JPH02284109A - Small-sized wide angle zoom lens - Google Patents

Abstract

PURPOSE:To provide the zoom lens which has >=35 deg. angle of view at a wide angle end and about 2 times variable power ratio with the constitution of the simple two- group zoom by constituting the zoom lens of a 1st lens group having a positive focal length and a 2nd lens group having a negative focal length and specifying the kinds and focal lengths of the lenses of the respective lens groups. CONSTITUTION:The 1st lens group of the two-group zoom lens which varies the power from the short focus end to the long focus end by shortening the spacing between the 1st lens group and the 2nd lens group consists, successively from an object side, of the positive lens, at least one negative lens and >=2 pieces of the positive lenses. The 2nd lens group is disposed, successively from the object side, with the positive lens, the convex face of which is directed to the image side, at least one negative lens and the negative meniscus lens, the convex face of which is directed to the image side, and disposed on the nearest image side of the 2nd lens group. The lens is so constituted as to satisfy condition equations of 1.0<fw/f<1.3, ¦f2/f1¦<1.1 when the focal length of the 1st lens group is designated as f1, the focal length of the 2nd lens group as f2 and the focal length of the entire system at the short focus end as fw. The angle of view of at the wide angle end is specified to about 37 deg. and the variable power ratio to about 2 times in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a compact zoom lens, and particularly to a zoom lens suitable for a lens-shutter type compact camera.

(Prior art) In recent years, compact cameras equipped with zoom lenses have become mainstream.Zoom lenses for compact cameras are not only compact, but also have a back focus similar to that used in reflex cameras. There are no restrictions on the length of the lens, and the total length including the back focus is required to be small. It is also required to be low cost. As zoom lenses used for such purposes, Japanese Patent Laid-Open No. 57-201213 and Japanese Patent Laid-open No. 58
-224322, JP-A-62-113120, JP-A-63-113120, and JP-A-6
One disclosed in Japanese Patent No. 3-148223 is known.

(Problem to be solved by this invention) Zoom lenses for compact cameras are required to include a wide angle, but these conventional zoom lenses have an angle of view of 32° at the wide angle end. The angle of view was narrow at about 28 degrees, and although the angle of view was 35 degrees or more, it was a three-group zoom system and had a complicated mechanism, so it did not necessarily meet the requirements.

The present invention aims to provide a wide-angle zoom lens that has a simple two-group zoom configuration, has an angle of view of 35 degrees or more at the wide-angle end, and has a variable power ratio of about 2x.

(Means for solving the problems) In order to achieve the above object, the zoom lens of the present invention has the following features:
A first lens group with a positive focal length and a second lens group with a negative focal length.
In a two-group zoom lens that is composed of a lens group and that changes magnification from a short focal length end to a long focal length end by shortening the distance between the first lens group and the second lens group, the first lens group is , consisting of a positive lens, at least one negative lens, and two or more positive lenses, wherein the second lens group includes, from the object side, a positive lens with a convex surface facing the image side, at least one negative lens, and A negative meniscus lens with a convex surface facing the image side is disposed closest to the image side of the second lens group, and the focal length of the first lens group is fl, and the focal length of the second lens group is f2.

When the focal length of the entire system at the short focus end is fw, the following conditional expression is satisfied.

1.0<fw/f, <1. a ■If, /f□
l<1.1 0 More specifically, the first lens group consists of, in order from the object side, a positive meniscus-shaped first lens with a convex surface facing the object side, a negative second lens, and a negative third lens. Consisting of a convex fourth lens and a biconvex fifth lens, the second lens group includes, in order from the object side, a positive sixth lens with a convex surface facing the image side, a negative seventh lens, and a negative seventh lens with a convex surface facing the image side. It is preferable that the negative third lens and the biconvex fourth lens are bonded together to form a positive lens.

Further, the above lens preferably satisfies the following conditional expression.

(n4+n5)/2<1.65 ■C, -
C3 〉10 ■(n, + n*)
/ 2 > 1, 7 ■(Y, +νm
) /2>44 ■Here n4. No
nl and nl are the fourth, fifth, seventh . The refractive index of the 8th lens is
These are the Abbe numbers of the fourth, seventh, and eighth lenses.

