JPH0735976A - Zoom lens - Google Patents

Abstract

PURPOSE:To obtain a zoom lens of miniaturization and light in weight, and high specification and high performance by employing four-lens constitution and in which a second lens group is provided with a lens surface of aspherical shape to satisfy a specific condition. CONSTITUTION:This lens is provided with a first to fourth lens groups G1-G4 with positive, negative, negative, and positive refracting powers sequentially from an object side. When variable magnification is performed, the second and third lens groups G2, G3 are moved on an optical axis. The second lens group G2 is provided with at least one lens surface of aspherical shape. The lens surface of aspherical shape satisfies condition 10<-31xa(h)-x(h)1/h<10<-1>. Where, the maximum effect radius of the lens surface of aspherical shape is assumed as (h), a value of (x) in the maximum effect radius (h) when the surface apex of the lens surface of aspherical shape is taken as an origin and an x-axis as the optical axis, and a y-axis is expressed in a coordinate system passing the origin and setting as a straight line perpendicular to the x-axis as xa(h), and the value of (x) in the paraxial radius of curvature of the lens surface of aspherical shape in the maximum effect radius (h) as x(h).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is small and lightweight, has a large diameter,
The present invention relates to a zoom lens having a large zoom ratio, and particularly to a zoom lens suitable for a television camera.

[0002]

2. Description of the Related Art Conventionally, a zoom lens having a large aperture and a large zoom ratio has a four-group structure having positive, negative, negative, positive or positive, negative, positive, positive refracting power in order from the object side. It has been known. In these zoom lenses, zooming is performed by moving the second lens group and the third lens group.

[0003]

In recent years, there has been an increasing demand for a compact, lightweight and high-performance zoom lens having a large aperture, a wide angle of view, and a large zoom ratio. Generally, as a method of further downsizing and weight reduction of a zoom lens, or maintaining higher downsizing and weight reduction, a configuration for strengthening the power of each lens group is used. However, there is a problem that the optical performance deteriorates.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a compact, lightweight, high-performance zoom lens having high performance.

[0005]

[Means for Solving the Problems]
Therefore, the zoom lens according to the present invention has the following configuration.
It For example, as shown in FIG. 1, the positive refracting power is increased in order from the object side.
First lens group G having ₁And a second lens with negative refractive power
Group G₂And the third lens unit G having negative refractive power₃And has positive refractive power
4th lens group G_FourIn a zoom lens having and
When changing the magnification from the wide-angle end to the telephoto end, the second lens group G₂But
Moves from the object side to the image side along the optical axis, and the third lens
Group G₃Is configured to move back and forth on the optical axis.
Be done.

The second lens group G ₂ has at least one aspherical lens surface. The aspherical lens surface is defined as a shape in which the positive refractive power gradually increases or a shape in which the negative refractive power gradually weakens from the optical axis toward the peripheral portion, and is configured to satisfy the following conditions.

[0007]

## EQU1 ## 10 ⁻³ <| xa (h) −x (h) | / h <10 ⁻¹ (1) where h is the maximum effective radius of the aspherical lens surface, and xa (h) is not The value of x at the maximum effective radius h is expressed by a coordinate system in which the apex of the spherical lens surface is the origin, the x axis is the optical axis, and the y axis is a straight line that passes through the origin and is perpendicular to the x axis. (H): When the apex of the aspherical lens surface is taken as the origin, the x-axis is the optical axis, and the y-axis is a straight line that passes through the origin and is perpendicular to the x-axis. X is the paraxial radius of curvature of the aspherical lens surface.

[0008]

According to the present invention, firstly, since the second lens group G ₂ having a negative refractive power, given the aberration correction in the second lens group G within _2, at least one surface of the second lens group G ₂ The aspheric surface of has a shape in which the positive refracting power becomes stronger or the negative refracting power becomes weaker from the optical axis toward the periphery as compared with the paraxial radius of curvature of this aspherical surface. desirable.

