JP2002228930A - Zoom lens and projecting device by zoom lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a zoom lens, is which performance for chromatic aberration can be improved more than the conventional one without increasing the number of diffraction optical element introducing spots needlessly though it consists of nearly the same number of lenses as the conventional one, and to provide a high-performance projecting device. SOLUTION: This zoom lens has at least one diffraction optical element at least in one lens group out of several lens groups, and at least one lens group having the diffraction optical element is a lens group where height (h) from the optical axis of paraxial and axial rays passing through the lens group and height from the optical axis of a pupil paraxial ray have the same sign, and the zoom lens satisfies a following conditional expression 1. 1 -7.0×10-2<C1<-7.0×10-5 Provided that C1 is a phase coefficient obtained when the phase shape of a diffraction surface is given by a following polynomial (a). (a) ϕ(H)=2π/λ(C1.H2+C2.H4+...+Ci.H2i) Where, ϕ(H) means the phase shape of the diffraction surface, H means height in a perpendicular direction to the optical axis, λmeans designed wavelength and Cn means the n-th order phase coefficient.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens and a projection apparatus using the zoom lens, and more particularly, to a lens system, in which various optical members such as a color combining prism, a color combining mirror, and a polarizing filter are arranged. The present invention relates to a zoom lens having a long back focus and high optical performance of a telecentric system, which is suitable for a projection apparatus for enlarging and projecting an original projected image displayed on a color liquid crystal display element on a screen surface.

[0002]

2. Description of the Related Art Conventionally, there are various types of optical systems used in such a projection apparatus. In a projection optical system using a color liquid crystal as a projection image original, a liquid crystal display is provided from a final lens surface. There is a demand for an optical system having a long back focus in order to arrange an optical member such as a reflection mirror or a dichroic prism in a space (back focus) up to the element. For this reason, as a projection optical system for a color liquid crystal, a retrofocus type in which a lens unit having a negative refractive power precedes is often used.

For example, JP-A-62-291613 and JP-A-3-145613 propose a retrofocus type lens system having a long back focus. Of these examples, the lens system disclosed in Japanese Patent Application Laid-Open No. 62-291613 has a distortion of about -5%.
The lens system of 145613 has a tendency to increase astigmatism.

[0004] Further, since the size deviation of the image due to each of the RGB colors, that is, the chromatic aberration of magnification is large, the color deviation sometimes becomes conspicuous when an image of a high-definition liquid crystal display device is projected. It has been known that an aspherical surface is used as a part of a lens system in order to correct various aberrations and reduce the number of lenses. When an 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. In a lens system corresponding to a high number of pixels, correction of chromatic aberration is particularly important among various aberrations. However, good correction of chromatic aberration is difficult with an aspherical surface. Recently, in order to suppress the aberration of the lens system, many zoom lenses have been proposed in which the number of constituent lens groups is increased and the degree of freedom is reduced by reducing the aberration sharing of each lens group.

When a zoom lens is used as a lens system,
In order to correct chromatic aberration, the lenses constituting each lens group often use lenses made of a plurality of materials having different dispersion values, or perform achromatization by using a cemented lens of a negative lens and a positive lens. Was. Therefore, the number of lenses constituting each lens group is increased, and the entire lens tends to be large.

On the other hand, as a method for suppressing the occurrence of chromatic aberration and the fluctuation of chromatic aberration due to zooming, it has recently been proposed to apply a diffractive optical element having a diffractive action to an optical system. For example, Japanese Patent Application Laid-Open Nos. 4-213421 and 6-324262 propose optical systems using such diffractive optical elements. However, optical systems using these diffractive optical elements include: This is an optical system in which a diffractive optical element is applied to a single lens.Although there is a reference to chromatic aberration, there is no consideration or description of the removal of fluctuation due to zooming of chromatic aberration peculiar to a zoom lens, and no application to a zoom lens is performed. .

[0007] On the other hand, those applied to a zoom lens have been proposed in, for example, JP-A-11-84244 and JP-A-2000-19400. JP-A-11-84244 and JP-A-200
In Japanese Patent Application Publication No. 0-19400, an optical system in which various aberrations, particularly chromatic aberrations, are sufficiently corrected is obtained by introducing a diffractive optical element to a zoom lens.

