JP4438076B2 - Projection zoom lens and image projection apparatus having the same - Google Patents

Description

  The present invention relates to a projection zoom lens and an image projection apparatus having the same, and is suitable for a liquid crystal projector apparatus that enlarges and projects an image displayed on an image display element such as a light valve on a screen.

  Projection-type image display devices such as a liquid crystal projector for enlarging and projecting a display image such as a liquid crystal panel have been greatly improved in recent years, and have been used in various places. This image display apparatus is required to be further improved with respect to the image quality of the display image, the brightness of the image, size reduction, weight reduction, and the like.

  As one of the liquid crystal projectors that is currently in the mainstream, a so-called “three-plate liquid crystal projector” is known in which liquid crystal panels are arranged for the red, blue, and green wavelength regions, respectively. This “three-plate liquid crystal projector” has a color combining optical system such as a dichroic prism on the optical path for projecting images based on the respective color lights displayed on the three liquid crystal panels on the screen and displaying them as color images. Used.

  In order to prevent unevenness in the color of the projected image caused by the angle dependence of the dichroic film in this dichroic prism, and the decrease in contrast caused by the viewing direction of the liquid crystal panel, the projection optical system has an image plane on the reduction conjugate side. Telecentricity is required. Further, in order to reduce the color shift of the enlarged images of the three liquid crystal panels, the projection lens is required to reduce the chromatic aberration of magnification. Further, in recent years, microlenses have been adopted for liquid crystal panels so that images can be observed even in relatively bright rooms. For this reason, the solid angle of the light radiated from the liquid crystal panel is increased, and in order to make effective use of this light, a brighter projection lens is required.

  In order from the magnification conjugate side to the reduction conjugate side, the first lens group having a negative refractive power, the second lens group having a positive refractive power, the third lens group having a positive refractive power, the fourth lens group having a negative refractive power, For a liquid crystal projector in which a second lens group, a third lens group, and a fifth lens group are moved during zooming, and are composed of a sixth lens group having a refractive power of 5 and a sixth lens group having a positive refractive power There is known a projection zoom lens (for example, Patent Document 1).

  In addition, in order from the magnification conjugate side to the reduction conjugate side, the first lens group having a negative refractive power, the second lens group having a positive refractive power, the third lens group having a positive refractive power, and a fourth lens having a negative refractive power. A lens group, a fifth lens group, and a sixth lens group having a positive refractive power, and when zooming from the wide-angle end to the telephoto end, three or more lenses among the second to fifth lens groups In the projection zoom lens in which the first lens group and the sixth lens group are fixed during zooming, one or more lens groups of the plurality of lens groups are arranged with respect to the optical axis. A projection zoom lens having a rotationally symmetric diffractive optical element is known (for example, Patent Documents 2 and 3).

In addition, there is known a projection zoom lens that corrects chromatic aberration (particularly lateral chromatic aberration), which has a large effect on high definition of the projection optical system, by using a diffractive optical element having a diffractive action to improve performance. (For example, patent document 4).
JP 2001-108900 A Japanese Patent Application Laid-Open No. 2000-131641 JP 2000-182111 A JP 2000-019400 A

  In general, in a color liquid crystal projector using a liquid crystal panel as an image display element, it is important to particularly correct chromatic aberration among various aberrations of a projection optical system. If the chromatic aberration of the projection optical system is not satisfactorily corrected, color blurring occurs in the projected image, which adversely affects the image quality. Furthermore, recently, it has become a problem to cope with the miniaturization of the projection lens accompanying the miniaturization of the entire projector apparatus.

  An object of the present invention is to provide a zoom lens suitable for, for example, a projection optical system of a liquid crystal projector, which corrects various aberrations over the entire zoom range and has excellent optical performance over the entire screen.

The projection zoom lens of the present invention includes, in order from the magnification conjugate side to the reduction conjugate side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, a third lens group having a positive refractive power, A fourth lens group with a refractive power of 5, a fifth lens group with a positive or negative refractive power, and a sixth lens group with a positive refractive power,
At the time of zooming from the wide angle end to the telephoto end, at least three of the lens groups are moved from the reduction conjugate side to the enlargement conjugate side,
When the focal length of the entire system at the wide angle end is fw and the focal length of the fifth lens group is f5,
-0.5 <fw / f5 <0.2
It is characterized by satisfying.

  According to the present invention, it is possible to obtain a projection zoom lens suitable for a liquid crystal projector having good optical performance over the entire screen by satisfactorily correcting various aberrations over the entire zoom range.

  Embodiments of the projection zoom lens according to the present invention will be described below with reference to the drawings.

  FIG. 1 is a main part schematic diagram of an image projection apparatus (liquid crystal video projector) using the projection zoom lens according to the first embodiment of the present invention.

  2, 3, and 4 show a wide angle end when an object distance (distance from the first lens group) of 2.8 m is expressed in millimeters, which is a numerical value of Numerical Example 1 (to be described later) corresponding to Example 1 of the present invention. FIG. 6 is an aberration diagram at a (short focal length), an intermediate focal length, and a telephoto end (long focal length).

