JPH0493810A - Small-sized zoom lens - Google Patents

Abstract

PURPOSE:To obtain high optical performance over the entire power variation range while the overall length of the lens is shortened by specifying the lens shapes, etc., of respective lens groups of the zoom lens which vary in power by the movement of two lens groups having specific refracting power. CONSTITUTION:The lens constitution of the lens groups I and II, the lens shape of the lens groups I and II, etc., are so specified so that inequalities I are satisfied. In the inequalities I, Fw is the focal length of the whole system at its wide-angle end, Ri a radius of curvature of an (i)th lens counted from the object side, DT the lens interval between the 1st and 2nd groups at the telephoto end, and NP the mean value of refractive indexes of the materials of 1st, 3rd, and 4th lenses. Consequently, the zoom lens is obtained which is shortened in overall length and has high optical performance over the entire power variation range while, specially, the power variation rate of focus and a photographic view angle are obtained.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a compact zoom lens consisting of two lens groups suitable for lens shutter cameras, video cameras, etc., and in particular, to appropriately set the lens configuration of each lens group. The present invention relates to a compact zoom lens that achieves good aberration correction and shortens the overall lens length (distance from the lens surface to the image plane).

(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, Japanese Unexamined Patent Publication No. 62-56917, etc.,
From the object side, the first group has positive refractive power and the second group has negative refractive power.
We have proposed a compact zoom lens that is composed of two lens groups and whose magnification can be varied by changing the distance between the two lens groups.

In this publication, a zoom lens with high optical performance is achieved by adopting a positive and negative refractive power arrangement in order from the object side, making the back focus relatively short, and shortening the overall lens length.

In addition, JP-A-62-284319, JP-A-62
-256915 publication, JP 6452111 publication,
In Japanese Unexamined Patent Publication No. 1-193807, etc., the first lens with positive refractive power
This disclosure discloses a zoom lens that is composed of an El lens and a second lens group having a negative refractive power, and that changes the magnification by moving both lens groups forward while changing the distance between the two lens groups.

In these zoom lenses, the first group consists of four lenses: a positive lens, a negative lens, a positive lens, and a positive lens, and the second group consists of three lenses: a positive lens, a negative lens, and a negative lens. There is.

(Problems to be Solved by the Invention) The first m group having positive refractive power and the second group having negative refractive power
It consists of two lens groups, and in order to achieve good optical performance over the entire zoom range while reducing the size of the entire lens system and having a zoom ratio of about 18 to 2, it is necessary to It is necessary to appropriately set the lens configuration of each lens group using about seven lenses with positive, positive, positive, negative, and negative refractive powers.

Previous Japanese Patent Application Publication No. 57-201213 and Japanese Patent Application Publication No. 1-19
The zoom lens disclosed in Japanese Patent Publication No. 3807 had a variable power ratio of about 1.5, and the zoom lens disclosed in Japanese Patent Application Laid-open No. 63-256915 had large variations in aberrations during zooming, particularly in spherical aberration and curvature of field.

Furthermore, the zoom lens disclosed in Japanese Patent Application Laid-Open No. 64-52111 did not necessarily have sufficient brightness at its wide-angle end F number or F4.5.

Generally the first. If the refractive power of both of the second group is strengthened, the amount of movement of each lens group during zooming will be reduced, and the total length of the lens can be shortened.

However, if the refractive power of each lens group is simply strengthened, aberration fluctuations due to zooming will become large, and this poses a problem in that it becomes difficult to properly correct this.

The present invention further improves the zoom lens proposed in each of the applicant's previous publications, and by appropriately setting the lens configuration of each lens group, the present invention has a particularly predetermined zoom ratio and photographing angle of view. The purpose of the present invention is to provide a compact zoom lens that has high optical performance over the entire zoom range and has a shortened overall lens length.

