Lens device

Abstract

To improve the quality of the entire image by performing the sufficient image plane correction in focusing adjustment and reduce the size and cost of the entire body of a lens device.SOLUTION: A lens device comprises: an image plane correction lens Lf1 which is arranged to be the closest to an object OBJ side, is constituted by an aspherical lens Ls and performs image plane correction by moving in an optical axis Dc direction; a front lens group Gf which is arranged on an image IMG side of the image plane correction lens Lf1, is constituted by an immovable lens group Gfs and whose entire body is constituted by the negative power; an intermediate lens group Gm whose entire body is constituted by the positive power by including at least one lens Lm1... moving in the optical axis Dc direction in zooming adjustment and in focusing adjustment; and a rear lens group Gr which includes at least one lens Lr1 having the positive power moving in the optical axis Dc direction in the zooming adjustment and at least one immovable lens Lre having the positive power.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a lens device suitable for use in a projection optical system provided in a projector or the like. [Background technology]

[0002] Conventionally, a lens device intended to correct the curvature of field that occurs when projecting from a projector onto a screen or the like has been known, and this type of lens device is described as a projection optical system in Patent Document 1.

[0003] The projection optical system described in Patent Document 1 aims to provide a projection optical system that has a simple configuration and is capable of adjusting the field curvature to an appropriate level. Specifically, the projection optical system includes a first lens whose power on the optical axis and the power in a meridian section at the outermost periphery are different from each other, a second lens adjacent to the first lens, and an aperture located at the position where the off-axis chief ray intersects with the optical axis. The projection optical system is configured so that the field curvature of the projected image can be adjusted by changing the distance between the first lens and the second lens in the optical axis direction, and is further configured to satisfy a predetermined conditional formula. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2017-126036 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, the conventional lens device disclosed in the above-mentioned Patent Document 1 has the following problems.

[0006] That is, since an image plane correction lens that performs image plane correction by moving in the optical axis direction, which is composed of an aspheric lens, is disposed in the front lens group in the optical system, and a focusing adjustment mechanism, that is, a focus lens or a focus lens group that moves in the optical axis direction, is disposed, a problem occurs in which the image plane correction is adversely affected by interference between the lenses. Specifically, during focusing adjustment, the image plane curvature fluctuates, and the image plane curvature cannot be sufficiently corrected by the movement of the image plane correction lens, resulting in a problem of a deterioration in the image quality of the entire projected image.

[0007] In addition, when the space available for installing the optical system is limited, the focusing adjustment mechanism and the image plane correction mechanism must be installed in closer proximity to each other, which not only complicates the mechanism of the lens device but also becomes an obstacle to making the entire lens device smaller and reducing its cost, presenting further issues that needed to be resolved.

[0008] SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to provide a lens device which overcomes the problems existing in the background art. [Means for solving the problem]

[0009] In order to solve the above-mentioned problems, the present invention provides a lens device 100 including, in order from the object OBJ side to the image IMG side, a front lens group Gf, an intermediate lens group Gm, and a rear lens group Gr, the lens device 100 including an image plane correction lens Lf1 arranged closest to the object OBJ, made up of an aspheric lens Ls, and performing image plane correction by moving in the direction of the optical axis Dc, a front lens group Gf arranged on the image IMG side of the image plane correction lens Lf1, made up of a stationary lens group Gfs, and having a negative power as a whole, and a lens group Gfs ... having a negative power as a whole, and a lens group Gfs arranged on the image IMG side of the image plane correction lens Lf1, having a negative power as a whole, and a lens group Gfs arranged on the image IMG side of the image plane correction lens Lf1, having a negative power as a whole, the optical system CS is characterized in that it comprises an intermediate lens group Gm configured with positive power as a whole by including at least one lens Lm1... that moves in the direction of the optical axis Dc when zooming, and a rear lens group Gr that includes at least one lens Lr1 or lens group having positive power that moves in the direction of the optical axis Dc during zooming adjustment, and at least one lens Lre or lens group that is stationary and has positive power, wherein fa is the paraxial focal length of the aspherical lens Ls and ft is the focal length of the entire system, and

