JPH04251211A - Two-component zoom lens - Google Patents

Abstract

PURPOSE:To reduce the cost of the two-component lens while well maintaining optical performance. CONSTITUTION:A negative 1st lens group I (focal length f1) and a positive 2nd lens group II (focal length f2) are provided. The focal lengths are specified to 1.0<¦f1¦/f2<1.5. The 1st lens group is constituted of a negative meniscus lens convex on an object side, a negative lens and a positive meniscus lens convex on the object side. The 2nd lens group is constituted of a biconvex positive lens, a positive meniscus lens, a biconcave negative lens, and a positive lens. An aperture diaphragm is disposed between the 1st lens group and the 2nd lens group. Variable power is executed by relatively moving the 1st lens group and the 2nd lens group. The focal lengths are specified to 1.4<¦f1¦/fW<1.9 (fW: the focal length of the entire system at a wide end W). 0.2<Dt/Df<0.4 (Dt: the spacing between the 1st lens group and the 2nd lens group at a telephoto end T, Df: the ratio of the sum of the core thickness and air spacing of the 1st lens group).

Description

[Detailed description of the invention]

0010

[Field of Industrial Application] The present invention relates to a two-component zoom lens, and more particularly to a two-component zoom lens that includes a wide-angle range and has a variable magnification ratio of about 3x, and is particularly suitable for single-lens reflex cameras. It is.

[0020]

2. Description of the Related Art Conventionally known standard zoom lenses for single-lens reflex cameras, which are inexpensive and have a variable power ratio of about 2 to 3 times, are composed of two components, negative and positive. This configuration is described, for example, in Japanese Patent Application Laid-open Nos. 58-5707 and 58-12.
No. 011, etc., and in these embodiments, the aperture stop is arranged in the positive second lens group.

[0030]

[Problem to be Solved by the Invention] However, in this arrangement, the lens frame of the second lens group is divided between the 2-1 group and the 2-2 group.
Since it needs to be divided into parts, it is disadvantageous in terms of cost and assembly man-hours. Moreover, in general, the error sensitivity of parallel eccentricity and tilt eccentricity between the 2-1st group and the 2-2nd group in a two-component zoom lens is high, and manufacturing errors in this area have a large impact on optical performance. .

The present invention solves these problems, eliminates the above-mentioned disadvantages caused by the aperture stop being located inside the second lens group, and provides good optical performance over the entire zoom range including the wide-angle range. The purpose of the present invention is to provide a zoom lens that is suitable and inexpensive.

[0050]

[Means for Solving the Problems] In order to achieve the above object, the two-component zoom lens of the present invention includes, in order from the object side, a first lens group having a negative refractive power and a second lens group having a positive refractive power. In a two-component zoom lens that performs magnification by relatively moving the first lens group and the second lens group, the first lens group has a convex surface facing the object side in order from the object side. The second lens group includes, in order from the object side, a biconvex positive lens, a positive meniscus lens, a biconcave negative lens, and a positive meniscus lens with a convex surface facing the object side. It consists of a positive lens, an aperture stop is disposed between the first lens group and the second lens group, and the following conditional expressions (1) to
It is characterized by satisfying (3). 0.2<Dt/Df<0.4...(1)1
．． 0<|f1|/f2<1.5 ...(2) 1.4<
|f1|/fW<1.9 (3) However, Dt: Distance between the first lens group and the second lens group at the telephoto end Df: Core thickness of the lenses constituting the first lens group and the distance between the lenses f1: Focal length of the first lens group f2: Focal length of the second lens group fW: Focal length of the entire system at the wide end.

By adopting the above-mentioned lens structure, the number of constituent lenses can be reduced as much as possible. Furthermore, by adopting a configuration that satisfies conditional expressions (1) to (3), it is possible to arrange the aperture diaphragm between the first lens group and the second lens group and obtain a desired variable power ratio. .

