JP3296878B2 - Small zoom lens - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a compact zoom lens, and more particularly to a zoom lens mainly used for a compact camera having a short back focus.

[0002]

2. Description of the Related Art A zoom lens used in a conventional compact camera is disclosed in Japanese Patent Application Laid-Open No. 56-128911.
JP-A-62-264019, JP-A-63-266
Many two-group zoom lenses including a positive lens group and a negative lens group are used in this order from the object side, as known from JP-A-413-413 and the like. In many cases, the angle of view at the wide-angle end is about 60 °, and the zoom ratio is 1.5 to 2 times.
It is about double.

In recent years, a wide angle and a high zoom ratio of a compact camera have been desired. Japanese Patent Application Laid-Open Nos. 3-213814 and 3-240013 disclose a zoom lens having a positive / negative two-group configuration. By providing a negative lens closest to the object side of the first lens group, the back focus at the wide-angle end is extended, the angle of view at the wide-angle end is increased to 70 ° or more, and a zoom lens with a zoom ratio of 2 or more is provided. are doing.

[0004]

However, as cameras become smaller year by year, zoom lenses that have been proposed have become too large and inadequate.

In JP-A-3-213814, the sagittal image surface is slightly over-generated.
In No. 013, distortion at the wide-angle end occurs on the plus side. If you try to further downsize this type,
These aberration performances will be further deteriorated, and it will be difficult to secure performance sufficient for use.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and it is an object of the present invention to provide a zoom lens of a two-group type, while ensuring a zoom ratio of at least two times, while maintaining the overall length of the lens. Is short, various aberrations are well corrected,
It is an object of the present invention to provide a compact zoom lens for a compact camera, which can widen the angle of view at the wide-angle end to 70 ° or more.

[0007]

According to the present invention, there is provided a small-sized zoom lens according to the present invention, in which, from the object side, a first lens unit having a positive refractive power and a second lens unit having a negative refractive power. Wherein the first lens group includes, in order from the object side, a negative lens in which the curvature of the object side surface is larger than the curvature of the image surface side surface. It comprises a lens, and a positive lens group including at least one negative lens and at least three positive lenses, and satisfies the following conditions. 1.45 <| f ₁ | / F _W <1.78 0.4 <| f _2G | / F _W <0.78 where f _{1 is} the focal length of the first negative lens in the first lens group, F _W ... focal length of the entire system at the wide-angle end, _f2G ... focal length of the second lens group.

[0008]

In the following, the reason why the above configuration is adopted in the present invention and the operation thereof will be described. In the positive / negative two-unit zoom lens, by disposing a negative lens closest to the object side of the first lens unit, the principal point of the first lens unit is moved to the image side,
By securing the group interval and extending the back focus, it is possible to widen the angle of the zoom lens. JP-A-3-213814
Also, the negative lens used in these devices has a negative curvature by making the curvature on the image plane side larger than the curvature on the object side. The aberration generated by the lens itself is reduced.

On the other hand, the negative lens disposed closest to the object used in the zoom lens according to the present invention, which uses the aberration generated by the negative lens positively, poses a problem when miniaturized. The aberration is corrected well.

For this reason, in the shape of this negative lens, the curvature on the object side is larger than the curvature on the image plane side. As a result, astigmatism and distortion generated mainly on the object-side surface become large, and various types of aberration that are generated largely by the negative lens of the second lens group when downsized, particularly astigmatism and distortion are generated. Can be corrected in a well-balanced manner.

In order to favorably correct spherical aberration,
The first lens group has at least three lenses behind the negative lens.
A positive lens group _G1R including one positive lens and at least one negative lens is arranged.

The spherical aberration is negative on the first lens group,
It occurs on the plus side in the second lens group. However, the first lens group has a larger luminous flux than the second lens group.
Spherical aberration generated in the lens group tends to be larger than spherical aberration generated in the second lens group.

Therefore, by using at least three positive lenses and at least one negative lens in the first lens group and reducing the spherical aberration generated in the first lens group, the spherical lens generated in the second lens group is reduced. Aberrations can be corrected in a well-balanced manner, and in particular, fluctuations in spherical aberration due to zooming can be reduced.

Next, conditions suitable for obtaining a more compact and high-performance zoom lens in the present invention will be described. First, it is desirable that the following conditions be satisfied for the power arrangement of each group. 1.45 <| f ₁ | / F _W <1.78 0.4 <| f _2G | / F _W <0.78 where f _{1 is} the focal length of the first negative lens in the first lens group, F _W ... focal length of the entire system at the wide-angle end, _f2G ... focal length of the second lens group.

