JP7790710B2 - Zoom lens - Google Patents

Description

The present invention relates to a zoom lens suitable for use in optical devices equipped with a projection optical system, such as a projector.

Conventionally, known zoom lenses included in projection optical systems that project images from a projector onto a screen or the like include the projection zoom lens described in Patent Document 1 and the projection optical system described in Patent Document 2.

The projection zoom lens in Patent Document 1 aims to achieve a projection zoom lens with a high zoom ratio, a small F-number, small chromatic aberration of magnification, high MTF characteristics, and high resolution characteristics, and is telecentric on the display device side. Specifically, from the magnification side, it is configured with 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, with an aperture stop disposed between the fourth and fifth lens groups. When the magnification is changed, the second The first to sixth lens groups move so that the distances between the first and second lens groups, the first and third lens groups, and the first and fourth lens groups all decrease when changing magnification from the wide-angle end to the telephoto end, and the focal length of the entire system at the wide-angle end is fw, the focal length of the first lens group is fl, the focal length of the second lens group is f2, the focal length of the third lens group is f3, and the focal length of the fourth lens group is f4, and these satisfy the relationships 1.3<|f|/fw<1.9, 0.6<f2/f3<3.5, and 0.4<f4/f3<3.7.

The projection optical system of Patent Document 2 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 meridian section at the outermost periphery are different from each other, a second lens adjacent to the first lens, and a diaphragm positioned at the position where the off-axis chief ray intersects with the optical axis. By changing the distance between the first lens and the second lens in the optical axis direction, the field curvature of the projected image can be adjusted, and the system is also configured to satisfy a predetermined conditional formula.

JP 2013-200454 A Japanese Patent Application Laid-Open No. 2017-126036

However, conventional zoom lenses, including the projection zoom lens and projection optical system described above, had the following issues that needed to be resolved:

In other words, in the case of a projector equipped with this type of zoom lens, in order to enlarge and project an optical image onto a distant screen, the zoom lens used must ensure the necessary brightness while providing the necessary zoom ratio and angle of view, as well as good image quality through the necessary correction of aberrations such as astigmatism, distortion, and chromatic aberration, as well as field curvature. Furthermore, because the zoom lens is supported in a state where it protrudes forward from the front of the projector body and is equipped with an optical adjustment system that includes a lens optical system with multiple lens groups and various adjustment units such as a zoom adjustment unit, the entire zoom lens must also be made smaller, lighter, and more affordable.

However, these required performance characteristics are mutually contradictory; improving some performance characteristics will result in the impairment of others. Therefore, in addition to improving each required performance characteristic, finding a good balance between the various requirements is an important issue for this type of zoom lens. However, the reality is that up until now, zoom lenses that rationally resolve these issues have not necessarily been provided.

The present invention aims to provide a zoom lens that solves the problems present in the background art.

In order to solve the above-mentioned problems, the present invention provides a zoom lens 1 comprising six lens groups, from the first lens group G1 to the sixth lens group G6, arranged in order from the enlargement side E to the reduction side S, in which the first lens group G1 has negative refractive power, the second lens group G2 has positive refractive power, the third lens group G3 has negative refractive power, the fourth lens group G4 has positive refractive power, the fifth lens group G5 has at least two cemented lenses J1 and J2, and the sixth lens group G6 has positive refractive power, and the first lens group is composed of two positive lenses and two negative lenses. 100, and an optical adjustment system 200 including a zoom adjustment unit Mcz 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 direction of the optical axis Dc, and a focusing adjustment unit Mcf that moves the first lens group G1 in the direction of the optical axis Dc, and is characterized in that, when the total length of the lens optical system (the distance from the lens surface (i=1) on the enlargement side E of the lens L1 arranged on the furthest enlargement side E of the first lens group G1 at the time of projection at the reference distance) is T, and the focal length of the entire system on the wide-angle side is fw, it is set to satisfy [Conditional Expression 1]: 5.0<[T/fw]<8.0.