By arranging the aperture stop between the first lens group and the second lens group, it is possible to simplify the lens frame structure of the second lens group. For example, since the lens frame member constituting the second lens group can be constructed from a single member, not only can costs be reduced, but also the deterioration of optical performance caused by manufacturing errors can be reduced. Furthermore, by placing the aperture stop in front of the second lens group, harmful light that enters from below can be removed, especially near wide-angle. Furthermore, if the aperture stop moves independently of the first lens group and the second lens group during zooming, flare from the wide end to the middle (intermediate focal length state),
In particular, harmful light near the wide-angle lens is more effectively removed, aberrations are corrected, and optical performance can be further improved.

The zoom lens of the present invention is particularly suitable as a standard zoom lens for an interchangeable lens for a single-lens reflex camera equipped with a power zoom. The power zoom motor is intended to be incorporated inside the lens, and the lens barrel structure requires that the space occupied by the motor and the space occupied by the aperture member not interfere with each other. In the present invention, the interference is eliminated by placing the aperture stop in front of the second lens group.

When arranging the aperture stop between the first lens group and the second lens group, at the telephoto end where the air gap between the first lens group and the second lens group is the smallest,
It is necessary to secure a space in which the aperture member can fit. Conditional expression (1) defines the air gap at the telephoto end. If Dt/Df exceeds the lower limit in conditional expression (1), there will be no space for an aperture stop between the first lens group and the second lens group at the telephoto end. When Dt/Df exceeds the upper limit value, the total lens length increases and the illuminance at the wide end becomes insufficient.

Conditional expression (2) defines the power relationship of each group. In order to achieve a zoom lens that has two components, negative and positive, and has a wide range of magnification from wide-angle to semi-telephoto, and that satisfies optical performance over the entire range, it is necessary to combine the first and second lens groups. Power relationships become important. In conditional expression (2), if |f1|/f2 exceeds the lower limit,
The power of the first lens group becomes relatively large, and the height of incidence of axial light on the second lens group on the telephoto side becomes large, making it difficult to properly correct spherical aberration. ｜
When f1|/f2 exceeds the upper limit value, the power of the first lens group becomes relatively small, making it difficult to secure illuminance on the wide-angle side.

The two-component zoom according to the present invention is particularly characterized in that it includes a wide angle range. In conditional expression (3), |f1|
When /fW exceeds the lower limit, the power of the first lens group must be increased in order to maintain a wide-angle range within the variable power range, making it difficult to correct spherical aberration at the telephoto end. . When |f1|/fW exceeds the upper limit, the first
The power of the lens group must be reduced, making it difficult to secure sufficient illuminance at the wide end.

[0120]

[Embodiments] Hereinafter, embodiments of a two-component zoom lens according to the present invention will be shown. However, in each example, ri (i=1,
2, 3, . ．． ．． ) is the radius of curvature of the i-th surface counting from the object side, di (i=1, 2, 3,...) is the i-th axial surface spacing counting from the object side, and Ni (i=1, 2,3
、． ．． ．． ), νi (i=1, 2, 3, . . . ) represent the refractive index and Abbe number for the d-line of the i-th lens counting from the object side. Further, f indicates the focal length of the entire system, and FNO indicates the open F number.

[0130] In the examples, a surface marked with an asterisk (*) on the radius of curvature indicates a surface composed of an aspherical surface, and is defined by the equation 1 below, which represents the surface shape of an aspherical surface. .

In the equation 1, X(h): Amount of deviation in the optical axis direction from the apex of the aspherical surface r: Reference radius of curvature h: Height in the vertical direction from the optical axis An: Nth-order aspherical surface It is a coefficient.

