JPH05249372A - Photographing lens - Google Patents

Abstract

PURPOSE:To simplify a focusing mechanism so that a cost can be lowered by adopting a method in which part of a lens system is interchanged in order to perform the focusing of a photographing lens. CONSTITUTION:A plastic lens L1 in a meniscus state whose concave surface is faced to a subject side is provided on a place nearest to the subject side, and the plastic lens L1 is switched to the plastic lenses 2-4 in the meniscus state which are integrally molded with the lens L1, whose concave surfaces are faced to the subject side and having different curvature based on an object distance so that the focusing can be performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photographic lens for a camera, and more particularly to a photographic lens for focusing by exchanging a lens arranged on the object side.

[0002]

2. Description of the Related Art In recent years, the price of small lens shutter cameras, CCD cameras, etc. has been rapidly reduced, and along with this, it is strongly desired to reduce the cost of photographing lens systems used in these cameras. ing.

Conventionally, in these cameras, focusing is performed by moving a part or all of a photographing lens along the optical axis.

[0004]

However, when focusing is performed by moving in the optical axis direction as described above, the lens frame structure is duplicated and complicated, and the position required for the lens group that moves during focusing is required. The accuracy becomes strict, and the cost tends to increase.

The present invention has been made in view of such a situation, and an object thereof is to adopt a system of exchanging a part of a lens system for focusing in a photographing lens to simplify a focusing mechanism. To lower costs.

[0006]

The taking lens of the present invention which achieves the above object has a meniscus-shaped plastic lens having a concave surface facing the object side on the most object side, and the plastic lens is adjusted according to the object distance. The lens is characterized in that focusing is performed by switching to a meniscus-shaped plastic lens which is molded integrally with this and has a concave surface facing another object side having a different curvature.

[0007]

The reason and operation of adopting the structure of the present invention will be described below. In the present invention, a meniscus-shaped plastic lens having a concave surface facing the object side of two or more types integrally formed is arranged so as to be switched to the most object side of the taking lens, and these are switched according to the object distance. Focusing is done. 1 and 2
FIG. 3 is a perspective view showing an example of arrangement of these plastic lenses. In FIG. 1, a triplet lens is used as the photographing lens body 1, and an image of a subject is formed on the image pickup device 5 by the lens 1. The plastic lens for long-distance photographing is provided on the object side of the photographing lens body 1. 2 and the plastic lens 3 for the intermediate distance and the plastic lens 4 for the short distance are integrally attached and are replaceable. In the case of FIG. 1, these lenses 2 to 4 are arranged in a turret shape, and they are exchanged by rotating this disk. In the case of FIG. 2, the lenses 2 to 4 are arranged on a single plate. Are exchanged by moving linearly in a direction perpendicular to the optical axis.

As described above, when focusing is performed by switching one lens closest to the object side, the difference in power between the lenses to be switched is determined by the object distance, but is relatively weak compared to the power of the entire lens system. Since the switching lens itself can be made of one having relatively weak power, even if plastic is used as the material, the influence of temperature change is small. Therefore, by making these several types of switching lenses into integrally molded plastic lenses, the number of parts is small,
The mechanical structure for focusing becomes simple, and the cost can be reduced.

Further, as described below, the focusing performance of the entire lens system can be improved by these focusing switching lenses.

In general, when it is attempted to construct a taking lens having an angle of view of a certain degree or more with a minimum number of lenses, the field curvature accompanying the increase of Petzval sum becomes a problem. In order to correct the field curvature that occurs when the number of constituents is reduced to reduce the cost of the lens system, in the present invention, the plastic lens is a meniscus shape with a concave surface facing the object side, The Petzval sum is corrected by increasing the height of the marginal ray that enters the lens system after that. Therefore, it is desirable that the above plastic lens satisfy the following equation.

0.8 <R ₁ n ₁ / {R ₁ n ₁ − (n ₁ −1) d ₁ } <1 (1) R ₁ /f<−0.5 (2) Here, R _{1 is the} radius of curvature of the object-side surface of the plastic lens, d _{1 is} the wall thickness of the plastic lens, n _{1 is} the refractive index of the plastic lens, and f is the focal length of the entire system.

The above conditional expression (1) defines a value obtained by dividing the axial marginal ray height on the object side surface of the plastic lens by that on the image side surface. The curvature of the surface becomes too large to generate astigmatism, or the wall thickness becomes too large to increase the height of light rays around the object-side surface and increase the size of the lens system. It is not desirable to invite. Further, the conditional expression (2) defines the radius of curvature of the plastic lens on the object side. When the upper limit is exceeded, the curvature of the concave surface becomes too large and the astigmatism generated on this surface becomes large. It becomes too much and is not preferable.