[0008]

However, Japanese Patent Application Laid-Open No. 11-84244 and Japanese Patent Application Laid-Open No. 2000-1940 describe the above.
In Japanese Patent Application Laid-Open No. 0-210, etc., the total number of lenses is 10-12
In order to improve the performance of each aberration, especially the performance of chromatic aberration, the number of places where a diffractive optical element is introduced is increased, and an aspheric lens is used in addition to the diffractive optical element. Then, since each aberration is corrected, it cannot be said that the diffractive optical element is always used efficiently.

In the present invention, a group for introducing a diffractive optical element,
Phase coefficient C representing the phase shape of the diffraction surface ₁The range of
As a result, the number of lenses is about the same
The number of places to introduce the diffractive optical element
Zoom that can improve chromatic aberration performance without doing anything
Lens and high-performance projection device using the zoom lens
It is intended to provide a device.

[0010]

In order to achieve the above object, the present invention provides a zoom lens constructed as in the following (1) to (9) and a projection device using the zoom lens. is there. (1) A zoom lens having at least one diffractive optical element in at least one of a plurality of lens groups, wherein at least one lens group having the diffractive optical element passes through the lens group. The height h of the paraxial ray on the optical axis and the height of the pupil paraxial ray on the optical axis. Is a lens group having the same sign, and satisfies the following conditional expression. −7.0 × 10 ⁻² <C ₁ <−7.0 × 10 ^−5, where C ₁ is a phase coefficient when the phase shape of the diffraction surface is given by the following polynomial (a). φ (H) = 2π / λ (C ₁ · H ² + C ₂ · H ⁴ +... + C _i · H ²ⁱ ) (a) φ (H): phase shape of diffraction surface H: on optical axis In contrast, the height in the vertical direction λ: design wavelength C _n : nth-order phase coefficient (2) The plurality of lens groups are closer to the second conjugate point from the longer first conjugate point. The zoom lens according to (1), further comprising three lens groups of a first group having a negative refractive power, a second group having a positive refractive power, and a third group having a negative refractive power. . (3) The zoom lens according to (1) or (2), wherein the diffractive optical element is an element having a diffraction grating that is rotationally symmetric with respect to an optical axis, and includes only one such element. (4) The zoom lens according to (2) or (3), wherein the second group has an aperture and moves for zooming. (5) The zoom lens according to any one of (2) to (4), wherein the first group is a lens group that moves on an optical axis to perform focusing. (6) A zoom lens having a movable lens group provided with a stop, wherein the lens group other than the movable lens group has a diffractive optical element and satisfies the following conditional expression. −7.0 × 10 ⁻² <C ₁ <−7.0 × 10 ⁻⁵ ... Where C ₁ is a phase coefficient when the phase shape of the diffraction surface is given by the following polynomial (a). φ (H) = 2π / λ (C ₁ · H ² + C ₂ · H ⁴ +... + C _i · H ²ⁱ ) (a) φ (H): phase shape of diffraction surface H: on optical axis Vertical height λ: Design wavelength C _n : nth-order phase coefficient (7) The zoom lens according to any one of (1) to (6), wherein the zoom lens is formed of a telecentric system. Zoom lens. (8) The zoom lens according to any one of (1) to (7), wherein the diffractive optical element includes a blazed diffraction grating having at least one layer. (9) In a projection device for projecting an image on a screen using a zoom lens, the zoom lens may be any of the above (1) to (1).
(8) A projection device comprising the zoom lens according to any one of (8) and (7).

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In an embodiment of the present invention,
By applying the above configuration, when introducing the diffractive optical element in the zoom lens, appropriately find the phase coefficients C ₁ representing the phase shape of the group or a diffraction surface for introducing said diffractive optical element, aberrations, particularly chromatic aberration Not only to obtain an optical system with sufficient correction of
It is possible to reduce as much as about 12 sheets, and without compromising the number of places where the diffractive optical element is introduced and without using the diffractive optical element and the aspherical lens at the same time, a high-performance with sufficient correction of various aberrations An optical system can be realized.

In this embodiment, with respect to the surface on which the diffractive optical element is provided, if an on-axis ray and an off-axis ray passing through each optical system have an angle shift with respect to the normal direction at each ray incident position, diffraction occurs. Since there is a concern that the efficiency is degraded, it is preferable to set the lens surface as concentric as possible with respect to the on-axis ray and the off-axis ray.

