JP2002372667A - Zoom lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a zoom lens which has both a wide viewing angle for a digital camera, a high variable power ratio and compactification performance, by which the various kinds of aberration are excellently corrected and that is suitable specially for a CCD. SOLUTION: In the zoom lens constituted of three lens groups having negative refracting power, positive refracting power and the positive refracting power in order from an object side, a second lens group incorporates a positive lens, the positive lens and a negative lens in order from the object side, and it is desirable that a lens positioned on a most image side is a plastic lens that is formed in a meniscus shape by making a convex surface faced to an image side and has an aspherical surface at least on one surface. Also, a first lens group is constituted of three or less lenses and it is desirable that a negative lens positioned at a most object side has at least one aspherical surface. A third lens group has one positive lens constituted of desirably the plastic lens, and it is desirable to have at least one aspherical surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a compact CCD (charged electric charge) having a zoom ratio of 2.5 times or more and an angle of view at the wide-angle end of 60 degrees or more, which is used for a zoom lens, especially a digital camera or a video camera. Coupling element).

[0002]

2. Description of the Related Art In recent years, a large number of digital still cameras and video cameras using a CCD have been used. Japanese Patent Laid-Open No. 2001-2001 discloses a CCD zoom lens having a negative, positive, and positive power arrangement to meet such demands.
Examples thereof can be found in JP-A-42218, JP-A-11-211984 and the like.

[0003]

However, in these prior arts, although the F-number is bright, the number of lenses is as large as 10 and the compactness is lacking. However, the angle of view was narrow at about twice, and it was difficult to say that all of the angle of view, the zoom ratio, and the compactness satisfied the sufficient specifications. The present invention has a wide angle of view, a high zoom ratio, and compactness,
Another object is to obtain a zoom lens in which various aberrations are corrected well.

[0004]

The zoom lens of the present invention has achieved its object by adopting the following constitution. That is, the zoom lens of the present invention includes, in order from the object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a positive refractive power. Upon zooming from the short focal end to the long focal end, in a zoom lens that performs zooming by changing the distance between the groups, the second lens group includes, in order from the object side,
At least positive 2a lens, positive 2b lens, negative 2c
A lens having a meniscus shape with a convex surface facing the image side and an aspherical surface on at least one surface thereof. The first lens group includes three or less lenses, and the second lens group includes at least a positive 2a in order from the object side.
A lens including a lens, a positive 2b lens, and a negative 2c lens, and the lens located closest to the image side is a lens having at least one aspheric surface. further,
In order from the object side, at least the positive 2a lens and the positive 2b
Including a lens and a negative 2c lens, the lens located closest to the image side is a plastic lens having at least one aspheric surface. And the 2a,
The 2b and 2c lenses are glass spherical lenses formed by polishing.

In the zoom lens having the above characteristics, it is preferable that the second lens group satisfies the following conditional expression. 1.0 <f ₂ / f _w <3.0 (1) where f _{2 is} the focal length of the second lens group f _{w is} the focal length of the entire lens system at the wide-angle end. The aspheric lens in the lens group is a plastic lens, and the plastic lens preferably satisfies the following conditional expression. _{-0.1 <f w / f p <} 0.1 It was but ··· (2) f _w: the focal length of the whole lens system at the wide-angle end f _p: The focus of the aspherical plastic lens in the second lens group Distance The 2a lens desirably satisfies the following conditional expression. n _2a > 1.80 (3) where n _{2a is the} refractive index for the d-line of the 2a lens.

It is preferable that the first lens group has at least one negative 1a lens located closest to the object side, and the negative lens has at least one aspheric surface. It is desirable that the 1a lens satisfies the following conditional expression. n _1a > 1.80 (4) where n _{1a is the} refractive index for the d-line of the 1a lens. The aspheric surface of the 1a lens is a composite aspherical surface in which an aspherical resin is formed on a glass spherical surface. Desirably.

