JPH1152238A - Zoom lens - Google Patents

Abstract

(57) [Problem] To provide a zoom lens in which the number of lenses is reduced, chromatic aberration that cannot be obtained with an aspherical surface is corrected in a zooming unit, and miniaturization is achieved while maintaining good performance. SOLUTION: In order from the object side, a zooming group consisting of a first lens unit L1 having a fixed positive refractive power fixed during zooming and a second lens unit L2 having a negative refractive power movable during zooming, a stop S,
It has an image forming group consisting of a third lens unit L3 having a positive refractive power and a lens unit after the fourth lens unit L4, and when zooming from the wide-angle end to the telephoto end, the second lens unit L2 is positioned on the image plane side. At the same time, the fourth lens unit L4 and the subsequent lens units correct the image plane fluctuation accompanying zooming. The first lens unit L1 includes two positive lenses, and has at least one diffractive optical surface on the surface of the image-side lens of the object-side lens. The second lens unit L2 is composed of two negative lenses, and has a diffractive optical surface on the object-side lens surface of the image-side lens. Further, the lens surfaces closest to the object in the third lens unit L3 and the fourth lens unit L4 are each aspherical.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is particularly used for a photograph or a video camera, and has a wide field angle and a high zoom ratio, while having a small front lens diameter and a compact rear focus zoom system as a whole. It is about a lens.

[0002]

2. Description of the Related Art Recently, as home video cameras and the like have become smaller and lighter, remarkable progress has been made in miniaturization of imaging zoom lenses. Emphasis is placed on simplification.

As one means for achieving these objects, a so-called rear focus type zoom lens is known as an optical system in which a lens group other than the first lens group on the object side is moved to perform focusing.

In general, a rear focus type zoom lens has a smaller effective diameter of the first lens group than a zoom lens which performs focusing by moving the first lens group.
The size of the entire lens system can be easily reduced. Also, close-up photography,
In particular, extremely close-up photography can be performed, and the relatively small and lightweight lens group is moved, so that the driving force of the lens group is small and quick focusing can be performed.

[0005] As such a rear focus type zoom lens, for example, Japanese Patent Application Laid-Open Nos. 62-24213 and 62-247316 disclose a positive first lens unit and a negative second lens unit in order from the object side. The zoom lens has a lens group, a positive third lens group, and a positive fourth lens group. The second lens group is moved to perform zooming, and the fourth lens group corrects an image plane variation caused by zooming. A zoom lens that performs focusing is disclosed. According to such a configuration, the diameter of the front lens can be relatively reduced, and a compact zoom lens can be achieved.

However, in recent years, there has been a great demand for a zoom lens capable of achieving a high zoom ratio of 10 times or more, and it has become difficult to achieve further miniaturization while maintaining good performance.

In other words, in order to reduce the occurrence of aberration of each lens group to increase the magnification, there is a tendency that the number of lenses constituting each lens group is increased to reduce the share of aberration of each lens. Going backwards.

In order to correct various aberrations and reduce the number of lenses, it is conventionally known to use an aspherical surface. When this aspherical surface is used, the number of lenses can be reduced and an aberration correction effect that cannot be obtained with a spherical surface can be expected and is effective.

[0009]

However, at a high zoom ratio exceeding 10 times, it is important to remove various aberrations, but it is important to correct chromatic aberration, and it is difficult to correct chromatic aberration with an aspherical surface.

In particular, in the first lens group on the object side of the movable group, unless the generation of chromatic aberration is suppressed to a small extent, the movement of the second lens group or the like, which is the main zooming group, causes a large variation in chromatic aberration accompanying zooming. Tend. Therefore, conventionally, the first lens group includes one or two high-dispersion negative lenses and one low-dispersion positive lens to perform achromatization. Further, the negative lens and the positive lens may be bonded together, and therefore the number of lenses constituting the first lens group is increased, which is not appropriate.

