JP2002277734A - Photography optical system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To constitute a lens system which has sufficient back focus, optical performance adaptive to high resolution, and good telecentricity by using a small number of elements. SOLUTION: A 1st negative lens, a 2nd positive lens, a 3rd negative lens, a 4th positive lens, and a 5th positive lens are arranged having mutual air gap, a stop is arranged between the 2nd and 3rd lenses, and conditions (1) 0.35<d2 <1.5, (2) 0.47<d2 /(d1 +d2 +d3 )<0.58, and (3) 0.2<d6 /d8 <0.46 are met.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photographic optical system mainly used in electronic still cameras and the like.

[0002]

2. Description of the Related Art In recent years, electronic still cameras that can be easily photographed and viewed as compared with cameras using silver halide films have become widespread. Also, a small and high-resolution electronic still camera is desired as a device for easily inputting a still image to a personal computer or the like that has been widely used in ordinary households.

An electronic still camera used for such a purpose is strongly required to have high performance and at the same time to be small and low in cost. Further, in a camera using a small image pickup device such as an electronic still camera, the size of one pixel becomes smaller as the size of the device becomes smaller, and a photographing optical system having a very high resolution is required. Further, in a camera using an image sensor, a space for disposing a filter or the like is required between the lens system and the image sensor, and an optical system having a sufficiently long back focus is required. In addition, an optical system using a color imaging device is required to have good telecentricity because light emitted from the optical system needs to be vertically incident on the imaging device in order to prevent color unevenness.

As a conventional example of a photographic optical system as described above and having a five-lens structure, there is an optical system described in Japanese Patent Application Laid-Open Nos. 2-85816 and 3-63613.

[0005] Among these conventional examples, the former has a large aperture, but has a narrow angle of view when the half angle of view is less than 20 °, and the latter has a wide angle of view with a half angle of view of around 27 ° but has large distortion. The optical performance is not sufficiently good.

Further, the conventional optical systems described in these publications are often intended for moving images, and have low resolution for use in electronic still cameras and the like.

As another conventional example of this type of optical system,
There is an optical system described in JP-A-10-213742. This optical system is assumed to be used for an electronic still camera or the like, but has a narrow angle of view with a half angle of view of 25 ° or less.

[0008]

SUMMARY OF THE INVENTION The present invention relates to a wide-angle optical system which has a sufficient back focus, has an optical performance capable of coping with a high resolution, has good telecentricity, is compact and has a small number of components. In particular, the present invention provides a photographing optical system suitable for a small-sized image sensor.

[0009]

According to the present invention, there is provided a photographing optical system comprising:
A first lens having a negative refractive power, a second lens having a positive refractive power, a third lens having a negative refractive power, and a positive refractive power arranged in order from the object side with an air gap therebetween. And a fifth lens having a positive refractive power and an aperture stop provided between the second lens and the third lens. The following conditions (1) and (2) ),
It satisfies (3). _{(1) 0.35 <d 2 /f<1.5} (2) 0.47 <d 2 / (d 1 + d 2 + d 3) <0.58 (3) 0.2 <d 6 / d 8 < 0.46 where, f is the focal length of the entire system, d ₁ is the thickness of the first lens, d ₂ is the air gap along the optical axis between the first lens and the second lens, d ₃ is the second lens The thickness d ₆ is the thickness of the third lens, and d ₈ is the thickness of the fourth lens.

In the photographing optical system of the present invention, a lens having a positive refractive power (the fifth lens of the optical system) is arranged closest to the image side in order to secure a sufficient back focus and widen the angle. And the first one with negative refractive power
The second lens, the third lens, and the fourth lens as described above, which are necessary at least to properly correct various aberrations, are disposed between the lens and the fifth lens. Then, in order to make the lens surfaces of the respective lenses function sufficiently, the lens surfaces of the respective lenses were configured to be air contact surfaces (with an air gap between the lenses).

If the lenses are joined, there is an advantage that the eccentricity sensitivity is reduced. However, the photographing optical system of the present invention is a single focus lens, and moves the lenses like a zoom lens to reduce the distance between the lenses. There is little need to change it, and there is little problem even if there is some eccentricity, and sufficient productivity can be secured.

