JP2008139706A - Zoom lens system and video projector using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wide angle zoom lens system in which distortion aberration is less and back focus is longer. <P>SOLUTION: The zoom lens system includes, in order as viewed from a longer conjugate distance: a first lens group having negative power; a second lens group having negative power; and a third lens group having positive power. When the zoom lens zooms from the wide angle end to the telephoto end, a face distance between the first and second lens groups monotonously increases, a face distance between the second and third lens groups monotonously decreases, and an amount of movement of the second lens group during zooming is largest. When the zoom lens zooms, a diaphragm moves on an optical axis together with the third lens group. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a video projector for enlarging and projecting an image of a zoom lens system and a spatial light modulator on a screen.

  A projector using a reflective spatial modulation element of the three primary colors of red, green, and blue usually has a projection lens system and a spatial modulation element including a prism for guiding illumination light and a color synthesis prism. For this reason, the projection lens requires a long back focus. Since the color-combining prism has an incident angle dependency in spectral characteristics, an optical system that makes the pupil position on the short conjugate distance side far enough from the spatial modulation element, that is, telecentricity is required.

As such a convex front four-group zoom lens system in which long back focus and telecentricity do not change even by zooming, there is a zoom lens system proposed in Patent Document 1, for example. Patent Document 2 proposes a compact three-group zoom by the present inventor. Patent Document 3 proposes a wide-angle zoom lens system by the present inventor. Furthermore, Patent Document 4 proposes a wide-angle fixed focus lens by the present inventor.
Japanese Patent Laid-Open No. 10-161027 JP 2004-138777 A JP 2004-138678 A JP 2004-138679 A

  When a reflective spatial modulation element is used in a video projector, a prism is required in addition to the color separation / synthesis prism in order to guide illumination light to the spatial modulation element. Therefore, a long back focus is required for the projection lens. Furthermore, there is a demand for shortening the projection distance from the screen to the video projector so that the projection lens can be used in a small space, and a wide-angle zoom lens system that can be used at a short projection distance is also demanded for the projection lens.

  On the other hand, the wide-angle lens proposed in Patent Document 4 has a sufficiently wide angle, but is a fixed-focus lens and has a limited degree of freedom in setting the set. The lens systems disclosed in Patent Document 1, Patent Document 2 and Patent Document 3 are zoom lens systems, but the half angle of view at the wide angle end is not sufficient. Furthermore, if these lenses are widened as they are, there is a problem that the distortion greatly exceeds the allowable range.

  An object of the present invention is to provide a zoom lens system with a wider angle and a video projector using the same while having a long back focus in order to realize a bright and high-definition projector.

  In order to achieve a compact, wide-angle zoom lens system with a long back focus, a negative, negative, and positive three-group zoom configuration is appropriate in order from the longest conjugate distance, making correction difficult with a wide-angle zoom lens system. In order to correct distortion, which is a special aberration, the second negative lens unit is negative so that it approaches the first negative lens unit at the wide-angle end and is farthest from the first negative lens unit at the telephoto end. The inventor has found that it is effective to increase the amount of movement of the two-group zoom lens system.

Based on the above knowledge, the above object can be achieved by the following zoom lens system. That is, the zoom lens system of the present invention is
A first lens group having a negative power, a second lens group having a negative power, and a third lens group having a positive power in order from the longest conjugate distance,
During zooming from the wide-angle end to the telephoto end, the surface distance between the first lens group and the second lens group monotonously increases, and the surface distance between the second lens group and the third lens group monotonously. The amount of movement of the second lens group at the time of zooming is the largest, and the diaphragm moves along the optical axis together with the third lens group at the time of zooming.

  According to the present invention, it is possible to provide a wide-angle zoom lens system and a video projector using the same while having a long back focus.

(Embodiments 1 to 5)
1 and 2 are configuration diagrams of a zoom lens system according to Embodiment 1 of the present invention, in which FIG. 1 corresponds to a wide angle end and FIG. 2 corresponds to a telephoto end. 5 and 6 are configuration diagrams of the zoom lens system according to Embodiment 2 of the present invention. FIG. 5 corresponds to the wide-angle end, and FIG. 6 corresponds to the telephoto end. 9 and 10 are configuration diagrams of a zoom lens system according to Embodiment 3 of the present invention, in which FIG. 9 corresponds to the wide-angle end and FIG. 10 corresponds to the telephoto end. FIGS. 13 and 14 are configuration diagrams of a zoom lens system according to Embodiment 4 of the present invention. FIG. 13 corresponds to the wide-angle end, and FIG. 14 corresponds to the telephoto end. 17 and 18 are configuration diagrams of a zoom lens system according to Embodiment 5 of the present invention, in which FIG. 17 corresponds to the wide-angle end and FIG. 18 corresponds to the telephoto end.