Although these diffractive optical elements are provided on an optical surface, the base may be a spherical surface, a planar surface, an aspherical surface, or a quadratic curved surface. Alternatively, the optical surface may be formed by a method of attaching a film of plastic or the like as the diffractive optical surface (a so-called replica aspheric surface).

The diffractive optical element in the present embodiment is binary-manufactured by a lithographic method which is a method of manufacturing a holographic optical element (HOE). The diffractive optical element is a binary optics (BINARY OPT)
ICS). In this case, in order to further increase the diffraction efficiency, a saw-like shape called a kinoform may be used. Further, it may be manufactured by molding using a mold manufactured by these methods.

Further, the shape of the diffractive optical element in the present embodiment is such that the reference wavelength (d-line) is λ, the nth-order phase coefficient is C _n , the height in the direction perpendicular to the optical axis (the distance from the optical axis). )
Where H is the phase shape of the diffraction surface and φ (H), φ (H) = 2π / λ (C ₁ · H ² + C ₂ · H ⁴ +... + C _i · H ²ⁱ ). a) can be represented by the following equation: As is apparent from the equation (a), the phase is adjusted by the distance H from the optical axis.
The larger the lens diameter, the greater the effect of higher order coefficients.

In the present invention, as a group into which the diffractive optical element is introduced, the height h from the optical axis of the paraxial ray passing through each lens group of each zoom lens and the height from the optical axis of the pupil paraxial ray. Sa Were introduced into groups with the same sign. If this Is a different sign, or If a diffractive optical element is introduced into the group of

Here, L is the axial chromatic aberration coefficient of the entire optical system before introducing the diffractive optical element, T is the chromatic aberration coefficient of magnification, and L is the axial chromatic aberration coefficient of the entire system after introducing the diffractive optical element.
_D , and the chromatic aberration of magnification coefficient is T _D , the following relational expression holds.

However, Represents the height from the optical axis of the height and the paraxial chief ray from the optical axis of a paraxial marginal ray passing through each lens group when introducing the diffractive optical element, phi _D is a refractive diffractive optical element And v _D is the Abbe number of the diffractive optical element, and ν _D = −3.45.

When considering the chromatic aberration of the projection optical system, since both on-axis and lateral chromatic aberration generally occur on the positive side,
It can be seen that both the axial chromatic aberration coefficient L and the lateral chromatic aberration coefficient T of the entire system before introducing the diffractive optical element are negative values. In order to correct the axial and lateral chromatic aberrations, the correction may be made to the negative side, and each chromatic aberration coefficient may be corrected to the positive side. That is, each chromatic aberration coefficient L _D after introducing the diffractive optical element,
So that the T _D may be corrected to the positive side.

From the above, When a diffractive optical element is introduced into a group having a different sign, the direction in which the axial chromatic aberration and the lateral chromatic aberration are corrected at the same time is eliminated,
Not preferred. Also When a diffractive optical element is introduced into the group It can be seen that this is not the direction in which the chromatic aberration of magnification is corrected, which is not preferable.

The diffractive optical surface according to the present invention has the above-mentioned formula (a).
When the phase coefficient C ₁ when the phase shape of the diffractive surface is given by the expression (a) satisfies the following conditional expression, it is possible to efficiently use the diffractive optical element in the zoom lens. And aberration can be effectively corrected. −7.0 × 10 ⁻² <C ₁ <−7.0 × 10 ⁻⁵ ... C ₁ in the above equation represents the paraxial refractive power of the diffractive optical element, and diffraction occurs when C ₁ has a positive value. The optical element has a negative refractive power, and has a positive refractive power when C ₁ has a negative value.

If the lower limit of the above conditional expression is deviated, the power of the diffractive optical element becomes too strong, and the difference between the center of the diffractive surface and the sawtooth-shaped pitch around the diffractive surface becomes large, making the production difficult. On the other hand, if the upper limit of the above conditional expression is deviated, the power of the diffractive optical element becomes too weak, and it becomes difficult to correct the desired chromatic aberration.

In the present invention, the stop is set to the second group because the second group is a main zooming group of the zoom lens, and in the zoom lens, the group having the stop is a pupil paraxial ray. Height from optical axis Is 0, the chromatic aberration of magnification generated in the first group is not increased by zooming. Therefore, an aperture is provided in the second group.

