JPH01284819A - Zoom lens - Google Patents

Abstract

PURPOSE:To attain a large zoom ratio and making the title zoom lens compact by constituting said lens of three components of negative, positive and negative, forming the first component by the first negative lens being convex to an object side, a second biconcave lens and a third positive lens being convex to the object side, and also, providing one aspherical face on a first and a third components, respectively. CONSTITUTION:The title zoom lens is constituted of three components of the first component G1 having negative refracting power, a second component G2 having positive refracting power and the third component G3 having negative refracting power in order from an object side. Also, said lens is constituted so that the first component G1 is constituted of a first lens L1 consisting of a negative meniscus lens being convex to the object side, the second biconcave lens L2 and the third lens L3 consisting of a positive meniscus lens being convex to the object side in order from the object side, and also, at least one aspherical face is provided on the first component G1 and the third component G3, respectively. In this state, by leading the aspherical face into the first component G1, a distortion on a short focus side especially can be corrected, and also, by leading the aspherical face into the third component G3, an effect is obtained for correcting an astigmatism extending over the whole focal area.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a zoom lens for a single-lens reflex camera.
A zoom ratio of 2.2 that covers everything from wide-angle to semi-telephoto.
This relates to a compact zoom lens that is approximately twice as large.

Conventionally, zoom lenses in this area have two negative and positive lenses from the object side.
Generally, it was composed of two components, but in recent years, it has been thought that a positive or negative lens group with relatively weak power is placed behind the two components, the tool and the positive, to make it more compact and create a three-component configuration. It is being (For example, see JP-A-58-11013.) For example, the zoom lens described in JP-A-58-11013 is composed of three components, negative, positive, and negative, in order from the object side. The zoom ratio is about 2 times.

The present invention employs the above-mentioned ingredient, positive and negative three-component configuration, and
It is an object of the present invention to provide a zoom lens that can achieve a larger zoom ratio than a conventional zoom lens with a three-component configuration and is more compact than the conventional zoom lens with a three-component configuration.

In order to achieve this objective, the present invention provides the following features:
3.5.7.9 As shown in the figure, in order from the object side, the first component (G,) having a negative refractive power, the second component (G2) having a positive refractive power, and the negative refractive power A third component having (
In a zoom lens consisting of G,), the first component (G+
) are, in order from the object side, a first lens (Ll) consisting of a negative meniscus lens convex to the object side, a second lens (L2) consisting of a biconcave lens, and a third lens consisting of a positive meniscus lens convex to the object side. It consists of (L,) and
The first component (G1) and the third component (G, ) each have at least one aspherical surface.

The present invention will be explained in detail below.

In the present invention, by introducing an aspherical surface into the first component (G1), it is possible to correct distortion especially on the short focus side, and by introducing an aspherical surface into the third component (G3), it is possible to correct distortion at all focal points. It is particularly effective in correcting astigmatism over a wide range. Furthermore, in the present invention, the first component (
The refractive power of G1) or the third component (03) can be further strengthened, and the zoom lens can be made more compact than a conventional zoom lens having a three-component configuration of negative, positive, and negative.

Furthermore, in the present invention, the second component (G2) includes, in order from the object side, a fourth lens (L, ) consisting of a biconcave lens, a diaphragm (S), and a fifth lens (L,) consisting of a positive lens convex toward the object side.
), a sixth lens (L6) consisting of a biconcave lens, and a seventh lens (L, ) consisting of a positive lens convex to the image side, and when zooming from the short focus side to the long focus side, the first component (G,) first moves to the image plane side and then moves to the object side, the second component (G2) monotonically moves to the object side, and the third component
It is desirable that the component (G,) be fixed or move monotonically toward the object.

By configuring the second component (G2) in this way,
The exit pupil position of the lens system and the object-side principal point position of the second component (G2) can be arranged at advantageous and optimal positions for correcting aberrations and making the lens system more compact.

In particular, regarding the aspherical surface provided in the third component (G,), it is desirable that the following conditions be satisfied.

(1) 0.20<(fT-fw)"'Ia<l<
0.85 However, here, a, when the apex of the aspheric surface is the origin, the optical axis direction is the axis, and the direction perpendicular to it is the y axis, and the paraxial radius of curvature of the aspheric surface is r, x = r [1f
l −(y/r)21”]+a*y'+asy'+...
The aspherical coefficient 84 is expressed as .fT is the composite focal length of the entire system at the long focal length end, and r- is the composite focal length of the entire system at the short focal length end.

