Projection zoom lens

Abstract

To provide a high-performance projection zoom lens by appropriately balancing suppression of various aberrations that arise when zooming while ensuring a high zoom ratio, a high aperture ratio, and brightness.SOLUTION: A projection zoom lens provided herein comprises: a lens optical system 100 consisting of a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, a third lens group G3 having positive refractive power, a fourth lens group G4 having positive refractive power, and a fifth lens group G5 having positive refractive power successively arranged in order from the magnification side E to the reduction side S; and an optical adjustment system 200 comprising a zooming adjustment unit Mcz configured to keep the first and fifth lens groups G1, G5 stationary and independently move the second lens group G2 from the magnification side E to the reduction side S, the third lens group G3 from the reduction side S to the magnification side E, and the fourth lens group G4 from the reduction side S to the magnification side E along an optical axis Dc. The projection zoom lens satisfies conditional expressions 1 through 3.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] Conventionally, as a projection 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 being telecentric. Specifically, in order from the magnification 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. During 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 of Patent Document 2 aims to provide a projection optical system that has a simple configuration and is capable of adjusting appropriate field curvature. 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]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-200454 [Patent Document 2] Japanese Patent Application Laid-Open No. 2017-126036 Summary of the Invention [Problem to be solved by the invention]

[0006] However, conventional projection zoom lenses, including the above-mentioned projection zoom lens and projection optical system, have had the following problems to be solved.

[0007] That is, in the case of a projector equipped with this type of projection zoom lens, in order to enlarge and project an optical image onto a distant screen, the projection zoom lens used is required to have the necessary zoom ratio and angle of view while ensuring the necessary brightness, as well as to provide good image quality through the necessary correction of various aberrations such as spherical aberration, coma aberration, astigmatism, field curvature, etc. Furthermore, since the projection zoom lens is supported in a state where it protrudes forward from the front surface of the projector body and is equipped with a lens optical system having multiple lens groups and an optical adjustment system having various adjustment units such as a zoom adjustment unit, there is also a demand for the entire projection zoom lens to be compact, lightweight, and inexpensive.

[0008] However, these various performance characteristics are interrelated and affect each other, such that improving one characteristic will impair another. Therefore, in addition to improving each required characteristic, there is also the fundamental challenge of achieving a high-performance projection zoom lens by achieving a good balance between the suppression of various aberrations that occur during zooming, such as spherical aberration, coma, astigmatism, and curvature of field, while ensuring the high magnification and large aperture ratio required.

[0009] SUMMARY OF THE INVENTION An object of the present invention is to provide a projection zoom lens that solves the problems present in the background art. [Means for solving the problem]

[0010] In order to solve the above-mentioned problems, the present invention provides a projection zoom lens 1 including five lens groups G1-G5, from a first lens group G1 to a fifth lens group G5, arranged in order from an enlargement side E to a reduction side S, the projection zoom lens 1 including a lens optical system 100 in which, from the enlargement side E to the reduction side S, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, a third lens group G3 having positive refractive power, a fourth lens group G4 having positive refractive power, and a fifth lens group G5 having positive refractive power are arranged in this order, and the first lens group G1 and the fifth lens group G5 are fixed and the second lens group G2 is moved to the enlargement side E when changing magnification from the wide-angle end to the telephoto end. and an optical adjustment system 200 having a zoom adjustment unit Mcz that moves the third lens group G3 from the reduction side S to the enlargement side E, and the fourth lens group G4 from the reduction side S to the enlargement side E, each independently in the optical axis direction Dc, and is characterized in that, when the F-number at the wide-angle side E is FNw, the focal length of the entire system at the wide-angle end is fw [mm], the focal length of the entire system at the telephoto end is ft [mm], and the air-equivalent back focus at the d-line is BF [mm], the following are satisfied: FNw>1.8...[Conditional formula 1], 2.2>(ft / fw)...[Conditional formula 2], 2.1>(fw / BF)>1.3...[Conditional formula 3].