  The zoom lens system according to each embodiment will be described with reference to the drawings. The zoom lens system of each embodiment has a three-group configuration of negative, negative, and positive when viewed from the longer conjugate distance. N is a glass block such as a prism. S represents an image plane, which is a film or CCD in the case of an imaging system, or an LCD that is a spatial light modulation element in the case of a projection apparatus.

  In the zoom lens system according to each embodiment, when zooming from the wide-angle end to the telephoto end, the first lens group (G1) moves to the short conjugate distance side, and the second lens group (G2) has a short conjugate distance. The third lens group (G3) moves to the longer conjugate distance side.

  The first lens group has a nine-lens configuration (L1, L2, L3, L4, L5) in order from the longest conjugate distance in order of negative, positive, negative, negative, negative, negative, positive, positive, and positive lenses. , L6, L7, L8, L9). The second lens group has a negative power, and is a variable power lens group in which the magnification decreases with an absolute rate from the wide-angle end toward the telephoto end. The configuration of the second lens group is a three-lens configuration (L10, L11, L12) in order from the longest conjugate distance, that is, positive, negative, and negative lenses. The third lens group has positive power and is a variable power lens group. The aperture position is arranged in the third lens group. The configuration of the third lens group is, in order from the longest conjugate distance, eight lens configurations (L13, L14, L15, L16, L17, L18) of positive, negative, positive, positive, negative, positive, negative, and positive lenses. , L19, L20).

  Thus, the zoom lens system of each embodiment has a first lens group having a negative power, a second lens group having a negative power, and a positive power as viewed from the longer conjugate distance. The third lens group has a three-group configuration. In this way, a compact zoom lens system is realized by adopting a three-group zoom configuration.

  Hereinafter, the zoom lens system of each embodiment will be described in detail. Conventionally, a two-group zoom is known as a zoom suitable for a wide angle. The zoom lens system of each embodiment is also based on a two-group zoom composed of negative and positive. The two-group zoom is suitable for a wide angle and has a feature that a long back focus can be easily obtained. However, it is difficult to achieve a large zoom and a large aperture, and there is a problem that the back focus changes due to zooming from the wide angle end to the telephoto end, and the F number changes. In the second group zoom, a stop is disposed in the positive rear group. In the two-group zoom, the position through which the principal ray passes does not change due to zooming in the positive rear group, and changes greatly in the negative front group. Therefore, it is the front group that corrects distortion that changes due to zooming. Therefore, in the two-group zoom lens, it is necessary to devise the configuration of the front group to suppress the variation in distortion due to zooming.

  In the two-group zoom, a positive lens is added to the configuration of the front group so that positive distortion is generated. In particular, it is effective for correcting the distortion to have a shape in which higher-order distortion is generated. On the other hand, since distortion cannot be corrected in the rear group, it is necessary to perform distortion correction in the front group at both the wide-angle end and the telephoto end. In particular, if the front group is configured so that there is no distortion at the telephoto end, the position of the chief ray at the front group is higher at the wide-angle end than at the telephoto end. The distortion becomes overcorrected. For this reason, the conventional lens is designed to have a negative distortion at the wide-angle end and a positive distortion at the telephoto end. If it is attempted to reduce distortion at the telephoto end, the distortion becomes positive at the wide-angle end than at the telephoto end. In order to reduce this tendency, it is necessary to reduce the amount of high-order distortion, and it is difficult to balance distortion and other aberrations. Introducing an aspheric lens in the front group is effective for correcting distortion aberrations, but the lens diameter increases and problems remain in the manufacture of the aspheric lens. Therefore, in the zoom lens system of each embodiment, in order to correct overcorrection distortion at the wide-angle end, the zoom configuration has three groups, and the second lens group corrects distortion.