(Means for Solving the Problems) The compact zoom lens of the present invention has two lens groups, a first group having a positive refractive power and a second group having a negative refractive power, in order from the object side. In a small zoom lens that changes the magnification by changing the distance between the groups, the first group has either a meniscus-shaped positive first lens surface with the convex surface facing the object side, or a concave negative second lens surface, or both lens surfaces or a convex surface. The second group includes a positive meniscus-like fifth lens with a convex surface facing the image plane, and a positive fourth lens with a double lens surface or a convex surface. It has three lenses: a meniscus-shaped negative sixth lens with a weakly convex refractive surface on the surface side, and a meniscus-shaped negative seventh lens with a convex surface facing the image side, and the entire system at the wide-angle end. The focal length of is Fw, the radius of curvature of the first lens surface counting from the object side is Ri, the distance between the lenses of the first and second groups at the telephoto end is DT, and the distance between the first and fourth lenses is When the average value of the refractive index of the material is NP, 0.3<R4/R5<0.6 (1)-5
0<R12/Fwku-15"...(2)011kuD
T/FwkuO16・・・・・・(3)48<NP<1
．． 57...It is characterized by satisfying the following condition (4).

(Example) FIG. 1 is a sectional view of a lens according to Numerical Example 1 of the present invention.

In the figure, (A) shows the zoom position at the wide-angle end, (B) shows the zoom position in the middle, and FC) shows the zoom position at the telephoto end.

In the figure, ■ is the first group with positive refractive power, and II is the second group with negative refractive power. While decreasing the distance between both lens groups, both lens groups are moved toward the object side as indicated by the arrows. The magnification is changed from the wide-angle end to the telephoto end.

R9 (SP) is a diaphragm, which is arranged between the first group and the second group, and moves integrally with the first group as the magnification changes.

In this embodiment, by employing such a zoom system and the above-mentioned refractive power arrangement and lens configuration, the overall lens length is shortened, particularly at the wide-angle end. Then, the lens configuration of each lens group and the lens shape of each lens group are specified so as to satisfy the above-mentioned conditional expressions (1) to (4). This lens provides excellent optical performance over the entire zoom range.

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

Conditional expression (1) is concerned with the ratio of the radius of curvature of the negative lens surface on the image side of the second lens and the lens surface on the object side of the positive third lens, and is mainly used to properly correct spherical aberration. be.

If the upper limit is exceeded and the negative refractive power of the image-side lens surface of the second lens becomes too weak compared to the positive refractive power of the object-side lens surface of the third lens, spherical aberration will be insufficiently corrected, and If the lower limit is exceeded and the negative refractive power of the image-side lens surface of the second lens becomes too strong compared to the positive refractive power of the object-side lens surface of the third lens, spherical aberration may be overcorrected. It's not good because it's getting worse.

Conditional expression (2) relates to the radius of curvature of the lens surface on the image plane side of the negative sixth lens of the second group, and is mainly used to satisfactorily correct the field curvature.

If the upper limit is exceeded and the negative refractive power of the lens surface becomes too strong, the meridional image plane will tend to be too large on the wide-angle side, and if the lower limit is exceeded and the negative refractive power of the lens surface becomes too weak, the meridional image plane will become too strong at the telephoto side. In this case, the meridional image plane tends to be too large, which is not good.

Conditional expression (3) is used to appropriately set the lens distance between the first and second groups at the telephoto end to effectively obtain a predetermined variable power ratio while downsizing the entire lens system. be.

If the distance between the lenses exceeds the two limit values and the distance between the lenses becomes too wide, the required magnification ratio can only be effectively achieved by 1 bar, and when the lower limit value is exceeded and the distance between the lenses becomes too narrow, the distance between the first and second groups becomes too narrow. If they are too close together, it becomes difficult to place an aperture between both lens groups.

Conditional expression (4) relates to the average value of the refractive index of the material of the positive lens in the first group, and is mainly used to correct the field curvature and spherical aberration in a well-balanced manner.

If the upper limit is exceeded and the average refractive index w becomes too high, the Petzval sum will increase too much in the negative direction, resulting in field curvature or insufficient compensation, which is not good.Also, if the lower limit is exceeded, the average refractive index NP If the lens diameter is too low, fluctuations in spherical aberration due to zooming will increase, which is not good.

In this embodiment, focusing may be performed using the first group or the second group, or may be performed by moving the entire lens system.

Next, in an example embodiment of the present invention, R
i is the radius of curvature of the first lens surface from the object side, D
i is the first lens thickness and air gap from the object side, Ni
and ν1 are the refractive index and Abbe number of the glass of the first lens, respectively, in order from the object side.

Note that R9 is shown on the assumption that it is stopped and has one clear lens surface.

Further, Table 1 shows the relationship between each of the above-mentioned conditional expressions and numerical examples.

