JPH0380210A - Zoom lens - Google Patents

Abstract

PURPOSE:To obtain the zoom lens which has a large aperture ratio and high variable power ratio while including a wide angle of view by regulating the refracting power distribution of respective lens groups with specific conditions. CONSTITUTION:This zoom lens is provided, successively from an object side, with the 1st lens group G1 having a negative focal length, the 2nd lens group G2 having a positive focal length, the 3rd lens group G3 having a positive focal length, the 4th lens group G4 having a negative focal length, the 5th lens group G5 having a positive focal length. The conditions expressed by equation I are satisfied when the focal length at the wide angle end of the zoom lens is desig nated as fW and the focal length at the i-th lens group as fi. The zoom lens which has the large aperture and has the excellent image forming performance from the wide angle end to the telephoto end is obtd. in this way.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a zoom lens, particularly a zoom lens that has a wide angle of view with a maximum angle of view of about 74° or more, a high zoom ratio of about 3x, and an F number of 2.
．． The present invention relates to a zoom lens having a large aperture ratio of about 8.

[Conventional technology]

Conventionally, zoom lenses including a wide-angle range include a first lens group G1 having a negative refractive power and a second lens group having a positive refractive power.
Many two-group zoom lenses consisting of lens group G have been proposed and are in practical use.

However, with this two-group zoom lens, it is extremely difficult to achieve both high magnification and a large aperture ratio, and a typical lens has a zoom ratio of 2x and an F number of 3.5. The mainstream was moderate.

Therefore, in recent years, the first lens group G+ having a negative refractive power and the second lens group G+ having a positive refractive power! , a third lens group G having negative refractive power, and a fourth lens group G having positive refractive power.
A four-group zoom lens consisting of lens group G is disclosed in, for example, Japanese Patent Laid-Open No. 62-63909 and Japanese Patent Laid-Open No. 63-24151.
This is proposed in Publication No. 1, etc.

[Problem to be solved by the invention]

However, in the methods proposed in the above-mentioned Japanese Patent Application Laid-Open No. 62-63909, although they achieve an angle of view of 74" or more at the wide-angle end and a zoom ratio of approximately 3x, the F number is 3. The brightness is about 5 to 4.5, and it is hard to say that it is sufficient in terms of brightness.

In addition, although the device proposed in Japanese Patent Application Laid-open No. 63-241511 has a large aperture with an F number of 2.8, the zoom ratio is about 2 times, and the angle of view at the wide-angle end is Since the angle is narrow at 63°, this also cannot be said to be sufficient.

Therefore, an object of the present invention is to provide a large aperture ratio and a high variable magnification ratio that includes a wide angle of view with a maximum angle of view of 74 degrees or more, has an F number as high as 2.8, and has a zoom ratio of about 3 times. Our goal is to provide a zoom lens with a wide range of features.

[Means to solve the problem]

In order to achieve the above object, the present invention, as shown in the first embodiment of the present invention, includes, in order from the object side, a first lens group G1 having a negative focal length and a first lens group G1 having a positive focal length. a second lens group G, a third lens group G having a negative focal length, and a fourth lens group G4 having a positive focal length;
a fifth lens group G having a positive focal length, and when zooming from the wide-angle end to the telephoto end, while the air distance between the first lens group G1 and the second lens group G decreases, the second lens group G, and the third lens group G,
The air distance between the third lens group G and the fourth lens group G decreases, and the air distance between the fourth lens group G4 and the fifth lens group Gs increases. will expand.

Based on this basic configuration, let fv be the focal length at the wide-angle end of the zoom lens, and let fv be the focal length of the fifth lens group.
When l, the following conditions are satisfied.

-2,1<f, /fW<-1,8(1)1.3<ft
/f, <1.7 (2)-2,1<fs
/fw <-1, 1 (3) 1.7 < f, /rv <2
．． 8 (4)3<fs/f,<9
(5) In order to achieve sufficient aberrations, the axial distance between the rear principal point of the fifth lens group at the wide-angle end and the front principal point of the j-th lens group should be D++w, and the distance between the fifth lens group and the front principal point of the When the axial distance between the rear principal point of the lens group and the front principal point of the j-th lens group is DIIT, it is desirable to satisfy the following conditions.

o, 5<Dot7fW<o, 9 (6) 0.
52<Dt*v/fvt<0.8 (7
)0.23<D$47/fw<9.4
(8) [Function] Basically, the zoom lens of the present invention has a first lens group G.
The zoom ratio from 1 to 4th lens group G4 reaches 3x,
A configuration in which a wide angle of view and a large aperture can be achieved in the fifth lens group G, which has positive refractive power and is located on the image side of the fourth lens group G, while providing imaging performance with aberrations corrected as much as possible. have.

