JPH01193807A - Small-sized zoom lens - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a small zoom lens suitable for lens shutter cameras, video cameras, etc. This relates to a compact zoom lens that aims to shorten the distance (to the surface).

(Prior Art) Recently, with the miniaturization of lens shutter cameras, video cameras, etc., there has been a demand for compact zoom lenses with short overall lens lengths. Particularly in the field of small cameras such as lens shutter cameras that do not require lens replacement, it is desired to attach a zoom lens, and there is a demand for a small zoom lens with a length comparable to that of conventional single focus lenses.

The applicant has previously published Japanese Patent Application Laid-Open Nos. 57-201213, 60-170816, and 60-19121.
In Publication No. 6, etc., in order from the object side, the first one with positive refractive power
We have proposed a compact zoom lens that is composed of two lens groups: a lens group and a second lens group with negative refractive power, and whose magnification can be varied by changing the distance between both lens groups.

In this publication, since a positive and negative refractive power arrangement is adopted in order from the object side, the back focus is relatively short and a zoom lens with a short overall lens length is achieved.

In these two-group zoom lenses, a material with a high refractive index and high dispersion is used for the negative lens included in the first lens group,
Furthermore, by using a material with a lower refractive index and lower dispersion than the negative lens for the material of the positive lens in the first lens group, mainly chromatic aberration and curvature of field are corrected in a well-balanced manner. In this way, if a material with a high refractive index and high dispersion is used for the negative lens, relatively good optical performance can be obtained.

However, materials with a high refractive index of about 1.74 or more and high dispersion are generally physically and chemically difficult to polish, and there is a problem in that it is difficult to obtain good surface precision. For this reason, it is conceivable to construct the negative lens from a material with a relatively low refractive index and low dispersion, but this tends to make it difficult to obtain good optical performance over the entire zoom range.

(Problems to be Solved by the Invention) The present invention provides a so-called two-group zoom lens, in particular, by appropriately setting the lens configuration in the first lens group.
An object of the present invention is to provide a compact zoom lens that can obtain good optical performance over the entire zoom range even if a negative lens in a lens group is made of a material with a low refractive index and low dispersion that is relatively easy to polish.

(Means for solving the problem) It has two lens groups, a first lens group with positive refractive power and a second lens group with negative refractive power, in order from the object side, and the distance between both lens groups is changed. In a small zoom lens that changes magnification,
The first lens group includes a positive eleventh lens group including at least one positive lens, a negative twelfth lens group including at least one negative lens, and a positive thirteenth lens group including at least one positive lens. , the focal length of the eleventh lens group is f1i, and the focal length of the first lens group is F
1. The average value of the refractive index of the material of the positive lens in the 11th lens group is N11P, and the average value of the refractive index and Atsube number of the material of the negative lens in the 12th lens group is N12N and ν1, respectively.
2N, and when the average value of the refractive index of the material of the positive lens in the 13th lens group is N13P, 0.5< fil/Fl <5...
・-(1)-1,0<f12/Fl<-0,3
...(2) 0.3< f13/Fl <5
...Auto-(:])N11P < 1.7
8 ・・・・・・・・・・・・・・・(4
)N12N < 1.68 ・
・・・・・・−・・・・・・−(5) ν12N <38
・・・・・・・・・・・・・・・・・・(6)
N13P < 1.68 -・・・・・・・・・
...-(7) is to be satisfied.

(Example) FIGS. 1 to 3 are cross-sectional views of lenses of numerical examples 1 to 3 of the present invention. The figure shows the zoom position at the wide-angle end.

In the figure, ■ is the first lens group with positive refractive power, ■ is the second lens group with negative refractive power, and while decreasing the distance between both lens groups, move both lens groups toward the object side as indicated by the arrows. This allows you to change the magnification from the wide-angle end to the telephoto end. Further, I-i is the 11th lens group in the first lens group, and ■-j is the 2j-th lens group in the second lens group.

In this embodiment, by employing such a zoom system and refractive power arrangement, the overall lens length is shortened, particularly at the wide-angle end.

As mentioned above, by specifying the lens configuration of the first lens group so as to satisfy conditional expressions (1) to (7), high optical performance is obtained that satisfactorily corrects aberration fluctuations associated with zooming. .

