JPH0470708A - Zoom lens - Google Patents

Abstract

PURPOSE:To make the zoom lens high in power and compact while high optical performance is maintained by employing five-group constitution of positive, negative, positive, positive, and negative elements and specifying a 4th group. CONSTITUTION:The zoom lens consists of a 1st positive group I, a 2nd negative group II, a 3rd positive group III, a 4th positive group IV, and a 5th negative group in order from the object side. For power variation from the short-focus side to the long-focus side, the 1st group I, 3rd group III, and 4th group IV move to the object side respectively and the 4th group IV consists of a positive lens, a positive lens, a positive lens, a biconcave lens, and a positive lens in order from the object side and has at least one aspherical surface. The 4th group needs to have high power for the high-power and compact constitution. For this purpose, the 1st positive element is given high power on the basis of the positive, negative, and positive power arrangement. Further, at least one aspherical surface is provided in the 4th group to compensate aberrations excellently and improve the optical performance. Consequently, the compact constitution and aberration compensation are both realized.

Description

[Detailed description of the invention] of The present invention relates to a zoom lens.

In recent years, the magnification of zoom lenses has increased, and the variable power ratio has increased from 6 to 7.
There are cases where the number is about twice as large (Unexamined Japanese Patent Application Publication No. 1983-1983).
No. 209508, No. 63-189819, 63-
No. 221312.

No. 63-195618, No. 63-20815,
63-221312, 64-7012, etc.).

However, as the magnification of zoom lenses increases, it becomes difficult to correct aberrations, making it inevitable to increase the size of the lens.

Further, in high-magnification zoom lenses, there is a problem that it is not easy to shorten the close-up shooting distance (1 close-up distance) due to difficulties in correcting aberrations and the large size of the front lens.

An object of the present invention is to provide a compact zoom lens with high magnification while maintaining high optical performance, and further to provide a zoom lens with a short close-up distance.

In order to achieve the above object, the zoom lens of the present invention includes, in order from the object side, a positive first group, a negative second group, a positive third group,
Consisting of a positive fourth group and a negative fifth group, when changing magnification from the short focus side to the long focus side, the first, third, and fourth groups move toward the object side, and the fourth group consists of a positive lens, a positive lens, a biconcave lens, and a positive lens in order from the object side, and has at least one aspherical surface. Note that the second group and the fifth group may be fixed or movable during zooming.

The fourth group is a zoom group that plays a decisive role in correcting spherical aberration and coma aberration over the entire focal length range, and also shares the correction of field curvature by changing the relative distance from the third group. . Moreover, in order to achieve high magnification and compactness, the fourth group needs to have strong power. Therefore, the present invention is based on a positive/negative power arrangement, and has a configuration in which the first positive component has strong power. Further, by providing at least one aspherical surface in the fourth lens group, aberrations are corrected well and optical performance is improved.

This makes it possible to achieve both compactness and aberration correction.

It is preferable that the aspherical surface provided in the fourth group satisfies the following conditional expression (2).

dφ/dH<O...■ However, dφ/dH is the rate of change in local power at the height (l()) of the aspherical surface from the optical axis.

This shows that the local power of the aspherical surface becomes more negative as it moves away from the optical axis. 4th with positive power
Positive aberrations (undercorrected spherical aberration and field curvature) occurring in the group tend to become stronger as the distance from the optical axis increases, but this can be alleviated by providing a configuration that satisfies conditional expression (2).

Further, in the present invention, it is also possible to configure the Wj5 group with one negative meniscus lens convex toward the image side. The fifth group plays the role of increasing the telephoto ratio and making the entire optical system compact, so making the fifth group as simple as possible is the purpose of the present invention, which is to achieve high magnification and compactness. It is more effective when achieved.

Now, in general, focusing in a zoom lens is
It is performed by letting out the front ball.

In this case, there is an advantage that the amount of extension is constant regardless of the zooming position, but there is a disadvantage that the close shooting distance cannot be shortened in terms of depiction performance and image plane illuminance.

In other words, when the front lens is extended, the off-axis light beam is eclipsed depending on the amount of extension.

As a result, the illuminance decreases, making it impossible to shorten the close-up shooting distance. Note that if the diameter of the front lens is increased in order to prevent vignetting of off-axis light beams, the lens will become larger.

In the present invention, when focusing from the infinity side to the near side, the third, fourth, and fifth groups are configured to move together toward the image plane side (rear focusing), whereby the front lens is moved out. Since there is no vignetting of the off-axis light beam, it is possible to shorten the close-up shooting distance.

