Zoom lens and image projection apparatus

The present invention relates to a zoom lens suitable for a projection lens of an image projection apparatus.

Projection lenses for image projection apparatuses (projectors) need a high-resolution performance capable of projecting a higher-definition image and a magnification variation (zooming) function capable of arbitrarily controlling a projection image size.

Japanese Patent Laid-Open No. 2003-241094 discloses a projection lens configured to move five lens units to perform variation of magnification.

However, it is difficult for conventional projection lenses including the one disclosed in Japanese Patent Laid-Open No. 2003-241094 to provide such a high-resolution performance over the entire zoom range from a wide-angle end to a telephoto end.

In other words, their resolution performance significantly changes at the wide-angle end and the telephoto end.

The present invention provides a zoom lens capable of providing a higher-resolution performance over the entire zoom range and provides an image projection apparatus using the zoom lens.

The present invention provides as an aspect thereof a zoom lens including a stop, at least three front side movable lens units that are disposed on an enlargement conjugate side further than the stop and that are movable for variation of magnification, and a front side fixed lens unit that is disposed on the enlargement conjugate side further than the at least three front side movable lens units and that is fixed for the variation of magnification. The at least three front side movable lens units include two lens movable lens units as first front side movable lens units that are movable to the enlargement conjugate side for variation of magnification from a wide-angle end to a telephoto end, and one movable lens unit as a second front side movable lens unit that is disposed on the reduction conjugate side further than the first front side movable lens units and is movable to the reduction conjugate side for the variation of magnification from the wide-angle end to the telephoto end.

The present invention provides as another aspect thereof an image projection apparatus including the above zoom lens as a projection lens.

Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.

FIG. 1 is a sectional view of a zoom lens (projection distance 2050 mm) that is Embodiment 1 of the present invention.

FIG. 2 illustrates aberration diagrams of the zoom lens of Embodiment 1 at its wide-angle end.

FIG. 3 illustrates aberration diagrams of the zoom lens of Embodiment 1 at its telephoto end.

FIG. 4 is a sectional view of a zoom lens (projection distance 2050 mm) that is Embodiment 2 of the present invention.

FIG. 5 illustrates aberration diagrams of the zoom lens of Embodiment 2 at its wide-angle end.

FIG. 6 illustrates aberration diagrams of the zoom lens of Embodiment 2 at its telephoto end.

FIG. 7 is a sectional view of a zoom lens (projection distance 2050 mm) that is Embodiment 3 of the present invention.

FIG. 8 illustrates aberration diagrams of the zoom lens of Embodiment 3 at its wide-angle end.

FIG. 9 illustrates aberration diagrams of the zoom lens of Embodiment 3 at its telephoto end.

FIG. 10 is a sectional view of a zoom lens (projection distance 2050 mm) that is Embodiment 4 of the present invention.

FIG. 11 illustrates aberration diagrams of the zoom lens of Embodiment 4 at its wide-angle end.

FIG. 12 illustrates aberration diagrams of the zoom lens of Embodiment 4 at its telephoto end.

FIG. 13 is a sectional view of a projector using the zoom lens of any one of Embodiments 1 to 4.

Preferred embodiments will be described below with reference to the attached drawings.

First, prior to description of specific embodiments (numerical examples) 1 to 4, with reference to FIG. 1 , description will be made of basic matters common to zoom lenses of the embodiments (denoted by 1 , 21 , 31 and 41 in FIGS. 1, 4, 7 and 10 ).

The zoom lens of each embodiment is used as a projection lens that projects light entering from a reduction conjugate side (light modulation element side) that is the right side in FIG. 1 to an enlargement conjugate side (projection surface side) that is the left side in FIG. 1 . A light modulation element 3 illustrated in FIG. 1 modulates light from a light source (not illustrated) depending on an input image signal. The light modulation element 3 is constituted by a liquid crystal panel, a digital micromirror device and others. An optical block 2 introduces the light from the light modulation element 3 to the projection lens. The optical block 2 is constituted by a prism, a filter and others.

