JP2871021B2 - Rear aperture triplet lens - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a triplet lens composed of three groups of three groups, positive, negative, and positive, which can be used as a photographing lens for a small-lens shutter camera. The present invention relates to a triplet lens of a post-aperture, in which a lens is made of a synthetic resin, and is small in size, and various aberrations are satisfactorily corrected.

[Conventional technology]

In the recent fierce competition, there has been a strong demand for small lens shutter cameras to be reduced in size and cost. Therefore, to reduce the size of the photographing lens, it is conceivable to reduce the telephoto ratio and widen the angle as one of the means. Also, for cost reduction, by reducing the number of lenses, using an inexpensive synthetic resin that is easy to mold instead of optical glass as a material, and by disposing a diaphragm behind the lens system, A method for simplifying the lens assembly by simplifying the configuration of the lens frame and simplifying the extension and exposure control mechanism can be considered.

As one of the lens systems satisfying these conditions, a triplet in which all lenses are made of a synthetic resin has been conventionally considered. US Pat. No. 3,194,116 and US Pat.
3,784,287 and JP-A-61-272710 are known.

[Problems to be solved by the invention]

However, at present, optical synthetic resins that can be easily produced by injection molding have a limited refractive index and Abbe number, and therefore it has been difficult to correct monochromatic aberration and chromatic aberration simultaneously. In the above-mentioned U.S. Pat. No. 3,194,116, chromatic aberration is corrected, but the telephoto ratio is 1.1 or more, and the lens is not a small lens. U.S. Patent No.
In 3,784,287, the telephoto ratio is small, but the angle of view is narrow, and as a result, it is not downsized. Also, JP-A-61-272710.
The correction of chromatic aberration is insufficient in the case of (1), and the astigmatism is large.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to solve the above-mentioned problems of the prior art, to make all lenses made of synthetic resin, to have a telephoto ratio of about 1, and a half angle of view.
An object of the present invention is to provide a triplet lens of a post-aperture having a monochromatic aberration and a chromatic aberration well corrected around 30 ° and an F number of about 5.6.

[Means for solving the problem]

The triplet lens of the post-aperture of the present invention includes, in order from the object side, a first lens having a positive refractive power in a meniscus shape directed toward a convex surface on the object side, a second lens having a negative refractive power, and a positive lens. A third lens having a refractive power and a brightness stop, wherein the lens is made of a synthetic resin, and at least one of the lens surfaces is provided with an aspheric surface; and the following condition (1) is satisfied. It is characterized by being satisfied.

_{-3.2 <φ 2 /φ<-1.5 ...... (1} ) However, phi represents the composite refractive power of the first lens to the third lens, the phi ₂ represents the refractive power of the second lens.

Furthermore, in order to perform better aberration correction, it is desirable to satisfy the following conditions in addition to the above conditions.

1 <φ ₁ /φ<2.5 (2) −1.5 <φ ₁₂ / φ <0 (3) 0.5 <f / r ₂ <5 (4) −0.3 <f / r ₃ <2.5 ... … (5) −7 × 10 ⁻² <(4φ ₁ ) / (ν ₁ φ) + (2φ ₂ ) / (ν ₂ φ) + φ ₃ / (ν ₃ φ) <3 × 10 ⁻² ... (6 ) However, f: focal length of the entire system, phi _1: refractive power of the first lens, phi _12: combined refractive power of the first lens and the second lens, phi _3: refractive power of the third lens, r _2: the object Radius of curvature of the second surface from the side, r ₃ : radius of curvature of the third surface from the object side, ν ₁ : Abbe number of the first lens, ν ₂ : Abbe number of the second lens, ν ₃ : third lens The Abbe number of.

[Action]

 Hereinafter, the operation of the present invention and each condition will be described.

As in the lens system of the present invention, when all the lenses of the triplet of the small post-aperture are made of optical synthetic resin,
Since the range of the Abbe number of the synthetic resin is limited, correction of chromatic aberration has been more difficult than before. Thus, in the present invention, correction of chromatic aberration, particularly correction of axial chromatic aberration, is realized by determining the refractive power of the negative second lens in the range of the condition (1). When the value exceeds the upper limit of the condition (1), the correction of the chromatic aberration becomes insufficient. When the value exceeds the lower limit, the correction becomes excessive. Even if other conditions are added, it is difficult to correct the axial chromatic aberration.

