JPH04153614A - Zoom lens - Google Patents

Abstract

PURPOSE:To reduce the size of the whole lens system and to obtain excellent optical performance over the entire power variation range of an about three power variation by composing four lens groups of single lenses, moving the four lens groups in the same direction, and varying the lens intervals of the respective lens groups and varying the power. CONSTITUTION:The zoom lens has the four lens groups which are a 1st group with a negative refracting power, a 2nd group with a positive refracting power, a 3rd group with a positive refracting power, and a 4th group with a negative refracting power in order from the object side. Those four lens groups are composed of the single lenses and moved in the same direction to vary the lens intervals of the respective lens groups, thereby varying the power. Consequently, the number of lens elements is decreased and the excellent optical performance is obtained over the entire power variation range of an about three power variation ratio.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a zoom lens with a simple structure consisting of four lens groups as a whole suitable for lens shutter cameras, video cameras, etc. This relates to a zoom lens with a zoom lens having a zoom ratio of about 3 and a short distance from the lens surface to the image plane, with a very small amount of aberrations and excellent aberration correction.

(Prior Art) With the miniaturization of lens shutter cameras, video cameras, etc., various types of zoom lenses with short overall lens lengths and simple configurations have been proposed.

The applicant has previously published Japanese Patent Application Laid-Open Nos. 57-201213, 170816-1980, and 1912-1981.
According to 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, in Japanese Patent Application Laid-open No. 63-271214 and Japanese Patent Application Laid-Open No. 64-72114, the present applicant has developed, in order from the object side, a first group with a negative refractive power, a second group with a positive refractive power, and a second group with a negative refractive power. We have proposed a zoom lens that has three lens groups, including a third lens group, and that changes magnification by moving these three lens groups.

This type of zoom lens is relatively easy to widen, so it is often used as a wide-angle photography system.

In the same bulletin, the first. Second. Variable power ratio 2 with high optical performance that performs zooming by moving the third group under certain conditions and also satisfactorily corrects aberration fluctuations due to zooming by specifying the lens configuration of the three lens groups. ~3x overall 8~
A relatively compact zoom lens consisting of nine lenses, particularly suitable for lens-shutter cameras, has been achieved.

In addition, JP-A-64-88512 discloses, in order from the object side, a first group with negative refractive power consisting of a single lens, a second group with positive refractive power consisting of a single lens, and a positive refractive group consisting of a cemented lens. A zoom lens has been proposed, which is composed of four lens groups, a third group having a strong refractive power, and a fourth group having a negative refractive power consisting of three lenses, and in which the magnification is changed by moving the four lens groups.

Furthermore, in Japanese Patent Application Laid-Open No. 62-235916, a first group with negative refractive power consisting of two lenses, a second group with positive refractive power consisting of three lenses, and a single lens, in order from the object side. It has a front group consisting of three lens groups, a third group with positive refractive power, and a rear group consisting of a fourth group of two lenses with negative refractive power, and zooms from the wide-angle end to the telephoto end. In this case, the air gap between the front group and the rear group is shortened, and the second
We have proposed a zoom lens in which the group is moved from the third group to the first group.

(Problem to be solved by invention) The above-mentioned Japanese Patent Application Laid-Open No. 64-88512 and Japanese Patent Application Laid-Open No. 62-2
The zoom lens proposed in Japanese Patent No. 35916 has a total of four lens groups, each of which is composed of one to three lenses. For this reason, the overall length of the lens (distance III from the lens surface to the image plane) has tended to become relatively long, and the entire lens system has also tended to become larger.

The present invention utilizes the refractive power arrangement of the zoom lens, which is composed of four lens groups as a whole, and further improves the lens configuration of each lens group, particularly aiming at an ultimate reduction in the number of lenses and achieving a variable power ratio of about 3. The purpose of the present invention is to provide a zoom lens having good optical performance over the entire zoom range and having an F number of about 4 at the wide-angle end, which is particularly suitable for lens shutter cameras.

(Means for Solving the Problems) The zoom lens of the present invention includes, in order from the object side, a first group with negative refractive power, a second group with positive refractive power, a third group with positive refractive power, and a third group with negative refractive power. It has four lens groups of the fourth group of refractive power, and these four lens groups are composed of a single lens, and the four lens groups are composed of a single lens.
The lens is characterized by variable power by moving two lens groups in the same direction and changing the distance between the lenses in each lens group.

