JPH07294813A - Zoom lens - Google Patents

Abstract

PURPOSE:To provide a bright and compact zoom lens having a large power variation ratio. CONSTITUTION:In a zoom lens varying the power by changing the interval between a first group of a positive refractive power and a second group of a negative refractive power, the first group is composed of a first lens 11 having a negative refractive power, a diaphragm S and a second lens 12 having a positive refractive power, the second group is composed of a third lens 13 having a negative refractive power alone and the first and the second lenses 11, 12 are axial type and the third lens is a radial type graded index lenses.

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 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, which can be realized compactly, and has a wide zooming range and brightness. An object of the present invention is to provide a new zoom lens that can easily achieve high performance.

[0005]

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 lenses according to the first to sixth aspects have a "common lens structure". That is, as shown in FIG. 1, of the first and second lenses 11 and 12 forming the first group, the first lens 11 has “negative refracting power”, and the second lens 12
Has a "positive refractive power", and the first group as a whole has a "positive refractive power". In addition, the third lens 13 forming the second group
Has "negative refractive power". In FIG. 1, reference symbol S indicates a “diaphragm” arranged between the first and second lenses 11 and 12 that form the first group.

A zoom lens according to a first aspect of the present invention has the first and second lens elements 1 in the common lens configuration.
1 and 12 are “a gradient index lens in which the refractive index changes in the optical axis direction”, and the third lens 13 is a “a gradient index lens in which the refractive index changes in the direction orthogonal to the optical axis” And

In this case, the "gradient distribution type lens whose refractive index changes in the direction of the optical axis" like the first and second lenses is called an "axial type" gradient index distribution type lens, and the above-mentioned third Like a lens, a “gradient distribution type lens whose refractive index changes in the direction orthogonal to the optical axis”, that is, a lens whose refractive index changes according to the distance from the optical axis is called a “radial type” refractive index distribution type lens.

In the zoom lens according to the first aspect, the first lens 11 may be a "meniscus lens having a convex surface facing the object side" and the second lens 12 may be a "meniscus lens having a convex surface facing the image side". Yes (Claim 2).

Further, in the case of an axial type gradient index lens, the refractive index at the intersection of the object side surface and the optical axis is d,
For the g line, n _dob and n _gob , respectively, and the refractive index at the intersection of the image side surface and the optical axis, for the d line and the g line, respectively.
When the n _dim, n _gim, these levels, defining equation: .DELTA..nu _gd = If _{(n gob -n dob) / (} n gim -n dim) in defining ".DELTA..nu _gd" qs, the claim 2 In the described zoom lens, this “Δν _gd ” is the first
For the lens 11, (3-1) 0.6 <Δν _gd <0.8 For the second lens 12, (3-2) 1.0 <Δν _gd <4.0 Yes (Claim 3).

According to a fourth aspect of the present invention, in the "common lens configuration", the first lens 11 and the third lens 13 having negative refracting power are "axial type" gradient index lens elements. , The second lens 12 having a positive refractive power
Is a "radial" gradient index lens, which is a zoom lens.

In the zoom lens of the fourth aspect, the first lens 11 is a "meniscus lens having a convex surface facing the object side" and the third lens 13 is a "meniscus lens having a convex surface facing the image side". It is possible (Claim 5).

With respect to the axial type gradient index lens, the amount "Δν _gd " defined as described above is the first lens 11 in the zoom lens according to claim 5.
In contrast, (6-1) 0.6 <Δν _gd <0.8 For the third lens 13, (6-2) 0.3 <Δν _gd <0.6 can be satisfied ( Claim 6).

The zoom lens according to claims 7 to 10 has a basic lens configuration as shown in FIG. Note that in order to avoid complication, the first to third lenses are also denoted by reference numeral 1 in FIG.
1 to 13, and the diaphragm is indicated by S.

In FIG. 2 showing the above "basic lens structure", the first lens 11 and the second lens 12 which constitute the first group.
And 3 have both "positive refractive power" and constitute the second group.
The lens 13 has "negative refracting power".

Each of the first to third lenses 11 to 13 is an "axial type" gradient index lens.