Also, if configured like this (especially at the wide-angle end)
The amount of focusing movement can be reduced, and the entire system can be configured compactly. Furthermore, the field illuminance does not decrease even if the diameter of the front lens is not increased, and the directions of fluctuations in spherical aberration and field curvature are aligned when focusing from infinity to close range, which is advantageous in terms of aberration correction. In other words, in the above-mentioned focusing in which the front lens is moved out, when focusing is performed on a close object point from a focusing state in which spherical aberration and field curvature have been corrected for an object point at infinity, spherical aberration and field curvature are They fluctuate in opposite directions. On the other hand, according to the above-mentioned 3rd to 5th group focusing, focusing is performed on a close object point from a focusing state in which spherical aberration and field curvature are corrected for an object point at infinity. Also, spherical aberration and field curvature vary in the same direction.As a result, aberration correction can be advantageously performed, which is also effective in shortening the close-up shooting distance.

However, in each example, r+(t・1,2,3.,,
, ) is the radius of curvature of the i-th surface counting from the object side, d:
(i・1,2゜3,,,,) indicates the i-th axis top surface interval counting from the object side, and N, (i=1.2,3.,,,)
, ν+(i: 1, 2, 3., , ) is the refractive index of the i-th lens counting from the object side with respect to the d-line.

Show the number to Ara. Further, f indicates the focal length of the entire system, and FNo indicates the open F number.

In each example, the closest distance and focusing movement amount (of the third to fifth groups) for each of the wide-angle end focal length, intermediate focal length, and telephoto end focal length are also shown.

In the examples, a surface with a radius of curvature marked with * indicates that it is an aspherical surface, and is defined by the following equation representing the shape of the aspherical surface.

2, where X: deviation amount from the reference plane in the optical axis direction, reference radius of curvature, height in the direction perpendicular to the optical axis, i-th order aspherical coefficient, quadratic curved surface parameter.

<Example 1> f = 28.8 ~ 80.0 ~ 195.0 F,, = 4.1 ~ 5.5 ~ 5.8 da 1.200 N4 1.111ri000ν
a 41J, U4 15.000 r27-50.848 r+27429.417 d+eo, 200 r+4-85.519 r+e 24.641 d+e3. ooo N91.51728 ν9 6
9.68r+v-105,581 d+vo, 120 r+s 239.384 d+J, 120 r21 197.755 Σd=84.175~97.123~103.263 Valve IJL JL r28:ε:1 A,=-0,42582X 10-' A6=-0.49696X 1O-7 As=-0,77675X 10-' A+e=0.44972X 10-" A+2=-0,32668X 10-th r2s-214
,492 d250.200 r2e 74.062 d262゜000 N+a1.51680 ν+
464.20d+31.20O N8 1.75450 51.57 <Example 2> f=36.0~80.0~195.0 Fso"4.1~5.5~5.8 Month 1 Deaf eye 11L Hi face IL Ku'bl 1 animal shifusan 76.313 1,20O 1,85000 40,04 l3 30.895 47.330 d331.88O 81,67(100 857,07 l3.-293.932 Σd 93.516~ 105.249～111.794夷]]
-傅1し2s :ε :1 A,=0.44923X 10 A6=0.64353X 10 Ae=-0,33889X 10-@A+I! "0.46696X 10-" A12 = 0.23410X 10 <Example 3> f = 38.0 ~ 80.0 ~ 195.0 FNo = 4.6 ~ 5, 5 ~ 5.8 0, 150 dHF), 15Utl~L,'dkoU~1. llJI
Jr2a 45.729 r2895.302 r2@$ -85,000 rz+ 52.452 rs3-43.284 Σd=94.383~105.468~112.378
Difference IJL grandchild 1 r28 :ε:1 Aa=-0,44131x 10-' Ae=-0,31599x 1O-7 A8=-0,16773X 1O-8 A+@=0.46907X 10-" A+2=-0, 39101
), (m=) and (ms) are the first group (1) and the second group (
■), Group 3 (■), Group 4 (IV), and Group 5 (V)
The movement from the widest angle end (w) to the far end (T) of the eel is schematically shown. Further, (A) in each figure indicates an aperture.

In Example 1, the positive first group (I) consists of, in order from the object side, a negative meniscus lens concave toward the image side, a biconvex positive lens, and a positive meniscus lens convex toward the object side; (IF) is a negative meniscus lens concave to the image side, a positive meniscus lens convex to the image side, a negative biconcave lens, in order from the object side.
It consists of a positive meniscus lens that is convex on the object side and a negative meniscus lens that is concave on the object side.The positive third group (I [I) consists of, in order from the object side, a diaphragm 9 double-convex positive lens, and a positive meniscus lens that is convex on the object side. The lens consists of a positive meniscus lens convex to the object side and a negative meniscus lens concave to the object side, with a positive fourth group (
IV) is a biconvex positive lens, a biconvex positive lens, and a negative meniscus lens concave on the object side, in order from the object side.

