JPH1184243A - Zoom lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten the total length of lenses and to provide high optical performance over a whole variable power range by composing a third group of one positive lens. SOLUTION: At the time of varying the power from the wideangle end to the telescopic end, a first group L1 is moved so that an air gap between the first group and a second group is decreased, and an air gap between the second group and a third group L3 is decreased and so as to have a projecting locus on the image plane side and both the second group L2 and the third group L3 are linearly or nonlinearly moved to the object side. The third group L3 is composed of a positive lens. Specially, the surface on the side of the image plane of the positive lens of the third group L3 is composed of an aspherical surface. The first group L1 is composed of two lenses of negative lenses whose concave surfaces confront the image plane side and a positive lens whose convex surface confronts the object side, the second group L2 is composed of two lenses of positive lenses whose both surfaces are convex and a negative lens whose concave surface confronts the object side, the third lens L3 is composed of a positive lens whose both surfaces are convex and a fourth group L4 is composed of a positive lens whose convex surface confronts the object side.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wide-angle zoom lens suitable for a film still camera, a video camera, an SV camera (electronic still camera), and the like. It has at least three lens groups, and by appropriately setting the lens configuration of each of these lens groups, a zoom ratio of 3, which reduces the size of the entire lens system, an F-number of 2.8 at the wide-angle end, and a wide-angle end And a zoom lens having a shooting angle of view of about 65 ° to 76 °.

[0002]

2. Description of the Related Art Conventionally, a so-called negative lead type zoom lens in which a lens unit having a negative refractive power precedes is relatively easy to widen the angle of view. Used.

For example, JP-A-59-16248 and JP-A-6-66008 have two lens groups, a first group having a negative refractive power and a second group having a positive refractive power. A so-called short zoom lens in which zooming is performed by changing the distance between the lenses has been proposed.

In Japanese Patent Application Laid-Open No. 7-52256, a first lens unit having a negative refractive power, a second lens unit having a positive refractive power,
A zoom lens has been proposed which has three lens groups of a third group having a positive refractive power and performs zooming from the wide-angle end to the telephoto end by increasing the distance between the second and third groups. .

Also, in US Pat. No. 5,543,710, a first group of negative refractive power and a second group of positive refractive power are arranged in order from the object side.
A zoom lens having three lens groups, a first lens group and a third lens group having a positive refractive power, and performing zooming from the wide-angle end to the telephoto end by reducing the distance between the second and third groups is disclosed. ing.

Japanese Patent Application Laid-Open No. 60-31110 discloses a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, a third lens unit having a positive refractive power, and a positive lens having a positive refractive power. There has been proposed a zoom lens having four lens groups of a fourth group, in which zooming from the wide-angle end to the telephoto end is performed with the fourth group fixed and the distance between the second and third groups reduced. I have.

[0007]

In general, a negative lead type zoom lens, which is preceded by a lens group having a negative refractive power, is relatively easy to reduce the size of the lens system and increase the angle of view. For this reason, they are frequently used in lens systems of small cameras such as electronic still cameras and lens shutter cameras.

However, in a negative lead type zoom lens, it is necessary to reduce the size of the entire lens system, widen the angle of view of 65 ° or more, and obtain good optical performance over the entire screen. Unless the refractive power arrangement and the lens configuration are properly set, aberration fluctuations at the time of zooming increase, and it becomes difficult to obtain an image of good image quality over the entire screen.

In particular, if the paraxial refractive power arrangement and the lens configuration of each lens unit are inappropriate, the size of the entire lens becomes large, and even if the number of lenses is increased, the aberration variation accompanying zooming becomes large. Obtaining high optical performance over a range becomes difficult.

According to the present invention, in a negative lead type zoom lens having at least three lens groups which are preceded by a lens group having a negative refractive power, the total lens length can be reduced by appropriately setting the lens configuration of each lens group. It is another object of the present invention to provide a zoom lens having a zoom ratio of about 3, a shooting angle of view of 65 ° to 75 ° at the wide angle end and a wide angle of view, and having high optical performance over the entire zoom range.