On the other hand, as a method of minimizing the occurrence and inflection of chromatic aberration, proposals for applying a diffractive optical surface to an image pickup optical system have recently been made, for example, in JP-A-4-213421 and JP-A-6-324262. It has been done. In these conventional examples, a diffractive optical element is applied to a single lens, and although there is a reference to chromatic aberration, there is no consideration or description of removal of fluctuation due to zooming of chromatic aberration peculiar to a zoom lens, and there is no application to a zoom lens. Has not been done.

An application to a zoom lens is described in US Pat. No. 5,268,790. In this conventional example, a diffractive optical element is used for a second lens group as a main variable power unit or a third lens group as a correction unit. It is disclosed that the first
The lens group has a conventional configuration. In this configuration, the chromatic aberration generated in the first lens group remains unchanged,
The chromatic aberration is not effective because the chromatic aberration is increased or fluctuated by the movement of the second lens unit and the zooming unit during zooming. In addition, a zoom lens of about 10 times is described as an example, but there is a description that higher magnification is achieved with the same size than that known in this publication. However, there are still many lenses and there is room for miniaturization.

An object of the present invention is to improve the above-mentioned drawbacks of the conventional example, achieve a high zoom ratio of 10 times or more, and reduce the number of lenses to be constituted even at a high zoom ratio. It is an object of the present invention to provide a zoom lens that achieves further miniaturization while maintaining good performance by correcting chromatic aberration that cannot be obtained with a spherical surface.

[0014]

A zoom lens according to the present invention for achieving the above object comprises, in order from the object side, a first lens unit having a fixed positive refractive power during zooming and a negative lens group movable during zooming. The zoom lens includes a variable power unit including a second lens unit having a refractive power, and an image forming unit including a third lens unit having a positive refractive power and lens units subsequent to a fourth lens unit. A zoom lens that moves the second lens group to the image plane side during magnification, and corrects an image plane variation caused by zooming by the fourth and subsequent lens groups;
The lens group and the second lens group each have at least one diffractive optical surface rotationally symmetric with respect to the optical axis.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail with reference to the illustrated embodiments. FIGS. 1 and 2 show lens sectional views of Examples 1 and 2, respectively. The first lens unit L1 has a fixed positive refractive power during zooming and the negative lens has a movable negative refractive power during zooming. A variable power unit composed of two lens units L2, a stop S, a third lens unit L3 having a positive refractive power, and a fourth lens unit L4
The zoom lens has an image forming group composed of the following lens units, and when zooming from the wide-angle end to the telephoto end, moves the second lens unit L2 to the image plane side and zooms with the lens unit after the fourth lens unit L4. In a zoom lens that corrects the image plane fluctuation due to
Each of the first lens unit L1 and the second lens unit L2 has a diffraction optical surface that is rotationally symmetric with respect to the optical axis.

In the first embodiment, the first lens unit L1 is composed of two positive lenses, and has a diffractive optical surface on the image side lens surface of the object side lens. The second lens unit L2 is composed of two negative lenses, and has a diffractive optical surface on the object-side lens surface of the image-side lens. Furthermore,
The lens surfaces closest to the object in the third lens unit L3 and the fourth lens unit L4 are each aspherical.

In the second embodiment, the first lens unit L1 includes a negative lens and a positive lens, and has a diffractive optical surface on the image-side lens surface of the image-side lens. The second lens unit L2 is composed of two positive lenses, and has a diffractive optical surface on the object-side lens surface of the image-side lens. Further, the most object-side lens surface of the third lens unit L3 is aspheric.

In these embodiments, the third lens unit L3 is a positive lens unit which has a stop and is fixed during zooming, and the fourth lens unit L4 corrects image plane fluctuation due to zooming and adjusts the distance. It is preferable that the processing be performed by the fourth lens unit L4.

As another configuration of the first lens unit L1, the first lens unit L1 is composed of two positive lenses as in the first embodiment, and at least one diffractive optical surface is provided before, after, or between them. May be provided.