  FIG. 5 is a schematic diagram of a main part of an image projection apparatus (liquid crystal video projector) using the projection zoom lens according to the second embodiment of the present invention.

  6, 7, and 8 are wide-angle ends when the object distance (distance from the first lens group) is 2.8 m, in which the numerical value of Numerical Example 2 (to be described later) corresponding to Example 2 of the present invention is displayed in mm. FIG. 6 is an aberration diagram at a (short focal length), an intermediate focal length, and a telephoto end (long focal length).

  FIG. 9 is a schematic diagram of a main part of an image projection apparatus (liquid crystal video projector) using the projection zoom lens according to the third embodiment of the present invention.

  10, 11, and 12 are wide-angle ends when the object distance (distance from the first lens unit) is 2.8 m, which is expressed in mm in numerical values of Numerical Example 3 to be described later, corresponding to Example 3 of the present invention. FIG. 6 is an aberration diagram at a (short focal length), an intermediate focal length, and a telephoto end (long focal length).

  FIG. 13 is a schematic diagram of a main part of an image projection apparatus (liquid crystal video projector) using the projection zoom lens according to the fourth embodiment of the present invention.

  14, 15, and 16 are wide-angle ends when the object distance (distance from the first lens group) is 2.8 m, which is expressed in millimeters in numerical values of Numerical Example 4 (to be described later) corresponding to Example 4 of the present invention. FIG. 6 is an aberration diagram at a (short focal length), an intermediate focal length, and a telephoto end (long focal length).

  In the image projection apparatuses according to the first to fourth embodiments shown in FIGS. 1, 5, 9, and 13, an original image (projected image) displayed on a liquid crystal panel LCD or the like is used using a zoom lens (projection lens, projection lens) PL. A state in which the image is enlarged and projected on the screen surface S is shown.

  S is a screen surface (projection surface), and LCD is an original image (projected image) such as a liquid crystal panel (liquid crystal display element). The screen surface S and the original image LCD are in a conjugate relationship. In general, the screen surface S is a conjugate point with a longer distance (enlarged conjugate point), and the original image LCD is a conjugate point with a shorter distance (reduced conjugate point). It corresponds to.

  GB is a glass block such as a color synthesis prism, a polarizing filter, and a color filter.

  The projection zoom lens PL is attached to a liquid crystal video projector main body (not shown) via a connection member (not shown). The liquid crystal display element LCD side after the glass block GB is included in the projector body.

  L1 is a first lens group having negative refractive power, L2 is a second lens group having positive refractive power, L3 is a third lens group having positive refractive power, L4 is a fourth lens group having positive refractive power, and L5 is A fifth lens group having positive or negative refractive power, and L6 is a sixth lens group having positive refractive power.

  The fifth lens unit L5 has a positive refractive power in the first and second embodiments, and a negative refractive power in the third and fourth embodiments. SP is a stop, which is provided between the third lens unit L3 and the fourth lens unit L4.

  In each embodiment, when zooming from the wide-angle end to the telephoto end, the second lens unit L2 is moved to the original image LCD side as indicated by an arrow, the third lens unit L3, the fourth lens unit L4, and the fifth lens unit L5 are screened. Each is moved independently to the S side. During zooming, the first lens unit L1 and the sixth lens unit L6 do not move. However, focusing is performed by moving the first lens unit L1 on the optical axis.

  Each lens surface is provided with a multilayer coating, which prevents a reduction in illuminance on the screen surface S.

  2-4, FIGS. 6-8, FIGS. 10-12, and FIGS. 14-16, G indicates aberration at a wavelength of 550 nm, R indicates a wavelength at 650 nm, B indicates an aberration at a wavelength of 470 nm, and S (tilt of sagittal image plane) ) And M (tilt of the meridional image plane) both indicate aberrations at a wavelength of 550 nm. ω is a half angle of view, and Fno is an F number.

  Each embodiment has six lens groups as a whole, and is characterized in that at least three lens groups are moved during zooming from the wide-angle end to the telephoto end.

  In each embodiment, a negative lead type configuration preceded by a lens unit having a negative refractive power facilitates securing a wide angle of view and a long back focus.

  At the time of zooming, the movable lens group is made up of three components or more to correct aberration fluctuation due to zooming, and high optical performance is obtained over the entire zooming range.

  Further, both the first and sixth lens groups are fixed with respect to the image plane (LCD) at the time of zooming. As a result, the robustness of the projection lens unit is secured, and the change in the weight balance is reduced by fixing the lens unit (first lens unit) having a large effective diameter at the time of zooming. Like to do.

The fourth lens unit L4 includes a single lens having a positive refractive power, and the fourth lens unit L4 moves from the reduction conjugate side to the enlargement conjugate side upon zooming from the wide-angle end to the telephoto end. When the movement amount (the sign of the movement amount is positive when moving from the enlargement conjugate side to the reduction conjugate side and the opposite is negative) is M4, and the focal length of the fourth lens unit L4 is f4.
0.01 <| M4 / f4 | <0.20 (1)
Is satisfied.