[0010] In this case, according to a preferred embodiment of the invention, it is desirable that the optical system CS satisfies -0.7≦[Pc / Pf]≦-0.1 (condition 2), where Pc is the power of the aspherical lens Ls on the optical axis Dc and Pf is the power of the aspherical lens Ls at the outermost periphery. It is also desirable that the optical system CS satisfies -20≦[fa / ff]≦-1 (condition 3), where ff is the combined focal length of the focus group. On the other hand, the rear lens group Gr may be provided, closest to the object OBJ, with one positive lens Lr1 or a cemented lens Jr1 having a positive power that moves in the direction of the optical axis Dc during zoom adjustment. It is to be noted that the optical system CS is most suitable for application to a projection optical system. Effect of the Invention

[0011] The lens device 100 according to the present invention having such a configuration provides the following remarkable effects.

[0012] (1) The intermediate lens group Gm and the image plane correction lens Lf1, which move during focusing adjustment, have optical and mechanical interference suppressed, so that sufficient image plane correction can be performed, particularly by effectively eliminating the curvature of field that occurs during focusing adjustment, and the quality of the entire image can be improved. In addition, the design freedom of the focusing adjustment mechanism and the image plane correction mechanism can be increased, so that the mechanism of the lens device 100 can be simplified, the lens device 100 as a whole can be made smaller and more compact, and further the cost can be reduced.

[0013] (2) In a preferred embodiment, when constructing the optical system CS, where Pc is the power of the aspherical lens Ls on the optical axis Dc and Pf is the power of the aspherical lens Ls at its outermost periphery, if the optical system CS is configured to satisfy -0.7≦[Pc / Pf]≦-0.1 (condition 2), the power ratio between the power Pc on the optical axis Dc of the aspherical lens Ls and the power Pf of the outermost periphery can be kept within a good range, and therefore, the optical system CS can be implemented as an optimal form from the viewpoint of eliminating field curvature by setting the power ratio of the aspherical lens Ls.

[0014] (3) In a preferred embodiment, when constructing the optical system CS, if it is configured to satisfy -20≦[fa / ff]≦-1 (condition 3), where ff is the composite focal length of the focus group, the focal length ratio of the paraxial focal length fa of the aspheric lens Ls to the composite focal length ff of the focus group (middle lens group Gm) can be ensured within a favorable range, and therefore, by setting these focal length ratios, it can be implemented as an optimal form from the viewpoint of eliminating field curvature.

[0015] (4) In a preferred embodiment, the rear lens group Gr is configured so that it is provided closest to the object OBJ with a single positive lens Lr1 or a cemented lens Jr1 having positive power that moves in the direction of the optical axis Dc during zooming adjustment. This makes it possible to construct a lens configuration for the entire optical system CS, including the rear lens group Gr, that is capable of obtaining optimal optical characteristics.

[0016] (5) In a preferred embodiment, when the optical system CS is applied to a projection optical system, it is possible to effectively eliminate the curvature of field that occurs due to focusing in a projector or the like that projects onto a screen. [Brief description of the drawings]

