Zoom lens

Abstract

To provide a zoom lens which offers good image quality through necessary correction of various aberrations and field curvature, and which nicely and rationally balances various qualities, including reduced overall size, weight, and costs.SOLUTION: A zoom lens provided herein comprises: a lens optical system 100 consisting of a first lens group G1 having negative refractive power, a second lens group G2 having positive refractive power, a third lens group G3 having positive refractive power, a fourth lens group G4 having positive refractive power, a fifth lens group G5 having positive or negative refractive power, and a sixth lens group G6 having positive refractive power successively arranged in order from the magnification side E; and an optical adjustment system 200 comprising a zooming adjustment unit Mcz configured to keep the first and sixth lens groups G1, G6 stationary and move the second through fifth lens groups G2-G5 independently along an optical axis Dc. The fourth lens group G4 consists of only single lenses, where convex lenses (La...(Lc...)) and concave lenses (Lb...) are alternately arranged along the optical axis Dc.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a zoom lens suitable for use in an optical device provided with a projection optical system such as a projector.

Background Art

[0002] Conventionally, as a zoom lens provided in a projection optical system that projects an image from a projector onto a screen or the like, a projection zoom lens described in Patent Document 1 and a projection optical system described in Patent Document 2 are known.

[0003] The projection zoom lens of Patent Document 1 aims to realize a projection zoom lens having a high zoom ratio, a small F-number, small magnification chromatic aberration suppressed, high MTF characteristics, and resolution characteristics, and the display device side is telecentric. Specifically, in order from the wide-angle side, a negative first lens group, a positive second lens group, a third lens group, a fourth lens group, a negative fifth lens group, a positive or negative sixth lens group, and a positive seventh lens group are arranged, and an aperture stop is arranged between the fourth and fifth lens groups. When zooming, the second to sixth lens groups move, and when zooming from the wide-angle end to the telephoto end, the distances between the first and second lens groups, the first and third lens groups, and the first and fourth lens groups all decrease. The focal length of the entire system at the wide-angle end: fw, the focal length of the first lens group: fl, the focal length of the second lens group: f2, the focal length of the third lens group: f3, and the focal length of the fourth lens group: f4 are configured to satisfy 1.3 < |f| / fw < 1.9, 0.6 < f2 / f3 < 3.5, and 0.4 < f4 / f3 < 3.7.

[0004] Furthermore, the projection optical system described in Patent Document 2 aims to provide a projection optical system that can adjust appropriate field curvature with a simple configuration. Specifically, the projection optical system comprises a first lens in which the power on the optical axis and the power of the meridional section at the outermost part are different from each other, a second lens adjacent to the first lens, and an aperture positioned where the off-axis principal ray intersects the optical axis. The system is configured to allow adjustment of the field curvature of the projected image by changing the distance between the first lens and the second lens in the optical axis direction, and is also configured to satisfy a predetermined conditional equation. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2013-200454 [Patent Document 2] Japanese Patent Publication No. 2017-126036 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] However, conventional zoom lenses, including the projection zoom lenses and projection optics mentioned above, also had the following issues that needed to be addressed.

[0007] In other words, in the case of a projector equipped with this type of zoom lens, in order to enlarge and project the optical image onto a distant screen, the zoom lens used must have the necessary brightness, the necessary zoom ratio and angle of view, and good image quality through necessary correction of various aberrations such as spherical aberration, coma aberration, astigmatism, and field curvature. Furthermore, since the zoom lens is supported in a position that protrudes forward from the front of the projector body and has an optical adjustment system with a lens optical system having multiple lens groups and various adjustment parts such as a zoom adjustment unit, there is a demand for miniaturization, weight reduction, and cost reduction of the entire zoom lens.

[0008] On the other hand, the performance characteristics required in this way are often mutually exclusive, as improving one characteristic may impair others. Therefore, in addition to improving each required performance characteristic, how to achieve a good balance between these characteristics, particularly aberrations such as spherical aberration, coma aberration, astigmatism, and field curvature, is a crucial challenge for this type of zoom lens. However, to date, zoom lenses that rationally address these challenges have not always been available.