The first lens group I of Numerical Examples 1 and 2.3 is
1st lens group I-1 is one positive lens, 12th lens group I
-2 is composed of one negative lens made of polycarbon plastic material, and the thirteenth lens group I-3 is composed of two positive lenses made of acrylic plastic material. Numerical example 1
The 21st lens group of the second lens group consists of one positive lens, and the 22nd lens group consists of two negative lenses. or,
The 21st lens group of the second lens group in Numerical Examples 2 and 3 is 1
The 22nd lens group consists of two positive lenses and one negative lens.

In this embodiment, by configuring each lens group as described above, aberration correction is performed in a well-balanced manner as a whole.

Next, the technical meaning of each of the above-mentioned conditional expressions will be explained.

Conditional expressions (1), (2), and (3) each represent the 11th lens group constituting the first lens group. 12th. This is to appropriately set the refractive power of the 13th lens group and to satisfactorily correct fluctuations in various aberrations mainly due to zooming.

If the lower limit of conditional expression (1) is exceeded and the positive refractive power of the 11th lens group becomes too strong, distortion on the wide-angle side increases,
Furthermore, if the upper limit is exceeded and the positive refractive power of the 11th lens group becomes too weak, spherical aberration becomes overcorrected.

If the lower limit of conditional expression (2) is exceeded and the negative refractive power of the twelfth lens group becomes too weak, correction of positive distortion will become insufficient on the wide-angle side. Furthermore, if the upper limit is exceeded and the negative refractive power of the 12th lens group becomes too strong, a large amount of coma aberration will occur on the telephoto side.

If the lower limit of conditional expression (3) is exceeded and the positive refractive power of the 13th lens group becomes too strong, spherical aberration will be undercorrected, and if the upper limit of conditional expression (3) is exceeded, the 11. It becomes insufficient to correct the spherical aberration occurring in the positive direction in the 12th lens group in the negative direction.

Conditional expression (4) is a positive lens in the 11th lens group, and conditional expression (
5) relates to the negative lens in the 12th lens group, conditional expression (7) relates to the average value of the refractive index of the material of the positive lens in the 13th lens group, and conditional expression (6) relates to the negative lens in the 12th lens group. By using a material that satisfies each conditional expression regarding the average value of the Abbe number of the material, various aberrations are corrected in a well-balanced manner overall.

If conditional expressions (4) and (7) are not satisfied, the image plane characteristics will be overcorrected, and lateral chromatic aberration and longitudinal chromatic aberration will be insufficiently corrected. In order to properly correct the image plane characteristics and chromatic aberration at this time, it is necessary to use a material with a high refractive index that does not meet conditional expression (5), which is difficult to polish, for the negative lens in the 12th lens group. not good.

Furthermore, if conditional expression (6) is not satisfied, chromatic aberration on the glaze and chromatic aberration of magnification will increase, which is not good.

By satisfying the above-mentioned conditions, the object of the present invention can be achieved. However, in this embodiment, it is possible to better correct aberration fluctuations associated with zooming and obtain high optical performance over the entire zooming range. should satisfy the following conditions.

The second lens group consists of a positive 21st lens group including at least one positive lens and a negative 22nd lens group including at least one negative lens, and the focal length of the 2j lens group is f2j, and the second The focal length of the lens group is F2, the average values of the refractive index and Atsube number of the material of the positive lens in the 21st lens group are N21P and ν21P, respectively, and the refractive index and Atsube number of the material of the negative lens in the 22nd lens group are respectively N21P and ν21P. When the average values of numbers are respectively N22N and ν22N, -3< f2
1/F2 <-0,5...-(8)0.3<
f22/F2 < 0.8 ...Axis (
9) N21P < 1.68
-...-(10)N22N < 1
．． 78 -1・-(11)・・
・・・－・・・・・・(12) It is to satisfy the following condition.

Conditional expressions (8) and (9) are for the second lens group in the second lens group.
This relates to the refractive powers of the first lens group and the 22nd lens group.

If the positive refractive power of the 21st lens group becomes too strong, exceeding the upper limit of conditional expression (8), the negative refractive power of the 22nd lens group is changed to The aberration must be made stronger beyond the lower limit, and as a result, positive distortion increases on the wide-angle side, which is not good.

