JP2007248840A - Zoom lens and projector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compact zoom lens having a variable power ratio larger than 1.3 times and a projector using the zoom lens. <P>SOLUTION: The zoom lens 1 is constituted so that a first lens group G1 having negative refractive power, a second lens group G2 having positive refractive power, a third lens group G3 having positive refractive power, a fourth lens group G4 having positive refractive power, and a fifth lens group G5 having positive refractive power are arrayed in order from the enlargement side, and when it is defined that the focal distance of the whole lens system on a telescopic end is ft and the focal distance of the whole lens system in a wide-angle end is fw, a conditional formula (1): ft/fw>1.3 is satisfied. In the case of varying power, the first lens group G1 and the fifth lens group G5 are fixed, the second, third and fourth lens groups G2, G3, G4 are moved so as to be located on the enlargement side on the telescopic side from the wide-angle side and lens surfaces constituting each lens group are composed only of spherical surfaces. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a novel zoom lens and projection apparatus. More specifically, the present invention relates to a zoom lens that is relatively small but easily corrected for aberrations, has a large zoom ratio, and can be configured at low cost, and a projection apparatus using the zoom lens.

  In recent projectors, the number of pixels and the resolution have been increased. In particular, the development of the reflective liquid crystal is remarkable as a device capable of realizing both a high contrast and a high aperture ratio as compared with the existing transmissive liquid crystal. However, with the existing technology, there is a new problem that when the reflective liquid crystal is used, the back focus of the lens used for projection must be longer than that using the transmissive liquid crystal. In addition, there is a growing need to change the screen size without moving the projector body, and a projection lens with a high zoom ratio is desired.

  Conventionally, in such a projection type zoom lens, a zoom lens having five groups of negative, positive, positive, positive, and positive, and three groups moving at the time of zooming is described in Patent Document 1 and Patent Document 2. Zoom optical systems and the like have been proposed. Further, Patent Document 3 and Patent Document 4 propose zoom lenses having a negative, positive, positive, positive, and positive five-group configuration in which aberrations are favorably corrected by using an aspheric lens as a constituent lens. Yes.

JP 2001-91829 A JP 2004-20765 A JP 2003-202498 A JP 2004-54021 A

  However, in the zoom lenses described in Patent Document 1 and Patent Document 2, the zoom ratio is only about 1.3, and the zoom ratio is low. There is a limit to changing the screen size without moving the projector.

  In addition, in the zoom lenses described in Patent Document 3 and Patent Document 2, an aspherical lens is adopted, and it is difficult to increase the diameter of the aspherical lens due to molding technology, mold costs, etc. There are problems such as large initial investment.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a zoom lens having a zoom ratio that is small and larger than 1.3 times at low cost.

A zoom lens according to an embodiment of the present invention includes, in order from the magnification 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 refractive power of 5 and a fifth lens group having a positive refractive power are arranged to satisfy the following conditional expression (1), and upon zooming, the first lens group and the fifth lens group The lens group is fixed, and the second lens group, the third lens group, and the fourth lens group move so as to be positioned closer to the enlargement side on the telephoto side than to the wide angle side, and the lens surfaces constituting each lens group Consists only of a spherical surface and satisfies the following conditional expressions (2), (3), and (4).
(1) ft / fw> 1.3
(2) 0.3 <G2t / fw <2.2
(3) 0.3 <G3t / fw <2.2
(4) 0.3 <G4t / fw <2.2
However,
ft: focal length of the entire lens system at the telephoto end fw: focal length of the entire lens system at the wide-angle end G2t: moving distance G3t for zooming from the wide-angle end to the telephoto end of the second lens group: wide-angle of the third lens group Moving distance G4t at the time of zooming from the end to the telephoto end: The moving distance at the time of zooming from the wide angle end to the telephoto end of the fourth lens group.

Further, a projection device according to an embodiment of the present invention includes an image forming unit and a zoom lens that magnifies and projects an image formed by the image forming unit, and the zoom lens performs negative refraction in order from the magnification side. First lens group having power, second lens group having positive refractive power, third lens group having positive refractive power, fourth lens group having positive refractive power, and fifth lens having positive refractive power The first lens group and the fifth lens group are fixed, and the second lens group, the third lens group, and the first lens group are fixed. The four lens groups move so as to be positioned closer to the enlargement side on the telephoto side than on the wide angle side, and the lens surfaces constituting each lens group consist only of spherical surfaces, and the following conditional expressions (2), (3), (4 ) Is satisfied.
(1) ft / fw> 1.3
(2) 0.3 <G2t / fw <2.2
(3) 0.3 <G3t / fw <2.2
(4) 0.3 <G4t / fw <2.2

  In the present invention, a small zoom lens having a zoom ratio of 1.3 times or more and a projection apparatus using the zoom lens can be provided at low cost.