[0011]

According to the present invention, there is provided a zoom lens comprising: (1-1) a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, and a second lens unit having a positive refractive power in order from the object side. The zoom lens has three lens groups, and changes the magnification from the wide-angle end to the telephoto end so that the distance between the first and second groups and the distance between the second and third groups are all reduced. In a zoom lens which is moved by moving the lens unit to the object side, the third unit is constituted by one positive lens.

(1-2) First negative refractive power from the object side
A first lens unit, a second lens unit having a positive refractive power, and a third lens unit having a positive refractive power. In a zoom lens that is moved by moving each lens group to the object side so that the distance between the second group and the third group is reduced, the second group is composed of two lenses, a positive lens and a negative lens. It is characterized by.

(1-3) First negative refractive power from the object side
A first lens unit, a second lens unit having a positive refractive power, and a third lens unit having a positive refractive power. In a zoom lens that is moved by moving each lens unit toward the object side so that the distance between the second unit and the third unit is reduced, the first unit and the third unit have an aspherical surface. Features.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1 to 5 are lens cross-sectional views of Numerical Examples 1 to 5 of the present invention, respectively. 6 to 8 are aberration diagrams at the wide-angle end, middle, and telephoto end of Numerical Embodiment 1 of the present invention. FIGS. 9 to 11 are aberration diagrams at the wide-angle end, middle, and telephoto end of Numerical Embodiment 2 of the present invention. 12 to 14 are aberration diagrams at the wide-angle end, a middle position, and a telephoto end according to Numerical Embodiment 3 of the present invention.
17 to 17 are aberration diagrams at the wide-angle end, middle, and telephoto end of Numerical Embodiment 4 of the present invention, and FIGS. 18 to 20 are aberration diagrams at the wide-angle end, middle, and telephoto end of Numerical Embodiment 5 of the present invention.

In the sectional views of the lenses shown in FIGS.
(A) shows the wide-angle end, (B) shows the middle, and (C) shows the telephoto end. In the figure, L1 is a first group having a negative refractive power, L2 is a second group having a positive refractive power, L3 is a third group having a positive refractive power, L4 is a fourth group having a positive refractive power, and SP is an aperture. The aperture and IP are image planes. G is a glass block such as a filter.

In the zoom lens system according to the present invention, at the time of zooming from the wide-angle end to the telephoto end, the air gap between the first and second groups is reduced, and the air gap between the second and third groups is reduced. The first unit has a locus convex toward the image plane side, and the second unit and the third unit have
The basic configuration is that each group moves linearly or non-linearly to the object side as indicated by an arrow.

The first aspect of the zoom lens according to the present invention is based on the above-described basic configuration. (A) The third group is constituted by one positive lens. In particular, the third lens unit is characterized in that the lens surface on the image plane side of the positive lens of the third group is formed of an aspherical surface.

A second invention resides in that (b) the second group is composed of two lenses, a positive lens and a negative lens. In particular, an aperture SP is provided in the second group, and the aperture is moved together with the second group when zooming,
When the radius of curvature of the lens surface on the object side of the negative lens of the second group is R2 _n1 , and the focal length at the wide-angle end of the entire system is fw, −2 <R2 _n1 / fw <−0.5 {( 1) It is characterized by satisfying the following conditions.

By satisfying conditional expression (1), coma flare accompanying zooming is corrected well. Still further preferably, the numerical value range in the conditional expression _{(1) -1.4 <R2 n1 /fw<-0.9} ‥‥‥ (1a) as may be set in.

A third aspect of the present invention resides in that (c) the first and third units have aspherical surfaces. In particular, the first group is characterized by having at least one positive lens and at least one negative lens.

In the first to third inventions, the first aspect
When lens distances between the wide-angle end and the telephoto end of the group and the second group are D12W and D12T, respectively, and lens distances between the wide-angle end and the telephoto end of the second and third groups are D23W and D23T, respectively, 2.5 <( (D12W-D12T) / (D23W-D23T) <20 (2)

Conditional expression (2) is for appropriately setting the air spacing of each lens unit during zooming to reduce the variation in the position of the exit pupil during zooming. In this case, the off-axis principal ray is always incident on a device such as a CCD under a constant condition regardless of magnification, thereby maintaining good image quality over the entire screen.