As the structure of the diffractive optical element used in this embodiment, a single-layer kinoform-shaped single-layer structure shown in FIG. 19, or a different grating thickness (or the same as shown in FIG. 20) as shown in FIG. And (2) a layered structure in which two layers are stacked is applicable.

FIG. 21 shows the diffractive optical element 101 shown in FIG.
Shows the wavelength dependence of the diffraction efficiency of the first-order diffracted light. The actual configuration of the diffractive optical element 101 is shown in FIG.
02 is coated with an ultraviolet curable resin, and a wavelength of 5
The diffraction grating 103 having a grating thickness d is formed so that the diffraction efficiency of the first-order diffracted light at 30 nm becomes 100%.

As is apparent from FIG. 21, the diffraction efficiency of the design order decreases as the distance from the optimized wavelength of 530 nm increases, while the diffraction efficiencies of the zero-order diffraction light and the second-order diffraction light of the orders near the design order increase. . An increase in diffracted light other than the design order causes a flare, leading to a decrease in the resolution of the optical system.

The two diffraction gratings 104 and 10 shown in FIG.
FIG. 22 shows the wavelength-dependent characteristics of the laminated diffractive optical element in which No. 5 is laminated. In FIG. 20, a first diffraction grating 104 made of an ultraviolet curable resin (nd = 1.499, vd = 54) is formed on a base material 102, and another ultraviolet curable resin (nd = 1.598, vd = 28). With this combination of materials, the grating thickness d1 of the first diffraction grating 104 is d1 = 13.8 μm.
m, the grating thickness d2 of the second diffraction grating 105 is d2 = 10.
It is 5 μm.

As can be seen from FIG. 22, by using a diffractive optical element having a laminated structure, the diffraction efficiency of the design order has a high diffraction efficiency of 95% or more over the entire wavelength range used. As described above, when the laminated structure is used as the diffractive optical element according to the embodiment of the present invention, the optical performance can be further improved.

The material of the diffractive optical element is not limited to an ultraviolet curable resin, but other plastic materials or the like can be used.
04 may be formed directly on the substrate. Further, each lattice thickness is not necessarily required, and two lattice thicknesses can be made equal by a combination of materials as shown in FIG. In this case, since the grating 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 provided.

As shown in FIG. 24, an ultraviolet curable resin (nd = 1.66585, vd = 19.7) is formed on the base material 102.
Is formed, and the interval between the peak portions of the sawtooth is set to about 1.5 μm with respect to the diffraction grating 107.
m, another ultraviolet curable resin (nd = 1.
5240, vd = 50.8)
In the diffractive optical element having the layered structure in which No. 06 is formed, the diffraction optical element shown in FIG.
A diffraction efficiency equivalent to that of the diffraction grating of 0 can be obtained. With this combination of materials, the grating thickness d of the first diffraction grating 107
1 is d1 = 5.0 μm, and the grating thickness d2 of the second diffraction grating 106 is d2 = 7.5 μm.

In the present embodiment, the use of the diffractive optical element having the above-described configuration makes it possible to reduce chromatic aberration, reduce the number of constituent lenses, and obtain an optical system having good optical performance. it can. Further, in the present embodiment, the first group having negative refractive power, the second group having positive refractive power, and the third group having negative refractive power are sequentially arranged from the first conjugate point side having the longer distance. In the four-group and five-group zoom lenses including the lens group, the height h from the optical axis of the paraxial ray passing through each lens h constituting the zoom lens and the optical axis of the pupil paraxial ray Height Introduce a diffractive optical element to a group having the same sign, and at that time, appropriately set the group to be introduced, and appropriately set a phase coefficient C ₁ representing a phase shape of a diffractive surface of the diffractive optical element. Accordingly, it is possible to achieve a telecentric zoom lens having a long back focus, in which various aberrations, particularly, chromatic aberration of magnification corresponding to a high-definition liquid crystal are satisfactorily corrected.

Also, in the present embodiment, by adopting the above-described configuration, the Fno at a zoom ratio of 1.3 or more can be obtained.
While ensuring a large aperture of about 1.8, various aberrations are sufficiently corrected, and the chromatic aberration of magnification is ensured while ensuring a sufficient back focus space for optical elements such as a color combining prism and optical elements of various filters. Is excellently corrected, and a telecentric zoom lens having excellent performance over the entire zoom range and all object distances can be realized. In addition, a liquid crystal projector suitable for the zoom lens can be realized. At that time, the number of constituent lenses is also 10 to 12
A high-performance optical system with sufficient correction of various aberrations is realized with as few sheets as possible, without unnecessarily increasing the places where the diffractive optical element is introduced, and without using a diffractive optical element and an aspheric lens at the same time. It becomes possible.

