Lens device

Abstract

To realize a high zoom ratio and further a widened angle of view while setting back focus to an optimum length and securing sufficient optical performance.SOLUTION: The present invention includes an optical adjustment system 100 in which a front lens group Gf is constituted by a first lens group G1 having negative refractive power overall, a second lens group G2 having positive refractive power overall, and a third lens group G3, and a rear lens group Gr is constituted by a fourth lens group G4 having positive refractive power overall, a fifth lens group G5 having at least two positive lenses L10..., and a sixth lens group G6 having positive refractive power overall. At zooming adjustment time, the G1 and the G6 are immobilized and the G2 group to the G5 group are moved independently in an optical axis Dc direction; at focusing adjustment time, the G2 is moved in the optical axis Dc direction. When it is assumed that bf represents back focus and fw represents the focal distance of an entire system G10 on the wide angle side, the conditional expression 2.3<[bf / fw]<3.8 is satisfied.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 with a simple configuration that can adjust the field curvature appropriately. Specifically, the projection optical system includes a first lens whose power on the optical axis and the power in the meridional section of the outermost periphery are different from each other, a second lens adjacent to the first lens, and a diaphragm 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] Japanese Patent Application Laid-Open No. 2017-126036 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] First, since a projection optical system such as a projector is equipped with a prism in the optical system on the projection device main body side, in a lens device (interchangeable lens) used in this type of projection device, if the focal length of the entire system on the wide-angle side is short, it becomes difficult to make the back focus long, and it becomes impossible to ensure space for arranging the prism. On the other hand, if the back focus is made long in order to ensure space for arranging the prism, it will lead to an increase in the diameter of the rear lens on the lens device side, and there is a risk that optical performance will be reduced. Therefore, with a lens device for such applications, it has been difficult to achieve a high zoom ratio and a wide angle of view while ensuring sufficient optical performance.

[0007] Second, because the projection optical system includes a front lens group that includes an aspherical lens and moves in the optical axis direction, and a focusing adjustment mechanism, i.e., a focus lens or focus lens group that moves in the optical axis direction, interference between the lenses can adversely affect the image plane correction. Specifically, the image plane curvature fluctuates during focusing adjustment, and the image plane correction lens movement cannot adequately correct the image plane curvature, resulting in a degradation of the overall image quality of the projected image. Furthermore, when the optical system installation space is limited, the focusing adjustment mechanism and the image plane correction mechanism must be located closer to each other, which increases the mechanical complexity of the lens device and hinders efforts to reduce the overall size and cost of the lens device, creating additional issues that need to be resolved.

[0008] SUMMARY OF THE INVENTION An object of the present invention is to provide a lens device that solves the problems present 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 1 that is configured to be used as a projection optical system as an optical system G, and that is composed of, in order from the object OBJ side to the image IMG side, a front lens group Gf and a rear lens group Gr, the front lens group Gf comprising, in order from the object OBJ side to the image IMG side, a first lens group G1 that has negative refractive power overall and is provided with, closest to the object OBJ, an image plane correction lens Ls that uses an aspherical lens that performs image plane correction by moving in the direction of the optical axis Dc, a second lens group G2 that has positive refractive power overall, and a third lens group G3, and the rear lens group Gr comprises, in order from the object OBJ side to the image IMG side, a fourth lens group G4 that has positive refractive power overall, at least The optical system is characterized in that it is composed of a fifth lens group G5 having two positive lenses L10... and a sixth lens group G6 having positive refractive power overall, and has a zoom ratio of 1.4 or more and a total angle of view on the wide-angle side of 70° or more, and is equipped with an optical adjustment system 100 that keeps the first lens group G1 and the sixth lens group G6 stationary and moves the second lens group G2 to the fifth lens group G5 independently along the optical axis Dc during zooming adjustment, and moves the second lens group G2 along the optical axis Dc during focusing adjustment, and is equipped with an optical system G that satisfies the conditional expression 2.3<[bf / fw]<3.8, where bf is the back focus and fw is the focal length of the entire system G10 on the wide-angle side.

