JP2000221402A - Lens optical system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain 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 negative 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. Then, the 1st group Gr1 is provided with a diffraction grating r3#.

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.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a lens optical system which is compact in terms of aberrations by effectively using a diffraction grating for a zoom type different from the above-mentioned conventional example. With the goal.

[0004]

In order to achieve the above object, a lens optical system according to a first aspect of the present invention comprises, in order from the object side, a first unit having a positive power and a second unit having a negative power. And a third group having a negative power and a fourth group having a positive power. The distance between the first group and the second group, and the distance between the third group and the fourth group A lens optical system that performs zooming by changing an interval, wherein the first group has a diffraction grating.

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. 0.004 <φDOE / φgr1 <0.02 where φDOE: lens power by the diffraction grating, φgr1: power of the first group.

According to a third aspect of the present invention, in the lens optical system according to the first or second aspect, the diffraction grating satisfies the following conditional expression. 0.5 <tT / fT <2.0 where tT is the distance between the top surface of the diffraction grating and the aperture at the telephoto end on the air-equivalent axis, and fT is the focal length of the entire zoom system at the telephoto end.

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.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a lens optical system embodying the present invention will be described with reference to the drawings. FIG. 1 is a lens configuration diagram showing a zoom lens according to the present embodiment, which has a wide-angle end [W], a middle (intermediate focal length state) [M], and a telephoto end [T].
2 shows the lens arrangement. In the lens configuration diagram, 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 this embodiment, a first lens unit (Gr1) having a positive power and a second lens unit (Gr1) having a negative power are arranged in order from the object side.
A four-component type zoom lens including a group (Gr2), a third group (Gr3) having negative power, and a fourth group (Gr4) having positive power, and a first group (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. Third group
Between the (Gr3) and the fourth lens unit (Gr4), an aperture (S) fixed at the zooming position is arranged together with the fourth lens unit (Gr4), and a low-pass filter (LPF) is located closest to the image plane (I). ) Is arranged.

In the embodiment (FIG. 1), each group is configured as follows in order from the object side. First group (Gr1)
Is composed of a negative meniscus lens convex on the object side and two positive meniscus lenses convex on the object side.
The plane (r3) has a diffraction grating. To make this zoom type lens optical system more compact, the first group (Gr1)
It is effective to use a diffraction grating for aberration correction, which will be described later in detail. 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 unit (Gr3) includes a negative meniscus lens concave on the object side. The fourth unit (Gr4) includes a biconvex positive lens, a cemented lens including a concave negative meniscus lens on the image side and a biconvex positive lens, and a negative meniscus lens concave on the image side. I have.

Next, as in this embodiment, the first lens unit (Gr1)
Next, a description will be given of a conditional expression desired to be satisfied by a zoom-type lens optical system having a positive, negative, negative, and positive component having a diffraction grating. 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). 0.004 <φDOE / φgr1 <0.02 (1) where φDOE: lens power by the diffraction grating, φgr1: power of the first lens unit (Gr1).

Conditional expression (1) indicates that the power φgr1 of the first lens unit (Gr1)
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, lateral chromatic aberration correction at the telephoto end [T] will be insufficient. If the upper limit of conditional expression (2) is exceeded, the size of the lens optical system will increase. 0.5 <tT / fT <2.0 (2) where tT is the distance between the diffraction grating and the diaphragm (S) at the telephoto end [T] on the upper surface of the air-equivalent axis, and fT is the entire zoom system at the telephoto end [T]. 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.

[0016]

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 example given below is
A lens configuration diagram (FIG. 1) corresponding to the above-described embodiment and showing the embodiment shows the lens configuration of the corresponding example. Further, a comparative example (having no diffraction grating) with respect to the example is also shown, and the lens configuration is shown in FIG.

In the construction data of the embodiment and the 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, 3, 3). , ...) indicates the i-th axial top surface distance counted from the object side, and Ni (i = 1,2,3, ...),
.nu.i (i = 1, 2, 3,...) indicate the refractive index (nd) and Abbe number (νd) of the i-th optical element counted from the object side with respect to the d-line. In the construction data, the axial top surface interval (variable interval) that changes during zooming is from the wide-angle end (short focal length end) [W] to the middle (intermediate focal length state) [M] to the telephoto end (long focal length end). It is the axial air gap between each group in [T]. The focal length f, the half angle of view ω (°) and the F-number FNO of the entire system corresponding to each focal length state [W], [M], [T], and the values corresponding to the conditional expressions are also shown.

A surface marked with an asterisk (*) in 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.

