JP2006039033A - Zoom lens and projection apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a zoom lens which contributes to reductions in size and weight and satisfactorily corrects various aberrations without increasing the number of lenses, and to provide a projection apparatus using the zoom lens. <P>SOLUTION: The zoom lens is composed of four groups of negative, positive, positive, and positive powers. Specifically, it is composed of in order from the enlargement side: the first lens group G1 fixed when a magnification change takes place, and having the negative refracting power for focusing; the second lens group G2 of the positive refracting power and third lens group having positive refracting power, which are moved having relative relations in order to compensate for a continuous magnification change and the movement of an image face caused by the continuous magnification change; and the fourth lens group G4 having the positive refracting power fixed when the magnification change takes place. In addition, the zoom lens satisfies conditional expressions (1) 0.2<G2t/fw<0.5 and (2) 0.2<G3t/fw<0.5, in which fw denotes the focal distance of the entire lens system at a wide angle end, G2t denotes the distance of movement of the second lens group between the wide angle end and a telephoto end when the magnification change takes place, and G3t is the distance of the movement of the third lens group between the wide angle end and the telephoto end when the magnification change takes place. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a novel zoom lens and a projection apparatus using the zoom lens. More specifically, the present invention relates to a zoom lens that is small in size and does not change its overall length upon zooming, has a good imaging performance, and can reduce the number of lenses, and a projection apparatus using the zoom lens.

  In recent projection apparatuses such as projectors, there is a great demand for downsizing and cost reduction as well as higher pixels and higher resolution. Therefore, it is desired to develop a projection zoom lens for use in a projector or the like that has high performance and is small and low cost.

  Conventionally, such a projection type zoom lens has a five-group configuration, and many zoom lenses in which three groups move upon zooming have been disclosed. However, a zoom lens in which three groups move during zooming in a five-group configuration increases the number of mechanical parts and the number of lenses during zooming, and it may be difficult to reduce costs in terms of cost.

  Patent Document 1 and Patent Document 2 show a zoom lens having a four-group configuration in which three groups move when zooming. However, there is a demand for downsizing the total lens length by changing the total length when zooming. I can't respond.

  Patent Document 3 discloses a zoom lens having a four-group structure in which the two lens groups move at the time of zooming and the total length does not change. However, the number of lenses is as large as 12 to 13, and there is a demand for cost reduction. I cannot respond to it. In addition, as a “conditional expression for satisfactorily correcting various aberrations even when zooming is performed while keeping the overall length short,” the product of the imaging magnifications of the second lens group and the third lens group (β2 Although the numerical value of × β3) is specified, only that β2 × β3 should exceed −2.2 is specified, and the upper limit is not mentioned. In addition, there is a statement that “the product of the imaging magnification of the moving group in which the correction of various aberrations is more easily corrected even when zooming is performed while keeping the overall length short, is about 1 time”. Only examples in the range of -1.95 to -1.41 are shown.

Japanese Patent Laid-Open No. 11-326763 JP 2001-188172 A JP 2000-275519 A

  The present invention has been made in view of the above-described circumstances. As a four-group lens system in which two lens groups move during zooming, the present invention achieves a reduction in size and weight, and various aberrations without increasing the number of lenses. It is an object of the present invention to provide a zoom lens that can be corrected satisfactorily and a projection device using the zoom lens.

  In order to solve the above-described problems, the zoom lens according to the present invention has a four-group configuration of negative, positive, positive, and positive, and in order from the magnification side, has a negative refractive power that is fixed during zooming and performs focusing. The first lens group G1 having a positive refractive power and the second lens group G2 having a positive refractive power that moves relative to each other for correction of image plane movement caused by continuous zooming and continuous zooming The third lens group G3 is formed by arranging a fourth lens group G4 having a fixed positive refractive power upon zooming, fw is the focal length of the entire lens system at the wide angle end, and G2t is between the wide angle end and the telephoto end. Conditional expression (1) 0.2 <G2t / fw <0, where G3t is the moving distance of the second lens group at the time of zooming, and G3t is the moving distance of the third lens group at the time of zooming between the wide angle end and the telephoto end. .5 and (2) 0.2 <G3t / fw <0. It is intended to satisfy.