If the change in the distance between the second unit and the third unit is smaller than the upper limit value of the conditional expression (2), the position of the exit pupil is greatly changed.

When the distance between the first lens unit and the second lens unit becomes smaller than the lower limit, a space for moving each lens unit to secure a predetermined zoom ratio is secured. Is not good because it becomes difficult.

It is more preferable to set the numerical range of the conditional expression (2) as follows: 4.0 <(D12W-D12T) / (D23W-D23T) <15 (2a).

Next, the features of the lens structure of each numerical example will be described. In Numerical Example 1 shown in FIG. 1, the first lens unit L1 is composed of two lenses, a negative lens having a concave surface facing the image surface side and a positive lens having a convex surface facing the object side. Positive lens and negative lens with concave surface facing the object side
The third lens unit L3 is composed of one positive lens whose both lens surfaces are convex, and the fourth lens unit L4 is composed of one positive lens whose convex surface faces the object side. In zooming, the fourth lens unit is fixed. Aperture SP is 2nd
It is provided on the image side of the group and is moved together with the second group during zooming.

In Numerical Embodiment 2 shown in FIG. 2, the first lens unit L1 is composed of two negative lenses having a concave surface facing the image side and a positive lens having a convex surface facing the object side. The third lens unit L3 is composed of a single positive lens having both convex lens surfaces. The third lens unit L3 includes two lenses, a positive lens having both convex surfaces and a negative lens having a concave surface facing the object side. Aperture SP
Is disposed between the positive lens and the negative lens of the second group, and is moved together with the second group during zooming.

In the numerical examples 3 and 4 shown in FIGS.
The second unit L2 has a positive lens whose both lens surfaces are convex and a concave surface facing the object side from two lenses: a negative lens having a concave surface facing the image side of the group L1 and a positive lens having a convex surface facing the object side. The third lens unit L3 is disposed between the positive lens and the negative lens of the second group, and the third lens unit L3 is disposed between the positive lens and the negative lens of the second lens unit. Is moved together with the second group.

In the numerical example 5 of FIG. 5, the first unit L1 is composed of two lenses, a negative lens having a concave surface facing the image surface side and a positive lens having a convex surface facing the object side. The third unit L3 is composed of two lenses, a positive lens having a convex surface and the negative lens having a concave surface facing the object side, and the fourth unit L4 is composed of a convex lens having a convex surface on both sides. Is composed of one positive lens which is directed toward the lens. During zooming, the fourth unit is fixed, and the stop SP is disposed between the positive lens and the negative lens of the second unit, and is moved together with the second unit during zooming.

Next, numerical examples of the present invention will be described. In the numerical examples, Ri is the radius of curvature of the ith lens surface in order from the object side, Di is the ith lens thickness and air spacing in order from the object side, and Ni and νi are the ith lens in order from the object side. Are the refractive index and Abbe number of the glass. Table 1 shows the relationship between the above-mentioned conditional expressions and various numerical values in the numerical examples.
It is shown in FIG.

In the numerical examples, the last two lens surfaces are glass blocks such as a face plate and a filter. The aspherical shape has an X axis in the optical axis direction, an H axis in a direction perpendicular to the optical axis, a positive traveling direction of light, and R is a paraxial radius of curvature.
When A, B, C, D, and E are each aspheric coefficients

[0032]

(Equation 1) This is represented by “E-0X” means “× 10 ^−X ”.

[0033]

[Outside 1]

[0034]

[Outside 2]

[0035]

[Outside 3]

[0036]

[Outside 4]

[0037]

[Outside 5]

[0038]

[Table 1]

[0039]

As described above, according to the present invention, in a negative lead type zoom lens having at least three lens groups preceding a lens group having a negative refractive power, the lens configuration of each lens group is appropriately set. A zoom lens that has a zoom ratio of about 3, a wide angle of view of 65 ° to 75 ° at the wide-angle end, and a high optical performance over the entire zoom range, while shortening the overall length of the lens. Can be achieved.

[Brief description of the drawings]

FIG. 1 is a sectional view of a lens according to a numerical example 1 of the present invention.