<< Example >> f = 5.1 to 16.0 to 29.4 ω = 31.2 to 11.0 to 6.0 (°) FNO = 4.1 to 4.1 to 4.1 [radius of curvature] [axis interval] [refractive index] [Abbe number] r1 = 65.90 d1 = 0.19 N1 = 1.805 ν1 = 25.5 r2 = 30.99 d2 = 0.08 r3 # = 31.42 d3 = 4.61 N2 = 1.603 ν2 = 60.7 r4 = 2132.74 d4 = 0.10 r5 = 29.89 d5 = 2.81 N3 = 1.713 ν3 = 53.9 r6 = 138.01 d6 = 0.2-16.7-22.3 r7 = 79.35 d7 = 0.19 N4 = 1.772 ν4 = 49.6 r8 = 10.37 d8 = 3.49 r9 = -61.35 d9 = 0.19 N5 = 1.772 ν5 = 49.6 r10 = 12.36 d10 = 2.20 N6 = 1.847 ν6 = 23.9 r11 = 159.73 d11 = 20.5 ~ 3.2 ~ 0.2 r12 = -7.99 d12 = 2.42 N7 = 1.546 ν7 = 64.9 r13 = -25.35 d13 = 1.9 ~ 2.7 ~ 0.1 r14 = ∞ (S) d14 = 2.00 r15 * = 10.05 d15 = 3.92 N8 = 1.603 ν8 = 60.7 r16 * =-17.18 d16 = 2.12 r17 = 49.13 d17 = 0.19 N9 = 1.847 ν9 = 23.9 r18 = 10.41 d18 = 1.07 N10 = 1.516 ν10 = 64.1 r19 = -10.43 d19 = 0.20 r20 = 15.77 d20 = 4.63 N11 = 1.541 ν11 = 47.2 r21 = 7.28 d21 = 1.40 r22 = ∞ d22 = 3.40 N12 = 1.517 ν12 = 64.1 r23 = ∞ d23 = 4.15 r24 = ∞ (I)

[Aspherical surface data of fifteenth surface (r15)] A = 3.69 × 10 ⁻⁵ , B = −8.06 × 10 ⁻⁶ , C = 3.73 × 10 ⁻⁶ , D = −3.23 × 10 ⁻⁷ Aspherical data of 16 surfaces (r16)] A = 5.22 × 10 ^-4 , B = 8.89 × 10 ^-6 , C = -1.80 × 10 ^-7 , D = -2.21 × 10 ^-9

[Diffraction Surface Data of Third Surface (r3)] C1 = −1.04 × 10 ⁻⁴ , C2 = 7.13 × 10 ⁻⁸

[Values Corresponding to Conditional Expressions] Conditional expression (1): φDOE / φgr3 = 0.0087 Conditional expression (2): tT / fT = 1.15 Conditional expression (3) (at wide-angle end [W], at telephoto end [T]) Both): | Y'max / PZ | = 0.17

<< Comparative Example >> f = 5.1 to 16.0 to 29.4 ω = 31.2 to 11.0 to 6.0 (°) FNO = 4.1 to 4.1 to 4.1 [radius of curvature] [axis interval] [refractive index] [Abbe number] r1 = 67.09 d1 = 0.18 N1 = 1.805 ν1 = 25.5 r2 = 31.58 d2 = 0.10 r3 = 31.82 d3 = 5.13 N2 = 1.603 ν2 = 60.7 r4 = 641.33 d4 = 0.10 r5 = 33.34 d5 = 2.83 N3 = 1.713 ν3 = 53.9 r6 = 141.04 d6 = 0.2-19.3-25.8 r7 = 70.86 d7 = 0.18 N4 = 1.772 ν4 = 49.6 r8 = 11.43 d8 = 3.83 r9 = -172.01 d9 = 0.18 N5 = 1.772 ν5 = 49.6 r10 = 13.13 d10 = 2.42 N6 = 1.847 ν6 = 23.9 r11 = 80.41 d11 = 23.3 ~ 3.1 ~ 0.2 r12 = -8.74 d12 = 1.53 N7 = 1.487 ν7 = 70.4 r13 = -23.90 d13 = 2.6 ~ 3.7 ~ 0.1 r14 = ∞ (S) d14 = 3.60 r15 * = 10.18 d15 = 5.95 N8 = 1.603 ν8 = 60.7 r16 * =-22.87 d16 = 2.20 r17 = 34.91 d17 = 0.26 N9 = 1.847 ν9 = 23.9 r18 = 9.07 d18 = 1.16 N10 = 1.516 ν10 = 64.1 r19 = -19.23 d19 = 1.05 r20 = 10.65 d20 = 6.28 N11 = 1.541 ν11 = 47.2 r21 = 6.81 d21 = 1.57 r22 = ∞ d22 = 3.40 N12 = 1.517 ν12 = 64.1 r23 = ∞ d23 = 1.39 r24 = ∞ (I)

