JPH0735973A - Wide angle lens - Google Patents

Abstract

PURPOSE:To obtain a wide angle lens with wide angle of field, small open F-number, simple constitution, and by which aberration up to the periphery of a screen can be corrected satisfactorily by employing four-group lens consitution and satisfying a specific condition. CONSTITUTION:This lens is constituted of first to third lens groups with positive, negative, and positive refracting powers, a diaphragm, and a fourth lens group with positive reftracting power sequentially from an object side. The planes of the first and second lens groups nearest to the object side and an image side are formed in meniscus shape with convex surface facing with the object side. The synthetic refracting power of the first to third lens groups is positive. The following conditions can be satisfied; 0.1<D4<f<0.3, -0.7<(r1b-r2a)/(r1b+ r2a)<-0.1, and 1.65<Np. Where, the thickness of the fourth lens group is assumed as D4, the focal length of the whole system as (f), the radius of curvature of the plane nearest to the image side of the first lens group as r1b, the radius of curvature of the plane nearest to the object side of the second lens group as r2a, and the mean value of the refractive indexes of all positive lenses included in the first to fourth lens groups as Np.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photographic lens having a simple structure, a compact size, and a bright performance.

[0002]

2. Description of the Related Art Generally, as a photographing lens having a simple structure,
Lens systems such as triplets, tessers, and positive / negative positive telephoto types have been used.

Of these, the triplet lens system is disclosed in JP-A-61-63815 and JP-A-4-1536.
Many photographing lenses such as a lens system having a half angle of view of about 29.5 ° and an F / 2.8 like the lens system described in Japanese Patent No. 12 are known.

As the tesser type lens system, many lens systems such as a lens system of F / 2.8 with an angle of view of 30 ° or more like the lens systems of JP-A-1-18813 and JP-A-60-176011 are used. The lens is known.

Further, as a lens system having a positive / negative positive / negative lens structure, many photographing lenses are known in addition to the lens system disclosed in Japanese Patent Laid-Open No. 50-155819.

Further, as a lens system having a positive, negative, positive and positive lens structure, Japanese Patent Laid-Open No. 61-258214 and Japanese Patent Laid-Open No. 64-9 are available.
The lens system of Japanese Patent No. 0409 is known, but the latter lens system is considered to be a modification of the triplet in which the third group of positive and negative positive triplets is divided into positive, negative, positive and positive. Further, as a lens system having a positive / negative positive positive lens configuration, Japanese Patent Laid-Open No. 58-4
A lens system for a single-lens reflex camera, such as the lens system described in Japanese Patent No. 112, is also known as a Gaussian deformation type photographing lens.

In each of the conventional examples described above, the number of constituent lenses is reduced, the lens system is downsized, and the cost is reduced. Further, conventionally, in order to reduce the size of the photographing device, a retractable type in which a photographing lens body of the optical system (the lens itself as a whole) is housed in a back focus portion of the optical system is widely used.

[0008]

Among the above-mentioned conventional examples,
The triplet type lens system disclosed in Japanese Patent Laid-Open No. 61-63815 is as dark as f / 4, and is also Japanese Laid-Open Patent Publication No. 4-153612.
According to the publication, the half angle of view is as small as 24 °. In the other triplet type conventional examples, there is no bright one with a wide angle of view, and the aberration cannot be sufficiently corrected because the number of constituent elements is small. Among the conventional tesser type lens systems, the lens system disclosed in Japanese Patent Laid-Open No. 1-188813 has a drawback that distortion is large. In addition, JP-A-60-1760
In the lens system disclosed in JP-A-11, the sagittal image plane is largely bent, and good image quality cannot be expected around the screen. Further, the other tesser-type conventional lens systems are not sufficiently corrected for astigmatism.

Further, the lens system disclosed in Japanese Patent Laid-Open No. 59-155819, which is a telephoto type lens system of positive, negative, positive and negative construction, does not sufficiently correct astigmatism, and the total length of the lens system is relative to the focal length. It is a lens system that is unsuitable for a long and retractable lens. Further, there is no other conventional example of the above-mentioned type which is of F / 2.8 class, has a short lens system construction length, and is well corrected for distortion and sagittal image plane curvature. Also, in this type of lens system, a diaphragm is generally arranged between the third lens group and the fourth lens group, but it is difficult to manufacture because the tolerance before and after the diaphragm is severe.