[0009] The present invention aims to provide a zoom lens that solves the problems present in the background technology described above. [Means for solving the problem]

[0010] In order to solve the above-mentioned problems, the present invention constructs a zoom lens 1 comprising six lens groups G1-G6 arranged in order from the magnification side E to the reduction side S, wherein the lens group G1 has negative refractive power, the second lens group G2 has positive refractive power, the third lens group G3 has positive refractive power, and the fourth lens group G4 has positive refractive power and includes at least two positive lenses that satisfy the Abbe number νd > 70 [condition equation 1] when νd is the Abbe number for the d line. The lens optical system 100 comprises a fifth lens group G5 having positive or negative refractive power and a sixth lens group G6 having positive refractive power arranged in sequence, and an optical adjustment system 200 including a zooming adjustment unit Mcz that fixes the first lens group G1 and the sixth lens group G6 and moves the second lens group G2 to the fifth lens group G5 independently in the optical axis direction Dc, and is characterized in that each lens of the fourth lens group G4 is composed of a single lens and convex lenses (La...(Lc...)) and concave lenses (Lb...) are arranged alternately in the optical axis direction Dc.

[0011] In this case, according to a preferred embodiment of the invention, the sixth lens group G6 is composed of a single lens Lz, and it is desirable that the refractive index nd satisfies the condition [Equation 2] such that nd > 1.7. On the other hand, the optical adjustment system 200 may be provided with a focusing adjustment unit Mcf that moves only the first lens group G1 in the optical axis direction Dc. The zoom ratio can be set in the range of 1.3 to 1.7 times, and the half angle of view on the wide-angle side can be set in the range of 25 to 35°. [Effects of the Invention]

[0012] The zoom lens 1 according to the present invention, having such a configuration, produces the following remarkable effects.

[0013] (1) A lens optical system 100 comprising a first lens group G1 having negative refractive power, a second lens group G2 having positive refractive power, a third lens group G3 having positive refractive power, a fourth lens group G4 having positive refractive power, a fifth lens group G5 having positive or negative refractive power, and a sixth lens group G6 having positive refractive power, arranged sequentially from the magnification side E to the reduction side S, and a zoomer 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 in the optical axis direction Dc. The lens is equipped with an optical adjustment system 200 including a lens adjustment section Mcz. In particular, each lens in the fourth lens group G4 is composed of a single lens, and convex lenses (La…(Lc…)) and concave lenses (Lb…) are arranged alternately in the optical axis direction Dc. This ensures the necessary brightness while obtaining good image quality through necessary corrections for various aberrations and field curvature, and also allows for overall miniaturization, weight reduction, and cost reduction, thus achieving a good and rational balance of each performance.

[0014] (2) When constructing the fourth lens group G4, the Abbe number for the d line is νd, and the group is constructed to include at least two positive lenses La…(Lc…) that satisfy the condition [Equation 1] νd > 70, thereby ensuring an appropriate range for the Abbe number νd. As a result, axial chromatic aberration and lateral chromatic aberration can be corrected well in particular.

[0015] (3) In a preferred embodiment, when the sixth lens group G6 is constructed using a single lens Lz and the refractive index is nd, if it is constructed to satisfy the condition [Equation 2] of nd > 1.7, an appropriate range of refractive index nd can be secured, thereby maintaining a good balance of the telecentric optical system, correcting field curvature well and contributing to improved image quality performance, and by constructing it with the minimum number of elements, the overall length of the zoom lens 1 can be shortened and miniaturization can be achieved.

[0016] (4) In a preferred embodiment, if the optical adjustment system 200 is provided with a focusing adjustment unit Mcf that moves only the first lens group G1 in the optical axis direction Dc, a focusing adjustment unit Mcf that moves only the first lens group G1, which is composed of multiple lenses, can be constructed. This contributes to simplifying and miniaturizing the focusing adjustment unit Mcf, and further to reducing the weight of the zoom lens 1, which is relatively long in the optical axis direction Dc. In addition, the movement stroke of the first lens group G1 during focusing adjustment can be shortened, which reduces the diameter of the zoom lens 1, and furthermore, various aberrations such as astigmatism and distortion can be corrected in a balanced manner, contributing to improved image quality performance.

[0017] (5) In a preferred embodiment, setting the zoom ratio in the range of 1.3 to 1.7 times ensures a good balance of each performance while securing the necessary zoom ratio for the zoom lens 1.

[0018] (6) In a preferred embodiment, by setting the half-angle of view on the wide-angle side to a range of 25-35°, the necessary angle of view for the zoom lens 1 can be secured while ensuring a good balance of each performance, and together with securing the zoom ratio, sufficient optical performance can be ensured, in particular for projectors and the like that project onto a screen. [Brief explanation of the drawing]