[0017] [Figure 1] FIG. 1 is a lens configuration diagram of a lens device according to a first embodiment of the present invention; [Diagram 2] FIG. 2 is a functional explanatory diagram of the lens configuration of the lens device according to the first embodiment; [Diagram 3] FIG. 3 is a diagram showing an optical path of the lens device according to the first embodiment; [Figure 4] FIG. 2 is a longitudinal aberration diagram of the lens device of the first embodiment at a reference distance on the wide side; [Diagram 5] FIG. 2 is a longitudinal aberration diagram of the lens device of the first embodiment at a reference distance on the telephoto side; [Figure 6] FIG. 2 is a longitudinal aberration diagram of the lens device of Example 1 at a close distance on the wide-angle side; [Figure 7] FIG. 2 is a longitudinal aberration diagram of the lens device of Example 1 at a close distance on the telephoto side; [Figure 8] FIG. 4 is a longitudinal aberration diagram of the lens device of Example 1 at a long distance on the wide side; [Figure 9] FIG. 4 is a longitudinal aberration diagram of the lens device of the first embodiment at a long distance on the telephoto side; [Figure 10] FIG. 2 is a diagram illustrating the lens configuration and functions of a lens device according to a second embodiment of the present invention; [Figure 11] FIG. 3 is a diagram showing an optical path of the lens device according to the second embodiment; [Figure 12] FIG. 11 is a longitudinal aberration diagram of the lens device of the second embodiment at a reference distance on the wide side; [Figure 13] FIG. 11 is a longitudinal aberration diagram of the lens device of the second embodiment at a reference distance on the telephoto side; [Figure 14] FIG. 11 is a longitudinal aberration diagram of the lens device of Example 2 at a close distance on the wide-angle side; [Figure 15] FIG. 11 is a longitudinal aberration diagram of the lens device of the second embodiment at a close distance on the telephoto side; [Figure 16]FIG. 11 is a longitudinal aberration diagram of the lens device of Example 2 at a long distance on the wide side; [Figure 17] FIG. 11 is a longitudinal aberration diagram of the lens device of the second embodiment at a long distance on the telephoto side; [Figure 18] A list of the various conditions for the lens device, DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Next, preferred embodiments of the present invention, that is, Examples 1 and 2, will be described in detail with reference to the drawings. EXAMPLES

[0019] First, a lens device 100 according to a first embodiment of the present invention will be specifically described with reference to FIGS. 1 to 9 and FIG. 18(a).

[0020] First, referring to FIG. 1, a lens device 100 according to this embodiment (Example 1) will be described. It is assumed that the lens device 100 is applied to a projection optical system, particularly a projection zoom optical system, as a projection lens (zoom lens) used in a projector P, that is, an optical system CS. In this way, when the lens device 100 is applied to a projection optical system (projection zoom optical system) as an optical system CS, it is possible to effectively eliminate the field curvature that occurs due to focusing of a projector that projects onto a screen. In FIG. 1, OBJ indicates an object such as a screen, and IMG indicates an image that becomes an image display element such as a liquid crystal panel. Therefore, the object OBJ side is the front side in the direction of the optical axis Dc, and the image IMG side is the rear side in the direction of the optical axis Dc. In FIG. 1, 200 indicates a lens barrel that is diagrammatically drawn, and 300 indicates a prism that is diagrammatically drawn.

[0021] A lens apparatus 100 according to the first embodiment basically includes, in order from the object OBJ side to the image IMG side, a front lens group Gf, a middle lens group Gm, and a rear lens group Gr, as shown in FIG.

[0022] In this case, the front lens group Gf is configured so that the entire lens group has negative power. An image plane correction lens Lf1 that performs image plane correction by moving in the direction of the optical axis Dc is disposed closest to the object OBJ. This image plane correction lens Lf1 is configured with an aspheric lens Ls and uses a meniscus lens having a convex surface on the object OBJ side. In addition, a fixed lens group Gfs consisting of four single lenses is disposed on the image IMG side of this image plane correction lens Lf1. This lens group Gfs is configured by arranging, in order from the object OBJ side, a negative meniscus lens Lf2 having a convex surface on the object OBJ side, a negative meniscus lens Lf3 having a convex surface on the object OBJ side, a negative meniscus lens Lf4 having a convex surface on the object OBJ side, and a biconcave lens Lf5.

[0023] On the other hand, the intermediate lens group Gm is configured with a positive power as a whole and includes at least one lens Lm1 ... that moves along the optical axis Dc during zooming adjustment and focusing adjustment. In the case of Example 1, the intermediate lens group Gm is configured with two cemented lenses, namely, from the object OBJ side, a cemented lens Jm1 formed by cementing a biconvex lens Lm1 to a negative meniscus lens Lm2 having a convex surface on the image IMG side, and a cemented lens Jm2 formed by cementing a biconcave lens Lm3 to a biconvex lens Lm4.