The above conditional expression relates to the first lens unit having the negative power which is disposed closest to the object side of the first lens unit. If the upper limit of 1.78 is exceeded, the negative power becomes too weak. As a result, it becomes difficult to secure the back focus at the wide-angle end, and it is also difficult to correct astigmatism and distortion. Conversely, if the lower limit of 1.45 is exceeded, the negative power becomes too strong, and the back focus becomes longer than necessary, or the group spacing becomes longer than necessary. This leads to an increase in the overall length.

The above-mentioned conditional expression relates to the power of the second lens group. If the upper limit of 0.78 is exceeded, the power of the second lens group becomes weak, and the second power due to zooming is reduced.
The amount of movement of the lens group increases, and the overall length of the lens increases. If the lower limit of 0.4 is exceeded, the second
Astigmatism and distortion generated in the lens group increase, and it becomes difficult to correct the whole.

Next, it is desirable that the shape of the first negative lens in the first lens group satisfies the following conditions. −2.5 <(r ₁ + r ₂ ) / (r ₁ −r ₂ ) <−
0.5 where r _{1 is the} radius of curvature of the first negative lens on the object side, and r _{2 is the} radius of curvature of the first negative lens on the image side.

If the upper limit of -0.5 of this conditional expression is exceeded, the astigmatism and distortion produced by this negative lens will be reduced, and if the lower limit of -2.5 is exceeded, they will be increased. Therefore, it is preferable to satisfy the conditional expression in order to correct the astigmatism and distortion generated in the second lens group in a well-balanced manner.

Further, regarding the lens arrangement of the positive lens group G _1R disposed behind the first negative lens in the first lens group, in order from the object side, the curvature on the object side is larger than the curvature on the image plane side. Spherical aberration and axial chromatic aberration can be satisfactorily corrected by using a positive lens group including a large positive lens, a negative lens, a positive lens, a biconvex lens, and a negative meniscus lens and having a positive refractive power as a whole.

The average refractive index of the positive lens in the positive lens group G _1R is <n _d1RP >, and the average refractive index of the negative lens is <n _d1RP >.
_{Assuming that d1RN} >, the two conditional expressions of < _nd1RP ><1.65< _nd1RN >> 1.75 are satisfied, so that Petzval sum can be reduced, and field curvature can be easily corrected.

The second lens group is composed of at least one positive meniscus lens and at least two negative lenses. The average Abbe number of the positive lens is <ν _d2GP >, The average Abbe number is <ν _d2GN >, and the Abbe number of the positive lens disposed closest to the object side in the positive lens group G _1R of the first lens group is ν _{d (2)} , and is disposed closest to the image plane. The average Abbe number of the positive lens and the negative lens in the positive lens group obtained is <ν _{d (5) P} >,
When <ν _{d (5) N} >, ν _{d (2)} <50 0.5 <(<ν _d2GN > − <ν _d2GP >) / (<ν
By satisfying the following two conditional expressions, _{d (5) P} >-<νd _{(5) N} >) <2.0, axial chromatic aberration and lateral chromatic aberration can be corrected in a well-balanced manner.

If the value of the conditional expression is out of the range of 50 or more, the chromatic aberration of magnification greatly fluctuates due to zooming. If the upper limit of 2.0 of the conditional expression is exceeded, the fluctuation due to magnification of the chromatic aberration of magnification will be large. If the lower limit of 0.5 is exceeded, the fluctuation due to the magnification of the axial chromatic aberration will be large.

These conditions, when applied alone or in combination, contribute to realizing better conditions in terms of miniaturization of the lens system, correction of aberrations, suppression of aberration fluctuation, and the like. is there.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments 1 and 2 of a small zoom lens according to the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view at the wide-angle end of the zoom lens according to the first embodiment. This lens has a focal length of 2 at which the angle of view at the wide-angle end is increased to 70 ° or more.
The first lens group G1 is a negative meniscus lens having a concave surface facing the object side, a biconvex lens, a biconcave lens, a biconvex lens, a biconvex lens and a zoom lens having a lens arrangement of 8.5 mm to 60.00 mm. The second lens group G2 is composed of six cemented lenses of a negative meniscus lens having a concave surface, and a diaphragm continuously formed. The second lens group G2 includes a positive meniscus lens having a concave surface facing the object side and two lenses having a concave surface facing the object side. It consists of three negative meniscus lenses.

The lens data of the first embodiment will be described later. The wide-angle end (a), the standard state (b), and the telephoto end (c)
FIG. 3 is an aberration diagram showing the spherical aberration, astigmatism, distortion, and chromatic aberration of magnification in FIG.