If the lower limit of condition (1) is exceeded, the effect of correcting astigmatism by the third component (G,) will be reduced, resulting in overcorrection of the image plane, and conversely, if the upper limit of condition (1) is exceeded, especially on the long focus side. This results in image surface characteristics that are insufficiently corrected, which is not good in either case.

Furthermore, in the present invention, it is desirable that the following conditions be satisfied.

(2) 0.75<lf'+l/(fT・h)""<0
．． 95(3) 0.55<fz/<fT-fw)
””<0.63(4)3.00<1fsl/(fT-f
w)”'<12.0(5) 0, 5 5
<rL4/ (fT - fw)fl2<0, 6
8 However, here, fi is the composite focal length of the i-th component, f
l4 is the focal length of the fourth lens.

Condition (2) defines the refractive power of the first component (G1), and if the lower limit of condition (2) is exceeded, it becomes difficult to correct negative distortion on the short focal length side, and conversely, the refractive power of the first component (G1) becomes difficult to correct. When the upper limit of /2 (2) is exceeded, the overall length becomes longer on the short focus side, and the amount of focusing increases, resulting in a larger front lens diameter, making it difficult to achieve overall compactness.

Condition 3) defines the refractive power of the second component (G2), and if the lower limit of condition (3) is exceeded, the second component (G, )
The refractive power of the lens becomes too strong, causing spherical aberration that is insufficiently corrected, and it becomes difficult to correct coma aberration.

If the upper limit of condition (3) is exceeded, the amount of movement of the second component (G2) during zooming becomes too large, which is disadvantageous to achieving compactness.

Condition (4) defines the refractive power of the third component (G,); if the lower limit of condition (4) is exceeded, sufficient back focus cannot be obtained; conversely, if the upper limit of condition (4) is exceeded, The effect of correcting astigmatism becomes smaller.

Condition 5) defines the refractive power of the fourth lens (L4) of the second component (G2).1 When the lower limit of condition (5) is exceeded, the refractive power of the fourth lens (L4) becomes stronger. Not only does this make it difficult to correct spherical aberration, but also the entrance pupil position moves too far toward the image side, which is a disadvantageous direction for correcting distortion aberration in the first component (G1). On the other hand, if the upper limit of condition (5) is exceeded, the object-side principal point of the second component (G2) moves away from the image side, making it difficult to achieve compactness.

In addition, in the present invention, the first component (G1) includes the first lens (L+) consisting of a negative meniscus lens convex to the object side and the second lens (L2) consisting of a biconcave lens, as described above.
, and a third lens (L,) consisting of a positive meniscus lens convex to the object side, but especially the third lens (L, )
It is desirable that the following conditions be satisfied.

(6) 0, 47 <r5/r6<0, 60 where ri is the radius of curvature of the first lens surface counting from the object side.

Condition (6) defines the shape of the third lens (L,), and if the lower limit of condition (6) is exceeded, undercorrected spherical aberration will occur on the long focal point side, and conversely, condition (6) When the upper limit is exceeded, the astigmatism difference on the short focus side increases.

Here, the configuration of the third component (G,) and its movement shape will be discussed. The third component (G3) is a negative lens component having a relatively weak refractive power, but its component may be a single negative lens or a plurality of lenses such as two positive and negative lenses.
Further, it may be fixed during zooming, but in order to enhance the multiplication effect, it may be moved monotonically toward the object side during zooming from the short focus side to the long focus side. At that time, if the third component (G3) is composed of multiple sheets, the condition (4
) It is also possible to further enhance the aberration correction effect by mixing fixed elements and movable elements or by changing the movement ratio of a plurality of movable elements. (In this case, the condition (
Parameters 4) are functions of the focal length of the entire system. ) Examples of the present invention are shown below in Tables 1 to 5, the surfaces marked with (*) are aspherical, and their shape is as follows:
It is expressed as '+asy'+may'+a+oy"+--. However, here, with the surface vertex of the aspherical surface as the origin, the optical axis direction is the X-axis, and the direction perpendicular to it is the y-axis.C is is the paraxial radius of curvature of the aspherical surface. In each example, "
is the focal length of the entire system, FNO is the F number, ri (i-1
, 2, 3s-...) is the radius of curvature of the first surface from the object side, di (i = 1.2.3).

...) is the distance between the first axis top surface from the object side, N
1 (i=1.2, 3...) is the first
The refractive index of the th lens, ν1 (i= 1.2.3, ・
) is the Atsube number of the first lens from the object side. Table 6 shows the relationship between each example and each condition.