[0024] The rear lens group Gr is composed of a biconvex lens Lr1, which is arranged at the front on the object OBJ side and is composed of a single lens having positive power that moves in the direction of the optical axis Dc during zooming adjustment, and a lens group Gre, which is stationary and has positive power as a whole, arranged on the image IMG side relative to the biconvex lens Lr1. The lens group Gre includes, from the object OBJ side, a negative meniscus lens Lr2 having a convex surface on the image IMG side, a cemented lens Jr1 made of a positive meniscus lens Lr3 having a convex surface on the image IMG side and a negative meniscus lens Lr4 having a convex surface on the image IMG side, a positive meniscus lens Lr5 having a convex surface on the image IMG side, a cemented lens Jr2 made of a biconcave lens Lr6 and a biconvex lens Lr7, a biconvex lens Lr8, and a biconvex lens Lre (see FIG. 2). Therefore, the rear lens group Gr includes at least one lens Lr1 having positive power that moves in the direction of the optical axis Dc during zooming adjustment, and at least one lens Lre that has positive power and remains stationary.

[0025] In this way, if the rear lens group Gr is configured with a single positive lens Lr1 that is positioned closest to the object OBJ and moves in the direction of the optical axis Dc during zooming adjustment, it is possible to construct a lens configuration for the entire optical system CS, including the rear lens group Gr, that is capable of obtaining optimal optical characteristics.

[0026] In the above optical system CS, the optical conditions are set so as to satisfy the following (Condition 1) to (Condition 3).

[0027] First, let fa be the paraxial focal length of the aspherical lens Ls, and let ft be the focal length of the entire system. -100≦〔fa / ft〕≦-10 …(Condition 1) This ensures that the focal length ratio between the paraxial focal length fa of the aspheric lens Ls and the focal length ft of the entire system falls within a favorable range, and therefore the setting of this focal length ratio can be implemented as an optimal form from the standpoint of eliminating field curvature.

[0028] In addition, when the power of the aspherical lens Ls on the optical axis Dc is Pc and the power of the aspherical lens Ls at the most peripheral portion is Pf, -0.7≦〔Pc / Pf〕≦-0.1 …(Condition 2) This ensures that the power ratio between the power Pc on the optical axis Dc of the aspherical lens Ls and the power Pf of the outermost periphery is within a favorable range, and therefore the setting of the power ratio in the aspherical lens Ls can be used as an optimal embodiment from the viewpoint of eliminating the curvature of field.

[0029] Furthermore, since the paraxial focal length of the aspherical lens Ls is fa, when the combined focal length of the focus group is ff, -20≦〔fa / ff〕≦-1 …(Condition 3) This ensures that the focal length ratio between the paraxial focal length fa of the aspheric lens Ls and the composite focal length ff of the focus group (middle lens group Gm) falls within a favorable range, and therefore the setting of this focal length ratio can be implemented as an optimal form from the standpoint of eliminating field curvature.

[0030] 2 is a functional diagram for explaining the lenses and lens groups that move in the direction of the optical axis Dc during zooming and focusing adjustment of the optical system CS. In the optical system CS of Example 1, as shown in FIG. 2, the lens group Gfs composed of four single lenses in the front lens group Gf is stationary, and all the other lenses in the rear lens group Gr are stationary except for the biconvex lens Lr1 arranged at the front of the rear lens group Gr on the object OBJ side.