As a means for reducing the telephoto ratio in order to reduce the size, the principal point of the entire lens system is positioned as close to the object side as possible with respect to the lens system.
It is necessary to position the principal point position of the positive first lens on the object side with respect to the first lens as much as possible.
It is necessary that the lens has a positive meniscus shape with the convex surface facing the object side.

Further, the condition (6) satisfies the above condition (1).
This is for better correction of chromatic aberration of magnification.
This is generally obtained from the fact that the chromatic aberration coefficient T of magnification is shown in the following (a). In the case of a triplet of a position stop, as shown in FIG. ₁ , h ₁ = h ₂ = h ₃ , ₂ = ₁ /
It is of the case of approximating 2, _{3 = 2/2.}

T = Σh _{k k} φ _k / v _k (a) where h _k is the height of a marginal ray that cuts through the thin k-th lens, as shown in FIG. 1, and _k is as shown in FIG. And the height of the principal ray when the thin film k-th lens is cut. If the upper limit of the condition (6) is exceeded, the g-line becomes excessive on the plus side, and if the lower limit is exceeded, the g-line becomes excessive on the minus side, making correction difficult.

Furthermore, in order to better correct aberrations in the above state, it is desirable to satisfy the conditions (2), (3), (4), and (5).

If the lower limit of the condition (2) is exceeded, the refractive power of the first positive lens becomes weak, and the lens system cannot be made sufficiently small. When the value exceeds the upper limit, the refractive power is too strong, and it becomes difficult to correct various aberrations.

When the value exceeds the lower limit of the condition (3), the back focus becomes too long and the lens system cannot be miniaturized. When the value exceeds the upper limit, it becomes difficult to correct axial chromatic aberration.

In condition (4), when the value goes below the lower limit, the principal point of the first positive lens does not sufficiently come out on the object side, so that the lens system cannot be miniaturized. When the value goes beyond the upper limit, the curvature of the second surface becomes strong. It becomes too thick, and the lens edge thickness cannot be sufficiently obtained.

The condition (5) is a condition for further reducing the astigmatic difference due to widening the angle for downsizing. If the lower limit is exceeded, the astigmatic difference becomes too large. The curvature of the image-side surface becomes too tight, which has an adverse effect on coma.

In addition, if the telephoto ratio is reduced and the angle of view is widened to reduce the size, the monochromatic aberration is deteriorated, but this is improved by using an aspheric surface. The aspheric surface is the first positive lens, the second
When used for a negative lens, it is effective for correcting coma aberration and astigmatism, which are off-axis aberrations, and when used for a third positive lens, it is effective for correcting spherical aberration.

〔Example〕

Hereinafter, examples of the present invention will be described. The symbols are
F _NO. Is F members, W is the half angle of view, r _1, r ₂ ... curvature radius of each lens surface, d _1, d ₂ ... the spacing between the lens surfaces, n _d1, n _d2
... is the d-line refractive index of each lens, ν _d1 , ν _d2 … is the Abbe number of each lens, and the aspherical shape is when the optical axis direction is x and the direction orthogonal to the optical axis is y. Is represented by the following equation.

^{x = (y 2 / r)} / {1+ (1-P (y 2 / r 2) 1/2} + Ey 4 + Fy 6 + Gy 8 + Hy 10 + Iy 12 + Jy14 where, r is the paraxial radius of curvature, P is a conical coefficient , E, F,
G, H, I, and J are aspheric coefficients.