(Function) Unlike photography lenses for single-lens reflex cameras, lens shutter cameras have no back focus restrictions. Taking advantage of this condition, the positive first lens group is used to reduce the total length of the lens including the back focus. This is a telephoto type two-group zoom lens consisting of a negative second lens group. If this type of lens configuration is adopted, the back focus at the short focal length end will be shortened, but the overall length can be made extremely short, making it ideal for lens-shutter cameras characterized by compactness. Further, in this type of zoom lens, the image-side principal point of the first lens group and the object-side principal point of the second lens group are close to each other at the long focal length end. Therefore, from the object side, a positive lens,
By arranging two or more negative lenses after that and further arranging two or more positive lenses after that, the image-side principal point of the first lens group is located as far back as possible from the lens,
This ensures that a sufficient zoom ratio can be obtained.

Generally, when trying to widen the angle of view to 35@ or more, it becomes difficult to correct off-axis aberrations, and this type of zoom lens is no exception. As previously mentioned.

In order to ensure a variable magnification ratio, the refractive power is concentrated on two or more positive lenses on the image side in the first lens group, so there is significant deterioration in off-axis aberrations such as coma and curvature of field. Therefore, if the refractive power of the first lens group is set small so as to satisfy the condition (2), it becomes easy to correct these off-axis aberrations.

In addition, with this type of zoom lens, both the third and second lens groups move forward at the long focal length end, and the difference in back focus between the short focal length end and the long focal length end is very large, resulting in a change in 1x chromatic aberration. The fluctuation due to doubling becomes large. When the focal length of the second lens group is f2 and the focal length of the entire system at the long focal length end is fT, the back focus difference R'C is calculated by the following equation.

ΔRC= (ft fw)f, /f1(fy-fw
) is a constant determined by the lens specifications, so △RC
In order to make small, it is necessary to make l f2/ f□1 small, so fl, f
Set 2.

In this way, the difference in chromatic aberration of magnification during zooming can be reduced, and the chromatic aberration of magnification can be favorably corrected from the short focal length end to the long focal length end.

Further, in the zoom lens of the present invention, the first lens group has a positive meniscus shape with a convex surface facing the object side in order from the object side.
lens, negative second lens, negative third lens and biconvex fourth lens
It is composed of a lens and a biconvex fifth lens, and the second lens group has a positive sixth lens with its convex surface facing toward the image side from the object side, and a negative seventh lens.

By configuring the eighth lens in a meniscus shape with a convex surface facing the image side, it is possible to obtain a small, wide-angle zoom lens in which off-axis aberrations are well corrected.

Furthermore, by bonding the negative third lens and the biconvex fourth lens together, astigmatism and chromatic aberration can be favorably corrected.

(2) If the upper limit of the equation is exceeded, or if the lower limit of the equation 0 is subtracted, the Petzval sum becomes negative and the image plane becomes over. ■
If the lower limit of the formula is exceeded, the axial chromatic aberration and lateral chromatic aberration generated in the first lens group become undervalued, and the amount of correction in the second lens group must be increased. Due to the difference in back focus at the long focal length, if lateral chromatic aberration is properly corrected at the short focal length, it will be too much at the long focal length. Equation 0 is a condition related to the amount of correction of chromatic aberration in this second lens group.

If the lower limit of formula 0 is exceeded, the amount of correction in the second lens group becomes excessive, making it difficult to satisfactorily correct lateral chromatic aberration over the entire zoom range.

(Example) In the following, third, third, and fourth examples of the present invention that satisfy each of the above conditions will be described.
+, It is a wide-angle zoom lens with a variable magnification ratio of approximately 1.9 times from the angle of view of 36.7" to the long focal length end of 55II11, and it excellently corrects off-axis aberrations including lateral chromatic aberration.Second
The embodiment has a zoom ratio of 2 times from 29 mm at the wide-angle end to 59 m at the long focal length end.

In the fifth embodiment, the third lens and the fourth lens are not laminated,
This is an example with a slight air gap. This embodiment also corrects off-axis aberrations well.

A zoom lens with a 2x zoom ratio and increased brightness compared to other embodiments is realized.