[0011] In this case, according to a preferred embodiment of the invention, the fifth lens group G5 can include a positive lens L20 that satisfies conditional formula 4 (nd>1.8), where nd is the refractive index at the d-line. The second lens group G2 can include at least one single lens L5 that satisfies conditional formula 5 (νd>70), where νd is the Abbe number at the d-line, and the fourth lens group G4 can include at least one positive lens L10 that satisfies conditional formula 6 (νd>70), where νd is the Abbe number at the d-line. [Effects of the Invention]

[0012] The projection zoom lens 1 according to the present invention having such a configuration provides the following significant effects.

[0013] (1) The present invention includes a lens optical system (100) including, in order from an enlargement side (E) to a reduction side (S), a first lens group (G1) having a positive refractive power, a second lens group (G2) having a negative refractive power, a third lens group (G3) having a positive refractive power, a fourth lens group (G4) having a positive refractive power, and a fifth lens group (G5) having a positive refractive power, and an optical adjustment system (200) including a zoom adjustment unit (Mcz) that, when varying magnification from a wide-angle end to a telephoto end, keeps the first lens group (G1) and the fifth lens group (G5) stationary and moves the second lens group (G2) from the enlargement side (E) to the reduction side (S), the third lens group (G3) from the reduction side (S) to the enlargement side (E), and the fourth lens group (G4) from the reduction side (S) to the enlargement side (E), independently in the optical axis direction (Dc), In addition, the lens is configured to satisfy the following conditions: FNw>1.8...[Conditional formula 1], 2.2>(ft / fw)...[Conditional formula 2], 2.1>(fw / BF)>1.3...[Conditional formula 3], where F-number at the wide-angle end E is FNw, the focal length of the entire system at the wide-angle end is fw [mm], the focal length of the entire system at the telephoto end is ft [mm], and the back focus in air equivalent at the d-line is BF [mm]. As a result, in addition to improving each required performance, it is possible to ensure each required item, particularly a high magnification ratio, a large aperture ratio, and brightness, while achieving a good balance in suppressing various aberrations that occur during magnification, such as spherical aberration, coma, astigmatism, and curvature of field, resulting in a high-performance projection zoom lens.

[0014] (2) In a preferred embodiment, when configuring the fifth lens group G5, by providing a positive lens L20 on the reduction side S that satisfies the following condition: nd>1.8 (conditional expression 4), where nd is the refractive index for the d-line, it is possible to ensure good aberration characteristics while maintaining appropriate telecentricity.

[0015] (3) In a preferred embodiment, when configuring the second lens group G2, if at least one single lens L5 that satisfies vd>70 [Conditional Expression 5] is included, where vd is the Abbe number at the d-line, it is possible to ensure that the Abbe number vd of the single lens L5 falls within an appropriate range, thereby enabling excellent correction of axial chromatic aberration and lateral chromatic aberration in particular.

[0016] (4) In a preferred embodiment, when configuring the fourth lens group G4, if at least one positive lens L10 that satisfies vd>70 [Conditional Expression 6] is included, where vd is the Abbe number at the d-line, then it is possible to ensure that the positive lens L10 has an appropriate range for the Abbe number vd. This makes it possible to more effectively correct axial chromatic aberration and chromatic aberration of magnification, in addition to the effect of the positive lens L5 described above. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a diagram showing the overall lens configuration on the WIDE side of a projection zoom lens according to Example 1 of a preferred embodiment of the present invention; [Figure 2] FIG. 2 is a diagram showing the overall lens configuration of the projection zoom lens of Example 1, comparing the lens positions on the WIDE side and the TELE side; [Figure 3] A list of conditional expressions [1]-[4] in the optical characteristics of the projection zoom lens according to the embodiment; [Figure 4] A list of conditional expressions [5]-[6] in the optical characteristics of the projection zoom lens according to the embodiment; [Figure 5] FIG. 2 is a longitudinal aberration diagram of the projection zoom lens of Example 1 at a reference distance on the WIDE side; [Figure 6] FIG. 2 is a longitudinal aberration diagram of the projection zoom lens of Example 1 at a reference distance on the TELE side; [Figure 7]FIG. 2 is a diagram showing the overall lens configuration of the wide-angle side of the projection zoom lens of the second embodiment; [Figure 8] FIG. 2 is a diagram showing the overall lens configuration of the telephoto side of the projection zoom lens of Example 2; [Figure 9] FIG. 10 is a longitudinal aberration diagram of the projection zoom lens of Example 2 at a reference distance on the WIDE side; [Figure 10] FIG. 10 is a longitudinal aberration diagram of the projection zoom lens of Example 2 at a reference distance on the TELE side; [Figure 11] FIG. 10 is a diagram showing the overall lens configuration of the projection zoom lens of Example 3 on the wide side; [Figure 12] FIG. 10 is a diagram showing the overall lens configuration of the telephoto side of the projection zoom lens of Example 3; [Figure 13] FIG. 10 is a longitudinal aberration diagram of the projection zoom lens of Example 3 at a reference distance on the WIDE side; [Figure 14] FIG. 10 is a longitudinal aberration diagram of the projection zoom lens of Example 3 at a reference distance on the TELE side; DETAILED DESCRIPTION OF THE INVENTION

