power of the group. 3. The lens optical system according to claim 1, wherein said diffraction grating satisfies the following conditional expression: 0.05 <tW / fW <0.4, where tW: diffraction grating at a wide-angle end. FW: focal length of the entire zoom system at the wide-angle end. 4. The lens optical system according to claim 1, wherein the following conditional expression is satisfied: | Y′max / PZ | <0.4, where Y′max: maximum image height, PZ: The distance from the image plane to the exit pupil position. 5. A lens optical system having a diffraction grating lens on a boundary surface where two different optical materials are in close contact with each other, wherein the diffraction grating has a blaze shape at an arbitrary height H in a direction perpendicular to the optical axis. | (H / d) tan θ | ≦ 0.045, where h is the height of the diffraction grating, d is the interval between the diffraction gratings, θ is the incident angle, and Ci : Phase coefficient, λ0: design wavelength, where: diffraction grating interval d is the equation of phase function Φ (H): The equation for the height H in the direction perpendicular to the optical axis is represented by: d (H) = − 2π / (dΦ / dH). 6. A lens optical system having a diffraction grating lens on a boundary surface where two different optical materials are in close contact with each other, wherein the diffraction grating satisfies the following conditional expression. 0.01 ≦ | {(h · φDOE · DDOE) / (2 · λ0)} · tan (ωmax) | ≦
0.06 where h: height of the diffraction grating, λ0: design wavelength, φDOE: lens power by the diffraction grating, DDOE: effective diameter of the lens by the diffraction grating, ωmax: maximum value of the half angle of view of the lens optical system. 7. A lens optical system having a diffraction grating lens at a boundary surface where two different optical materials are in close contact with each other, wherein the diffraction grating satisfies the following conditional expression. 0.005 ≦ | (h / dmin) · tan (ωmax) | ≦ 0.07, where h: height of the diffraction grating, dmin: minimum diffraction grating interval within the effective diameter range of the lens by the diffraction grating, ωmax: half of the lens optical system The maximum value of the angle of view.