Numerical Example 1 Numerical Example 2 F=39.2~736 R1= 19.98 DI= R2= 94.01 D2= R3= -18,1403= R4= 32.52 04= R5= 67.64 D5= 86= -15,8206= R7= 28.19 07= R8= -28,19D8= R9・ (Aperture 109・R10= −39,8201O= R11= −20,96011= R12= −28,76D12= R13= -975,33DI3= R14= -14,14014= R15= -39,16 FNO=3.91~7352ω;578''~32262
．． 26 N l=1.57501 ν l=
41.54.98 N2=1.83400
ν 2=37.20.24 4, 58 N 3=1.51602 ν 3
= 56.83, 48 N 4 = 1.48749
ν 4=70.21.20 variable 2.78 N 5=1.63636 ν5=3
5.41, 50 N 6 = 1.7 + 299 White = 53.81.50 N 7 = 1.7 + 299
Schiff = 53.8F = 39.2 ~ 736 R1 = 21.10 DI = R2 = 109.88 02 = R3 = -17,9803 = R4 = 33.74 D4 = R5 = 71.36 D5 = R6 = -15 , 39D6= R7= 28.76 07= R8= -28,76D8= R9・ (Aperture) D9= R1O= -39,82DlO= R11= -20,96Dll= R12= -28,711+ DI2=R13=
-975,33D13= R14= -14,14DI4= R15= -39,16 FNO=3.91~7.35 2ω=57.11''~
322+2.26 N l=1.60342
ν l= 38.04.97 N 2=1.8
3400 ν 2=37.20.22 4, 55 N 3=1.49831 ν
3=65.00.22 3.55 N 4=1.49831 ν
4=65.0 variable 2.78 N S=1.63636 ν5=
35.43.04 1,50 N 6=1.71299 Shiro=
53.81.50 N 7=1.71299
Schiff = 53.8 Numerical Example 3 F = 39.2 ~ 736 R1 = 20.18 DI = R2 = 91.33 02 = R3 = -17,97 D3 = R4 = 33.24 04 = R5 = 72.52 05 = R6= -15,71D6= R7= 28.08 07- R8= -28,0808= R9・ (Aperture LD9・R1G= −39,820IO= R11= −20,96DII= R12= −28,76DI2= R13 = -975,33013= RI4= -14,14014= R15= -39,16 FNO=3.91~7352ω=57.8"~322+
2.25 N I=1.58+44 ν 1
=40.84.97 N2=1.83400
ν 2=37.24.48 N 3=1.5
1823 ν 3=59.03, 59 N
4=1.48749 ν 4=70.2 variable 2.78 N S=1.63636 ν5=3
5.43.04 1.50 N 6=1.71299 Shiro=
53.84.28 1.50 N 7=1.7+299 Schiff=
53.8 Table-1 (Effects of the Invention) According to the present invention, the lens shape, etc. of each lens group of a zoom lens that changes magnification by moving two lens groups having a predetermined refractive power are set as described above. As a result, it is possible to achieve a compact zoom lens having a simple structure and having high optical performance over the entire zooming range with a zoom ratio of about 2, in which the overall length of the lens is shortened.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a lens according to Numerical Example 1 of the present invention, and FIGS. 2 to 4 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, ■ and II indicate the first and second lens groups, sp indicates the diaphragm, and arrows indicate the moving direction of each group during zooming.

Claims (1)

[Claims] (1) In a small zoom lens that has two lens groups, a first group with positive refractive power and a second group with negative refractive power, in order from the object side, and zooms by changing the distance between both lens groups. , the first group consists of a meniscus-shaped positive first lens with a convex surface facing the object side, a negative second lens with both concave lens surfaces, a positive third lens with both convex lens surfaces, and a positive third lens with both lens surfaces convex. The second group includes a positive meniscus fifth lens with a convex surface facing the image side, and a meniscus lens with a weakly convex refractive surface facing the image side. a negative sixth lens with a negative shape, and a negative seventh lens with a meniscus shape with a convex surface facing the image plane
The lens has three lenses, the focal length of the entire system at the wide-angle end is Fw, the radius of curvature of the i-th lens surface counting from the object side is Ri, and the first and second group lenses at the telephoto end. When the interval is DT and the average value of the refractive index of the materials of the first lens, third lens, and fourth lens is @NP@, 0.3<R4/R5<0.6 -50<R12/Fw< A compact zoom lens characterized by satisfying the following conditions: -15 0.11<DT/Fw<0.16 1.48<@NP@<1.57.