The third lens group has at least one positive 3a lens positioned closest to the image, and the 3a lens preferably has at least one aspheric surface. The 3a lens may be a plastic lens or a compound aspherical lens in which an aspherical resin is formed on a glass spherical surface.

Further, it is desirable that the zoom lens satisfies the following conditional expression. 1.0 <SD / _Ymax <3.0 (5) where SD is the sum of the distances from the most object-side surface to the most image-side surface of each lens group _Ymax : the diagonal length of the image sensor The third lens group moves to the image side when zooming from the short focal end to the long focal end, and focusing from infinity to a finite distance requires moving at least the third lens group. Do.

[0009]

According to the zoom lens type of the present invention, the first lens group has a negative refractive power and the second lens group has a positive refractive power. Back focus sufficient to dispose a filter, cover glass, etc. can be obtained, and when the aperture stop is located after the first negative lens group, the diverging effect of this negative lens group can increase the peripheral light amount ratio. There is. In addition, by making the third lens group have a positive refractive power, sufficient telecentricity can be ensured, which is particularly advantageous when the imaging device is a CCD. To achieve both compactness and telecentricity,
It is preferable to provide an aperture stop on the object side of the second lens group.

By including at least the positive, negative, and positive arrangements in order from the object side in the second lens group, spherical aberration and coma can be corrected well, Petzval sum can be reduced, and field curvature can be suppressed. Furthermore, by making the lens closest to the image in the second lens group aspherical, astigmatism can be corrected well. As described above, the aberration generated in the second lens group can be suppressed to a small value, so that the aberration variation during zooming can be reduced. In addition, since the positive power can be divided and reduced by using positive / negative as compared with a configuration including only positive / negative, spherical aberration and coma generated by the positive lens can be reduced. Furthermore, even if lens eccentricity occurs during assembly, fluctuations in aberrations caused by the eccentricity can be suppressed to a small level, and good productivity can be maintained.

If the aspherical lens closest to the image side of the second lens group has a meniscus shape with the convex surface facing the image side, it is possible to reduce the performance deterioration when this lens is decentered. Also, by making this lens plastic,
It is possible to easily add an aspheric surface by injection molding and to reduce the weight of the entire lens system. By forming the lenses other than the aspherical lens in the second lens group into glass spherical lenses by polishing, a glass molded lens by molding,
Curvature radius error and surface undulation error during manufacturing can be kept smaller than plastic lenses produced by injection molding.
Good optical performance can be ensured.

By satisfying conditional expression (1), the zoom lens of the present invention can achieve both compactness and good optical performance. If the lower limit of this conditional expression is exceeded, the second
The power of the lens group becomes too strong, and various aberrations generated in this group become large. Conversely, if the upper limit is exceeded, the power of the second lens group becomes too small, and the amount of movement of the second lens group necessary for zooming becomes large, so that the compactness is impaired. Upper and lower limits of the conditional expression is desirably preferable to be _{1.5 <f 2 / f w <} 2.5 ··· (1 ').

By satisfying conditional expression (2), the power of the plastic lens is reduced, so that the amount of focus movement when the temperature of the plastic lens changes can be reduced. The upper and lower limits is desirably preferably set to _{-0.05 <f w / f p <} 0.05 ··· (2 ').

By satisfying conditional expression (3) and increasing the refractive index of the positive lens closest to the object side in the second lens unit, the power of this lens increases when the entire lens system is made compact. Also, since the curvature can be reduced as compared with a glass material having a low refractive index, it is possible to reduce the occurrence of spherical aberration and coma generated by this lens. This lower limit is preferably n _2a > 1.85 (3 ′).

By forming the first lens group of a negative lens and a positive lens in order from the object side, a compact optical system having a small lens thickness and a small front lens diameter can be obtained. In the case of a three-lens configuration including a negative lens, a negative lens, and a positive lens, negative power can be divided and reduced, so that negative distortion and the like generated in this group can be corrected well.