  In order to solve the above-described problem, the projection apparatus 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 is negative, positive, positive. The first lens group G1, which has a positive four-group configuration and is fixed at the time of zooming, and has a negative refractive power for performing focusing, in order from the magnification side, continuous zooming and image plane movement caused by continuous zooming A second lens group G2 having a positive refractive power and a third lens group G3 having a positive refractive power that move relative to each other for correction, and a fourth lens having a fixed positive refractive power upon zooming Group G4 is arranged, and satisfies the conditional expressions (1) 0.2 <G2t / fw <0.5 and (2) 0.2 <G3t / fw <0.5.

  Therefore, in the present invention, the first lens group is moved only during focusing, and the total lens length does not change during zooming. In addition, the overall lens length can be shortened, and various aberrations can be corrected well without increasing the number of lenses.

  The zoom lens of the present invention has a four-group configuration of negative, positive, positive, and positive, and in order from the magnifying side, the first lens group G1, which is fixed during zooming and has a negative refractive power for performing focusing, The second lens group G2 having a positive refractive power and a third lens group G3 having a positive refractive power that move relative to each other in order to correct image plane movement caused by magnification and continuous zooming. The fourth lens group G4 having a fixed positive refractive power is arranged, fw is the focal length of the entire lens system at the wide angle end, and G2t is the second lens group at the time of zooming between the wide angle end and the telephoto end. Conditional expression (1) 0.2 <G2t / fw <0.5, (2) 0,..., G3t as the movement distance of the third lens group during zooming between the wide-angle end and the telephoto end. 2 <G3t / fw <0.5 is satisfied.

  The projection device of the present invention is a projection device including an image forming unit and a zoom lens that magnifies and projects an image formed by the image forming unit, and the zoom lens includes negative, positive, positive, and positive First lens group G1, which has a four-group structure and is fixed at the time of zooming and has a negative refractive power for focusing, in order from the magnification side, for continuous zooming and correction of image plane movement caused by continuous zooming A second lens group G2 having a positive refractive power that moves relative to each other, a third lens group G3 having a positive refractive power, and a fourth lens group G4 having a fixed positive refractive power upon zooming. Fw is the focal length of the entire lens system at the wide angle end, G2t is the moving distance of the second lens unit during zooming between the wide angle end and the telephoto end, and G3t is between the wide angle end and the telephoto end Third lens group at variable magnification As the moving distance, the conditional expression (1) 0.2 <G2t / fw <0.5, and satisfies the (2) 0.2 <G3t / fw <0.5.

  Accordingly, in the present invention, the first lens group is movable only during focusing and is fixed during zooming, which contributes to a reduction in the overall length of the lens. In addition, since the ratio of the moving distance to the focal length at the time of zooming of the two moving lens groups is appropriately defined, the overall length of the lens can be reduced, and various aberrations can be corrected without increasing the number of lenses. Image plane correction at the time of zooming can be easily performed.

  In the invention described in claim 2, conditional expression (3) 1.0 <bf / fw <1.5 is satisfied with bf as an air-converted back focus, so that telecentricity is ensured and color synthesis is performed. A sufficient back focus for inserting elements and the like can be ensured, and various aberrations can be corrected well without increasing the number of lenses.

  In the invention described in claims 3 and 4, conditional expression (4) -1.4 <β2 is assumed, where β2 is the imaging magnification of the second lens group and β3 is the imaging magnification of the third lens group. Since × β3 <−0.8 is satisfied, the movement of the image plane at the time of zooming can be reliably corrected by the movement group of only two groups, and the movement amount of the movement group does not increase. Contributes to the miniaturization of the entire lens length.

  In the invention described in claims 5 to 8, conditional expression (5) 2.0 <f2 / fw <where f2 is the focal length of the second lens group and f3 is the focal length of the third lens group. Since 5.0 and (6) 2.0 <f3 / fw <5.0 are satisfied, it is possible to satisfactorily correct the image plane movement and various aberrations at the time of zooming, and reduce the total lens length. Contributes to

  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 accompanying drawings.