  The best mode for carrying out the zoom lens and the projection apparatus of the present invention will be described below with reference to the drawings.

The zoom lens according to the present invention has, in order from the magnification 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, and a positive refractive power. A fourth lens group and a fifth lens group having a positive refractive power are arranged to satisfy the following conditional expression (1). When zooming, the first lens group and the fifth lens group are fixed. The second lens group, the third lens group, and the fourth lens group move so as to be positioned on the enlargement side on the telephoto side rather than on the wide-angle side, and the lens surfaces constituting each lens group consist only of spherical surfaces. The following conditional expressions (2), (3), and (4) are satisfied.
(1) ft / fw> 1.3
(2) 0.3 <G2t / fw <2.2
(3) 0.3 <G3t / fw <2.2
(4) 0.3 <G4t / fw <2.2
However,
ft: focal length of the entire lens system at the telephoto end fw: focal length of the entire lens system at the wide-angle end G2t: moving distance G3t for zooming from the wide-angle end to the telephoto end of the second lens group: wide-angle of the third lens group Moving distance G4t at the time of zooming from the end to the telephoto end: The moving distance at the time of zooming from the wide angle end to the telephoto end of the fourth lens group.

  In the zoom lens according to the present invention, the zoom lens has a five-group configuration in which three lens groups (second lens group, third lens group, and fourth lens group) are movable at the time of zooming. Various aberrations can be favorably corrected using only a spherical lens while having a zoom ratio and being small and light. The initial investment can be made relatively inexpensive by not using an aspheric lens.

  Conditional expression (1) defines the zoom ratio. If the lower limit of conditional expression (1) is not reached, the desired screen size cannot be changed without the movement of the position of the projection apparatus.

Preferably,
(1A) ft / fw> 1.5
And more preferably,
(1B) 1.5 <ft / fw <2.5
It is good to do.

  When the zoom ratio is greater than 1.5, the desired screen size can be changed without moving the projection apparatus. On the contrary, if the zoom ratio exceeds 2.5, the total length of the zoom lens must be increased. If the total length is not increased, the refractive power of each lens group must be increased. Without use, good aberration correction becomes difficult.

  Conditional expressions (2) to (4) define the ratio of the moving distance of each movable lens group to the focal length. If this value exceeds the upper limit value, each movable lens group becomes larger than the focal length. It will move, and it will be difficult to shorten the total length of the zoom lens because the distance between the lens groups must be kept larger. Also, if this value falls below the lower limit, each movable lens group will move small compared to the focal length, increasing the power with the refractive index and curvature of each lens in each movable lens group, or increasing the number of lenses. It is difficult to reduce the cost, and it is necessary to move the lens group with a large power, which makes it difficult to correct the aberrations. become.

Regarding the conditional expression (2), preferably,
(2A) 0.35 <G2t / fw <2.0
And more preferably,
(2B) 0.35 <G2t / fw <1.5
It is good to do.

Regarding the conditional expression (3), preferably,
(3A) 0.5 <G3t / fw <2.2
And more preferably,
(3B) 1.0 <G3t / fw <2.2
It is good to do.
Further, regarding the conditional expression (4), preferably (4A) 0.5 <G4t / fw <2.0
And more preferably,
(4B) 0.8 <G4t / fw <1.5
It is good to do.

  As described above, by adopting a five-group configuration in which the three lens groups are moved during zooming, it is possible to reduce the size and weight and correct various aberrations satisfactorily.

The zoom lens according to an embodiment of the present invention preferably satisfies the following conditional expression (5) with bf as an air equivalent back focus.
(5) 0.9 <bf / fw <2.2
Conditional expression (5) defines the ratio of the back focus to the focal length, and if this value exceeds the upper limit value, the design must further enhance the retrofocus. It becomes difficult to reduce costs. On the other hand, if this value is below the lower limit, it is difficult to ensure sufficient space for insertion of a color composition element or the like and to ensure telecentricity.

Regarding the conditional expression (5), preferably,
(5A) 1.0 <bf / fw <2.1
It is good to do.