[0018] Next, preferred embodiments of the present invention will be described in detail with reference to the drawings. [Example]

[0019] First, the lens optical system 100 and the optical adjustment system 200 of the projection zoom lens 1 according to Example 1 of this embodiment will be described with reference to FIGS.

[0020] It is assumed that this projection zoom lens 1 is used as a long focal length projection zoom lens for a projector.

[0021] 1, E indicates the enlargement side of a screen or the like, and S indicates the reduction side (reduction conjugate side) which becomes an image display element such as a liquid crystal panel. Therefore, the enlargement side E is in front of the optical axis Dc, and the reduction side S is in back of the optical axis Dc.

[0022] As shown in FIG. 1, the lens optical system 100 comprises five lens groups G1, G2, G3, G4, and G5, arranged in order from the enlargement side E to the reduction side S, from the first lens group G1 to the fifth lens group G5, and comprises a prism Pr, shown in the schematic diagram, on the reduction side S relative to the fifth lens group G5.

[0023] The first lens group G1 has positive refractive power overall and is composed of, arranged in order from the magnification side E to the reduction side S, a positive lens L1 using a biconvex lens, a positive lens L2 using a biconvex lens, a negative lens L3 using a biconcave lens, and a positive lens L4 using a positive meniscus lens with a convex surface on the magnification side E. The first lens group G1 has a total of four lenses L1, L2, L3, and L4, all of which are single lenses.

[0024] The second lens group G2 has negative refractive power overall and is composed of, arranged in order from the magnification side E to the reduction side S, a negative lens L5 that is a negative meniscus lens with a convex surface on the magnification side E, a negative lens L6 that is a biconcave lens, and a positive lens L7 that is a positive meniscus lens with a convex surface on the magnification side E. The second lens group G2 has three lenses L5, L6, and L7, all of which are single lenses.

[0025] When configuring the second lens group G2, at least one single lens L5 (one lens in the first embodiment) that satisfies [Conditional Expression 5] is included, where νd is the Abbe number for the d-line. νd>70 … [Conditional expression 5]

[0026] This makes it possible to ensure an appropriate range of Abbe number vd for the single lenses L5 . . . , and therefore makes it possible to effectively correct axial chromatic aberration and chromatic aberration of magnification in particular.

[0027] The third lens group G3 has positive refractive power overall and is composed of, arranged in order from the enlargement side E to the reduction side S, a positive lens L8 that is a biconvex lens and a negative lens L9 that is a negative meniscus lens with a convex surface on the reduction side S. The third lens group G3 has two lenses L8 and L9, each of which is a single lens.

[0028] The fourth lens group G4 has positive refractive power overall and is composed of, arranged in order from the enlargement side E to the reduction side S, a positive lens L10 using a biconvex lens, a positive lens L11 using a biconvex lens, a negative lens L12 using a biconcave lens, and a positive lens L13 using a biconvex lens. The fourth lens group G4 has a total of four lenses L10, L11, L12, and L13, all of which are single lenses.

[0029] When the fourth lens group G4 is configured, it includes at least one (three in the first embodiment) positive lens L10, L11, L13 that satisfies [Conditional Expression 6], where νd is the Abbe number for the d-line. νd>70 … [Conditional expression 6]

[0030] This ensures that the positive lenses L10... have an appropriate range of Abbe numbers vd, and therefore, in addition to the effect of the positive lenses L5... described above, axial chromatic aberration and chromatic aberration of magnification can be corrected more satisfactorily.