[0019] [Figure 1] Overall lens configuration diagram of the wide side of the zoom lens according to Embodiment 1 of a preferred embodiment of the present invention. [Figure 2] A diagram illustrating the principle configuration of the optical adjustment system in the zoom lens of the same embodiment 1. [Figure 3] Overall lens configuration diagram of the TELE side of the zoom lens in the same Example 1, [Figure 4] Longitudinal aberration diagram of the reference distance on the WIDE side of the zoom lens in the same Example 1, [Figure 5] Longitudinal aberration diagram of the reference distance on the TELE side of the zoom lens in the same Example 1, [Figure 6] Overall lens configuration diagram of the WIDE side of the zoom lens in the same Example 2, [Figure 7] Overall lens configuration diagram of the TELE side of the zoom lens in the same Example 2, [Figure 8] Longitudinal aberration diagram of the reference distance on the WIDE side of the zoom lens in the same Example 2, [Figure 9] Longitudinal aberration diagram of the reference distance on the TELE side of the zoom lens in the same Example 2, [Figure 10] Overall lens configuration diagram of the WIDE side of the zoom lens in the same Example 3, [Figure 11] Overall lens configuration diagram of the TELE side of the zoom lens in the same Example 3, [Figure 12] Longitudinal aberration diagram of the reference distance on the WIDE side of the zoom lens in the same Example 3, [Figure 13] Longitudinal aberration diagram of the reference distance on the TELE side of the zoom lens in the same Example 3, [Figure 14] Overall lens configuration diagram of the WIDE side of the zoom lens in the same Example 4, [Figure 15] Overall lens configuration diagram of the TELE side of the zoom lens in the same Example 4, [Figure 16] Longitudinal aberration diagram of the reference distance on the WIDE side of the zoom lens in the same Example 4, [Figure 17] Longitudinal aberration diagram of the reference distance on the TELE side of the zoom lens in the same Example 4, [Figure 18] Optical characteristic table of the zoom lens according to the same embodiment

Modes for Carrying Out the Invention

[0020] Next, preferred embodiments according to the present invention will be given and described in detail based on the drawings. [Examples]

[0021] First, the lens optical system 100 and optical adjustment system 200 of the zoom lens 1 according to Embodiment 1 of this embodiment will be described with reference to Figures 1-5.

[0022] This zoom lens 1 is intended for use as a projection lens (zoom lens) in a projector, that is, in a projection zoom optical system.

[0023] In Figure 1, E represents the magnification side, such as a screen, and S represents the reduction side (reduction conjugate side), which becomes an image display element such as a liquid crystal panel. Therefore, the magnification side E (OBJ) is in front in the direction of the optical axis Dc, and the reduction side S is in the direction of the optical axis Dc.

[0024] As shown in Figure 1, the lens optical system 100 comprises six lens groups G1, G2, G3, G4, G5, and G6, arranged in order from the magnification side E to the reduction side S, and a prism Pr, as shown in the schematic diagram, is provided on the reduction side S relative to the sixth lens group G6.

[0025] The first lens group G1 has a negative refractive power as a whole and is composed of, in order from the magnifying side E, a positive lens L1 using a positive meniscus lens with a convex surface on the magnifying side E, negative lenses L2, L3, L4 using negative meniscus lenses with a convex surface on the magnifying side E, and a negative lens L5 using a biconcave lens. Each of the lenses L1, L2, L3, L4, and L5 is a single lens. In this way, the first lens group G1 is composed of five lenses, and as shown in Figure 2, it is possible to construct a focusing adjustment unit Mcf in the optical adjustment system 200 that moves only the first lens group G1 in the optical axis direction Dc. This contributes to the simplification and miniaturization of the focusing adjustment unit Mcf, and further contributes to the weight reduction of the zoom lens 1, which is relatively long in the optical axis direction Dc. In addition, shortening the movement stroke of the first lens group G1 during focusing adjustment allows for a smaller diameter of the zoom lens 1, and furthermore, it contributes to improved image quality by correcting various aberrations such as astigmatism and distortion in a balanced manner.

[0026] The second lens group G2 has a positive refractive power as a whole and is composed of a first cemented lens J1 and a second cemented lens L2 arranged in order from the magnifying side E. In this case, the first cemented lens J1 is composed of a balsam lens consisting of a positive lens L6 using a positive meniscus lens with a concave surface on the magnifying side E and a negative lens L7 using a negative meniscus lens with a concave surface on the magnifying side E, while the second cemented lens J2 is composed of a balsam lens consisting of a biconcave lens L8 and a biconvex lens L9, arranged in order from the magnifying side E.

[0027] The third lens group G3 consists of a single lens with positive refractive power, that is, a positive lens L10 made of a single biconvex lens.

