JPH07325253A - Zoom lens - Google Patents

Abstract

PURPOSE:To provide a novel zoom lens which is composed of three elements in two groups, is small in the number of constituting lens elements and is realized with compact and with which a wide variable power region, brightness and high performance are easily realizable. CONSTITUTION:The first group is constituted by disposing, successively from an object side, a first lens 1 having a positive refracting power, a diaphragm S and a second lens 3 having a positive refracting power and has a positive refracting power. The second group is composed of a third lens 5 having a negative refracting power. The zoom lens composed of the three elements in two groups executes zooming from a short focal length side to a long focal length side by moving both of the first group and the second group to the object side while narrowing the spacing therebetween. The first lens 1 is a meniscus lens of which the convex face is directed to the object side, the second lens 3 is a meniscus lens of which the convex side is directed to the image side and the third lens 5 is a biconcave lens. The second lens 3 is a distributed refractive index lens of which the refractive index changes in a direction orthogonal with the optical axis.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a "zoom lens", and more particularly to a zoom lens having a two-group, three-lens structure. The zoom lens of the present invention can be used as a zoom lens for a lens shutter camera.

[0002]

2. Description of the Related Art The number of lens shutter cameras equipped with zoom lenses has increased, and in combination with the downsizing of cameras,
There is also a demand for compact zoom lenses to be installed. The most effective way to make the lens compact is to reduce the number of constituent lenses, but it is not always easy to reduce the number of constituent lenses while maintaining performance.

Japanese Patent Application Laid-Open No. 2-69 discloses that good performance is achieved with an extremely small number of lenses, which is three.
The one disclosed in Japanese Patent Publication No. 17 as "First Example" is known, but the zoom ratio is as small as 1.36, and the brightness is 5.6 at the short focus end and 7.6 at the long focus end. Yes, it is dark on the short focus side.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances and has a two-group, three-lens structure and a small number of constituent lenses, can be realized compactly, and has a wide zooming range and brightness. An object of the present invention is to provide a novel zoom lens that can easily realize high performance (claims 1 to 4).

Another object of the present invention is to provide a zoom lens system capable of favorably correcting spherical aberration of the entire system and having good performance (claims 2 and 4).

[0006]

The "zoom lens" of the present invention comprises first and second groups arranged in order from the object side to the image side, and the first group and the second group are spaced apart from each other. By moving both toward the object side while narrowing, the zooming is performed from the short focal length side to the long focal length side.

The first group comprises, in order from the object side, the first lens,
The diaphragm and the second lens are arranged to have a "positive refractive power", and the second group is composed of one third lens and has a "negative refractive power". Therefore, the overall configuration is "two-group, three-sheet configuration".

The "zoom lens" described in claim 1 is as shown in FIG.
As shown in FIG. 1, the first lens 1 is a “positive meniscus lens with the convex surface facing the object side”, and the second lens 3 disposed on the image side of the first lens 1 via the diaphragm S is “a convex surface facing the image side. The positive lens is a positive meniscus lens "and the third lens 5 is a" concave lens ".

The second lens 3 is a "refractive index distribution type lens whose refractive index changes in the direction orthogonal to the optical axis". As described above, the gradient index lens in which the refractive index changes in the direction orthogonal to the optical axis according to the distance from the optical axis is referred to as a “radial gradient index lens”.

A "zoom lens" according to a second aspect is the zoom lens according to the first aspect, wherein the focal length of the first lens 1 is f ₁ , and the combined focal length of the entire system at the short focal end is f _w . The condition (1) is characterized by satisfying 1.2 <f ₁ / f _W <1.6.

The "zoom lens" described in claim 3 is as shown in FIG.
As shown in, the first lens 2 is a “positive meniscus lens with the convex surface facing the object side”, and the second lens 4 disposed on the image side of the first lens 2 via the diaphragm S is “a convex surface facing the image side. The third lens 6 is a "negative meniscus lens having a convex surface directed toward the image side".

The third lens 6 is a "radial type gradient index lens".