The zoom lens of each embodiment includes, in order from the enlargement conjugate side to the reduction conjugate side, a first lens unit B 1 (denoted by B 21 , B 31 and B 41 in FIGS. 4, 7 and 10 ) to an eighth or seventh lens unit as a final lens unit (denoted by B 8 , B 27 , B 38 and B 48 in FIGS. 1, 4, 7 and 10 ). The zoom lens of each embodiment moves multiple movable lens units (second to seventh lens units B 2 to B 7 in FIG. 1 ) in an optical axis direction of the zoom lens such that distances between mutually adjacent lens units are changed to perform variation of magnification from a wide-angle end to a telephoto end.

The distance between the mutually adjacent lens units is, for example, a distance between the first and second lens units B 1 and B 2 , and a distance between the third and fourth lens units B 3 and B 4 . That is, the distance between the mutually adjacent lens units, which changes with the variation of magnification, is a boundary between these lens units. The change of the distance between the mutually adjacent lens units also includes a change of a distance between lens units fixed and moved for the variation of magnification, such as that between the first and second lens units B 1 and B 2 . Each lens unit (or each lens group) in each embodiment may include multiple lenses or only one lens.

The zoom lens of each embodiment includes an aperture stop (or a stop) ST 1 (ST 2 , ST 3 and ST 4 in FIGS. 4, 7 and 10 ) disposed between the fourth lens unit B 4 (B 24 , B 34 and B 44 in the same figures) and the fifth lens unit B 5 (B 25 , B 35 and B 45 in the same figures). The zoom lens of each embodiment further includes at least three front side movable lens units B 2 to B 4 (B 22 to B 24 , B 32 to B 34 and B 41 to B 44 in FIGS. 4, 7 and 10 ) that are disposed on the enlargement conjugate side (left side in the drawing) further than the aperture stop ST 1 and are movable for the variation of magnification.

Although the number of the front side movable lens units is three or four in each embodiment, the number thereof may be more than four.

The at least three front side movable lens units include first front side movable lens units B 2 and B 3 (B 22 and B 23 , B 32 and B 33 , and B 42 and B 43 in FIGS. 4, 7 and 10 ) that are movable to the enlargement conjugate side for the variation of magnification from the wide-angle end to the telephoto end. The at least three front side movable lens units further include a second front side movable lens unit B 4 (B 24 , B 34 and B 44 in FIGS. 4, 7 and 10 ) that is disposed on the reduction conjugate side further than the first front side movable lens units B 2 and B 3 and is movable to the reduction conjugate side for the variation of magnification from the wide-angle end to the telephoto end. Although the zoom lens of each embodiment includes two first front side movable lens units, it is enough that the zoom lens includes at least one first front side movable lens unit. On the other hand, although the zoom lens of each embodiment includes one second front side movable lens unit, the zoom lens may include two or more second front side movable lens units.

The zoom lenses of Embodiments 1 to 3 (except Embodiment 4) each include a front side fixed lens unit B 1 (B 21 and B 31 in FIGS. 4 and 7 ) that is disposed on the enlargement conjugate side further than the front side movable lens units B 2 to B 4 and is fixed (unmoved) for the variation of magnification. The front side fixed lens unit is a first lens unit disposed at a most-enlargement conjugate side position in Embodiments 1 to 3.

Furthermore, the zoom lens of each embodiment includes at least two rear side movable lens units B 5 to B 7 (B 25 and B 26 , B 35 to B 37 , and B 45 to B 47 in FIGS. 4, 7, and 10 ) that are disposed on the reduction conjugate side further than the aperture stop ST 1 and are movable for the variation of magnification.

Moreover, at least one of the at least three front side movable lens units includes at least one cemented lens (constituted by lenses L 17 and L 18 in FIG. 1 ). This makes it possible to reduce a variation in chromatic aberration of magnification for the variation of magnification.

The zoom lens of each embodiment having the above-described configuration enables providing a high-definition performance (that is, reducing a variation in resolution performance) over the entire zoom range, thereby providing a good optical performance over the entire angle of field.

Next, description will be made of conditions that the zoom lens of each embodiment is desirable to satisfy.

The zoom lens of each embodiment satisfies the following condition expressed by expression (1) to provide a high-resolution performance over the entire zoom range from the wide-angle end to the telephoto end.