  Further, by arranging the stop in the vicinity of the third lens group and effectively utilizing the negative lens group to enhance the retrofocus, it is possible to simultaneously realize a long back focus and a large zoom ratio.

In the zoom lens according to the embodiment of the present invention, β2 is the imaging magnification of the second lens group, β3 is the imaging magnification of the third lens group, β4 is the imaging magnification of the fourth lens group, and β = β2 × It is desirable that the following conditional expression (6) is satisfied as β3 × β4.
(6) −2.0 <β <−0.8
Conditional expression (6) represents the product of the imaging magnifications of the moving groups (second lens group, third lens group, and fourth lens group) during zooming. If this value exceeds the upper limit value, the moving group Therefore, it becomes difficult to shorten the overall length of the zoom lens. If this value is below the lower limit value, it becomes difficult to correct the movement of the image plane during zooming, and it is difficult to configure a moving group that can suppress aberration fluctuations.

The zoom lens according to an embodiment of the present invention has the following conditional expressions (7), where f2 is the focal length of the second lens group, f3 is the focal length of the third lens group, and f4 is the focal length of the fourth lens group. , (8), (9) should be satisfied.
(7) 2.0 <f2 / fw <9.0
(8) 2.0 <f3 / fw <9.0
(9) 2.0 <f4 / fw <9.0
Conditional expressions (7) to (9) define the ratio of the focal length of each moving group (second lens group, third lens group, fourth lens group) to the focal length of the entire lens system at the wide angle end. If this value exceeds the upper limit, the power of each moving group will be weak, and unless the moving distance of each moving group is increased, zooming cannot be performed, and it becomes difficult to shorten the overall length of the zoom lens. . On the other hand, if this value is below the lower limit, problems such as difficulty in image plane correction occur and aberration correction becomes difficult.

Regarding the conditional expression (7), preferably,
(7A) 2.3 <f2 / fw <8.7
It is good to do.

Regarding the conditional expression (8), preferably,
(8A) 2.1 <f3 / fw <6.0
It is good to do.

Furthermore, regarding the conditional expression (9), preferably,
(9A) 2.5 <f4 / fw <7.0
It is good to do.

  In a zoom lens according to an embodiment of the present invention, it is desirable to perform focusing using the first lens group.

  Next, specific embodiments of the zoom lens according to the present invention and numerical examples in which specific numerical values are applied to the embodiments will be described.

  FIG. 1 is a diagram showing a lens configuration of a zoom lens 1 according to the first embodiment of the present invention. The zoom lens 1 includes a first lens group G1 having a negative refractive power, a second lens group G2 having a positive refractive power, and a third lens group having a positive refractive power, which are arranged in order from the enlargement side to the reduction side. G3 includes a fourth lens group G4 having a positive refractive power and a fifth lens group G5 having a positive refractive power. The upper part of FIG. 1 shows the position of each lens group at the wide-angle end, and the lower part of FIG. 1 shows the position of each lens group at the telephoto end. The second lens group G2, the third lens group G3, and the fourth lens group G4 during the zooming from the wide-angle end to the telephoto end are used to correct the continuous zooming and the image plane movement caused by the continuous zooming. As indicated by arrows in FIG. 1, they move on the optical axis x with mutual relations. The first lens group G1 moves on the optical axis x to perform focusing. The fifth lens group G5 is fixed in the optical axis direction upon zooming.

  The first lens group G1 is composed of a biconvex lens L1, a positive meniscus lens L2, a biconcave lens L3, and a biconcave lens L4, which are positioned in order from the enlargement side to the reduction side. The second lens group G2 is composed of a cemented positive lens of a negative meniscus lens L5 having a convex surface on the enlargement side and a positive meniscus lens L6 having a concave surface on the reduction side, which are positioned in order from the enlargement side to the reduction side. The third lens group G3 is composed of a cemented positive lens composed of a negative meniscus lens L7 and a biconvex lens L8, which are located in order from the enlargement side to the reduction side and have a convex surface facing the enlargement side. The fourth lens group G4 is composed of a cemented lens of a biconvex lens L9 and a biconcave lens L10, a cemented lens of a biconcave lens L11 and a biconvex lens L12, and a positive meniscus with a concave surface facing the reduction side. It consists of a lens L13 and a biconvex lens L14. The fifth lens group G5 includes a positive meniscus lens L15 having a concave surface directed toward the reduction side. The lens surfaces of the lenses L1 to L15 are constituted only by spherical surfaces. The diaphragm S is located on the enlargement side of the fourth lens group G4, and moves together with the fourth lens group G4 upon zooming. In FIG. 1, GB denotes an original image (projection surface) such as a liquid crystal panel (liquid crystal display element), and an image forming unit composed of a color synthesis prism, a polarizing filter, and a glass block such as a color filter. It is indicated by