However, as the aperture ratio is increased, various aberrations tend to worsen, and in particular, the occurrence of spherical aberration becomes serious. Further, as the angle of view is widened, various aberrations tend to worsen as with the case of increasing the aperture ratio, but there is a risk that off-axis aberrations in particular will worsen.

Therefore, in the present invention, in order to achieve both a large aperture ratio and a wide angle of view while maintaining a good aberration balance, we set the condition (1) for optimal refractive power distribution in each lens group. - (5).

Condition (1) defines the optimal focal length range of the first lens group GI. This condition is a condition for achieving a wide angle of view and a high zoom ratio while maintaining particularly good aberration correction.

If the upper limit of condition (1) is exceeded, the refractive power of the first lens group G1 becomes strong, which is advantageous for achieving a high zoom ratio, but it becomes difficult to correct aberrations such as spherical aberration and curvature of field, which is rather undesirable. . Conversely, if the lower limit of condition (1) is exceeded, the first
The refractive power of the lens group G+ becomes weaker, which is advantageous in correcting aberrations, but it becomes difficult to achieve a wide angle of view and a high zoom ratio.

Condition (2) is the second lens group G, mainly for good correction of spherical aberration when increasing the aperture.

This defines the range of the optimal focal length.

If the lower limit of condition (2) is exceeded, the refractive power of the second lens group G becomes excessive, resulting in insufficient correction of spherical aberration, especially spherical aberration at the telephoto end, making it difficult to correct this aberration. On the other hand, if the upper limit of condition (2) is exceeded, the refractive power of the second lens group G becomes weaker, which is advantageous for aberration correction, especially spherical aberration correction, but it is not possible to achieve high zoom while keeping the total length compact. In order to increase the ratio, the distance between the principal points of the second lens group G and the third lens group G at the wide-angle end becomes shorter, which is not preferable because there is a possibility that mechanical interference will occur.

Condition (3) defines the optimal focal length range of the third lens group G3 for good correction of various aberrations including spherical aberration.

If the upper limit of condition (3) is exceeded, the third lens group G.

The refractive power of the lens becomes excessive, making it extremely difficult to achieve a good aberration balance among various aberrations. In particular, at the wide-angle end, the upper light beam of the off-axis light beam is subjected to a strong diverging effect, resulting in outward coma aberration. On the other hand, if the lower limit of condition (3) is exceeded, the third lens group G.

The refractive power of the lens becomes weaker, which is advantageous in correcting aberrations, but this is not preferable because it increases the overall length at the wide-angle end, which goes against compact design.

Condition (4) relates to compactness of the lens system and good correction of various aberrations.

Exceeding the upper limit of condition (4) weakens the refractive power of the fourth lens group G4, which is advantageous for correcting various aberrations, but is not preferable because it increases the total length of the lens system at the wide-angle end. Conversely, if the lower limit of condition (4) is exceeded, the fourth lens group G
4 becomes strong, the aberration balance of various aberrations is greatly disrupted, and it becomes difficult to obtain good imaging performance.

Condition (5) is for obtaining sufficient back focus while achieving a large aperture ratio.

If the upper limit of condition (5) is exceeded, the refractive power of the fifth lens group G becomes weaker, which is advantageous in securing a sufficient back focus, but the light beam passing through the fourth lens group G becomes convergent. This weakens the effect of increasing the aperture ratio, making it difficult to increase the aperture ratio. Therefore, the fourth lens group G
If an attempt is made to secure a sufficient amount of light by increasing the refractive power of the lens, various aberrations will worsen, making it difficult to obtain good imaging performance.

On the other hand, if the lower limit of condition (5) is exceeded, the refractive power of the fifth lens group G6 becomes strong, which is advantageous for increasing the aperture ratio, but -
It becomes difficult to secure the back focus for an eye reflex camera.