  Conditional expression (1) relates to the ratio of the amount of movement and the focal length during zooming of the fourth lens unit L4. Exceeding the lower limit of conditional expression (1) is not preferable because the absolute value of the moving amount of the fourth lens unit L4 becomes too small and correction of various aberrations becomes insufficient. Exceeding the upper limit of conditional expression (1) is not preferable because the positive refractive power of the fourth lens unit L4 becomes too strong and the spherical aberration generated in the fourth lens unit L4 increases.

  More preferably, the numerical range of conditional expression (1) is set as follows.

0.02 <| M4 / f4 | <0.19 (1a)
The fifth lens unit L5 includes, in order from the magnification conjugate side to the reduction conjugate side, a negative refractive power 51st lens having a convex meniscus surface on the magnification conjugate side, and a 52nd lens having a strong negative refractive power on the magnification conjugate side. The lens is composed of a 53rd lens having a strong positive refractive power on the reduction conjugate side and a 54th lens having a strong positive refractive power on the reduction conjugate side, and the 52nd lens group and the 53rd lens are cemented.

When the focal length of the entire system at the wide angle end is fw and the focal length of the fifth lens unit L5 is f5,
-0.5 <fw / f5 <0.2 (2)
Is satisfied. Conditional expression (2) relates to the ratio between the focal length of the entire system at the wide-angle end and the focal length of the fifth lens unit L5. Exceeding the lower limit of conditional expression (2) is not preferable because the negative refractive power of the fifth lens unit L5 becomes too strong and the telecentricity with respect to the reduction conjugate surface (liquid crystal panel surface) is destroyed. When the upper limit of conditional expression (2) is exceeded, the positive refractive power of the fifth lens unit L5 becomes too strong, and it becomes difficult to obtain a long back focus necessary for arranging a glass block such as a color synthesis prism. Therefore, it is not preferable.

  More preferably, the numerical range of conditional expression (2) is set as follows.

-0.45 <fw / f5 <0.1 (2a)
The first lens unit L1 includes, in order from the magnification conjugate side to the reduction conjugate side, a biconvex eleventh lens having a positive refractive power, a meniscus negative twelfth lens having a convex convex meniscus surface, It consists of a concave negative refractive power thirteenth lens. The average value of d-line Abbe number of the positive refractive power lens in the first lens unit L1 is νdlpa, and the average value of d-line Abbe number of the negative refractive power lens in the first lens unit L1 is νdlna. and when,
35 <νdlpa (3)
35 <νdlna <75 (4)
Is satisfied.

  Conditional expressions (3) and (4) are mainly related to the average value of the Abbe number (d line) of the materials of the positive refractive power lens and the negative refractive power lens constituting the first lens unit L1. This is a condition for satisfactorily correcting chromatic aberration and lateral chromatic aberration. If the lower limit value of conditional expression (3) and the upper limit value of conditional expression (4) are exceeded, axial chromatic aberration and lateral chromatic aberration occurring in the first lens unit L1 become too small, and axial chromatic aberration in the entire lens system and The lateral chromatic aberration is not preferable because the correction becomes insufficient. If the lower limit value of conditional expression (4) is exceeded, the longitudinal chromatic aberration and lateral chromatic aberration occurring in the first lens unit L1 become too large, and the longitudinal chromatic aberration and lateral chromatic aberration in the entire lens system become overcorrected. This is not preferable because the chromatic aberration in the reference state of the entire optical system is greatly deteriorated.

  More preferably, the numerical ranges of conditional expressions (3) and (4) are set as follows.

42 <νdlpa (3a)
45 <νdlna <65 (4a) The projection zoom lens according to the present invention achieves better optical performance over the entire zooming range by satisfying the above conditions.

  Next, specific features of each embodiment will be described with reference to each drawing.

  In Example 1 of FIG. 1, in order from the magnification conjugate side to the reduction conjugate side, the first lens unit L1 having a negative refractive power, the second lens unit L2 having a positive refractive power, and the third lens unit L3 having a positive refractive power. The fourth lens unit L4 has a positive refractive power, the fifth lens unit L5 has a positive refractive power, and the sixth lens unit L6 has a positive refractive power. As a group configuration of each lens group, the lens unit having the negative refractive power is arranged on the most magnification conjugate side, and it is necessary to arrange a glass block such as a color synthesis prism by adopting a retro focus configuration as a whole. In order to obtain a long back focus, the lens unit having a positive refractive power on the reduction conjugate side is arranged to be telecentric with respect to the reduction conjugate surface (liquid crystal panel surface).

  The lens configuration in each lens group is as follows.