Furthermore, if the lower limit of conditional expression (8) is exceeded and the positive refractive power of the 21st lens group becomes too weak, the negative refractive power of the 22nd lens group is changed to conditional expression ( 9) must be weakened beyond the upper limit value, which is not good because it becomes difficult to properly correct the image plane characteristics.

Conditional expression (10) concerns the average value of the refractive index of the material of the positive lens in the 21st lens group, conditional expression (11) concerns the average value of the refractive index of the material of the negative lens in the 22nd lens group, and conditional expression (12) concerns the average value of the refractive index of the material of the negative lens in the 21st lens group. This relates to the Abbe numbers of the materials of the positive lens and the negative lens in the 22nd lens group.

If conditional expressions (10) and (11) fail, conditional expression (8)
, Even though (9) is satisfied, it becomes difficult to satisfactorily correct the image plane characteristics, and it also becomes difficult to polish the material, which is not good.

If Conditional Expression (12) is not satisfied, the amount of chromatic aberration generated in the second lens group will increase, and in particular, the fluctuation of chromatic aberration due to zooming will increase, which is not good.

In the present invention, it is preferable to perform focusing by extending the entire lens system because it reduces fluctuations in aberrations.
It is also possible to move only the lens group or the second lens group, or by moving a part of the second lens group. According to this, the lens barrel becomes simple.

In each of the embodiments shown in FIGS. 1 to 3, a single lens in each lens group may be composed of a cemented lens in which a positive lens and a negative lens are bonded together.

In addition, the positive lens in the 11th lens group and the negative lens in the 12th lens group may be bonded together, or the negative lens in the 12th lens group and the positive lens in the 13th lens group may be bonded together. Even with this configuration, good aberration correction can be achieved.

In this embodiment, the object of the present invention can also be achieved even if the third lens group, which is fixed during zooming, is disposed behind the second lens group.

Next, numerical examples of the present invention will be shown. In numerical examples R
i is the radius of curvature of the i-th lens surface in order from the object side, D
i is the i-th lens thickness and air distance from the object side, Ni
and νi are the refractive index and Abbe number of the glass of the i-th lens, respectively, in order from the object side.

Furthermore, Table 1 shows the relationship between each of the conditional expressions described above and the various numerical values in the numerical examples.

The aspherical shape has an X axis in the optical axis direction, an H axis in a direction perpendicular to the optical axis,
The traveling direction of the light is positive, R is the paraxial radius of curvature, A, B, C,
When D, E, A', B", and C' are aspherical coefficients, +DH8+El+10+A"l+3+B'l13+ (:'11').