By using a surface having a large curvature of the negative lens in the first lens unit and using an aspherical surface in the third lens unit,
Distortion and astigmatism can be effectively corrected. Further, by combining the glass spherical lens and the aspherical resin, the selection range of glass types is widened and the effect of correcting various aberrations is increased as compared with the plastic lens. However, the third
In the lens group, aberrations may be well corrected even with a refractive index equivalent to that of a plastic lens. Therefore, by using a plastic lens lighter than glass for this group, driving when moving the third lens group by zooming or focusing is performed. The load on the mechanism is small. When a plastic lens is used for the third lens group, the height of the axial ray passing therethrough is low, so that even if a change in the refractive index or a change in the lens shape due to a temperature change occurs, the change in the imaging position is relatively small. I can do it. Note that good optical performance can be maintained even if a glass mold aspheric surface is used for the aspheric surface used for the first and third lens groups.

By satisfying conditional expression (4), the refractive index of the negative lens closest to the object side in the first lens group can be increased, so that the power of this lens increases when the entire lens system is made compact. However, it is possible to reduce the curvature of the lens as compared with a glass material having a low refractive index, and it is possible to reduce distortion, astigmatism, and the like generated in the lens. The lower limit is desirably n _1a > 1.85 (4 ′).

By satisfying conditional expression (5), it is possible to achieve both compactness of the lens and good optical performance. If the upper limit of the conditional expression is exceeded, the lens becomes too thick and the compactness is lost. Conversely, if the lower limit is exceeded, the aberration correction will be insufficient, and the sensitivity of the eccentric error of each lens will increase, which is not preferable in manufacturing. The upper and lower limits are desirably 1.5 <SD / _Ymax <2.5 (5 ').

In the case of a so-called rear focus type in which focusing is performed by the third lens unit, zooming is performed on the third lens unit by moving the third lens unit toward the image side during zooming from the short focus end to the long focus end. Can have an effect,
The power or the movement amount of the second lens group can be reduced. In addition, since the movement path required for focusing from infinity to the close distance at the short focal length end can be included in the movement path required for focusing at the long focal length end, the lens driving mechanism is made compact. I can do it. In particular, when the third lens group is composed of one positive lens, the third lens group is lighter than the other groups, so that it is possible to use the focusing lens with the least load applied to the drive mechanism. In addition, when focusing is performed by the first lens unit, the front lens diameter becomes large in order to secure a peripheral light amount ratio at a close distance. However, focusing is not performed by the third lens unit. Can be kept.

Since the infrared cut filter is of a reflection type in which the surface of the low-pass filter is coated, it is not necessary to separately insert an absorption type infrared cut filter glass into the lens system, and the thickness in the optical axis direction is reduced. Can be made thinner, and when the lens groups and filters are stored in the camera body in close proximity to each other, more compact storage becomes possible.

Hereinafter, embodiments of the present invention will be described. In the table, f is the focal length of the entire system, F is F number, omega denotes a half angle, r is the paraxial radius of curvature, d is the axial distance, n _d is the refractive index at the d-line, [nu _d is Abbe's number is there. The aspherical shape has a paraxial curvature radius of r, a conic coefficient of κ, and an aspherical coefficient of A in an orthogonal coordinate system having the vertex of the surface as the origin and the optical axis direction as the X axis.
_{As 2i} ,