  The zoom lens of the present invention is based on a four-group configuration of negative, positive, positive, and positive. In order from the magnification side, the first lens group G1 having negative refractive power, the second lens group G2 having positive refractive power, the third lens group G3 having positive refractive power, and the fourth lens having positive refractive power The group G4 is arranged, and the second lens group G2 and the third lens group G3 are related to each other for the purpose of continuous zooming and to correct the movement of the image plane caused by the continuous zooming. The first lens group G1 and the fourth lens group G4 are fixed during zooming, and the first lens group G1 is movable to perform focusing.

  As described above, in the zoom lens of the present invention, only the second lens group G2 and the third lens group G3 move during zooming, so there are few movable lens groups during zooming, and the entire drive mechanism is reduced. It can be made compact and contributes to miniaturization. Further, since the first lens group G1 does not move at the time of zooming, the total lens length hardly changes, and this contributes to the miniaturization of the total lens length.

In the zoom lens of the present invention, fw is the focal length of the entire lens system at the wide-angle end, G2t is the moving distance of the second lens unit during zooming between the wide-angle end and the telephoto end, and G3t is between the wide-angle end and the telephoto end. The following conditional expressions (1) and (2) are satisfied as the moving distance of the third lens unit during zooming.
(1) 0.2 <G2t / fw <0.5
(2) 0.2 <G3t / fw <0.5
The conditional expressions (1) and (2) define the ratio of the moving distance of the moving lens groups G2 and G3 to the focal length. If the upper limit value of the conditional expressions (1) and (2) is exceeded, the focal length The moving distance of the moving lens groups G2 and G3 with respect to the lens becomes too large, and the distance between the second lens group G2 and the third lens group G3 must be kept larger, thereby shortening the overall length of the zoom lens. It becomes difficult.

  If the lower limit value of the conditional expressions (1) and (2) is not reached, the moving distance of each moving lens group G2, G3 becomes too small with respect to the focal length. The power of the lens groups G2 and G3 must be increased. For that purpose, the power must be increased by the refractive index and the curvature of each lens constituting each lens group G2 and G3, or the number of lenses must be increased. In addition, it is difficult to reduce the cost, and it is necessary to move a lens group having a large power, which causes problems such as difficulty in correcting the image plane, and makes it difficult to correct aberrations. In addition, since the movable lens groups G2 and G3 have a large power, higher accuracy is required for the relative movement of the two movable lens groups G2 and G3, and a highly accurate lens moving mechanism is required, which increases costs. Problem arises.

The zoom lens according to the present invention preferably satisfies the following conditional expression (3) with bf as an air-converted back focus.
(3) 1.0 <bf / fw <1.5
Conditional expression (3) defines the ratio of the back focus with respect to the focal length. If the upper limit of conditional expression (3) is exceeded, the retrofocus must be designed to be further emphasized. In addition, the number of lenses must be increased, which makes it difficult to reduce the cost.

  On the other hand, if the lower limit of conditional expression (3) is not reached, it will be difficult to ensure sufficient space for insertion of a color synthesizing element or the like and to ensure telecentricity.

  In the projection optical system, a polarizing beam splitter and a color synthesis prism are arranged between the projection lens and an image display unit such as a liquid crystal element. For this reason, the projection lens requires a long back focus. Further, when using a liquid crystal element in the image display unit, in order to eliminate the influence of the light distribution characteristic of the liquid crystal element or the angle dependency of the color synthesis dichroic film when synthesizing a plurality of color lights, and the illumination system Therefore, it is desirable to use a so-called telecentric optical system in which the exit pupil is at infinity in order to achieve good matching with the above and to ensure good illuminance in the vicinity. Therefore, it is preferable that the conditional expression (3) is satisfied.

The zoom lens according to the present invention preferably satisfies the following conditional expression (4), where β2 is the imaging magnification of the second lens group and β3 is the imaging magnification of the third lens group.
(4) -1.4 <β2 × β3 <−0.8
Conditional expression (4) prescribes the product of the imaging magnifications of the second lens group G2 and the third lens group G3, which are moving groups at the time of zooming, and if the upper limit of conditional expression (4) is exceeded, The amount of movement of the second lens group G2 and the third lens group G3, which are the moving groups, increases, and it becomes difficult to shorten the overall length of the zoom lens.