FIG. 2 is a sectional view of a lens according to a numerical example 2 of the present invention.

FIG. 3 is a sectional view of a lens according to a numerical example 3 of the present invention.

FIG. 4 is a sectional view of a lens according to a numerical example 4 of the present invention.

FIG. 5 is a sectional view of a lens according to a numerical example 5 of the present invention.

FIG. 6 is an aberration diagram at a wide-angle end according to Numerical Embodiment 1 of the present invention.

FIG. 7 is an intermediate aberration diagram of the numerical example 1 of the present invention.

FIG. 8 is an aberration diagram at a telephoto end in Numerical Example 1 of the present invention;

FIG. 9 is an aberration diagram at a wide-angle end according to Numerical Example 2 of the present invention.

FIG. 10 is a diagram showing aberrations in the middle of the numerical example 2 of the present invention.

FIG. 11 is an aberration diagram at a telephoto end in Numerical Example 2 of the present invention.

FIG. 12 is an aberration diagram at a wide angle end according to Numerical Example 3 of the present invention.

FIG. 13 is an intermediate aberration diagram of the numerical example 3 of the present invention.

FIG. 14 is an aberration diagram at a telephoto end in Numerical Example 3 of the present invention.

FIG. 15 is an aberration diagram at a wide angle end according to Numerical Example 4 of the present invention.

FIG. 16 is an intermediate aberration diagram of the numerical example 4 of the present invention.

FIG. 17 is an aberration diagram at a telephoto end in Numerical Example 4 of the present invention.

FIG. 18 is an aberration diagram at a wide angle end according to Numerical Example 5 of the present invention.

FIG. 19 is an intermediate aberration diagram of the numerical example 5 of the present invention.

FIG. 20 is an aberration diagram at a telephoto end in Numerical Example 5 of the present invention.

[Explanation of symbols]

 L1 First lens unit L2 Second lens unit L3 Third lens unit L4 Fourth lens unit SP Aperture IP image plane d d-line g g-line S Sagittal image plane M Meridional image plane

Claims (11)

[Claims] 1. 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 which performs zooming by moving each lens group toward the object side such that the distance between the first and second groups and the distance between the second and third groups are all reduced, A zoom lens comprising three groups including one positive lens. 2. The zoom lens according to claim 1, wherein said third group positive lens has an aspheric surface. 3. The zoom lens according to claim 1, wherein a lens surface on the image plane side of said third group positive lens is an aspheric surface. 4. From the object side, the zoom lens includes three lens units, 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 which performs zooming by moving each lens group toward the object side such that the distance between the first and second groups and the distance between the second and third groups are all reduced, A zoom lens, comprising two groups of two lenses, a positive lens and a negative lens. 5. The radius of curvature of the lens surface on the object side of the negative lens of the second group is R2 _n1 , and the focal length at the wide-angle end of the entire system is fw.
A zoom lens according to claim 4, characterized by satisfying the -2 <R2 _n1 /fw<-0.5 following condition when the. 6. The zoom lens according to claim 5, wherein the second group has a stop, and the stop moves integrally with the second group during zooming. 7. From the object side, there are three lens groups, a first group having a negative refractive power, a second group having a positive refractive power, and a third group having a positive refractive power, in order from the wide-angle end to the telephoto end. In a zoom lens which performs zooming by moving each lens group toward the object side such that the distance between the first and second groups and the distance between the second and third groups are all reduced, A zoom lens wherein the first and third units have aspheric surfaces. 8. The zoom lens according to claim 7, wherein said first group has at least one positive lens and at least one negative lens. 9. A zoom system according to claim 1, wherein said first lens unit moves with a locus convex toward an image surface side when zooming from a wide-angle end to a telephoto end. lens. 10. The lens intervals at the wide-angle end and the telephoto end of the first and second units are D12W and D12T, respectively, and the lens intervals at the wide-angle end and the telephoto end of the second and third units are D23W and D23T, respectively. 2.5 <(D12W-D12T) / (D23W-D23
The zoom lens according to any one of claims 1 to 8, wherein a condition of T) <20 is satisfied. 11. The zoom lens according to claim 1, further comprising a fourth group fixed during zooming on the image side of said third group.