  In the zoom lens system of each embodiment, the first lens group has negative power. The first lens group needs negative power to ensure a back focus longer than the focal length. A lens having a positive power is added to correct distortion. In order to reduce the occurrence of high-order distortion, a large number of lenses having a positive power to be added are arranged on the side having a short conjugate distance. For a lens with positive power, a glass with a lower refractive index than a lens with negative power is selected. This is to generate a lot of positive distortion. Lenses with negative power have more meniscus lenses with convex surfaces facing longer conjugate distances, and lenses with positive power have more meniscus lenses with convex surfaces facing shorter conjugate distances. This is to reduce the occurrence of negative distortion and increase the occurrence of positive distortion. Thus, the first lens group is composed of a large number of lenses in order to form a negative lens group with less distortion. This is because the half angle of view of the zoom lens system is as large as 39 °, and if the half angle of view is reduced, the first lens group can be configured with a small number of components.

  In the zoom lens system of each embodiment, the second lens group has a negative power. Since the stop is arranged in the third lens group, negative distortion occurs in the second lens group having negative power. The distance between the second lens group and the third lens group is wide at the wide angle end, and the distance between the second lens group and the third lens group is narrow at the telephoto end. Therefore, the negative distortion occurring in the second lens group is large at the wide-angle end and small at the telephoto end. Although the first lens group is configured to minimize distortion as much as possible, positive overcorrection distortion occurs at the wide angle end where the field angle increases. It is the negative distortion of the second lens group that cancels the positive distortion at the wide-angle end. At the telephoto end, the distortion aberration generated in the first lens group is small, and since the distortion aberration generated in the second lens group is also small, the distortion aberration is small at the telephoto end.

  In this way, in order to generate negative distortion at the wide-angle end in the second lens group and to suppress the occurrence of distortion at the telephoto end, the position of the second lens group is the first at the wide-angle end. It is better to be closer to the first lens group and farther from the third lens group. Conversely, it is better that the telephoto end is closer to the third lens group. That is, since the position of the second lens group is close to the stop, the height of the principal ray can be lowered at the position of the second lens group, so that the occurrence of distortion can be reduced. In order to reduce the fluctuation of distortion at the wide-angle end and the telephoto end, it is better that the height of the principal ray passing through the second lens group has a large difference between the wide-angle end and the telephoto end. For this reason, it is preferable that the amount of movement of the second lens group is large.

  In the zoom lens system of each embodiment, the third lens group has positive power. Since the stop is located in the third lens group, the position through which the chief ray passes in the third lens group does not change due to zooming, and the occurrence of distortion does not change due to zooming.

  In the zoom lens system of each embodiment, the second lens group and the third lens group are variable power lens groups. The magnification of the third lens group increases from the wide-angle end toward the telephoto end. However, the magnification of the second lens group decreases from the wide-angle end toward the telephoto end. That is, the zooming of the second lens group does not contribute to zooming from the wide-angle end to the telephoto end, but acts to prevent zooming. Therefore, the third lens group requires a change in magnification that is larger than the amount of zooming of the entire zoom lens system.

  The zoom lens system according to each embodiment preferably satisfies the following conditions in terms of optical performance. A plurality of preferable conditions are defined for the zoom lens system according to each embodiment, but a zoom lens system configuration that satisfies all of the plurality of conditions is most desirable. However, by satisfying individual conditions, it is possible to obtain a zoom lens system that exhibits the corresponding effects.

It is desirable that the zoom lens system of each embodiment satisfies the following conditional expression (1).
3 <bfw / fw <5 (1)
here,
bfw: Air-focused back focus at infinity at the wide-angle end,
fw: focal length at the wide angle end.

  Conditional expression (1) defines the back focus at the wide-angle end with respect to the focal length at the wide-angle end, and defines the necessary back focus of the projection lens used in the projector. In particular, when a reflective element is used for the spatial modulation element, a prism block for introducing illumination light is disposed between the projection lens and the spatial modulation element in addition to the color synthesis prism. For this reason, the projector projection lens requires a long back focus. If the lower limit of conditional expression (1) is not reached, a necessary space cannot be obtained between the projection lens and the spatial modulation element, and the projector cannot be configured. On the other hand, if the upper limit of conditional expression (1) is exceeded, the total length and outer diameter of the lens will increase, making it impossible to make it compact.

It is desirable that the zoom lens system of each embodiment satisfies the following conditional expression (2).
1.3 <VD2 / fw <3.5 (2)
here,
VD2: the amount of movement of the second lens group when moving from the wide-angle end to the telephoto end,
fw: focal length at the wide angle end.