Further, the photographic lens described in Japanese Patent Laid-Open No. 61-258214, which is a conventional example of a type having a positive and negative positive and positive refractive power arrangement, has an open F value of 2.5, which is bright, but has a half angle of view. Is as small as 25 °. Further, the lens system described in JP-A-64-90409 has a short lens configuration length, and some of them have a wide angle of view such as a half field angle of 31.7 °, but astigmatism is excellent. Not corrected.

Further, as a conventional Gaussian deformation type lens system, there is a lens system described in JP-A-58-4112. This lens system is a standard lens for single-lens reflex cameras with a small angle of view of 56 ° and a total length of 164 with respect to a focal length of 100, and the taking lens object of the present invention is the angle of view, size, and application. Is a different lens system.

The present invention has a wide angle of view, a small open F-number, a simple structure, good aberration correction up to the periphery of the screen, and a compact lens system with a structural length relatively shorter than the focal length. It is to provide a photographic lens.

[0013]

The taking lens of the present invention comprises:
From the object side, in order from the object side, the most object side surface and the most image side surface are both meniscus-shaped with convex surfaces toward the object side, and the first lens group having a positive refracting power as a whole, and the most object side surface Of the second lens group having a negative refracting power as a whole, and the third lens group having a negative refracting power as a whole, in which the first surface and the surface closest to the image side are convex surfaces on the object side.
It is composed of a lens group, a diaphragm, and a fourth lens group having a positive refracting power as a whole, and the combined refracting power of the first to third lens groups is positive, and the following condition (1) is satisfied.
It is a bright wide-angle lens that satisfies the condition (3).

(1) 0.1 <D ₄ /f<0.3 (2) −0.7 <(r _1b −r _2a ) / (r _1b + r _2a ).
<−0.1 (3) 1.65 <N _p where D ₄ is the thickness of the fourth lens group, f is the focal length of the entire system, and r _1b is the radius of curvature of the most image-side surface of the first lens group. , R
_2a is the radius of curvature of the most object side surface of the second lens group, the N _p is the average value of the refractive index of all the positive lenses included in the first to fourth lens groups.

The photographic lens of the present invention has the first structure as described above.
If the combined refractive power of the lens groups to the third lens group is positive,
By composing the front lens group, the diaphragm, and the fourth lens group having a positive refractive power, which are rear groups, that is, by composing the positive front lens group, the diaphragm, and the negative rear lens group, And symmetrical power arrangement. Further, by making the first lens group and the second lens group in the front lens group as a whole convex toward the object side to have a meniscus shape, it is possible to reduce the incident angle of off-axis rays to these two lens groups. Generation of aberrations on the surface is suppressed to a low level. In this manner, the amount of aberration generated on each surface is suppressed to a small level, and the aberrations of the front group and the rear group are canceled by each other, thereby enabling sophisticated aberration correction.

In particular, by making the first lens group a meniscus shape, it becomes possible to bring the principal point closer to the object side, which is also effective for shortening the overall length of the lens system.
Further, by making the most image-side surface of the second lens group convex to the object side like the most object side surface of the first lens group, spherical aberration is corrected by both surfaces. Further, the distortion aberration generated on the most image side surface of the first lens group is corrected on the most object side surface of the second lens group.

Further, the taking lens of the present invention is characterized by satisfying the above conditions (1) to (3).

The condition (1) defines the thickness of the fourth lens group, and is particularly for correcting astigmatism.
If the lower limit of 0.1 is exceeded under this condition (1), astigmatism will be significantly generated. In addition, the upper limit of 0.
If it exceeds 3, it is preferable for correction of astigmatism, but it becomes impossible to make the lens system compact.