  If the lower limit of conditional expression (4) is not reached, it will be difficult to correct the movement of the image plane at the time of zooming, and it will be difficult to configure only two moving groups.

  In the zoom lens of the present invention, the product of the imaging magnifications of the second lens group G2 and the third lens group G3, which are the moving group, is set to -1.4 to -0.8, which is close to 1 ×. Thus, it is made easier to correct various aberrations easily without changing the number of moving groups, even if zooming is performed while keeping the total length short. This is very different from the zoom lens embodiments disclosed in Patent Document 3 described above in which the product of the imaging magnification of the moving group is in the range of -1.95 to -1.41.

The zoom lens according to the present invention preferably satisfies the following conditional expressions (5) and (6), where f2 is the focal length of the second lens group and f3 is the focal length of the third lens group.
(5) 2.0 <f2 / fw <5.0
(6) 2.0 <f3 / fw <5.0
Conditional expressions (5) and (6) define the ratio of the focal lengths of the moving groups G2 and G3 to the focal length of the entire lens system at the wide-angle end. The upper limit values of conditional expressions (5) and (6) Exceeding the range, the power of each of the moving groups G2 and G3 is weak, and a desired zoom ratio cannot be obtained unless the moving distance is large, and it becomes difficult to shorten the overall length of the zoom lens.

  If the lower limit value of conditional expressions (5) and (6) is not reached, problems such as difficulty in correcting image plane movement during zooming occur, and aberration correction becomes difficult.

  According to the zoom lens of the present invention as described above, it is possible to project image information displayed on a liquid crystal display element or the like on a screen surface while maintaining high optical performance while reducing the overall length.

  Specific examples of the zoom lens according to the present invention will be described below.

  FIG. 1 is a diagram showing a lens configuration according to Example 1 of the present invention. The upper stage of FIG. 1 shows the state at the wide-angle end, and the lower stage shows the state at the telephoto end.

  The zoom lens 1 includes, in order from the magnification side, a first lens group G1 having a negative refractive power, a second lens group G2 having a positive refractive power, a third lens group G3 having a positive refractive power, and a positive refractive power. The fourth lens group G4 and the third lens group G4 are arranged so that the second lens group G2 and the third lens are used for continuous zooming from the wide-angle end to the telephoto end and for correcting the movement of the image plane caused by the continuous zooming. The group G3 moves in the direction of the optical axis as indicated by a correlatively thick arrow. The first lens group G1 is fixed at the time of zooming, but moves for focusing.

  The first lens group G1 is arranged in order from the enlargement side, the negative meniscus lens L11 having a convex surface on the enlargement side, the negative meniscus lens L12 having a convex surface on the enlargement side and having both surfaces aspheric, and on the enlargement side Consists of a positive meniscus lens L13 with a convex surface, and the second lens group G2 has a cemented lens L21 of a biconvex lens and a negative lens with a concave surface facing the magnification side, arranged in order from the magnification side, and a concave surface on the magnification side. A positive meniscus lens L22, a cemented lens L23 of a biconcave lens and a biconvex lens, the third lens group is composed of a positive meniscus lens L3 having a convex surface facing the reduction side, and the fourth lens group G4 is a biconvex lens L4. It consists of In FIG. 1, GB denotes an image forming unit composed of an original image (projection surface) such as a liquid crystal panel (liquid crystal display element), a color synthesis prism, a polarizing filter, and a glass block such as a color filter.

  Table 1 shows lens data of the zoom lens 1 according to the first example. In Table 1 and the following table, the surface number “i” is the i-th surface from the enlarged side, the curvature radius “r” is the curvature radius of the i-th surface, and the surface interval “d” is the i-th surface. The refractive index “n” is the refractive index with respect to the d-line of the glass material having the i-th surface on the enlargement side, and the Abbe number “ “ν” indicates the Abbe number with respect to the d-line of the glass material having the i-th surface on the enlargement side, “f” indicates the focal length, and “F” indicates the F number.

  Moreover, in this specification, an aspherical surface is represented by the following formula 1.

Here, “Y” is the height from the optical axis, “Z” is the distance in the optical axis direction at the height Y from the optical axis between the tangential plane and the aspheric surface at the aspherical vertex, and “C” is the aspherical vertex. Of curvature (= 1 / r), “K” is a conic constant, and A ₄ , A ₆ , A ₈ , and A ₁₀ are aspheric coefficients.