FIG. 2 is a cross-sectional view of the zoom lens of Embodiment 2 at the wide-angle end. This lens is a zoom lens having a focal length of 35 mm to 80 mm and a zoom ratio of about 2.3.
An aspherical surface is used for the eighth surface (the image-side surface of the fourth biconvex lens from the object side) in the first lens group G1, and spherical aberration particularly at the telephoto end is favorably corrected. The lens arrangement
The first lens group G1 includes a negative meniscus lens having a concave surface facing the object side, a positive meniscus lens having a convex surface facing the object side,
The second lens group G2 is composed of a biconcave lens, a biconvex lens, and a cemented lens of a biconvex lens and a negative meniscus lens having a concave surface facing the object side. The lens consists of three negative meniscus lenses, each having a concave surface facing the object side.

The lens data of the second embodiment will be described later. The wide-angle end (a), the standard state (b), and the telephoto end (c)
FIG. 4 is an aberration diagram showing the spherical aberration, astigmatism, distortion, and chromatic aberration of magnification in FIG.

Next, lens data of each embodiment will be shown.
In the following, the symbols are the above, f is the focal length of the entire system, F _NO is the F number, ω is the half angle of view, f _B is the back focus, r ₁ , r _2, ... d ₁ ,
d ₂ ... the spacing between the lens surfaces, n _d1, n _d2 ... d-line refractive index of each lens, ν _d1, ν _d2 ... is the Abbe number of each lens. The aspherical shape is represented by the following equation, where x is the optical axis direction and y is the direction orthogonal to the optical axis. ^{x = cy 2 / {1+ (} 1 2 -c 2 y 2) 1/2} + A 4 y 4
+ A ₆ y ⁶ + A ₈ y ⁸ where r is the radius of curvature on the optical axis, A ₄ , A ₆ , and A ₈ are aspherical coefficients, and c = 1 / r. Furthermore, represents the value of the parameter described in the condition.

[0029] Example _{1 f = 28.51~ 40.00~ 60.00 F NO} = 3.58 ~ 5.02 ~ 7.53 ω = 37.12~ 28.84~ 20.09 ° f B = 5.31 ~ 16.23 ~ 35.24 r 1 = -25.388 d 1 = 1.32 n d1 = 1.65844 _{ν d1 = 50.86 r 2 = -156.695} d 2 = 1.80 r 3 = 19.750 d 3 = 2.94 n d2 = 1.60342 ν d2 = 38.01 r 4 = -146.970 d 4 = 1.72 r 5 = -15.786 d 5 = 1.22 n d3 = _{1.80100 ν d3 = 34.97 r 6 =} 35.907 d 6 = 0.11 r 7 = 41.019 d 7 = 4.42 n d4 = 1.58913 ν d4 = 61.18 r 8 = -13.393 d 8 = 0.10 r 9 = 18.228 d 9 = 3.80 n d5 = 1.57099 ν _d5 = 50.80 r ₁₀ = -11.757 d ₁₀ = 1.20 nd ₆ = 1.78590 ν _d6 = 44.18 r ₁₁ = -34.270 d ₁₁ = 0.80 r ₁₂ = ∞ (aperture) d ₁₂ = (variable) r ₁₃ = -49.372 d _{13 = 3.30 n d7 = 1.63930 ν d7} = 44.88 r 14 = -12.430 d 14 = 0.10 r 15 = -15.452 d 15 = 1.20 n d8 = 1.65844 ν d8 = 50.86 r 16 = -152.470 d 16 = 4.94 r 17 = -9.446 _{d 17 = 1.80 n d9 = 1.69680} ν d9 = 55.52 r 18 = -31.784 f ₁ = −46.197, f _1G = 20.826, f _2G = −19.795,
= 1.62, = 0.69, =-1.39, = 1.59
, = 1.79, = 38.01, = 1.25
.