The photographic optical system of the present invention has a small number of lenses, is compact, and has a good connection by arranging the aperture stop between the second lens and the third lens as described above. It has image performance and can satisfy telecentricity.

The conditions (1) and (2) are provided for correcting off-axis aberrations when the optical system is wide-angled, and particularly for maintaining good coma. .

If the lower limits of the conditions (1) and (2) are exceeded, off-axis aberrations, particularly coma aberration (off-axis spherical aberration), deteriorate, and the performance of the optical system deteriorates. Further, the first lens and the third lens become thicker, which increases the total length, lens diameter, and weight of the optical system, which is not preferable. If the upper limits of the conditions (1) and (2) are exceeded, the curvature of the surface of the first lens on the image plane side will be sharp when the aberration is to be corrected well, and the productivity of the lens will be poor. Cannot be constructed. Further, if the curvature of the surface is too large, ghost tends to occur, which is not preferable.

The condition (3) is for reducing the influence when the size of the image pickup device is reduced. When the value goes below the lower limit of the condition (3), the thickness of the third lens becomes too thin.
The productivity of this lens deteriorates, or the thickness of the fourth lens becomes too large, so that the optical system cannot be made compact. In particular, as the size of the imaging device decreases, the size of the optical system also decreases accordingly. When the value exceeds the upper limit of the condition (3), the fourth lens becomes thin, and the productivity of the lens deteriorates. Further, the thickness of the peripheral portion of the lens requires a certain thickness for manufacturing and assembling the lens itself. Therefore, if the wall thickness is too thin, it is not possible to secure a necessary peripheral portion thickness.

Instead of the condition (1), the following condition (1-
It is desirable to satisfy 1). (1-1) 0.48 <d ₂ /f<1.0

That is, in the optical system having the above-described configuration, it is more preferable that the conditions (1-1), (2), and (3) are satisfied.

Instead of the condition (2), the following condition (2-
It is desirable to satisfy 1). (2-1) 0.49 ≦ d ₂ / (d ₁ + d ₂ + d ₃ ) ≦ 0.
56

That is, in the optical system having the above-described configuration, it is more preferable that the conditions (1), (2-1), and (3) are satisfied.

Further, instead of the condition (3), the following condition (3)
It is desirable to satisfy -1). (3-1) 0.3 <d ₆ / d ₈ <0.4

That is, in the optical system having the above configuration, the condition (1)
It is desirable to satisfy (2) and (3-1).

Also, in the optical system having the above-mentioned configuration, instead of the conditions (1), (2) and (3), each of the conditions (1-
It is more desirable that any two conditions or all three conditions of 1), (2-1), and (3-1) be satisfied.

In each of the above-mentioned optical systems of the present invention,
It is more desirable to satisfy the following condition (4). (4) 0.5 <r ₂ / d ₂ <1.25 where r ₂ is the radius of curvature of the image-side surface of the first lens.

When the value exceeds the upper limit of the condition (4), it is difficult to achieve both a wide angle and a small size. If the lower limit of the condition (4) is exceeded, it becomes difficult to correct aberration.

Instead of the condition (4), the following condition (4-
It is preferable to satisfy 1). _{(4-1) 0.7 <r 2 /} d 2 <1.0

Further, in the optical system of the present invention, if all of the first lens, the second lens, the third lens, the fourth lens, and the fifth lens are spherical lenses having no aspheric surface, the optical system can be manufactured at low cost. This is desirable because it can be configured.

It is preferable to use an optical system having a half angle of view of more than 29 ° because a balance between small size, wide angle and low cost can be obtained. It is particularly desirable that the half angle of view is 29 ° to 50 °. More preferably, it is 30 ° to 40 °.

In order to better correct spherical aberration, astigmatism, distortion and the like after miniaturization and widening of the angle, a negative meniscus lens having a convex surface directed to the object side in order from the object side is used. Biconvex positive lens, aperture stop, biconcave negative lens,
It is more desirable that the image side surface is configured with a stronger curvature than the object side surface in the order of a positive lens and a biconvex positive lens.
In particular, it is preferable that the biconvex positive lens, which is the second lens, is a biconvex positive lens in which the image side surface has a stronger curvature than the object side surface.