  The first lens unit L1 includes, in order from the magnification conjugate side to the reduction conjugate side, a biconvex eleventh lens having a positive refractive power, a meniscus negative twelfth lens having a convex meniscus shape on the magnification conjugate side, It consists of a concave negative refractive power thirteenth lens. The eleventh lens is used to correct distortion at a position where the most off-axis light beam passes. The twelfth lens has the above shape in order to reduce coma and astigmatism generated in the first lens unit L1. The thirteenth lens is arranged to jump up the light incident on the thirteenth lens and obtain a long back focus.

  The second lens unit L2 is composed of one of a biconvex 21st lens having a positive refractive power. The twenty-first lens functions to cancel spherical aberration and distortion occurring in the first lens unit L1.

  The third lens unit L3 includes, in order from the magnification conjugate side to the reduction conjugate side, a 31st lens having a positive refractive power, a meniscus-shaped negative 32nd lens having a convex surface on the reduction conjugate side, It consists of a cemented lens 31 that is cemented. The cemented lens 31 cancels the field curvature (Petzbar sum) that occurs in the first lens unit L1 and the second lens unit L2.

  The fourth lens unit L4 includes one of the forty-first lenses having a positive refractive power whose convex surface is convex. The forty-first lens has a lens shape that reduces spherical aberration generated in the fourth lens unit L4.

  The fifth lens unit L5 includes, in order from the magnification conjugate side to the reduction conjugate side, a negative refractive power 51st lens having a convex meniscus surface on the magnification conjugate side, and a 52nd lens having a strong negative refractive power on the magnification conjugate side. The lens is composed of a 53rd lens having a strong positive refractive power on the reduction conjugate side and a 54th lens having a strong positive refractive power on the reduction conjugate side, and the 52nd lens group and the 53rd lens are cemented. The 51st lens located closest to the magnification conjugate side in the fifth lens unit L5 serves to cancel coma and astigmatism generated from the second lens unit L2 to the fourth lens unit L4. The 52nd lens constituting the cemented lens 52 made up of the 53rd lens jumps up the light ray incident on the 52nd lens and obtains a long back focus. It is arranged to make it telecentric with respect to the surface (liquid crystal panel surface).

  The cemented lens 52 has a function of canceling out spherical aberration generated in the third lens group L3 and the fourth lens group L4.

  The sixth lens unit L6 includes one lens of the 61st lens having strong positive refractive power on the magnification conjugate side. The 61st lens has a function of canceling the distortion generated in the third lens unit L3 to the fifth lens unit L5.

  In Example 2 of FIG. 5, the lens configurations of the first to fifth lens groups are the same as those of Example 1 of FIG. In Example 2, a diffractive optical element is introduced into the sixth lens unit L6. The lens configuration in each lens group is substantially the same as that of Example 1 in FIG. 1, but the sixth lens group L6 is provided with a laminated diffractive optical element DOE in the sixth lens group L6. Is different from that of the cemented lens 61a. At this time, the laminated diffractive optical element DOE is provided on the cemented surface of the cemented lens 61a. By introducing the laminated diffractive optical element DOE, the overall length of the lens is reduced and various aberrations, particularly lateral chromatic aberration, are corrected more satisfactorily than in Example 1 of FIG.

  In Example 3 of FIG. 9, in order from the magnification conjugate side to the reduction conjugate side, the first lens unit L1 having a negative refractive power, the second lens unit L2 having a positive refractive power, and the third lens unit L3 having a positive refractive power. The fourth lens unit L4 has a positive refractive power, the fifth lens unit L5 has a negative refractive power, and the sixth lens unit L6 has a positive refractive power.

  The lens configuration in each lens group is as follows.

  The lens configurations in the first lens unit L1 and the sixth lens unit L6 are the same as those in Example 1 in FIG. 1, and the functions of the respective lenses are substantially the same.

  The second lens unit L2 includes, in order from the magnification conjugate side to the reduction conjugate side, a 21st lens having a negative refractive power and a 22nd lens having a strong positive refractive power on the reduction conjugate side.

  By providing an air lens between the 21st lens and the 22nd lens, spherical aberration and astigmatism occurring in the second lens unit L2 are suppressed.

  The third lens unit L3 is composed of one lens of the 31st lens having a strong positive refractive power on the magnification conjugate side. The thirty-first lens functions to cancel spherical aberration and distortion occurring in the first lens unit L1.

  The fourth lens unit L4 includes one forty-first lens having strong positive refractive power on the magnification conjugate side. The 41st lens has a function of canceling the distortion occurring in the second lens unit L2.

  The fifth lens unit L5 includes, in order from the magnification conjugate side to the reduction conjugate side, a 51st lens with strong negative refractive power on the reduction conjugate side, a 52nd lens with strong negative refractive power on the enlargement conjugate side, and a strong positive on the reduction conjugate side. The 53rd lens having a refractive power of 50% and the 54th lens having a strong positive refractive power on the reduction conjugate side, and the 52nd lens and the 53rd lens are composed of a cemented lens 52 which is cemented.