  Conditional expression (2) defines the amount of movement from the wide-angle end to the telephoto end of the second lens group with respect to the imaging plane of the lens as a ratio of the focal length at the wide-angle end. Defines the amount of group movement. If the lower limit of conditional expression (2) is not reached, the difference in distortion between the wide-angle end and the telephoto end will increase, making it difficult to correct the distortion. On the other hand, if the upper limit of conditional expression (2) is exceeded, the total lens length increases and the lens outer diameter also increases, making it impossible to form a compact configuration.

  In the zoom lens system of each embodiment, the second lens group has a positive power when viewed from the longest conjugate distance, and the second lens when viewed from the longest conjugate distance. It has negative power and is composed of at least three lenses. In this way, by using a lens having positive and negative power when viewed from the longer conjugate distance, the difference in distortion between the wide-angle end and the telephoto end can be kept small.

It is desirable that the zoom lens system of each embodiment satisfies the following conditional expression (3).
-0.2 <fw / f2g <-0.03 (3)
here,
f2g: focal length of the second lens group,
fw: focal length at the wide angle end.

  Conditional expression (3) defines the focal length of the second lens group by the ratio of the focal lengths at the wide angle end, and defines the focal length of the second lens group. If the lower limit of conditional expression (3) is not reached, large spherical aberration and coma occur in the second lens group, and correction cannot be made sufficiently. On the other hand, if the upper limit of conditional expression (3) is exceeded, it will be difficult to correct distortion.

  In the zoom lens system of each embodiment, it is preferable that the refractive index nd is 1.75 or more or the Abbe number νd is 80 or more for all the negative lenses constituting the first lens group. Since the first lens group has negative power, negative distortion occurs. However, by making the refractive index of all negative lenses 1.75 or more, the amount of generation of such negative distortion is reduced. Can do. Further, chromatic aberration of magnification is greatly generated, but by setting the Abbe number of all negative lenses to 80 or more, such chromatic aberration of magnification can be suppressed to a small value.

  In the zoom lens system according to each embodiment, the first lens group includes, in order from the longest conjugate distance, the first lens is a meniscus negative lens having a convex surface toward the longer conjugate distance, and the second lens is the conjugate distance. The positive meniscus lens with the convex surface facing the longer side, the third lens, the fourth lens, and the fifth lens with the convex surface facing the longer conjugate distance, the sixth lens the negative lens, and the seventh lens A positive meniscus lens with a convex surface facing the longer conjugate distance, a positive meniscus lens with a convex surface facing the shorter conjugate distance, an eighth lens, and a positive meniscus lens with the convex surface facing the shorter conjugate distance It is preferable that the lens is composed of at least nine lenses.

  Since the first lens group generates a large amount of distortion, it is preferable to have a configuration in which the generation of distortion is minimized and the generation of higher-order distortion is small. Correspondingly, in the zoom lens system of each embodiment, the first lens has a shape with little negative distortion, the second lens has a shape with little positive high-order distortion, the third, fourth, and third lenses. The fifth lens has a shape with little negative distortion, the seventh lens has a shape with little positive high-order distortion, and the eighth and ninth lenses have a shape with a large positive distortion, and the first lens group has a distortion aberration. Can be reduced.

  In the zoom lens systems according to the respective embodiments, it is preferable that the first lens group is movable on the optical axis separately from zooming. In a wide-angle lens such as the zoom lens system of each embodiment, the amount of field curvature changes when the conjugate distance changes. This is because the chief ray height in each lens changes depending on the conjugate distance. A change in field curvature due to the conjugate distance can be corrected by moving the first lens group on the optical axis.

It is desirable that the zoom lens system of each embodiment satisfies the following conditional expression (4).
−0.2 <fw / f1g <−0.08 (4)
here,
f1g: focal length of the first lens group,
fw: focal length at the wide angle end.

  Conditional expression (4) defines the focal length of the first lens group by the focal length at the wide angle end, and defines the focal length of the first lens group. If the lower limit of conditional expression (4) is not reached, it will be difficult to correct distortion. Conversely, if the upper limit of conditional expression (4) is exceeded, the total lens length and the lens outer diameter will increase.

It is desirable that the zoom lens system of each embodiment satisfies the following conditional expression (5).
1.0 <(B3t / B3w) / (ft / fw) <1.07 (5)
here,
B3w: the magnification at the wide-angle end of the third lens group,
B3t: magnification at the telephoto end of the third lens group,
fw: focal length at wide-angle end,
ft: focal length at the telephoto end.