[0010] In this case, according to a preferred embodiment of the present invention, the second lens group G2 can be composed of, in order from the object OBJ side to the image IMG side, a positive lens L4 using a single lens, a negative lens L5 using a single lens, and a positive lens L6 using a single lens, and the focal length fg2 of the second lens group G2 can be set to less than 80 mm. Meanwhile, the fifth lens group G5 can be provided, closest to the object OBJ, with a cemented lens J9 (J10) formed by cementing together a negative lens Ln9 (Ln10) located on the object OBJ side and a positive lens Lp9 (Lp10) located on the image IMG side. In this case, it is desirable to set the refractive index of the negative lens Ln9 (Ln10) to 1.85 or more at the d-line and to set the Abbe number of at least two positive lenses L10... in the fifth lens group G5 to 70 or more at the d-line. [Effects of the Invention]

[0011] The lens device 1 according to the present invention having such a configuration provides the following significant effects.

[0012] (1) The front lens group Gf is composed of, in order from the object OBJ side to the image IMG side, a first lens group G1 having negative refractive power as a whole, a second lens group G2 having positive refractive power as a whole, and a third lens group G3, and the rear lens group Gr is composed of, in order from the object OBJ side to the image IMG side, a fourth lens group G4 having positive refractive power as a whole, a fifth lens group G5 having at least two positive lenses L10 and L12, and a sixth lens group G6 having positive refractive power as a whole, and during zooming adjustment, The optical system includes an optical adjustment system 100 that keeps the first lens group G1 and the sixth lens group G6 stationary, and moves the second lens group G2 through the fifth lens group G5 independently along the optical axis Dc, and moves the second lens group G2 along the optical axis Dc during focusing adjustment. The optical system G satisfies the condition 2.3<[bf / fw]<3.8, where bf is the back focus and fw is the focal length of the entire system G10 on the wide-angle side. This allows the back focus to be set to an optimal length. This ensures sufficient optical performance while achieving a high zoom ratio (1.4x or greater) and a wide angle of view (70° or greater).

[0013] (2) The first lens group G1 includes an image plane correction lens Ls, which moves in the direction of the optical axis Dc to perform image plane correction, closest to the object OBJ. This suppresses optical and mechanical interference between the second lens group G2, which moves during focusing adjustment, and the image plane correction lens Ls. This allows for sufficient image plane correction, particularly by effectively eliminating field curvature that occurs during focusing adjustment, thereby improving the overall image quality. In addition, this increases the design freedom of the focusing adjustment mechanism and the image plane correction mechanism, thereby simplifying the lens device 1's mechanics, making the entire lens device 1 smaller and more compact, and reducing costs.

[0014] (3) Because an aspherical lens is used for the image plane correction lens Ls, the power ratio between the power on the optical axis Dc and the power at the outermost periphery of the aspherical lens can be set within a favorable range. This makes it possible to effectively eliminate field curvature by optimizing the power ratio.

[0015] (4) As the optical system G is applied to a projection optical system, it is possible to achieve a high zoom ratio and a wide angle of view while ensuring sufficient optical performance, particularly for projectors that project onto a screen, and it is also possible to effectively eliminate the curvature of field that occurs during focusing.

[0016] (5) In a preferred embodiment, when constructing the second lens group G2, it is composed of, in order from the object OBJ side to the image IMG side, a positive lens L4 using a single lens, a negative lens L5 using a single lens, and a positive lens L6 using a single lens. If the focal length of the second lens group G2 is set to less than 80 mm, various aberrations such as coma, astigmatism, and field curvature can be corrected in a balanced manner. In particular, the amount of movement of the lens groups during focusing adjustment can be reduced, thereby making it possible to shorten the overall length of the lens device 1.

[0017] (6) In a preferred aspect, when configuring the fifth lens group G5, if a cemented lens J9 (J10) is provided closest to the object OBJ, which is formed by cementing together a negative lens Ln9 (Ln10) located on the object OBJ side and a positive lens Lp9 (Lp10) located on the image IMG side, it is possible to construct a desirable lens configuration for the entire optical system G, including the fifth lens group G5, from the perspective of obtaining optimal optical characteristics.

[0018] (7) In a preferred embodiment, by setting the refractive index for the d-line of the negative lens Ln9 of the cemented lens J9 in the fifth lens group G5 to 1.85 or more, spherical aberration, coma, and astigmatism can be effectively corrected, and in addition, axial chromatic aberration and chromatic aberration of magnification can also be corrected.