Numerical Example I F-40~60 FNO-1:4~62ω-56,8
° ~ 39.7 ° Rl-17,76D I-2,00 old visit, 64769 S1-33.8R2-51,66D
2-2.31 R3--13,49D 3-2.5082=1.583
47 y2=30.2R4-19,74D 4-0.
63 R5-28,83D 5-3.50 N3-1.491
71 C3-57. flR6--13,42D 6-
0.13 R7-60,65D 7-2.0084-1.4917
1 ν4-57.4R8--27,0208-Variable R9 loincloth -28,45D 9- 3.00 85-1
．． 59270 Shi5-35.3RIO--13,5
4DIO-2, 78R11--14, 70Dll-1,
5086-1, 60311 Jiro 60.7R12--4
3,98DI2・2.33R13--18,2901
3-1,50~7-1.60311 υ7-60.
7Rth--81,98 Numerical Example 2 F-40~60 FNO-1:4~6 2ω-56,
8@~39.7”R1-17,59D 1-2.00
N1-1.64769ν1-33.882- 45.0
602-2.29 R3--13,3603=2.5082-1.5834
7 v2-30.2R4-20,93D 4 0.32 R5-28,33D 51-3.50 N5I11.4
9171 Shi3-57.486--13.6106-0
．． 13 R7-71,7807-2,00N4~1.49171
ν4 servings 57.4+' (8--26,8508-variable R9--35,2909-3,00N5 servings 1.5955
1 ν5 irises 39.2RIO--14,75DIO-2
,671111--12,76Dll-1,50-6-
1.60311 Jiro 60.71112-391.
11 R11 Aspherical shape factor A = -7,34897x 1O-3B =
1.7:t029 x 1O-5C= 4.2391
:l x 10-'D = -3,72473xlO
OE=1.08507 xlO−A”=
−3,25107x 1O−5B” = −4,28
66x 1O-6C'= -7,21606xlO-9 Numerical Example 3 F -36~68 FNO-1: 3.6~6.82ω-
62＠〜35.3゜RI-17,34D I-2,00
N1-1.58347 Si1-30.2R2-47,
90D 2-1.77 rl 3--14.94 D 3-2.50 N2-
1.58347 Shi2-30.284 Mu 22.7
8 D 4-0.47R5-33, 7505-3,
50N3-1.49171 Shi3-57.4R6 Heat -16,40D 6-0.13R7-74,210
7-2,00N4J, 49171 v4-57.4
R8, -22,18D 8-variable R9--39,1709-3,70~5-1.5342
0 v5-41.2RIO--14,89DIO-
2,58R11--12,52Dll-1,50-6-
1.60311 shi8-60.7112- 337
．． 97 R7 surface spherical shape factor R11 surface aspheric shape factor B--
7,70931Xl0-5A-5,35012Xl
0-3G-2,29518x 10-' B-
-2,49468x 10-'D--4.14509
Xl0-9G -2,89631Xl0-'D-
1,69062xlO-8 E--2,83768x 10-”A'-7,0
5679x 1O-5 B'-8,50985x 1O-6 G"--1,52837x 10-'Table-1 (Effects of the Invention) According to the present invention, the lens configurations of two lens groups with predetermined refractive powers are as described above. By specifying as follows, even if the negative lens in the first lens group is made of a material with a low refractive index that is relatively easy to polish, a compact lens with a simple configuration can be obtained that provides good optical performance over the entire zoom range. A zoom lens can be achieved.

[Brief explanation of the drawing]

1 to 3 are lens sectional views of numerical examples 1 to 3 of the present invention, and FIGS. 4 to 6 are various aberration diagrams of numerical examples 1 to 3 of the present invention. In the aberration diagrams, (A) is at the wide-angle end, (B) is at the middle, and (C) is at the wide-angle end.
is an aberration diagram at the telephoto end. In the figure, I and n are respectively 1st. The arrows in the second lens group indicate the movement direction of each group during zooming. Patent applicant Hiroshi Canon Co., Ltd. 2 Monryo 3 Figure ■ 4 Figure 5

Claims (1)

[Claims] (1) It has two lens groups, a first lens group with positive refractive power and a second lens group with negative refractive power, in order from the object side, and can be changed by changing the interval between both lens groups. In a compact zoom lens that performs magnification, the first lens group includes a positive eleventh lens group including at least one positive lens, a negative twelfth lens group including at least one negative lens, and at least one positive lens. The focal length of the 1i-th lens group is f1i, the focal length of the first lens group is F1, and the average value of the refractive index of the material of the positive lens in the 11th lens group is N11P, the average value of the refractive index and Abbe number of the material of the negative lens in the 12th lens group is N12N, respectively.
, ν12N, 0.5<f11/F1<5 -1.0<f12/F1<-0.3 0.3 when the average value of the refractive index of the material of the positive lens in the thirteenth lens group is N13P A compact zoom lens that satisfies the following conditions: <f13/F1<5 N11P<1.78 N12N<1.68 ν12N<38 N13P<1.68. (2) The second lens group consists of a positive 21st lens group including at least one positive lens and a negative 22nd lens group including at least one negative lens, and the focal length of the 2j lens group is f2j, The focal length of the second lens group is F
2. The average values of the refractive index and Abbe number of the material of the positive lens in the 21st lens group are N21P, ν21P, and the second
When the average values of the refractive index and Abbe number of the negative lens material in the two lens groups are N22N and ν22N, respectively, -3<f21/F2<-0.5 0.3<f22/F2<0.8 N21P< 1.68 N22N<1.78 0.002<(1/ν21P)-(1/ν22N)<0
．． Claim 1 characterized in that the condition 018 is satisfied.
The small zoom lens described.