[0033]

Next, an embodiment of the present invention will be described.
1 to 6 are lens cross-sectional views of Examples 1 to 6 of the present invention. In the figure, S is a screen surface, and LCD is a liquid crystal display element as an image to be projected. Screen surface S
Is closer to the first conjugate point on the longer side, and the liquid crystal display element L
CD is at the second conjugate point with the shorter distance. GB is a glass block such as a color combining prism, a polarizing filter, and a color filter.

1 to 6, L1 is a first group having a negative refractive power, L2 is a second group having a positive refractive power, L3 is a third group having a negative refractive power, and L4 is a positive refractive power. The fourth group of forces, L5, represents the fifth group of positive refractive power. The liquid crystal display element LCD corresponds to an image plane. Arrows indicate the movement trajectories of the respective lens units when zooming from the wide-angle end to the telephoto end.

In FIGS. 1 to 6, Li indicates the ith group (i = 1 to 5), and FIGS.
4 to 6, and L1 to L4 in FIGS. 4 to 6 constitute zoom lens units, which are mounted on the main body of the liquid crystal projector via connection members. Therefore, the liquid crystal display element LCD side after the glass block GB is included in the projector main body.

The first embodiment of the present invention shown in FIGS.
In the sixth embodiment, focusing is performed by moving the first lens unit on the optical axis, and the second lens unit has an aperture. In each of the zoom lenses of FIGS. 1 to 6, the height h from the optical axis of the paraxial ray passing through each lens group of each zoom lens and the height of the pupil paraxial ray from the optical axis. Are provided with at least one diffractive optical element rotationally symmetric with respect to the optical axis in at least one lens group among the groups having the same reference numerals. Hereinafter, each lens configuration of each embodiment will be further described.

[Embodiment 1] The embodiment 1 of the present invention shown in FIG. 1 is a five-unit zoom lens, and has a diffractive optical element in the third unit. At the time of zooming from the wide-angle end to the telephoto end, the second unit L2, the third unit L3, and the fourth unit L4 have trajectories that are monotonic toward the first conjugate point or convex toward the first conjugate point. While moving. At this time, the first
The group L1 and the fifth group L5 are fixed.

[Embodiment 2] The embodiment 2 of the present invention shown in FIG. 2 is a five-unit zoom lens, and the fourth unit has a diffractive optical element. At the time of zooming from the wide-angle end to the telephoto end, the second unit L2 is moved while having a convex locus toward the first conjugate point, and the third unit L3 is moved toward the first conjugate point.
The trajectory of the group L2 is moved to the second conjugate point side while having a gentler convex trajectory, and the fourth group L4 is monotonously moved to the first conjugate point side. At this time, the first lens unit L1 and the fifth lens unit L5 are fixed.

Embodiment 3 Embodiment 3 of the present invention shown in FIG. 3 is a five-unit zoom lens, and has a diffractive optical element in the fifth unit. Upon zooming from the wide-angle end to the telephoto end, the second unit L2 is moved to the first conjugate point side while having a locus convex toward the first conjugate point side, and the third unit L3 is moved to the second conjugate point side. The fourth unit L4 is moved monotonically to the first conjugate point side. At this time, the first lens unit L1 and the fifth lens unit L5 are fixed.

[Embodiment 4] In Embodiment 4 of the present invention shown in FIG. 4, there is a four-unit zoom lens, and the third unit L3
Has a diffractive optical element. In zooming from the wide-angle end to the telephoto end, the second unit L2 and the third unit L3 are moved while having a locus convex toward the first conjugate point. Note that the first lens unit L
The first and fourth lens units L4 are fixed during zooming. The optical system of FIG. 4 has the same number of lenses as the optical system of FIG. 1, but the zoom type has a five-group configuration to a four-group configuration.