Further, in order to satisfactorily correct various aberrations, in the present invention, the optimum range of the amount of aspherical surface is defined by the above condition (1). Here, if the upper limit of the condition (1) is exceeded, distortion is increased in a pincushion type from the intermediate focal length state to the telephoto end, which is not preferable. On the other hand, when the value goes below the lower limit, fluctuations in various aberrations due to zooming, especially fluctuations in field curvature become remarkable, and spherical aberration on the telephoto side is also overcorrected, which is not preferable.

Further, in the present invention, the first lens group G ₁ includes, in order from the object side, the negative lens group L ₁₁ and at least three positive lens groups because of the high specifications and high performance required for the zoom lens for the television camera. Desirably, the second lens group G ₂ is configured to include L ₁₂ , L ₁₃ , and L ₁₄ , and the second lens group G ₂ is configured to include at least three lens groups L ₂₁ , L ₂₂ , and L ₂₃ .

Further, in the present invention, the first lens group G
It is desirable that the negative lens unit L ₁₁ of ₁ satisfy the following condition.

[0012]

## EQU2 ## −2.0 <(R ₂ + R ₁ ) / (R ₂ −R ₁ ) <− 1.5 (2) where R _{1 is} the most object side lens surface of the negative lens group L ₁₁ . Paraxial radius of curvature, R ₂ : Paraxial radius of curvature of the lens surface of the negative lens group L ₁₁ closest to the image.

The condition (2) defines the optimum shape of the negative lens unit L _11. If the upper limit of the condition (2) is exceeded, spherical aberration on the telephoto side will be under, which is not preferable. . On the other hand, if the value exceeds the lower limit, pincushion distortion aberration increases, which is not preferable. The zoom lens according to the present invention has the following condition (3) in addition to the above configuration.
It is desirable to be configured to satisfy

[0014]

## EQU3 ## 0.6 <F _T ¹ / 2f ₁ / f _T <0.9 (3) where f _T : composite focal length of the entire system at the telephoto end, F _T : F number at the telephoto end F ₁ is the focal length of the first lens group G ₁ .

The condition (3) defines the optimum power of the zooming portion in order to reduce the size of the zooming portion of the zoom lens while maintaining the imaging performance. With this, it is possible to define the optimum power range of the zooming unit according to the zoom ratio and the maximum aperture ratio of the zoom lens. When the value exceeds the upper limit of the condition (3), it becomes difficult to reduce the size of the variable power portion, which is not preferable. On the other hand, when the value goes below the lower limit, it is effective for downsizing, but aggravation of various aberrations accompanying this is remarkable. In particular, since the Petzval sum is deteriorated due to the stronger powers of the second lens group G ₂ and the third lens group G ₃ and the apparent F number of the first lens group G _{1 at} the telephoto end becomes too small, at the telephoto end. Spherical aberration becomes difficult to correct. Further, manufacturing tolerances become strict, and the image quality is significantly deteriorated due to decentering of each lens.

The zoom lens according to the present invention preferably satisfies the following condition (4) in addition to the above configuration.

[0017]

## EQU4 ## 0.9 <| β _2W · V ^1/2 | <1.3 (4) where β _2W is the magnification at the wide-angle end of the second lens group G ₂ , and V is the zoom ratio.

The condition (4) is a condition for keeping good Petzval sum. As a result, although the zooming unit is downsized under the condition (3),
Since the power of the lens group G ₂ can be reduced,
It can prevent the deterioration of Petzval sum. As in the present invention
In a negative / negative / positive type zoom lens, the power of the second lens group G ₂ tends to be the strongest in each lens group, so the negative power of the second lens group G ₂ should be made as weak as possible. Is most effective for keeping the Petzval sum to a proper value.