According to a fourth aspect of the present invention, in the zoom lens according to the third aspect, the focal length of the first lens 2 is f ₁ , and the combined focal length of the entire system at the short focal end is f _w . Condition (2) is characterized by satisfying 1 <f ₁ / f _W <1.2.

[0014]

As described above, according to the present invention, the whole is composed of the three lenses of the first, second and third lenses, and the first of them is the first lens.
The first lens group having a positive refracting power is composed of the lens and the second lens, and the second lens group is composed of only the third lens, thereby forming a compact lens structure of "2 groups 3 elements".

Of the three lenses, the second or third lens is a "radial type gradient index lens", and the "refractive index distribution state" in the lens is added to the items which can be designated by design. The degree of freedom in lens design is increased, and it is possible to realize a zoom lens with good performance.

"Radial type gradient index lens" is
Since the refractive index changes depending on the distance from the optical axis, the refractive index changes depending on the height of the light ray. Therefore, in this type of gradient index lens, part of the power to be shared by the lens surface can be shared by the gradient index distribution, and good correction of the “Petzval sum” is facilitated.

Conditions (1) and (2) in the zoom lens according to the second and fourth aspects are conditions for favorably correcting spherical aberration in the zoom lens according to the first and third aspects, respectively. The conditions (1) and (2) both define the ratio of the power of the first lens in the first group to the power of the entire system at the short focus end.

In the conditions (1) and (2), if the lower limit is exceeded, the positive power of the first lens becomes too strong and the spherical aberration is overcorrected. If the upper limit is exceeded, the positive power of the first lens is increased. It becomes too weak and spherical aberration is undercorrected.

[0019]

[Examples] Four specific examples will be given below. Examples 1 and 2 are examples of the invention described in claims 1 and 2, and Examples 3 and 4 are examples of the invention described in claims 3 and 4.

Throughout the embodiments, f represents the combined focal length of the entire system, and F / No represents the brightness. Further, in each embodiment, r _i (i = 1 to 7) is the radius of curvature of the i-th surface (including the surface of the stop) counted from the object side, and d _i (i = 1 to 1).
6) is the axial upper surface distance between the i-th surface and the (i + 1) -th surface counting from the object side, and n _j , ν _j (1 to 3) is the refractive index of the j-th lens counting from the object side. And Abbe number.

The refractive index distribution in the gradient index lens is specified as follows. That is, the refractive index distribution: n _j (r) of the “radial type” gradient index lens is set on the optical axis when the distance coordinate from the optical axis is set to the origin: r (≧ 0). Using the refractive index N ₀₀ and the refractive index distribution coefficients N ₁₀ , N ₂₀ , N ₃₀ , and N ₄₀ , n _j (r) = N ₀₀ + N ₁₀ r + N ₂₀ r ² + N ₃₀ r ³ + N ₄₀ r ⁴ It is expressed as (2). Therefore, given the refractive index: N ₀₀ and the refractive index distribution coefficients: N ₁₀ , N ₂₀ , N ₃₀ , N ₄₀ , the refractive index distribution:
Identify n _j (r).

In displaying the refractive index distribution coefficient,
"E-number" represents "power". That is, for example, "E-
If you say " ⁹ ", this means "1/10 ⁹ ", and this number is multiplied by the number before it.

Example 1 f = 41.0 to 59.0 mm, F / No = 6.4 to 9.2 i r _i d _i j n _j ν _j 1 15.094 1.50 1 1.883 40. 8 2 19.916 0.41 3 ∞ (aperture) 0.20 4 −28.113 12.08 2 n ₂ (r) 5 −15.569 Variable 6 −23.180 1.00 3 1.497 81. 6 7 138.060.

Variable amount f: 41.0 51.0 59.0 F / No: 6.4 7.9 9.2 d ₅ : 22.15 15.97 12.53.

Refractive index n ₂ (r): [d line] [g line] N ₀₀ : 1.49598 1.51251 N ₁₀ : -0.5411E-4 -0.1343E-4 N ₂₀ : 0.3199E- _{5 0.3193E-5 N 30: -0.6692E} -8 0.5815E-8 N 40: 0.9772E-9 0.8821E-9 condition parameter values: f ₁ / f _W = 1.5
.