[Aspherical surface data of fifteenth surface (r15)] A = 7.51 × 10 ⁻⁵ , B = −1.09 × 10 ⁻⁶ , C = 1.05 × 10 ⁻⁶ , D = -7.38 × 10 ⁻⁸ Aspherical surface data of 16 planes (r16)] A = 2.72 × 10 ^-4 , B = 4.78 × 10 ^-6 , C = 3.08 × 10 ^-8 , D = -5.70 × 10 ^-9

The above comparative example is a positive, negative, negative and positive four-component zoom lens. The first unit (Gr1) has three negative lenses, a positive lens and a positive lens, and the second unit (Gr2) has a negative lens. The third group (Gr3) is composed of one negative lens, and the fourth group (Gr4) is composed of four lenses of a positive lens, a negative lens, a positive lens and a negative lens. ing. Table 1 shows the wide-angle end of the comparative example.
[W] and the chromatic aberration coefficient of the entire optical system and the chromatic aberration coefficient of each group (Gr1 to Gr4) at the telephoto end [T] (here, LC: axial chromatic aberration coefficient, TC: magnification chromatic aberration coefficient). From the chromatic aberration coefficient values of the entire optical system of the comparative example, the axial chromatic aberration coefficient LC and the lateral chromatic aberration coefficient TC at the wide-angle end [W] are slightly larger, and the lateral chromatic aberration coefficient TC at the telephoto end [T] is negative. You can see that it is big. First group (Gr1), second group of this comparative example
The chromatic aberration correction effect when a diffractive lens is used for (Gr2), the third unit (Gr3) or the fourth unit (Gr4) will be discussed below.

[0028]

[Table 1]

It is assumed that a diffractive lens is arranged in the first group (Gr1) of the comparative example. The lens configuration in this case corresponds to the above embodiment. Table 2 shows the wide-angle end [W] and the telephoto end of the embodiment.
In [T], the chromatic aberration coefficient of the entire optical system and each group (Gr1 to Gr)
The chromatic aberration coefficient of 4) is shown in the same manner as in Table 1. However, the first group
The chromatic aberration coefficient generated in (Gr1) is shown separately for the chromatic aberration coefficient of the entire first group (Gr1) and the chromatic aberration coefficient generated by the diffractive lens.

[0030]

[Table 2]

Since the first lens unit (Gr1) is located away from the stop (S) and forward, the chromatic aberration of magnification coefficient TC increases. Since the magnification chromatic aberration coefficient TC of the comparative example changes from positive to negative from the wide-angle end [W] to the telephoto end [T], the overall chromatic aberration coefficient TC generated by the diffraction lens of the first group (Gr1) gives The chromatic aberration of magnification coefficient TC cannot be reduced from the wide-angle end [W] to the telephoto end [T]. However, in the comparative example, the telephoto end
Since the degree of deterioration of the lateral chromatic aberration coefficient TC at [T] is larger, in the embodiment, the first group (Gr1) diffractive lens generates a positive lateral chromatic aberration coefficient TC, and the magnification at the telephoto end [T]. The chromatic aberration coefficient TC is improved. Therefore, the first group (Gr
By having a diffractive lens in 1), it is possible to perform a somewhat effective correction.

It is assumed that a diffractive lens is disposed in the second group (Gr2) of the comparative example. The second lens unit (Gr2) is located away from the stop (S) at the wide-angle end [W] and is located immediately before the stop (S) at the telephoto end [T]. TC
At the telephoto end [T], and the axial chromatic aberration coefficient LC increases. Therefore, having the diffractive lens in the second group (Gr2) is equivalent to the chromatic aberration of magnification T at the wide-angle end [W] of the comparative example.
It is expected to be effective in correcting C. However, in the comparative example, since the chromatic aberration of magnification at the wide-angle end [W] is not as bad as the chromatic aberration of magnification at the telephoto end [T], the influence of the improvement of the chromatic aberration of magnification at the wide-angle end [W] on the entire optical system is telephoto. It is not as large as when improving the lateral chromatic aberration at the end [T].

It is assumed that a diffractive lens is arranged in the third group (Gr3) of the comparative example. The third lens unit (Gr3) is located slightly away from the stop (S) at the wide-angle end [W], and is stopped at the telephoto end [T].
(S), the chromatic aberration coefficient TC at the wide-angle end [W] is large at the wide-angle end [W], and the axial chromatic aberration coefficient L at the telephoto end [T].
C increases. However, the degree of separation from the stop at the wide-angle end [W] is inferior to that of the second lens unit (Gr2), so that the correction of the chromatic aberration of magnification TC at the wide-angle end [W] is slightly inferior to that of the second lens unit (Gr2). Will be. Therefore, the degree of effect when the third lens unit (Gr3) has a diffractive lens is slightly inferior to that of the second lens unit (Gr2).