(Equation 1) It is represented by

The following table shows the lens data of the first embodiment. FIG. 1 shows a lens section of this embodiment, and FIG. 7 shows aberration diagrams. The 1a lens is a compound aspheric lens (surface No. 1)
3), the aspheric lenses in the second lens group are plastic aspheric lenses (surface Nos. 11 to 12), and the 3a lens is a compound aspheric lens (surface Nos. 13 to 15). f = from 8.25 to 23.35 diaphragm position: sixth surface front 0.30mm surface _{No. r d n d ν d 1} 149.804 0.95 1.88300 40.8 2 8.946 0.05 1. 50706 53.6 3 7.469 2.44 4 12.503 1.83 1.866666 23.8 5 33.629 d ₅ (variable) 6 19.191 1.83 1.88300 40.87-57. 513 0.20 8 7.684 1.99 1.72916 54.7 9-160.000 2.68 1.84666 23.8 10 6.023 1.68 11-8.232 1.05 1.52500 56 .0 ₁₂ -7.980 d 12 (variable) 13 41.287 2.35 1.58913 61.2 14 -17.932 0.05 1.50706 53.6 15 -21.599 d 15 Variable) 16 ∞ 1.35 1.54880 67.0 17 ∞ 0.39 18 ∞ 0.50 1.51633 64.1 19 ∞ Variable spacing _{f d 5 d 12 d 15 8.25} 17.84 4.20 3.16 14.22 7.64 10.31 2.95 23.35 1.96 19.13 2.95 Aspherical surface third surface κ = −1.12460 A ₄ = 8.884430 / 10 ⁵ A ₆ = 9.77360 / 10 ⁷ A ₈ = -3.67080 / 10 ⁸ A ₁₀ = 4.3341 ^10/10 The eleventh surface κ = 0.0 A ₄ = -2.664380 / 10 ⁴ A ₆ = 1.35280 / 10 ⁴ A ₈ = −1.10100 / 10 ⁵ A ₁₀ = 7.5020 / 10 ⁷ twelfth surface κ = 0.0 A ₄ = 3.464620 10 ⁴ A ₆ = 1.022110 ⁴ A ₈ = −4.001190 / 10 ⁶ A ₁₀ = 2.779 20/10 ⁷ fifteenth surface _{^{κ = -5.59300 / 10 3 A 4}} = 3.70120 / 10 5 A 6 = -3.35500 / 10 6 A 8 = 1.00550 / 10 7 A 10 = -9. 98320/10 ¹⁰

The following table shows the lens data of the second embodiment. FIG. 2 shows a lens section of this embodiment, and FIG. 8 shows aberration diagrams. The 1a lens is a compound aspheric lens (surface No. 1)
3), the aspheric lenses in the second lens group are plastic aspheric lenses (surface Nos. 11 to 12), and the 3a lens is a compound aspheric lens (surface Nos. 13 to 15). f = from 8.25 to 23.35 diaphragm position: sixth surface front 0.30mm surface _{No. r d n d ν d 1} 149.804 0.95 1.88300 40.8 2 8.946 0.05 1. 50706 53.6 3 7.469 2.44 4 12.503 1.83 1.866666 23.8 5 33.629 d ₅ (variable) 6 19.191 1.83 1.88300 40.87-57. 513 0.20 8 7.684 1.99 1.72916 54.7 9-160.000 2.68 1.84666 23.8 10 6.023 1.68 11-8.232 1.05 1.52500 56 .0 ₁₂ -7.980 d 12 (variable) 13 41.287 2.35 1.58913 61.2 14 -17.932 0.05 1.50706 53.6 15 -21.599 d 15 Variable) 16 ∞ 1.35 1.54880 67.0 17 ∞ 0.39 18 ∞ 0.50 1.51633 64.1 19 ∞ Variable spacing _{f d 5 d 12 d 15 8.25} 17.84 4.20 3.16 13.88 7.57 9.42 3.46 23.35 1.70 18.85 3.46 Aspherical surface third surface κ = −1.12460 A ₄ = 8.884430 / 10 ⁵ A ₆ = 9.77360 / 10 ⁷ A ₈ = -3.67080 / 10 ⁸ A ₁₀ = 4.3341 ^10/10 The eleventh surface κ = 0.0 A ₄ = -2.664380 / 10 ⁴ A ₆ = 1.35280 / 10 ⁴ A ₈ = −1.10100 / 10 ⁵ A ₁₀ = 7.5020 / 10 ⁷ twelfth surface κ = 0.0 A ₄ = 3.464620 10 ⁴ A ₆ = 1.022110 ⁴ A ₈ = −4.001190 / 10 ⁶ A ₁₀ = 2.7792 0/10 ⁷ 15th surface κ = -5.59 300/10 ³ A ₄ = 3.70 120/10 ⁵ A ₆ = -3.35 500/10 ⁶ A ₈ = 1.00550 / 10 ⁷ A ₁₀ = -9. 98320/10 ¹⁰