Further, another configuration of the first lens unit L1 is that it comprises a positive lens, a negative lens or a negative lens, and a positive lens, and has a diffractive optical element on either surface. At this time, the positive lens and the negative lens may be bonded. At that time, the chromatic aberration is corrected in cooperation with this bonding surface,
The diffractive optical element needs to increase the positive refractive power.

Further, as another configuration of the second lens unit L2, as in Embodiments 1 and 2, a plate composed of two negative lenses and having at least one diffractive optical surface before, behind, or in the middle thereof is used. You may have it.

Further, another second lens unit L2 is constituted by a positive lens, a negative lens or two negative lenses and a positive lens, and has a diffractive optical element on any surface. You may.

In each case, the lens surface closest to the object side has
It is better not to dispose a diffractive optical surface except in special cases such as unavoidable aberration correction. The diffractive optical element is formed of a groove having a considerably narrow width, for example, on the order of several μm or sub-μm. In order to protect the lens surface from dust and the like, it is preferable that the diffraction optical element is not disposed closest to the object.

When the diffractive optical element is arranged in the first lens unit L1, the chromatic aberration generated in the first lens unit L1, for example, two wavelengths such as d-line and g-line can be obtained by appropriately selecting the phase of the diffractive optical element. Chromatic aberration can be suppressed to a small extent, and fluctuations of the chromatic aberration as a whole due to zooming can be suppressed to a small extent. In particular, chromatic aberration remaining at the telephoto end (secondary spectrum)
The width itself becomes large.

Even if a diffractive optical element is arranged in the second lens unit L2, the chromatic aberration generated in the second lens unit L2, for example, d-line and g-line can be obtained by appropriately selecting the phase of the diffractive optical element. Chromatic aberration of two wavelengths such as
Variations due to zooming of the chromatic aberration as a whole can be suppressed to a small value. In particular, the width of the chromatic aberration (secondary spectrum) remaining at the telephoto end becomes large in the direction opposite to the first lens unit L1.

As described above, one of the lens units in the zooming unit on the object side of the stop S, that is, the first lens unit L1 and the second lens unit
When a diffractive optical element is used for the lens unit L2, 2
The width of the next spectrum becomes large, and there is a problem in practical use.

Under such circumstances, at least one diffractive optical surface rotationally symmetric with respect to the optical axis is disposed in each of the first lens unit L1 and the second lens unit L2, which are the variable power units as described above. As a result, the chromatic aberration of the reference wavelength (d-line and g-line) is suppressed to be small in the first and second lens units L1 and L2, and the secondary spectra respectively generated in the variable power unit are generated in the opposite directions. The lens unit L1 and the second lens unit L2 cooperate to achieve good chromatic aberration as a whole.

With such a configuration, the lens constituting the first lens unit L1 has one or two high-dispersion negative lenses and one low-dispersion positive lens, respectively, and further has a negative lens and a positive lens. Are achromatic or achromatic by sharing a plurality of lenses. However, the number of lenses used for correcting chromatic aberration is reduced by the diffractive optical element, the number of constituent lenses can be reduced, and the second lens unit L2 is formed. The lens also has two or one low dispersion negative lens and one high dispersion positive lens, respectively.
Although achromatism is shared by a plurality of lenses, the number of lenses used for correcting chromatic aberration is reduced by the diffractive optical element, and the number of constituent lenses can be reduced.

As a result, even in a zoom lens which achieves a high zoom ratio of 10 times or more, further miniaturization can be achieved while maintaining good performance.

The diffraction optical surface has a phase φ (h), a wavelength λ,
Coefficient representing the phase of the C _i, when the height from the optical axis h, the following expression.