[0028] On the other hand, the fourth lens group G4 has a positive refractive power as a whole, and its basic configuration consists of single lenses, with convex lenses (La, Lc, Le) and concave lenses (Lb, Ld) arranged alternately in the optical axis direction Dc. Specifically, starting from the magnification side E, it comprises a positive lens La using a biconvex lens, a negative lens Lb using a biconcave lens, a positive lens Lc using a biconvex lens, a negative lens Ld using a negative meniscus lens with a concave surface on the magnification side E, and a positive lens Le using a positive meniscus lens with a concave surface on the magnification side E.

[0029] Furthermore, when constructing the fourth lens group G4, the optical conditions of the three positive lenses La, Lc, and Le, that is, when the Abbe number for the d line is νd, are configured to satisfy the following [Condition Equation 1]. νd>70 … [Conditional expression 1]

[0030] Thus, when constructing the fourth lens group G4, if at least two (three in Example 1) positive lenses La, Lc, and Le satisfying [Condition Equation 1] are included, an appropriate range of Abbe number νd can be secured, which has the advantage of being able to correct axial chromatic aberration and lateral chromatic aberration particularly well.

[0031] The fifth lens group G5 has either a positive or negative refractive power as a whole. Example 1 is configured by arranging, in order from the magnification side E, a positive lens L11 using a positive meniscus lens with a concave surface on the magnification side E, a third cemented lens J3 using a balsam lens consisting of a biconcave lens L12 and a biconvex lens L13, and a positive lens L14 using a biconvex lens.

[0032] The sixth lens group G6 is composed of a single lens with positive refractive power, that is, a single biconvex lens (positive lens) Lz. Furthermore, when constructing the sixth lens group G6, the following condition [Equation 2] is satisfied when the refractive index is nd. nd > 1.7 … [Condition 2]

[0033] Thus, by configuring the sixth lens group G6 to satisfy [condition equation 2], an appropriate range of refractive index nd can be secured, which in turn allows for a good balance of the telecentric optical system, effectively corrects field curvature, contributes to improved image quality, and, by using the minimum number of elements, shortens the overall length of the zoom lens 1, contributing to miniaturization.

[0034] On the other hand, the zoom lens 1 includes an optical adjustment system 200, which includes a zoom adjustment unit Mcz shown in the principle configuration diagram in Figure 2, and the aforementioned focusing adjustment unit Mcf.

[0035] In this case, the zoom adjustment unit Mcz has the function of fixing the first lens group G1 and the sixth lens group G6, and independently moving the second lens group G2 to the fifth lens group G5, i.e., the second lens group G2, the third lens group G3, the fourth lens group G4, and the fifth lens group G5, in the optical axis direction Dc. In addition, the focusing adjustment unit Mcf has the function of moving only the first lens group G1, which is composed of five lenses L1-L5, in the optical axis direction Dc.

[0036] Table 1 shows the lens data (surface data) of zoom lens 1 according to Example 1.

[0037] [Table 1]

[0038] The surface data in [Table 1] shows the surface number of the lens surface, counted from the magnification side E, denoted by i. This surface number i corresponds to the symbol (number) shown in Figure 1. Correspondingly, the radius of curvature R(i), axial spacing D(i), refractive index nd(i), and Abbe number νd(i) of the lens surface are shown. nd(i) and νd(i) are values ​​relative to the d line (587.56 [nm]). The axial spacing D(i) indicates the lens thickness or air space between opposing surfaces. The units for the radius of curvature R(i) and spacing D(i) are [mm]. INFINITY for the radius of curvature R(i) represents a plane. Blank spaces for refractive index nd(i) and Abbe number νd(i) indicate air.

[0039] Figure 18 shows (a) lens conditions, (b) optical characteristics, and (c) F-number for each embodiment of the zoom lens 1, including Embodiment 1. In Embodiment 1, (a) the lens conditions are as follows: the Abbe number νd of the positive lens "La" in "G4" (fourth lens group) is "70.4362", the Abbe number νd of the positive lens "Lc" is "81.6087", and the Abbe number νd of the positive lens "Le" is "70.4362", and all lenses La, Lc, and Le satisfy [Condition Equation 1] "νd>70". The refractive index nd of "G6" (sixth lens group) is "1.80610", and satisfies [Condition Equation 2] "nd>1.7".

[0040] Furthermore, in the optical characteristics of Example 1 (b), a zoom ratio of "1.559" times is obtained. In this way, by setting the zoom ratio of zoom lens 1 in the range of 1.3 to 1.7 times, it is possible to ensure the necessary zoom ratio for zoom lens 1 while maintaining a good balance of each performance. The half-angle of view at the WIDE (wide-angle side) is obtained at "31.8" [°]. In this way, by setting the half-angle of view of zoom lens 1 in the range of 25 to 35 [°], it is possible to ensure the necessary angle of view for zoom lens 1 while maintaining a good balance of each performance, and in addition to ensuring the zoom ratio, it is possible to ensure sufficient optical performance, especially for projectors that project onto a screen.