In this case, according to a preferred embodiment of the invention, the first lens group G1 is desirably set to satisfy conditional formula 2: -70<f1<-45, where f1 is the focal length of the first lens group G1 (mm). The fifth lens group G5 can be configured to include at least two positive lenses Lp6 and Lp8, which satisfy conditional formula 3: vd>70, where vd is the Abbe number for the d-line. The sixth lens group G6 can be configured with a single lens Lpe, and this single lens Lpe is desirably set to satisfy conditional formula 4: nd>1.8, where nd is the refractive index. Meanwhile, the zoom lens 1 can be set to a zoom ratio of 1.45 or more, and the full angle of view on the wide-angle side can be set to 36° or less.

The zoom lens 1 according to the present invention, which has this configuration, offers the following significant advantages:

(1) A lens optical system 100 is configured by sequentially arranging, from the enlargement side E to the reduction side S, a first lens group G1 having negative refractive power, a second lens group G2 having positive refractive power, a third lens group G3 having negative refractive power, a fourth lens group G4 having positive refractive power, a fifth lens group G5 having at least two cemented lenses J1 and J2, and a sixth lens group G6 having positive refractive power, and a lens optical system in which the first lens group G1 and the sixth lens group G6 are fixed and the second lens group G2 to the fifth lens group G5 are independently movable in the direction of the optical axis Dc. The lens has an optical adjustment system 200 that includes a zoom adjustment unit Mcz that moves the first lens group G1 in the direction of the optical axis Dc, and a focusing adjustment unit Mcf that moves the first lens group G1 in the direction of the optical axis Dc, and is designed to satisfy conditional formula 1 of 5.0<[T/fw]<8.0. This ensures the necessary brightness while achieving good image quality through the necessary correction of various aberrations and curvature of field, and also allows for the overall lens to be made smaller, lighter, and more inexpensive, achieving a good and reasonable balance of each performance feature.

(2) Because the first lens group G1 is constructed using two positive lenses Lp1, Lp2 and two negative lenses Ln1, Ln2, it is possible to construct a focusing adjustment unit Mcf that moves only the first lens group G1 using four lenses. 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 direction of the optical axis Dc.

(3) In a preferred embodiment, when configuring the first lens group G1, if the focal length of this first lens group G1 is set to f1 [mm] and conditional expression 2 of -70<f1<-45 is satisfied, the movement stroke of the first lens group G1 during focusing adjustment can be shortened, allowing the diameter of the zoom lens 1 to be made smaller, and various aberrations such as astigmatism and distortion to be corrected in a balanced manner, contributing to improved image quality.

(4) In a preferred embodiment, when the fifth lens group G5 is configured, if it includes at least two positive lenses Lp6 and Lp8 that satisfy conditional expression 3, where vd is the Abbe number for the d-line, and vd > 70, then an appropriate range for the Abbe number vd can be ensured, enabling particularly good correction of axial chromatic aberration and lateral chromatic aberration.

(5) In a preferred embodiment, when configuring the sixth lens group G6, if it is configured using a single lens Lp10, the overall length of the zoom lens 1 can be shortened by configuring it using the minimum number of lenses, which contributes to miniaturization.

(6) In a preferred embodiment, if the single lens Lpe in the sixth lens group G6 is formed to satisfy conditional expression 4, nd > 1.8, an appropriate range of refractive index nd can be ensured. This not only maintains a good balance in the telecentric optical system, but also effectively corrects field curvature, contributing to improved image quality.

(7) In a preferred embodiment, when constructing the zoom lens 1, if the zoom ratio is set to 1.45 or more, the necessary zoom ratio of the zoom lens 1 can be ensured while maintaining a good balance of each performance.

(8) In a preferred embodiment, when constructing the zoom lens 1, if the total angle of view on the wide-angle side is set to 36° or less, it is possible to ensure a well-balanced and rational balance of performance while ensuring the necessary angle of view for the zoom lens 1. In addition to ensuring the zoom ratio, it is also possible to ensure sufficient optical performance, particularly for projectors that project onto a screen.