Example 2 f = 41.0 to 59.0 mm, F / No = 6.4 to 9.2 i r _i d _i j n _j ν _j 1 12.681 1.00 1 1.598274 63. 9 2 20.527 0.30 3 ∞ (aperture) 4.12 4 -18.076 5.72 2 n ₂ (r) 5 -13.299 Variable 6 -28.109 6.13 23 1.497 81. 6 7 123.810.

Variable amount f: 41.0 51.0 59.0 F / No: 6.4 7.9 9.2 d ₅ : 20.31 13.12 9.13.

Refractive index n ₂ (r): [d line] [g line] N ₀₀ : 1.50474 1.52635 N ₁₀ : -0.1733E-3 -0.9759E-3 N ₂₀ : 0.9390E- _{5 0.8890E-5 N 30: -0.2347E} -7 0.3982E-7 N 40: 0.3839E-8 0.2875E-8 condition parameter values: f ₁ / f _W = 1.29
.

Example 3 f = 41.0 to 59.0 mm, F / No = 6.4 to 9.2 i r _i d _i j n _j ν _j 1 17.740 10.00 1 1.4977349 81. 5 2 70.230 2.35 3 ∞ (aperture) 3.20 4 −53.801 10.00 2 1.872870 41.4 5 −28.127 Variable 6 −13.659 10.00 3 n ₃ (r ) 7-94.359.

Variable amount f: 41.0 51.0 59.0 F / No: 6.4 7.9 9.2 d ₅ : 14.51 5.60 0.65.

Refractive index n ₃ (r): [d line] [g line] N ₀₀ : 1.64667 1.67483 N ₁₀ : -0.9539E-3 -0.9879E-3 N ₂₀ : 0.2483E- _{5 0.2421E-5 N 30: -0.5028E} -8 -0.4228E-8 N 40: 0.1380E-11 -0.1047E-12 condition parameter _{values: f 1 / f W = 1} . 1
.

Example 4 f = 41.0 to 59.0 mm, F / No = 6.4 to 9.2 i r _i d _i j n _j ν _j 1 18.305 10.00 1 1.497 81. 6 2 74.037 1.54 3 ∞ (aperture) 3.32 4 −64.009 10.00 2 1.755 52.3 5 −26.825 Variable 6 −13.904 10.00 3 n ₃ (r ) 7-560.092.

Variable amount f: 41.0 51.0 59.0 F / No: 6.4 7.9 9.2 d ₅ : 22.85 16.91 13.60.

Refractive index n ₃ (r): [d line] [g line] N ₀₀ : 1.85000 1.88701 N ₁₀ : -0.1841E-2 -0.1919E-2 N ₂₀ : 0.5135E- _{5 0.5227E-5 N 30: -0.1023E} -7 -0.9856E-8 N 40: 0.6701E-11 0.5747E-11 condition parameter values: f ₁ / f _W = 1.13
.

FIG. 3 to FIG. 5 sequentially show aberration diagrams of the first embodiment. 3 shows the short focal length, FIG. 4 shows the intermediate focal length,
FIG. 5 is an aberration diagram at the long focus end.

FIG. 6 to FIG. 8 sequentially show aberration diagrams for the second embodiment. 6 is the short focal end, FIG. 7 is the intermediate focal length,
FIG. 8 is an aberration diagram at the long focus end.

9 to 11 sequentially show aberration diagrams of the third embodiment. 9 is an aberration diagram at the short focal end, FIG. 10 is an intermediate focal length, and FIG. 11 is an aberration diagram at the long focal end.

12 to 14 sequentially show aberration diagrams of the fourth embodiment. 12 is an aberration diagram at the short focal end, FIG. 13 is an intermediate focal length, and FIG. 14 is an aberration diagram at the long focal end.

In the diagram of spherical aberration, the solid line shows "spherical aberration", the broken line shows "sine condition", the solid line in the diagram of astigmatism shows sagittal, and the broken line shows meridional. Also, "d,
"g" indicates that they are for the d line and the g line, respectively.