A photographing lens for a CCD camera is described later as an embodiment of the present invention. However, in such a photographing lens for a CCD camera having a standard angle of view, if the number of lenses is three, as described above. The problem often remains that the field curvature cannot be corrected completely. In the present invention, the plastic lens has a role of correcting the field curvature as described above, so that the configuration thereafter is positive, negative, and positive.
That is, it can be composed of triplets. Also,
In the case of such a configuration, it is desirable that the so-called triplet lens on the image surface side of the plastic lens satisfies the following conditional expression.

0.4 <| R ₄ | / R ₃ <1.1 (3) 1.75 <n ₂ , n ₄ (4) 0.7 <| R ₅ | / | R ₄ | <1.6 (5) where R ₃ and R ₄ are the radii of curvature of the object-side surface and the image-side surface of the most object-side lens of the triplet, respectively, and R ₅ is the negative of the triplet. The radius of curvature of the object side surface of the lens, n
₂ and n ₄ are the refractive indices of the positive lens on the object side and the positive lens on the image side of the triplet, respectively.

The conditional expression (3) relates to the radius of curvature of the positive lens closest to the object in the triplet. If the lower limit is exceeded, the Petzval sum increases too much. If the upper limit is exceeded, astigmatism or coma flare occurs. Is not corrected enough. The conditional expression (4) relates to the refractive index of the material of the positive lens in the triplet, and if the refractive index becomes smaller than the lower limit thereof, the Petzval sum increases. Further, the conditional expression (5) defines the relationship between the radius of curvature of the image-side surface of the positive lens closest to the object and the object-side surface of the negative lens of the triplet, and even if the upper limit is exceeded, the lower limit is Even if it exceeds, it becomes difficult to correct spherical aberration and coma.

Further, in the lens system of the present invention, if one or both surfaces of the plastic lens are made aspherical, the curvature of field due to astigmatism can be better corrected.

[0017]

EXAMPLES Examples 1 to 4 of the taking lens of the present invention will be described below. Although the lens data of each example will be described later, FIG. 3 shows a lens cross section in the case of switching to the plastic lens for long distance in the example 1. The shapes are substantially the same when switching between the intermediate distance and the short distance, and the other Embodiments 2 to 4 also have substantially the same shape, and therefore the illustration is omitted.

Regarding the shape of the constituent lens, the first plastic lens which can be switched for focusing is used.
The lens L1 is a weak meniscus lens having a weak power with a concave surface facing the object side for any shooting distance in the case of Examples 1, 3, and 4, and for any shooting distance in the case of Example 2. Further, it is a positive meniscus lens of weak power with a concave surface facing the object side, and in any of the examples, the second lens L2 is a biconvex lens, the third lens L3 is a biconcave lens, with a diaphragm interposed therebetween.
The fourth lens L4 is a positive meniscus lens having a concave surface facing the object side.

With respect to the aspherical surface, in the case of Examples 1 and 3, it is used for one object-side surface of the first lens L1 for any photographing distance, and in the case of Example 2, any image is taken. It is also used for the distance on both sides of the first lens L1. In Example 4, no aspherical surface is used.

In the following lens data of Examples 1 to 4, the symbols are the above, f is the focal length of the entire system, and F _NO is F.
No., 2ω is the angle of view, r ₁ , r ₂ ... Is the radius of curvature of each lens surface, d ₁ , d ₂ ... Is the distance between the lens surfaces, n _d1 , n
_d2 ... d-line refractive index of each lens, ν _d1, ν _d2 ... is the Abbe number of each lens. Further, the aspherical shape is expressed by the following formula, where x is the optical axis direction and y is the direction orthogonal to the optical axis. ^{x = (y 2 / r)} / [1+ {1-P (y 2 / r 2)} 1/2] + A 4
However ^{_{y 4 + A 6 y 6 +}} A 8 y 8, r is a paraxial radius of curvature, P is a conical _{coefficient, A 4, A 6, A} 8 are aspherical coefficients.