A detailed description will be given below with reference to FIG. Figure 9
Second lens group G₂In the figure which shows the state of the magnification change by
is there. In FIG. 9, P is the first lens group G₁Image point by
Position, that is, the second lens group G₂Object position with respect to
2 lens group G₂The locus | trajectory of the image point formed by is shown.
Here, the second lens group G₂Let v be the scaling factor due to
Second lens group G₂The magnification at the wide-angle end and the telephoto end.
-1 / v each^1/2, -V^1/2Range W₀
-T₀If is selected as the reference variable range, the position of the image point Q is wide-angle.
The third lens group G is the same at the end and the telephoto end.₃Position of both ends
Matches with. At this time, the second lens group G ₂The scaling factor v of
It becomes equal to the zoom ratio V.

At the wide-angle end where the first lens group G ₁ and the second lens group G ₂ are closest to each other, when the space required to prevent mechanical interference between the lens groups is Δ, the second lens at the wide-angle end is Magnification β _2W of lens group G ₂ and its focal length f ₂
Between

[0021]

[Formula 5] f ₂ = (f ₁ −Δ) · β _2W / (1−β _2W ) (5). From this equation, if β _2W is made larger than −1 / V ^1/2 , | f ₂ | becomes large, and the second lens group G ₂
It is clear that the power of is weakened. This is shown in FIG.
Reference zoom range of the second lens group G ₂ in zoom range W ₀ -
This is equivalent to selecting the area WT below T ₀ . In the present invention, the zoom range of the second lens group G ₂ be in the range of the condition (4), it is possible to weaken the negative power of the second lens group G _2.

When the value goes below the lower limit of the condition (4), the power of the second lens group G ₂ becomes strong, and the Petzval sum is unavoidably deteriorated. On the other hand, if the upper limit is exceeded, the movable space required for zooming the second lens group G ₂ becomes large, which leads to an increase in the total length of the lens system and the diameter of the front lens. Two
The ratio of the amount of movement of the third lens group G ₃ to the amount of movement of the lens group G ₂ becomes extremely large, which is not preferable because the lens barrel mechanism for moving both groups is inconvenient.

Further, in the present invention, in order to satisfactorily correct various aberrations and maintain high performance in spite of the large aperture ratio,
It is desirable that the third lens group G ₃ and the fourth lens group G ₄ have the following configurations. First, the third lens group G ₃
It is desirable that the negative lens L ₃ is composed of a biconcave negative lens and a biconvex positive lens cemented together. Next, the fourth lens group G ₄ includes, in order from the object side, a positive meniscus lens L ₄₁ having a convex surface directed toward the image side, a biconvex positive lens L ₄₂ , a biconvex positive lens L _43, and this biconvex positive lens L _43. A front lens group having a negative lens L ₄₄ cemented to the object side and having a surface having a stronger curvature toward the object side, a biconvex positive lens L ₄₅ , two cemented lenses L ₄₆ and L _47, and a surface having a stronger curvature toward the object side. And a rear lens group having a positive lens L ₄₈ directed toward the lens.

[0024]

Embodiments Referring to the drawings, embodiments of the present invention will be described below.
I will explain. 1, 3, 5, and 7 are respectively
FIG. 3 is a lens configuration diagram of Embodiments 1 to 4 according to the present invention.
It In each of the examples, the first lens having the positive refractive power is sequentially arranged from the object side.
Group G ₁And the second lens group G having negative refractive power₂And negative refraction
Third lens group G of power₃And the fourth lens unit G having positive refractive power_Four
Have and. And when changing the magnification from the wide-angle end to the telephoto end
The first lens group G₁And the fourth lens group G_FourAnd is the optical axis direction
Is fixed with respect to the second lens group G₂Along the optical axis
The third lens group G is monotonically extended toward the object side.₃Is on the optical axis
It is configured to move back and forth. In addition, each real
In the example, the lens surface of the zoom lens closest to the image and the image
Color separation prism and various filters placed between the surface and
A plane parallel plate such as is shown as a prism block PB.
It