[0031] The fifth lens group G5 has positive refractive power as a whole and is composed of, arranged in order from the magnification side E to the reduction side S, the following: a positive lens L14 using a biconvex lens, a negative lens L15 using a negative meniscus lens with a convex surface on the magnification side E, a positive lens L16 using a biconvex lens, a negative lens L17 using a biconcave lens, a negative lens L18 using a biconcave lens, a positive lens L19 using a biconvex lens, and a positive lens L20 using a biconvex lens. The fifth lens group G5 has a total of seven lenses L14, L15, L16, L17, L18, L19, and L20, all of which are single lenses.

[0032] When the fifth lens group G5 is configured, a positive lens L20 that satisfies [Conditional Expression 4] is provided on the most reduction side S, where the refractive index at the d-line is nd. nd>1.8 … [Conditional Expression 4]

[0033] This makes it possible to ensure good aberration characteristics while maintaining appropriate telecentricity.

[0034] Furthermore, the entire lens optical system 100 is configured to satisfy [Conditional Expression 1] when the F-number on the wide-angle side is FNw. FNw>1.8 … [Conditional Expression 1]

[0035] Furthermore, when the focal length of the entire system at the wide-angle end is fw (mm) and the focal length of the entire system at the telephoto end is ft (mm), the lens is configured to satisfy [Conditional Expression 2]. 2.2>(ft / fw) … [Conditional Expression 2]

[0036] In addition, when the air-equivalent back focus at the d-line is BF (mm), the lens is configured to satisfy [Conditional Expression 3]. 2.1>(fw / BF)>1.3 … [Conditional expression 3]

[0037] On the other hand, the projection zoom lens 1 is provided with an optical adjustment system 200 having a zoom adjustment unit Mcz, the principle configuration of which is shown in FIG.

[0038] In this case, as shown in Fig. 2, the zoom adjustment unit Mcz has the function of keeping the first lens group G1 and the fifth lens group G5 stationary and moving the second lens group G2 independently in the optical axis direction Dc from the enlargement side E to the reduction side S, the third lens group G3 independently in the optical axis direction Dc from the reduction side S to the enlargement side E, and the fourth lens group G4 independently in the optical axis direction Dc when changing magnification from the wide-angle end to the telephoto end. In Fig. 2, the movement directions of the second lens group G2, the third lens group G3, and the fourth lens group G4 are indicated by arrows M1, M2, and M3, respectively.

[0039] Table 1 shows the lens data (surface data) of the projection zoom lens 1 according to the first embodiment.

[0040] [Table 1]

[0041] In the surface data in Table 1, i indicates the surface number of the lens surface counted from the magnification side E, and this surface number i 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), and lens Abbe number vd(i) are also shown. nd(i) and vd(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 units for radius of curvature R(i) and surface spacing D(i) are mm. The infinity symbol for radius of curvature R(i) indicates a flat surface. Blank spaces for refractive index nd(i) and Abbe number vd(i) indicate air.

[0042] 3 and 4 show condition values ​​in the conditional expressions of the projection zoom lens 1 according to each of the examples including Example 1. FIG.

[0043] In Example 1, the F-number FNw at the wide-angle end is 1.80, and sufficient brightness is achieved by satisfying [Conditional Expression 1] of "FNw>1.8." The total system focal length fw at the wide-angle end is 86.63 mm, and the total system focal length ft at the telephoto end is 167.40 mm, so ft / fw is 1.93, which satisfies [Conditional Expression 2], i.e., the condition "2.2>(ft / fw)." The air-equivalent back focal length BF at the d-line is 48.813 mm, so fw / BF is 1.77, which satisfies [Conditional Expression 3], i.e., the condition "2.1>(fw / BF)>1.3." The refractive index nd at the d-line of the positive lens L20 at the most reduction side S of the fifth lens group G5 is 1.80420, which satisfies [Conditional Expression 4], i.e., the condition "nd>1.8."