Example 1 f = 6.9983 F _NO = 4.00 2ω = 48.5 ° [at long distance: shooting distance ∞] r ₁ = -25.8526 (aspherical surface) d ₁ = 2.5175 n _d1 = 1.49241 ν _d1 = 57.66 r ₂ = -38.0345 d ₂ = 1.4995 r ₃ = ∞ (aperture) d ₃ = 0.1000 r ₄ = 4.4444 d ₄ = 3.2919 n _d2 = 1.83481 ν _d2 = 42.72 r ₅ = -2.4258 d ₅ = 0.0580 r ₆ = -2.1080 d ₆ = 0.7034 n _d3 = 1.67270 ν _d3 = 32.10 r ₇ = 3.4396 d ₇ = 0.6245 r ₈ = -109.3535 d ₈ = 3.1557 n _d4 = 1.83481 ν _d4 = 42.72 r ₉ = -6.4594 First surface P = 1 A ₄ = -0.14679 × 10 ^-2 A ₆ = 0.490 93 × 10 ^-3 A ₈ = -0.61938 × 10 ^-4 │R ₄ ｜ / R ₃ = 0.55 R ₁ /f=-3.69 R ₁ n ₁ / {R ₁ n ₁ -(N ₁ -1) d ₁ } = 0.97 [intermediate distance: shooting distance about 30 cm] r ₁ = -22.0661 (aspherical surface) d ₁ = 2.6666 n _d1 = 1.49241 ν _d1 = 57.66 r ₂ = -25.8873 d ₂ = 1.4995 (Hereinafter, the same as for long distance) Aspheric surface coefficient 1st surface P = 1 A ₄ ＝ -0.16477 × 10 ^-2 A ₆ ＝ 0.46 200 × 10 ⁻³ A ₈ = −0.49867 × 10 ⁻⁴ R ₁ /f=−3.21 R ₁ n ₁ / {R ₁ n ₁ − (n ₁ −1) d ₁ } = 0.96 [Short distance: shooting distance Approximately 18 cm] r ₁ = -17.3216 (aspherical surface) d ₁ = 2.8775 n _d1 = 1.49241 ν _d1 = 57.66 r ₂ = -18.6534 d ₂ = 1.4995 (hereinafter, the same as at long distance) Aspherical surface 1st surface P = ^{_{1 A 4 = -0.16288 × 10 -2}} A 6 = 0.41907 × 10 -3 A 8 = -0.41935 × 10 -4 R 1 /f=-2.57 R 1 n 1 / {R 1 n 1 - (n 1 -1 ) D ₁ } = 0.95
.

Example 2 f = 9.2983 F _NO = 3.50 2ω = 48.5 ° [at long distance: shooting distance ∞] r ₁ = -14.7617 (aspherical surface) d ₁ = 4.1810 n _d1 = 1.49241 ν _d1 = 57.66 r ₂ = -8.8978 (aspherical surface) d ₂ = 1.9897 r ₃ = ∞ (aperture) d ₃ = 0.1000 r ₄ = 6.5552 d ₄ = 2.8821 n _d2 = 1.83481 ν _d2 = 42.72 r ₅ = -3.6592 d ₅ = 0.0760 r ₆ =- 3.2835 d ₆ = 0.7513 n _d3 = 1.67270 ν _d3 = 32.10 r ₇ = 4.3350 d ₇ = 1.8418 r ₈ = -52.5414 d ₈ = 2.5650 n _d4 = 1.83481 ν _d4 = 42.72 r ₉ = -9.5011 Aspheric surface 1st surface P = 1 A ₄ = -0.81496 x 10 ^-3 A ₆ = 0.610 83 x 10 ^-4 A ₈ = -0.91285 x 10 ^-6 2nd surface P = 1 A ₄ = 0.20349 x 10 ^-3 A ₆ = 0.67969 x 10 ^-4 A ₈ = 0.45548 × 10 ^-5 │R ₄ ｜ / R ₃ = 0.56 R ₁ /f=-1.58 R ₁ n ₁ / {R ₁ n ₁ − (n ₁ −1) d ₁ } = 0.91 [At short distance] : Shooting distance of about 30 cm] r ₁ = -14.4400 (aspherical surface) d ₁ = 4.2931 n _d1 = 1.49241 ν _d1 = 57.66 r ₂ = -8.3986 (aspherical surface) d ₂ = 1 .9897 (Hereinafter, the same as for long distance) Aspheric surface coefficient 1st surface P = 1 A ₄ ＝ -0.94548 × 10 ^-3 A ₆ ＝ 0.60192 × 10 ^-4 A ₈ ＝ -0.69690 × 10 ^-6 2nd surface P _{= 1 A 4 = 0.18892 × 10} -3 A 6 = 0.61947 × 10 -4 A 8 = 0.45427 × 10 -5 R 1 /f=-1.59 R 1 n 1 / {R 1 n 1 - (n 1 -1) d ₁ } = 0.91
.