The condition (2) defines the shape of the air lens sandwiched between the first lens group and the second lens group, and is a condition relating to the correction of coma aberration, astigmatism and distortion. is there. In condition (2), when the lower limit of -0.7 is exceeded and the power of the air lens becomes strong, the distortion aberration generated on the most object side surface of the second lens group becomes large, and this must be corrected by the entire system. Becomes difficult. In condition (2), when the upper limit of -0.1 is exceeded and the power of the air lens becomes weak, the effect of correcting distortion becomes weak, and correction in the entire system becomes difficult.

By satisfying the above condition (2), the off-axis rays and the most image side surface of the first lens group and the most object side surface of the second lens group are important for the wide-angle type lens system. Since the angles formed by and can be made smaller, it becomes possible to satisfactorily correct various aberrations while keeping the optical system compact.

The condition (3) defines the refractive index of the glass material used for the positive lens in the lens system and is a condition relating to the correction of the field curvature. That is, by satisfying the condition (3), the Petzval sum is appropriately set to sufficiently correct the curvature of field. If the lower limit of 1.65 is exceeded in condition (3), field curvature cannot be sufficiently corrected.

Further, in the taking lens of the present invention, since the diaphragm is arranged between the front group and the rear group as described above, the peripheral light amount is richer than that of a general behind-type diaphragm type lens system. Can be maintained at

In the present invention, it is desirable that the following condition (4) is further satisfied.

(4) 1 <r _1a / r _2b <2 where r _1a is the radius of curvature of the most object side surface of the first lens group, and r _2b is the radius of curvature of the most image side surface of the second lens group. Is.

The condition (4) relates to correction of spherical aberration. In the lens system of the present invention, the surface of the first lens group closest to the object has a strong converging action.
Therefore, spherical aberration that is insufficiently corrected occurs on this surface. In order to correct this spherical aberration, it is necessary to give a strong divergent action to the most image side surface of the second lens group, and it is desirable that these surfaces satisfy the condition (4). In this condition (4), if the lower limit of 1 is exceeded, the spherical aberration falls to the undercorrected side, and if it exceeds the upper limit of 2, the spherical aberration falls to the overcorrected side.

In order to correct the aberration of the lens system even better, it is preferable to satisfy the following conditions (5) and (6).

(5) 0.4 <(r _2a −r _2b ) / (r
_{2a + r 2b) <0.9 (} 6) -0.4 <(r 3a -r 3b) / (r 3a + r 3b)
<0 where r _3a is the radius of curvature of the most object side surface of the third lens group, and r _3b is the radius of curvature of the most image side surface of the third lens group.

The conditions (5) and (6) define the shapes of the entire second lens group and the entire third lens group, respectively.

The condition (5) is, in combination with the conditions (2) and (4), for favorably correcting spherical aberration and distortion. When the lower limit of 0.4 in the condition (5) is exceeded, the positive distortion becomes large and the spherical aberration is overcorrected. If the upper limit of 0.9 is exceeded, it is preferable for correction of distortion, but spherical aberration falls to the side of undercorrection.

The condition (6) is for correcting the coma aberration and the distortion aberration together with the condition (2). Coma is likely to occur on the object side surface of the third lens group, and distortion is likely to occur on the image side surface of the third lens group. Therefore, it is desirable to satisfy the condition (6) in order to appropriately suppress these aberrations generated in the third lens group and satisfactorily correct the aberrations in the entire system. In this condition (6), if the upper limit of 0 or the lower limit of -0.4 is exceeded, the balance of coma aberration and distortion aberration generated in the third lens group will be lost.

When the fourth lens unit is composed of only a single lens or a cemented lens, it is particularly important to correct astigmatism under the above condition (1). Further, in the lens system of the present invention, it is desirable to provide at least one aspherical surface in the front group before the diaphragm, and at least one of the aspherical surfaces has a negative refractive power with increasing distance from the optical axis. It is desirable that the shape be gradually stronger. As a result, the spherical aberration can be tilted to the undercorrected side to improve the balance of the image plane of the entire screen.