[0044] The Abbe number vd at the d-line of the single lens L5 (i=9) in the second lens group G2 is 81.6, which satisfies conditional formula 5, i.e., condition vd > 70. The Abbe numbers vd at the d-line of the positive lenses L10 (i=19), L11 (i=21), and L13 (i=25) in the fourth lens group G4 are 70.4, 70.4, and 81.6, respectively, which satisfies conditional formula 6, i.e., condition vd > 70.

[0045] Figures 1 and 2(a) show the lens positions of each lens L1... in the direction of the optical axis Dc when the projection zoom lens 1 of Example 1 is adjusted to the WIDE side, and Figure 2(b) shows the lens positions of each lens L1... in the direction of the optical axis Dc when the projection zoom lens 1 is adjusted to the TELE side.

[0046] 5 and 6 show longitudinal aberration diagrams of the projection zoom lens 1 according to Example 1 at a reference distance (E=8550 mm). FIG. 5 shows the WIDE side, and FIG. 6 shows the TELE side. From the left, each longitudinal aberration diagram shows spherical aberration (610 nm, 550 nm, 455 nm), astigmatism (550 nm), and distortion (550 nm). Each scale division (1 division) is ±0.10 mm, ±0.10 mm, and ±1.0%.

[0047] As shown in FIGS. 5 and 6, it can be confirmed that the projection zoom lens 1 according to Example 1 has no significant disturbance in any of the longitudinal aberrations and has good aberration characteristics, that is, good projection performance (optical performance).

[0048] As described above, the projection zoom lens 1 according to this embodiment (Example 1) has a basic configuration including a lens optical system 100 in which, from the enlargement side E to the reduction side S, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, a third lens group G3 having positive refractive power, a fourth lens group G4 having positive refractive power, and a fifth lens group G5 having positive refractive power are sequentially arranged, and a zoom adjustment unit Mcz that, during zooming from the wide-angle end to the telephoto end, keeps the first lens group G1 and the fifth lens group G5 stationary and moves the second lens group G2 from the enlargement side E to the reduction side S, the third lens group G3 from the reduction side S to the enlargement side E, and the fourth lens group G4 from the reduction side S to the enlargement side E independently in the optical axis direction Dc. and an optical adjustment system 200 including: a lens element including: a lens element having a lens barrel having a lens barrel width of 1.5 mm and a lens barrel having a lens barrel length of 1.5 mm; a lens element having a lens barrel width of 1.5 mm and ... [Example]

[0049] Next, the lens optical system 100 of the projection zoom lens 1 according to Example 2 of this embodiment will be described with reference to FIGS. 7 to 10, 3 and 4. FIG.

[0050] 7 shows the overall lens configuration of the projection zoom lens of Example 2 on the WIDE side, and FIG. 8 shows the overall lens configuration of the projection zoom lens of Example 2 on the TELE side.

[0051] As shown in Figures 7 and 8, the lens optical system 100 has five lens groups G1, G2, G3, G4, and G5, from the first lens group G1 to the fifth lens group G5, arranged in order from the enlargement side E to the reduction side S, and has a prism Pr, shown in a schematic diagram, on the reduction side S relative to the fifth lens group G5.

[0052] The first lens group G1 of Example 2 has positive refractive power overall, and the basic lens configuration is the same as that of Example 1. The difference from Example 1 is that while a biconvex lens was used for the positive lens L2 in Example 1, a positive meniscus lens having a convex surface on the magnification side E is used as the positive lens L2 in Example 2. Therefore, the first lens group G1 of Example 2 has a total of four lenses L1, L2, L3, and L4, all of which are single lenses.

[0053] The second lens group G2 has negative refractive power overall, and the basic lens configuration is the same as in Example 1. In this case, when the Abbe number at the d-line is vd, it includes at least one single lens L5, L6 (two lenses in Example 2) that satisfies Conditional Expression 5, and has three lenses in total: L5, L6, and L7, all of which are single lenses.

[0054] The third lens group G3 has positive refractive power overall and is composed of, arranged in order from the enlargement side E to the reduction side S, a negative lens L8 that is a negative meniscus lens with a convex surface on the enlargement side E, and a positive lens L9 that is a biconvex lens. The third lens group G3 has two lenses L8 and L9, each of which is a single lens.