[Embodiment 5] In Embodiment 5 of the present invention shown in FIG. 5, there is a four-unit zoom lens, and the third unit L3
Has a diffractive optical element. In zooming from the wide-angle end to the telephoto end, the second unit L2 and the third unit L3 are moved while having a locus convex toward the first conjugate point. Note that the first lens unit L
The first and fourth lens units L4 are fixed during zooming. The optical system in FIG. 5 has a configuration in which the number of lenses in the third lens unit L3 is reduced by one compared to the optical system in FIG.

[Embodiment 6] The embodiment 6 of the present invention shown in FIG. 6 is a four-unit zoom lens, and the third unit L3
Has a diffractive optical element. In zooming from the wide-angle end to the telephoto end, the second unit L2 is moved with a convex trajectory toward the first conjugate point, and the third unit L3 is monotonously moved toward the first conjugate point. Note that the first lens unit L1 and the fourth lens unit L4 are fixed during zooming. The optical system of FIG. 6 has a configuration in which the number of lenses of the third lens unit L3 is further reduced by one compared to the optical system of FIG.

7 to 18 show aberration diagrams for each of the above embodiments. FIG. 7 is an aberration diagram at a wide-angle end according to the first embodiment.
FIG. 8 is an aberration diagram at a telephoto end according to the first embodiment. FIG. 9 is an aberration diagram at a wide angle end according to the second embodiment, and FIG. 10 is an aberration diagram at a telephoto end according to the second embodiment. FIG. 11 is an aberration diagram at the wide-angle end of the third embodiment, and FIG. 12 is an aberration diagram at the telephoto end of the third embodiment. FIG. 13 is an aberration diagram at the wide-angle end of the fourth embodiment, and FIG. 14 is an aberration diagram at the telephoto end of the fourth embodiment. Also,
FIG. 15 is an aberration diagram at the wide-angle end of the fifth embodiment, and FIG. 16 is an aberration diagram at the telephoto end of the fifth embodiment. FIG. 17 is an aberration diagram at the wide-angle end of the sixth embodiment, and FIG. 18 is an aberration diagram at the telephoto end of the sixth embodiment. 7 to 18, B, G, and R are 470 nm, 550 nm, and 650 nm.
nm, ΔM, and ΔS indicate a meridional image plane and a sagittal image plane.

Tables 1 to 6 below show Numerical Embodiments 1 to 6 corresponding to the above-described Embodiments 1 to 6. In these numerical examples, ri is the radius of curvature of the i-th lens surface in order from the first conjugate point side, di is the i-th lens thickness and air space in order from the first conjugate point side, and ni and vi are each The glass refractive index and the Abbe number of the i-th lens are shown in order from the first conjugate point side. In each numerical example, for example, the display of [e-Z] means “10 ^−z ”.

[0045]

[Table 1] (Numerical Example 1)

[0046]

[Table 2] (Numerical example 2)

[0047]

[Table 3] (Numerical example 3)

[0048]

[Table 4] (Numerical example 4)

[0049]

[Table 5] (Numerical example 5)

[0050]

[Table 6] (Numerical example 6)

[0051]

As described above, according to the present invention, a zoom lens capable of improving the performance of chromatic aberration without increasing the number of diffractive optical elements with a small number of lenses, and a high performance by the zoom lens It is possible to realize a simple projection device.

[Brief description of the drawings]

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

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

FIG. 3 is a sectional view of a lens according to a third embodiment of the present invention.

FIG. 4 is a sectional view of a lens according to a fourth embodiment of the present invention.

FIG. 5 is a sectional view of a lens according to a fifth embodiment of the present invention.

FIG. 6 is a sectional view of a lens according to a sixth embodiment of the present invention.

FIG. 7 is an aberration diagram at a wide-angle end in Embodiment 1 of the present invention.

FIG. 8 is an aberration diagram at a telephoto end in Example 1 of the present invention.

FIG. 9 is an aberration diagram at a wide-angle end in Embodiment 2 of the present invention.

FIG. 10 is an aberration diagram at a telephoto end in Embodiment 2 of the present invention.

FIG. 11 is an aberration diagram at a wide-angle end according to a third embodiment of the present invention.

FIG. 12 is an aberration diagram at a telephoto end in Embodiment 3 of the present invention.

FIG. 13 is an aberration diagram at a wide-angle end in Embodiment 4 of the present invention.

FIG. 14 is an aberration diagram at a telephoto end in Example 4 of the present invention.

FIG. 15 is an aberration diagram at a wide-angle end in Embodiment 5 of the present invention.