[0041] Furthermore, in the F-number (c) of Example 1, the F-number for the wide-angle side (WIDE) is "1.765" and the F-number for the telephoto side (TELE) is "2.16", ensuring sufficient brightness. As shown in (b), the total focal length fw for the wide-angle side (WIDE) is "29.91" [mm], and the total focal length ft for the telephoto side (TELE) is "46.63" [mm].

[0042] Figures 1 and 2 show the position of each lens L1... in the optical axis Dc direction when the zoom lens 1 according to Embodiment 1 is adjusted to the WIDE side, and Figure 3 shows the position of each lens L1... in the optical axis Dc direction when it is adjusted to the TELE side.

[0043] Figures 4 and 5 show the longitudinal aberration diagrams of the zoom lens 1 according to Example 1 at a reference distance OBJ(E) = 2932 mm. Figure 4 shows the wide side, and Figure 5 shows the telephoto side. Each longitudinal aberration diagram shows, from left to right, spherical aberration (610 nm, 550 nm, 460 nm), astigmatism (550 nm), and distortion (550 nm). Each scale division (1 division) represents ±0.10 mm, ±0.10 mm, and ±1.0%.

[0044] As shown in Figures 4 and 5, the zoom lens 1 according to Example 1 exhibits excellent aberration characteristics, i.e., projection performance (optical performance), with no significant distortion in any of the longitudinal aberrations.

[0045] Thus, the zoom lens 1 according to this embodiment (Example 1) has a basic configuration of a lens optical system 100 in which a first lens group G1 having negative refractive power, a second lens group G2 having positive refractive power, a third lens group G3 having positive refractive power, a fourth lens group G4 having positive refractive power, a fifth lens group G5 having positive or negative refractive power, and a sixth lens group G6 having positive refractive power are arranged sequentially from the magnification side E to the reduction side S, and the first lens group G1 and the sixth lens group G6 are fixed, while the second lens group G2 to the fifth lens group G5 are independently positioned along the optical axis. The zoom lens 1 is equipped with an optical adjustment system 200 including a zoom adjustment unit Mcz that moves toward Dc, and in particular, each lens of the fourth lens group G4 is composed of a single lens, and convex lenses (La, Lc, Le) and concave lenses (Lb, Ld) are arranged alternately toward the optical axis direction Dc, thereby ensuring the necessary brightness while obtaining good image quality through necessary corrections for various aberrations and field curvature, and enabling overall miniaturization, weight reduction, and cost reduction, thus providing a zoom lens 1 that balances each performance well and rationally. In particular, it is possible to ensure the necessary angle of view in the zoom lens 1, and together with ensuring the zoom ratio, sufficient optical performance can be ensured for projectors and other devices that project onto a screen. [Examples]

[0046] Next, the lens optical system 100 of the zoom lens 1 according to Embodiment 2 of this embodiment will be described with reference to Figures 6-9.

[0047] As shown in Figure 6, the lens optical system 100 comprises six lens groups G1, G2, G3, G4, G5, and G6, arranged in order from the magnification side E to the reduction side S, and the reduction side S relative to the sixth lens group G6 is equipped with a prism Pr as shown in the schematic diagram.

[0048] The first lens group G1 in Example 2 is the same as in Example 1. Furthermore, the second lens group G2, third lens group G3, fifth lens group G5, and sixth lens group G6 in Example 2 have the same basic lens configuration as in Example 1, except for differences in detailed lens characteristics.

[0049] On the other hand, the fourth lens group G4, as a basic configuration, consists of single lenses and has convex lenses (La, Lc, Le) and concave lenses (Lb, Ld) arranged alternately in the optical axis direction Dc, just like in Example 1, but differs in the following respect. Specifically, while Example 1 used a positive meniscus lens with a concave surface on the magnification side E for the positive lens Le, Example 2 uses a biconvex lens for the positive lens Le, and the optical conditions of only the two positive lenses Lc and Le are configured to satisfy "νd>70" [condition equation 1]. The optical adjustment system 200, including the zooming adjustment unit Mcz and the focusing adjustment unit Mcf, is also the same as in Example 1.

[0050] Table 2 shows the lens data (surface data) of zoom lens 1 according to Example 2.