In the zoom lens according to claim 7,
The first lens 11 is a “meniscus lens having a convex surface facing the object side”, the second lens 12 is a “meniscus lens having a convex surface facing the image side”, and the third lens 13 is “a meniscus lens having a convex surface facing the image side”. It can be a "lens" (claim 8).

In the zoom lens according to claim 8,
The amount “Δν _gd ” defined for the axial gradient index lens is (9-1) 0.5 <Δν _gd <1.0 for the first lens 11, and 9-2) 1.0 <Δν _gd <2.1 For the third lens 13, (9-3) 0.3 <Δν _gd <1.0 can be satisfied (claim 9).

In the zoom lens according to the ninth aspect, Δν _gd for the first lens 11 is Δν
_gd (1), Δν _gd for the second lens is Δν
_{When gd} (2), the amount “Δν _gd (I)” defined by the definition equation: Δν _gd (I) = Δν _gd (1) / Δν _gd (2) for the first group The condition: (10-1) 0.4 <Δν _gd (I) <0.6 can be satisfied (claim 10).

[0021]

As described above, according to the present invention, the whole is composed of the three lenses of the first, second, and third lenses 11, 12, and 13, and the first lens 11 and the second lens among them constitute the first lens. By forming the first group and forming the second group by the third lens 13, a compact lens structure of "3 elements in 2 groups" is formed.

These three lenses are referred to as a "refractive index distribution type lens", and the "refractive index distribution state" within the lens is added to the items which can be designated by design, thereby increasing the degree of freedom in lens design and providing good performance. A zoom lens can be realized.

Since the refractive index of the "axial type" gradient index lens changes in the optical axis direction of the lens, it is similar to bonding a number of thin lenses having different refractive indexes,
Since the "degree of freedom of aberration correction" on the lens surface is increased, it becomes possible to excellently correct various aberrations such as distortion, spherical aberration, and coma by using such an axial type gradient index lens.

The "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.

When the first lens 11 and the second lens 12 are the axial type gradient index lenses as in the zoom lens according to the first aspect, aberrations generated before and after the stop S are favorably corrected. To cancel, the first lens 11 is a “meniscus lens having a convex surface facing the object side” and the second lens 12 is a “meniscus lens having a convex surface facing the image side”, as in the zoom lens according to claim 2. Preferably.

Furthermore, in this case, the second lens 12 which must have a strong positive refractive power in order to be combined with the first lens having a negative refractive power to form the first group having a positive refractive power. Increases the dispersion on the concave side more than the convex side (Claim 3: Conditional Expression (3-2)), and the first lens 11 having a weak negative refractive power disperses the concave side more than the convex side. Is increased (Claim 3: Conditional expression: (3-1)), the chromatic aberration of the first group can be satisfactorily corrected.

When the first lens 11 and the third lens 13 are axial type gradient index lenses as in the zoom lens according to the fourth aspect, the first lens 11 causes aberrations as much as possible. Instead, in order to smoothly pass the light rays from the object to the diaphragm S, a “meniscus lens having a convex surface facing the object side” is used, and the third lens 13 is used to satisfactorily correct field curvature and astigmatism. , “A meniscus lens having a convex surface facing the image side” is preferable (claim 5).

Further, in this case, in the first lens 11 having a weak negative refractive power, since the first group has a positive refractive power, the dispersion on the concave surface side is increased to suppress the occurrence of chromatic aberration in the first group. (Claim 6: Conditional expression (6-1)), the third lens 13 having a strong negative refractive power makes the dispersion on the convex surface side larger than that on the concave surface side (Claim 6: Conditional expression: (6- 2)) makes it possible to suppress the chromatic aberration generated in the third lens 13 and satisfactorily correct the chromatic aberration of the entire system.

According to a seventh aspect of the present invention, the first and second lenses are lenses having a positive refracting power, the third lens is a lens having a negative refracting power, and any one of the first to third lenses is used. Also, in the case of using the axial type gradient index lens, the first lens 11 is set to “2” in order to cancel the aberration generated by the one lens 11 by the second lens 12 as in the invention of claim 8. The second lens 12 is a “meniscus lens having a convex surface facing the object side” and the second lens 12 is a “meniscus lens having a convex surface facing the image side”, and the concave surfaces of the lenses are opposed to each other.
By making the third lens 13 a “meniscus lens having a convex surface facing the image side”, it becomes possible to satisfactorily correct the overall aberration.