  During zooming, the axial upper surface distance d6 between the first lens group G1 and the second lens group G2, the axial upper surface distance d14 between the second lens group G2 and the third lens group G3, and the third lens group G3. The axial upper surface distance d16 between the fourth lens group G4 is variable. Table 2 below shows the values at the wide-angle end and the telephoto end of the axial distances d6, d14, and d16.

  Both surfaces (third surface and fourth surface) of the second lens L12 of the first lens group G1 are aspherical surfaces. Table 3 below shows the aspheric coefficients of the above surfaces together with the conic constant.

  Table 4 below shows values corresponding to the conditional expressions (1) to (6) of the zoom lens 1 according to the first example.

  An aberration diagram at the wide-angle end of the zoom lens 1 is shown in FIG. 2, and an aberration diagram at the telephoto end is shown in FIG. 2 and 3, the solid line d represents spherical aberration with respect to the d line, the dotted line g represents spherical aberration with respect to the g line, the broken line C represents spherical aberration with respect to the C line, and the solid line S represents astigmatism on the sagittal surface. The broken line M represents astigmatism on the meridional surface. “F” indicates an F number, and “W” indicates a half angle of view.

  From these figures, it can be seen that the zoom lens 1 according to the example 1 has excellent aberrations and excellent optical performance.

  FIG. 4 is a diagram showing a lens configuration according to Example 2 of the present invention. The upper stage in FIG. 4 shows the state at the wide-angle end, and the lower stage shows the state at the telephoto end.

  The zoom lens 2 includes, in order from the magnification side, a first lens group G1 having a negative refractive power, a second lens group G2 having a positive refractive power, a third lens group G3 having a positive refractive power, and a positive refractive power. The fourth lens group G4 and the third lens group G4 are arranged so that the second lens group G2 and the third lens are used for continuous zooming from the wide-angle end to the telephoto end and for correcting the movement of the image plane caused by the continuous zooming. The group G3 moves in the direction of the optical axis as indicated by a correlatively thick arrow. The first lens group G1 is fixed at the time of zooming, but moves for focusing.

  The first lens group G1 includes a negative meniscus lens L11 having a convex surface on the magnification side, a negative lens L12 having a strong concave surface on the reduction side, and a double-sided aspheric surface, and arranged on the magnification side. The second lens group G2 is composed of a cemented lens L13 of two positive meniscus lenses having a convex surface, and is arranged in order from the magnifying side, a positive lens L21 having a strong convex surface on the magnifying side, a biconcave lens and a biconvex lens The third lens group is composed of a positive lens L3 having a strong convex surface facing the reduction side, and the fourth lens group G4 is composed of a positive lens L4 having a strong convex surface facing the magnification side. Yes. In FIG. 4, GB denotes an image forming unit composed of an original image (projected surface) such as a liquid crystal panel (liquid crystal display element), a color synthesis prism, a polarizing filter, and a glass block such as a color filter.

  Table 5 shows lens data of the zoom lens 2 according to the second example.

  During zooming, the axial upper surface distance d7 between the first lens group G1 and the second lens group G2, the axial upper surface distance d12 between the second lens group G2 and the third lens group G3, and the third lens group G3. The axial upper surface distance d14 between the fourth lens group G4 and the fourth lens group G4 is variable. Table 6 below shows the values at the wide-angle end and the telephoto end of the axial distances d7, d12, and d14.

  Both surfaces (third surface and fourth surface) of the second lens L12 of the first lens group G1 are aspherical surfaces. Table 7 below shows the aspheric coefficients of the above surfaces together with the conic constant.

  Table 8 below shows values corresponding to the conditional expressions (1) to (6) of the zoom lens 2 according to the second example.

  FIG. 5 shows aberration diagrams of the zoom lens 2 at the wide-angle end, and FIG. 6 shows aberration diagrams at the telephoto end. 5 and 6, the solid line d represents spherical aberration with respect to the d line, the dotted line g represents spherical aberration with respect to the g line, the broken line C represents spherical aberration with respect to the C line, and the solid line S represents astigmatism on the sagittal surface. The broken line M represents astigmatism on the meridional surface. “F” indicates an F number, and “W” indicates a half angle of view.