[0051] [Table 2]

[0052] In the embodiment 2 shown in Figure 18, (a) the lens conditions are as follows: the Abbe number νd of the positive lens "Lc" of "G4" (fourth lens group) is "81.6087", and the Abbe number νd of the positive lens "Le" is "70.2334", so both lenses Lc and Le satisfy condition 1, "νd > 70". The refractive index nd of "G6" (sixth lens group) is "1.80610", which satisfies condition 2, "nd > 1.7".

[0053] Furthermore, in the optical characteristics of Example 2 (b), a zoom ratio of "1.558" times is obtained. The half-angle of view at the WIDE (wide-angle) end is "31.9" [°]. In addition, in the F-number of Example 2 (c), the F-number at the wide-angle end (WIDE) is "1.74", and the F-number at the telephoto end (TELE) is "2.16". Note that in the optical characteristics of (b), the total system focal length fw at the wide-angle end (WIDE) is "30.01" [mm], and the total system focal length ft at the telephoto end (TELE) is "46.76" [mm].

[0054] Figure 6 shows the position of each lens L1... in the optical axis Dc direction when the zoom lens 1 according to Example 2 is adjusted to the WIDE side, and Figure 7 shows the position of each lens L1... in the optical axis Dc direction when it is adjusted to the TELE side. Figures 8 and 9 show the longitudinal aberration diagrams of the zoom lens 1 according to Example 2 at a reference distance OBJ(E) = 2932 mm. Figure 8 shows the WIDE side, and Figure 9 shows the TELE side. As shown in Figures 8 and 9, the zoom lens 1 according to Example 2 exhibits good aberration characteristics, i.e., projection performance (optical performance), without significant disturbances in any of the longitudinal aberrations.

[0055] Thus, the zoom lens 1 according to Example 2 also has the basic configuration of the zoom lens 1 according to the present invention. In particular, since each lens of the fourth lens group G4 is composed of a single lens, and convex lenses (La, Lc, Le) and concave lenses (Lb, Ld) are arranged alternately in the optical axis direction Dc, and at least two positive lenses Lc, Le that satisfy [conditional equation 1] are included, the same effect as in Example 1 can be obtained. [Examples]

[0056] Next, the configuration of the lens optical system 100 of the zoom lens 1 according to Embodiment 3 of this embodiment will be described with reference to Figures 10-13.

[0057] As shown in Figure 10, the lens optical system 100 comprises six lens groups G1, G2, G3, G4, G5, and G6, arranged in order from the magnification side E to the reduction side S, and the reduction side S relative to the sixth lens group G6 is equipped with a prism Pr as shown in the schematic diagram.

[0058] In Example 3, the first lens group G1, the second lens group G2, and the sixth lens group G6 have the same basic lens configuration as in Example 1, except that the detailed lens characteristics differ.

[0059] On the other hand, the third lens group G3 has a positive refractive power as a whole and, as shown in Figure 10, consists of three single lenses in order from the magnifying side E: a positive lens L101 using a plano-convex lens with a convex surface on the magnifying side E, a positive lens L102 using a positive meniscus lens with a convex surface on the magnifying side E, and a negative lens L103 using a negative meniscus lens with a convex surface on the magnifying side E.

[0060] Furthermore, the fourth lens group G4 has a positive refractive power as a whole, and its basic configuration consists of single lenses, with convex lenses (La, Lc) and concave lenses (Lb) arranged alternately in the optical axis direction Dc. Specifically, starting from the magnifying side E, it comprises three single lenses: a positive lens La using a plano-convex lens with a convex surface on the reducing side S, a negative lens Lb using a negative meniscus lens with a convex surface on the reducing side S, and a positive lens Lc using a biconvex lens. When constructing the fourth lens group G4, the optical condition of only the two positive lenses La and Lc was configured to satisfy "νd>70" [Condition Equation 1].

[0061] Furthermore, the fifth lens group G5 has either a positive or negative refractive power as a whole. In Example 3, the lenses are configured as follows, starting from the magnification side E: a positive lens L11 using a positive meniscus lens with a concave surface on the magnification side E; a biconcave lens L12; a positive lens L13 using a balsam lens; and a positive lens L14 using a biconvex lens. The optical adjustment system 200, including the zoom adjustment unit Mcz and the focusing adjustment unit Mcf, is the same as in Example 1.

[0062] Table 3 shows the lens data (surface data) of zoom lens 1 according to Example 3.

[0063] [Table 3]

[0064] In Example 3 shown in Figure 18, (a) the lens conditions are as follows: the Abbe number νd of the positive lens "La" in "G4" (fourth lens group) is "81.6087", and the Abbe number νd of the positive lens "Lc" is "81.6087", so both lenses La and Lc satisfy condition 1, "νd > 70". The refractive index nd of "G6" (sixth lens group) is "1.72916", which satisfies condition 2, "nd > 1.7".