<Example 1> f=29.0-41.0-77.5
FNO=4.1~5.0~5.8 [Radius of curvature] [Axis spacing] [Refractive index]
[Abbe number] r1 46.
401 d1 1
．． 500 N1 1.77551
ν1 37.90r2 23.326 d2 4
．． 370r3 47.604 d3 1
．． 450 N2 1.71300
ν2 53.93r4 19.199 d4 3
．． 800r5 24.982 d5 5
．． 900 N3 1.67339
ν3 29.25r6 79.724 d6 0
．． 035 N4 1.51790
ν4 52.31r7* 55.000 d7 3
2.821~17.132~3.100r8 ∞ (aperture stop) d8 9
．． 000~6.954~0.800r9 25.35
1 d9 4
．． 000 N5 1.58913
ν5 61.11r10 -77.742 d10
0.200r11 19.200d11
3.250 N6 1.51680
ν6 64.20r12 104.98
2 d12
1.850r13 -59.250d13
5.000 N7 1.80741
ν7 31.59r14 17.662 d14
2.450r15 -2620.888 d15
2.250 N8 1.59551
ν8 39.22r16 -24.75
3 d16
-0.500~3.766~16.906r17 ∞
(Shading aperture) Σd=77.376
~63.907~56.861 [Aspheric coefficient] r7: ε=0.10000×10 A4=-0.99822×10−5 A6=0.87184×10−8 A8=−0.27198×10− 9 A10=0.11548×10-11
A12=-0.22704×10-14 [conditional expression (1)
~(3)] Dt/Df=0.229 |f1|/f2=1.297 |f1|/fW=1.646

<Example 2> f=28.8-41.0-72.7
FNO=4.1~5.0~5.8 [Radius of curvature] [Axis spacing] [Refractive index]
[Abbe number] r1 46.
309 d1 1
．． 500 N1 1.77551
ν1 37.90r2 24.631 d2 4
．． 000r3 49.304 d3 1
．． 500 N2 1.72000
ν2 50.31r4 18.850 d4 4
．． 050r5 25.112 d5 5
．． 500 N3 1.67339
ν3 29.25r6 79.386 d6 0
．． 035 N4 1.51790
ν4 52.31r7* 55.000 d7 3
2.588~16.680~3.800r8 ∞ (aperture stop) d8 9
．． 000~6.780~1.000r9 27.
585 d9 3
．． 400 N5 1.58913
ν5 61.11r10 -79.388 d10
0.200r11 18.593 d11
3.300 N6 1.51680
ν6 64.20r12 108.60
7 d12
2.050r13 -73.614 d13
5.600 N7 1.80741
ν7 31.59r14 17.0
26 d14
2.300r15 290.703 d15
2.200 N8 1.58144
ν8 40.89r16 -26.57
0 d16
-0.500~3.244~12.986r17 ∞
(Shading aperture) Σd=76.723
~62.338~53.421 [Aspheric coefficient] r7: ε=0.10000×10 A4=-0.99770×10−5 A6=0.14357×10−7 A8=−0.29773×10− 9 A10=0.11386×10-11 A12=-0.21732×10-14 [conditional expression (1)
~(3)] Dt/Df=0.289 |f1|/f2=1.343 |f1|/fW=1.686

FIGS. 1 and 2 are lens configuration diagrams corresponding to the first and second embodiments, respectively, and show the arrangement at the wide end.

In both Examples 1 and 2, in order from the object side, the positive first lens group (I), the aperture stop (S1)
, a negative second lens group (II), and a light shielding aperture (S2) (FIG. 1). The first lens group (I) consists of, in order from the object side, two negative meniscus lenses with a convex surface facing the object side and a positive meniscus lens with a convex surface facing the object side,
The second lens group (II) includes, in order from the object side, a biconvex positive lens, a positive meniscus lens convex to the object side, a biconcave negative lens, and a positive meniscus lens convex to the image side. Note that the image-side surface of the positive meniscus lens convex toward the object side in the first lens group (I) is an aspheric surface.

Arrows (m1) to (m4) in FIGS. 1 and 2
are the first lens group (
I), schematically shows the movement of the aperture stop (S1), the second lens group (II), and the light shielding stop (S2) from the wide end (W) to the telephoto end (T). 1st lens group (I)
When changing the magnification from the wide end (W) to the tele end (T),
It moves in a U-turn-shaped trajectory that moves once toward the image side and then returns to the object side. The aperture diaphragm (S1), the light-shielding diaphragm (S2), and the second lens group (II) are arranged at the wide end (W
) to the telephoto end (T), both move linearly toward the object side. However, the second lens group (II) has a narrower distance from the aperture diaphragm (S1), and a light-shielding diaphragm (S2).
Move to increase the distance between the two.