  Among these lenses, the 51st lens functions to cancel astigmatism occurring in the first lens group L1 to the fourth lens group L4, and the 52nd lens constituting the cemented lens 52 is the 51st lens. This is used to jump up the light incident on the lens and obtain a long back focus. The 54th lens is arranged to make the light beam telecentric with respect to the reduction conjugate surface (liquid crystal panel LCD surface). The cemented lens 52 has a function of canceling out spherical aberration generated in the fourth lens unit L4.

  In Example 4 of FIG. 13, the lens configuration of the first to fifth lens groups is the same as that of Example 3 of FIG. 9. In Example 4, a diffractive optical element is introduced into the sixth lens unit L6. The lens configuration in each lens group is substantially the same as that of Example 3 in FIG. 9, but a laminated diffractive optical element is provided in the sixth lens group L6. A cemented lens 61b is used. At this time, the laminated diffractive optical element is provided on the cemented surface of the cemented lens 61b. By introducing the laminated diffractive optical element, the refractive power of each lens group is suppressed as a whole, the total lens length is reduced compared to Example 3 in FIG. 9, and various aberrations, particularly lateral chromatic aberration, are further increased. Corrected well.

  As the structure of the diffractive optical element used in Example 2 and Example 4, for example, a single-layer structure having a single kinoform shape shown in FIG. 17 or a different grating thickness (or the same as shown in FIG. 18). (B) A layered structure in which two layers are stacked is applicable.

  FIG. 19 shows the wavelength dependence of the diffraction efficiency of the first-order diffracted light of the diffractive optical element 101 shown in FIG. As shown in FIG. 17, the actual configuration of the diffractive optical element 101 is a grating in which an ultraviolet curable resin is applied to the surface of the base material 102, and the diffraction efficiency of the first-order diffracted light is 100% at a wavelength of 550 nm. A diffraction grating 103 having a thickness d is formed.

  As is clear from FIG. 19, the diffraction efficiency of the designed order decreases with increasing distance from the optimized wavelength of 550 nm, while the diffraction efficiency of the 0th order diffracted light and the second order diffracted light near the designed order (first order) increases. Yes. An increase in the diffracted light other than the design order becomes a flare, leading to a decrease in the resolution of the optical system (zoom lens).

FIG. 20 shows the wavelength dependence characteristics of the laminated diffractive optical element in which the two diffraction gratings 104 and 105 shown in FIG. 18 are laminated. In FIG. 18, a first diffraction grating 104 made of an ultraviolet curable resin (refractive index nd = 1.499, Abbe number vd = 54) is formed on a substrate 102, and another ultraviolet curable resin (refractive index) is formed thereon. The second diffraction grating 105 having nd = 1.598 and Abbe number vd = 28) is formed. In this combination of materials, the grating thickness d1 of the first diffraction grating 104 is d1 = 13.8 μm, and the grating thickness d2 of the second diffraction grating 105 is d2 = 10.5 μm. As can be seen from FIG. 20, by using a diffractive optical element having a laminated structure, the diffraction efficiency of the designed order has a high diffraction efficiency of 95% or more over the entire operating wavelength range.

  The diffractive optical element applicable to the present invention is not limited to ultraviolet curable resin, and other plastic materials can be used. Depending on the base material, the first diffraction grating portion 104 may be directly attached to the lens surface. You may form in. Further, each lattice thickness is not necessarily required, and two lattice thicknesses can be made equal as shown in FIG. In this case, since the grating shape is not formed on the surface of the diffractive optical element 101, it is excellent in dustproofness, the assembling workability of the diffractive optical element is improved, and a cheaper optical system can be provided.

  Furthermore, in the laminated diffractive optical element, in order to expand the selectivity of two resin materials to be used and improve the optical characteristics, it is preferable to sandwich an air layer between the resin layers as shown in FIG. In FIG. 22, a first diffraction grating 107 made of an ultraviolet curable resin (refractive index nd = 1.635, Abbe number νd = 22.1) is formed on the base material 102. The second diffraction grating 106 made of another ultraviolet-curing resin (refractive index nd = 1.513, Abbe number νd = 50.0) is placed at a position spaced apart by about 1.5 μm between the crests of the saw. This is a diffractive optical element 101 having a laminated structure formed by sandwiching layers. In the case of the laminated diffractive optical element 101 of FIG. 22, high diffraction efficiency can be obtained in the entire wavelength region as shown in FIG. In this combination of materials, the grating thickness d1 of the first diffraction grating 107 is d1 = 6.8 μm, and the grating thickness d2 of the second diffraction grating 106 is d2 = 9.5 μm.

  As described above, the structure of the diffractive optical element used in Example 2 and Example 4 is a laminated diffractive optical element in which an air layer is provided between two resin layers as shown in FIG. Higher optical performance can be obtained.

  The shape ψ of the diffractive optical element 101 used in Examples 2 and 4 is expressed by the following equation.