FIG. 1 is a diagram showing the overall lens configuration of a zoom lens of Example 1 according to a preferred embodiment of the present invention, on the telephoto side; FIG. 2 is a diagram showing the principle of the optical adjustment system in the zoom lens of the first embodiment; FIG. 2 is a diagram showing the overall lens configuration of the zoom lens of Example 1 on the WIDE side; FIG. 2 is a longitudinal aberration diagram of the zoom lens of Example 1 on the WIDE side; FIG. 2 is a longitudinal aberration diagram of the zoom lens of Example 1 on the telephoto side; FIG. 2 is a diagram showing the overall lens configuration of the zoom lens of Example 2 on the telephoto side; FIG. 2 is a diagram showing the principle of the optical adjustment system in the zoom lens of the second embodiment; FIG. 2 is a diagram showing the overall lens configuration of the zoom lens of Example 2 on the WIDE side; FIG. 2 is a longitudinal aberration diagram of the zoom lens of Example 2 on the WIDE side; FIG. 10 is a longitudinal aberration diagram of the zoom lens of Example 2 on the telephoto side; Optical characteristics table of the zoom lens according to the embodiment

Next, we will present a preferred embodiment of the present invention and explain it in detail based on the drawings.

First, the configuration of the lens optical system 100 of the zoom lens 1 according to Example 1 of this embodiment will be described with reference to Figures 1 to 3.

Note that this zoom lens 1 is intended to be used as a projection lens (zoom lens) for a projector, i.e., a projection zoom optical system.

In Figure 1, E indicates the enlargement side, such as a screen, and S indicates the reduction side (reduction conjugate side), which becomes an image display element, such as an LCD panel. Therefore, the enlargement side E is in front of the optical axis Dc, and the reduction side S is in the rear of the optical axis Dc.

As shown in FIG. 1, the lens optical system 100 comprises six lens groups G1, G2, G3, G4, G5, and G6, arranged in order from the enlargement side E to the reduction side S, from the first lens group G1 to the sixth lens group G6, and is equipped with a prism Pr, shown in the schematic diagram, on the reduction side S relative to the sixth lens group G6.

The first lens group G1 has negative refractive power overall and is composed of, in order from the magnification side E, a positive lens Lp1 using a biconvex lens, a negative lens Ln1 using a negative meniscus lens with a convex surface on the magnification side E, a positive lens Lp2 using a positive meniscus lens with a convex surface on the magnification side E, and a negative lens Ln2 using a biconcave lens. Each of the lenses Lp1, Ln1, Lp2, and Ln2 is a single lens.

In this way, by configuring the first lens group G1 using two positive lenses Lp1, Lp2 and two negative lenses Ln1, Ln2, it is possible to construct the focusing adjustment unit Mcf (described below) that moves only the first lens group G1 using four lenses, which has the advantage of simplifying and miniaturizing the focusing adjustment unit Mcf and further contributing to reducing the weight of the zoom lens 1, which is relatively long in the direction of the optical axis Dc.

Furthermore, when configuring the first lens group G1, when the focal length of this first lens group G1 is f1 (mm), the configuration is such that the following (Conditional Expression 2) is satisfied.
-70<f1<-45... [Conditional expression 2]

Setting the value so that Conditional Expression 2 is satisfied shortens the stroke of movement of the first lens group G1 during focusing adjustment, allowing for a smaller diameter for the zoom lens 1, while also contributing to improved image quality through well-balanced correction of aberrations such as astigmatism and distortion. Therefore, if the magnitude of f1 is below "-70", the stroke of movement of the first lens group G1 during focusing adjustment becomes longer, resulting in an increase in the overall length and outer diameter of the zoom lens 1, which leads to an increase in size of the zoom lens 1. On the other hand, if the magnitude of f1 is above "-45", it is not possible to properly correct the aforementioned astigmatism, distortion, and other aberrations, resulting in a deterioration in image quality.

The second lens group G2 has positive refractive power overall and is composed of, from the magnification side E, a positive lens Lp3 made of a biconvex lens and a positive lens Lp4 made of a positive meniscus lens with a convex surface on the magnification side E. Both lenses Lp3 and Lp4 are single lenses. The third lens group G3 also includes a single lens with negative refractive power, i.e., a negative lens Ln3 made of a biconcave lens. The fourth lens group G4 has positive refractive power overall and is composed of a cemented lens J1 composed of, from the magnification side E, a negative lens Ln4 made of a negative meniscus lens with a convex surface on the magnification side E and a positive lens Lp5 made of a biconvex lens.