[0019] (8) In a preferred embodiment, if the Abbe number for the d-line of at least two positive lenses L10 in the fifth lens group G5 is set to 70 or more, axial chromatic aberration and lateral chromatic aberration in particular can be corrected well. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1 is a lens configuration diagram of a lens device according to a first embodiment of the present invention; [Figure 2] FIG. 2 is a functional explanatory diagram of an optical adjustment system in the lens device of the first embodiment; [Figure 3] FIG. 2 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 Example 1 at a reference distance on the wide-angle side; [Figure 5] FIG. 2 is a longitudinal aberration diagram of the lens device of Example 1 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. 2 is a longitudinal aberration diagram of the lens device of Example 1 at a long distance on the wide side; [Figure 9] FIG. 2 is a longitudinal aberration diagram of the lens device of Example 1 at a long distance on the telephoto side; [Figure 10] FIG. 2 is a lens configuration diagram of the lens device of the second embodiment; [Figure 11] FIG. 10 is a functional explanatory diagram of an optical adjustment system in the lens device of the second embodiment; [Figure 12] FIG. 3 is a diagram showing an optical path of the lens device according to the second embodiment; [Figure 13] FIG. 10 is a longitudinal aberration diagram of the lens device of Example 2 at a reference distance on the wide side; [Figure 14] FIG. 10 is a longitudinal aberration diagram of the lens device of Example 2 at a reference distance on the telephoto side; [Figure 15] FIG. 10 is a longitudinal aberration diagram of the lens device of Example 2 at a close distance on the wide-angle side; [Figure 16]FIG. 10 is a longitudinal aberration diagram of the lens device of Example 2 at a close distance on the telephoto side; [Figure 17] FIG. 10 is a longitudinal aberration diagram of the lens device of Example 2 at a long distance on the wide side; [Figure 18] FIG. 10 is a longitudinal aberration diagram of the lens device of Example 2 at a long distance on the telephoto side; [Figure 19] A list of the conditions and conditional expressions for the lens device, DETAILED DESCRIPTION OF THE INVENTION

[0021] Next, Examples 1 and 2, which are preferred embodiments of the present invention, will be described in detail with reference to the drawings. [Example]

[0022] First, a lens device 1 according to Example 1 of the present embodiment will be specifically described with reference to FIGS. 1 to 9 and 19. FIG.

[0023] First, referring to FIG. 1, a lens device 1 according to this embodiment (Example 1) will be described. It is assumed that this lens device 1 is applied to a projection optical system, particularly a projection zoom optical system, as a projection lens (zoom lens) used in a projector, i.e., as an optical system G. When applied to a projection optical system (projection zoom optical system) as the optical system G, it is possible to achieve a high zoom ratio and a wide angle of view while ensuring sufficient optical performance, particularly for a projector that projects onto a screen, and to effectively eliminate field curvature that occurs during focusing. In FIG. 1, OBJ denotes an object such as a screen, and IMG denotes an image that will become an image display element such as a liquid crystal panel. Therefore, the object OBJ side is in front of the optical axis Dc, and the image IMG side is in back of the optical axis Dc. In FIG. 1, Pb denotes a schematic prism.

[0024] 1, the lens apparatus 1 according to the first embodiment includes an optical system G, and G10 indicates the entire system in the optical system G. This entire system G10 basically includes, in order from the object OBJ side to the image IMG side, a front lens group Gf and a rear lens group Gr. The front lens group Gf is further configured, in order from the object OBJ side to the image IMG side, by a first lens group G1 having negative refractive power overall, a second lens group G2 having positive refractive power overall, and a third lens group G3.

[0025] In this case, the first lens group G1 is made up of three single lenses, and includes, in order from the object OBJ side to the image IMG side, a first lens L1, a second lens L2, and a third lens L3.

[0026] The first lens L1, which is positioned closest to the object OBJ, functions as an image plane correction lens Ls that performs image plane correction by moving in the direction of the optical axis Dc, and this image plane correction lens Ls uses an aspherical meniscus lens with a convex surface facing the object OBJ.

[0027] In this way, by providing an image plane correction lens Ls, which moves along the optical axis Dc to perform image plane correction, closest to the object OBJ in the first lens group G1, optical and mechanical interference with the second lens group G2 (described later), which moves during focusing adjustment, is suppressed. This effectively eliminates field curvature that occurs during focusing adjustment, thereby enabling sufficient image plane correction and improving overall image quality. In addition, the design flexibility of the focusing adjustment mechanism and the image plane correction mechanism is increased, allowing for mechanical simplification of the lens device 1, a compact and compact overall lens device 1, and lower costs. Furthermore, using an aspherical lens for the image plane correction lens Ls allows the power ratio between the power on the optical axis Dc of the aspherical lens and the power at the outermost periphery to be set within a favorable range, thereby optimizing the power ratio and effectively eliminating field curvature.