Further, in this case, both the first lens 11 and the second lens 12 having a positive refracting power have a large dispersion on the concave side (claim 9: conditional expression (9-1, 2)), and a strong negative value. The third lens 13 having the refracting power is generated in each of the first to third lenses by increasing the dispersion on the convex surface side rather than on the concave surface side (claim 9: conditional expression (9-3)). It becomes possible to suppress chromatic aberration.

In this case, as indicated by the conditional expression (10-1) in the tenth aspect, in the first lens unit, the degree of dispersion in the optical axis direction of the lens: "Δν"
_{By making gd} "larger in the second lens than in the first lens 11, chromatic aberration in the first group can be effectively corrected, and chromatic aberration of the entire system can be effectively corrected.

Incidentally, the conditions (3-1), (3-2), (6)
-1), (6-2), (9-1), (9-2), (9-
Outside the ranges of 3) and (10-1), the effective effect of chromatic aberration correction cannot be obtained.

[0033]

[Examples] Eight specific examples will be given below. Examples 1 and 2 are examples of the invention described in claims 1, 2 and 3, Examples 3 and 4 are examples of the invention described in claims 4, 5 and 6, and Examples 5 to 8 are It is an embodiment of the invention described in claims 7, 8, 9, and 10.

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
7 to 7) are the radii of curvature of the i-th surface (including the surface of the diaphragm) counted from the object side, and d _i (i = 1 to 6) are the i-th surface and the i + 1-th surface counted from the object side. Axial spacing of the second face,
n _j (1 to 3) represents the refractive index of the j-th lens counted from the object side. The refractive index distribution in the gradient index lens is specified as follows. That is, the refractive index distribution of the “axial type” gradient index lens: n _j (x)
When the coordinate: x is set to be positive toward the image side with the vertex on the object side of the lens (intersection with the optical axis) as the origin, the refractive index at the origin position: N ₀ and the refraction Using rate distribution coefficients: N ₁ , N ₂ , N ₃ and N ₄ , it is expressed as n _j (x) = N ₀ + N ₁ x + N ₂ x ² + N ₃ x ³ + N ₄ x ⁴ (1). Therefore, given the above refractive index: N ₀ and the refractive index distribution coefficients: N ₁ , N ₂ , N ₃ , N ₄ , the refractive index distribution:
Identify n _j (x).

The refractive index distribution: n _j (h) of the “radial type” gradient index lens is set with the distance coordinate from the optical axis: h (≧ 0) with the optical axis position as the origin. Refractive index on optical axis: N ₀₀ and refractive index distribution coefficient:
Using N ₁₀ , N ₂₀ , N ₃₀ and N ₄₀ , n _j (h) = N ₀₀ + N ₁₀ h ² + N ₂₀ h ⁴ + N ₃₀ h ⁶ + N ₄₀ h ⁸ (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 (h).

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

Example 1 f = 40 to 60 mm, F / No = 5.0 to 7.4 i r _i d _i j n _j 1 16.246 46.660 1 n ₁ (x) 2 12.357 3. 000 3 ∞ (aperture) 3.000 2 n ₂ (x) 4 −2734.068 8.000 5 −14.944 Variable 6 −25.088 1.600 3 n ₃ (h) 7 −301.130.

Variable amount f: 40.5 51.0 60.0 F / No: 5.0 6.3 7.4 d ₅ : 21.958 16.521 13.375.

Refractive index n ₁ (x): [d line] [g line] N ₀ : 1.62532 1.64590 N ₁ : -0.5040E-2 -0.2237E-2 N ₂ : -0.5759E _{-4 -0.2691E-2 n 3: -0.2065E} -3 0.3485E-3 n 4: 0.6175E-4 0.3092E-4 n 2 (x): [d -ray] [g line] n _{0: 1.85000 1.87404 N 1: -0.3872E} -1 -0.3213E-1 N 2: 0.1750E-2 0.1097E-3 N 3: -0.4907E-4 -0.1231E- _{4 n 4: 0.5566E-5 0.1175E} -4 n 3 (h): [d -ray] _{[g-ray] n 00: 1.83238 1.85689 n 10} : -0.1443E-3 -0.3112E _{-3 N 20: 0.1711E-5 0} . _{3054E-5 N 30: -0.5582E-} 8 -0.1135E-7 N 40: 0.1326E-10 0.2331E-10.