Φ (h) = (2π / λ) (C ₁ · h ² + C ₂ · h ⁴ + C ₃ · h ⁶ +... + C _i · h ^{2 · i} ) (1)

As a specific method for reducing the chromatic aberration of the zoom lens, when the refractive power of the i-th lens unit having the diffractive optical element is Fi, it is preferable to have at least one surface satisfying the following expression.

Fi · C _i <0 (i = 1, 2) (2)

[0034] Here, C _i represents the paraxial refractive power by the diffractive optical surface in the first lens unit L1, the paraxial refractive power
Power when C _i has a positive value negative, when a negative value has a positive refractive power. In both the positive lens unit and the negative lens unit, the curvature of the lens unit can be reduced, which is effective for aberration correction.

It can be seen from equation (1) that the phase can be adjusted by the distance h from the optical axis. The greater the lens diameter, the greater the effect of higher order coefficients. The miniaturization of the consumer zoom lens described in the present embodiment, particularly the video zoom lens, is being promoted, and there are few lenses that are too large, that is, lenses with large h. In addition, it is preferable that the following conditional expression is satisfied in order to achieve effective aberration correction by efficiently using the coefficient even with a small lens. Here, C _2i and C _3i are 4 in Expression (1) of the diffractive optical surface in the i-th lens group, respectively.
These are the coefficients of the next and sixth order terms.

1 · 10 ⁻⁴ <| C _2i / C _i | <1 · 10 ⁻¹ (3) 1 · 10 ⁻⁷ <| C _3i / C _i | <1 · 10 ⁻² (4)

As described above, these equations are for effectively correcting aberrations at a small diameter. If these conditional expressions are not satisfied, not only is it difficult to correct aberrations, but also it becomes difficult to manufacture a diffractive optical surface, which is not appropriate.

As described above, the diffractive optical surfaces arranged in the first lens unit L1 and the second lens unit L2 suppress chromatic aberration (secondary spectrum) generated in each lens unit to a small value. In addition, the fluctuation due to zooming of the chromatic aberration due to the movement of the second lens unit L2 can be suppressed to be small. At this time, a fixed fifth negative lens unit may be further disposed on the image plane side of the fourth lens unit L4. At this time, the fifth lens group may be configured to be a telephoto type as a whole to further reduce the size.

As in the embodiment, when the chromatic aberration is corrected on the diffractive optical surface instead of the achromatism such as the bonding of the first lens unit L1 and the second lens unit L2, the refractive power is not so necessary.

Here, a refractive power may be provided for correcting some off-axis aberrations, particularly curvature of field and distortion.
In that case, the focal lengths of the diffractive optical surfaces of the first and second lens units L1 and L2 are Fbo1, Fbo2, and the first and second lens units L1, L
Assuming that the following conditions are satisfied when the focal length of the lens 2 is F1 and F2, fabrication is not difficult and aberration correction including chromatic aberration is excellent.

0.05 <F1 / Fbo1 <0.7 (5) 0.05 <F2 / Fbo2 <0.7 (6)

In particular, a lens group having a diffractive optical element includes:
It is preferably within the following numerical range.

1.0 <F1 / (Fw · Ft) ^1/2 <2.5 (7)

Here, Fw and Ft are the focal lengths of the entire system at the wide-angle end and the telephoto end, respectively. Within this range, the function of the diffractive optical element can be effectively brought out. this
If the lower limit of the expression (7) is not satisfied, the refractive power of the first lens unit L1 is too strong, so that chromatic aberration cannot be corrected by the diffractive optical system, and manufacturing becomes difficult. If the value exceeds the upper limit, chromatic aberration can be easily removed without using a diffractive optical element. In addition, in order to obtain a lens having a desired focal length, the refractive power of the second lens unit L2 becomes particularly strong, and the amount of aberration generated in the second lens unit L2 increases, which is not appropriate. That is,
The Petzval sum becomes negatively large, and the field curvature becomes overcorrected.