Example 3 f = 7.0094 F _NO = 4.00 2ω = 48.5 ° [at long distance: shooting distance ∞] r ₁ = -4.8668 (aspherical surface) d ₁ = 2.3464 n _d1 = 1.49241 ν _d1 = 57.66 r ₂ = -9.1278 d ₂ = 1.6895 r ₃ = ∞ (aperture) d ₃ = 0.1000 r ₄ = 3.9626 d ₄ = 3.5571 n _d2 = 1.77250 ν _d2 = 49.66 r ₅ = -4.0040 d ₅ = 0.1768 r ₆ = -2.5753 d ₆ = 0.7405 n _d3 = 1.69895 ν _d3 = 30.12 r ₇ = 5.1536 d ₇ = 0.6453 r ₈ = -13.1147 d ₈ = 1.7500 n _d4 = 1.83481 ν _d4 = 42.72 r ₉ = -4.2623 Aspheric surface 1st surface P = 1 A ₄ = 0.69824 x 10 ^-3 A ₆ = 0.53274 x 10 ^-3 A ₈ = -0.76668 x 10 ^-4 │R ₄ ｜ / R ₃ = 1.01 R ₁ /f=-0.70 R ₁ n ₁ / {R ₁ n ₁ − (N ₁ -1) d ₁ } = 0.86 [Near distance: shooting distance approx. 30 cm] r ₁ = -4.6376 (aspherical surface) d ₁ = 2.3965 n _d1 = 1.49241 ν _d1 = 57.66 r ₂ = -8.2231 d ₂ = 1.6111 (hereinafter, the same as during long-distance) aspheric coefficients first surface _{P = 1 a 4 = 0.96211 ×} 10 -3 a 6 = 0.50894 _{^{10 -3 A 8 = -0.89362 × 10}} -4 R 1 /f=-0.67 R 1 n 1 / {R 1 n 1 - (n 1 -1) d 1} = 0.85
.

Example 4 f = 6.9992 F _NO = 4.00 2ω = 48.5 ° [at long distance: shooting distance ∞] r ₁ = -6.0173 d ₁ = 2.5719 n _d1 = 1.49241 ν _d1 = 57.66 r ₂ = -6.7674 d ₂ = 1.5000 r ₃ = ∞ (aperture) d ₃ = 0.1000 r ₄ = 4.3731 d ₄ = 2.8816 n _d2 = 1.83481 ν _d2 = 42.72 r ₅ = -2.7750 d ₅ = 0.0696 r ₆ = -2.3594 d ₆ = 0.7000 n _d3 = 1.72825 ν _d3 = 28.46 r ₇ = 3.8826 d ₇ = 0.4550 r ₈ = -14.6693 d ₈ = 2.6116 nd ₄ = 1.83481 ν _d4 = 42.72 r ₉ = -5.4886 ｜ R ₄ ｜ / R ₃ = 0.63 R ₁ / f =- 0.86 R ₁ n ₁ / {R ₁ n ₁ − (n ₁ −1) d ₁ } = 0.88 [Near distance: shooting distance approx. 30 cm] r ₁ = -5.1657 d ₁ = 2.0575 n _d1 = 1.49241 ν _d1 = 57.66 r ₂ = -5.6464 d ₂ = 1.5000 (hereinafter, the same as at long distance) R ₁ /f=-0.74 R ₁ n ₁ / {R ₁ n ₁ − (n ₁ −1) d ₁ } = 0.88
.

FIG. 4 is an aberration diagram showing spherical aberration, astigmatism, distortion, and chromatic aberration of magnification of Example 1 at long distance (a), intermediate distance (b), and short distance (c). In addition, spherical aberration at long distance (a) and short distance (b) in Examples 2 to 4,
Aberration diagrams showing astigmatism, distortion, and lateral chromatic aberration are shown in FIGS.

[0026]

As is apparent from the above description, according to the present invention, it is possible to reduce the cost of the focusing mechanism, and it is possible to realize a compact photographing lens in which the field curvature is well corrected.

[Brief description of drawings]

FIG. 1 is an illustration of a plastic lens arrangement 1 according to the present invention.
It is a perspective view which shows an example.

FIG. 2 is a perspective view showing an example of arrangement of another plastic lens.

FIG. 3 is a diagram showing a lens cross section when a plastic lens for long distance is switched to in Example 1.

FIG. 4 is an aberration diagram showing spherical aberration, astigmatism, distortion, and chromatic aberration of magnification at a long distance (a), an intermediate distance (b), and a short distance (c) in Example 1.

FIG. 5 is an aberration diagram showing spherical aberration, astigmatism, distortion, and chromatic aberration of magnification of Example 2 at long distance (a) and short distance (b).

FIG. 6 is an aberration diagram similar to FIG. 5 of Example 3.

FIG. 7 is an aberration diagram similar to FIG. 5 of Example 4.

[Explanation of symbols]

 1 ... Shooting lens main body 2 ... Long-distance shooting plastic lens 3 ... Intermediate-distance shooting plastic lens 4 ... Short-distance shooting plastic lens 5 ... Imaging element L1 ... First lens L2 ... Second lens L3 ... Third Lens L4 ... 4th lens

Claims (1)

[Claims] 1. A meniscus-shaped plastic lens having a concave surface facing the object side is provided on the most object side, and the plastic lens is formed integrally with the object lens side according to the object distance, and the meniscus-shaped plastic lens is formed on another object side having a different curvature. A photographic lens characterized in that focusing is performed by switching to a meniscus-shaped plastic lens having a concave surface.