Parameter of conditional expression: Value of Δν _gd First lens: 0.67, Second lens: 2.1
.

Example 2 f = 40 to 60 mm, F / No = 5.0 to 7.4 i r _i d _i j n _j 1 20.157 6.900 1 n ₁ (x) 2 16.025 2. 419 3 ∞ (aperture) 3.000 2 n ₂ (x) 4 -197.719 9.000 5 -16.364 Variable 6 -23.479 1.600 3 n ₃ (h) 7 3925.603.

Variable amount f: 40.5 51.0 60.0 F / No: 5.0 6.3 7.4 d ₅ : 23.165 17.529 14.268.

Refractive index n ₁ (x): [d line] [g line] N ₀ : 1.55257 1.57162 N ₁ : -0.1408E-1 -0.1522E-1 N ₂ : -0.2345E _{-2 -0.2267E-2 n 3: 0.1647E} -3 0.2342E-3 n 4: 0.8232E-4 0.7691E-4 n 2 (x): [d -ray] [g-ray] n _{0 : 1.80363 1.83862 N 1: -0.1399E-} 1 -0.1735E-1 N 2: -0.2357E-4 -0.1298E-3 N 3: -0.1002E-4 -0.4139E _{-5 n 4: 0.2006E-5 0.3477E} -5 n 3 (h): [d -ray] _{[g-ray] n 00: 1.67542 1.68716 n 10} : 0.1652E-4 -0.5462E _{-4 N 20: 0.4409E-6 0} . _{1076E-5 N 30: -0.1446E-} 8 -0.4064E-8 N 40: 0.3173E-11 0.7130E-11.

Parameter of conditional expression: Value of Δν _gd First lens: 0.72, Second lens: 3.5
.

Example 3 f = 40 to 60 mm, F / No = 5.0 to 7.4 i r _i d _i j j n _j 1 13.754 6361 1 n ₁ (x) 2 12.508 2. 433 3 ∞ (aperture) 3.000 2 n ₂ (h) 4 −480.296 8.000 5 −19.452 Variable 6 −21.975 1.600 3 n ₃ (x) 7 −144.760.

Variable amount f: 40.5 51.0 60.0 F / No: 5.0 6.3 7.4 d ₅ : 19.807 13.794 10.514.

Refractive index n ₁ (x): [d line] [g line] N ₀ : 1.54993 1.56832 N ₁ : -0.4159E-2 -0.4102E-2 N ₂ :: 0.1209E _{-2 -0.1088E-2 n 3: 0.2078E} -3 0.2363E-3 n 4: 0.4901E-4 0.4629E-4 n 2 (h): [d -ray] [g-ray] n _{00 : 1.73165 1.76077 N 10: -0.1223E-} 3 -0.5738E-4 N 20: -0.2309E-5 -0.2356E-5 N 30: -0.3304E-7 -0.2064E -7 N ₄₀ : 0.1887E-9 0.3937E-10 n ₃ (x): [d line] [g line] N ₀ : 1.75917 1.77236 N ₁ : 0.4491E-2 0.8992E- ₂ N 2: 0.1633E-1 0 _{1885E-1 N 3: 0.8258E-} 2 0.7912E-2 N 4: 0.1225E-2 0.1011E-2.

Parameter of conditional expression: Value of Δν _gd First lens: 0.69, Third lens: 0.55
.

Example 4 f = 36 to 55 mm, F / No = 5.0 to 7.6 i r _i d _i j n _j 1 14.410 7000 1 n ₁ (x) 2 12.210 2. 419 3 ∞ (aperture) 3.000 2 n ₂ (h) 4 641.771 8.000 5 -15.935 Variable 6 -20.749 1.600 3 n ₃ (x) 7 -220.147.