Example 1 f = 100, W = 31.1 °, F _NO. = 5.75 r ₁ = 20.0879 (aspheric surface) d ₁ = 12.5618 n _d1 = 1.50050 ν _d1 = 56.68 r ₂ = 46.5368 d ₂ = 2.2346 r ₃ = 119.8008 d ₃ = 3.0726 n _d2 = 1.58362 v _d2 = 30.37 r ₄ = 18.1999 (aspheric surface) d ₄ = 4.8436 r ₅ = 3214.9490 d ₅ = 6.9023 n _d3 = 1.50050 v _d3 = 56.68 r ₆ = -29.1219 (aspheric surface) d ₆ = 2.2346 r ₇ = ∞ (aperture) 1 aspherical surface P = 1, E = 0.15447 × 10 ⁻⁵ , F = 0.78897 × 10 ⁻⁸ , G = −0.37244 × 10 ⁻¹⁰ , H = 0.15005 × 10 ⁻¹² Four spherical surfaces P = 1, E = 0.48393 × 10 ⁻⁴ , F = 0.27730 × 10 ⁻⁶ , G = 0.99241 × 10 ⁻¹⁰ , H = 0.38893 × 10 ⁻¹⁰ Aspherical six surfaces P = 1, E = −0.33358 × 10 ^-4 , F = 0.72692 × 10 ^-8 , G = 0.13169 × 10 ^-9 , H = −0.28884 × 10 ^-10 (telephoto ratio) = 1.039 φ ₁ /φ=1.64 φ ₂ /φ=−2.69 φ ₁₂ /φ=−0.287 r ₂ /f=0.465 r ₃ /f=1.20 (4φ ₁ ) / (ν ₁ φ) + (2φ ₂ ) / (ν ₂ φ) + φ ₃ / (ν ₃ φ) = − 3.1 × Ten ^-2 This embodiment has the lens configuration shown in FIG. 2, in which the first lens is a positive meniscus lens having a convex surface facing the object side, the second lens is a negative meniscus lens having a convex surface facing the object side,
The lens is a biconvex positive lens. FIG. 5 shows an aberration diagram due to this lens configuration. Telephoto ratio 1.039, half angle of view 31.1
球面, Despite 5.75 F member, spherical aberration, on-axis,
Off-axis chromatic aberration is small, and astigmatism is also small. The curvature of field is rather large, but this can be improved by bending the film surface with an appropriate curvature in the short side direction.

Example 2 f = 100, W = 31.4 °, F _NO. = 5.75 r ₁ = 19.6476 (aspherical surface) d ₁ = 12.6316 n _d1 = 1.50050 ν _d1 = 56.68 r ₂ = 55.3318 d ₂ = 1.3559 r ₃ = 84.9619 d ₃ = 2.9830 n _d2 = 1.58362 ν _d2 = 30.37 r ₄ = 16.7438 (aspheric surface) d ₄ = 6.5330 r ₅ = −217.8325 d ₅ = 4.8813 n _d3 = 1.50050 ν _d3 = 56.68 r ₆ = −28.2188 d (aspheric surface) d ₆ = 2.1694 r ₇ = ∞ (aperture) 1 aspherical surface P = 1, E = 0.20249 × 10 ⁻⁵ , F = −0.29506 × 10 ⁻⁸ , G = −0.15436 × 10 ⁻¹⁰ , H = 0.52192 × 10 ^{− 13} aspherical 4 surfaces P = 1, E = 0.58484 × 10 ⁻⁴ , F = 0.37455 × 10 ⁻⁶ , G = −0.11132 × 10 ⁻⁸ , H = 0.54702 × 10 ⁻¹⁰ 6 aspherical surfaces P = 1, E = −0.27338 × 10 ⁻⁴ , F = −0.15070 × 10 ⁻⁶ , G = 0.1032 × 10 ⁻⁸ , H = −0.28408 × 10 ⁻¹⁰ (telephoto ratio) = 1.019 φ ₁ /φ=1.84 φ ₂ / φ = −2.75 φ ₁₂ /φ=−0.137 r ₂ /f=0.553 r ₃ /f=0.850 (4φ ₁ ) / (ν ₁ φ) + (2φ ₂ ) / (ν ₂ φ) + φ ₃ / (ν ₃ φ) = 2.4 × 10 ^-2 present embodiment is a lens configuration shown in FIG. 3, the first lens is a positive meniscus lens having a convex surface directed toward the object side, a negative meniscus lens the second lens having a convex surface directed toward the object side, Third
The lens is a positive meniscus lens with the convex surface facing the image side. FIG. 6 shows an aberration diagram due to this lens configuration. Despite the telephoto ratio of 1.019, half angle of view of 30.4 °, and F member of 5.75, the spherical aberration, on-axis and off-axis chromatic aberration, and astigmatism are also small. The curvature of field is rather large, but this can be improved by curving the film surface with an appropriate curvature in the short side direction.