The fifth lens group G5 has at least two (three in Example 1) cemented lenses J2, J3, and J4, and also includes at least two positive lenses Lp6 and Lp8 that satisfy the following Conditional Expression 3, where νd is the Abbe number for the d-line:
νd>70 … [Conditional expression 3]

By including at least two positive lenses Lp6 and Lp8 that satisfy conditional formula 3, the appropriate range of Abbe number νd can be ensured, allowing for particularly good correction of axial chromatic aberration and lateral chromatic aberration. Therefore, if the Abbe number νd is less than 70, there is a risk that axial chromatic aberration and lateral chromatic aberration cannot be sufficiently corrected.

The specific lens configuration of the fifth lens group G5 includes, from the magnification side E, a cemented lens J2, a cemented lens J3, a cemented lens J4, and a positive lens Lp9 using a biconvex lens. Of these, the cemented lens J2 is a cemented lens formed by cementing a positive lens Lp6 using a biconvex lens to a negative lens Ln5 using a biconcave lens, the cemented lens J3 is a cemented lens formed by cementing a positive lens Lp7 using a biconvex lens to a negative lens Ln6 using a biconcave lens, and the cemented lens J4 is a cemented lens formed by cementing a negative lens Ln7 using a biconcave lens to a positive lens Lp8 using a biconvex lens.

The sixth lens group G6 includes a single lens having positive refractive power, i.e., a positive lens Lp10 using a positive meniscus lens having a convex surface on the magnification side E. When configuring the sixth lens group G6, if the sixth lens group G6 is configured with a single single lens Lpe, the configuration using the minimum number of lenses can shorten the overall length of the zoom lens 1 and contribute to downsizing. Furthermore, when the refractive index of this single lens Lpe is nd, it is formed so as to satisfy the following [Conditional Expression 4]:
nd>1.8 (Conditional Expression 4)

By forming the lens so that conditional expression 4 is satisfied, the appropriate range of refractive index nd can be ensured, thereby maintaining good balance in the telecentric optical system and effectively correcting field curvature, contributing to improved image quality. Therefore, if the refractive index nd is below 1.8, there is a risk that the balance of the telecentric optical system will be impaired and sufficient correction of field curvature will not be possible.

On the other hand, the zoom lens 1 is equipped with an optical adjustment system 200 including a zoom adjustment unit Mcz and a focusing adjustment unit Mcf, the basic configuration of which is shown in Figure 2. In this case, the zoom adjustment unit Mcz has the function of keeping the first lens group G1 and the sixth lens group G6 stationary 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 direction of the optical axis Dc. Furthermore, the focusing adjustment unit Mcf has the function of moving the first lens group G1 in the direction of the optical axis Dc.

Furthermore, in the entire system, when the total length of the lens optical system (the distance from the lens surface (i=1) on the enlargement side E of the lens L1 arranged on the most enlargement side E of the first lens group G1 at the time of projection at the reference distance to the image plane on the reduction side S) is T and the focal length of the entire system on the wide-angle side is fw, the configuration is such that the following [Conditional Expression 1] is satisfied.
5.0<[T/fw]<8.0 (Conditional Formula 1)

By satisfying [Conditional Expression 1], good image quality can be achieved through the necessary correction of various aberrations and field curvature, while also achieving a compact, lightweight, and inexpensive overall design. Therefore, if [T/fw] exceeds 8.0, the overall length will be long and the outer diameter will also be large, resulting in an increase in the size of the zoom lens 1. On the other hand, if [T/fw] is less than 5.0, the overall length can be shortened, but performance with regard to various aberrations, including chromatic aberration, will be impaired.

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

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

Figure 11 shows (a) the optical characteristic conditions, (b) the F-number, and (c) the lens characteristics of the zoom lens 1 according to Example 1. As shown in (a) the optical characteristic conditions, the total length T of the lens optical system of the zoom lens 1 according to Example 1 is 263.25 mm, and the focal length fw of the entire system on the wide-angle side is 38.04 mm, so [T/fw] is 6.92, which satisfies Conditional Expression 1 of 5.0 < [T/fw] < 8.0. Furthermore, the focal length f1 of the first lens group G1 is -62.07 mm, which satisfies Conditional Expression 2 of -70 < f1 < -45. On the other hand, the Abbe number vd of the positive lens Lp6 is 70.4362, and the Abbe number vd of the positive lens Lp8 is 81.6087, so each of the positive lenses Lp6 and Lp8 satisfies conditional formula 3 of vd > 70. Furthermore, the refractive index nd of the single lens Lpe is 1.80810, which satisfies conditional formula 4 of nd > 1.8.