The variable amount f: 36.0 51.0 54.9 F / No : 5.0 7.1 7.6 d 5: 17.364 10.757 9.603.

Refractive index n ₁ (x): [d line] [g line] N ₀ : 1.56330 1.57346 N ₁ : -0.2870E-2 -0.3159E-2 N ₂ : -0.1766E _{-2 -0.1642E-2 n 3: 0.2472E} -3 0.2429E-3 n 4: 0.5045E-4 0.5090E-4 n 2 (h): [d -ray] [g-ray] n _{00 : 1.72678 1.75346 N 10: -0.7737E-} 4 0.1520E-4 N 20: -0.1749E-5 -0.1501E-5 N 30: -0.3807E-7 -0.2644E- 7 N ₄₀ : 0.1974E-9 0.9624E-10 n ₃ (x): [d line] [g line] N ₀ : 1.78981 1.80354 N ₁ : 0.4162E-2 0.9547E-2 N _2: 0.1143E-1 0. _{620E-1 N 3: 0.4616E-} 2 0.5347E-2 N 4: 0.8198E-3 0.7371E-3.

Parameter of conditional expression: Value of Δν _gd First lens: 0.72, Third lens: 0.37
.

Example 5 f = 40 to 60 mm, F / No = 5.0 to 7.5 i r _i d _i j _j j _j 1 18.746 3.107 1 n ₁ (x) 2 25.071 1. 788 3 ∞ (aperture) 1.300 2 n ₂ (x) 4-23.110 8.000 5-18.399 Variable 6-23.793 1.600 3 n ₃ (x) 7-101.263.

Variable amount f: 40.5 51.0 60.0 F / No: 5.0 6.3 7.4 d ₅ : 25.521 17.982 13.619.

Refractive index n ₁ (x): [d line] [g line] N ₀ : 1.55452 1.56838 N ₁ : -0.2707E-1 -0.2707E-1 N ₂ :: 0.1132E _{-1 -0.1334E-1 n 3: -0.6278E} -3 0.7663E-3 n 4: 0.1347E-2 0.1120E-2 n 2 (x): [d -ray] [g line] n _{0: 1.69659 1.72277 N 1: 0.9817E} -2 0.1252E-1 N 2: 0.1653E-2 0.8630E-3 N 3: 0.5205E-4 0.2506E-4 N 4: _{-0.1406E-4 -0.6413E-5 n 3} (h): [d -ray] _{[g-ray] n 0: 1.71971 1.73221 n 1} : -0.8755E-2 -0.3547E-2 N _{2: 0.4722E-2} 0.809 _{9E-2 N 3: 0.5143E-} 2 0.5829E-2 N 4: 0.6965E-3 0.7084E-3.

[0057] Condition Parameters: .DELTA..nu _gd value first lens: 0.93, second lens: 1.77, the third lens: 0.39 condition parameters: .DELTA..nu value of _gd (I) Δν _gd ( I) = 0.53
.

Example 6 f = 40 to 60 mm, F / No = 5.0 to 7.5 i r _i d _i j _j j _j 1 19.139 3.445 1 n ₁ (x) 2 25.418 1. 788 3 ∞ (aperture) 1.300 2 n ₂ (x) 4 -23.140 8000 5 -18.577 variable 6 -23.696 1.600 3 n ₃ (x) 7 -82.576.

Variable amount f: 40.5 51.0 60.0 F / No: 5.0 6.3 7.4 d ₅ : 25.310 17.902 13.616.

Refractive index n ₁ (x): [d line] [g line] N ₀ : 1.53856 1.55648 N ₁ : -0.2544E-1 -0.2204E-1 N ₂ : -0.1018E _{-1 -0.1462E-1 n 3: -0.1133E} -2 0.5024E-3 n 4: 0.1213E-2 0.1038E-2 n 2 (x): [d -ray] [g line] n _{0: 1.66296 1.69183 N 1: 0.1447E} -1 0.1719E-1 N 2: 0.2012E-2 0.1138E-2 N 3: 0.4991E-4 0.2454E-4 N 4: _{-0.2027E-4 -0.1219E-4 n 3} (h): [d -ray] _{[g-ray] n 0: 1.76933 1.81024 n 1} : -0.2650E-2 0.4012E-2 n ₂ : 0.8768E-2 0.1228 _{E-1 N 3: 0.7107E-} 2 0.7885E-2 N 4: 0.9706E-3 0.1011E-2.