  Conditional expression (5) is obtained by dividing the magnification ratio of the third lens unit at the telephoto end and the wide-angle end by the ratio of the focal lengths at the telephoto end and the wide-angle end. It defines the degree of contribution to the zoom amount of the entire zoom lens system. If the lower limit of conditional expression (5) is surpassed, the second lens group will be positioned closer to the third lens group at the wide-angle end and away from the third lens group at the telephoto end, making it difficult to correct distortion. Conversely, if the upper limit of conditional expression (5) is exceeded, the amount of movement of the third lens group will increase, and the F-number will change between the wide-angle end and the telephoto end, making it difficult to keep the brightness constant. .

  It should be noted that, as in the zoom lens system of each embodiment, it is desirable that all lens groups move during zooming. Various aberrations can be corrected satisfactorily by moving all the lens groups by zooming.

(Embodiment 6)
FIG. 21 is a schematic configuration diagram of a video projector according to the sixth embodiment of the present invention. In FIG. 21, the video projector includes a zoom lens system (projection lens system) A, a spatial light modulation element B, a light source C, and a color wheel D. Light from the light source C is temporally decomposed into three colors of blue, green, and red by a color wheel D that is temporally limited to three colors of blue, green, and red, and illuminates the spatial light modulator B. The spatial light modulation element B is formed by temporally dividing three types of optical images of blue, green, and red, and the formed optical image is enlarged and projected by a zoom lens system (projection lens system) A. By using the zoom lens system according to Embodiments 1 to 5 as the zoom lens system (projection lens system) A, it is possible to realize a compact video projector capable of obtaining a bright image with less color blur and distortion. it can.

(Embodiment 7)
FIG. 22 is a schematic configuration diagram of a rear projector according to the seventh embodiment of the present invention. In FIG. 22, the rear projector includes a video projector G, a mirror H, a transmissive screen I, and a housing J. The video projector G is the video projector described in the sixth embodiment. The image projected from the video projector G is reflected by the mirror H and formed on the transmission screen I. According to the seventh embodiment, a high-definition rear projector can be realized in a compact manner.

(Embodiment 8)
FIG. 23 is a schematic configuration diagram of a multivision system according to Embodiment 8 of the present invention. In FIG. 23, the multi-vision system includes a plurality of video projectors G, a transmissive screen I, and a housing K, respectively. Each video projector G is the video projector described in the sixth embodiment. The video signal is processed and divided by the video dividing circuit L and sent to a plurality of video projectors G. The image projected from the video projector G is formed on the transmission screen I. According to the eighth embodiment, the multivision system can be realized in a compact manner.

  Hereinafter, numerical examples in which the zoom lens systems according to Embodiments 1 to 5 are specifically implemented will be described. In each numerical example, the unit of length in the table is mm. In each numerical example, r is a radius of curvature, d is a surface interval, nd is a refractive index in the d line, and νd is an Abbe number in the d line.

  FIG. 3 is a longitudinal aberration diagram at the wide-angle end of the zoom lens system according to Example 1. FIG. 4 is a longitudinal aberration diagram of the zoom lens system according to Example 1 at the telephoto end. FIG. 7 is a longitudinal aberration diagram at the wide-angle end of the zoom lens system according to Example 2. FIG. 8 is a longitudinal aberration diagram at the telephoto end of the zoom lens system according to Example 2. FIG. 11 is a longitudinal aberration diagram at the wide-angle end of the zoom lens system according to Example 3. FIG. 12 is a longitudinal aberration diagram at the telephoto end of the zoom lens system according to Example 3. FIG. 15 is a longitudinal aberration diagram at the wide-angle end of the zoom lens system according to Example 4; FIG. 16 is a longitudinal aberration diagram of the zoom lens system at a telephoto end according to Example 4. FIG. 19 is a longitudinal aberration diagram at the wide-angle end of the zoom lens system according to Example 5. FIG. 20 is a longitudinal aberration diagram at the telephoto end of the zoom lens system according to Example 5. Each longitudinal aberration diagram shows spherical aberration (mm), astigmatism (mm), and distortion (%) in order from the left side.

(Example 1)
The zoom lens system of Example 1 corresponds to the first embodiment shown in FIGS. 1 and 2, and is a design example for the purpose of reducing distortion. Table 1 shows lens data of the zoom lens system of Example 1.