The following table shows the lens data of the third embodiment. FIG. 3 shows a lens section of this embodiment, and FIG. 9 shows aberration diagrams. The 1a lens is a compound aspheric lens (surface No. 1)
3), the aspheric lenses in the second lens group are plastic aspheric lenses (surface Nos. 11 to 12). f = from 8.25 to 23.35 diaphragm position: sixth surface front 0.30mm surface _{No. r d n d ν d 1} 149.804 0.95 1.88300 40.8 2 8.946 0.05 1. 50706 53.6 3 7.469 2.44 4 12.503 1.83 1.866666 23.8 5 33.629 d ₅ (variable) 6 19.191 1.83 1.88300 40.87-57. 513 0.20 8 7.684 1.99 1.72916 54.7 9-160.000 2.68 1.84666 23.8 10 6.023 1.68 11-8.232 1.05 1.52500 56 .0 ₁₂ -7.980 d 12 (variable) 13 40.414 2.40 1.58313 59.4 14 -20.904 d 14 ( variable) 15 ∞ 1.35 1.54880 67.0 16 ９ 0.39 17 ∞ 0.50 1.51633 64.1 18 面 Variable surface spacing f d ₅ d ₁₂ d ₁₄ 8.25 17.84 4.20 3.16 13.88 7.57 9.42 3. 46 23.35 1.70 18.85 3.46 Aspherical surface coefficient Third surface κ = −1.12460 A ₄ = 8.844430 / 10 ⁵ A ₆ = 9.7773 / 10 ⁷ A ₈ = −3.67080 / 10 ⁸ A ₁₀ = 4.334110 / 10 ^10th eleventh surface κ = 0.0 A ₄ = −2.64380 / 10 ⁴ A ₆ = 1.35280 / 10 ⁴ A ₈ = −1.10 100/10 ⁵ A ₁₀ = 7.5280 / 10 ⁷ twelfth surface κ = 0.0 A ₄ = 3.46620 / 10 ⁴ A ₆ = 1.210210 / 10 ⁴ A ₈ = −4.001190 / 10 ⁶ A ₁₀ = 2.777920 / 10 ⁷ 14th surface κ = 5.19770 / 10 ³ A ₄ = 3.37080 / 10 ⁵ A ₆ = −3.0060 / 10 ⁶ A ₈ = 9.0860 / 10 ⁸ A ₁₀ = −8.96180 / 10 ¹⁰