Example 3 f = 100, W = 30.4 °, F _NO. = 5.75 r ₁ = 21.1307 (aspherical surface) d ₁ = 12.3664 n _d1 = 1.50050 ν _d1 = 56.68 r ₂ = 35.3023 d ₂ = 1.3587 r ₃ = 54.1023 d ₃ = 2.9892 n _d2 = 1.58362 ν _d2 = 30.37 r ₄ = 19.5329 (aspheric surface) d ₄ = 6.3697 r ₅ = −108.3488 d ₅ = 4.6039 n _d3 = 1.50050 ν _d3 = 56.68 r ₆ = −25.6708 d (aspheric surface) d ₆ = 2.1740 r ₇ = ∞ (aperture) 1 aspherical surface P = 1, E = 0.17914 × 10 ⁻⁵ , F = 0.56664 × 10 ⁻⁸ , G = −0.40448 × 10 ⁻¹¹ , H = 0.84507 × 10 ⁻¹³ Four aspherical surfaces P = 1, E = 0.44599 × 10 ⁻⁴ , F = 0.34346 × 10 ⁻⁶ , G = −0.11164 × 10 ⁻⁸ , H = 0.49698 × 10 ⁻¹⁰ Aspherical six surfaces P = 1, E = −0.26599 × 10 ⁻⁴ , F = −0.32155 × 10 ⁻⁶ , G = 0.92139 × 10 ⁻⁸ , H = −0.11722 × 10 ⁻⁹ (telephoto ratio) = 1.052 φ ₁ /φ=1.23 φ ₂ / φ = − 1.85 φ ₁₂ /φ=−0.160 r ₂ /f=0.353 r ₃ /f=0.541 (4φ ₁ ) / (ν ₁ φ) + (2φ ₂ ) / (ν ₂ φ) + φ ₃ / (ν ₃ φ) = −8. 2 × 10 ⁻³ This embodiment has the lens configuration shown in FIG. 3 similarly to the second embodiment. The first lens has a positive meniscus lens with the convex surface facing the object side, and the second lens has the convex surface with the object side. The negative meniscus lens and the third lens are positive meniscus lenses having a convex surface facing the image side. FIG. 7 shows an aberration diagram due to this lens configuration. Telephoto ratio 1.052, half angle of view 30.4 ゜, F member
Despite 5.75, spherical aberration, on-axis, off-axis chromatic aberration,
Also, the astigmatic difference is small. The curvature of field is rather large, but this can be improved by bending the film surface with an appropriate curvature in the short side direction.

Example 4 f = 100, W = 30.0 °, F _NO. = 5.75 r ₁ = 20.1922 (aspherical surface) d ₁ = 12.5222 n _d1 = 1.50050 ν _d1 = 56.68 r ₂ = 50.6270 d ₂ = 2.6721 r ₃ = −891.2617 d ₃ = 2.9393 n _d2 = 1.58362 ν _d2 = 30.37 r ₄ = 20.1510 (aspheric surface) d ₄ = 4.8098 r ₅ = 32.0528 d ₅ = 7.0252 n _d3 = 1.50050 ν _d3 = 56.68 r ₆ = −126.1766 d ₆ = 2.1377 r ₇ = ∞ (aperture) 1 aspherical surface P = 1.0148, E = 0.28276 × 10 ⁻⁶ , F = −0.97736 × 10 ⁻⁸ , G = −0.66746 × 10 ⁻¹⁰ , H = −0.10418 × 10 ⁻¹² , I = −0.55548 × 10 ⁻¹⁵ , J = 0.20911 × 10 ⁻¹⁷ 4 aspherical surfaces P = 0.426, E = 0.17048 × 10 ⁻⁴ , F = 0.25036 × 10 ⁻⁶ , G = −0.47221 × 10 ⁻⁸ , H = 0.61553 × 10 ⁻¹⁰ , I = −0.32211 × 10 ⁻¹² , J = 0.34624 × 10 ⁻¹⁵ (telephoto ratio) = 1.004 φ ₁ /φ=1.69 φ ₂ /φ=−2.97 φ ₁₂ /φ=−0.432 r ₂ /f=0.506 r ₃ /f=−8.91 (4φ ₁ ) / (ν ₁ φ) + (2φ ₂ ) / (ν ₂ φ) + φ ₃ / (ν ₃ φ) = − 4.2 × 10 ⁻² Is 4 lens configuration shown in FIG., A positive meniscus lens first lens having a convex surface facing the object side, the second lens is a negative lens of biconvex shape, the third lens is a positive lens of biconvex shape. FIG. 8 shows an aberration diagram due to this lens configuration. Despite the telephoto ratio of 1.004, half angle of view of 30.0 °, and F member of 5.75, the spherical aberration, on-axis and off-axis chromatic aberrations, and astigmatism are small. The curvature of field is rather large, but this can be improved by bending the film surface with an appropriate curvature in the short side direction.