−0.6≤φ b/φw< 0  (1)

In expression (1), φw represents a refractive power of the entire zoom lens at the wide-angle end, and φb represents a refractive power of the second front side movable lens unit that is movable to the reduction conjugate side for the variation of magnification from the wide-angle end to the telephoto end. A higher value of φb/φw than the upper limit of expression (1) and a lower value of φb/φw than the lower limit thereof make it impossible to reduce a variation in field curvature for the variation of magnification.

It is more desirable that the zoom lens of each embodiment satisfy the following condition expressed by expression (1)′ having a narrower range than that of expression (1).

−0.4≤φ b/φw≤− 0.2  (1)′

The projector needs a space in which an optical element such as a prism that combines multiple color lights modulated by multiple light modulation elements (such as liquid crystal elements) between these light modulation elements and the projection lens. Therefore, it is necessary that the projection lens has a back focus of a sufficient length. Thus, it is desirable that the zoom lens satisfy the following condition expressed by expression (2).

−0.7≤φ1/ φw≤− 0.1  (2)

In expression (2), φ1 represents a refractive power of the first lens unit (front side fixed lens unit) B 1 . Satisfying this condition enables the zoom lens to have a back focus of a sufficient length over the entire zoom length. It is more desirable that the zoom lens of each embodiment satisfy the following condition expressed by expression (2)′ having a narrower range than that of expression (2).

−0.6≤φ1/φ w≤− 0.2  (2)′

Furthermore, in the zoom lens of each embodiment, a negative refractive power of the second front side movable lens unit B 4 satisfying the following condition expressed by (3) enables providing a good optical performance over the entire zoom range.

−0.2≤φ br 1 /φw≤ 0.3  (3)

In expression (3), φbr1 represents a refractive power of an enlargement conjugate side lens surface R 1 of a most-reduction conjugate side lens of the second front side movable lens unit B 4 .

In each embodiment, the second front side movable lens unit B 4 is constituted by one (single) lens in order to reduce its weight and simplify its configuration, and the lens surface R 1 is an enlargement conjugate side lens surface of that lens. The second front side movable lens unit may include two or more lenses. In this case, the lens surface R 1 is an enlargement conjugate side lens surface of a most-reduction conjugate side lens of the two or more lenses.

A value of φbr1 making a value of φbr1/φw higher than the upper limit of expression (3) excessively corrects distortion aberration of the zoom lens. On the other hand, a value of φbr1 making the value of φbr1/φw lower than the lower limit of expression (3) insufficiently corrects the distortion aberration. That is, these values of φbr1 make it impossible to provide a good optical performance.

It is more desirable that the zoom lens of each embodiment satisfy the following condition expressed by expression (3)′ having a narrower range than that of expression (3).

−0.1≤φ br 1 /φw≤ 0  (3)′

Satisfying the above-described conditions of expressions (1) to (3) enables providing a zoom lens having a high-resolution performance over the entire zoom range and a telecentric zoom lens having a good optical performance over the entire angle of field.

Although in each embodiment the second lens unit B 2 is also constituted by one lens in order to reduce its weight and simplify its configuration, the second lens unit B 2 may be constituted by two or more lenses.

Although the zoom lens of each embodiment includes the aperture stop as a physical aperture stop, such a physical aperture stop is not necessarily needed to be provided. When the physical aperture stop is not provided, the position of the aperture stop may be defined as a position at which off-axis principal rays intersect with an optical axis of the zoom lens. Even when the physical aperture stop is provided, this physical aperture stop is not necessarily to be an aperture stop device and may be a member such as a barrel member housing the zoom lens.

Description will be made of Embodiment 1 (Numerical example 1). FIG. 1 is a sectional view of a projection lens (whose projection distance 2050 mm) 60 using the zoom lens of Embodiment 1. The zoom lens 1 includes the following first to eighth lens units B 1 to B 8 disposed in order from the enlargement conjugate side to the reduction conjugate side.