The following table shows the lens data of the fourth embodiment. FIG. 4 shows a lens section of this embodiment, and FIG. 10 shows aberration diagrams. The aspheric lens in the second lens group is a plastic aspheric lens (surface Nos. 10 to 11). f = from 8.25 to 23.35 diaphragm position: fifth surface front 0.30mm surface _{No. r d n d ν d 1} 108.308 1.00 1.88300 40.8 2 7.837 2.42 3 12 0.813 1.84 1.86666 23.8 4 36.670 d ₄ (variable) 5 16.408 1.43 1.88300 40.8 6 -77.585 0.20 7 7.349 1.81 1.81. 72916 54.7 8 307.449 2.27 1.84666 23.8 9 5.713 1.64 10 -8.540 1.10 1.52500 56.0 11 -8.247 d 11 ( variable) 12 25 _{.595 2.40 1.48749 70.2 13 -22.550 d 13} ( variable) 14 ∞ 1.50 1.54880 67.0 15 ∞ 0.20 16 ∞ 0.50 1.51633 64. 17 ∞ Variable spacing _{f d 4 d 11 d 13 8.25} 17.66 4.68 3.03 13.88 7.32 9.79 3.33 23.35 1.40 19.02 3.33 aspherical Coefficient Second surface κ = −1.244457 A ₄ = 1.72190 / 10 ⁴ A ₆ = 9.69190 / 10 ⁷ A ₈ = −8.9975 / 10 ⁹ A ₁₀ = −2.117180 / 10 ¹¹ Tenth Surface κ = 0.0 A ₄ = −2.64380 / 10 ⁴ A ₆ = 1.35280 / 10 ⁴ A ₈ = −1.10100 / 10 ⁵ A ₁₀ = 7.5280 / 10 ⁷ Eleventh surface κ = 0 ^{_{.0 A 4 = 3.46620 / 10 4}} A 6 = 1.02210 / 10 4 A 8 = -4.01190 / 10 6 A 10 = 2.77920 / 10 7 thirteenth surface κ = 0.0 A ₄ = _{^{5.27620 / 10 5 A 6 = -4.18230}} / 10 6 A 8 = 1. _{^{2850/10 7 A 10 = -1.36850 / 10}} 9

The following table shows the lens data of the fifth embodiment. FIG. 5 shows a lens section of this embodiment, and FIG. 11 shows aberration diagrams. The aspheric lens in the second lens group is a plastic aspheric lens (surface Nos. 10 to 11). f = from 8.25 to 23.35 diaphragm position: fifth surface front 0.30mm surface _{No. r d n d ν d 1} 95.117 1.00 1.88300 40.8 2 7.690 2.33 3 12 .461 1.86 1.84666 23.8 4 35.212 d ₄ (variable) 5 14.541 1.45 1.88300 40.8 6-110.621 0.207 7.432 1.93 1.93. 72916 54.7 8 -738.378 2.09 1.86666 23.8 9 5.635 1.58 10 -9.893 1.10 1.58300 30.0 11 -9.493 d ₁₁ (variable) 12 _{23.589 2.55 1.48749 70.2 13 -24.321 d 13} ( variable) 14 ∞ 1.50 1.54880 67.0 15 ∞ 0.20 16 ∞ 0.50 1.51633 64 1 17 ∞ variable spacing _{f d 4 d 11 d 13 8.25} 17.58 4.80 2.59 13.88 7.30 9.73 2.89 23.35 1.40 18.64 2.89 Non Spherical coefficient Second surface κ = -1.27958 A ₄ = 1.97640 / 10 ⁴ A ₆ = 9.88270 / 10 ⁷ A ₈ = -9.667440 / 10 ⁹ A ₁₀ = -1.58110 / 10 ¹¹ Tenth surface κ = 0.0 A ₄ = −3.6363 / 10 ⁴ A ₆ = 1.266620 / 10 ⁴ A ₈ = −1.15670 / 10 ⁵ A ₁₀ = 7.60940 / 10 ⁷ Eleventh surface κ = ^{_{0.0 A 4 = 2.46390 / 10 4}} A 6 = 9.52900 / 10 5 A 8 = -4.19910 / 10 6 A 10 = 2.66440 / 10 7 thirteenth surface κ = 0.0 A _{4 ^{= 4.98030 / 10 5 A 6 =}} -4.90470 / 10 6 A 8 = 1 _{^{51280/10 7 A 10 = -1.79280 / 10}} 9