  Table 1 shows values of specifications of Numerical Example 1 in which specific numerical values are applied to the first embodiment. Note that “surface number i” in each of the following specification tables indicates the i-th surface from the object side, “curvature radius r” indicates the paraxial radius of curvature of the i-th surface, and “axial distance d” "Represents the axial upper surface distance between the i-th surface and the (i + 1) -th surface," refractive index n "represents the refractive index for the d-line (λ = 587.6 nm) of the surface, and" Abbe number ν ”Indicates the Abbe number of the surface with respect to the d-line, and“ ∞ ”for“ curvature radius r ”indicates that the surface is a plane, and“ variable ”for“ axis upper surface distance d ”indicates that the surface upper surface distance is Each indicates a variable interval.

  During zooming from the wide-angle end to the telephoto end, the axial upper surface distance d8 between the first lens group G1 and the second lens group G2, and the axial upper surface distance d11 between the second lens group G2 and the third lens group G3. The axial upper surface distance d14 between the third lens group G3 and the stop S and the axial upper surface distance d25 between the fourth lens group G4 and the fifth lens group G5 vary. Therefore, Table 2 shows values at the wide-angle end and the telephoto end of each variable interval in Numerical Example 1.

  Table 3 shows values corresponding to the conditional expressions (1) to (9) in Numerical Example 1.

  Various aberration diagrams of Numerical Example 1 are shown in FIGS. 2 shows spherical aberration, astigmatism and distortion at the wide-angle end, and FIG. 3 shows spherical aberration, astigmatism and distortion at the telephoto end. In the spherical aberration diagram, the solid line is spherical aberration with respect to the d line, the broken line is spherical aberration with respect to the g line, and the alternate long and short dash line Represents the spherical aberration with respect to the C line. In the astigmatism diagram, the solid line represents the astigmatism on the sagittal surface, and the broken line represents the astigmatism on the meridional surface.

  From these figures, it can be seen that the zoom lens of Numerical Example 1 satisfies the conditional expressions (1) to (9), the aberration is corrected well, and has excellent optical performance.

  FIG. 4 is a diagram showing a lens configuration of the zoom lens 2 according to the second embodiment of the present invention. The zoom lens 2 includes a first lens group G1 having a negative refractive power, a second lens group G2 having a positive refractive power, and a third lens group having a positive refractive power, which are arranged in order from the enlargement side to the reduction side. G3 includes a fourth lens group G4 having a positive refractive power and a fifth lens group G5 having a positive refractive power. The upper part of FIG. 4 shows the position of each lens group at the wide-angle end, and the lower part of FIG. 4 shows the position of each lens group at the telephoto end. The second lens group G2, the third lens group G3, and the fourth lens group G4 during the zooming from the wide-angle end to the telephoto end are used to correct the continuous zooming and the image plane movement caused by the continuous zooming. As indicated by arrows in FIG. 4, they move on the optical axis x with mutual relations. The first lens group G1 moves on the optical axis x to perform focusing. The fifth lens group G5 is fixed in the optical axis direction upon zooming.

  The first lens group G1 is composed of a biconvex lens L1, a negative meniscus lens L2 with a convex surface facing the magnification side, a negative meniscus lens L3 with a convex surface facing the magnification side, and a biconcave lens L4, which are positioned in order from the magnification side to the reduction side. . The second lens group G2 is composed of a cemented positive lens composed of a negative meniscus lens L5 and a biconvex lens L6, which are located in order from the enlargement side to the reduction side and have a convex surface facing the enlargement side. The third lens group G3 is composed of a cemented positive lens of a biconcave lens L7 and a biconvex lens L8, which is positioned in order from the enlargement side to the reduction side. The fourth lens group G4 has a cemented lens of a biconvex lens L9 and a biconcave lens L10, a cemented lens of a biconcave lens L11 and a biconvex lens L12, a biconvex lens L13, and a concave surface on the magnification side, which are positioned in order from the magnification side to the reduction side. It consists of a positive meniscus lens L14 directed. The fifth lens group G5 includes a positive meniscus lens L15 having a concave surface directed toward the reduction side. The lens surfaces of the lenses L1 to L15 are constituted only by spherical surfaces. The diaphragm S is located on the enlargement side of the fourth lens group G4, and moves together with the fourth lens group G4 upon zooming. In FIG. 4, GB denotes an image forming unit composed of an original image (projection surface) such as a liquid crystal panel (liquid crystal display element) and a glass block such as a color synthesizing prism, a polarizing filter, and a color filter. It is indicated by

  Table 4 shows values of specifications of Numerical Example 2 in which specific numerical values are applied to the second embodiment.