In the first to third embodiments, the first lens group G ₁ comprises, in order from the object side, a meniscus negative lens L ₁₁ having a convex surface facing the object side and a biconvex positive lens L _12.
And a biconvex positive lens L having a stronger curvature on the object side.
₁₃ and a meniscus-shaped positive lens L ₁₄ having a convex surface facing the object side. The second lens group G ₂ includes, in order from the object side, a negative meniscus lens L ₂₁ having a concave surface facing the image side, a positive meniscus lens having a concave surface facing the object side, and a biconcave negative lens. A cemented lens L ₂₂ consisting of
And a cemented lens L ₂₃ consisting of a negative meniscus lens having a concave surface facing the positive lens and the object side of the biconvex shape.

Here, in the first and second embodiments,
An aspherical layer having an aspherical surface on the image side is provided on the most image side lens surface of the cemented lens L ₂₂ . Further, in the third example, the most image-side lens surface of the cemented lens L ₂₂ is formed in an aspherical shape. The third lens group G ₃ includes a cemented lens L _{3 including} a biconcave negative lens and a biconvex positive lens having a stronger curvature on the object side.

The fourth lens group G_FourFrom the object side
In order, a positive meniscus lens with concave surface facing the object side
L₄₁And a biconvex positive lens L₄₂And a biconvex positive lens
Z L ₄₃And a negative meniscus lens with a concave surface facing the object side.
Z L₄₄And a cemented lens composed of and a biconvex positive lens L
₄₅From the biconcave negative lens and the biconvex positive lens
Cemented lens L₄₆And biconvex with stronger curvature on the image side
-Shaped positive lens and meniscus shape with concave surface facing the object side
Cemented lens L consisting of a negative lens of₄₇And the object side
Biconvex positive lens L with strong curvature₄₈Have and.

The values of specifications according to each embodiment are shown below.
In the specification table of the embodiment, f is the focal length and F is the F number. The number at the left end represents the order from the object side of the lens surface, r is the radius of curvature of the lens surface, d is the distance between the lens surfaces, and n and ν are the refractive index and the Abbe number d line (λ =
587.6 nm). In the zoom lens according to the present embodiment, the aberration is corrected including the prism block PB showing the plane-parallel plate such as the color separation prism and various filters, and therefore these data are also shown.

Further, the aspherical shape is such that r is a paraxial axis of an aspherical surface in a coordinate system in which the apex of the aspherical surface is the origin, the optical axis is the X axis, and a straight line passing through the origin and orthogonal to the X axis is the Y axis. When the radius of curvature, k are conic constants, and A, B, C, and D are aspherical coefficients,

[0030]

[Expression 6] X = y ² · r ⁻¹ · {1+ [1- (1 + k) (y / r) ² ] ^1/2 } ⁻¹ + Ay ⁴ + By ⁶ + Cy ⁸ + Dy ¹⁰ (6) .

[0031]

[Table 1] [First embodiment] f = 8.75 to 127 F = 1.72 to 2.24 (Variable spacing in zooming) f 8.75 40 127 d 8 0.7326 30.3323 39.7802 d17 39.0272 5.3495 3.4605 d20 7.5525 11.6305 4.0715 ( aspherical coefficients) 14th surface k = 0.0000 A = -3.8436 × 10 -5 B = -1.4528 × 10 - ⁸ C = -7.3974 × 10 ^-10 D = 0.0000 ｜ xa (h) -x (h) ｜ = 0.215mm (h = 8.4mm) (Values corresponding to conditions) (1) 2.560 × 10 ^-2 (2) -1.820 (3) 0.704 (4) 1.165

[0032]

[Table 2] [Second embodiment] f = 8.75 to 127 F = 1.72 to 2.21 (Variable spacing in zooming) f 8.75 40 127 d 8 0.6743 30.2148 39.6414 d17 39.2815 5.6739 3.8561 d20 7.9358 12.0029 4.3941 ( aspherical coefficients) 14th surface k = 0.0000 A = -3.8757 × 10 -5 B = -1.6642 × 10 - ⁸ C = -7.2796 × 10 ^-10 D = 0.0000 ｜ xa (h) -x (h) ｜ = 0.223mm (h = 8.45mm) (Condition-compliant numerical value) (1) 2.639 × 10 ^-2 (2) -1.761 (3) 0.698 (4) 1.168