[0031] On the other hand, the image plane correction lens Lf1 arranged closest to the object OBJ in the front lens group Gf can be moved in the direction of the optical axis Dc by rotating an image plane correction ring (not shown) arranged on the lens barrel 200. This changes the position of the image plane correction lens Lf1 in the direction of the optical axis Dc, and image plane correction can be performed. During focusing adjustment, the middle lens group Gm can be moved in the direction of the optical axis Dc by rotating a focus adjustment ring (not shown) arranged on the lens barrel 200. During zooming adjustment, the middle lens group Gm and the biconvex lens Lr1 arranged at the front of the rear lens group Gr can be moved in the direction of the optical axis Dc by rotating a zoom adjustment ring (not shown) arranged on the lens barrel 200. Note that FIG. 3 shows a light ray diagram of the lens device 100 in the first embodiment.

[0032] Tables 1a and 1b show lens data for the entire lens system in the lens device 100 of Example 1, where Table 1a shows surface data and Table 1b shows the focus and image plane correction intervals and aspheric coefficients. The entire lens system at an object point of infinity has an F-number of F1.7 and an image height of 10.00 mm.

[0033] [Table 1a]

[0034] [Table 1b]

[0035] In the surface data of Table 1a, the surface number of the lens surface counted from the object OBJ side is indicated by i, and this surface number i corresponds to the code (number) shown in Figure 1. Correspondingly, the radius of curvature R(i) of the lens surface, the axial surface distance D(i), the refractive index nd(i), the Abbe number νd(i), and the effective radius Re(i) of the lens surface are indicated. nd(i) and νd(i) are values ​​for the d-line (550 [nm]). The axial surface distance D(i) indicates the lens thickness or air space between the opposing surfaces. The radius of curvature R(i) and the surface distance D(i) are in units of [mm]. The surface number OBJ indicates the object, and IMG indicates the image position. The Infinity of the radius of curvature R(i) is a flat surface. The blanks for the refractive index nd(i) and the Abbe number νd(i) indicate air.

[0036] Table 1b shows the air gap (THI) for focus and image plane correction. In addition, in an orthogonal coordinate system (X, Y, Z) with the center of the surface as the origin and the direction of the optical axis Dc as Z, when S2... is the aspheric surface number, Z is expressed by equation 1. In equation 1, R is the central radius of curvature, A4, A6, A8, A10, A12, and A14 are the 4th-order, 6th-order, 8th-order, 10th-order, 12th-order, and 14th-order aspheric coefficients, respectively, and H is the distance from the origin on the optical axis. In Table 1b, "E" means "×10".

[0037]

number

[0038] As shown in FIG. 18(a), in the lens device 100 of Example 1, the paraxial focal length fa of the aspheric lens Ls is -784.6 mm, the focal length ft of the entire system on the WIDE side is 10.8 mm, and therefore fa / ft is "-72.6", and the focal length ft of the entire system on the TELE side is 11.1 mm, and therefore fa / ft is "-70.7", and both the WIDE side and the TELE side satisfy (condition 1) "-100≦[fa / ft]≦-10".

[0039] In addition, the power Pc on the optical axis Dc of the aspherical lens Ls is 0.0013, and the power Pf of the lens Ls at the outermost periphery is -0.0051, so Pc / Pf is -0.25, which satisfies (condition 2) -0.7≦[Pc / Pf]≦-0.1. Furthermore, the paraxial focal length fa of the aspherical lens Ls is -784.6 [mm], and the combined focal length ff of the focus group is 57.6 [mm], so fa / ff is -13.6, which satisfies (condition 3) -20≦[fa / ff]≦-1.

[0040] 4 to 9 show longitudinal aberration diagrams after image surface correction in the lens device 100 of the first embodiment. Figs. 4 and 5 show longitudinal aberration diagrams on the WIDE side and TELE side at a reference distance (OBJ=1650 mm), Figs. 6 and 7 show longitudinal aberration diagrams on the WIDE side and TELE side at a close distance (OBJ=840 mm), and Figs. 8 and 9 show longitudinal aberration diagrams on the WIDE side and TELE side at a long distance (OBJ=4200 mm). From the left, each longitudinal aberration diagram shows spherical aberration (610 nm, 550 nm, 470 nm), astigmatism (550 nm), and distortion aberration (550 nm). The scales are ±0.10 mm, ±0.10 mm, and ±1.0%.