[0055] The fourth lens group G4 has positive refractive power overall, and the basic lens configuration is the same as in Example 1. The difference from Example 1 is that in Example 1, a biconvex lens was used for the positive lens L11, but in Example 2, a positive meniscus lens having a convex surface on the magnification side E is used for the positive lens L11. Furthermore, when the Abbe number for the d-line is vd, the positive lenses L10, L11, and L13 satisfy Conditional Expression 6 above, and the total number of lenses L10, L11, L12, and L13 is four, all of which are single lenses.

[0056] The fifth lens group G5 has positive refractive power overall, and the basic lens configuration is the same as in Example 1. The difference from Example 1 is that, while in Example 1 the positive lens L14 and the negative lens L15 are each configured as single lenses, in Example 2 they are configured as a cemented lens J1 formed by cementing together a positive lens (biconvex lens) L14 and a negative lens (biconcave lens) L15. Furthermore, when configuring the positive lens L20 located closest to the reduction side S, in Example 1 a biconvex lens was used, but in Example 2 a positive meniscus lens having a convex surface on the enlargement side E was used. Therefore, the fifth lens group G5 has a total of seven lenses L14, L15, L16, L17, L18, L19, and L20.

[0057] Furthermore, when the refractive index of the positive lens L20 at the d-line is nd, the configuration is such that the above-mentioned [Conditional Expression 4] is satisfied. Note that the optical adjustment system 200 including the zoom adjustment unit Mcz is the same as in the first embodiment.

[0058] Table 2 shows the lens data (surface data) of the projection zoom lens 1 according to the second embodiment.

[0059] [Table 2]

[0060] 3 and 4 show the conditional values ​​for each conditional expression, including Example 2. In Example 2, the F-number FNw at the wide-angle end is 1.92, and sufficient brightness is obtained by satisfying [Conditional Expression 1] of "FNw>1.8." The total system focal length fw at the wide-angle end is 93.65 [mm], and the total system focal length ft at the telephoto end is 170.17 [mm], so ft / fw is 1.82, which satisfies [Conditional Expression 2], i.e., the condition "2.2>(ft / fw)." The air-equivalent back focal length BF at the d-line is 47.847 [mm], so fw / BF is 1.96, which satisfies [Conditional Expression 3], i.e., the condition "2.1>(fw / BF)>1.3." The refractive index nd for the d-line of the positive lens L20 on the most reduction side S of the fifth lens group G5 is 1.80611, which satisfies [Conditional Expression 4], ie, the condition "nd>1.8".

[0061] Furthermore, the Abbe numbers vd at the d-line of the single lenses L5 (i=9) and L6 (i=11) in the second lens group G2 are 81.6 and 70.4, respectively, which satisfy Conditional Formula 5, i.e., the condition vd > 70. Furthermore, the Abbe numbers vd at the d-line of the positive lenses L10 (i=19), L11 (i=21), and L13 (i=25) in the fourth lens group G4 are 70.4, 70.4, and 81.6, respectively, which satisfy Conditional Formula 6, i.e., the condition vd > 70.

[0062] 9 and 10 show longitudinal aberration diagrams of the projection zoom lens 1 according to Example 2 at a reference distance (E=8913 mm). Fig. 9 shows the WIDE side, and Fig. 10 shows the TELE side. As shown in Figs. 9 and 10, it can be confirmed that the projection zoom lens 1 according to Example 2 also has no significant disturbance in any of the longitudinal aberrations, and thus has good aberration characteristics, i.e., good projection performance (optical performance).

[0063] Since the second embodiment is configured under the same conditions as the first embodiment, it is possible to obtain the same effects as the first embodiment, that is, to improve each required performance, and in addition, it is possible to obtain a high-performance projection zoom lens by achieving a good balance between suppressing various aberrations that occur during zooming, such as spherical aberration, coma, astigmatism, and field curvature, while ensuring each required item, particularly a high magnification ratio, a large aperture ratio, and brightness. [Example]

[0064] Next, the lens optical system 100 of the projection zoom lens 1 according to Example 3 of this embodiment will be described with reference to FIGS. 11 to 14, 3 and 4. FIG.