In the zoom lens system of Example 1, the F number (FNo) and the half angle of view (ω (°)) at the wide angle end are as follows.
FNo 2.50
ω 39.9

Further, with respect to the zoom lens system of Example 1, the focal length (f (mm)) and the variable surface interval (d (mm)) are as follows.
Wide angle end Intermediate position Telephoto end f 19.10 20.84 22.91
d18 4.30 14.74 27.38
d24 74.26 49.71 24.98
d41 13.74 17.02 21.06

(Example 2)
The zoom lens system of Example 2 corresponds to Embodiment 2 shown in FIGS. 5 and 6 and is a design example for the purpose of reducing distortion. Table 2 shows lens data of the zoom lens system of Example 2.

In the zoom lens system of Example 2, the F number (FNo) and the half angle of view (ω (°)) at the wide angle end are as follows.
FNo 2.51
ω 39.9

Further, regarding the zoom lens system of Example 2, the focal length (f (mm)) and the variable surface interval (d (mm)) are as follows.
Wide-angle end Intermediate position Telephoto end f 19.10 20.60 22.91
d18 4.30 12.97 27.60
d24 75.16 53.12 24.89
d41 13.74 17.02 21.06

(Example 3)
The zoom lens system of Example 3 corresponds to the third embodiment shown in FIGS. 9 and 10 and is a design example for the purpose of reducing distortion. Table 3 shows lens data of the zoom lens system of Example 3.

In the zoom lens system of Example 3, the F number (FNo) and the half angle of view (ω (°)) at the wide-angle end are as follows.
FNo 2.51
ω 39.9

Further, regarding the zoom lens system of Example 3, the focal length (f (mm)) and the variable surface interval (d (mm)) are as follows.
Wide-angle end Intermediate position Telephoto end f 19.10 20.76 22.93
d18 4.30 17.24 35.42
d24 75.72 49.21 19.24
d41 13.74 16.89 21.18

Example 4
The zoom lens system of Example 4 corresponds to Embodiment 4 shown in FIGS. 13 and 14 and is a design example for the purpose of reducing distortion. Table 4 shows lens data of the zoom lens system of Example 4.

In the zoom lens system of Example 4, the F-number (FNo) and the half angle of view (ω (°)) at the wide-angle end are as follows.
FNo 2.58
ω 39.9

Further, with respect to the zoom lens system of Example 4, the focal length (f (mm)) and the variable surface interval (d (mm)) are as follows.
Wide angle end Intermediate position Telephoto end f 19.10 20.79 22.92
d18 3.12 22.24 47.38
d24 78.81 45.84 10.00
d41 14.30 17.30 21.26

(Example 5)
The zoom lens system of Example 5 corresponds to the fifth embodiment shown in FIGS. 17 and 18 and is a design example for the purpose of reducing distortion. Table 5 shows lens data of the zoom lens system of Example 5.

In the zoom lens system of Example 5, the F number (FNo) and the half angle of view (ω (°)) at the wide-angle end are as follows.
FNo 2.51
ω 39.9

Further, regarding the zoom lens system of Example 5, the focal length (f (mm)) and the variable surface interval (d (mm)) are as follows.
Wide-angle end Intermediate position Telephoto end f 19.10 21.16 22.92
d18 39.88 44.98 48.53
d24 36.27 16.43 2.38
d41 14.48 17.99 21.01

Table 6 below shows corresponding values of the conditional expressions described above.

  The zoom lens system of the present invention is particularly suitable as a projection lens system of a video projector using a reflective spatial light modulator. It can also be used as an imaging optical system for a digital still camera or a digital video camera.