[0032]

EXAMPLES Examples of the bright wide-angle lens of the present invention will be described below. Example 1 f = 100, F-number _{= 2.9, f B = 62.16,} 2ω = 64.4 ° r 1 = 27.9430 ( _{aspherical) d 1 = 8.6500 n 1 =} 1.77250 ν 1 = 49.66 r 2 = 51.2630 d 2 = 2.0700 r _{3 = 107.2150 d 3 = 2.9600 n} 2 = 1.64769 ν 2 = 33.80 r 4 = 23.3080 ( _{aspherical) d 4 = 3.3900 r 5 =} 38.6670 d 5 = 5.9900 n 3 = 1.83481 ν 3 = 42.72 r 6 = 978.6600 d 6 = 2.9600 n ₄ = 1.67270 ν ₄ = 32.10 r ₇ = 59.3970 (aspherical surface) d ₇ = 4.4400 r ₈ = ∞ (aperture) d ₈ = 3.1000 r ₉ = 2217.5780 d ₉ = 16.7600 n ₅ = 1.77250 ν ₅ = 49.66 r ₁₀ = -145.0250 (aspherical) aspherical coefficients (first surface) P = 1.0000, E = -0.70423 × 10 -8, F = -0.63984 × 10 -10 G = 0.26951 × 10 -12, H = 0.48715 × 10 - ¹⁵ (4th surface) P = 0.7541, E = 0.50131 × 10 ^-5 , F = -0.887449 × 10 ^-8 G = 0.96677 × 10 ^-10 , H = -0.13800 × 10 ^-12 (7th surface) P = 1.0000 , E = 0.19813 x 10 ^-6 , F = -0.57451 x 10 ^-9 G = -0.52665 x 10 ^-11 , H = 0.38267 × 10 ^-14 (10th surface) P = 1.0000, E = 0.13632 × 10 ^-6 , F = -0.56110 × 10 ^-9 G = -0.20035 × 10 ^-12 , H = 0.19542 × 10 ^-14 D _{4 /f=0.168, (r 1B -r 2a} ) / (r 1b + r 2a) = - 0.353 N p = 1.793, r 1a / r 2b = 1.199 (r 2a -r 2b) / (r 2a + r 2b) = _{0.643 (r 3a -r 3b) /} (r 3a + r 3b) = - 0.211

Example 2 f = 100, F number = 2.9, f _B = 62.22, 2ω = 64.4 ° r ₁ = 27.3380 d ₁ = 8.9200 n ₁ = 1.77250 ν ₁ = 49.66 r ₂ = 44.8430 d ₂ = 1.7500 r _{3 = 68.1190 d 3 = 2.9600 n 2} = 1.69895 ν 2 = 30.12 r 4 = 24.1910 ( _{aspherical) d 4 = 5.9200 r 5 =} 40.7890 d 5 = 6.2900 n 3 = 1.83481 ν 3 = 42.72 r 6 = -785.4460 d 6 = 2.9600 n ₄ = 1.60342 ν ₄ ＝ 38.01 r ₇ ＝ 47.9990 d ₇ ＝ 2.9600 r ₈ ＝ ∞ (aperture) d ₈ ＝ 3.1000 r ₉ ＝ -712.5610 d ₉ = 15.3600 n ₅ ＝ 1.61800 ν ₅ ＝ 63.38 r ₁₀ ＝ -96.9650 Aspherical surface coefficient P = 0.9680, E = 0.30247 × 10 ⁻⁵ , F = 0.31266 × 10 ⁻⁸ G = 0.32717 × 10 ⁻¹⁰ , H = −0.26578 × 10 ⁻¹³ D ₄ /f=0.154, (r _1B −r _2a ) / (r _1b + r _2a ) =-0.206 N _p = 1.742, r _1a / r _2b = 1.130 (r _2a −r _2b ) / (r _2a + r _2b ) = 0.476 (r _3a −r _3b ) / (r _3a + r _3b ) =-0.081