Note that focusing according to the present invention is performed by extending the first lens group. The amount of extension is less than the total extension, making it ideal for autofocus mechanisms such as lens-shutter cameras. Furthermore, when taking macro photography of a subject at a close distance, simply extending the first lens group tends to result in an under meridional image plane, but the distance between the first and second lenses, or the distance between the second lens and By extending the first lens group while leaving an interval between the third lenses, fluctuations in the image plane can be suppressed and good macro photography can be performed.

In addition, each symbol in Table 1 is as follows: R is the radius of curvature of each refractive surface, D is the distance between the refractive surfaces, Nj is the refractive index of the lens material, ν is the Atsube number, f is the focal length of the entire lens system, and ω is the Half angle of view, F
indicates the F number.

1st example f: 29.02-54.85 F=3.5-6.
6ω=36.7'~21.52' RD N-ν 4 1 21.639 2.60 1.59270
35.32 4g, 912 2.80 3 -22.037 0.80 1.83400
37.24 55.905 3.00 5 23.832 4.50 1.80610
40.96 9.950 4.10 1.612
72 58.77 -44.581 0.10 29.104 -29.104 -39.664 -20.129 -66.333 255.812 -12.297 -42.017 2.50 Variable 3.00 0. 50 0.80 6.30 1.00 1.61272 1.54814 1.71300 1.71300 58.7 45.8 53.9 53.9 Variable interval 29, 02 39, 80 54, 85 13, 17 7, 55 3, 40 fw/ft=1.18 1 f2/f,
I = 1.0(n4+ns)/2=1.6127
2 v4− v, = 17.8 (n, + nl)/
2=1.713 (W, +V5)/2=53.9 Second Example f=29.31~58.71 ω=36.43'''~20.22'' F=3.05~6. 10 18.336 40.501 -17.626 -108.175 -99.671 14.897 -18.880 26.263 -25.905 -59.177 -20.344 -38.273 408.337 -12 .988 -35.792 2.00 2.80 0.70 0.60 4.40 4.00 0.10 2.50 Variable 3.00 0.50 0.80 6.30 0.8O N-ν - 1,5927035,3 1,83400 37,2 1,8044039,6 1,5688356,3 1,58913 61,2 1,60342 38,0 1,77250 49,6 1,77250 49,6 Variable interval 29, 32 43, 36 58, 71 13, 80 7, 81 3, 50 fw/f, = 1. ．． 20 1 f, /
f, I = 1.02(n4+ns)/2=1.
580 ν, -v, = 16.7 (n 7+
n s)/2= 1,7725 (Schiff+ν5)/2
= 49.6 Third Example f = 29.02 ~ 54.94 (, l: 36.7" ~ 21.49" 1 19
．． 376 2 45.315 3 -20.700 4 57.415 5 28.158 6 10.422 ? -35,804 831,637 9-25,919 10-50,712 11-19,025 12-32,575 2,30 2,80 0,70 3,00 2,80 4,00 0,10 2, 50 Variable 3.00 0.50 0.80 F=3.17~6.0O Nj νd 1.59270 35.3 1.83400 37.2 1.80610 40,9 1.62299 58.2 1.58913 61 .2 1.60342 38.0 1.77250 49.6 -431.777 Variable interval 1], 2.123 6.30 0.80 3,. 72000 52.0 -37,062 29.02 40, 00 54.94 13, 15 7, 70 3, 76 fW/f, = 1.19 1 f2/f, l
= 0.98 (n, + n S)/2 = 1.60
6 ν4−ν, = 17.3(nt + n
i)/2=1.746 (Schiff+ν.)/2=50.
8 Fourth Example f = 29.07 ~ 54.87 ω = 36.7° ~ 21.5° 1 18.563 2 41.698 3 -22.875 4 36.874 2.60 2.80 0. 80 3.00 F = 3.50 ~ 6.61 N - 1.59551 39.2 1.83400 37.2 25.791 10.774 -35.442 29.358 -28,668 -30.235 -17,712 -57,606 -2074.460 -11,798 -37.392 3.36 4.10 0.10 2.50 Variable 3.00 0.50 6.30 1.00 1.805+8 25. 4 1.60342 38.0 1.61272 58.7 1.56732 42.8 1.71300 53.9 1.71300 53.9 Variable interval 29, 07 39, 80 54, 87 13.53 7, 72 3, 40 fw/f1=1,17 1 f,/f11
= 1.04(n4+ns)/2=1.608
v4v,=12.6(n 7+ na>72=
1.713 (Schiff + ν8)/2 = 53" 5th Example f = 29.16 ~ 58.46 ω = 36.6" ~ 20.30' 21.259 50.046 -18.754 -1861.810 45.634 15.968 18.904 -26.093 38.473 -26.656 -37.880 IL591 -37.818 -2790.920 -12.133 -29.207 2.00 2.80 1.50 1.50 2.70 0.50 4.00 0.10 2.50 Variable 3.00 0.50 0.80 6.30 0.80 F=3.04~6.09 N-ν − 1,5927035 ,3 1,83400 37,2 JO440 39,6 1,60311 60,7 1,60311 60,7 1,62004 36,3 1,77250 49,6 Variable interval f D929.16
13.82 41.29 7.77 58.46 3.50 fe, / f, = 1,20 1 f2/
f□l = 1.02(n4+ns)/2=1.6
12 V, v5:2], 1(nt
+ n s)/2=1.7725 (v t +
v Il)/2=49.6 (Effects of the Invention) As shown in the examples and the aberration diagrams, the compact wide-angle zoom lens of the present invention has a simple configuration of two-group zoom, and has a half-field at the wide-angle end. Including a wide angle with an angle of approximately 37°, 2
Even though it is a zoom lens with a variable power ratio of around 100%, aberrations are well corrected over the entire variable power range. In addition, since the change in bank focus due to magnification is small, the lens barrel can be made compact, making it ideal for lens shutter cameras.