[0033]

[Table 3] [Third embodiment] f = 8.75 to 127 F = 1.72 to 2.25 (Variable spacing in zooming) f 8.75 40 127 d 8 0.6978 30.2975 39.7454 d16 39.2759 5.5981 3.7092 d19 7.5525 11.6305 4.0715 ( aspherical coefficients) 13th surface k = 0.0000 A = -2.7319 × 10 -5 B = -1.3187 × 10 - ⁸ C = -6.3498 × 10 ^-10 D = 0.0000 ｜ xa (h) -x (h) ｜ ＝ 0.161mm (h = 8.45mm) (Values corresponding to conditions) (1) 1.905 × 10 ^-2 (2) -1.815 (3) 0.704 (4) 1.165 Figures 2 (a), (b), (c), Figures 4 (a), (b), (c) and Figures 6 (a), (b),
(c) shows various aberration diagrams at the wide-angle end, various aberration diagrams at the intermediate focal length state, and various aberration diagrams at the telephoto end of the first to third examples, respectively. In each aberration diagram, F is the F number, y is the image height, d is the d line (λ = 587.6 nm), and SC is the sine condition. In the diagram of astigmatism, the broken line M indicates the meridional image plane and the solid line S indicates the sagittal image plane.

From comparison of the respective aberration diagrams, it is apparent that the first to third examples have excellent imaging performance in which various aberrations are favorably corrected from the wide-angle end to the telephoto end.
Next, a fourth embodiment of the present invention will be described with reference to FIG. FIG. 7 is a lens configuration diagram of the fourth example. Fourth
The example is different from the first example shown in FIG. 1 in the configuration of the second lens group G ₂ . Therefore, in the present embodiment, the configuration of the second lens group G ₂ will be described for the sake of simplicity.

In FIG. 7, the second lens group G ₂ includes, in order from the object side, a meniscus negative lens L ₂₁ having a concave surface facing the image side, and a meniscus positive lens having a concave surface facing the object side. A cemented lens L _{22 including a} concave negative lens
And a biconvex positive lens L ₂₃ and a meniscus negative lens L ₂₄ having a concave surface facing the object side. The fourth
In the embodiment, the most image-side lens surface of the cemented lens L ₂₂ is
An aspherical layer having an aspherical surface on the image side is provided.

The specifications according to this embodiment are shown in Table 4 below.
In the specification table of the embodiment, f is the focal length and F is the F number. The number at the left end represents the order from the object side of the lens surface, r is the radius of curvature of the lens surface, d is the distance between the lens surfaces, and n and ν are the refractive index and the Abbe number d line (λ =
587.6 nm). Further, the aspherical shape is represented by the above formula (6). In the zoom lens according to the present embodiment as well, the aberration correction is performed including the prism block PB showing the parallel plane plate such as the color separation prism and various filters, and therefore these data are also shown.

[0037]

[Table 4] [Fourth embodiment] f = 8.75 to 127 F = 1.72 to 2.21 (Variable spacing in zooming) f 8.75 40 127 d 8 0.6738 30.2143 39.6408 d18 38.5731 4.9655 3.1477 d21 7.9358 12.0029 4.3941 ( aspherical coefficients) 14th surface k = 0.0000 A = -3.9671 × 10 -5 B = -1.7847 × 10 - ⁸ C = -7.8052 × 10 ^-10 D = 0.0000 ｜ xa (h) -x (h) ｜ ＝ 0.261mm (h = 8.7mm) (Condition-compliant numerical value) (1) 3.000 × 10 ^-2 (2) -1.770 (3) 0.698 (4) 1.168 FIGS. 8 (a), (b), and (c) show various aberration diagrams at the wide-angle end, various aberration diagrams at the intermediate focal length state, and the telephoto end, respectively, of the fourth embodiment. The various aberration figures of are shown. In each aberration diagram, F is the F number,
y is the image height, d is the d line (λ = 587.6 nm), and SC is the sine condition. In the diagram of astigmatism, the broken line M indicates the meridional image plane and the solid line S indicates the sagittal image plane.