When there is only one diffractive optical surface, it is preferable that the following expression is satisfied.

| Fi / Rboi | <1.8 (8)

Here, Rboi is the radius of curvature of the surface in group i forming the diffractive optical element. When Rboi = ∞, the base surface is flat. If the value deviates from the expression (8), the aberration generated on the curved surface of the base cannot be corrected by the diffractive optical system, and the effect of the diffractive optical system cannot be sufficiently brought out.

In general, chromatic aberration opposite to chromatic aberration caused by ordinary refraction occurs on a diffractive optical surface. For example, when removing a lens that has been achromatized by a conventional bonding surface or the like and reducing the number of lenses, diffracting a surface having chromatic aberration sharing opposite to the chromatic aberration sharing that occurred on the bonding surface It may be an optical surface. In that case, chromatic aberration opposite to chromatic aberration caused by ordinary refraction occurs on the diffractive optical surface, and the direction becomes the same as the direction of chromatic aberration occurrence on the originally attached laminating surface, and achromatization such as lamination is performed. It becomes possible on a single lens.

From the viewpoint of the chromatic aberration coefficient (published by Kyoritsu Shuppan Co., Ltd., Yoshiya Matsui, “Lens Design Method”, page 89),
On the surface on the object side of the stop S, the diffractive optical surface is arranged on a surface having the same sign of the axial chromatic aberration coefficient L and the magnification chromatic aberration coefficient T, and on the surface on the image side of the stop S, both surfaces have opposite signs. It is preferable to arrange a diffractive optical surface.

As a result, the lenses constituting the first lens unit L1 are reduced in chromatic aberration by the diffractive optical element, the number of constituent lenses can be reduced, and further miniaturization can be achieved while maintaining good performance.

In particular, when the thickness of the lens constituting the first lens unit L1 on the optical axis is t1, it is preferable that the following conditional expression is satisfied.

0.1 <t1 / F1 <0.33 (9)

In particular, when the thickness of the lens constituting the second lens unit L2 on the optical axis is t2, it is preferable that the following conditional expression is satisfied.

0.55 <t2 / F1 <0.4 (10)

Equations (9) and (10) show the range where the diffractive optical element was effectively used.
As described in the expression (2), a desired refractive power can be obtained even with a small curvature. A concave lens (first lens group L1) and a convex lens (second lens group L2) for correcting chromatic aberration
If the combination with can be abolished by the diffractive optical element,
Further, the thickness of the lens is reduced, and the lens is effectively used.

If the values deviate from the upper limits of the expressions (9) and (10), the thickness is possible even with a normal glass lens, and the diffractive optical element is not effectively used. In addition, when the value deviates from the lower limit, refracting power due to diffraction is greatly required, and the occurrence of aberration increases, which is not appropriate.

Although not described in the present embodiment, the first lens unit L1 or the second lens unit L2 can also be achieved by using one diffractive optical element.

The aspherical shape has an X axis in the direction of the optical axis, a distance Y in a direction perpendicular to the optical axis, a positive traveling direction of light, a point of intersection between the vertex of the lens and the X axis taken as an origin, and r as a lens surface. Let k, B, C, D, and E be the aspherical surface coefficients of the paraxial radius of curvature, and are expressed by the following equation.

X = (Y ² / r) / [1+ ｛1- (1 + K) (Y / r) ² } ^1/2 ] + BY ⁴ + CY ⁶ + DY ⁸ + EY ¹⁰ (11)

Next, numerical embodiments 1 and 2 of the first and second embodiments will be described. In these numerical examples, ri is the radius of curvature of the i-th lens surface in order from the object side, di is the i-th lens thickness and air gap, and ni and νi are the refractive power of the i-th lens. Is a number.