Generally speaking, in order to achieve excellent imaging performance while achieving a high zoom ratio with a large aperture ratio and wide angle of view, it is necessary to increase the number of lenses constituting each lens group. We have no choice but to overcome this by increasing the number of cases.

However, if priority is given to making the overall length of the lens system compact, it becomes difficult to secure sufficient air space for zooming as the number of lenses constituting each lens group increases.

Therefore, in order to achieve both a compact overall length of the lens system and a high zoom ratio, the axial distance between the rear principal point of the fifth lens group and the front principal point of the j-th lens group at the wide-angle end must be set to D.
++w, and when the axial distance between the rear principal point of the fifth lens group and the front principal point of the j-th lens group at the telephoto end is DIIT, it is more desirable to satisfy the following conditions.

0, 5<DIIT/fw<0.9'(
6) 0.52<D*s-/fv<0.8
(7) 0.23<D347/fv<0.4
(8) If the lower limits of each of the above conditions (6) to (8) are exceeded, it becomes difficult to ensure an air gap between each lens group, and it becomes difficult to achieve a high zoom ratio. In other words, if you try to forcefully increase the zoom ratio, there is a risk that mechanical interference will occur in each lens group, which is undesirable. On the other hand, if the upper limits of each of conditions (6) to (8) are exceeded, it becomes difficult to make the overall length of the lens system compact.

Now, in order to correct spherical aberration and chromatic aberration in a better balance, the second lens group G, in order from the object side, consists of a biconvex positive lens component, a negative lens L28, and a positive lens L28.
0. A cemented positive lens component L! ! It is desirable to have a positive lens component L□. At this time, the positive lens component L located on the image side of the second lens group! When the radius of curvature on the object side and image side of is ra and rb, respectively, it is desirable to satisfy the following condition (9).

If the lower limit of rb ra condition (9) is exceeded, the negative spherical aberration generated on the image side surface of the positive lens component L□ becomes excessive, making it difficult to achieve a large aperture ratio. Conversely, if the upper limit of condition (9) is exceeded, the second lens group G! This is not preferable because it becomes difficult to secure an air gap between the lens group G and the third lens group G, and mechanical interference occurs.

〔Example〕

The zoom lenses according to the embodiments of the present invention all have a focal length f of 28.8 to 83.2, and an angle of view at the wide-angle end of 74.
Even though the brightness exceeds 2.8 degrees, the brightness of F number 2.8 can be ensured.

FIG. 1 and FIG. 3 show the first and second embodiments according to the present invention, respectively.
FIG. 2 is a lens configuration diagram of an example.

The specific lens configuration in the first embodiment is that the first lens group G1 includes, in order from the object side, a biconvex positive lens Lll;
A negative meniscus lens L18 with a convex surface facing the object side, a cemented negative lens Lll which is made of a cemented negative lens and a positive lens and has a surface with a stronger curvature toward the image side as a whole, and a positive meniscus lens L14 with a convex surface facing the object side. and the second
The lens group G is a double-convex positive lens L□, and a cemented positive lens L formed by cementing a negative lens and a positive lens! ! , and a positive lens L with a surface of stronger curvature facing the object side. The third lens group G is composed of a cemented negative lens L0 which is made of a positive lens and a negative lens and has a biconcave shape as a whole, and a negative lens Lo which is biconcave. , a positive meniscus lens L41 with a convex surface facing the image side, and a cemented positive lens L that is made of a cemented positive lens and a negative lens and has a biconvex shape as a whole. The fifth lens group G is composed of a biconvex positive lens L□.

The specific lens configuration in the second example basically has the same lens configuration as the first example, but the fifth example has the same lens configuration as the first example.
The lens group G is composed of a cemented positive lens L1 consisting of a negative lens and a positive lens, and this cemented positive lens L1 has a meniscus shape with a convex surface facing the image side.

Now, in each of the embodiments of the present invention, a wide angle of 74'' or more is attempted, but at this time, especially at the wide-angle end, negative distortion is large in the first lens group G1 having negative refractive power. Therefore, in order to properly correct this, an aspherical surface is provided in the first lens group.

In Table 19 and Table 2 below, specifications for the first and second embodiments of the present invention are listed. The numbers on the left side of the table represent the order from the object side, r is the radius of curvature of the lens, d is the lens thickness and distance between lens surfaces, Abbe number, and refractive index n is the d-line (λ = 587.6 nm). ) is the value for

Note that an aspherical surface is generally expressed by the following formula.

however, h: Height from the optical axis.