[0028] The second lens L2 is a negative meniscus lens with a convex surface facing the object OBJ, and the third lens L3 is a biconcave lens, so that the first lens group G1 as a whole has negative refractive power.

[0029] On the other hand, the second lens group G2 is composed of three single lenses, and from the object OBJ side to the image IMG side, it includes, in order, a positive lens L4 using a biconvex lens, a negative lens L5 using a biconcave lens, and a positive lens L6 using a biconvex lens, so that the second lens group G2 as a whole has a positive refractive power. The focal length of the second lens group G2 is set to less than 80 mm. Setting these conditions allows for well-balanced correction of aberrations such as coma, astigmatism, and field curvature, and in particular, reduces the amount of movement of the lens groups during focusing adjustment, thereby shortening the overall length of the lens device 1.

[0030] Furthermore, the third lens group G3 is configured using a cemented lens J7, which is formed by cementing together a biconvex lens on the object side and a biconcave lens on the image side, so that the third lens group G3 as a whole has negative refractive power.

[0031] On the other hand, the rear lens group Gr is composed of, in order from the object OBJ side to the image IMG side, a fourth lens group G4 having positive refractive power overall, a fifth lens group G5 having at least two positive lenses (three positive lenses Lp9, L10, L12 in Example 1), and a sixth lens group G6 having positive refractive power overall.

[0032] In this case, the fourth lens group G4 is constructed using a cemented lens J8 formed by cementing together a negative meniscus lens with a convex surface facing the object OBJ, located on the object OBJ side, and a biconvex lens, located on the image IMG side, and has positive refractive power as a whole.

[0033] The fifth lens group G5 is composed of one cemented lens J9 and four single lenses. The fifth lens group G5 has, closest to the object OBJ, a cemented lens J9 formed by cementing together a negative lens Ln9 using a negative meniscus lens located on the object OBJ side and a positive lens Lp9 using a biconvex lens located on the image IMG side. By providing such a cemented lens J9, it is possible to achieve a desirable lens configuration for the entire optical system G, including the fifth lens group G5, in order to obtain optimal optical characteristics.

[0034] In this cemented lens J9, the refractive index of the negative lens Ln9 at the d-line is set to 1.85 or greater. Setting these conditions has the advantage of enabling excellent correction of spherical aberration, coma, and astigmatism, as well as longitudinal chromatic aberration and lateral chromatic aberration. Furthermore, the Abbe numbers at the d-line of at least two (three in Example 1) positive lenses Lp9, L10, and L12 in the fifth lens group G5 are set to 70 or greater. Setting these conditions enables excellent correction of longitudinal chromatic aberration and lateral chromatic aberration in particular.

[0035] On the other hand, on the image IMG side of this cemented lens J9, a positive lens L10 using a biconvex lens, a negative meniscus lens L11 having a convex surface on the image IMG side, a positive lens L12 using a positive meniscus lens having a convex surface on the image IMG side, and a negative meniscus lens L13 having a convex surface on the image IMG side are arranged in this order, forming a fifth lens group G5 having at least two positive lenses (three positive lenses Lp9, L10, and L12 in Example 1), and the fifth lens group G5 has positive refractive power as a whole.

[0036] Furthermore, the sixth lens group G6 is composed of a positive lens L14 that is a single biconvex lens.

[0037] Furthermore, when bf is the back focus and fw is the focal length of the entire system G10 on the wide-angle side, the following condition is satisfied: 2.3<[bf / fw]<3.8 … [conditional expression] This allows the optimum back focal length to be set. In this case, if [bf / fw] is less than 2.3, the back focal length will be too short, making it impossible to secure space for prism placement on the projection device body, while if [bf / fw] is more than 3.8, the back focal length will be too long, increasing the outer diameter of the rear lens and resulting in a decrease in performance.

[0038] 2 is a functional diagram illustrating the optical adjustment system 100, specifically, the lenses and lens groups that move along the optical axis Dc during zoom and focus adjustment of the optical system G. The optical adjustment system 100 has an image plane correction function, a zoom adjustment function, and a focus adjustment function. In this case, the image plane correction lens Ls, which is located closest to the object OBJ in the first lens group G1, can be moved along the optical axis Dc by rotating an image plane correction ring (not shown). During zoom adjustment, the first lens group G1 and the sixth lens group G6 remain stationary, while the second lens group G2, the third lens group G3, the fourth lens group G4, and the fifth lens group G5 can be moved independently along the optical axis Dc by rotating a zoom adjustment ring (not shown) on the lens barrel. Furthermore, when adjusting focusing, the second lens group G2 can be moved in the direction of the optical axis Dc by turning a focus adjustment ring arranged on the lens barrel (not shown), while the other lens groups G1, G3-G6 remain stationary.