Configuration diagram of the zoom lens system at the wide-angle end according to Embodiment 1 (Example 1) Configuration diagram of a telephoto end of a zoom lens system according to Embodiment 1 (Example 1) Longitudinal aberration diagram at the wide-angle end of the zoom lens system according to Example 1 Longitudinal aberration diagram at the telephoto end of the zoom lens system according to Example 1 Configuration diagram of the zoom lens system at the wide-angle end according to Embodiment 2 (Example 2) Configuration diagram of a telephoto end of a zoom lens system according to Embodiment 2 (Example 2) Longitudinal aberration diagram at the wide-angle end of the zoom lens system according to Example 2 Longitudinal aberration diagram at the telephoto end of the zoom lens system according to Example 2 Configuration diagram of the zoom lens system at the wide angle end according to Embodiment 3 (Example 3) Configuration diagram of a telephoto end of a zoom lens system according to Embodiment 3 (Example 3) Longitudinal aberration diagram at the wide-angle end of the zoom lens system according to Example 3 Longitudinal aberration diagram at the telephoto end of the zoom lens system according to Example 3 Block diagram of the zoom lens system at the wide-angle end according to Embodiment 4 (Example 4) Configuration diagram of a telephoto end of a zoom lens system according to Embodiment 4 (Example 4) Longitudinal aberration diagram at the wide-angle end of the zoom lens system according to Example 4 Longitudinal aberration diagram at the telephoto end of the zoom lens system according to Example 4 Configuration diagram of the zoom lens system at the wide-angle end according to Embodiment 5 (Example 5) Configuration diagram of a telephoto end of a zoom lens system according to Embodiment 5 (Example 5) Longitudinal aberration diagram at the wide-angle end of the zoom lens system according to Example 5 Longitudinal aberration diagram at the telephoto end of the zoom lens system according to Example 5 Schematic configuration diagram of a video projector according to a sixth embodiment Schematic configuration diagram of a rear projector according to a seventh embodiment Schematic configuration diagram of a multi-vision system according to Embodiment 8

Explanation of symbols

A Zoom lens system (projection lens system)
B Spatial light modulation element C Light source D Color wheel G Video projector H Mirror I Transmission type screen J Case K Case L Image division circuit N Glass block S Image plane G1 First lens group G2 Second lens group G3 Third lens group

Claims (10)

A first lens group having a negative power, a second lens group having a negative power, and a third lens group having a positive power in order from the longest conjugate distance,
During zooming from the wide-angle end to the telephoto end, the surface distance between the first lens group and the second lens group monotonously increases, and the surface distance between the second lens group and the third lens group monotonously. The zoom lens system is characterized in that the amount of movement of the second lens group during zooming is the largest, and the diaphragm moves on the optical axis together with the third lens group during zooming. The zoom lens system according to claim 1, wherein the zoom lens system satisfies the following conditional expression (1):
3 <bfw / fw <5 (1)
here,
bfw: Air-focused back focus at infinity at the wide-angle end,
fw: focal length at the wide angle end. The zoom lens system according to claim 1, wherein the following conditional expression (2) is satisfied:
1.3 <VD2 / fw <3.5 (2)
here,
VD2: the amount of movement of the second lens group when moving from the wide-angle end to the telephoto end,
fw: focal length at the wide angle end.   When the second lens group has a long conjugate distance, the first lens has a positive power, and the second lens has a negative power as seen from the long conjugate distance. The zoom lens system according to claim 1, comprising a lens. The zoom lens system according to claim 1, wherein the following conditional expression (3) is satisfied:
-0.2 <fw / f2g <-0.03 (3)
here,
f2g: focal length of the second lens group,
fw: focal length at the wide angle end.   2. The zoom lens system according to claim 1, wherein the refractive index nd is 1.75 or more or the Abbe number νd is 80 or more for all negative lenses constituting the first lens group.   The first lens group is a meniscus negative lens in which the first lens has a convex surface toward the longer conjugate distance and the second lens has a convex surface toward the longer conjugate distance in order from the longer conjugate distance. The lens, the third lens, the fourth lens, and the fifth lens have a negative meniscus lens having a convex surface toward the longer conjugate distance, the sixth lens has a negative lens, and the seventh lens has a convex surface toward the longer conjugate distance. The positive meniscus lens, the eighth lens is a positive meniscus lens having a convex surface toward a shorter conjugate distance, and the ninth lens is a positive meniscus lens having a convex surface toward a shorter conjugate distance, and is composed of at least nine lenses. The zoom lens system according to claim 1.   The zoom lens system according to claim 1, wherein the first lens group is movable on the optical axis separately from zooming. The zoom lens system according to claim 1, wherein the following conditional expression (4) is satisfied:
−0.2 <fw / f1g <−0.08 (4)
here,
f1g: focal length of the first lens group,
fw: focal length at the wide angle end. The zoom lens system according to claim 1, wherein the following conditional expression (5) is satisfied:
1.0 <(B3t / B3w) / (ft / fw) <1.07 (5)
here,
B3w: the magnification at the wide-angle end of the third lens group,
B3t: magnification at the telephoto end of the third lens group,
fw: focal length at wide-angle end,
ft: focal length at the telephoto end.

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