The first lens unit B 1 has a negative refractive power and is fixed for the variation of magnification. The second lens unit B 2 has a positive refractive power and is moved for the variation of magnification. The third lens unit B 3 has a positive refractive power and is moved for the variation of magnification. The fourth lens unit B 4 has a negative refractive power and is moved for the variation of magnification. The fifth lens unit B 5 has a positive refractive power and is moved for the variation of magnification. The sixth lens unit B 6 has a positive refractive power and is moved for the variation of magnification. The seventh lens unit B 7 has a positive refractive power and is moved for the variation of magnification. The eighth lens unit B 8 has a positive refractive power and is fixed for the variation of magnification.

The aperture stop ST 1 is disposed on the enlargement conjugate side further than the fifth lens unit B 5 and is moved for the variation of magnification together with the fifth lens unit B 5 .

The first lens unit B 1 is constituted by five lenses L 11 to L 15 that are negative, negative, negative, negative and positive lenses disposed in order from the enlargement conjugate side. The second lens unit B 2 is constituted by one positive lens L 16 . The third lens unit B 3 is constituted by two lenses L 17 and L 18 that are positive and negative lenses disposed in order from the enlargement conjugate side. The fourth lens unit B 4 is constituted by one negative lens L 19 . The fifth lens unit B 5 is constituted by two lenses L 20 and L 21 that are negative and positive lenses disposed in order from the enlargement conjugate side. The sixth lens unit B 6 is constituted by four lenses L 22 to L 25 that are negative, positive, positive and negative lenses disposed in order from the enlargement conjugate side. The seventh lens unit B 7 is constituted by two lenses L 26 and L 27 that are positive and negative lenses disposed in order from the enlargement conjugate side. The eighth lens unit B 8 is constituted by one positive lens L 28 .

The zoom lens 1 of this embodiment satisfies the above-described conditions of expressions (1) to (3). The values of expressions (1) to (3) are shown in Table 1(C).

FIG. 13 illustrates a configuration of a liquid crystal projector using the projection lens of this embodiment (or of the other embodiments described later).

Light as white non-polarized light emitted from a light source 51 is converted by an illumination optical system 52 into linearly-polarized light having a specific polarization direction. The white linearly-polarized light subjected to optical actions of the illumination optical system 52 illuminates evenly each of three liquid crystal elements 57 , 58 and 59 . The white linearly-polarized light exiting from the illumination optical system 52 is separated by a dichroic mirror 53 and a first polarization beam splitter 55 into a red (R) light, a green (G) light and a blue (B) light. The R light, the G light and the B light are respectively introduced to the liquid crystal elements 57 , 58 and 59 for R, G and B. The R light, the G light and the B light respectively modulated by the liquid crystal elements 57 , 58 and 59 are combined by a second polarization beam splitter 54 and a color combining prism 56 to be introduced to the projection lens 60 . The combined light is projected through the projection lens 60 onto a screen 61 . The projection lens 60 is the zoom lens 1 described in this embodiment (or any one of the zoom lenses 21 , 31 and 41 described later in the other embodiments) held by a lens barrel 60 a.

The screen 61 may have a planar surface or a curved surface such as a concave surface and a convex surface.

FIG. 2 and FIG. 3 respectively illustrate spherical aberrations (for a d-line), astigmatisms (S indicates a sagittal plane, and T indicates a tangential plane) and distortions (for the d-line) that are longitudinal aberrations of the projection lens 60 (whose projection distance is 2050 mm) of Numerical example 1 at the wide-angle end and the telephoto end.

FIG. 4 is a sectional view of a projection lens (whose projection distance 2050 mm) using the zoom lens 21 of Embodiment 2 (Numerical example 2).

The zoom lens 21 includes the following first to seventh lens units B 21 to B 27 disposed in order from the enlargement conjugate side to the reduction conjugate side. This embodiment includes two rear side movable lens units whose number is smaller than that of Embodiment 1.

The first lens unit B 21 has a negative refractive power and is fixed for the variation of magnification. The second lens unit B 22 has a positive refractive power and is moved for the variation of magnification. The third lens unit B 23 has a positive refractive power and is moved for the variation of magnification. The fourth lens unit B 24 has a negative refractive power and is moved for the variation of magnification. The fifth lens unit B 25 has a positive refractive power and is moved for the variation of magnification. The sixth lens unit B 26 has a positive refractive power and is moved for the variation of magnification. The seventh lens unit B 27 has a positive refractive power and is fixed for the variation of magnification. This embodiment has a configuration corresponding to a case where the fifth and sixth lens units B 5 and B 6 in Embodiment 1 are integrally moved as the fifth lens unit B 25 .