[0039] Therefore, as described above, since the image plane correction lens Ls is disposed closest to the object OBJ in the first lens group G1, optical and mechanical interference between the second lens group G2, which moves during focusing adjustment, and the image plane correction lens Ls is suppressed. As a result, sufficient image plane correction can be performed, particularly by effectively eliminating field curvature that occurs during focusing adjustment, thereby improving the overall image quality. Furthermore, since the design freedom of the focusing adjustment mechanism and the image plane correction mechanism can be increased, the lens device 1 can be simplified in terms of mechanism, the entire lens device 1 can be made smaller and more compact, and even costs can be reduced. Note that FIG. 3 shows a ray diagram of the lens device 1 in Example 1.

[0040] Furthermore, Tables 1a and 1b show lens data for the entire lens system in the lens device 1 of Example 1, with Table 1a showing the surface data and Table 1b showing the aspherical data (aspherical coefficients) of the image plane correction lens Ls. The entire lens system at the time of projection at the reference distance has a zoom ratio of 1.406, an F-number on the wide-angle side of 1.86, an F-number on the telephoto side of 2.20, a total angle of view on the wide-angle side of 90.4°, and an image height of 11.80 mm.

[0041] [Table 1a]

[0042] [Table 1b]

[0043] The surface data in Table 1a indicates the surface number of the lens surface counted from the object (OBJ), i, which corresponds to the symbol (number) shown in Figure 1. Correspondingly, the radius of curvature R(i), on-axis surface spacing D(i), lens refractive index nd(i), lens Abbe number νd(i), and effective radius Re(i) of the lens surface are also shown. nd(i) and νd(i) are values ​​relative to the d-line (587.56 nm). On-axis surface spacing D(i) indicates the lens thickness or air space between opposing surfaces. The radius of curvature R(i) and surface spacing D(i) are measured in mm. The surface number OBJ indicates the object position, and IMG indicates the image position. The "INFINITY" symbol in the radius of curvature R(i) indicates a flat surface. Blank spaces for the refractive index nd(i) and Abbe number νd(i) indicate air.

[0044] In Table 1b, the aspherical coefficients are expressed by Equation 1 in a Cartesian coordinate system (X, Y, Z) with the center of the surface as the origin and the direction of the optical axis Dc as Z, where S1 (i=1) and S2 (i=2) are the aspherical surface numbers. 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 aspherical coefficients, respectively, and H is the distance from the origin on the optical axis. In Table 1b, "E" means "power of 10."

[0045]

number

[0046] As shown in FIG. 19, in the lens apparatus 1 of Example 1, the back focus bf is 40.58 [mm], and the focal length fw of the entire system G10 on the wide-angle side is 11.76 [mm], so bf / fw is "3.45", which satisfies the conditional expression "2.3<[bf / fw]<3.8".

[0047] The focal length fg2 of the second lens group G2 is 72.29 mm, which satisfies the requirement of being less than 80 mm, the refractive index nd of the negative lens Ln9 in the cemented lens J9 located closest to the object OBJ in the fifth lens group G5 is 1.95375, which satisfies the requirement of being 1.85 or greater, and the Abbe numbers vd for the d-line of the at least two (three in Example 1) positive lenses Lp9, L10, and L12 constituting the fifth lens group G5 are 81.730, 81,730, and 95.1036, respectively, which are all 70 or greater. Furthermore, as described above, the desirable zoom ratio of the lens apparatus 1 is 1.406, which ensures 1.4x or greater, and the total angle of view on the wide-angle side is 90.4°, which ensures 70° or greater.