[0041] As shown in Figures 4 to 9, it can be confirmed that the lens device 100 of Example 1 has good aberration characteristics with no significant disturbance in any of the longitudinal aberrations, that is, imaging performance (optical performance) with image plane correction performed. EXAMPLES

[0042] Next, a lens device 100 according to a second embodiment of the present invention will be described with reference to FIGS. 10 to 17 and FIG. 18(b).

[0043] The lens apparatus 100 according to the second embodiment basically includes, in order from the object OBJ side to the image IMG side, a front lens group Gf, a middle lens group Gm, and a rear lens group Gr, as in the first embodiment, as shown in FIG.

[0044] In this case, the front lens group Gf is configured so that the entire lens group has negative power. An image plane correction lens Lf1 that performs image plane correction by moving in the direction of the optical axis Dc is disposed closest to the object OBJ. This image plane correction lens Lf1 is configured with an aspheric lens Ls and uses a meniscus lens having a convex surface on the object OBJ side. In addition, in the case of the second embodiment, a fixed lens group Gfs made of two single lenses is disposed on the image IMG side of this image plane correction lens Lf1. This lens group Gfs is configured by arranging, in order from the object OBJ side, a negative meniscus lens Lf2 having a convex surface on the object OBJ side and a biconcave lens Lf3.

[0045] On the other hand, the intermediate lens group Gm is configured with a positive power as a whole and includes at least one lens Lm1... that moves along the optical axis Dc during zooming adjustment and focusing adjustment. In the illustrated example, the intermediate lens group Gm is configured with two cemented lenses, namely, from the object OBJ side, a cemented lens Jm1 cemented with a biconvex lens Lm1 and a biconcave lens Lm2, and a cemented lens Jm2 cemented with a biconvex lens Lm3 and a negative meniscus lens Lm4 having a convex surface on the image IMG side.

[0046] The rear lens group Gr is arranged at the front of the object OBJ side and includes a cemented lens Jr1, which is made by cementing a biconvex lens Lr1 having positive power that moves in the direction of the optical axis Dc during zooming adjustment and a negative meniscus lens Lr2 having a convex surface on the image IMG side. On the image IMG side of the cemented lens Jr1, a biconcave lens Lr3 and a biconvex lens Lr4 are arranged, which move in the direction of the optical axis Dc during zooming adjustment. On the image IMG side of the cemented lens Jr1, a cemented lens Jr2 (see FIG. 11) is arranged, which is made by cementing a biconvex lens Lr5 and a biconcave lens Lr6, and on the image IMG side of the cemented lens Jr2, a biconvex lens Lr7 and a positive meniscus lens Lr8 having a convex surface on the image IMG side are arranged. On the image IMG side of the positive meniscus lens Lr8, a biconvex lens Lr9 that is fixed and has positive power is arranged. Therefore, the cemented lens Jr1, the biconcave lens Lr3, the biconvex lens Lr4, the cemented lens Jr2, the biconvex lens Lr7, and the positive meniscus lens Lr8 in the rear lens group Gr move along the optical axis Dc during zoom adjustment. Thus, the rear lens group Gr includes at least one lens Lr1 having positive power that moves along the optical axis Dc during zoom adjustment, and at least one lens Lre having positive power that is stationary.

[0047] In the above optical system CS, the optical conditions are set so as to satisfy the following (Condition 1) to (Condition 3), which is the same as in the above-described first embodiment.