On the other hand, (b) the F-number is 1.85 on the wide side and 2.32 on the telephoto side, ensuring sufficient brightness, and (c) in terms of lens characteristics, the zoom ratio is 1.491 and the total angle of view (wide side) is 34.9°, achieving the required target lens characteristics (lens performance).

Note that Figures 1 and 2 show the position of each lens Lp1, Ln1...Lp10 along the optical axis Dc when the zoom lens 1 according to Example 1 is adjusted to the TELE side, and Figure 3 shows the position of each lens Lp1, Ln1...Lp10 along the optical axis Dc when adjusted to the WIDE side.

Figures 4 and 5 show longitudinal aberration diagrams of the zoom lens 1 according to Example 1. Figure 4 shows longitudinal aberration diagrams on the WIDE side, with (a) reference distance OBJ(E) = 5645 mm, (b) close distance OBJ(E) = 2650 mm, and (c) long distance OBJ(E) = 35,000 mm. Figure 5 shows longitudinal aberration diagrams on the TELE side, with (a) reference distance OBJ(E) = 5645 mm, (b) close distance OBJ(E) = 4050 mm, and (c) long distance OBJ(E) = 52,000 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). Each scale division (1 division) is ±0.1 mm, ±0.10 mm, or ±1.0%.

As shown in Figures 4 and 5, it can be confirmed that the zoom lens 1 according to Example 1 exhibits no significant disturbance in any of the longitudinal aberrations, and exhibits good aberration characteristics, i.e., good projection performance (optical performance).

As described above, the zoom lens 1 according to this embodiment (Example 1) has a basic configuration including a lens optical system 100 including, in order from the enlargement side E to the reduction side S, a first lens group G1 having negative refractive power, a second lens group G2 having positive refractive power, a third lens group G3 having negative refractive power, a fourth lens group G4 having positive refractive power, a fifth lens group G5 having at least two cemented lenses J1 and J2, and a sixth lens group G6 having positive refractive power; a zoom adjustment unit Mcz 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 direction of the optical axis Dc; and a zoom adjustment unit Mcz that moves the first lens group G1 in the direction of the optical axis Dc. The zoom lens 1 has an optical adjustment system 200 including a focusing adjustment unit Mcf, and is designed to satisfy the following conditional expression 1: 5.0<[T/fw]<8.0, where T is the overall length of the lens optical system (the distance from the lens surface (i=1) on the enlargement side E of the lens L1, which is located closest to the enlargement side E of the first lens group G1, to the image plane on the reduction side S when projected at the reference distance), and fw is the focal length of the entire system on the wide-angle side. This ensures the necessary brightness while providing good image quality through the necessary correction of various aberrations and curvature of field, and allows for a compact, lightweight, and inexpensive overall design, while providing a zoom lens 1 that rationally satisfies all performance requirements in a well-balanced manner.

In addition, by ensuring a zoom ratio of 1.45x or more, the necessary zoom ratio for the zoom lens 1 can be ensured while maintaining a well-balanced and rational performance profile. By setting the full angle of view on the wide-angle side to 36° or less, the necessary angle of view for the zoom lens 1 can be ensured, and in addition to ensuring the zoom ratio, sufficient optical performance can be ensured, particularly for projectors that project onto a screen.

Next, the configuration of the lens optical system 100 of the zoom lens 1 according to Example 2 of this embodiment will be described with reference to Figures 6-8.

In Figures 6-8, components and functions that are the same as those in Figures 1-3 are designated by the same reference numerals to clarify the configuration. Therefore, the basic configuration and functions of Example 2 are the same as those of Example 1.

Like Example 1, the lens optical system 100 of Example 2 also includes six lens groups G1, G2, G3, G4, G5, and G6 arranged in order from the enlargement side E to the reduction side S, as shown in FIG. 6, from the first lens group G1 to the sixth lens group G6, and includes a prism Pr, shown in the schematic diagram, on the reduction side S relative to the sixth lens group G6.