Example 3 f = 100, F number = 2.9, f _B = 68.00, 2ω = 64.4 ° r ₁ = 31.2770 d ₁ = 10.7200 n ₁ = 1.77250 ν ₁ = 49.66 r ₂ = 106.4350 d ₂ = 1.4800 r _{3 = 274.6030 d 3 = 2.9300 n 2} = 1.67270 ν 2 = 32.10 r 4 = 27.0140 ( _{aspherical) d 4 = 6.8600 r 5 =} 65.6480 d 5 = 6.8000 n 3 = 1.80440 ν 3 = 39.58 r 6 = 87.6500 d 6 = 2.3700 r ₇ = ∞ _{(stop) d 7 = 1.1800 r 8 =} 302.3190 d 8 = 9.1300 n 4 = 1.77250 ν 4 = 49.66 r 9 = -33.7000 d 9 = 2.9600 n 5 = 1.54869 ν 5 = 45.55 r 10 = 1794.2090 aspherical Coefficients P = 0.9201, E = 0.28017 × 10 ^-5 , F = 0.66547 × 10 ^-8 G = -0.41277 × 10 ^-12 , H = 0.18896 × 10 ^-13 D ₄ /f=0.121, (r _1B -r _2a ). _{/ (r 1b + r 2a)} = - 0.441 N p = 1.783, r 1a / r 2b = 1.158 (r 2a -r 2b) / (r 2a + r 2b) = 0.821 (r 3a -r 3b) / (r 3a + r _3b ) = -0.144

Example 4 f = 100, F number = 2.9, f _B = 60.88, 2ω = 64.4 ° r ₁ = 30.2190 d ₁ = 10.1700 n ₁ = 1.77250 ν ₁ = 49.66 r ₂ = 89.6470 d ₂ = 2.0700 r _{3 = 284.9810 d 3 = 2.9600 n 2} = 1.64769 ν 2 = 33.80 r 4 = 22.6830 ( _{aspherical) d 4 = 1.7000 r 5 =} 30.8330 d 5 = 4.0400 n 3 = 1.80440 ν 3 = 39.58 r 6 = 41.9860 d 6 = 6.5200 r ₇ = ∞ (aperture) d ₇ = 0.2600 r ₈ = 145.2110 d ₈ = 4.8700 n ₄ = 1.77250 ν ₄ = 49.66 r ₉ = -91.6240 d ₉ = 17.7100 n ₅ = 1.71736 ν ₅ = 29.51 r ₁₀ = -247.6530 non Spherical coefficient P = 0.9033, E = 0.25938 × 10 ^-5 , F = -0.60442 × 10 ^-8 G = 0.43368 × 10 ^-10 , H = -0.62848 × 10 ^-13 D ₄ /f=0.226, (r _1B −r _2a ) / (r _1b + r _2a ) =-0.521 N _p = 1.783, r _1a / r _2b = 1.322 (r _2a −r _2b ) / (r _2a + r _2b ) = 0.853 (r _3a −r _3b ) / (r _3a + r _3b ) =-0.153 where r ₁ , r ₂ , ... is the radius of curvature of each lens surface, d
_1, d _2, ··· wall thickness of each lens, n _1, n _2, ··· is the refractive index of each lens, ν _1, ν _2, ··· is the Abbe number of each lens.

The shape of the aspherical surface used in the above embodiment is expressed by the following equation.

X = (y² / R) / [1+ {1-p (y /
r)² } ^1/2] + Ey^Four+ Fy⁶ + Gy⁸ + Hy^Ten In the above equation, the direction of the optical axis is x-axis, and the direction orthogonal to the optical axis is y.
Taken on the axis, r is the paraxial radius of curvature, p is the conic constant,
E, F, G and H are aspherical coefficients.

In Example 1, the first lens group has a positive meniscus lens whose convex surface faces the object side, the second lens group has a negative meniscus lens whose convex surface faces the object side, and the third lens group has an object side. A positive meniscus lens having a convex surface and a cemented surface convex toward the object side is a meniscus-like positive cemented lens, and these first, second, and third lens groups form a front group having a positive refractive power. Further, the fourth lens group is composed of a biconvex positive lens, and this constitutes a rear group having a positive refractive power. Aspherical surfaces are used in all the lens groups of the first to fourth lens groups, and the aspherical surface in the second lens group has a shape in which the negative refractive power increases toward the periphery. is there.

The first embodiment is a wide-angle lens having the above-described structure, which is bright with an open F-number of 2.9 and in which various aberrations are well corrected.