From the comparison of each aberration diagram, it is apparent that this embodiment has excellent imaging performance in which various aberrations are satisfactorily corrected from the wide-angle end to the telephoto end. As described above, according to each of the above-described embodiments, it is possible to realize a high-performance zoom lens that has a large zoom ratio, is bright, and is small in size, and that various aberrations are well corrected.

[0039]

As described above, according to the present invention, it is possible to provide a compact and lightweight zoom lens having high specifications and high performance.

[Brief description of drawings]

FIG. 1 is a lens configuration diagram of a first embodiment according to the present invention.

FIG. 2 is a diagram of various types of aberration in each focal length state of the first example.

FIG. 3 is a lens configuration diagram of a second embodiment according to the present invention.

FIG. 4 is a diagram of various types of aberration in each focal length state of the second example.

FIG. 5 is a lens configuration diagram of a third embodiment according to the present invention.

FIG. 6 is a diagram of various types of aberration in each focal length state of the third example.

FIG. 7 is a lens configuration diagram of a fourth example according to the present invention.

FIG. 8 is a diagram of various types of aberration in each focal length state of the fourth example.

FIG. 9 is a second lens group G ₂ of the zoom lens according to the present invention.
It is explanatory drawing which shows the effect | action of.

[Explanation of symbols]

G ₁ ... 1st lens group, G ₂ ... 2nd lens group, G ₃ ... 3rd lens group, G ₄ ... 4th lens group,

Claims (3)

[Claims] 1. A first lens group G ₁ having a positive refractive power, a second lens group G ₂ having a negative refractive power, a third lens group G ₃ having a negative refractive power, and a positive refractive power in order from the object side. And a fourth lens group G ₄ having a zoom lens having a second lens group G ₄ at the time of zooming from the wide-angle end to the telephoto end.
₂ moves from the object side to the image side along the optical axis, and the third lens group G ₃ moves so as to reciprocate on the optical axis, and the second lens group G ₂ has at least one aspherical surface. The aspherical lens surface is defined as a shape in which the positive refracting power gradually increases or a negative refracting power gradually weakens from the optical axis toward the peripheral portion. A zoom lens that is characterized by its satisfaction. 10 ⁻³ <| xa (h) −x (h) | / h <10 ⁻¹ where, h: maximum effective radius of the aspherical lens surface, xa (h): of the aspherical lens surface When expressed in a coordinate system with the surface vertex as the origin, the x-axis as the optical axis, and the y-axis as a straight line passing through the origin and perpendicular to the x-axis, the value of x at the maximum effective radius h, x (h): When expressed in the coordinate system, the value of x of the paraxial radius of curvature of the aspherical lens surface at the maximum effective radius h. 2. The first lens group G ₁ has, in order from the object side, a negative lens group L ₁₁ and at least three positive lens groups L ₁₂ , L ₁₃ , and L _14, and the second lens group G 1 ₂ is at least three lens groups L
The zoom lens according to claim 1, further comprising: ₂₁ , L ₂₂ and L ₂₃ . 3. The negative lens unit L _{11 in} the first lens unit G ₁ has a paraxial radius of curvature of a lens surface closest to the object side and a lens surface closest to the image side of the negative lens unit L ₁₁ to R, respectively. ₁ ,
When the _{R 2, -2.0 <(R 2} + R 1) / (R 2 -R 1) <- 1.5 zoom lens according to claim 2, characterized by satisfying the.