[0029]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the photographing optical system according to the present invention will be described based on respective examples.

The first to sixth embodiments of the photographing optical system according to the present invention have the structures shown in FIGS. 1 to 6, respectively, and have the following data.

Example 1 f = 4.53, F / 4, 2ω = 64 ° r ₁ = 18.9356 d ₁ = 1.0000 n ₁ = 1.48749 ν ₁ = 70.23 r ₂ = 3.0500 d ₂ = 3.6000 r ₃ = 17.77738 d ₃ = 2.3000 n ₂ = 1.777250 v ₂ = 49.60 r ₄ = −6.4310 d ₄ = 2.1607 r ₅ = ∞ d ₅ = 1.3700 r ₆ = −6.1002 d ₆ = 1.0000 n ₃ = 1.84666 ν ₃ = 23.78 r ₇ = 7.6993 d _{7 = 0.2100 r 8 = 28.5604 d 8} = 3.1000 n 4 = 1.72916 ν 4 = 54.68 r 9 = -4.7552 d 9 = 0.2000 r 10 = 8.4810 d 10 = 3.0500 n 5 = 1.58913 ν 5 = 61.14 r 11 = -15.9811 d 11 = 0.8000 r ₁₂ = ∞ d ₁₂ = 1.2000 n ₆ = 1.51633 ν ₆ = 64.14 r ₁₃ = ∞ d ₁₃ = 1.4400 n ₇ = 1.54771 ν ₇ = 62.84 r ₁₄ = ∞ d ₁₄ = 0.8000 r ₁₅ = ∞ d ₁₅ = 0.8000 n ₈ = 1.51633 v ₈ = 64.14 r ₁₆ = ∞ d ₁₆ = 0.9700 r ₁₇ = ∞ (image plane) d ₂ /f=0.79 d ₂ / (d ₁ + d ₂ + d ₃ ) = 0.52 d ₆ / d ₈ = 0.32 r ₂ / d ₂ = 0.85

Example 2 f = 4.6, F / 4, 2ω = 70 ° r ₁ = 20.0357 d ₁ = 1.0000 n ₁ = 1.48749 ν ₁ = 70.23 r ₂ = 3.2100 d ₂ = 3.8000 r ₃ = 18.2875 d ₃ = 2.3000 n ₂ = 1.77250 v ₂ = 49.60 r ₄ = −6.8418 d ₄ = 2.3950 r ₅ = ∞ d ₅ = 1.3750 r ₆ = −5.7817 d ₆ = 1.0000 n ₃ = 1.84666 v ₃ = 23.78 r ₇ = 8.4936 d ₇ = 0.2100 r ₈ = 44.3111 d ₈ = 2.9900 n ₄ = 1.72916 v ₄ = 54.68 r ₉ = -4.7041 d ₉ = 0.2000 r ₁₀ = 8.5288 d ₁₀ = 3.1200 n ₅ = 1.58913 v ₅ = 61.14 r ₁₁ = -14.7620 d ₁₁ = 1.0000 r ₁₂ = ∞ d ₁₂ = 1.2000 n ₆ = 1.51633 v ₆ = 64.14 r ₁₃ = ∞ d ₁₃ = 1.4400 n ₇ = 1.54771 v ₇ = 62.84 r ₁₄ = ∞ d ₁₄ = 0.8000 r ₁₅ = ∞ d ₁₅ = 0.8000 n ₈ = 1.51633 v ₈ = 64.14 r ₁₆ = ∞ d ₁₆ = 0.9700 r ₁₇ = ∞ (image plane) d ₂ /f=0.83 d ₂ / (d ₁ + d ₂ + d ₃ ) = 0.54 d ₆ / d ₈ = 0.34 r ₂ / d ₂ = 0.85