[0065] 11 shows the overall lens configuration on the WIDE side of the projection zoom lens of Example 3, and FIG. 12 shows the overall lens configuration on the TELE side of the projection zoom lens of Example 3.

[0066] As shown in Figures 11 and 12, the lens optical system 100 has five lens groups G1, G2, G3, G4, and G5, from the first lens group G1 to the fifth lens group G5, arranged in order from the enlargement side E to the reduction side S, and has a prism Pr, shown in a schematic diagram, on the reduction side S relative to the fifth lens group G5.

[0067] The first lens group G1 of Example 3 has positive refractive power as a whole, and unlike Example 1, is composed of three single lenses as a whole, namely, in order from the enlargement side E to the reduction side S, a positive lens L1 that is a biconvex lens, a negative lens L2 that is a biconcave lens, and a positive lens L3 that is a positive meniscus lens having a convex surface on the enlargement side E. All of these are single lenses.

[0068] The second lens group G2 has negative refractive power overall, and the basic lens configuration is the same as in Example 1. Therefore, when the Abbe number at the d-line is vd, it includes single lenses (biconcave lenses) L4 and L5 that satisfy Conditional Expression 5, and has three lenses in total: L4, L5, and L6.

[0069] The third lens group G3 has a positive refractive power overall and is composed of, in order from the enlargement side E, a positive lens L7 using a biconvex lens, and a negative lens L8 using a negative meniscus lens with a convex surface on the reduction side S.

[0070] The fourth lens group G4 has positive refractive power overall, and has the same basic lens configuration as in Example 1, including four lenses L9, L10, L11, and L12. When the Abbe number for the d-line is vd, the fourth lens group G4 includes positive lenses L9 and L12 that satisfy Conditional Expression 6, and each of the lenses is a single lens.

[0071] The fifth lens group G5 has positive refractive power overall, and the basic lens configuration is the same as in Example 1. That is, the fifth lens group G5 includes lenses L13, L14, L15, L16, L17, L18, and L9, which are made up of a total of seven single lenses. The fifth lens group G5 in Example 3 differs from Example 1 in that, when configuring lens L16 (Example 1), Example 1 uses a biconvex lens L16, while Example 3 uses a positive meniscus lens L15 (corresponding to L16 in Example 1) having a convex surface on the magnification side E. Furthermore, when configuring lens L17 (Example 1), Example 1 uses a biconcave lens L17, while Example 3 uses a negative meniscus lens L16 (corresponding to L17 in Example 1) having a convex surface on the magnification side E.

[0072] Additionally, in Example 3, when the refractive index of the positive lens (biconvex lens) L19 at the d-line is nd, the configuration is such that the above-mentioned [Conditional Expression 4] is satisfied. Note that the optical adjustment system 200 including the zoom adjustment unit Mcz is the same as in Example 1.

[0073] Table 3 shows the lens data (surface data) of the projection zoom lens 1 according to the third embodiment.

[0074] [Table 3]

[0075] 3 and 4 show the conditional values ​​for each conditional expression, including Example 3. In Example 3, the F-number FNw at the wide-angle end is 1.97, and sufficient brightness is obtained by satisfying [Conditional Expression 1] of "FNw>1.8." The total system focal length fw at the wide-angle end is 58.25 [mm], and the total system focal length ft at the telephoto end is 110.40 [mm], so ft / fw is 1.90, which satisfies [Conditional Expression 2], i.e., the condition "2.2>(ft / fw)." The air-equivalent back focal length BF at the d-line is 40.725 [mm], so fw / BF is 1.43, which satisfies [Conditional Expression 3], i.e., the condition "2.1>(fw / BF)>1.3." The refractive index nd for the d-line of the positive lens L19 on the most reduction side S of the fifth lens group G5 is 1.83481, which satisfies [Conditional Expression 4], ie, the condition "nd>1.8".

[0076] Furthermore, the Abbe numbers vd at the d-line of the single lenses L4 (i=7) and L5 (i=9) in the second lens group G2 are 70.4 and 70.4, respectively, which satisfy Conditional Formula 5, i.e., the condition vd > 70. Furthermore, the Abbe numbers vd at the d-line of the positive lenses L9 (i=17) and L12 (i=23) in the fourth lens group G4 are 70.4 and 95.1, respectively, which satisfies Conditional Formula 6, i.e., the condition vd > 70.