  Here, H is the height in the direction perpendicular to the optical axis, m is the design order (here, m = 1), λ0 is the design wavelength (here, wavelength 550 nm), and Ci is the phase coefficient (i = 1, 2). , 3... As apparent from the above equation (a), the phase is adjusted by the distance H from the optical axis. The larger the lens diameter (lens effective diameter), the greater the influence of higher order coefficients. Further, the refractive power φD of the diffractive optical element with respect to an arbitrary wavelength λ and a design order m (here, m = 1st order) can be expressed as follows using the lowest-order phase coefficient C1.

  Further, in Example 2 and Example 4, when the diffractive optical element is introduced into a position that satisfies the following conditions as a position in the optical system, chromatic aberration can be corrected well.

  Here, in examining the position where the diffractive optical element is introduced, in order to easily handle the problem, the paraxial arrangement in which the optical system is composed of a thin single lens as shown in FIGS. Let's consider using. FIG. 24A shows a case where the diffractive optical element D is arranged on the enlargement conjugate side from the stop SP, and FIG. 24B shows a case where the diffractive optical element D is arranged on the reduction conjugate side from the stop SP. ing. In each figure, M represents a part of the refractive optical system constituting the optical system, D represents a diffractive optical element, P represents a paraxial ray, Q represents a pupil paraxial ray, and IP represents an image plane. ing.

  In an optical arrangement consisting of a refractive optical system (thin single lens) and a diffractive optical element (FIGS. 24A and 24B), the axial chromatic aberration coefficient (L) and lateral chromatic aberration coefficient (T) of this optical system are as follows: It is expressed as follows.

However,
φM: refractive power of the refractive optical system part (thin single lens) constituting the optical system.
φD: Refractive power (power) for diffracted light of the design order of the diffractive optical element.
νm: Abbe number of the refractive optical system part (thin single lens) constituting the optical system.
νD: conversion Abbe number of the diffractive optical element. (Equivalent to -3.45)
hM: height of a paraxial axial ray incident on a refractive optical system part (thin single lens) constituting the optical system.
hD: height of a paraxial axial ray incident on the diffractive optical element.

Respectively.

  Further, the following relational expressions are established between the chromatic aberration coefficients of the longitudinal chromatic aberration coefficient (L) and the lateral chromatic aberration coefficient (T) and the chromatic aberrations of the longitudinal chromatic aberration and the lateral chromatic aberration.

Here, ω represents the half angle of view of each ray.
In general, the chromatic aberration of the refractive optical system for projection used in a liquid crystal projector or the like tends to occur on the positive side in both axial and lateral chromatic aberrations. Both the lateral chromatic aberration coefficients are negative values from the equation (e). That is, in the expressions (c) and (d),

It becomes.

  In order to correct on-axis and lateral chromatic aberration generated in the refractive optical system, when considering the level of the third-order aberration coefficient, the chromatic aberration coefficients L and T of the entire optical system including the refractive optical system and the diffractive optical element are considered. It suffices if the values of (Equations (c) and (d)) approach 0 respectively. From the above, considering that the axial chromatic aberration coefficient and the lateral chromatic aberration coefficient of the refractive optical system part are negative values (equation (f)), and considering the above expressions (c) and (d), the entire system (refractive optical system) In order to bring the values of the chromatic aberration coefficients L and T of the (part + diffractive optical element) close to 0, both the axial chromatic aberration coefficient and the lateral chromatic aberration coefficient of the diffractive optical element may be set to positive values. That is, in the expressions (c) and (d),

If a diffractive optical element is introduced at a position satisfying the above expression (g) at the same time, axial and lateral chromatic aberration can be corrected simultaneously.

  Here, let us consider a case where the diffractive optical element D is arranged on the enlargement conjugate side with respect to the stop SP as shown in FIG. At this time, at the position of the diffractive optical element D,

Therefore, there is no refractive power φD of the diffractive optical element that satisfies the above two expressions (g) at the same time. This means that if a diffractive optical element is placed at this position, either chromatic aberration of longitudinal or lateral chromatic aberration is in the direction of correction, but the other chromatic aberration is in the direction of increasing. Therefore, since it is impossible to correct both chromatic aberrations simultaneously, it is not preferable to dispose the diffractive optical element D closer to the magnification conjugate side than the stop SP.

  On the other hand, when the case where the diffractive optical element D is arranged on the reduction conjugate side with respect to the stop SP as shown in FIG.

It becomes. At this time, there is a refractive power φD of the diffractive optical element that satisfies the above two formulas (g) at the same time, and is in a direction to simultaneously correct the longitudinal chromatic aberration and the lateral chromatic aberration. Therefore, it is preferable to dispose the diffractive optical element D closer to the reduction conjugate side than the stop SP.