Parameter of conditional expression: Value of Δν _gd First lens: 0.94, Second lens: 1.95, Third lens: 0.38.

[0062] the condition of parameters: the value of _{Δν gd (I) Δν gd (} I) = 0.48
.

Example 7 f = 40 to 60 mm, F / No = 5.0 to 7.5 i r _i d _i j n _j 1 19.135 3.241 1 n ₁ (x) 2 29.332 1. 788 3 ∞ (aperture) 1.300 2 n ₂ (x) 4 -21.117 8000 5 -18.455 Variable 6 -25.140 1.600 3 n ₃ (x) 7 -104.917.

Variable amount f: 40.5 51.0 60.0 F / No: 5.0 6.3 7.4 d ₅ : 25.649 18.202 13.894.

Refractive index n ₁ (x): [d line] [g line] N ₀ : 1.50773 1.52067 N ₁ : -0.2349E-1 -0.1762E-1 N ₂ : -0.8377E _{-2 -0.1663E-1 n 3: -0.1518E} -2 0.1260E-2 n 4: 0.1433E-2 0.1249E-2 n 2 (x): [d -ray] [g line] n _{0: 1.63541 1.65581 N 1: 0.1200E} -1 0.2005E-1 N 2: 0.2728E-2 0.1176E-2 N 3: 0.9667E-4 0.2439E-4 N 4: _{-0.2576E-4 -0.9595E-5 n 3} (h): [d -ray] _{[g-ray] n 0: 1.78639 1.80011 n 1} : -0.2751E-2 0.1496E-2 n ₂ : 0.1017E-1 0.1393 _{E-1 N 3: 0.8354E-} 2 0.9776E-2 N 4: 0.1183E-2 0.1346E-2.

Parameter of conditional expression: Value of Δν _gd First lens: 0.66, Second lens: 1.40, Third lens: 0.37.

[0067] the condition of parameters: the value of _{Δν gd (I) Δν gd (} I) = 0.47
.

Example 8 f = 40 to 60 mm, F / No = 5.0 to 7.5 i r _i d _i j n _j 1 19.013 3.245 1 n ₁ (x) 2 27.550 1. 788 3 ∞ (aperture) 1.300 2 n ₂ (x) 4 -21.623 8.000 5 -18.540 Variable 6 -24.666 1.600 3 n ₃ (x) 7-95.065.

Variable amount f: 40.5 51.0 60.0 F / No: 5.0 6.3 7.4 d ₅ : 25.463 17.989 13.664.

Refractive index n ₁ (x): [d line] [g line] N ₀ : 1.53221 1.54804 N ₁ : -0.2403E-1 -0.2117E-1 N ₂ :: 0.9051E _{-2 -0.1433E-1 n 3: -0.1406E} -2 0.9437E-3 n 4: 0.1337E-2 0.1068E-2 n 2 (x): [d -ray] [g line] n _{0: 1.64783 1.67604 N 1: 0.1233E} -1 0.1709E-1 N 2: 0.2352E-2 0.1196E-2 N 3: 0.7239E-4 0.3924E-4 N 4: _{-0.2053E-4 -0.1004E-4 n 3} (h): [d -ray] _{[g-ray] n 0: 1.79087 1.80461 n 1} : -0.2492E-2 0.2304E-2 n ₂ : 0.9342E-2 0.1197 _{E-1 N 3: 0.7817E-} 2 0.7818E-2 N 4: 0.1096E-2 0.9664E-3.

Parameter of conditional expression: value of Δν _gd First lens: 0.79, second lens: 1.54, third lens: 0.50.

[0072] the condition of parameters: the value of _{Δν gd (I) Δν gd (} I) = 0.51
.