Numerical Example 1 f = 4.19000-4.19 fno = 1: 1.850-2.82 2ω = 60.6-6.7 ° r1 = 42.051 d1 = 2.80 n1 = 1.51633 ν1 = 64.2 r2 = −95.964 (diffractive surface) d2 = 0.17 r3 = 14.187 d3 = 2.60 n2 = 1.551633 ν2 = 64.2 r4 = 61.567 d4 = variable r5 = 50.589 d5 = 0.50 n3 = 1.72000 ν3 = 50.3 r6 = 4.533 d6 = 2.17 r7 = -5.516 (diffractive surface) d7 = 0.50 n4 = 1.53172 ν4 = 48.8 r8 = -12.444 d8 = 1.53 r9 = 0.000 (aperture) d9 = 1.00 * r10 = 5.044 d10 = 3.02 n5 = 1.58313 ν5 = 59.4 r11 = -77.651 d11 = 0.08 r12 = 6.832 d12 = 0.55 n6 = 1.84666 ν6 = 23.8 r13 = 4.350 d13 = Variable * r14 = 9.425 d14 = 2.09 n7 = 1.58313 ν7 = 59.4 r15 = -6.413 d15 = 0.50 n8 = 1.84666 ν8 = 23.8 r16 = -12.465 d16 = 1.50 r17 = 0.000 d17 = 3.27 n9 = 1.51633 ν9 = 64.2 r18 = 0.000

[0062] Focal length 4.19 22.02 41.89 d4 0.70 9.40 11.85 d8 11.95 3.25 0.80 d13 6.22 2.50 6.20

Aspherical surface coefficient 10 surface K = -1.35672 ・ 10 ⁰ B = 4.42384 ・ 10 ^-4 C = 1.54512 ・ 10 ^-7 D = -5.25350 ・ 10 ^-9 E = -2.87640 ・ 10 ^-10 14 surface K = − 1.65726 ・ 10 ⁰ B = -8.73147 ・ 10 ^-5 C = -2.54226 ・ 10 ^-7 D = 7.20396 ・ 10 ^-7 E = -5.63081 ・ 10 ^-9

[0064] Phase coefficients dihedral ^{_{C 1 = -1.58547 · 10 -3 C}} 2 = 3.74388 · 10 -6 C 3 = -2.07446 · 10 -9 C 4 = 2.71374 · 10 -11 7 surface C ₁ = 9.12449 · 10 ^{- 3} C ₂ = -4.40286 ・ 10 ^-4 C ₃ = 4.76936 ・ 10 ^-5 C ₄ = -5.12756 ・ 10 ^-6

Numerical Example 2 f = 4.19000-4.19 fno = 1: 1.85-2.59 2ω = 60.6-6.7 ° r1 = 13.837 d1 = 0.70 n1 = 1.84666 ν1 = 23.8 r2 = 10.944 d2 = 0.81 r3 = 12.206 d3 = 4.60 n2 = 1.69680 ν2 = 55.5 r4 = -164.997 (diffractive surface) d4 = variable r5 = 100.902 d5 = 0.50 n3 = 1.72000 ν3 = 50.3 r6 = 4.643 d6 = 1.98 r7 = -6.408 (diffractive surface) d7 = 0.50 n4 = 1.53172 ν4 = 48.8 r8 = -32.148 d8 = Variable r9 = 0.000 (aperture) d9 = 1.00 * r10 = 4.930 d10 = 3.02 n5 = 1.58313 ν5 = 59.4 r11 = 176.932 d11 = 0.08 r12 = 6.674 d12 = 0.55 n6 = 1.84666 ν6 = 23.8 r13 = 4.350 d13 = Variable * r14 = 9.369 d14 = 2.60 n7 = 1.58313 ν7 = 59.4 r15 = -5.726 d15 = 0.50 n8 = 1.80518 ν8 = 25.4 r16 = -11.150 d16 = 1.50 r17 = 0.000 d17 = 3.27 n9 = 1.51633 ν9 = 64.2 r18 = 0.000

Focal length 4.19 22.12 41.91 d4 11.95 9.70 12.15 d8 11.95 3.25 0.80 d13 5.98 2.49 6.13