[Brief explanation of drawings]

1, 4, 7, 10, and 13 are cross-sectional views of the first to fifth embodiments of the present invention, respectively, and FIG. 1 shows the zoom lens of the present invention. FIG. 2, FIG. 5, FIG. 8, FIG. 11, and FIG. 14, which also show movement trajectories for zooming, are aberration diagrams of the first to fifth embodiments of the present invention, respectively. In each aberration diagram, (A) is the short focus end, (B) is the black dot,
(C) is an aberration diagram at the long focal point end. Figures 3 and 6. 9, 12, and 15 respectively show the first embodiment of the present invention.
- It is a magnification chromatic aberration diagram of the fifth example, and corresponds to (A), (B), and (C) in the aberration diagram in order from the right side.

Claims (4)

[Claims] (1) Consisting of a first lens group with a positive focal length and a second lens group with a negative focal length, the first lens group and the second lens group have a negative focal length.
In a two-group zoom lens that changes magnification from a short focus end to a long focus end by shortening the distance between the lens groups, the first lens group includes, from the object side, a positive lens, at least one negative lens, and two lenses. The second lens group includes, from the object side, a positive lens with a convex surface facing the image side, at least one negative lens, and a convex surface facing the image side closest to the image side of the second lens group. When a negative meniscus lens is arranged, the focal length of the first lens group is f_1, the focal length of the second lens group is f_2, and the focal length of the entire system at the short focus end is f_w, the following A compact wide-angle zoom lens 1.0<f_w/f_1<1.3 |f_2/f_1|<1.1 (2) The first lens group has a positive meniscus-shaped first lens with a convex surface facing the object side in order from the object side, a negative second lens, a negative third lens, a biconvex fourth lens, and a biconvex lens. The second lens group consists of a fifth lens, and the second lens group consists of, in order from the object side, a positive sixth lens with a convex surface facing the image side, a negative seventh lens, and a meniscus-shaped eighth lens with a convex surface facing the image side. The small wide-angle zoom lens according to claim 1, characterized in that: (3) The small wide-angle zoom lens according to claim 2, wherein the negative third lens and the biconvex fourth lens are bonded together to form a positive lens. (4) The small wide-angle zoom lens according to claim 2, which satisfies the following conditional expression (n_4+n_5)/2<1.65 ν_4-ν_3>10 (n_7+n_8)/2>1.7 (ν_7+ν_8)/2> 44 Here, n_4, n_5, n_7, n_8 are the fourth
, the refractive index of the fifth, seventh, and eighth lenses, ν_3, ν
_4, ν_7, ν_8 are the third, fourth, seventh,
This is the Atsube number of the eighth lens.