[0048] On the other hand, in the optical system CS of the second embodiment, as shown in FIG. 10, the lens group Gfs composed of two single lenses in the front lens group Gf and the biconvex lens Lre arranged closest to the image IMG side in the rear lens group Gr are fixed. On the other hand, the image plane correction lens Lf1 arranged closest to the object OBJ side in the front lens group Gf can be moved in the direction of the optical axis Dc by rotating an image plane correction ring (not shown) arranged in the lens barrel 200. This changes the position of the image plane correction lens Lf1 in the direction of the optical axis Dc, and image plane correction can be performed. In addition, during focusing adjustment, the middle lens group Gm can be moved in the direction of the optical axis Dc by rotating a focus adjustment ring (not shown) arranged in the lens barrel 200. Furthermore, during zoom adjustment, the cemented lens Lr1, the biconcave lens Lr3, the biconvex lens Lr4, the cemented lens Jr2, the biconvex lens Lr7, and the positive meniscus lens Lr8 in the middle lens group Gm and the rear lens group Gr can be moved in the direction of the optical axis Dc by rotating a zoom adjustment ring (not shown) disposed on the lens barrel 200. Note that FIG. 11 shows a ray diagram of the lens device 100 in the second embodiment.

[0049] Tables 2a and 2b show the lens data of the entire lens system in the lens device 100 of Example 2, where Table 2a shows the surface data and Table 2b shows the focus and image plane correction intervals and aspheric coefficients. The entire lens system at an infinite object point has an F-number of F1.9 and an image height of 12.25 mm.

[0050] [Table 2a]

[0051] [Table 2b]

[0052] The format of the lens data in Tables 2a and 2b is basically the same as that in Example 1. As shown in Fig. 18(b), in the lens device 100 of Example 2, the paraxial focal length fa of the aspheric lens Ls is -221.5 [mm], and the focal length ft of the entire system on the WIDE side is 14.7 [mm], so fa / ft is "-15.1", and the focal length ft of the entire system on the TELE side is 19.7 [mm], so fa / ft is "-11.2", and both the WIDE side and the TELE side satisfy (Condition 1) "-100≦[fa / ft]≦-10".

[0053] In addition, the power Pc on the optical axis Dc of the aspherical lens Ls is 0.0045, and the power Pf of the lens Ls at the outermost periphery is -0.0101, so Pc / Pf is -0.45, which satisfies (condition 2) -0.7≦[Pc / Pf]≦-0.1. Furthermore, the paraxial focal length fa of the aspherical lens Ls is -221.5 [mm], and the combined focal length ff of the focus group is 79.4 [mm], so fa / ff is -2.79, which satisfies (condition 3) -20≦[fa / ff]≦-1.

[0054] 12 to 17 show longitudinal aberration diagrams after image surface correction in the lens device 100 of the first embodiment. Figs. 12 and 13 show longitudinal aberration diagrams on the WIDE side and TELE side at a reference distance (OBJ=1650mm), Figs. 14 and 15 show longitudinal aberration diagrams on the WIDE side and TELE side at a close distance (OBJ=840mm), and Figs. 16 and 17 show longitudinal aberration diagrams on the WIDE side and TELE side at a long distance (OBJ=4200mm). From the left, each longitudinal aberration diagram shows spherical aberration (610nm, 550nm, 470nm), astigmatism (550nm), and distortion aberration (550nm). The scales are ±0.10mm, ±0.10mm, and ±1.0%.

[0055] As in the case of the lens device 100 of the second embodiment, as shown in FIGS. 12 to 17, it can be confirmed that there is no significant disturbance in any of the longitudinal aberrations and that good aberration characteristics, that is, imaging performance (optical performance) with image plane correction is obtained.