Aspherical surface coefficient 10 surface K = -1.55272 ・ 10 ⁰ B = 7.38545 ・ 10 ^-4 C = -9.57222 ・ 10 ^-7 D = -4.39693 ・ 10 ^-9 E = 5.99116 ・ 10 ^-10 14 surface K = − 1.81706 ・ 10 ⁰ B = -1.36047 ・ 10 ^-4 C = 7.60311 ・ 10 ^-7 D = 7.13090 ・ 10 ^-7 E = -6.08475 ・ 10 ^-9

Phase coefficient 4 plane C ₁ = -1.27721 ・ 10 ^-3 C ₂ = 1.64604 ・ 10 ^-5 C ₃ = -7.08588 ・ 10 ^-8 C ₄ = -5.54317 ・ 10 ^-10 7 plane C ₁ = 8.60805 ・ 10 ^-3 C ₂ = -3.89554 ・ 10 ^-4 C ₃ = 4.77344 ・ 10 ^-5 C ₄ = -5.12753 ・ 10 ^-6

The following table shows numerical values in Numerical Examples 1 and 2 of each value. Numerical example 1 Numerical example 2 Within first lens unit L1 | C ₂ / C ₁ | 2.36 · 10 ^-3 1.29 · 10 ^-2 | C ₃ / C ₁ | 1.31 · 10 ^-6 5.55 · 10 ^-5 lens group _{L2 | C 2 / C 1 |} 4.82 · 10 -2 4.53 · 10 -2 | C 3 / C 1 | 5.23 · 10 -3 5.54 · 10 -3 F1 20.53 20.84 F2 -3.914 -3.936 Fw 4.19 4.19 Ft ^{41.886 41.91 (Fw · Ft) 1/2} 13.248 13.251 Fbo1 116.94 147.55 Fbo2 -8.723 -9.981 Rbo1 -94.96 -164.99 Rbo2 -5.516 -6.408 F1 / Fbo1 0.176 0.141 F2 / Fbo2 0.449 0.394 F1 / (Fw · F t) 1 / ² 1.549 1.573 F1 / Rbo1 0.214 0.126 F2 / Rbo2 0.710 0.614 t1 / F1 0.271 0.293 t2 / F2 0.154 0.143

FIGS. 3 to 6 are aberration diagrams of the numerical examples 1 and 2 in the wide-angle state and the telephoto state, respectively.

The diffractive optical element described up to this point is manufactured by a binary optics (BINARY OPTICS) which is an optical element manufactured in a binary manner by a lithographic technique which is a manufacturing technique of a holographic optical element (HOE). Is also good. In this case, in order to further increase the diffraction efficiency, a saw-like shape called a kinoform may be used. Moreover, it can also be manufactured by molding using a mold prepared by these methods.

Although these diffractive optical elements are provided on an optical surface, their bases may be spherical, planar or aspheric without any problem. Further, a method of attaching a film of plastic or the like as a diffractive optical surface to those optical surfaces, that is, a so-called replica aspheric surface may be used.

The diffraction grating shape of the diffractive optical element in the above-mentioned embodiment has a kinoform shape shown in FIG.
In this diffraction grating, an ultraviolet-curing resin is applied to the surface of a substrate 1, and the first-order diffraction efficiency at a wavelength of 530 nm is 1
The diffraction grating 3 having a grating thickness d that is 00% is formed. FIG. 8 shows the wavelength dependence of the first-order diffraction efficiency of this diffractive optical element.
The distance decreases as the distance from 30 nm increases, while the 0th-order and second-order diffracted lights near the design order increase. This increase in diffracted light other than the design order causes a flare, which leads to a decrease in the resolution of the optical system.

FIG. 9 shows an MTF (Modulation transfer functi) with respect to the spatial frequency in the numerical example 1 of the lattice shape shown in FIG.
on) characteristic, and it can be seen that the MTF in the low frequency region is lower than a desired value.