  During zooming from the wide-angle end to the telephoto end, the axial upper surface distance d8 between the first lens group G1 and the second lens group G2, and the axial upper surface distance d11 between the second lens group G2 and the third lens group G3. The axial upper surface distance d14 between the third lens group G3 and the stop S and the axial upper surface distance d25 between the fourth lens group G4 and the fifth lens group G5 vary. Accordingly, Table 5 shows values at the wide-angle end and the telephoto end of each variable interval in Numerical Example 2.

  Table 6 shows values corresponding to the conditional expressions (1) to (9) in Numerical Example 2.

  Various aberration diagrams of Numerical Example 2 are shown in FIGS. FIG. 5 shows spherical aberration, astigmatism and distortion at the wide-angle end, and FIG. 6 shows spherical aberration, astigmatism and distortion at the telephoto end. In the spherical aberration diagram, the solid line is the spherical aberration with respect to the d line, the broken line is the spherical aberration with respect to the g line, Represents the spherical aberration with respect to the C line. In the astigmatism diagram, the solid line represents the astigmatism on the sagittal surface, and the broken line represents the astigmatism on the meridional surface.

  From these figures, it can be seen that the zoom lens of Numerical Example 2 satisfies the conditional expressions (1) to (9), the aberration is corrected well, and has excellent optical performance.

  FIG. 7 is a diagram showing a lens configuration of the zoom lens 3 according to the third embodiment of the present invention. The zoom lens 3 includes a first lens group G1 having a negative refractive power, a second lens group G2 having a positive refractive power, and a third lens group having a positive refractive power, which are arranged in order from the enlargement side to the reduction side. G3 includes a fourth lens group G4 having a positive refractive power and a fifth lens group G5 having a positive refractive power. The upper part of FIG. 7 shows the position of each lens group at the wide-angle end, and the lower part of FIG. 7 shows the position of each lens group at the telephoto end. The second lens group G2, the third lens group G3, and the fourth lens group G4 during the zooming from the wide-angle end to the telephoto end are used to correct the continuous zooming and the image plane movement caused by the continuous zooming. As shown by the arrows in FIG. 7, they move on the optical axis x with mutual relations. The first lens group G1 moves on the optical axis x to perform focusing. The fifth lens group G5 is fixed in the optical axis direction upon zooming.

  The first lens group G1 is composed of a positive meniscus lens L1, a biconvex lens L2, a biconcave lens L3, and a biconcave lens L4, which are positioned in order from the enlargement side to the reduction side and have a convex surface facing the reduction side. The second lens group G2 is composed of a cemented positive lens composed of a negative meniscus lens L5 and a biconvex lens L6, which are located in order from the enlargement side to the reduction side and have a convex surface facing the enlargement side. The third lens group G3 is composed of a cemented positive lens of a biconcave lens L7 and a biconvex lens L8, which is positioned in order from the enlargement side to the reduction side. The fourth lens group G4 is composed of a cemented lens of a biconvex lens L9 and a biconcave lens L10, which is located in order from the enlargement side to the reduction side, a negative meniscus lens L11 having a convex surface on the reduction side, and a positive meniscus having a concave surface on the enlargement side. It consists of a cemented lens with the lens L12, a positive meniscus lens L13 with a concave surface facing the magnification side, and a positive meniscus lens L14 with a concave surface facing the magnification side. The fifth lens group G5 includes a positive meniscus lens L15 having a concave surface directed toward the reduction side. The lens surfaces of the lenses L1 to L15 are constituted only by spherical surfaces. The diaphragm S is located on the enlargement side of the fourth lens group G4, and moves together with the fourth lens group G4 upon zooming. In FIG. 7, GB denotes an original image (projection surface) such as a liquid crystal panel (liquid crystal display element), and an image forming unit composed of a color synthesis prism, a polarizing filter, and a glass block such as a color filter. It is indicated by

  Table 7 shows the values of specifications of Numerical Example 3 in which specific numerical values are applied to the third embodiment.