(Left below) Aspherical coefficient: r4: a4=o, 68131X10 as=o
, 31212X10-" as=o, 85376X10 0 rls: an=-0, 39167XlO-'
a4=-0,32037X10-'as=0.2542
5. Xl0-10 Table 2 (Example 2) f=36.4-50.1-77, OFNO=4.1-5
．． 7 Radius of curvature Axial surface spacing Refractive index (Ncl)
Atsbe number (νd) aspheric coefficient: rg: a4=0.14866X10-' a6
=-0,72506X10-'aa=o,16603X
lO-' al. =-0,48342x 10 visits 2r
I@: a4=-0,41196X10-5ag=
-0.45007X10-・as=o, 91474X1
0-1+ *r6* is formed on the optical resin d and '.

Aspherical coefficient: am=o, 21887X10-" Table 4 (Example 4) Aspherical coefficient: r4: a4=0.69586XIO-' a@
=-0,14598X10-"ag=0.72620X
10-'.

rla: a4=-0,40007X10-5as
=-0,35216X10-"am=o,16819X
10-10 Table 5 (Implementation PA5) f=36.1~52.9~77.75 FNO=
4.1~5.7 Radius of curvature Distance between upper surfaces of shaft Refractive index (N
d) Atsbe number (νd) aspheric coefficient; r5: a4=-0,12815XIO-'
a,=-0,20026XIO-fas=0.5
1826X10-〇r+s: a4=0.16451X10-' a
i=o, 86916X10-'as=0.16204X
10-” Table 6 (margins below)

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a zoom lens according to Example 1 of the present invention;
2 is an aberration diagram thereof, FIG. 3 is a cross-sectional view showing the zoom lens according to Example 2 of the present invention, FIG. 4 is a diagram showing its aberration, and FIG. 5 is a cross-sectional view showing the zoom lens according to Example 3 of the present invention. 6 is an aberration diagram thereof, FIG. 7 is a cross-sectional view showing the zoom lens according to Example 4 of the present invention, FIG. 8 is a diagram showing its aberration, and FIG. 9 is a cross-sectional view showing the zoom lens according to Example 5 of the present invention. FIG. 10 is an aberration diagram. GI: first component, G2: second component, G: third component, Ll: first lens, L2: second lens, L3 = third lens. Applicant: Minolta Camera Co., Ltd. 2D
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Claims (1)

[Claims] 1. A zoom lens comprising, in order from the object side, a first component having a negative refractive power, a second component having a positive refractive power, and a third component having a negative refractive power, One component consists of, in order from the object side, a first lens consisting of a negative meniscus lens convex to the object side, and a second lens consisting of a biconcave lens.
What is claimed is: 1. A zoom lens comprising: a lens; and a third lens consisting of a positive meniscus lens convex to the object side, and each of the first component and the third component has at least one aspherical surface. 2. In the zoom lens according to claim 1, the second component includes, in order from the object side, a fourth lens made of a biconcave lens, an aperture, a fifth lens made of a positive lens convex to the object side, and a sixth lens made of a biconcave lens. When zooming from the short focus side to the long focus side, the first component first moves to the image side, then moves to the object side, and A zoom lens characterized in that two components move monotonically toward the object side, and a third component is fixed or moves monotonically toward the object side. 3. The zoom lens according to claim 2, wherein the aspherical surface provided in the third component satisfies the following condition: 0.20<(fT・fw)^3^/^ 2｜a_4｜<0
．． 85 However, here, a_4: When the surface vertex of the aspherical surface is the origin, the optical axis direction is the x-axis, and the direction perpendicular to it is the y-axis, the paraxial radius of curvature of the aspherical surface is r, and x=r[1 -(1-(y/r)^2)^1^/^2]+
Aspheric coefficient a_4 when expressed as a_4y^4+a_5y^5+..., fT: composite focal length of the entire system at the long focal length end, fw: composite focal length of the entire system at the short focal length end. 4. The zoom lens according to claim 3, further satisfying the following condition: 0.75<|f_1|/(fT·fw)^1^/^2<
0.950.55<f_2/(fT・fw)^1^/^
2<0.633.00<｜f_3｜/(fT・fw)＾
1^/^2<12.00.55<fL_4/(fT・f
w)^1^/^2<0.68 However, here, f_i: composite focal length of the i-th component, fL_4: focal length of the fourth lens. 5. In the zoom lens according to claim 2, the third lens satisfies the following conditions: 0.47<r_5/r_6<0.60, where: r_i: i-th lens as counted from the object side The radius of curvature of the lens surface is .