[0048] 4 to 9 show longitudinal aberration diagrams of the lens apparatus 1 of Example 1 after image plane correction. Fig. 4 shows longitudinal aberration diagrams at the reference distance (WIDE side, OBJ = 1730 mm), Fig. 5 shows longitudinal aberration diagrams at the reference distance (TELE side, OBJ = 1730 mm), Fig. 6 shows longitudinal aberration diagrams at the close distance (WIDE side, OBJ = 1030 mm), Fig. 7 shows longitudinal aberration diagrams at the close distance (TELE side, OBJ = 1460 mm), Fig. 8 shows longitudinal aberration diagrams at the long distance (WIDE side, OBJ = 10800 mm), and Fig. 9 shows longitudinal aberration diagrams at the long distance (TELE side, OBJ = 15200 mm). Each longitudinal aberration diagram shows, from left to right, spherical aberration (610 nm, 550 nm, 460 nm), astigmatism (550 nm), and distortion (550 nm). The scale graduations are ±0.10mm, ±0.10mm, and ±1.0%.

[0049] As shown in Figures 4 to 9, it can be confirmed that the lens device 1 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. [Example]

[0050] Next, a lens device 1 according to a second example of the present embodiment will be described with reference to FIGS.

[0051] As shown in Fig. 10, the lens apparatus 1 according to the second embodiment includes an optical system G, and G10 indicates the entire system in the optical system G. This entire system G10 basically includes, in order from the object OBJ side to the image IMG side, a front lens group Gf and a rear lens group Gr. The front lens group Gf is further configured, in order from the object OBJ side to the image IMG side, with a first lens group G1 having negative refractive power overall, a second lens group G2 having positive refractive power overall, and a third lens group G3. In Fig. 10, OBJ indicates an object such as a screen, IMG indicates an image, and Pb indicates a prism.

[0052] The first lens group G1 is composed of three single lenses, and includes, in order from the object OBJ side to the image IMG side, a first lens L1, a second lens L2, and a third lens L3. The first lens L1, which is arranged closest to the object OBJ, functions as an image plane correction lens Ls that performs image plane correction by moving in the direction of the optical axis Dc, and this image plane correction lens Ls uses an aspherical meniscus lens with a convex surface facing the object OBJ side. Therefore, the first lens group G1 of Example 2 has the same basic lens configuration as Example 1, except for the lens characteristics and lens spacing.

[0053] On the other hand, the second lens group G2 is composed of three single lenses. That is, from the object OBJ side to the image IMG side, it includes, in order, a positive lens L4 using a biconvex lens, a negative lens L5 using a negative meniscus lens with a convex surface on the object OBJ side, and a positive lens L6 using a positive meniscus lens with a convex surface on the object OBJ side. As a result, the second lens group G2 of Example 2 has positive refractive power overall, similar to the second lens group G2 of Example 1, and the focal length of the second lens group G2 is set to less than 80 mm. Therefore, the second lens group G2 of Example 2 has the same basic lens configuration as Example 1, except for the lens types, lens characteristics, and lens spacing.

[0054] Furthermore, the third lens group G3 is composed of two single lenses. That is, the third lens group G3 is composed of a positive lens L7 located on the object OBJ side and using a positive meniscus lens with a convex surface on the object OBJ side, and a negative lens L8 located on the image IMG side and using a negative meniscus lens with a convex surface on the object OBJ side, and has a negative refractive power as a whole. While the third lens group G3 of Example 1 uses a cemented lens J7, the third lens group G3 of Example 2 differs from Example 1 in that it is composed of two single lenses.

[0055] On the other hand, the rear lens group Gr is composed of, in order from the object OBJ side to the image IMG side, a fourth lens group G4 having positive refractive power overall, a fifth lens group G5 having at least two positive lenses (three positive lenses Lp10, L11, L13 in Example 2), and a sixth lens group G6 having positive refractive power overall.

[0056] The fourth lens group G4 is located on the object OBJ side and uses a cemented lens J9 formed by cementing a negative meniscus lens with a convex surface facing the object OBJ side to a biconvex lens located on the image IMG side, giving the group an overall positive refractive power. The fifth lens group G5 is composed of one cemented lens J9 and four single lenses. Specifically, from the object OBJ side to the image IMG side, the group is composed of a cemented lens J10 formed by cementing a negative lens Ln10 using a biconcave lens located on the object OBJ side to a positive lens Lp10 using a biconvex lens located on the image IMG side, a positive lens L11 using a biconvex lens, a negative meniscus lens L12 with a convex surface facing the image IMG side, a positive lens L13 using a biconvex lens, and a negative meniscus lens L14 with a convex surface facing the image IMG side. This configuration gives the fifth lens group G5 at least two positive lenses L11, L13, and so on, giving the group G5 overall positive refractive power. Furthermore, the sixth lens group G6 includes a positive lens L15 that is a single positive meniscus lens having a convex surface on the image IMG side.