Therefore, it is conceivable to form a lattice shape by using a laminated diffraction grating shown in FIG. A first diffraction grating 4 made of an ultraviolet curable resin (nd = 1.499, νd = 54) is formed on the substrate 1, and another ultraviolet curable resin (nd = 1.598, νd = 28) is formed thereon. The second consisting of
Are formed. With this combination of materials, the grating of the first diffraction grating 4 is dl = dl = 18.8 μm.
m, the grating of the second diffraction grating 5 is d2, d = 10.5 μm
And

FIG. 11 shows the wavelength dependence of the first-order diffraction efficiency of the diffractive optical element having this structure. As can be seen from FIG. 11, the diffraction efficiency of the design order can be reduced by using a diffraction grating having a laminated structure. It has a high diffraction efficiency of 95% or more throughout the castle. FIG. 12 shows the MTF characteristic with respect to the spatial frequency of Numerical Example 1 in this case. By using the diffraction grating having the laminated structure, the MTF at a low frequency is improved and the desired MTF is improved.
TF characteristics are obtained. As described above, by using a diffraction grating having a laminated structure as the diffractive optical element of the embodiment of the present invention, the optical performance is further improved.

The material of the diffractive optical element having the above-mentioned laminated structure is not limited to an ultraviolet-curable resin, but other plastic materials can be used. It may be formed on the material 1. Further, the thicknesses of the respective gratings do not need to be different, and depending on the combination of materials, the thicknesses of the two gratings can be made equal as shown in FIG. In this case, since the lattice shape is not formed on the surface of the diffractive optical element, it is excellent in dust resistance, the workability of assembling the diffractive optical element is improved, and a more inexpensive optical system can be obtained.

[0078]

As described above, the zoom lens according to the present invention has a small front lens diameter, a wide angle of view, a high zoom ratio, and simplification and downsizing including a mechanism. Good performance can be obtained over the entire zoom range and all object distances.

[Brief description of the drawings]

FIG. 1 is a sectional view of a lens according to a first embodiment.

FIG. 2 is a sectional view of a lens according to a second embodiment.

FIG. 3 is an aberration diagram of a wide-angle state according to the first embodiment.

FIG. 4 is an aberration diagram of a wide-angle state according to the first embodiment.

FIG. 5 is an aberration diagram of a wide-angle state according to the first embodiment.

FIG. 6 is an aberration diagram of a wide-angle state according to the first embodiment.

FIG. 7 is a sectional view of a diffraction grating.

FIG. 8 is a graph showing wavelength dependence.

FIG. 9 is a graph of MTF.

FIG. 10 is a sectional view of a diffraction grating having a laminated structure.

FIG. 11 is a graph showing wavelength dependence characteristics.

FIG. 12 is a graph of MTF.

FIG. 13 is a cross-sectional view of a diffraction grating having another laminated structure.

[Explanation of symbols]

 L1 First lens group L2 Second lens group 1 Base material 2 Resin part 3, 4, 5 Diffraction grating

Claims (3)

[Claims] 1. A zooming unit comprising a first lens unit having a fixed positive refractive power during zooming and a second lens unit having a negative refractive power movable during zooming, in order from the object side; An image forming group including a third lens group and a fourth lens group and subsequent lens groups, wherein the second lens group is moved to the image plane side during zooming from the wide-angle end to the telephoto end; In a zoom lens that corrects an image plane variation caused by zooming by a lens group subsequent to the lens group, the first lens group and the second lens group each include at least one lens rotationally symmetric with respect to an optical axis.
A zoom lens having a number of diffractive optical surfaces. 2. The lens system according to claim 1, wherein the third lens group is a positive lens group fixed during zooming with a stop, and the fourth lens group corrects an image plane variation due to zooming and adjusts a distance. The zoom lens described. 3. The zoom lens according to claim 1, wherein the diffractive optical surface comprises a laminated diffraction grating.