Example 3 f = 4.53, F / 4, 2ω = 70 ° r ₁ = 22.54747 d ₁ = 1.0000 n ₁ = 1.48749 ν ₁ = 70.23 r ₂ = 2.9500 d ₂ = 3.2389 r ₃ = 15.1225 d ₃ = 2.3000 n ₂ = 1.777250 ν ₂ = 49.60 r ₄ = −6.2998 d ₄ = 2.0294 r ₅ = ∞ d ₅ = 1.3700 r ₆ = −6.0417 d ₆ = 1.0000 n ₃ = 1.84666 ν ₃ = 23.78 r ₇ = 7.9795 d _{7 = 0.2100 r 8 = 41.4923 d 8} = 3.0943 n 4 = 1.72916 ν 4 = 54.68 r 9 = -4.6988 d 9 = 0.2000 r 10 = 8.7227 d 10 = 3.0474 n 5 = 1.58913 ν 5 = 61.14 r 11 = -14.6228 d 11 = 0.8000 r ₁₂ = ∞ d ₁₂ = 1.2000 n ₆ = 1.51633 ν ₆ = 64.14 r ₁₃ = ∞ d ₁₃ = 1.4400 n ₇ = 1.54771 ν ₇ = 62.84 r ₁₄ = ∞ d ₁₄ = 0.8000 r ₁₅ = ∞ d ₁₅ = 0.8000 n ₈ = 1.51633 v ₈ = 64.14 r ₁₆ = ∞ d ₁₆ = 0.9700 r ₁₇ = ∞ (image plane) d ₂ /f=0.71 d ₂ / (d ₁ + d ₂ + d ₃ ) = 0.50 d ₆ / d ₈ = 0.32 r ₂ / d ₂ = 0.91

Example 4 f = 6.6, F / 2.8, 2ω = 62 ° r ₁ = 43.4115 d ₁ = 1.0000 n ₁ = 1.48749 ν ₁ = 70.23 r ₂ = 3.9166 d ₂ = 3.1937 r ₃ = 8.4360 _{d 3 = 2.2782 n 2 = 1.77250} ν 2 = 49.60 r 4 = -10.5871 d 4 = 1.2802 r 5 = ∞ d 5 = 1.9197 r 6 = -6.3844 d 6 = 1.0000 n 3 = 1.84666 ν 3 = 23.78 r 7 = 10.9484 d ₇ = 0.2749 r ₈ = 88.2331 d ₈ = 2.7087 n ₄ = 1.72916 v ₄ = 54.68 r ₉ = -5.9288 d ₉ = 0.2000 r ₁₀ = 12.5825 d ₁₀ = 2.6275 n ₅ = 1.72916 ν ₅ = 54.68 r ₁₁ = -22.2819 d ₁₁ = 1.9124 r ₁₂ = ∞ d ₁₂ = 1.2000 n ₆ = 1.51633 v ₆ = 64.14 r ₁₃ = ∞ d ₁₃ = 1.9000 n ₇ = 1.54771 v ₇ = 62.84 r ₁₄ = ∞ d ₁₄ = 0.8000 r ₁₅ = ∞ d ₁₅ = 0.7500 n ₈ = 1.51633 ν ₈ = 64.14 r ₁₆ = ∞ d ₁₆ = 1.2000 r ₁₇ = ∞ (image plane) d ₂ /f=0.49 d ₂ / (d ₁ + d ₂ + d ₃ ) = 0.49 d ₆ / d ₈ = 0.37 r ₂ d ₂ = 1.23

