JP4616566B2 - Imaging optics - Google Patents

Description

    The present invention relates to an imaging optical system used in combination with a solid-state imaging device such as a CCD or CMOS. For example, the present invention relates to an imaging optical system used for a digital still camera, a digital video camera, a small camera mounted on a mobile phone or a personal computer, a surveillance camera, and the like. The present invention also relates to an optical device using this imaging optical system.

    In recent years, electronic cameras that take a picture of a subject using a solid-state imaging device such as a CCD or a CMOS instead of a silver salt film have become widespread. Among such electronic cameras, an imaging device mounted on a portable computer, a mobile phone, or the like is particularly required to be small and light.

    Conventionally, as an imaging optical system used in such an imaging apparatus, there is an optical system configured with one or two lenses. However, such an optical system cannot correct the curvature of field, as is apparent from the aberration theory, and high performance cannot be expected.

    On the other hand, in the CCD, when the off-axis light beam emitted from the imaging optical system is incident on the image plane at a very large angle, the condensing performance of the microlens is not sufficiently exhibited. For this reason, a phenomenon occurs in which the brightness of the image changes extremely between the central portion of the image and the peripheral portion of the image. Since this phenomenon relates to the exit pupil position of the optical system, the exit pupil position is important in designing the optical system. The exit pupil and the aperture stop are in a conjugate relationship. Therefore, in an optical system composed of a small number of lenses, the aperture stop position is important.

As an optical system in consideration of this point, there is an optical system of a type in which a stop is disposed in front of the first lens or between the first lens and the second lens. As conventional examples of this type of optical system, optical systems described in the following patent documents are known.
Japanese Patent Laid-Open No. 5-188284 JP-A-9-288235 JP 2001-83409 A Among these, in the optical systems described in Documents 1 and 2, the first positive lens is a biconvex shape, and the second negative lens is a biconcave lens. Therefore, the performance of this optical system is significantly deteriorated when there is decentration between lenses. In other words, in order to ensure performance, a very high assembly system is required. For this reason, in the optical systems of Documents 1 and 2, the number of assembling steps increases, and it is difficult to reduce the cost of the optical system. In addition, this optical system cannot suppress the occurrence of distortion and lateral chromatic aberration because the aperture position is not appropriate. Therefore, none of the conventional examples can take a large angle of view. In addition, sufficient optical performance cannot be obtained unless high refractive index glass is used for the first lens. For this reason, it is impossible to achieve cost reduction and weight reduction.

    Further, in the optical system described in Document 3, since the first positive lens has a concave surface directed toward the object side, the lens periphery prevents the entire length of the optical system from being shortened. Further, the angle of incidence of light on the first surface becomes tight, and it is difficult to increase the angle of view.

    In the optical system described in Document 4, the first positive lens has a meniscus shape that is convex toward the object side. The second negative lens has a meniscus shape convex toward the image side. This overcomes the difficulty of increasing the angle of view. However, there is a drawback that the total length is long and the optical system cannot be miniaturized.

    The present invention has been made in view of the problems of the conventional optical system as described above, and provides an imaging optical system that satisfies both high performance and downsizing.

The imaging optical system of the present invention includes, in order from the object side, a first positive meniscus lens having a convex surface facing the object side, an aperture stop, a second negative meniscus lens having a convex surface facing the image side, and a third positive meniscus lens. A surface of the third lens on the object side is an aspheric surface whose curvature decreases toward the periphery, and an image side surface of the third lens is an aspheric surface whose curvature increases toward the periphery, The following condition ( 3-2 ) is satisfied.
( 3-2 ) 1. 7 <f23 / f <4.0
Here, f23 is the combined focal length of the second lens and the third lens, and f is the focal length of the entire system.

    The imaging optical system of the present invention is configured by the three lenses of the first, second, and third lenses as described above in consideration of performance and miniaturization. Here, it is obvious that the performance can be further improved if the number of lenses constituting the optical system is four. However, when one lens is added, it is inevitable that the thickness of the lens, the distance between the lenses, and the space of the frame become large, and the size of the optical system increases. Further, when the optical system is composed of two or less lenses, as described in the prior art, the field curvature cannot be reduced, and the peripheral performance deteriorates. From the above, in the present invention, the optical system is constituted by three lenses as described above.

    In addition, when an image pickup device such as a CCD is used, it is necessary to reduce the incident angle of light on the image pickup device in order to maintain good light condensing performance on the surface of the image pickup device. For that purpose, it is desirable to arrange the aperture stop or the image of the aperture stop at a position far from the image plane.