As can be seen from the aberration diagrams, in each of Examples 1 to 4, the various aberrations were corrected very well and the performance was good, the zoom ratio was large at about 1.5, and the brightness was F /.
No: Bright as 6.4 to 9.2.

[0041]

As described above, according to the present invention, a novel zoom lens can be provided. Since the zoom lens of the present invention is configured as described above, it is preferable to use the radial type gradient index lens as the second or third lens although it has a compact configuration of two groups and three elements. It is possible to realize a zoom lens that has high performance, is bright, and has a large zoom ratio (claims 1 to 4). The inventions according to claims 2 and 4 respectively satisfy the condition (1),
By satisfying (2), spherical aberration can be corrected well.

As the gradient index lens material used as the material of the gradient index lens according to the present invention, various materials have been known as "GRIN glass or GRIN monomer", etc., and actively developed today. Various methods such as an ion exchange method, an electric field diffusion transfer method, an ion stuffing method, a molecular stuffing method, a sol-gel method, and an ion implantation method are known.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a lens configuration of a zoom lens according to claims 1 and 2.

FIG. 2 is a diagram illustrating a lens configuration of a zoom lens according to claims 3 and 4;

FIG. 3 is an aberration diagram at a short focal end of Example 1.

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

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

FIG. 6 is an aberration diagram for Example 2 at the short focus end.

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

FIG. 8 is an aberration diagram at a long focal length end of Example 2;

FIG. 9 is an aberration diagram for Example 3 at the short focus end.

FIG. 10 is an aberration diagram for Example 3 at the intermediate focal length.

FIG. 11 is an aberration diagram at a long focal length end of Example 3;

FIG. 12 is an aberration diagram at a short focal end of Example 4.

FIG. 13 is an aberration diagram at an intermediate focal length of Example 4.

FIG. 14 is an aberration diagram at the long focal length end of Example 4;

[Explanation of symbols]

 1, 2 1st lens 3, 4 2nd lens 5, 6 3rd lens

Claims (4)

[Claims] 1. A first lens group and a second lens group are sequentially arranged from an object side to an image side, and the first group is a first lens having a positive refractive power, an aperture stop, and a positive lens group in order from the object side. A second lens having a positive refracting power, a second lens group having a negative refracting power, and a first lens group and a second lens group having a space between the first lens group and the second lens group. Is a two-lens-three-lens configuration that performs zooming from the short focal length side to the long focal length side by moving together while narrowing the lens. The first lens is a meniscus lens having a convex surface facing the object side, The second lens is a meniscus lens having a convex surface facing the image side, the third lens is a biconcave lens, and the second lens is a gradient index lens whose refractive index changes in the direction orthogonal to the optical axis. A zoom lens featuring. 2. The zoom lens according to claim 1, wherein when the focal length of the first lens is f ₁ and the combined focal length of the entire system at the short focal end is f _W , these conditions (1) 1.2. A zoom lens characterized by satisfying <f ₁ / f _W <1.6. 3. A first lens group and a second lens group are arranged in order from the object side to the image side, and the first group has, in order from the object side, a first lens having a positive refractive power, an aperture stop, and a positive lens. A second lens having a positive refracting power, a second lens group having a negative refracting power, and a first lens group and a second lens group having a space between the first lens group and the second lens group. Is a two-lens-three-lens configuration that performs zooming from the short focal length side to the long focal length side by moving together while narrowing the lens. The first lens is a meniscus lens having a convex surface facing the object side, The second lens is a meniscus lens having a convex surface facing the image side, the third lens is a meniscus lens having a convex surface facing the image side, and the third lens is a refractive lens whose refractive index changes in a direction orthogonal to the optical axis. A zoom lens characterized by being a rate distribution type lens. 4. The zoom lens according to claim 3, wherein, when the focal length of the first lens is f ₁ and the combined focal length of the entire system at the short focal end is f _W , these conditions (2) 1 <f A zoom lens characterized by satisfying ₁ / f _W <1.2.