X(h): Distance in the optical axis direction from the apex of the aspherical surface to the tangential plane at the height h from the optical axis.

r: Paraxial radius of curvature.

k: conic constant.

C2t: 21st-order aspheric coefficient.

Vga old low cIJ ma's Φ g's Φ l eJ cIJ CJ k OJ ('J C'
Jt! J eJ Ct11! If similar old. -a), 1! ! Total 1 & 111 - Pressure Fluorescence Table 3 lists the values corresponding to the conditions for each example according to the present invention.

In addition, in FIGS. 2 and 4, the first and second
Aberrations for Examples are shown. In each figure (a
) shows various aberrations in the shortest focal length state at the wide-angle end, (b) in the intermediate focal length state, and (C) in the longest focal length state at the telephoto end.

Regarding astigmatism in each aberration diagram, the meridional image plane is indicated by M1, and the sagittal image plane is indicated by S.

Comparison of each aberration diagram shows that even though the maximum angle of view is 74° or more, the F number reaches 2.8, and the zoom ratio is about 3x, It is clear that the lens has extremely excellent imaging performance over the telephoto end.

It goes without saying that if an aspherical surface is appropriately provided in each lens group in the present invention, further compactness and higher performance can be expected.

〔Effect of the invention〕

As described above, according to the present invention, although the maximum angle of view includes a wide angle of view of 74 degrees or more and has a zoom ratio of about 3 times, it has a large aperture with an F number as high as 2.8. This makes it possible to create a zoom lens with extremely excellent imaging performance from the wide-angle end to the telephoto end.

[Brief explanation of drawings]

FIG. 1 and FIG. 3 show the first and second embodiments according to the present invention, respectively.
FIG. 2 is a lens configuration diagram of an example. FIG. 2(a) is a diagram of various aberrations in the shortest focal length state at the wide-angle end in the first embodiment, FIG. 2(b) is a diagram of various aberrations in the intermediate focal length state in the first embodiment, and FIG. C1 is a diagram showing various aberrations in the longest focal length state at the telephoto end in the first embodiment.
a) is a diagram of various aberrations in the shortest focal length state at the wide-angle end in the second embodiment, FIG. 4(b) is a diagram of various aberrations in the intermediate focal length state in the second embodiment, and FIG. FIG. 6 is a diagram of various aberrations in the longest focal length state at the telephoto end in Example 2; [Explanation of symbols of main parts] G1...first lens group, G1...second lens group G1...
Third lens group, G...Fourth lens group Gs...Fifth
lens group

Claims (1)

[Claims] 1) In order from the object side, a first lens group G_1 having a negative focal length and a second lens group G_2 having a positive focal length.
, a third lens group G_3 having a negative focal length, a fourth lens group G_4 having a positive focal length, and a fifth lens group G_5 having a positive focal length, from the wide-angle end to the telephoto end. During zooming, while the air distance between the first lens group G_1 and the second lens group G_2 decreases, the air distance between the second lens group G_2 and the third lens group G_2 increases, and While the air distance between the third lens group G_3 and the fourth lens group G_4 is reduced, the air distance between the fourth lens group G_4 and the fifth lens group G_5 is increased, and the focal length at the wide-angle end of the zoom lens is increased. A zoom lens that satisfies the following conditions, where f_w is the focal length of the i-th lens group and f_1 is the focal length of the i-th lens group. -2.1<f_1/f_w<-1.8 (1) 1.3<f
_2/f_w<1.7(2) -2.1<f_2/f_w<-1.1(3) 1.7<f
_4/f_w<2.8(4) 3<f_5/f_w<9(5) 2) The axial distance between the rear principal point of the i-th lens group and the front principal point of the j-th lens group at the wide-angle end is D_i_j_w When the axial distance between the rear principal point of the i-th lens group and the front principal point of the j-th lens group at the telephoto end is D_i_j_T, the following condition is satisfied. The zoom lens described in item 1. 0.5<D_1_2_T/f_w<0.9(6)0.5
2<D_2_3_w/f_w<0.8(7)0.23<
D_2_4_T/fw<0.4(8)