FIGS. 3 to 5 show aberration diagrams of the first embodiment. 3 is for the short focal length, FIG. 4 is for the intermediate focal length, and FIG. 5 is for the long focal length. 6 to 8 are aberration diagrams of the second embodiment. 6 is for the short focal length, FIG. 7 is for the intermediate focal length, and FIG. 8 is for the long focal length. 9 to 1
Aberration diagrams relating to Example 3 are shown in FIG. FIG. 9 relates to the short focal length, FIG. 10 to the intermediate focal length, and FIG. 11 to the long focal length. 12 to 14 show aberration diagrams of the fourth embodiment. 12 is a short focal length, FIG. 13 is an intermediate focal length,
FIG. 14 relates to the long focal length.

15 to 17 are aberration diagrams for the fifth embodiment. FIG. 15 is for the short focal length, FIG. 16 is for the intermediate focal length, and FIG. 17 is for the long focal length. 18 to 20 are aberration diagrams related to Example 6. 18 shows the short focal length,
FIG. 19 relates to the intermediate focal length, and FIG. 20 relates to the long focal length. 21 to 23 show aberration diagrams for Example 7. 21 is a short focal length, FIG. 22 is an intermediate focal length, and FIG.
3 relates to the long focal length. 24 to 26 are aberration diagrams related to Example 8. 24 relates to the short focal length, FIG. 25 relates to the intermediate focal length, and FIG. 26 relates to the long focal length.

In the diagram of spherical aberration, the solid line indicates spherical aberration,
The broken line shows the sine condition, the solid line in the diagram of astigmatism shows the sagittal image plane, and the broken line shows the meridional image plane. In each aberration diagram, d and g refer to "d line" and "g line", respectively. Represents

Short focal length, intermediate focal length,
Aberration is well corrected at any of the long focal lengths,
The performance is good.

[0077]

As described above, according to the present invention, a novel zoom lens can be provided. Since the zoom lens according to the present invention has the above-described configuration, the number of constituent lenses is three groups and three, and the number of constituent lenses is extremely small, and although it can be realized in an extremely compact manner, the zoom lens according to each of the above-described embodiments is provided. As shown, the F / No is as bright as about 5.0 to 7.5, and a large zoom ratio of 1.5 times or more can be realized with good performance.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a lens configuration of a zoom lens according to claims 1 to 6.

FIG. 2 is a diagram for explaining a lens configuration of a zoom lens according to claims 7-10.

FIG. 3 is an aberration diagram at a short focal length of the zoom lens of Example 1.

FIG. 4 is an aberration diagram at an intermediate focal length of the zoom lens of Example 1.

FIG. 5 is an aberration diagram at a long focal length of the zoom lens of Example 1.

FIG. 6 is an aberration diagram at a short focal length of the zoom lens of Example 2.

FIG. 7 is an aberration diagram at an intermediate focal length of the zoom lens of Example 2.

FIG. 8 is an aberration diagram at a long focal length of the zoom lens of Example 2.

FIG. 9 is an aberration diagram at a short focal length of the zoom lens of Example 3.

FIG. 10 is an aberration diagram at an intermediate focal length of the zoom lens of Example 3.

FIG. 11 is an aberration diagram at a long focal length of the zoom lens in Example 3;

FIG. 12 is an aberration diagram at a short focal length of the zoom lens in Example 4;

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

FIG. 14 is an aberration diagram at a long focal length of the zoom lens of Embodiment 4.

FIG. 15 is an aberration diagram at a short focal length of the zoom lens of Example 5.

FIG. 16 is an aberration diagram at an intermediate focal length of the zoom lens of Example 5.

FIG. 17 is an aberration diagram at a long focal length of the zoom lens of Example 5.

FIG. 18 is an aberration diagram at a short focal length of the zoom lens of Example 6;

19 is an aberration diagram at an intermediate focal length of the zoom lens in Example 6. FIG.

FIG. 20 is an aberration diagram at a long focal length of the zoom lens of Example 6;

FIG. 21 is an aberration diagram at a short focal length of the zoom lens of Example 7.

FIG. 22 is an aberration diagram at an intermediate focal length of the zoom lens in Example 7;

FIG. 23 is an aberration diagram at a long focal length of the zoom lens of Example 7.