The aperture stop ST 2 is disposed on the enlargement conjugate side further than the fifth lens unit B 25 and is moved for the variation of magnification together with the fifth lens unit B 25 . The aperture stop ST 2 and the fifth lens unit B 25 may be moved independently from each other.

The first lens unit B 21 is constituted by five lenses L 31 to L 35 that are negative, negative, negative, negative and positive lenses disposed in order from the enlargement conjugate side. The second lens unit B 22 is constituted by one positive lens L 36 . The third lens unit B 23 is constituted by two lenses L 37 and L 38 that are positive and negative lenses disposed in order from the enlargement conjugate side. The fourth lens unit B 24 is constituted by one negative lens L 39 . The fifth lens unit B 25 is constituted by six lenses L 40 to L 45 that are negative, positive, negative, positive, positive and negative lenses disposed in order from the enlargement conjugate side. The sixth lens unit B 26 is constituted by two lenses L 46 and L 47 that are positive and negative lenses disposed in order from the enlargement conjugate side. The seventh lens unit B 27 is constituted by one positive lens L 48 .

The zoom lens 21 of this embodiment satisfies the above-described conditions of expressions (1) to (3). The values of expressions (1) to (3) are shown in Table 2(C).

FIG. 5 and FIG. 6 respectively illustrate spherical aberrations (for the d-line), astigmatisms (S indicates the sagittal plane, and T indicates the tangential plane) and distortions (for the d-line) that are longitudinal aberrations of the projection lens (whose projection distance is 2050 mm) of Numerical example 2 at the wide-angle end and the telephoto end.

FIG. 7 is a sectional view of a projection lens (whose projection distance 2050 mm) using the zoom lens 31 of Embodiment 3 (Numerical example 3). The zoom lens 31 includes the following first to eighth lens units B 31 to B 38 disposed in order from the enlargement conjugate side to the reduction conjugate side.

In this embodiment, the aperture stop ST 3 is moved independently from the other movable lens units.

The first lens unit B 31 has a negative refractive power and is fixed for the variation of magnification. The second lens unit B 32 has a positive refractive power and is moved for the variation of magnification. The third lens unit B 33 has a positive refractive power and is moved for the variation of magnification. The fourth lens unit B 34 has a negative refractive power and is moved for the variation of magnification. The fifth lens unit B 35 has a positive refractive power and is moved for the variation of magnification. The sixth lens unit B 36 has a positive refractive power and is moved for the variation of magnification. The seventh lens unit B 37 has a positive refractive power and is moved for the variation of magnification. The eighth lens unit B 38 has a positive refractive power and is fixed for the variation of magnification.

The aperture stop ST 3 is moved for the variation of magnification between the fourth lens unit B 34 and the fifth lens unit B 35 in the same direction as that of the fifth lens unit B 35 by a movement amount different from that of the fifth lens unit B 35 .

The first lens unit B 31 is constituted by five lenses L 51 to L 55 that are negative, negative, negative, negative and positive lenses disposed in order from the enlargement conjugate side. The second lens unit B 32 is constituted by one positive lens L 56 . The third lens unit B 33 is constituted by two lenses L 57 and L 58 that are positive and negative lenses disposed in order from the enlargement conjugate side. The fourth lens unit B 34 is constituted by one negative lens L 59 . The fifth lens unit B 35 is constituted by two lenses L 60 and L 61 that are negative and positive lenses disposed in order from the enlargement conjugate side. The sixth lens unit B 36 is constituted by four lenses L 62 to L 65 that are negative, positive, positive and negative lenses disposed in order from the enlargement conjugate side. The seventh lens unit B 37 is constituted by two lenses L 66 and L 67 that are positive and negative lenses disposed in order from the enlargement conjugate side. The eighth lens unit B 38 is constituted by one positive lens L 68 .

The zoom lens 31 of this embodiment satisfies the above-described conditions of expressions (1) to (3). The values of expressions (1) to (3) are shown in Table 3(C).