The following table shows the lens data of the sixth embodiment. FIG. 6 shows a lens cross section of this embodiment, and FIG. 12 shows aberration diagrams. The aspheric lens in the second lens group is a plastic aspheric lens (surface Nos. 10 to 11), and the 3a lens is a plastic aspheric lens (surface Nos. 12 to 13). f = 4.53-12.82 diaphragm position: fifth surface front 0.30mm surface _{No. r d n d ν d 1} 40.542 0.60 1.74400 44.8 2 4.529 2.15 3 7 .840 1.78 1.84666 23.8 4 14.648 d ₄ (variable) 5 7.817 1.27 1.83400 37.2 6 -108.628 0.20 7 5.368 1.47 1.47 72916 54.7 8 -13.808 0.60 1.80518 25.4 9 3.992 1.47 10 -4.024 0.80 1.52500 56.0 11 -4.140 d ₁₁ (variable) 12 _{12.422 1.97 1.52500 56.0 13 -16.028 d 13} ( variable) 14 ∞ 1.35 1.54880 67.0 15 ∞ 0.39 16 ∞ 0.50 1.51633 64.1 1 ∞ Variable spacing _{f d 4 d 11 d 13 4.53} 14.42 3.24 0.60 7.62 6.22 6.32 0.90 12.82 1.70 12.22 0.90 aspheric coefficients Second surface κ = −1.03378 A ₄ = 6.2358 / 10 ⁴ A ₆ = 1.190260 / 10 ⁵ A ₈ = −2.14210 / 10 ⁷ A ₁₀ = 4.338610 ⁹ Tenth surface κ = -1.74180 / 10 ² A ₄ = -3.35830 / 10 ³ A ₆ = 2.09220 / 10 ³ A ₈ = -7.3650 / 10 ⁴ A ₁₀ = 1.277010 ⁴ 11th surface κ _{^{= 4.77490 / 10 2 A 4 =}} -4.96770 / 10 4 A 6 = 1.28310 / 10 3 A 8 = -3.18620 / 10 4 A 10 = 4.88170 / 10 5 thirteenth surface kappa = ^{_{1.63703 A 4 = 3.75000 / 10 4}} A 6 = - 4.2020 / 10 ⁵ A ₈ = 3.184510 ⁶ A ₁₀ = −9.0310 / 10 ⁸

The values of the conditional expressions for each embodiment are as follows. Conditional expression 1 Conditional expression 2 Conditional expression 3 Conditional expression 4 Conditional expression 5 Example 1 1.71 0.04 1.88300 1.88300 1.91 Example 2 1.71 0.04 1.88300 1.88300 1. 91 Example 3 1.71 0.04 1.88300 1.88300 1.91 Example 4 1.70 0.04 1.88300 1.88300 1.83 Example 5 1.67 0.04 1.88300 1 0.888300 1.83 Example 6 2.17 0.02 1.72916 1.74400 2.20

[0029]

As described above, the zoom lens according to the present invention has the following advantages.
As seen from the examples and the aberration curve diagrams, the lens configuration is 7
Despite its compact size, it has a high zoom ratio of about 3 times, a wide angle of view of 60 ° or more at the wide-angle end, and a bright F-number of about 2.8 was obtained. As can be seen from the aberration diagrams, various aberrations were successfully corrected in a well-balanced manner.

[Brief description of the drawings]

FIG. 1 is a sectional view of a first embodiment of a zoom lens according to the present invention.

FIG. 2 is a sectional view of a second embodiment of the zoom lens according to the present invention.

FIG. 3 is a sectional view of a third embodiment of the zoom lens according to the present invention.

FIG. 4 is a sectional view of a fourth embodiment of the zoom lens according to the present invention;

FIG. 5 is a sectional view of a fifth embodiment of the zoom lens according to the present invention;

FIG. 6 is a sectional view of a sixth embodiment of the zoom lens according to the present invention;

FIG. 7 is an aberration diagram of the first embodiment of the zoom lens according to the present invention.

FIG. 8 is an aberration diagram of a second embodiment of the zoom lens according to the present invention.

FIG. 9 is an aberration diagram of a third embodiment of the zoom lens according to the present invention.

FIG. 10 is an aberration diagram of a fourth embodiment of the zoom lens according to the present invention.

FIG. 11 is an aberration diagram of a fifth embodiment of the zoom lens according to the present invention.