Example 5 f = 6.15, F / 3.2, 2ω = 64 ° r ₁ = 18.00898 d ₁ = 1.0000 n ₁ = 1.48749 ν ₁ = 70.23 r ₂ = 3.6672 d ₂ = 3.8806 r ₃ = 9.2103 _{d 3 = 2.4428 n 2 = 1.77250} ν 2 = 49.60 r 4 = -9.4959 d 4 = 1.3841 r 5 = ∞ d 5 = 1.9620 r 6 = -6.1985 d 6 = 1.0000 n 3 = 1.84666 ν 3 = 23.78 r 7 = 10.1924 d ₇ = 0.4760 r ₈ = 264.6241 d ₈ = 2.5700 n ₄ = 1.72916 v ₄ = 54.68 r ₉ = -5.7391 d ₉ = 0.2000 r ₁₀ = 10.4467 d ₁₀ = 2.5300 n ₅ = 1.72916 v ₅ = 54.68 r ₁₁ = -26.3461 d ₁₁ = 1.1051 r ₁₂ = ∞ d ₁₂ = 1.2000 n ₆ = 1.51633 v ₆ = 64.14 r ₁₃ = ∞ d ₁₃ = 1.9000 n ₇ = 1.54771 v ₇ = 62.84 r ₁₄ = ∞ d ₁₄ = 0.8000 r ₁₅ = ∞ d ₁₅ = 0.7500 n ₈ = 1.51633 ν ₈ = 64.14 r ₁₆ = ∞ d ₁₆ = 1.2000 r ₁₇ = ∞ (image plane) d ₂ /f=0.63 d ₂ / (d ₁ + d ₂ + d ₃ ) = 0.53 d ₆ / d ₈ = 0.39 r ₂ / d ₂ = 0.95

Example 6 f = 5.9, F / 3.5, 2ω = 66 ° r ₁ = 22.3367 d ₁ = 1.0000 n ₁ = 1.48749 ν ₁ = 70.23 r ₂ = 3.7003 d ₂ = 4.1246 r ₃ = 8.9428 _{d 3 = 2.1974 n 2 = 1.77250} ν 2 = 49.60 r 4 = -9.8436 d 4 = 1.4850 r 5 = ∞ d 5 = 1.7669 r 6 = -7.0888 d 6 = 1.0000 n 3 = 1.84666 ν 3 = 23.78 r 7 = 8.5845 d ₇ = 0.3648 r ₈ = 35.3633 d ₈ = 2.6118 n ₄ = 1.72916 ν ₄ = 54.68 r ₉ = −6.4976 d ₉ = 0.2000 r ₁₀ = 16.1291 d ₁₀ = 2.5800 n ₅ = 1.79216 ν ₅ = 54.68 r ₁₁ = -11.7625 d ₁₁ = 1.2261 r ₁₂ = ∞ d ₁₂ = 1.2000 n ₆ = 1.51633 v ₆ = 64.14 r ₁₃ = ∞ d ₁₃ = 1.9000 n ₇ = 1.54771 v ₇ = 62.84 r ₁₄ = ∞ d ₁₄ = 0.8000 r ₁₅ = ∞ d ₁₅ = 0.7500 n ₈ = 1.51633 v ₈ = 64.14 r ₁₆ = d ₁₆ = 1.2000 r ₁₇ = ∞ (image surface) d ₂ /f=0.69 d ₂ / (d ₁ + d ₂ + d ₃ ) = 0.56 _{d 6 / d 8 = 0.38 r} 2 d ₂ = 0.90 However, r _1, r _2, ··· is the radius of curvature of each lens surface, d
₁ , d ₂ ,... Are the thickness of each lens and the air gap,
, n ₁ , n ₂ ,... are the refractive indices of the lenses, ν ₁ , ν ₂ ,.
* Is the Abbe number of each lens. In the data, the unit of the length such as the focal length f, the radius of curvature r ₁ ,... Is mm.

Embodiments 1 to 6 of the present invention correspond to FIGS.
The optical system according to any of the embodiments includes a first lens having a negative refractive power and a second lens having a positive refractive power, which are disposed from the object side with an air gap therebetween. It comprises a third lens having a negative refractive power, a fourth lens having a positive refractive power, and a fifth lens having a positive refractive power. That is, as shown in the figure, the first lens is a negative meniscus lens whose surface (r ₂ ) on the image side has a strong porosity, the second lens is a biconvex lens, and the third lens is a biconcave lens. The fourth and fifth lenses are both biconvex lenses. Further, an aperture stop S is arranged between the second lens and the third lens.

As shown in the data, the first to third embodiments and the fifth and sixth embodiments of the present invention all have the condition (1),
(1-1), (2), (2-1), (3), (3-
1) and (4) are satisfied. Further, Embodiment 4 of the present invention
Conditions (1), (1-1), (2), (2-1),
(3), (3-1) and (4) are satisfied.