[0065] Furthermore, in the optical characteristics of Example 3 (b), a zoom ratio of "1.591" times is obtained. The half-angle of view at the WIDE (wide-angle) end is "34.4" [°]. In addition, in the F-number of Example 3 (c), the F-number at the wide-angle end (WIDE) is "1.80", and the F-number at the telephoto end (TELE) is "2.25". Note that in the optical characteristics of (b), the total system focal length fw at the wide-angle end (WIDE) is "27.69" [mm], and the total system focal length ft at the telephoto end (TELE) is "44.06" [mm].

[0066] Figure 10 shows the position of each lens L1… in the optical axis Dc direction when the zoom lens 1 according to Example 3 is adjusted to the WIDE side, and Figure 11 shows the position of each lens L… in the optical axis Dc direction when it is adjusted to the TELE side. Figures 12 and 13 show the longitudinal aberration diagrams of the zoom lens 1 according to Example 3 at a reference distance OBJ(E) = 2700 mm. Figure 12 shows the WIDE side, and Figure 13 shows the TELE side. As shown in Figures 12 and 13, the zoom lens 1 according to Example 3 exhibits good aberration characteristics, i.e., projection performance (optical performance), without significant disturbances in any of the longitudinal aberrations.

[0067] Thus, the zoom lens 1 according to Example 3 also has the basic configuration of the zoom lens 1 according to the present invention. In particular, since each lens of the fourth lens group G4 is composed entirely of single lenses, and convex lenses (La,Lc) and concave lenses (Lb) are arranged alternately in the optical axis direction Dc, and at least two positive lenses La,Lc that satisfy [conditional equation 1] are included, the same effects as in Example 1 can be obtained. [Examples]

[0068] Next, the configuration of the lens optical system 100 of the zoom lens 1 according to Embodiment 4 of this embodiment will be described with reference to Figures 14-17.

[0069] As shown in Figure 14, the lens optical system 100 comprises six lens groups G1, G2, G3, G4, G5, and G6, arranged in order from the magnification side E to the reduction side S, and the reduction side S relative to the sixth lens group G6 is equipped with a prism Pr as shown in the schematic diagram.

[0070] In Example 4, the first lens group G1 has a negative refractive power as a whole and is composed of, in order from the magnification side E, a positive lens L1 using a positive meniscus lens with a convex surface on the magnification side E, negative lenses L2 and L3 using negative meniscus lenses with a convex surface on the magnification side E, and a negative lens L4 using a biconcave lens. Each of the lenses L1, L2, L3, and L4 is a single lens. Thus, the first lens group G1 is composed of four lenses, which differs from the configuration of Example 1 which uses five lenses. However, the basic functions are the same as in Example 1, such as constructing the focusing adjustment section Mcf in the optical adjustment system 200 that moves only the first lens group G1 in the optical axis direction Dc.

[0071] The second lens group G2, the third lens group G3, the fifth lens group G5, and the sixth lens group G6 have the same basic lens configuration as in Example 1, except that the detailed lens characteristics differ.

[0072] On the other hand, the fourth lens group G4 has a positive refractive power as a whole and, as a basic configuration, consists of four single lenses, and, starting from the magnifying side E, comprises a negative lens Lb using a biconcave lens, a positive lens Lc using a biconvex lens, a negative lens Ld using a negative meniscus lens with a convex surface on the reducing side S, and a positive lens Le using a biconvex lens. Therefore, the arrangement of concave lenses (Lb, Ld) and convex lenses (Lc, Le) alternately in the optical axis direction Dc is the same as the basic configuration of this embodiment.

[0073] Table 4 shows the lens data (surface data) of zoom lens 1 according to Example 4.

[0074] [Table 4]

[0075] In Example 4 shown in Figure 18, (a) the lens conditions are as follows: the Abbe number νd of the positive lens "Lc" of "G4" (fourth lens group) is "81.6087", and the Abbe number νd of the positive lens "Le" is "81.6087", so both lenses Lc and Le satisfy condition 1, "νd > 70". The refractive index nd of "G6" (sixth lens group) is "1.80420", which satisfies condition 2, "nd > 1.7".

[0076] Furthermore, in the optical characteristics of Example 4 (b), a zoom ratio of "1.557" times is obtained. The half-angle of view at the WIDE (wide-angle) end is "32.0" [°]. In addition, in the F-number of Example 4 (c), the F-number at the wide-angle end (WIDE) is "1.85", and the F-number at the telephoto end (TELE) is "2.32". Note that in the optical characteristics of (b), the total system focal length fw at the wide-angle end (WIDE) is "23.93" [mm], and the total system focal length ft at the telephoto end (TELE) is "37.25" [mm].