  From these figures, it can be seen that the zoom lens 2 according to Example 2 has excellent aberrations and excellent optical performance.

  FIG. 7 is a diagram showing a lens configuration according to Example 3 of the present invention. The upper stage of FIG. 7 shows the state at the wide-angle end, and the lower stage shows the state at the telephoto end.

  The zoom lens 3 includes, in order from the magnification side, a first lens group G1 having a negative refractive power, a second lens group G2 having a positive refractive power, a third lens group G3 having a positive refractive power, and a positive refractive power. The fourth lens group G4 and the third lens group G4 are arranged so that the second lens group G2 and the third lens are used for continuous zooming from the wide-angle end to the telephoto end and for correcting the movement of the image plane caused by the continuous zooming. The group G3 moves in the direction of the optical axis as indicated by a correlatively thick arrow. The first lens group G1 is fixed at the time of zooming, but moves for focusing.

  The first lens group G1 includes a negative meniscus lens L11 having a convex surface on the enlargement side, a negative meniscus lens L12 having a concave surface on both sides and an aspheric surface, and an enlargement side. The second lens group G2 is composed of a biconvex lens L21 and a cemented lens L22 of a biconcave lens and a biconvex lens, which are arranged in order from the enlargement side, and a third lens group. Is composed of a positive lens L3 having a strong convex surface facing the reduction side, and the fourth lens group G4 is composed of a positive lens L4 having a strong convex surface facing the magnification side. In FIG. 7, GB denotes an image forming unit including an original image (projected surface) such as a liquid crystal panel (liquid crystal display element), a color synthesis prism, a polarizing filter, and a glass block such as a color filter.

  Table 9 shows lens data of the zoom lens 3 according to the third example.

  During zooming, the axial upper surface distance d6 between the first lens group G1 and the second lens group G2, the axial upper surface distance d11 between the second lens group G2 and the third lens group G3, and the third lens group G3. The axial upper surface distance d13 between the fourth lens group G4 is variable. Table 10 below shows the values at the wide-angle end and the telephoto end of the axial distances d6, d11, d13.

  Both surfaces (third surface and fourth surface) of the second lens L12 of the first lens group G1 are aspherical surfaces. Table 11 below shows the aspheric coefficients of the above surfaces together with the conic constant.

  Table 12 below shows values corresponding to the conditional expressions (1) to (6) of the zoom lens 3 according to the third example.

  FIG. 8 shows aberration diagrams of the zoom lens 2 at the wide-angle end, and FIG. 9 shows aberration diagrams at the telephoto end. 8 and 9, the solid line d represents spherical aberration with respect to the d line, the dotted line g represents spherical aberration with respect to the g line, the broken line C represents spherical aberration with respect to the C line, and the solid line S represents astigmatism on the sagittal surface. The broken line M represents astigmatism on the meridional surface. “F” indicates an F number, and “W” indicates a half angle of view.

  From these figures, it can be seen that the zoom lens 3 according to Example 3 has excellent aberrations corrected and has excellent optical performance.

  FIG. 10 is a diagram showing a lens configuration according to Example 4 of the present invention. The upper stage in FIG. 10 shows the state at the wide-angle end, and the lower stage shows the state at the telephoto end.

  The zoom lens 4 includes, in order from the magnification side, a first lens group G1 having a negative refractive power, a second lens group G2 having a positive refractive power, a third lens group G3 having a positive refractive power, and a positive refractive power. The fourth lens group G4 and the third lens group G4 are arranged so that the second lens group G2 and the third lens are used for continuous zooming from the wide-angle end to the telephoto end and for correcting the movement of the image plane caused by the continuous zooming. The group G3 moves in the direction of the optical axis as indicated by a correlatively thick arrow. The first lens group G1 is fixed at the time of zooming, but moves for focusing.