[0030] Example _{2 f = 34.99~ 54.96~ 79.92 F NO} = 3.60 ~ 5.65 ~ 8.22 ω = 31.69~ 21.45~ 15.12 ° f B = 6.08 ~ 24.65 ~ 47.86 r 1 = -26.612 d 1 = 1.30 n d1 = 1.65830 _{ν d1 = 57.33 r 2 = -84.007} d 2 = 1.80 r 3 = 17.236 d 3 = 2.34 n d2 = 1.66892 ν d2 = 44.98 r 4 = 47.927 d 4 = 1.20 r 5 = -43.062 d 5 = 1.20 n d3 = 1.80100 ν _d3 = 34.97 r ₆ = 38.181 d ₆ = 0.70 r ₇ = 51.336 d ₇ = 2.16 n _d4 = 1.57250 ν _d4 = 57.76 r ₈ = -39.936 (aspherical surface) d ₈ = 2.40 r ₉ = 31.441 d ₉ = 4.38 n _d5 = 1.61765 ν _d5 = 55.05 r ₁₀ = -8.940 d ₁₀ = 1.20 nd ₆ = 1.79952 ν _d6 = 42.24 r ₁₁ = -18.730 d ₁₁ = 0.80 r ₁₂ = ∞ (aperture) d ₁₂ = (variable) r ₁₃ =- _{20.146 d 13 = 2.04 n d7 =} 1.66998 ν d7 = 39.27 r 14 = -13.667 d 14 = 2.82 r 15 = -13.740 d 15 = 1.20 n d8 = 1.63854 ν d8 = 55.38 r 16 = -52.693 d 16 = 3.61 r 17 _{= -12.882 d 17 = 1.80 n d9} = 1.69680 ν d9 = 55.52 r 18 = -26.219 Aspheric surface eighth surface A ₄ = 1.8719 × 10 ^-5 A ₆ = 1.4994 × 10 ^-7 A ₈ = -6.9203 × 10 ^-9 f ₁ = -59.706, f _1G = 24.8, f _2G = -23.065,
= 1.7, = 0.66, = -1.93, = 1.62
, = 1.80, = 44.98, = 1.26
.

[0031]

As is apparent from the above description, according to the present invention, while being a two-unit type zoom lens, the zoom lens has a variable length at least twice, the entire length of the lens is short, and various aberrations are good. And the angle of view at the wide-angle end is 70 °
A compact zoom lens for a compact camera that can be expanded as described above can be obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view of a zoom lens according to a first embodiment of the present invention at a wide-angle end.

FIG. 2 is a sectional view of a zoom lens at a wide-angle end according to a second embodiment.

FIG. 3 is an aberration diagram illustrating spherical aberration, astigmatism, distortion, and chromatic aberration of magnification at a wide-angle end (a), in a standard state (b), and at a telephoto end (c) in Example 1.

FIG. 4 is an aberration diagram similar to FIG. 3 of the second embodiment.

[Explanation of symbols]

 G1: first lens group G2: second lens group

Continuation of the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) G02B 9/00-17/08 G02B 21/02-21/04 G02B 25/00-25/04

Claims (5)

(57) [Claims] 1. A zoom lens system comprising a first lens group having a positive refractive power and a second lens group having a negative refractive power in order from the object side. Wherein the first lens group includes, in order from the object side, a negative lens whose curvature on the object side is larger than the curvature on the image side, at least one negative lens and at least three positive lenses. A compact zoom lens comprising a positive lens group and satisfying the following conditions . 1.45 <| f ₁ | / F _W <1.78 0.4 <| f _2G | / F _W <0.78 where f _{1 is} the focal length of the first negative lens in the first lens group.
Away, the focal length of the entire system at F _W ... wide-angle end, f _2G ... focal length of the second lens group. Wherein said compact zoom lens of claim 1, wherein the shape of the first negative lens of the first lens group satisfies the following condition. −2.5 <(r ₁ + r ₂ ) / (r ₁ −r ₂ ) <− 0.5 where r _{1 is the} radius of curvature of the first negative lens on the object side, and r _{2 is} the image of the first negative lens. The surface side radius of curvature, 3. When the average refractive index of the positive lens in the positive lens group in the first lens group is < _nd1RP > and the average refractive index of the negative lens is < _nd1RN >, the following condition is satisfied. 3. The compact zoom lens according to claim 1, wherein: < _Nd1RP ><1.65< _nd1RN >> 1.75 4. The second lens group includes at least one positive meniscus lens and at least two negative lenses, wherein the average Abbe number of the positive lens is <ν _d2GP >, and the average Abbe number of the negative lens is _{Is set} to <ν _d2GN >, and the Abbe number of the positive lens arranged closest to the object side in the positive lens group of the first lens group is set to ν _{d (2)} , and the positive lens arranged closest to the image plane side When the average Abbe number of the positive lens and the negative lens in the group is <ν _{d (5) P} > and <ν _{d (5) N} >, respectively, the following condition is satisfied. One
4. The compact zoom lens according to any one of claims 3 to 3 . _{νd (2)} <50 0.5 <(< _νd2GN > − < _νd2GP >) / (< _{νd (5) P} > − < _{νd (5) N} >) <2.0 5. The compact zoom lens of any one of claims 1 to 4, wherein the variable power ratio is at least 2-fold.