[0056] Therefore, the lens device 1 according to the present embodiment (Examples 1 and 2) basically includes an image plane correction lens Lf1 arranged closest to the object OBJ, made up of an aspheric lens Ls, and performing image plane correction by moving in the direction of the optical axis Dc, a front lens group Gf arranged on the image IMG side of the image plane correction lens Lf1, made up of a stationary lens group Gfs, and configured with negative power as a whole, and at least one lens Lm1... that moves in the direction of the optical axis Dc during zooming adjustment and focusing adjustment, thereby making the whole lens group Gf have positive power. The optical system CS includes an intermediate lens group Gm and a rear lens group Gr including at least one lens Lr1 or lens group having positive power that moves in the direction of the optical axis Dc during zooming adjustment and at least one lens Lre or lens group having positive power that is stationary, and satisfies -100≦[fa / ft]≦-10 (condition 1), where fa is the paraxial focal length of the aspherical lens Ls and ft is the focal length of the entire system. This suppresses optical and mechanical interference between the intermediate lens group Gm and the image surface correction lens Lf1 that moves during focusing adjustment. As a result, sufficient image surface correction can be performed, such as effectively eliminating the curvature of field that occurs during focusing adjustment, and the quality of the entire image can be improved. In addition, the degree of freedom in designing the focusing adjustment mechanism and the image surface correction mechanism can be increased, so that the lens device 100 can be simplified in terms of mechanism, the lens device 100 as a whole can be made compact and inexpensive.

[0057] Although the preferred embodiments including Examples 1 and 2 have been described in detail above, the present invention is not limited to such embodiments, and the detailed configuration, shape, material, quantity, numerical values, etc. can be arbitrarily changed, added, or deleted without departing from the gist of the present invention.

[0058] For example, including at least one lens Lm1... includes a single lens, a cemented lens, and a lens group, and the number of lenses is arbitrary. Similarly, at least one lens Lr1 and at least one lens Lre each include a single lens, a cemented lens, and a lens group, and the number of lenses is arbitrary. Meanwhile, in the optical system CS, it is desirable to satisfy -0.7≦[Pc / Pf]≦-0.1 (condition 2), but this is not an essential component requirement. Furthermore, in the optical system CS, it is desirable to satisfy -20≦[fa / ff]≦-1 (condition 3), but this is not an essential component requirement. [Industrial Applicability]

[0059] The lens device according to the present invention can be used as a dedicated lens or a projection lens (projection zoom lens) including an interchangeable lens in various optical devices such as a projector. [Explanation of symbols]

[0060] 100: lens device, OBJ: object, IMG: image, Gf: front lens group, Gfs: lens group, Gm: intermediate lens group, Gr: rear lens group, Dc: optical axis, CS: optical system, Ls: aspheric lens, Lf1: image plane correction lens, Lm1: lens, Lr1: lens, Lre: lens, fa: paraxial focal length of aspheric lens, ft: focal length of entire system, Pc: power on optical axis of aspheric lens, Pf: power of aspheric lens at the most periphery, ff: composite focal length of focus group, Jr1: cemented lens

Claims

1. a front lens group arranged on the image side of the image plane correction lens, the front lens group being arranged on the image side of the image plane correction lens and being composed of stationary lens groups, the front lens group being composed of negative power as a whole; an intermediate lens group arranged on the image side of the image plane correction lens, the intermediate lens group being composed of positive power as a whole and moving in the optical axis direction during zooming adjustment and focusing adjustment; and a rear lens group including at least one lens or lens group having positive power that moves in the optical axis direction during zooming adjustment, and at least one lens or lens group having positive power that is stationary, the rear lens group being characterized in that the lens device is equipped with an optical system that satisfies the following (Condition 1), where fa is the paraxial focal length of the aspherical lens and ft is the focal length of the entire system. -100≦[fa / ft]≦-10 ... (Condition 1)

2. 2. The lens device according to claim 1, wherein the optical system satisfies the following condition 2, where Pc is the power on the optical axis of the aspherical lens and Pf is the power of the aspherical lens at its outermost periphery. −0.7≦[Pc / Pf]≦−0.1 … (Condition 2)

3. 3. The lens apparatus according to claim 1, wherein the optical system satisfies the following condition 3, where ff is a combined focal length of the focus group: -20≦[fa / ff]≦-1 ... (Condition 3)

4. 4. A lens apparatus according to claim 1, wherein the rear lens group comprises, closest to the object side, one positive lens or one cemented lens having positive power which moves in the optical axis direction during zooming adjustment.

5. 4. The lens device according to claim 1, wherein the optical system is applied to a projection optical system.

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