  During zooming from the wide-angle end to the telephoto end, the axial upper surface distance d8 between the first lens group G1 and the second lens group G2, and the axial upper surface distance d11 between the second lens group G2 and the third lens group G3. The axial upper surface distance d14 between the third lens group G3 and the stop S and the axial upper surface distance d25 between the fourth lens group G4 and the fifth lens group G5 vary. Therefore, Table 8 shows the values at the wide-angle end and the telephoto end of each variable interval in Numerical Example 3.

  Table 9 shows values corresponding to the conditional expressions (1) to (9) in Numerical Example 3.

  Various aberration diagrams of Numerical Example 3 are shown in FIGS. FIG. 8 shows spherical aberration, astigmatism and distortion at the wide-angle end, and FIG. 9 shows the spherical aberration, astigmatism and distortion at the telephoto end. In the spherical aberration diagram, the solid line shows the spherical aberration with respect to the d line, the broken line shows the spherical aberration with respect to the g line, Represents the spherical aberration with respect to the C line. In the astigmatism diagram, the solid line represents the astigmatism on the sagittal surface, and the broken line represents the astigmatism on the meridional surface.

  From these figures, it can be seen that the zoom lens of Numerical Example 3 satisfies the conditional expressions (1) to (9), the aberration is corrected well, and has excellent optical performance.

  FIG. 10 is a diagram showing a lens configuration of a zoom lens 4 according to the fourth embodiment of the present invention. The zoom lens 4 includes a first lens group G1 having a negative refractive power, a second lens group G2 having a positive refractive power, and a third lens group having a positive refractive power, which are arranged in order from the enlargement side to the reduction side. G3 includes a fourth lens group G4 having a positive refractive power and a fifth lens group G5 having a positive refractive power. The upper part of FIG. 10 shows the position of each lens group at the wide angle end, and the lower part of FIG. 10 shows the position of each lens group at the telephoto end. The second lens group G2, the third lens group G3, and the fourth lens group G4 during the zooming from the wide-angle end to the telephoto end are used to correct the continuous zooming and the image plane movement caused by the continuous zooming. As indicated by arrows in FIG. 10, they move on the optical axis x with mutual relations. The first lens group G1 moves on the optical axis x to perform focusing. The fifth lens group G5 is fixed in the optical axis direction upon zooming.

  The first lens group G1 is composed of a biconvex lens L1, a positive meniscus lens L2 having a concave surface facing the reduction side, a biconcave lens L3, and a biconcave lens L4, which are located in order from the enlargement side to the reduction side. The second lens group G2 includes a positive meniscus lens L5 having a concave surface directed toward the reduction side. The third lens group G3 is composed of a cemented positive lens composed of a negative meniscus lens L6 and a biconvex lens L7, which are located in order from the enlargement side to the reduction side and have a convex surface directed toward the enlargement side. The fourth lens group G4 has a cemented lens of a biconvex lens L8 and a biconcave lens L9, a cemented lens of a biconcave lens L10 and a biconvex lens L11, a biconvex lens L12, and a concave surface on the magnification side, which are positioned in order from the magnification side to the reduction side. The positive meniscus lens L13. The fifth lens group G5 includes a positive meniscus lens L14 having a concave surface directed toward the reduction side. Each lens surface of each of the lenses L1 to L14 is composed only of a spherical surface. The diaphragm S is located on the enlargement side of the fourth lens group G4, and moves together with the fourth lens group G4 upon zooming. In FIG. 10, GB denotes an original image (projection surface) such as a liquid crystal panel (liquid crystal display element) and an image forming unit composed of a color synthesizing prism, a polarizing filter, and a glass block such as a color filter. It is indicated by

  Table 10 shows the values of specifications of Numerical Example 4 in which specific numerical values are applied to the fourth embodiment.

  During zooming from the wide angle end to the telephoto end, the axial upper surface distance d8 between the first lens group G1 and the second lens group G2, and the axial upper surface distance d10 between the second lens group G2 and the third lens group G3. The axial upper surface distance d13 between the third lens group G3 and the stop S and the axial upper surface distance d24 between the fourth lens group G4 and the fifth lens group G5 vary. Therefore, Table 11 shows values at the wide-angle end and the telephoto end of each variable interval in Numerical Example 4.

  Table 12 shows values corresponding to the conditional expressions (1) to (9) in Numerical Example 4.