  The first lens group G1 includes, in order from the magnification side, a positive meniscus lens L11 having a convex surface on the magnification side, a negative meniscus lens L12 having a strong concave surface on the reduction side, a biconcave lens L13, a biconcave lens and a biconvex lens The second lens group G2 is composed of a biconvex lens L21 and a cemented lens L22 of a biconcave lens and a biconvex lens arranged in order from the enlargement side, and the third lens group is strong on the reduction side. The fourth lens group G4 includes a positive meniscus lens L4 having a strong convex surface on the enlargement side. In FIG. 10, GB denotes an image forming unit including an original image (projected surface) such as a liquid crystal panel (liquid crystal display element), a color synthesis prism, a polarizing filter, and a glass block such as a color filter.

  Table 13 shows lens data of the zoom lens 4 according to the fourth example.

  During zooming, the axial upper surface distance d9 between the first lens group G1 and the second lens group G2, the axial upper surface distance d14 between the second lens group G2 and the third lens group G3, and the third lens group G3. The axial upper surface distance d16 between the fourth lens group G4 is variable. Table 14 below shows the values at the wide-angle end and the telephoto end of the shaft upper surface distances d9, d14, and d16.

  The values corresponding to the conditional expressions (1) to (6) of the zoom lens 4 according to the example 4 are shown in Table 15 below.

  FIG. 11 shows aberration diagrams of the zoom lens 4 at the wide-angle end, and FIG. 12 shows aberration diagrams at the telephoto end. 11 and 12, the solid line d represents spherical aberration with respect to the d line, the dotted line g represents spherical aberration with respect to the g line, the broken line C represents spherical aberration with respect to the C line, and the solid line S represents astigmatism on the sagittal surface. The broken line M represents astigmatism on the meridional surface. “F” indicates an F number, and “W” indicates a half angle of view.

  From these figures, it can be seen that the zoom lens 4 according to Example 4 has excellent aberrations and excellent optical performance.

  As described above, according to the present invention, as a zoom lens having a four-group configuration in which two lens groups move during zooming, a conventional five-group zoom lens and a four-group zoom lens in which three lens groups move are used. The size and weight can be reduced, and the cost can be reduced by reducing the number of lenses.

  In addition, while being compact and lightweight, various aberrations are corrected well, and it is possible to cope with higher pixels and higher resolution, has telecentricity, and has a sufficiently long back focus and is used for a projection device. A zoom lens suitable for the above can be provided.

  FIG. 13 shows an embodiment of the projection apparatus of the present invention.

  The projection device 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 the screen by the projection lens 20. The projection lens 20 is arranged in a lens barrel 21 such that a plurality of lenses (not shown) have a four-group configuration. Specifically, the projection lens 20 is shown in the zoom lens of the present invention, for example, in the first to fourth embodiments. The lens lenses 1-4 are 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 combining 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 forward 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 is polarized by the polarization conversion element 45 via the total reflection mirror 44. The direction is aligned and sent to the 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 mirror 47c, and is irradiated to the liquid crystal panel 31B by the condenser lens 48c.

  Then, the light R light, G light, and B light, which are transmitted through the liquid crystal panels 31R, 31G, and 31B and spatially modulated, are individually color-combining prisms 32 from the incident surfaces 32r, 32g, and 32b of the color-combining prism 32. And is synthesized in the color synthesizing prism 32 and emitted from the emission surface 32o, and further projected onto a front screen (not shown) by the projection lens 20.

  In the above projection apparatus, a transmissive liquid crystal panel is used as means for spatially modulating the projection light. However, the spatial modulation means is not limited to the liquid crystal panel, and a liquid crystal panel is used. Even in this case, not only the transmission type but also a reflection type liquid crystal panel can be used.

  Further, the projection device 10 is the one in which the present invention is applied as a device for projecting an image on an external reflective screen, but as a device for projecting from the back side of a transmissive screen, for example, as a projection television. You can also.

  In addition, the shapes and numerical values of the respective parts shown in the above-described embodiments and examples are merely examples of the implementation performed in carrying out the present invention, and thus the technical scope of the present invention. Should not be interpreted in a limited way.

  Although it is small and has high performance, the cost can be reduced, and a zoom lens suitable for use in a projection apparatus can be obtained.