In particular, in the present invention, the focal length of the iuth lens is FI, the focal length of the entire system at the wide-angle end is FW, and the air spacing between the first group and the (i+1)th group at the wide-angle end and the telephoto end are DiW and D, respectively.
When iT is -4<Fl/FW<-2, 3...(
1) 0.5<F2/FW<0.8 (2
)1.6<F3/FW<2 (3)
-0,6<F4/FW<-0,4...(4)0.8
<D1T/D1W<1.1 (5) 0.1<D2
T/D2W<0.4...(6)1<D3T/D3W
It is characterized by satisfying the condition <1.2...(7).

(Example) FIGS. 1 and 2 are cross-sectional views of a lens according to a numerical example 1°2 of the present invention. In the figure, the symbol is the first group with negative refractive power, ■ is the second group with positive refractive power, ■ is the third group with positive refractive power, ■ is the fourth group with negative refractive power, and the arrow indicates the wide-angle side. This shows the direction in which each lens group moves when changing magnification from to telephoto.

When changing the magnification from the wide-angle end to the telephoto end, the zoom lens according to this embodiment moves all four lens groups independently in the object side direction while changing the air distance between each lens group, as shown in each figure. ing. In particular, a predetermined variable power ratio is effectively obtained by greatly changing the distance between the second and third groups. Note that sp is a diaphragm, which is disposed on the image plane side of the second group, and moves integrally with the second group during zooming.

The zoom lens of the present invention is the first one. As shown in Figure 2, it consists of four lens groups with negative, positive, positive, and negative refractive powers in order from the object side, that is, the second and third groups have positive refractive power, and both sides have negative refractive power. The first and fourth groups are arranged, and the SP is arranged between the second and third groups, so that the lens has a medium-variable refractive power arrangement or a substantially symmetrical lens structure. There is. In addition, a high refractive index and high dispersion glass (Nl>1.65.ν1<35
) Low refractive index low dispersion glass (N2 × 1.52.ν) in the second group
2>75) is adopted.

By adopting such a nearly symmetrical lens arrangement and constructing each lens group from a single lens of an appropriate shape, the entire lens system is Chromatic aberrations are corrected in a well-balanced manner. That is, the aberrations of the four lens groups cancel each other out.

In addition, the first group is a meniscus-shaped negative lens with a convex surface facing the object side, and the second group is a bilens lens whose refractive power is stronger on the image side than the object side, or a convex positive lens. 2 lenses, 3rd
The lens group consists of a meniscus-shaped positive third lens with a convex surface facing the image side, and a negative fourth lens with strong refractive power facing the object side compared to the fourth group facing the image side, shortening the overall lens length. Even if the zoom lens is designed to have a high optical performance, it is possible to correct various aberrations including chromatic aberration in a well-balanced manner over the entire zoom range, making it possible to obtain a zoom lens with high optical performance.

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

Conditional expressions (1) to (4) suitably set the refractive powers of the first to fourth groups in order, and when changing the magnification by moving the four lens groups, it is possible to shorten the total lens length while changing the power. This is to easily obtain a magnification ratio of about 3, to reduce aberration fluctuations during zooming, and to obtain high optical performance over the entire zooming range.

If the refractive power of each lens group becomes too strong or too weak, exceeding the upper or lower limits of conditional expressions (1) to (4), spherical aberration and astigmatism will occur over the entire magnification range in either case. It becomes difficult to correct various aberrations such as aberration and coma in a well-balanced manner.

Conditional expressions (5) to (7) are set by appropriately setting the air spacing between the first group and the second group, the second group and the third group, and the third group and the fourth group at the wide-angle end and the telephoto end. This is to effectively obtain a predetermined zoom ratio while reducing the overall lens length based on equations (1) to (4), and to correct various aberrations in a well-balanced manner over the entire zoom range.

When the upper limit of conditional expression (5) is exceeded, the curvature of field becomes overcorrected on the telephoto side. Moreover, if the lower limit is exceeded, the field curvature will change in the direction of insufficient correction when changing the magnification from the wide-angle end to the telephoto end, which is not good.

If the upper limit of conditional expression (6) is exceeded, the change in the distance between the second and third groups during zooming will be too small, making it difficult to obtain a predetermined zoom ratio. Also, if the lower limit value is exceeded, the distance between the second and third groups will become too narrow on the telephoto side, which is not good because mechanical interference will easily occur. The distance between the third group and the fourth group becomes too large, and the entire lens system becomes large. Furthermore, if the lower limit is exceeded, fluctuations in spherical aberration due to zooming become large, and it becomes difficult to correct this well.