FIG. 12 is an aberration diagram of a sixth embodiment of the zoom lens according to the present invention.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H087 KA03 MA14 NA08 PA06 PA18 PA19 PA20 PB07 PB08 PB09 QA02 QA07 QA17 QA21 QA22 QA25 QA34 QA37 QA41 QA45 QA46 RA05 RA12 RA13 RA36 RA42 RA43 SA14 SA16 SB19 SB03 SA64 SB23 UA01

Claims (15)

[Claims] 1. A lens system comprising: a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a positive refractive power. In a zoom lens that performs zooming by changing the distance between the respective groups when zooming to the focal end, the second lens group includes at least a positive 2 in order from the object side.
a lens, a positive 2b lens, and a negative 2c lens, and the lens closest to the image side is a lens having a meniscus shape having a convex surface facing the image side and having at least one aspheric surface. Zoom lens 2. A lens system comprising a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, and a third lens unit having a positive refractive power. In a zoom lens that performs zooming by changing the distance between the respective groups when zooming to the focal end, the first lens group includes three or less lenses, and the second lens group includes at least A zoom lens including a positive 2a lens, a positive 2b lens, and a negative 2c lens, and a lens located closest to the image side having at least one aspheric surface. 3. In order from the object side, the first lens unit has a negative refractive power, the second lens unit has a positive refractive power, and the third lens unit has a positive refractive power. In a zoom lens that performs zooming by changing the distance between the respective groups when zooming to the focal end, the second lens group includes at least a positive 2 in order from the object side.
a zoom lens comprising: a lens, a positive 2b lens, and a negative 2c lens, and a lens located closest to the image is a plastic lens having at least one aspheric surface. 4. The zoom lens according to claim 1, wherein the 2a, 2b, and 2c lenses are glass spherical lenses formed by polishing. 5. The zoom lens according to claim 1, wherein the second lens group satisfies the following conditional expression: 1.0 <f ₂ / _fw <3. 2.0 f ₂ : focal length of the second lens group f _w : focal length of all lens systems at the wide-angle end 6. The zoom lens according to claim 1, wherein the aspherical lens in the second lens group is a plastic lens and satisfies the following conditional expression. .1 <f _w / f _p <it was but 0.1 f _w: the focal length f _p of the entire lens system at the wide angle end focal length of the aspherical plastic lens in the second lens group 7. The zoom lens according to claim 1, wherein the 2a lens satisfies the following conditional expression: n _2a > 1.80, where n _2a is d of the 2a lens. Refractive index for line 8. The system according to claim 1, wherein the first lens group includes at least one negative 1a lens located closest to the object side, and the negative lens has at least one aspheric surface. A zoom lens according to any one of claims 1 to 7. 9. The zoom lens according to claim 8, wherein the 1a lens satisfies the following conditional expression: n _1a > 1.80, where n _{1a is the} refractive index of the 1a lens with respect to d-line. 10. The zoom lens according to claim 8, wherein the aspherical surface of the 1a lens is a composite aspherical surface in which an aspherical resin is formed on a glass spherical surface. 11. The third lens group includes at least one positive 3a lens located closest to the image, and the 3a lens has at least one aspheric surface. The zoom lens according to claim 1. 12. The zoom lens according to claim 11, wherein the 3a lens is a plastic lens or a compound aspherical lens having an aspherical resin formed on a glass spherical surface. 13. The zoom lens according to claim 1, wherein the zoom lens satisfies the following conditional expression: 1.0 <SD / Y _max <3.0. SD: Sum of distances from the most object side surface to the most image side surface of each lens group Y _max : Diagonal length of image sensor 14. The zoom lens according to claim 1, wherein the third lens group moves to the image side when zooming from the short focal length end to the long focal length end. 15. The zoom lens according to claim 1, wherein the zoom lens moves at least the third lens group to perform focusing from infinity to a finite distance.