In Example 2, the first lens group has a positive meniscus lens whose convex surface faces the object side, the second lens group has a negative meniscus lens whose convex surface faces the object side, and the third lens group has an object side. The positive cemented lens having a meniscus shape with the convex surface facing and the cemented surface convex toward the image side constitutes the front group having a positive refractive power. Further, the fourth lens group is a positive meniscus lens having a convex surface on the image side, which constitutes the rear group of positive refractive power.

In Example 3, the first lens group has a positive meniscus lens whose convex surface faces the object side, the second lens group has a negative meniscus lens whose convex surface faces the object side, and the third lens group has an object side. A positive meniscus lens having a convex surface. These lens groups constitute a front group having a positive refracting power as a whole, and the fourth lens group has a cemented surface which is convex on the image side. The positive cemented lens forms the rear group of these positive refracting powers.

In Example 4, the first lens group is a positive meniscus lens having a convex surface directed toward the object side, the second lens group is a negative meniscus lens having a convex surface directed toward the object side, and the third lens group is an object surface. A positive meniscus lens having a convex surface directed to the side constitutes a front group having a positive refracting power as a whole by these lens groups, and a fourth lens group is a biconvex cemented lens, and a positive refracting power is formed by this lens group. It constitutes the rear group.

In each of the above embodiments, both the first lens group and the second lens group are composed of a single lens, but a meniscus-shaped cemented lens may be used for at least one of these lens groups. Has the same effect.

[0044]

The wide-angle lens of the present invention has an angle of view of about 65 °.
It is a bright lens system with a wide open F-number as small as 2.9, and the configuration is simple and aberrations are well corrected to the periphery of the screen, and the lens system configuration length is relatively longer than the focal length. It is a short and compact lens system.

[Brief description of drawings]

FIG. 1 is a sectional view of a first embodiment of the present invention.

FIG. 2 is a sectional view of a second embodiment of the present invention.

FIG. 3 is a sectional view of a third embodiment of the present invention.

FIG. 4 is a sectional view of a fourth embodiment of the present invention.

FIG. 5 is an aberration curve diagram of Example 1 of the present invention.

FIG. 6 is an aberration curve diagram of Example 2 of the present invention.

FIG. 7 is an aberration curve diagram of Example 3 of the present invention.

FIG. 8 is an aberration curve diagram of Example 4 of the present invention.

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[Procedure amendment]

[Submission date] September 22, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0002

[Correction method] Change

[Correction content]

[0002]

2. Description of the Related Art Generally, as a photographing lens having a simple structure,
Lens systems such as triplets, tessers, and positive / negative positive / positive telephoto types have been used.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] 0003

[Correction method] Change

[Correction content]

Of these, a triplet lens system is disclosed in Japanese Patent Laid-Open No. 61-63815.
A lens having a half angle of view of about 30 ° or more, such as a lens system,
The lens system described in Japanese Patent Laid-Open No. 4-153612
Many shooting lenses such as F / 2.8 are known.
It

Claims (1)

[Claims] 1. A first lens group having a meniscus shape having a convex surface facing the object side and having a positive refracting power as a whole, both of the surface closest to the object side and the surface closest to the image side, and the surface closest to the object side and the image side. Both have a meniscus shape with a convex surface facing the object side and have a negative refracting power as a whole, a third lens group having a positive refracting power as a whole, a diaphragm, and a positive refracting power as a whole. A bright wide-angle lens that is configured of a fourth lens group that has, has a positive combined refractive power of the first, second, and third lens groups, and that satisfies the following conditions (1) to (3). _{(1) 0.1 <D 4 /f<0.3} (2) -0.7 <(r 1b -r 2a) / (r 1b + r 2a)
<−0.1 (3) 1.65 <N _p where D ₄ is the thickness of the fourth lens group, f is the focal length of the entire system, and r _1b is the radius of curvature of the most image-side surface of the first lens group. , R
_2a is the radius of curvature of the most object side surface of the second lens group, the N _p is the average value of the refractive index of all the positive lenses included in the first to fourth lens groups.