FIG. 16 is an aberration diagram at a telephoto end in Example 5 of the present invention.

FIG. 17 is an aberration diagram at a wide angle end in Embodiment 6 of the present invention.

FIG. 18 is an aberration diagram at a telephoto end in Example 6 of the present invention.

FIG. 19 is an explanatory diagram of the diffractive optical element according to the embodiment of the present invention.

FIG. 20 is an explanatory diagram of the diffractive optical element according to the embodiment of the present invention.

FIG. 21 is an explanatory diagram of a wavelength dependence characteristic of the diffractive optical element (FIG. 19) according to the embodiment of the present invention.

FIG. 22 is an explanatory diagram of the wavelength dependence of the diffractive optical element (FIG. 20) according to the embodiment of the present invention.

FIG. 23 is an explanatory diagram of a diffractive optical element according to an embodiment of the present invention.

FIG. 24 is an explanatory diagram of a diffractive optical element according to an embodiment of the present invention.

[Explanation of symbols]

 S: Screen surface LCD: Liquid crystal display element GB: Glass block L1: First group lens with negative refractive power L2: Second group lens with positive refractive power L3: Third group lens with negative refractive power L4: Positive Fourth lens unit having refractive power L5: Fifth lens unit having positive refractive power 101: Diffractive optical element 102: Substrate 103: Diffraction grating 104, 107: First diffraction grating 105, 106: Second diffraction grating

Continued on front page F-term (reference) 2H087 KA06 KA07 MA12 NA02 PA09 PA10 PA18 PA19 PB10 PB11 PB12 QA02 QA07 QA14 QA22 QA26 QA32 QA34 QA41 QA42 QA46 RA05 RA12 RA13 RA36 RA41 RA43 RA45 RA46 SA24 SA26 SA30 SA32 SA52 SA64 SA65 SA72 SA75 SA76 SB05 SB14 SB22 SB24 SB32 SB34 SB42

Claims (9)

[Claims] 1. A zoom lens having at least one diffractive optical element in at least one lens group of a plurality of lens groups, wherein at least one lens group having the diffractive optical element has the lens group. The height h of the passing paraxial ray from the optical axis and the height of the pupil paraxial ray from the optical axis Is a lens group having the same sign, and satisfies the following conditional expression. −7.0 × 10 ⁻² <C ₁ <−7.0 × 10 ^−5, where C ₁ is a phase coefficient when the phase shape of the diffraction surface is given by the following polynomial (a). φ (H) = 2π / λ (C ₁ · H ² + C ₂ · H ⁴ +... + C _i · H ²ⁱ ) (a) φ (H): phase shape of diffraction surface H: on optical axis Vertical height λ: Design wavelength C _n : n-order phase coefficient 2. The method according to claim 1, wherein the plurality of lens groups are arranged from a first conjugate point having a longer distance to a second conjugate point having a shorter distance.
The zoom lens according to claim 1, further comprising three lens groups, a first group having a negative refractive power, a second group having a positive refractive power, and a third group having a negative refractive power. 3. The zoom lens according to claim 1, wherein the diffractive optical element is an element having a diffraction grating that is rotationally symmetric with respect to an optical axis, and has only one such element. 4. The zoom lens according to claim 2, wherein the second group has a stop and moves for zooming. 5. The zoom lens according to claim 2, wherein the first group is a lens group that moves on an optical axis to perform focusing. 6. A zoom lens having a movable lens group provided with a stop, wherein the lens group other than the movable lens group has a diffractive optical element and satisfies the following conditional expression. −7.0 × 10 ⁻² <C ₁ <−7.0 × 10 ^−5, where C ₁ is a phase coefficient when the phase shape of the diffraction surface is given by the following polynomial (a). φ (H) = 2π / λ (C ₁ · H ² + C ₂ · H ⁴ +... + C _i · H ²ⁱ ) (a) φ (H): phase shape of diffraction surface H: on optical axis Vertical height λ: Design wavelength C _n : n-order phase coefficient 7. The zoom lens according to claim 1, wherein said zoom lens comprises a telecentric system. 8. The zoom lens according to claim 1, wherein said diffractive optical element comprises a blazed diffraction grating having at least one layer. 9. A projection device for projecting an image on a screen using a zoom lens, wherein the zoom lens is constituted by the zoom lens according to claim 1. Description: .