[0057] In this case, the refractive index at the d-line of the negative lens Ln10 in the cemented lens J10 constituting the fifth lens group G5 is set to 1.85 or more, and the Abbe number at the d-line of at least two (three in Example 2) positive lenses Lp10, L11, and L13 in the fifth lens group G5 is set to 70 or more. Therefore, the basic lens configuration of the rear lens group Gr in Example 2 is the same as that in Example 1, except for the lens types, lens characteristics, and lens spacing. Note that Pb represents a plane-parallel plate similar to that in Example 1.

[0058] Similarly to the first embodiment, the second embodiment satisfies the conditional expression "2.3<[bf / fw]<3.8," where bf is the back focus and fw is the focal length of the entire system G10 on the wide-angle side. Fig. 11 is a functional explanatory diagram of the optical adjustment system 100, i.e., a functional explanatory diagram for explaining the lenses and lens groups that move in the direction of the optical axis Dc during zoom adjustment and focusing adjustment of the optical system G. The image plane correction function using the image plane correction lens Ls, the zoom adjustment function, and the focusing adjustment function are the same as those of the optical adjustment system 100 of the first embodiment shown in Fig. 2. Fig. 12 shows a ray diagram of the lens device 1 in the second embodiment.

[0059] Furthermore, Tables 2a and 2b show lens data for the entire lens system in the lens apparatus 1 of Example 2, with Table 2a showing the surface data and Table 2b showing the aspherical data (aspherical coefficients) of the image plane correction lens Ls. The entire lens system during projection at the reference distance has a zoom ratio of 1.490, an F-number on the wide-angle side of 1.86, an F-number on the telephoto side of 2.18, a total angle of view on the wide-angle side of 72.2°, and an image height of 11.80 mm.

[0060] [Table 2a]

[0061] [Table 2b]

[0062] On the other hand, as shown in FIG. 19, in the lens apparatus 1 of Example 2, the back focus bf is 41.53 [mm], and the focal length fw of the entire system G10 on the wide-angle side is 16.20 [mm], so bf / fw is "2.56", which satisfies the conditional expression "2.3<[bf / fw]<3.8".

[0063] The focal length fg2 of the second lens group G2 is 77.62 mm, which satisfies the requirement of being less than 80 mm, the refractive index nd of the negative lens Ln10 in the cemented lens J10 located closest to the object OBJ in the fifth lens group G5 is 1.87071, which satisfies the requirement of 1.85 or more, and the Abbe numbers νd for the d-line of the at least two (three in Example 2) positive lenses Lp10, L11, and L13 constituting the fifth lens group G5 are 81.6087, 95.1036, and 81.6087, respectively, all of which are 70 or more. Furthermore, as described above, the desirable zoom ratio of the lens apparatus 1 is 1.490, which ensures 1.4x or more, and the total angle of view on the wide-angle side is 72.2°, which ensures 70° or more.

[0064] 13 to 18 show longitudinal aberration diagrams of the lens apparatus 1 of Example 2 after image plane correction. Fig. 13 shows longitudinal aberration diagrams at a reference distance (WIDE side, OBJ = 2490 mm), Fig. 14 shows longitudinal aberration diagrams at a reference distance (TELE side, OBJ = 2490 mm), Fig. 15 shows longitudinal aberration diagrams at a close distance (WIDE side, OBJ = 1520 mm), Fig. 16 shows longitudinal aberration diagrams at a close distance (TELE side, OBJ = 2070 mm), Fig. 17 shows longitudinal aberration diagrams at a long distance (WIDE side, OBJ = 14900 mm), and Fig. 18 shows longitudinal aberration diagrams at a long distance (TELE side, OBJ = 20980 mm). Each longitudinal aberration diagram shows, from left to right, spherical aberration (610 nm, 550 nm, 460 nm), astigmatism (550 nm), and distortion (550 nm). The scale graduations are ±0.10mm, ±0.10mm, and ±1.0%.

[0065] As shown in Figures 13 to 18, it can be confirmed that the lens device 1 of Example 2 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.