The first lens group G1 has negative refractive power overall and is the same as in Example 1 in that it is configured with the basic lens configuration, namely, two positive lenses Lp1, Lp2 and two negative lenses Ln1, Ln2. The only difference is that when configuring the second negative lens Ln2 from the magnification side E, Example 1 uses a negative meniscus lens with a convex surface on the magnification side E, whereas Example 2 uses a biconcave lens. Also, like Example 1, when configuring the first lens group G1, it is configured to satisfy [Conditional Expression 2].

The second lens group G2 has positive refractive power overall and uses two positive lenses Lp3 and Lp4, just like in Example 1. However, Example 1 differs in that the positive lens Lp4 located on the reduction side S is a positive meniscus lens with a convex surface on the enlargement side E, whereas Example 2 uses a biconvex lens.

The third lens group G3 is the same as in Example 1 in that it is composed of a single lens with negative refractive power, but Example 2 differs in that, while Example 1 uses a negative biconcave lens Ln3, Example 2 uses a negative meniscus lens with a convex surface on the reduction side S. The fourth lens group G4 has positive refractive power overall, and its basic configuration is the same as in Example 1, and is composed of a cemented lens J1.

The fifth lens group G5 has positive refractive power overall and is basically the same as in Example 1, except that, in constructing the cemented lens J2, Example 1 uses a cemented lens formed by cementing together a positive lens Lp6 using a biconvex lens and a negative lens Ln5 using a biconcave lens, whereas Example 2 uses a cemented lens formed by cementing together a positive lens Lp6 using a positive meniscus lens having a convex surface on the magnification side E and a negative lens Ln5 using a negative meniscus lens having a convex surface on the magnification side E. Similar to Example 1, Example 2 has at least two cemented lenses J2, J3, and J4 (three in Example 1) and satisfies Conditional Expression 3. Similarly to Example 1, the sixth lens group G6 uses a single lens Lpe having positive refractive power and satisfies Conditional Expression 4.

On the other hand, it is also equipped with an optical adjustment system 200 including a zoom adjustment unit Mcz and a focusing adjustment unit Mcf, the principle configuration of which is shown in Figure 7, and it also satisfies Conditional Expression 1, just like Example 1.

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

Figure 11 shows (a) the optical characteristic conditions, (b) the F-number, and (c) the lens characteristics of the zoom lens 1 according to Example 2. As shown in (a) the optical characteristic conditions, the total length T of the lens optical system of the zoom lens 1 according to Example 2 is 225.00 mm, and the focal length fw of the entire system on the wide-angle side is 37.98 mm, so [T/fw] is 5.92, which satisfies Conditional Expression 1 of 5.0 < [T/fw] < 8.0. Furthermore, the focal length f1 of the first lens group G1 is -46.56 mm, which satisfies Conditional Expression 2 of -70 < f1 < -45. On the other hand, the Abbe number vd of the positive lens Lp6 is 70.4364, and the Abbe number vd of the positive lens Lp8 is 81.6087, so each of the positive lenses Lp6 and Lp8 satisfies conditional formula 3 of vd > 70. Furthermore, the refractive index nd of the single lens Lpe is 1.84666, which satisfies conditional formula 4 of nd > 1.8.

On the other hand, (b) the F-number is "1.85" on the WIDE side and "1.94" on the TELE side, ensuring sufficient brightness, and (c) in terms of lens characteristics, the zoom ratio is "1.493" and the total angle of view (WIDE side) is "34.9°", achieving the required target lens characteristics (lens performance).

Note that Figures 6 and 7 show the position of each lens Lp1, Ln1...Lp10 along the optical axis Dc when the zoom lens 1 according to Example 2 is adjusted to the TELE side, and Figure 8 shows the position of each lens Lp1, Ln1...Lp10 along the optical axis Dc when adjusted to the WIDE side. Also, Figures 9 and 10 show longitudinal aberration diagrams of the zoom lens 1 according to Example 2, with Figure 9 corresponding to Figure 4 and Figure 10 corresponding to Figure 5. As shown in Figures 9 and 10, it can be confirmed that the zoom lens 1 according to Example 2 exhibits no significant disturbance in any of the longitudinal aberrations, providing good aberration characteristics, i.e., good projection performance (optical performance).