Example 5 f = 100, W = 29.6 °, F _NO. = 5.75 r ₁ = 17.9871 (aspherical surface) d ₁ = 111.1986 n _d1 = 1.50050 ν _d1 = 56.68 r ₂ = 61.9155 d ₂ = 1.1012 r ₃ = 101.5577 d ₃ = 2.8968 n _d2 = 1.58362 ν _d2 = 30.37 r ₄ = 16.0263 (aspheric surface) d ₄ = 5.7587 r ₅ = 484.0766 d ₅ = 6.6224 n _d3 = 1.58362 v _d3 = 30.37 r ₆ = -44.0753 (aspheric surface) d ₆ = 2.1068 r ₇ = ∞ (aperture) 1 aspherical surface P = 1, E = 0.18174 × 10 ^-5 , F = −0.46721 × 10 ^-8 , G = 0.46006 × 10 ^-11 , H = 0.11624 × 10 ^-12 Four spherical surfaces P = 1, E = 0.45194 × 10 ⁻⁴ , F = 0.45729 × 10 ⁻⁷ , G = 0.40498 × 10 ⁻⁸ , H = 0.17992 × 10 ⁻¹¹ Aspherical six surfaces P = 1, E = −0.25135 × 10 ^-4 , F = 0.23358 × 10 ^-6 , G = −0.6838 × 10 ^-8 , H = 0.46961 × 10 ^-10 (telephoto ratio) = 0.998 φ ₁ /φ=2.14 φ ₂ /φ=−3.03 φ ₁₂ /φ=−0.044 r ₂ /f=0.618 r ₃ /f=1.02 (4φ ₁ ) / (ν ₁ φ) + (2φ ₂ ) / (ν ₂ φ) + φ ₃ / (ν ₃ φ) = − 1.1 × 10 ^-3 The embodiment has a lens configuration shown in FIG. 2 like the first embodiment. The first lens is a positive meniscus lens having a convex surface facing the object side, the second lens is a negative meniscus lens having a convex surface facing the object side, The three lenses are biconvex positive lenses.
FIG. 9 shows an aberration diagram due to this lens configuration. Telephoto ratio 0.
998, half angle of view 29.6 ゜, F member 5.75,
Spherical aberration, on-axis and off-axis chromatic aberration, astigmatism, and field curvature are small.

〔The invention's effect〕

In the post-aperture triplet lens according to the present invention, the telephoto ratio can be suppressed to as small as about 1 and the half angle of view can be as wide as about 30 °, and the lens system can be reduced in size, although it can be manufactured at low cost. At the same time, the lens is relatively bright at around the F-member 5.6, and can satisfactorily correct each aberration, particularly, spherical aberration, astigmatism, and chromatic aberration.

[Brief description of the drawings]

FIG. 1 is a diagram showing optical paths and heights of a marginal ray and a principal ray when a triplet lens of a post-aperture of the present invention is represented by three thin lenses, and FIG. 2 is a lens cross section of Examples 1 and 5. FIG. 3 is a lens cross-sectional view of Examples 2 and 3, FIG. 4 is a lens cross-sectional view of Example 4, and FIGS. 5 to 9 are aberration diagrams of Examples 1 to 5. 1... First positive lens, 2... 2nd negative lens, 3.
Positive lens, 4 ... Aperture

Claims (1)

(57) [Claims] 1. A first lens having a positive refractive power in a meniscus shape directed toward a convex surface on the object side, a second lens having a negative refractive power, and a third lens having a positive refractive power.
A lens and a brightness stop, wherein the lens is made of synthetic resin, and at least one of the lens surfaces
A triplet lens of a post-aperture, characterized by providing an aspheric surface on one surface and satisfying the following condition: −3.1 <φ ₂ /φ<−1.5 where φ is the first lens to the third lens represents a refractive power of the synthesis, phi ₂ represents a second lens optical power.