[0077] 13 and 14 show longitudinal aberration diagrams of the projection zoom lens 1 according to Example 3 at a reference distance (E=7070 mm). Fig. 13 shows the WIDE side, and Fig. 14 shows the TELE side. As shown in Figs. 13 and 14, it can be confirmed that the projection zoom lens 1 according to Example 3 also has no significant disturbance in any of the longitudinal aberrations, and thus has good aberration characteristics, i.e., good projection performance (optical performance).

[0078] Since the third embodiment is basically configured under the same conditions as the first embodiment, it is possible to obtain the same effects as the first embodiment, that is, to improve each required performance, and in addition, it is possible to obtain a high-performance projection zoom lens by achieving a good balance between suppressing various aberrations that occur during zooming, such as spherical aberration, coma aberration, astigmatism, and curvature of field, while ensuring each required item, particularly a high magnification ratio, a large aperture ratio, and brightness.

[0079] The above describes in detail preferred embodiments including Examples 1-3, 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.

[0080] For example, while the lens optical system 100 is configured with five lens groups G1-G5, adding additional lens groups to form six or more lens groups G1... is not excluded. Furthermore, the number of lenses in each of the lens groups G1-G5, including the first lens group G1, is not limited to the number of lenses shown in the embodiment (example) and can be any number required. Meanwhile, the fifth lens group G5 is configured with a positive lens L20... on the reduction side S, which satisfies Conditional Formula 4, where nd is the refractive index at the d-line. However, this is not a required condition. Furthermore, the second lens group G2 includes at least one single lens L7... that satisfies Conditional Formula 5, where νd is the Abbe number at the d-line, and the fourth lens group G4 includes at least one positive lens L10... that satisfies Conditional Formula 6, where νd is the Abbe number at the d-line. However, this is not a required condition. [Industrial Applicability]

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

[0082] 1: projection zoom lens, 100: lens optical system, 200: optical adjustment system, E: enlargement side, S: reduction side, G1: first lens group, G2: second lens group, G3: third lens group, G4: fourth lens group, G5: fifth lens group, Dc: optical axis direction, Mcz: zooming adjustment section, νd: Abbe number, nd: refractive index

Claims

1. In a projection zoom lens having five lens groups arranged in order from the enlargement side to the reduction side, from the enlargement side to the reduction side, the lens optical system is arranged in the order of the first lens group having positive refractive power, the second lens group having negative refractive power, the third lens group having positive refractive power, the fourth lens group having positive refractive power, and the fifth lens group having positive refractive power, and when changing magnification from the wide-angle end to the telephoto end, the first lens group and the fifth lens group are fixed, and the second lens group is enlarged. and an optical adjustment system including a zoom adjustment unit that moves the third lens group from the reduction side to the enlargement side, the third lens group from the reduction side to the enlargement side, and the fourth lens group from the reduction side to the enlargement side, respectively, in the optical axis direction, and the projection zoom lens satisfies [Conditional Formula 1] to [Conditional Formula 3] when the F-number on the wide-angle side is FNw, the total system focal length at the wide-angle end is fw [mm], the total system focal length at the telephoto end is ft [mm], and the air-equivalent back focus at the d-line is BF [mm]. FNw>1.8 ... [Conditional formula 1] 2.2>(ft / fw) ... [Conditional Expression 2] 2.1>(fw / BF)>1.3... [Conditional expression 3]

2. 2. The projection zoom lens according to claim 1, wherein the fifth lens group has, at the most reduction side, a positive lens that satisfies conditional expression 4, where nd is the refractive index for the d-line. nd>1.8 ... [Conditional Expression 4]

3. 2. The projection zoom lens according to claim 1, wherein the second lens group includes at least one single lens that satisfies conditional expression 5, where νd is the Abbe number for the d-line. νd>70... [Conditional expression 5]

4. 3. The projection zoom lens according to claim 1, wherein the fourth lens group includes at least one positive lens that satisfies conditional expression 6, where νd is the Abbe number for the d-line. νd>70 … [Conditional expression 6]

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