Consists of a biconcave negative lens and a biconvex positive lens, with a negative fifth lens.
Group (V) consists of a negative meniscus lens convex toward the image side. Note that the object-side surface of the third lens from the object side of the fourth group (IV) is an aspherical surface.

In Examples 2 and 3, the positive first group (I) is a negative meniscus lens concave from the object side to the image side.

Consisting of a positive lens convex to the object side and a positive meniscus lens convex to the object side, the negative second group (II) includes, in order from the object side, a negative meniscus lens concave to the image side, a positive meniscus lens convex to the image side, Consisting of a biconcave negative lens, a biconvex positive lens, and a biconcave negative lens, the positive third group (III) stops in order from the object side, a positive meniscus lens convex to the object side, a biconvex positive lens, It consists of a biconvex positive lens and a concave negative meniscus lens on the object side, and the positive fourth group (IV) is a biconvex positive lens in order from the object side.

Biconvex positive lens, positive meniscus lens convex on the image side.

Consists of a biconcave negative lens and a biconvex positive lens, with a negative fifth lens.
Group (V) consists of a negative meniscus lens convex toward the image side. Note that the object-side surface of the third lens from the object side of the fourth group (IV) is an aspherical surface.

In Examples 1 to 3, the fifth group (V) is linked to the third group (III), and moves together when changing power from the wide-angle side to the telephoto side. This is to simplify the lens barrel configuration. In addition, as shown in FIGS. 1 to 3, the third group (I
II) to fifth group (V) move together toward the image plane during focusing from the infinity side to the near side.

4 to 6 are aberration diagrams for an object point at infinity corresponding to Examples 1 to 3, respectively, and FIGS. 7 to 9 are aberration diagrams for the nearest object point corresponding to Examples 1 to 3, respectively. It is an aberration diagram (at close shooting distance) for an object point. In each figure,
(W) is the focal length at the wide-angle end.

(M) shows the aberration at the intermediate focal length, and (T) shows the aberration at the telephoto end focal length. Furthermore, the solid line (d) represents the aberration for the d-line, the broken line (SC) represents the sine condition, and the broken line (DM) and solid line (DS) represent astigmatism on the meridional plane and sagittal plane, respectively. 6. As explained above, according to the present invention, in order from the object side, the positive first group, the negative second group, the positive third group,
Consisting of a positive fourth group and a negative fifth group, when changing magnification from the short focus side to the long focus side, the first, third, and fourth groups move toward the object side, and the fourth group consists of a positive lens, a positive lens, a biconcave lens, and a positive lens in order from the object side, and has at least one aspherical surface, so it is possible to realize a compact zoom lens with high magnification while maintaining high optical performance. I can do it.

Furthermore, when the aspherical surface in the fourth group is configured to satisfy the conditional expression (2), the above optical performance can be maintained at a higher level.

In addition, when the fifth group is composed of one negative meniscus lens convex toward the image side, it is possible to advantageously achieve high magnification and compactness.

Furthermore, when focusing from the infinity side to the near side, the third, fourth, and fifth groups are configured to move together toward the image plane side, thereby realizing a zoom lens with a short close shooting distance. I can do it.

[Brief explanation of drawings]

FIG. 1, FIG. 2, and FIG. 3 are lens configuration diagrams corresponding to Examples 1 to 3 of the present invention, respectively. 4, 5, and 6 are aberration diagrams for an object point at infinity corresponding to Examples 1 to 3 of the present invention, and FIGS. 7, 8, and 9 are aberration diagrams, respectively, according to the present invention. Example 1 of the invention
It is an aberration diagram for the nearest object point corresponding to ~3. Applicant Minolta Camera Co., Ltd.

Claims (4)

[Claims] (1) Consists of a positive first group, a negative second group, a positive third group, a positive fourth group, and a negative fifth group in order from the object side, and zooms from the short focus side to the long focus side. In this case, the first group, the third group and the fourth group
A zoom lens characterized in that each of the groups moves toward the object side, and the fourth group consists of a positive lens, a positive lens, a biconcave lens, and a positive lens in order from the object side, and has at least one aspherical surface. (2) The zoom lens according to claim 1, wherein the aspherical surface in the fourth group satisfies the following condition; dφ/dH<0, where dφ/dH: from the optical axis of the aspherical surface. is the rate of change of local power at the height (H) of . (3) The zoom lens according to claim 2, wherein the fifth group comprises one negative meniscus lens convex toward the image side. (4) The zoom lens according to claim 3, wherein the third, fourth, and fifth groups are moved together toward the image plane during focusing from the infinity side to the near side.