FIG. 24 is an aberration diagram at a short focal length of the zoom lens in Example 8;

FIG. 25 is an aberration diagram at an intermediate focal length of the zoom lens in Example 8;

FIG. 26 is an aberration diagram at a long focal length of the zoom lens in Example 8;

[Explanation of symbols]

 11 1st lens 12 2nd lens 13 3rd lens S diaphragm

Claims (10)

[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 negative 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. It is a two-group, three-lens configuration that zooms from the short focal length side to the long focal length side by moving both toward the object side while narrowing the lens. The first and second lenses have a change in refractive index in the optical axis direction. The zoom lens, wherein the third lens is a gradient index lens in which the refractive index changes in the direction orthogonal to the optical axis. 2. The zoom lens according to claim 1, wherein the first lens is a meniscus lens having a convex surface directed toward the object side, and the second lens is a meniscus lens having a convex surface directed toward the image side. Zoom lens. 3. The zoom lens according to claim 2, which is a gradient index lens in which the refractive index changes in the optical axis direction, wherein the refractive index at the intersection of the object side surface and the optical axis is d, g.
N _dob and n _gob for the line, and the refractive index at the intersection of the image side surface and the optical axis for the lines d and g, respectively.
_dim, when the n _gim, these levels, defining _{equation: Δν gd = (n gob -n} dob) / (n gim -n dim) Δν gd defined in the, with respect to the first lens, (3 -1) 0.6 <Δν _gd <0.8 The second lens satisfies (3-2) 1.0 <Δν _gd <4.0. 4. A first lens group and a second lens group are arranged in this 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 negative 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. The two-group, three-lens configuration performs zooming from the short focal length side to the long focal length side by moving both toward the object side while narrowing the lens. The first and third lenses have a refractive index change in the optical axis direction. A zoom lens, wherein the second lens is a gradient index lens in which the refractive index changes in the direction orthogonal to the optical axis. 5. The zoom lens according to claim 4, wherein the first lens is a meniscus lens having a convex surface facing the object side, and the third lens is a meniscus lens having a convex surface facing the image side. Zoom lens. 6. The zoom lens according to claim 5, which is a gradient index lens in which the refractive index changes in the optical axis direction, wherein the refractive index at the intersection of the object side surface and the optical axis is d, g.
N _dob and n _gob for the line, and the refractive index at the intersection of the image side surface and the optical axis for the lines d and g, respectively.
_dim, when the n _gim, these levels, defining _{equation: Δν gd = (n gob -n} dob) / (n gim -n dim) Δν gd defined in the, with respect to the first lens, (6 -1) 0.6 <[Delta] [gamma] _gd <0.8 The third lens satisfies (6-2) 0.3 <[Delta] [nu] _gd <0.6. 7. 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 both toward the object side while narrowing the lens. All of the first to third lenses have a refractive index in the optical axis direction. A zoom lens characterized by being a gradient index lens in which 8. The zoom lens according to claim 7, wherein 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, and the third lens is an image. A zoom lens characterized by being a meniscus lens with a convex surface facing the side. 9. The zoom lens according to claim 8, which is a gradient index lens in which the refractive index changes in the optical axis direction, wherein the refractive index at the intersection of the object side surface and the optical axis is d, g.
N _dob and n _gob for the line, and the refractive index at the intersection of the image side surface and the optical axis for the lines d and g, respectively.
_dim, when the n _gim, these levels, defining _{equation: Δν gd = (n gob -n} dob) / (n gim -n dim) Δν gd defined in the, with respect to the first lens, (9 -1) 0.5 <Δν _gd <1.0 For the second lens, (9-2) 1.0 <Δν _gd <2.1 For the third lens, (9-3) 0.3 <Δν A zoom lens characterized by satisfying _gd <1.0. 10. The zoom lens according to claim 9, wherein when Δν _gd for the first lens is Δν _gd (1) and Δν _gd for the second lens is Δν _gd (2), the first lens group in contrast, defining _{equation: Δν gd (I) = Δν} gd (1) / Δν gd (2) is defined by Δν _gd (I) is, _{conditions: (10-1) 0.4 <Δν gd} (I) A zoom lens characterized by satisfying <0.6.