Further, in the present invention, as shown in numerical examples to be described later, an aspherical surface is formed on the object-side lens surface of the second lens, the image-side lens of the second lens, and the image-side lens surface of the third lens. , aberration fluctuations associated with zooming are well corrected, and high optical performance is achieved over the entire zooming range.

Next, numerical examples of the present invention will be shown. In numerical examples R
1 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 numbers corresponding to the refractive index of the glass of the i-th lens in order from the object side.

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 and E are each aspherical coefficients, it is expressed by the following formula: +DH8+EH''.

In addition, Table 1 shows the relationship between each conditional expression in the description and the various numerical values in the numerical examples.

Numerical Example I F-36,1 ~101.5 Rl-21,03 R2-15,5] 8 3- 149.2] R4--13,04 R5- (aperture) R6- -67,52 87- -23,0O R8~ -14,18 R9-1945,58 FNa~4,1 ~8.8] -1,5 2.Variable 3-3.0 4-1.0 5.Variable 6-3.3 7 to variable 8・1.7 2 ω-51,7° to 24.18 1-1.68893 1-31.1 2-1.49700 2-81.6 3-1.54814 3-45.8 4 −49.6 Aspherical surface A −OB −−6,51xli) −5G ・ −
4,22xlO-'D--: ], 92xl
O-9E --4,74Xl0 A-D B ・1.95
x 1O-5G --9,05xlO-90・
0ε・OA-OB--3,43xlO-5C-1,71
xlO-13D ・-4,62X 10sOE
-- 2,93 R7--23,21 R8--14,43 R9-4555], 80 FNoi, 1 to 8.8 DI-1,5 D2・Variable D 3・3.0 D 4 electric 1.0 D5・Variable D 6-3.0 D7・Variable D 8-1.7 2 ω-6170 ~ 2410 1-1.84666 ν I・23 2-1.49700 2-81.6 3-1.59551 3-39.2 4 ~1.77250 4-49.6 Aspheric surface R7゜A -OB --4,83xlO-'C・-2,
41x 10-'D ・-3,+4 Xl0
-9E ・ -1,78x to”12 ＾ ・ OB ・ 2.05 Xl0-5C-Ri,
82 Xl0-80・OE・0＾・OB・−:1. ] X 1O-5C-
7,72xlO-'D--1,73xlO-'
E 4.32 A zoom lens having good optical performance over the entire zoom range with a magnification ratio of about 3 can be achieved.

[Brief explanation of the drawing]

FIGS. 1 and 2 are cross-sectional views of lenses of Numerical Example 1゜2 of the present invention, and FIGS. 3 and 4 are lens cross-sectional views of Numerical Example 1 of the present invention, respectively.
．． FIG. 2 is a diagram showing various aberrations of No. 2. I, I on the right side of the cross-sectional view of the lens
I, III, and IV are the first group in that order. The 2nd, 3rd, and 4th groups, the arrows indicate the movement direction of each lens group during zooming from the wide-angle end to the telephoto end, and the aberration diagram (
A), (B), and (C:) are respectively at the wide-angle end, middle, and
In the aberration diagram at the telephoto end, d is the d-line, g is the g-line, S and C are the sine conditions, ΔS is the sagittal image plane, and 6M is the meridional image plane. Figure 2

Claims (1)

[Claims] (1) In order from the object side, the first group has a negative refractive power, the second group has a positive refractive power, the third group has a positive refractive power, and the fourth group has a negative refractive power.
The four lens groups are composed of a single lens, and the four lens groups are moved in the same direction to change the lens spacing of each lens group to change the magnification. A zoom lens featuring (2) When the focal length of the i-th group is Fi, the focal length of the entire system at the wide-angle end is FW, and the air spacing between the i-th group and the (i+1)-th group at the wide-angle end and the telephoto end is DiW and DiT, respectively. -4<F1/FW<-2.3 0.5<F2/FW<0.8 1.6<F3/FW<2 -0.6<F4/FW<-0.4 0.8<D1T/ 2. The zoom lens according to claim 1, wherein the zoom lens satisfies the following conditions: D1W<1.1 0.1<D2T/D2W<0.4 1<D3T/D3W<1.2.