The zoom lens 1 according to Example 2 has the same basic configuration as Example 1, and therefore, like Example 1, it is possible to provide a zoom lens 1 that can ensure the required brightness while obtaining good image quality through the necessary correction of various aberrations and curvature of field, while also achieving a compact, lightweight, and inexpensive overall lens, and that satisfies each performance requirement in a well-balanced and rational manner. Furthermore, in Example 2, the zoom ratio is set to 1.45 or more, so the required zoom ratio for the zoom lens 1 can be ensured while ensuring a well-balanced and rational manner in each performance requirement, and the full angle of view on the wide-angle side is set to 36° or less, so the required angle of view for the zoom lens 1 can be ensured, and in addition to ensuring the zoom ratio, sufficient optical performance can be ensured, particularly for projectors that project onto a screen.

Although the preferred embodiment has been described in detail above, the present invention is not limited to such an embodiment, and the detailed configuration, shape, materials, quantities, numerical values, etc. can be freely changed, added, or deleted without departing from the spirit of the present invention.

For example, while the lens optical system 100 is configured with six lens groups G1-G6, adding additional lens groups to form seven or more lens groups G1... is not excluded. Furthermore, while it is desirable to satisfy the following conditions: [Conditional Formula 2] (-70<f1<-45), [Conditional Formula 3] (νd>70), and [Conditional Formula 4] (nd>1.8), these are not essential constituent requirements. Meanwhile, the number of lenses and cemented lenses in each of the lens groups G1-G5 can be any number, except where otherwise specified as constituent requirements of the invention. Similarly, it is desirable to set the zoom ratio to 1.45 or greater and the total angle of view on the wide-angle side to 36° or less, but these values are not limiting.

The zoom lens according to the present invention can be used as a projection lens, including a dedicated lens or an interchangeable lens, in various optical devices such as projectors.

1: Zoom lens, 100: Lens optical system, 200: Optical adjustment system, E: 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, J1: Cemented lens, J2: Cemented lens, Dc: Optical axis direction, Mcz: Zooming adjustment section, Mcf: Focusing adjustment section, (i=1): Lens surface, T: Total length of lens optical system, fw: Focal length of entire system at wide-angle side, f1: Focal length of first lens group, Lp1: Positive lens, Lp2: Positive lens, Ln1: Negative lens, Ln2: Negative lens, Lp6: Positive lens, Lp8: Positive lens, Lpe: Single lens, νd: Abbe number, nd: Refractive index

Claims (7)

a first lens group having negative refractive power, a second lens group having positive refractive power, a third lens group having negative refractive power, a fourth lens group having positive refractive power, a fifth lens group having at least two cemented lenses, and a sixth lens group having positive refractive power, the first lens group being composed of two positive lenses and two negative lenses; and an optical adjustment system including a zoom adjustment unit that keeps the first lens group and the sixth lens group stationary and moves the second lens group through the fifth lens group independently in the optical axis direction, and a focusing adjustment unit that moves the first lens group in the optical axis direction, the zoom lens being characterized in that, when T is the total length of the lens optical system and fw is the focal length of the entire system on the wide-angle side, the zoom lens satisfies the following conditional expression 1:
5.0<[T/fw]<8.0 (Conditional Formula 1) 2. The zoom lens according to claim 1, wherein the first lens group satisfies the following conditional expression 2, where f1 (mm) is the focal length of the first lens group:
-70<f1<-45... [Conditional expression 2] 2. The zoom lens according to claim 1, wherein the fifth lens group includes at least two positive lenses that satisfy the following conditional expression 3, where νd is the Abbe number for the d-line:
νd>70 … [Conditional expression 3] A zoom lens according to claim 1, characterized in that the sixth lens group is composed of a single lens. 5. The zoom lens according to claim 4, wherein the single lens satisfies the following conditional expression 4, where nd is a refractive index of the single lens:
nd>1.8 (Conditional Expression 4) The zoom lens of claim 1, characterized in that the zoom ratio is set to 1.45 or more. A zoom lens according to claim 1, characterized in that the full angle of view on the wide-angle side is set to 36° or less.