It is assumed that a diffractive lens is arranged in the fourth group (Gr4) of the comparative example. Since the fourth lens unit (Gr4) is located slightly away from the stop (S) and behind, the axial chromatic aberration coefficient LC and the lateral chromatic aberration coefficient TC are large. When a fourth lens unit (Gr4) is provided with a diffractive lens that generates a negative axial chromatic aberration coefficient LC in order to correct axial chromatic aberration at the wide-angle end [W], the diffractive lens simultaneously causes a negative chromatic aberration coefficient TC. Also occurs. Therefore, the magnification chromatic aberration coefficient T of the entire optical system at the telephoto end [T] is obtained.
C becomes negatively large. Therefore, it is not appropriate to have a diffractive lens in the fourth group (Gr4). From the above examination results, it is appropriate that the diffractive lens is disposed in the first group (Gr1), and the chromatic aberration correction effect by the diffractive lens is in the first group (Gr1).
It turns out that it becomes the largest.

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 first group (Gr1) of the comparative example is composed of a positive lens and a negative lens, and the glass type of the positive lens is relatively low refractive index and low dispersion, and the glass type of the negative lens is relatively high 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. Table 3 shows each glass type data (however, nd: refractive index for d-line, νd: Abbe number).

[0037]

[Table 3]

Table 4 shows aberration coefficients of the entire optical system of each of the models (a) to (c) (where PT: Petzval coefficient,
AS: astigmatism coefficient). In the comparative example, the first group (Gr
1) is located before the aperture (S), so each model (a) to
Similarly, the aberration coefficient was calculated assuming that (c) was located before the stop (S). 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. Table 4 shows that the Petzval coefficient PT decreases as the lens power of the diffraction lens increases. Also, the astigmatism coefficient AS
It can be seen that becomes larger as the lens power of the diffractive lens becomes smaller or larger, and becomes minimum at a predetermined lens power.

[0039]

[Table 4]

Table 5 shows the Petzval coefficient PT and the astigmatism coefficient AS of the comparative example and the example {the optical system having the diffractive lens in the first group (Gr1)}. The two optical systems were designed to have the same lens performance. As can be seen from Table 5, the comparative example had a slightly larger Petzval coefficient PT,
The astigmatism coefficient AS is slightly positive at the telephoto end [T]. Petzval coefficient P of the first group (Gr1) due to the effect of the diffractive lens
It is conceivable that a margin arises in aberrations due to a decrease in T and the astigmatism coefficient AS, and as a result, a zoom type having a small size is obtained.

[0041]

[Table 5]

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. If a diffractive lens is used in the first group (Gr1) of the zoom type having four components of positive, negative, negative, and positive as in this embodiment, a compact optical system can be obtained by the chromatic aberration correction effect. .

FIG. 2 is an aberration diagram of the embodiment, and FIG. 4 is an aberration diagram of the comparative example. The wide-angle end [W], the middle [M], and the telephoto end are respectively shown.
Various aberrations at [T] are shown. The aberration diagrams at each focal length state are [A] spherical aberration, [B] astigmatism, [C]
This represents distortion. 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. The broken line indicates the spherical aberration for the C line (wavelength: λC = 656.3 nm), the solid line indicates the spherical aberration for the d line (wavelength: λd = 587.6 nm), and the dashed line indicates the spherical aberration for the g line (wavelength: λg = 435.8 nm). It represents the quantity. 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 (%).

[0044]

As described above, according to the present invention, since the diffraction grating is used effectively, the lens optical system can be made compact in terms of aberration.

[Brief description of the drawings]

FIG. 1 is a lens configuration diagram of an embodiment (example).

FIG. 2 is an aberration diagram of an example.

FIG. 3 is a lens configuration diagram of a comparative example.

FIG. 4 is an aberration diagram of a comparative example.

FIG. 5 is a diagram for explaining the effects of astigmatism and Petzval when a diffractive lens is used.

[Explanation of symbols]

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

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H087 KA02 KA03 NA14 PA09 PA19 PB11 QA02 QA06 QA17 QA21 QA25 QA37 QA41 QA46 RA12 RA13 RA32 RA43 RA46 SA23 SA27 SA30 SA32 SA63 SA64 SA72 SA75 SB04 SB14 SB22 SB35

Claims (4)

[Claims] 1. a first group having a positive power, a second group having a negative power, a third group having a negative power, a fourth group having a positive power, and With
A lens optical system that performs zooming by changing a distance between the first group and the second group and a distance between the third group and the fourth group, wherein the first group is a diffraction grating. A lens optical system comprising: 2. The lens optical system according to claim 1, wherein the diffraction grating satisfies the following conditional expression: 0.004 <φDOE / φgr1 <0.02, where φDOE: lens power by the diffraction grating, φgr1: first The power of the group. 3. The lens optical system according to claim 1, wherein said diffraction grating satisfies the following conditional expression: 0.5 <tT / fT <2.0, where tT: a diffraction grating at a telephoto end. FT is the focal length of the entire zoom system at the telephoto 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.