  Various aberration diagrams of Numerical Example 4 are shown in FIGS. FIG. 11 shows spherical aberration, astigmatism and distortion at the wide-angle end, and FIG. 12 shows the spherical aberration, astigmatism and distortion at the telephoto end. In the spherical aberration diagram, the solid line is the spherical aberration with respect to the d line, the broken line is the spherical aberration with respect to the g line, Represents the spherical aberration with respect to the C line. In the astigmatism diagram, the solid line represents the astigmatism on the sagittal surface, and the broken line represents the astigmatism on the meridional surface.

From these figures, it can be seen that the zoom lens of Numerical Example 4 satisfies the conditional expressions (1) to (9), the aberration is corrected well, and has excellent optical performance.
FIG. 13 shows an example of an embodiment of the projection apparatus of the present invention.

  The projection apparatus 10 is configured as a liquid crystal projector, and includes a projection lens 20 and an image forming unit 30 and a light source unit 40 that form an image projected on a screen by the projection lens 20. The projection lens 20 is configured such that a plurality of lenses (not shown) are arranged in a lens barrel 21 so as to form a five-group structure. Specifically, the zoom lens of the present invention described above, for example, the first to fourth embodiments described above. The zoom lenses 1 to 4 shown in FIG. 4 or zoom lenses configured in forms other than the embodiment shown in this specification can be used.

  The image forming unit 30 includes liquid crystal panels 31R, 31G, and 31B and a color combining prism 32 that display images corresponding to red (R), green (G), and blue (B) colors. The liquid crystal panels 31R, 31G, and 31B are disposed to face the incident surfaces 32r, 32g, and 32b of the color synthesis prism 32, respectively.

  The light source unit 40 includes a white light source 41, a reflector 42, a fly-eye lens 43, a total reflection mirror 44, a polarization conversion element 45, dichroic mirrors 46a and 46b, total reflection mirrors 47a, 47b and 47c, condenser lenses 48a, 48b and 48c, A relay lens 49 and the like are provided.

  White light emitted from the white light source 41 is reflected by the reflector 42, the light amount is made uniform in a plane perpendicular to the optical axis by the fly-eye lens 43, and the polarization direction is changed by the polarization conversion element 45 via the total reflection mirror 44. Prepared and sent to color separation system. The R light is transmitted through the first color separation dichroic mirror 46a, and the G light and B light are reflected. The R light that has passed through the first dichroic mirror 46a is totally reflected by the total reflection mirror 47a and irradiated onto the liquid crystal panel 31R by the condenser lens 48a.

  The G light and B light reflected by the first dichroic mirror 46a are split by the second dichroic mirror 46b. That is, the G light is reflected by the second dichroic mirror 46b and the B light is transmitted. The G light is irradiated to the liquid crystal panel 31G by the condenser lens 48b.

  The B light transmitted through the second dichroic mirror 46b passes through the total reflection mirror 47b, the relay lens 49, and the total reflection millet 47c, and is irradiated to the liquid crystal panel 31B by the condenser lens 48c.

  The R light, G light, and B light that have been spatially modulated through the liquid crystal panels 31R, 31G, and 31B are individually transmitted from the incident surfaces 32r, 32g, and 32b of the color combining prism 32 into the color combining prism 32. , Is combined in the color combining prism 32, is output from the output surface 32o, and is further projected by the projection lens 20 onto a front screen (not shown).

  In the projection device 10 described above, a transmissive liquid crystal panel is used as means for spatially modulating the projection light. However, a reflective liquid crystal panel may be used, and is not limited to a liquid crystal panel. It is also possible to use other spatial modulation means such as Light Processing (trademark of Texas Instruments, USA).

  It should be noted that the specific shapes, structures, and numerical values of the respective parts shown in the respective embodiments and numerical examples are merely examples of the specific examples in carrying out the present invention, and therefore The technical scope of the present invention should not be interpreted in a limited manner.