3 to 5 are aberration diagrams corresponding to the first embodiment, and FIGS. 6 to 8 are aberration diagrams corresponding to the second embodiment. Figures 3 and 6 are aberration diagrams at the wide end focal length (W), Figures 4 and 7 are aberration diagrams at the intermediate focal length (M),
5 and 8 are aberration diagrams at the telephoto end focal length (T). In addition, the solid line (d) represents the aberration for the d-line, and the broken line (
SC) represents the sine condition. Furthermore, the dashed line (DM) and the solid line (
DS) represents astigmatism on the meridional plane and the sagittal plane, respectively.

[0210]

[Math 1]

[0220]

As explained above, according to the present invention, the first lens group includes, in order from the object side, a first lens group having a negative refractive power and a second lens group having a positive refractive power. In a two-component zoom lens that performs magnification by relatively moving a lens group and a second lens group, the first lens group includes, in order from the object side, a negative meniscus lens with a convex surface facing the object side, a negative lens, and It is composed of a positive meniscus lens with a convex surface facing the object side, and the second lens group is composed of, in order from the object side, a biconvex positive lens, a positive meniscus lens, a biconcave negative lens, and a positive lens. , the number of constituent lenses is reduced, and as a result, cost reduction is achieved.

Furthermore, an aperture stop is disposed between the first lens group and the second lens group, and conditional expressions (1) to
Since the configuration satisfies (3), the aperture stop is the second
Inconveniences such as deterioration of optical performance due to manufacturing errors caused by being inside the lens group are eliminated, and optical performance is good over the entire zoom range including the wide-angle range.
Moreover, it is possible to realize an inexpensive zoom lens.

[0240] Furthermore, by moving the aperture stop independently of the first and second lens groups during zooming, harmful light (flare, etc.) especially near the wide end is removed, further improving optical performance. be able to.

[Brief explanation of the drawing]

FIG. 1 is a lens configuration diagram of Example 1 of the present invention.

FIG. 2 is a lens configuration diagram of Example 2 of the present invention.

FIG. 3 is an aberration diagram at the wide end focal length of Example 1.

FIG. 4 is an aberration diagram at an intermediate focal length in Example 1.

FIG. 5 is an aberration diagram at the telephoto end focal length of Example 1.

FIG. 6 is an aberration diagram at the wide end focal length of Example 2.

FIG. 7 is an aberration diagram at an intermediate focal length in Example 2.

FIG. 8 is an aberration diagram at the telephoto end focal length of Example 2.

[Explanation of symbols]

(I)...First lens group (II)...Second lens group (S1)...Aperture diaphragm (S2)...Shade diaphragm

Claims (2)

[Claims] Claim 1: In order from the object side, the first lens has a negative refractive power.
In a two-component zoom lens that is composed of a lens group and a second lens group having positive refractive power, and that performs magnification by relatively moving the first lens group and the second lens group, the first lens The group consists of, in order from the object side, a negative meniscus lens with a convex surface facing the object side, a negative lens, and a positive meniscus lens with a convex surface facing the object side, and the second lens group consists of a biconvex positive lens in order from the object side. , a positive meniscus lens, a biconcave negative lens, and a positive lens, an aperture stop is disposed between the first lens group and the second lens group, and the following conditions are satisfied: Two-component zoom lens; 0.2<Dt/Df<0.4 1.0<|f1|/f2<1.5 1.4<|f1|/fW<1.9 However, Dt: At the telephoto end Distance Df between the first lens group and the second lens group: sum of the core thickness of the lenses constituting the first lens group and the air distance between the lenses f1: focal length of the first lens group f2: of the second lens group Focal length fW: Focal length of the entire system at the wide end. 2. The two-component zoom lens according to claim 1, wherein the aperture stop moves independently of the first lens group and the second lens group during zooming.