FIG. 2 and FIG. 3 show Example 1 of the zoom lens according to the present invention, and FIG. It is a figure which shows the spherical aberration, the distortion aberration, and the astigmatism at the wide angle end. It is a figure which shows the spherical aberration, the distortion aberration, and the astigmatism at the telephoto end. FIG. 5 and FIG. 6 show Example 2 of the zoom lens of the present invention, and this figure shows the lens configuration. It is a figure which shows the spherical aberration, the distortion aberration, and the astigmatism at the wide angle end. It is a figure which shows the spherical aberration, the distortion aberration, and the astigmatism at the telephoto end. FIG. 8 and FIG. 9 show Example 3 of the zoom lens according to the present invention, and this figure shows the lens configuration. It is a figure which shows the spherical aberration, the distortion aberration, and the astigmatism at the wide angle end. It is a figure which shows the spherical aberration, the distortion aberration, and the astigmatism at the telephoto end. FIG. 11 and FIG. 12 show Example 4 of the zoom lens according to the present invention, and FIG. It is a figure which shows the spherical aberration, the distortion aberration, and the astigmatism at the wide angle end. It is a figure which shows the spherical aberration, the distortion aberration, and the astigmatism 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, 10 ... Projector, 30 ... image forming unit

Claims (9)

The first lens group G1, which has a negative refractive power for performing focusing, in order from the magnification side, is fixed at the time of zooming, and has four groups of negative, positive, positive, and positive. The second lens group G2 having a positive refractive power and a third lens group G3 having a positive refractive power that move relative to each other to correct the image plane movement that occurs, and a fixed positive refractive power at the time of zooming A zoom lens comprising: a fourth lens group G4 having: and satisfying the following conditional expressions (1) and (2):
(1) 0.2 <G2t / fw <0.5
(2) 0.2 <G3t / fw <0.5
However,
fw: focal length of the entire lens system at the wide-angle end G2t: movement distance of the second lens unit at the time of zooming between the wide-angle end and the telephoto end G3t: third at the time of zooming between the wide-angle end and the telephoto end Moving distance of lens group The zoom lens according to claim 1, wherein the following conditional expression (3) is satisfied.
(3) 1.0 <bf / fw <1.5
However,
bf: Air equivalent back focus The zoom lens according to claim 1, wherein the following conditional expression (4) is satisfied.
(4) -1.4 <β2 × β3 <−0.8
However,
β2: Imaging magnification of the second lens group β3: Imaging magnification of the third lens group The zoom lens according to claim 2, wherein the following conditional expression (4) is satisfied.
(4) -1.4 <β2 × β3 <−0.8 2. The zoom lens according to claim 1, wherein the following conditional expressions (5) and (6) are satisfied.
(5) 2.0 <f2 / fw <5.0
(6) 2.0 <f3 / fw <5.0
However,
f2: focal length of the second lens group f3: focal length of the third lens group The zoom lens according to claim 2, wherein the following conditional expressions (5) and (6) are satisfied.
(5) 2.0 <f2 / fw <5.0
(6) 2.0 <f3 / fw <5.0 The zoom lens according to claim 3, wherein the following conditional expressions (5) and (6) are satisfied.
(5) 2.0 <f2 / fw <5.0
(6) 2.0 <f3 / fw <5.0 The zoom lens according to claim 4, wherein the following conditional expressions (5) and (6) are satisfied.
(5) 2.0 <f2 / fw <5.0
(6) 2.0 <f3 / fw <5.0 A projection apparatus comprising an image forming unit and a zoom lens for enlarging and projecting an image formed by the image forming unit,
The zoom lens has a negative, positive, positive, and positive four-group configuration. In order from the magnification side, the zoom lens is fixed at the time of zooming, and has a negative refractive power for performing focusing. And a second lens group G2 having a positive refractive power and a third lens group G3 having a positive refractive power, which move relative to each other, for correction of image plane movement caused by continuous zooming, fixed at zooming A projection apparatus comprising: a fourth lens group G4 having a positive refracting power and satisfying the following conditional expressions (1) and (2):
(1) 0.2 <G2t / fw <0.5
(2) 0.2 <G3t / fw <0.5
However,
fw: focal length of the entire lens system at the wide-angle end G2t: movement distance of the second lens unit at the time of zooming between the wide-angle end and the telephoto end G3t: third at the time of zooming between the wide-angle end and the telephoto end Moving distance of lens group

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