The state of aberration of the optical system according to the first embodiment is as shown in FIG. 7, and various aberrations are satisfactorily corrected. Also, the aberration states of the second to sixth embodiments are satisfactorily corrected in the same correction state as the first embodiment.

As described above, each of the embodiments has only a single lens and a compact configuration with a small number of lenses, and has a wide angle of view in which the half angle of view exceeds 30 °, has good optical performance, and has good telecentricity. Optical system. In addition, all lenses are spherical lenses without an aspheric surface and are inexpensive optical systems. Thus, these embodiments are balanced, small-sized, wide-angle, low-cost optical systems.

1 to 6, F1 is an infrared cut filter, F2 is an optical low-pass filter, and C is a cover glass.

According to the present invention, the optical system as described above and having the configurations described in the following items can also achieve the object of the present invention.

(1) Claims 1 and 2 of the claims
The optical system according to item 3 or 4, wherein the first lens, the second lens,
An imaging optical system, wherein all of the lens, the third lens, the fourth lens, and the fifth lens are spherical lenses having no aspheric surface.

(2) Claims 1 and 2 of the claims
3 or 4, or optical system as described in the section of said (1), imaging optical system radius of curvature r ₂ of the image-side surface of the first lens and satisfies the following condition (4). (4) 0.5 <r ₂ / d ₂ <1.25

(3) An optical system described in the above item (2), wherein the following condition (4-1) is satisfied instead of the condition (4). _{(4-1) 0.7 <r 2 /} d 2 <1.0

(5) Claims 1, 2,
3 or 4 or the above (1), (2) or (3)
Wherein the half angle of view is 29 ° to 50 °.

[0047]

According to the present invention, the total length of the optical system is short,
A small optical system having a small lens diameter, a small number of lenses, a long back focus, and various filters can be arranged, and a photographing optical system with good telecentricity can be realized.

[Brief description of the 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 a sectional view of a fifth embodiment of the present invention.

FIG. 6 is a sectional view of a sixth embodiment of the present invention.

FIG. 7 is an aberration curve diagram of the first embodiment.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yukiyuki Sabeya 2-43-2 Hatagaya, Shibuya-ku, Tokyo Inside Olympus Optical Industrial Co., Ltd. (72) Inventor Toshihide Nozawa 2-43 Hatagaya, Shibuya-ku, Tokyo No. 2 F-term in Olympus Optical Co., Ltd. (reference) 2H087 KA03 LA03 NA02 PA05 PA17 PB05 QA02 QA07 QA17 QA21 QA26 QA34 QA41 QA46 RA32 RA42 RA43

Claims (4)

[Claims] 1. A first lens having a negative refractive power, a second lens having a positive refractive power, and a third lens having a negative refractive power, which are arranged in order from the object side with an air gap therebetween. , A fourth lens having a positive refractive power, and a fifth lens having a positive refractive power.
An imaging optical system that has an aperture stop provided between the lens and the lens and satisfies the following conditions (1), (2), and (3). _{(1) 0.35 <d 2 /f<1.5} (2) 0.47 <d 2 / (d 1 + d 2 + d 3) <0.58 (3) 0.2 <d 6 / d 8 < 0.46 where, f is the focal length of the entire system, d ₁ is the thickness of the first lens, d ₂ is the air gap along the optical axis between the first lens and the second lens, d ₃ is the second lens The thickness d ₆ is the thickness of the third lens, and d ₈ is the thickness of the fourth lens. 2. The photographing optical system according to claim 1, wherein the following condition (1-1) is satisfied instead of the condition (1). (1-1) 0.48 <d ₂ /f<1.0 3. The imaging optical system according to claim 1, wherein the following condition (2-1) is satisfied instead of the condition (2). (2-1) 0.49 ≦ d ₂ / (d ₁ + d ₂ + d ₃ ) ≦ 0.
56 4. The photographing optical system according to claim 1, wherein the following condition (3-1) is satisfied instead of the condition (3). (3-1) 0.3 <d ₆ / d ₈ <0.4