[0066] Therefore, according to the lens device 1 of the present embodiment (Examples 1 and 2), the basic configuration is such that the front lens group Gf is made up of, in order from the object OBJ side to the image IMG side, a first lens group G1 having negative refractive power as a whole, a second lens group G2 having positive refractive power as a whole, and a third lens group G3, and the rear lens group Gr is made up of, in order from the object OBJ side to the image IMG side, a fourth lens group G4 having positive refractive power as a whole, a fifth lens group G5 having at least two positive lenses L10..., and a sixth lens group G6 having positive refractive power as a whole. The optical system G is provided with an optical adjustment system 100 that, during zooming adjustment, keeps the first lens group G1 and the sixth lens group G6 stationary and moves the second lens group G2 through the fifth lens group G5 independently along the optical axis Dc, and during focusing adjustment, moves the second lens group G2 along the optical axis Dc. Furthermore, the optical system G satisfies the conditional expression 2.3<[bf / fw]<3.8, where bf is the back focus and fw is the focal length of the entire system G10 on the wide-angle side. This allows the back focus to be set to an optimal length. This ensures sufficient optical performance while achieving a high zoom ratio (1.4x or greater) and a wide angle of view (70° or greater).

[0067] The above describes in detail preferred embodiments including Examples 1 and 2, but the present invention is not limited to such embodiments, and the detailed configuration, shape, material, quantity, numerical values, etc. can be changed, added, or deleted as desired within the scope of the gist of the present invention.

[0068] For example, when configuring the second lens group G2, it is desirable to configure it from the object OBJ side to the image IMG side with a single positive lens L4, a single negative lens L5, and a single positive lens L6, and set the focal length fg2 of the second lens group G2 to less than 80 mm, but other lens configurations and conditions are not excluded. Meanwhile, it is desirable to set the refractive index of the negative lens Ln9 (Ln10) located on the object OBJ side in the fifth lens group G5 to 1.85 or greater at the d-line, but this is not a required component. Furthermore, although three positive lenses have been exemplified as the two or more positive lenses L10 in the fifth lens group G5, any two positive lenses L10 or four or more positive lenses L10 may be used. Therefore, in these cases, it is desirable to set the Abbe number at the d-line of the two positive lenses L10 or three or more positive lenses L10 to 70 or greater. [Industrial Applicability]

[0069] 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]

[0070] 1: lens device, 100: optical adjustment system, OBJ: object, IMG: image, Dc: optical axis, G: optical system, G10: entire system, Gf: front lens group, Gr: rear lens group, G1: first lens group, G2: second lens group, G3: third lens group, G4: fourth lens group, G5: fifth lens group, G6: sixth lens group, L4: positive lens, L5: negative lens, L6: positive lens, L10...: positive lens, Ln9: negative lens, Lp9: positive lens, Ln10: negative lens, Lp10: positive lens, Ls: image plane correction lens, J7: cemented lens, J8: cemented lens, J9: cemented lens, J10: cemented lens

Claims

1. In a lens device that is applied to a projection optical system and that is composed of, in order from the object side to the image side, a front lens group and a rear lens group, the front lens group is composed of, in order from the object side to the image side, a first lens group that has negative refractive power overall and is provided with an image plane correction lens using an aspherical lens that is closest to the object and that performs image plane correction by moving in the optical axis direction, a second lens group that has positive refractive power overall, and a third lens group, and the rear lens group is composed of, in order from the object side to the image side, a fourth lens group that has positive refractive power overall, a fifth lens group that has at least two positive lenses. a first lens group, a second lens group, and a sixth lens group having positive refractive power overall, wherein a zoom ratio is set to 1.4 or more and a total angle of view on the wide-angle side is set to 70° or more, wherein an optical adjustment system is provided in which, during zooming adjustment, the first lens group and the sixth lens group are fixed and the second lens group through the fifth lens group are moved independently in the optical axis direction, and during focusing adjustment, the second lens group is moved in the optical axis direction, and wherein the optical system satisfies the following conditional expression, where bf is a back focus and fw is a focal length of the entire system on the wide-angle side: 2.3<[bf / fw]<3.8... [Conditional expression]

2. 2. The lens device according to claim 1, wherein the second lens group is composed of, in order from the object side to the image side, a single lens using a positive lens, a single lens using a negative lens, and a single lens using a positive lens, and the focal length is set to less than 80 mm.

3. 2. The lens apparatus according to claim 1, wherein the fifth lens group includes, at its most object side, a cemented lens formed by cementing together a negative lens positioned on the object side and a positive lens positioned on the image side.

4. 4. The lens device according to claim 3, wherein the refractive index of the negative lens constituting the cemented lens in the fifth lens group is set to 1.85 or more for the d-line.

5. 5. A lens device according to claim 1, wherein the fifth lens group has at least two positive lenses whose Abbe numbers with respect to the d-line are set to 70 or more.

Images