It is a figure which shows the lens structure of 1st Embodiment of this invention zoom lens. FIG. 3 shows various aberration diagrams of Numerical Example 1 in which specific numerical values are applied to the first embodiment of the zoom lens according to the present invention, and FIG. 3 shows spherical aberration, astigmatism, and distortion at the wide angle end. Is shown. It shows spherical aberration, astigmatism and distortion at the telephoto end. It is a figure which shows the lens structure of 2nd Embodiment of this invention zoom lens. FIG. 9 shows various aberration diagrams of Numerical Example 2 in which specific numerical values are applied to the second embodiment of the zoom lens according to the present invention, and FIG. 6 shows spherical aberration, astigmatism, and distortion at the wide angle end. Is shown. It shows spherical aberration, astigmatism and distortion at the telephoto end. It is a figure which shows the lens structure of 3rd Embodiment of this invention zoom lens. FIG. 9 shows various aberration diagrams of Numerical Example 3 in which specific numerical values are applied to the third embodiment of the zoom lens according to the present invention, and FIG. 9 shows spherical aberration, astigmatism, and distortion at the wide angle end. Is shown. It shows spherical aberration, astigmatism and distortion at the telephoto end. It is a figure which shows the lens structure of 4th Embodiment of the zoom lens of this invention. 12 shows various aberration diagrams of Numerical Example 4 in which specific numerical values are applied to the fourth embodiment of the zoom lens according to the present invention, and FIG. 12 shows spherical aberration, astigmatism, and distortion at the wide angle end. Is shown. It shows spherical aberration, astigmatism and distortion at the telephoto end. It is a schematic block diagram which shows embodiment of the projection apparatus of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Zoom lens, 2 ... Zoom lens, 3 ... Zoom lens, 4 ... Zoom lens, G1 ... 1st lens group, G2 ... 2nd lens group, G3 ... 3rd lens group, G4 ... 4th lens group, G5 ... 5th lens group, 10 ... projection device, 20 ... projection lens, 30 ... image forming unit

Claims (6)

In order from the magnification side, the first lens group having negative refractive power, the second lens group having positive refractive power, the third lens group having positive refractive power, the fourth lens group having positive refractive power, and the positive In a zoom lens that includes a fifth lens group having the following refractive power and that satisfies the following conditional expression (1):
At the time of zooming, the first lens group and the fifth lens group are fixed, and the second lens group, the third lens group, and the fourth lens group are positioned closer to the magnification side on the telephoto side than on the wide angle side. The zoom lens is characterized in that the lens surfaces constituting each lens group consist of only spherical surfaces and satisfy the following conditional expressions (2), (3), and (4).
(1) ft / fw> 1.3
(2) 0.3 <G2t / fw <2.2
(3) 0.3 <G3t / fw <2.2
(4) 0.3 <G4t / fw <2.2
However,
ft: focal length of the entire lens system at the telephoto end fw: focal length of the entire lens system at the wide-angle end G2t: movement distance G3t for zooming from the wide-angle end to the telephoto end of the second lens group: wide-angle of the third lens group Moving distance G4t at the time of zooming from the end to the telephoto end: The moving distance at the time of zooming from the wide angle end to the telephoto end of the fourth lens group. The zoom lens according to claim 1, wherein the following conditional expression (5) is satisfied.
(5) 0.9 <bf / fw <2.2
However,
bf: Air-converted back focus. The zoom lens according to claim 1, wherein the following conditional expression (6) is satisfied.
(6) −2.0 <β <−0.8
However,
β2: Imaging magnification of the second lens group β3: Imaging magnification of the third lens group β4: Imaging magnification of the fourth lens group β: β2 × β3 × β4
And The zoom lens according to claim 1, wherein the following conditional expressions (7), (8), and (9) are satisfied.
(7) 2.0 <f2 / fw <9.0
(8) 2.0 <f3 / fw <9.0
(9) 2.0 <f4 / fw <9.0
However,
f2: focal length of the second lens group f3: focal length of the third lens group f4: focal length of the fourth lens group. The zoom lens according to claim 1, wherein focusing is performed by the first lens group. In a projection apparatus including an image forming unit and a zoom lens that magnifies and projects an image formed by the image forming unit,
The zoom lens includes, in order from the enlargement 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, and a first lens group having a positive refractive power. 4 lens groups and a fifth lens group having positive refractive power are arranged to satisfy the following conditional expression (1):
At the time of zooming, the first lens group and the fifth lens group are fixed, and the second lens group, the third lens group, and the fourth lens group are positioned closer to the magnification side on the telephoto side than on the wide angle side. The projection apparatus is characterized in that the lens surfaces constituting each lens group are composed only of spherical surfaces and satisfy the following conditional expressions (2), (3), and (4).
(1) ft / fw> 1.3
(2) 0.3 <G2t / fw <2.2
(3) 0.3 <G3t / fw <2.2
(4) 0.3 <G4t / fw <2.2

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