[0077] Figure 14 shows the position of each lens L1… in the optical axis Dc direction when the zoom lens 1 according to Example 4 is adjusted to the WIDE side, and Figure 15 shows the position of each lens L… in the optical axis Dc direction when it is adjusted to the TELE side. Figures 16 and 17 show the longitudinal aberration diagrams of the zoom lens 1 according to Example 4 at a reference distance OBJ(E) = 2938 mm. Figure 16 shows the WIDE side, and Figure 17 shows the TELE side. As shown in Figures 16 and 17, the zoom lens 1 according to Example 4 exhibits good aberration characteristics, i.e., projection performance (optical performance), without significant disturbances in any of the longitudinal aberrations.

[0078] Thus, the zoom lens 1 according to Example 4 also has the basic configuration of the zoom lens 1 according to the present invention. In particular, since each lens of the fourth lens group G4 is composed of a single lens, and concave lenses (Lb, Ld) and convex lenses (Lc, Le) are arranged alternately in the optical axis direction Dc, and at least two positive lenses Lc, Le that satisfy [conditional equation 1] are included, the same effect as in Example 1 can be obtained.

[0079] Although preferred embodiments, including Examples 1-4, have been described in detail above, the present invention is not limited to these embodiments, and the details of the configuration, shape, materials, quantity, numerical values, etc., can be arbitrarily changed, added, or deleted without departing from the spirit of the present invention.

[0080] For example, although the lens optical system 100 is configured with six lens groups G1-G6, this does not preclude the case where additional lens groups are added to form seven or more lens groups G1.... Furthermore, the number of lenses in each lens group G1-G5, including the first lens group G1, is not limited to the number of lenses shown in the embodiment (example), and can be implemented with any necessary number of lenses. Also, when configuring the fourth lens group G4, the lens placed at the front (magnifying side) of the fourth lens group G4 may be a convex lens La... or a concave lens Lb.... On the other hand, it is desirable to satisfy [condition 2] (nd>1.7), but it is not an essential component. Furthermore, it is desirable to set the zoom ratio in the range of 1.3-1.7 times and the half-angle of view on the wide-angle side in the range of 25-35 [°], but these values ​​are not limited. [Industrial applicability]

[0081] The zoom lens according to the present invention can be used as a projection lens, including dedicated lenses or interchangeable lenses, in various optical devices such as projectors. [Explanation of symbols]

[0082] 1: Zoom lens, 100: Lens optics, 200: Optical adjustment system, E(OBJ): Magnification side, S: Reduction side, G1: First lens group, G2: Second lens group, G3: Third lens group, G4: Fourth lens group, G5: Fifth lens group, G6: Sixth lens group, Dc: Optical axis direction, Mcz: Zooming adjustment unit, Mcf: Focusing adjustment unit, La…(Lc…): Convex lens (positive lens), Lb…: Concave lens, Lz: Single lens, J1…: Cemented lens, νd: Abbe number, nd: Refractive index

Claims

1. A zoom lens comprising six lens groups, from the first to the sixth lens group, arranged in order from the magnification side to the reduction side, wherein the lens optical system is characterized by sequentially arranging, from the magnification side to the reduction side, a first lens group having negative refractive power, a second lens group having positive refractive power, a third lens group having positive refractive power, a fourth lens group having positive refractive power and containing at least two positive lenses that satisfy the following [condition 1] when the Abbe number for the d line is νd, a fifth lens group having positive or negative refractive power, and a sixth lens group having positive refractive power; and an optical adjustment system including a zoom adjustment unit that fixes the first and sixth lens groups and moves the second to fifth lens groups independently in the optical axis direction, wherein each lens in the fourth lens group is composed of a single lens, and convex and concave lenses are arranged alternately in the optical axis direction. νd>70 … [Conditional expression 1]

2. The zoom lens according to claim 1, wherein the sixth lens group is composed of a single lens and satisfies the following [conditional equation 2] when the refractive index is nd. nd > 1.7 ... [Conditional Equation 2]

3. The zoom lens according to claim 1, characterized in that the optical adjustment system includes a focusing adjustment unit that moves only the first lens group in the optical axis direction.

4. The zoom lens according to claim 1, characterized in that the zoom ratio is set in the range of 1.3 to 1.7 times.

5. The zoom lens according to claim 1 or 4, characterized in that the half-angle of view on the wide-angle side is set in the range of 25-35°.

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