  When the above is made to correspond to each embodiment of the present invention, both the embodiment 2 and the embodiment 4 are lenses on the reduction conjugate side with respect to the stop SP between the third lens unit L3 and the fourth lens unit L4. If a diffractive optical element is introduced into at least one of the fourth lens group L4, the fifth lens group L5, or the sixth lens group L6, the chromatic aberration of both axial chromatic aberration and lateral chromatic aberration can be simultaneously obtained. It is in the direction of correction, which is preferable. Among them, the surface on which the diffractive optical element is provided is more effective in correcting chromatic aberration if it is arranged at a portion where the height from the optical axis of the paraxial axial ray and the pupil paraxial ray is as high as possible ( (From the formulas (c) and (g) and FIG. 201 (b)), it is preferable to provide the lens group as close to the reduction conjugate side as possible, and the outermost lens surface is affected by the influence of dust and heat from the light source. Considering that it is better to avoid it as much as possible, it is particularly preferable to introduce it to the cemented surface in the sixth lens unit L6.

  Furthermore, as the surface on which the diffractive optical element is provided, if the axial ray and off-axis ray passing through each optical system have a difference in angle with respect to the normal direction at each ray incident position, the diffraction efficiency may deteriorate. Because of concern, it is more preferable to set the lens surface as concentric as possible with respect to on-axis rays and off-axis rays.

  These diffractive optical elements are provided on an optical surface, but their base may be a spherical surface, a flat surface, an aspherical surface, or a quadratic surface. Further, it may be formed by a method (so-called replica aspherical surface) in which a film such as plastic is attached to the optical surfaces as the diffractive optical surface.

  As a manufacturing method of the diffractive optical element in this embodiment, in addition to a method of directly forming a binary optics shape on the lens surface with a photoresist, a method of performing replica molding or molding using a mold created by this method is applicable. is there. In addition, if a saw-shaped kinoform is used, the diffraction efficiency increases, and a diffraction efficiency close to the ideal value can be expected.

  In Example 2 and Example 4, by using the diffractive optical element configured as described above, an optical system (zoom lens) in which various aberrations, in particular chromatic aberration, are sufficiently corrected and the total lens length is shortened is realized. Yes.

  Numerical examples 1 to 4 corresponding to the numerical data of the projection zoom lenses according to the first to fourth embodiments will be described below. In each numerical example, i indicates the order of the optical surfaces from the enlargement conjugate side to the reduction conjugate side, ri is the radius of curvature of the i-th optical surface (i-th surface), and di is the i-th surface and the i + 1-th surface. , Ni and νi represent the refractive index and Abbe number of the material of the i-th optical member with respect to the d-line, respectively. f is a focal length, and Fno is an F number.

  In addition, the two surfaces on the reduction conjugate side of Numerical Examples 1 and 2 and the four rearmost surfaces of Numerical Examples 3 and 4 are glass blocks GB corresponding to color separation prisms, face plates, various filters, and the like. It is a surface to compose.

  C1, C2, and C3 are phase coefficients in the equation (a).

  Table 1 shows the relationship between the above-described conditional expressions 1 to 4 and various numerical values in the numerical examples 1 to 4.

  FIG. 25 is a schematic view of the essential portions of an embodiment using the projection zoom lens of the present invention.

  In the figure, the projection zoom lens described above is applied to a three-plate color liquid crystal projector, and image information of a plurality of color lights based on a plurality of liquid crystal display elements is synthesized through a color synthesis unit, and the projection zoom lens is used on the screen surface. Fig. 2 shows an image projection apparatus for enlarging and projecting. In FIG. 25, the color liquid crystal projector 1 synthesizes each color light of RGB from the three liquid crystal panels 5B, 5G, and 5R, R, G, and B into one optical path by the prism 2 as a color synthesizing unit. The image is projected on the screen 4 using a projection lens 3 made of a lens.

  FIG. 26 is a schematic view of the essential portions of an embodiment of an optical apparatus using the zoom lens of the present invention. In this embodiment, an example in which the above-described zoom lens is used as an imaging lens in an optical apparatus including an imaging apparatus such as a video camera, a film camera, or a digital camera is shown.

  In FIG. 26, an image of the subject 9 is formed on the photoconductor 7 by the photographing lens 8 to obtain image information.