FIG. 8 and FIG. 9 respectively illustrate spherical aberrations (for the d-line), astigmatisms (S indicates the sagittal plane, and T indicates the tangential plane) and distortions (for the d-line) that are longitudinal aberrations of the projection lens (whose projection distance is 2050 mm) of Numerical example 3 at the wide-angle end and the telephoto end.

FIG. 10 is a sectional view of a projection lens (whose projection distance 2050 mm) using the zoom lens 41 of Embodiment 4 (Numerical example 4). The zoom lens 41 includes the following first to eighth lens units B 41 to B 48 disposed in order from the enlargement conjugate side to the reduction conjugate side. In this embodiment, the first to fourth lens units B 41 to B 44 that are the front side movable lens units are included on the enlargement conjugate side further than the aperture stop ST 4 .

The first lens unit B 41 has a negative refractive power and is moved for the variation of magnification. The second lens unit B 42 has a positive refractive power and is moved for the variation of magnification. The third lens unit B 43 has a positive refractive power and is moved for the variation of magnification. The fourth lens unit B 44 has a negative refractive power and is moved for the variation of magnification. The fifth lens unit B 45 has a positive refractive power and is moved for the variation of magnification. The sixth lens unit B 46 has a positive refractive power and is moved for the variation of magnification. The seventh lens unit B 47 has a positive refractive power and is moved for the variation of magnification. The eighth lens unit B 48 has a positive refractive power and is fixed for the variation of magnification.

The aperture stop ST 4 is disposed on the enlargement conjugate side further than the fifth lens unit B 45 and is moved for the variation of magnification together with the fifth lens unit B 45 .

The first lens unit B 41 is constituted by five lenses L 71 to L 75 that are negative, negative, negative, negative and positive lenses disposed in order from the enlargement conjugate side. The second lens unit B 42 is constituted by one positive lens L 76 . The third lens unit B 43 is constituted by two lenses L 77 and L 78 that are positive and negative lenses disposed in order from the enlargement conjugate side. The fourth lens unit B 44 is constituted by one negative lens L 79 . The fifth lens unit B 45 is constituted by two lenses L 80 and L 81 that are negative and positive lenses disposed in order from the enlargement conjugate side. The sixth lens unit B 46 is constituted by four lenses L 82 to L 85 that are negative, positive, positive and negative lenses disposed in order from the enlargement conjugate side. The seventh lens unit B 47 is constituted by two lenses L 86 and L 87 that are positive and negative lenses disposed in order from the enlargement conjugate side. The eighth lens unit B 48 is constituted by one positive lens L 88 .

The zoom lens 41 of this embodiment satisfies the above-described conditions of expressions (1) to (3). The values of expressions (1) to (3) are shown in Table 4(C).

FIG. 11 and FIG. 12 respectively illustrate spherical aberrations (for the d-line), astigmatisms (S indicates the sagittal plane, and T indicates the tangential plane) and distortions (for the d-line) that are longitudinal aberrations of the projection lens (whose projection distance is 2050 mm) of Numerical example 4 at the wide-angle end and the telephoto end

In the following Tables 1 to 4, (A) shows a lens configuration, f represents a focal length, and F represents an aperture ratio.

Furthermore, ri represents a curvature radius (mm) of an i-th surface counted from the enlargement conjugate side, di represents a distance (mm) between the i-th surface and a (i+1)-th surface, ni and vi respectively represent a refractive index and abbe number of an i-th optical member counted from the enlargement conjugate side for the d-line, and ST represents a position of the aperture stop.

A surface to which “*” is added on its left side has an aspheric surface expressed by the following function. In the following Tables 1 to 4, (B) shows aspheric coefficients A to G. Moreover, y represents a coordinate in a lens radial direction, z represents a coordinate in the optical axis direction, k represents a conic coefficient, and “e-X” represents “×10 −X ”.

z ( y )=( y 2 /ri )/{1+[1−(1+ k )( y 2 /ri 2 )] 1/2 }+Ay 4 +By 6 +Cy 8 +Dy 10 +Ey 12 +Fy 14 +Gy 16

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

This application claims the benefit of Japanese Patent Application No. 2017-132431, filed on Jul. 6, 2017, which is hereby incorporated by reference herein in its entirety.