Cross-sectional view of a lens according to Example 1 of the present invention Aberration diagram at the wide-angle end when the object distance is 2.8 m when the zoom lens of Numerical Example 1 is expressed in mm. Aberration diagram at the intermediate focal length when the object distance is 2.8 m when the zoom lens of Numerical Example 1 is expressed in mm. Aberration diagram at the telephoto end when the object distance is 2.8 m when the zoom lens of Numerical Example 1 is expressed in mm. Lens sectional drawing of Example 2 of the present invention Aberration diagram at the wide-angle end when the object distance is 2.8 m when the zoom lens of Numerical Example 2 is expressed in mm. Aberration diagram at the intermediate focal length when the object distance is 2.8 m when the zoom lens of Numerical Example 2 is expressed in mm. Aberration diagram at the telephoto end when the object distance is 2.8 m when the zoom lens of Numerical Example 2 is expressed in mm. Lens sectional view of Example 3 of the present invention Aberration diagram at the wide-angle end when the object distance is 2.8 m when the zoom lens of Numerical Example 3 is expressed in mm. Aberration diagram at the intermediate focal length when the object distance is 2.8 m when the zoom lens of Numerical Example 3 is expressed in mm. Aberration diagram at the telephoto end when the object distance is 2.8 m when the zoom lens of Numerical Example 3 is expressed in mm. Lens sectional view of Example 4 of the present invention Aberration diagram at the wide-angle end when the object distance is 2.8 m when the zoom lens of Numerical Example 4 is expressed in mm. Aberration diagram at the intermediate focal length when the object distance is 2.8 m when the zoom lens of Numerical Example 4 is expressed in mm. Aberration diagram at the telephoto end when the object distance is 2.8 m when the zoom lens of Numerical Example 4 is expressed in mm. Explanatory drawing of the diffractive optical element according to the present invention Explanatory drawing of the diffractive optical element according to the present invention Explanatory drawing of the diffraction efficiency wavelength dependence characteristic of the diffractive optical element according to the present invention Explanatory drawing of the diffraction efficiency wavelength dependence characteristic of the diffractive optical element according to the present invention Explanatory drawing of the diffractive optical element according to the present invention Explanatory drawing of the diffractive optical element according to the present invention Explanatory drawing of the diffraction efficiency wavelength dependence characteristic of the diffractive optical element according to the present invention Arrangement diagram of paraxial refractive power for explaining the optical action of the optical system of the present invention Schematic of an image projection apparatus using the zoom lens of the present invention Schematic of an optical apparatus using the zoom lens of the present invention

Explanation of symbols

L1 1st lens group L2 2nd lens group L3 3rd lens group L4 4th lens group L5 5th lens group L6 6th lens group LCD Liquid crystal display device (image surface)
GB glass block (color synthesis prism)
ΔS Sagittal image plane tilt ΔM Commercial image plane tilt 1 Liquid crystal projector 2 Color synthesis means 3 Projection lens 4 Screen 5 (5B, 5G, 5R) Liquid crystal panel 6 Imaging device 7 Imaging means 8 Zoom lens 9 Subject 101 Diffractive optical element 103 ~ 107 Diffraction grating

Claims (9)

In order from the magnification conjugate side to the reduction conjugate side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, a third lens group having a positive refractive power, a fourth lens group having a positive refractive power, A fifth lens group having a positive or negative refractive power and a sixth lens group having a positive refractive power;
At the time of zooming from the wide angle end to the telephoto end, at least three of the lens groups are moved from the reduction conjugate side to the enlargement conjugate side,
When the focal length of the entire system at the wide angle end is fw and the focal length of the fifth lens group is f5,
-0.5 <fw / f5 <0.2
Projection zoom lens characterized by satisfying The fourth lens group is composed of a single lens having a positive refractive power, and when zooming from the wide-angle end to the telephoto end, the fourth lens group moves from the reduction conjugate side to the enlargement conjugate side. Is M4, and the focal length of the fourth lens group is f4.
0.01 <| M4 / f4 | <0.20
The projection zoom lens according to claim 1, wherein: The fifth lens group in order from the magnification conjugate side to the reduction conjugate side,
A negative 51st lens having a convex meniscus surface on the magnification conjugate side,
A 52nd lens in which the refractive power of the surface on the enlargement conjugate side is stronger than the refractive power of the surface on the reduction conjugate side and has a negative refractive power as a whole;
A 53rd lens in which the refractive power of the surface on the reduction conjugate side is stronger than the refractive power of the surface on the magnification conjugate side, and has a positive refractive power as a whole;
The refractive power of the surface on the reduction conjugate side is stronger than the refractive power of the surface on the magnification conjugate side, and consists of a 54th lens having a positive refractive power as a whole,
3. The projection zoom lens according to claim 1, wherein the 52nd lens group and the 53rd lens are cemented. The first lens group includes, in order from the magnification conjugate side to the reduction conjugate side, a biconvex eleventh lens having a positive refractive power, a meniscus negative twelfth lens having a convex meniscus surface on the magnification conjugate side, An average value of d-line Abbe numbers of positive refractive power lenses in the first lens group is νdlpa, and the negative refractive power is in the first lens group. When the average value of the Abbe number of the d-line of the lens is νdlna,
35 <νdlpa
35 <νdlna <75
The zoom lens for projection according to claim 1, wherein the zoom lens for projection is satisfied. 5. The projection zoom lens according to claim 1, further comprising a stop between the third lens group and the fourth lens group. 6. The projection zoom lens according to claim 1, wherein the projection zoom lens includes at least one diffractive optical element. 7. The projection zoom lens according to claim 6, wherein the diffractive optical element is a single-layer type composed of a single diffraction grating or a laminated type in which a plurality of diffraction gratings are laminated. 7. The projection zoom lens according to claim 6, wherein when the diffractive optical element is a laminated type in which a plurality of diffraction gratings are laminated, the diffraction grating is provided on each of two adjacent optical surfaces. An image display element and the projection zoom lens according to any one of claims 1 to 8 are provided, and an original image displayed on the image display element is projected onto the screen surface using the projection zoom lens. An image projection apparatus characterized by the above.