    In addition, a wide-angle optical system needs to reduce the occurrence of distortion and chromatic aberration at the periphery. For this purpose, it is desirable to arrange the aperture stop at a position where the power arrangement of the optical system is symmetric.

    For the above two reasons, in the imaging optical system of the present invention, the brightness stop is arranged between the first lens and the second lens as described above. In other words, the imaging optical system of the present invention is an optical system that emphasizes wide angle and telecentricity.

    In the imaging optical system of the present invention, the first lens is a meniscus lens having a positive power with the convex surface facing the object side, and the second lens is a meniscus lens having a negative power with the convex surface facing the image side. did. Accordingly, the refractive powers on the surfaces of the first lens and the second lens were set to positive, negative, negative, and positive in order from the object side. Thus, the surface having negative refractive power was divided into the refractive surfaces of two lenses (first and second lenses). As a result, it has become possible to minimize the performance fluctuation when the lens is relatively decentered.

    Next, in the optical system of the present invention, the third lens is an important lens for reducing the incident angle to the image sensor.

    Therefore, as described above, the third lens has an aspheric surface whose curvature decreases toward the periphery on the object side surface, and an aspheric surface whose curvature increases toward the periphery on the image side surface. I made it. This makes it possible to reduce the incident angle of the surrounding light rays on the image sensor. It has a shape that minimizes the angle formed by the incident light beam and the outgoing light beam, that is, the deflection angle. Thus, by making the refracting surface of the third lens as described above, it becomes possible to allow peripheral rays to enter the imaging element at a small angle while suppressing the occurrence of aberration.

The imaging optical system of the present invention described above can correct various aberrations such as spherical aberration and coma aberration more satisfactorily by satisfying the following condition (1).
(1) −100 <(r1r ² / f1) / (r2f ² / f2) <− 1
Where r1r is the radius of curvature of the image side surface of the first positive lens, r2f is the radius of curvature of the object side surface of the second negative lens, f1 is the focal length of the first positive lens, and f2 is the focal point of the second negative lens. Distance.

    This condition (1) is for sharing negative power between the first lens and the second lens. By satisfying this condition, it is possible to suppress performance degradation due to the relative eccentricity of the lens.

    If the upper limit of -1 of the condition (1) is exceeded, the power of the object side surface of the second lens becomes too weak, and it becomes impossible to suppress performance deterioration due to the relative eccentricity of the lens. On the other hand, if the lower limit value −100 of the condition (1) is not reached, the negative power of the object side surface of the second lens becomes too strong, and the spherical aberration and coma generated on this surface become large. It becomes impossible to correct on the other side.

It is more desirable if the following condition (1-1) is satisfied instead of the condition (1).
(1-1) −60 <(r1r ² / f1) / (r2f ² / f2) <− 10

It is more desirable to satisfy the following condition (1-2) instead of condition (1).
(1-2) −40 <(r1r ² / f1) / (r2f ² / f2) <− 20

The imaging optical system of the present invention can further reduce the overall length of the optical system by satisfying the following condition (2).
(2) 0.1 <f1 / f <3.0
Here, f1 is the focal length of the first positive lens, and f is the focal length of the entire system.

    In order to shorten the overall length of the optical system, it is necessary to position the principal point of the optical system closer to the object side. For this purpose, the power of the first lens is important. Condition (2) defines the focal length of the first lens.

    If the upper limit of 3.0 to condition (2) is exceeded, the power of the first lens will be too weak, making it difficult to shorten the overall length. On the other hand, if the lower limit of 0.1 is not reached, the power of the first lens becomes too strong, and aberrations occurring in this lens cannot be corrected by the second lens. For this reason, it becomes difficult to obtain an imaging optical system having good optical performance.

It is more desirable to satisfy the following condition (2-1) instead of this condition (2).
(2-1) 0.5 <f1 / f <2.0

Moreover, it is more preferable if the following condition (2-2) is satisfied instead of condition (2).
(2-2) 0.8 <f1 / f <1.2

In the imaging optical system of the present invention having the above-described configuration, it is preferable that the following condition (3) is satisfied.
(3) 1.0 <f23 / f <4.0
Here, f23 is the combined focal length of the second lens and the third lens, and f is the focal length of the entire system.

    In the imaging optical system of the present invention, since the second negative lens has a diverging action, it acts in a disadvantageous direction with respect to the incident angle of the light ray on the image plane. Therefore, the configuration of the third positive lens next to the second negative lens is important.

    If the upper limit of 4.0 of the condition (3) is exceeded, the negative power becomes too strong and the incident angle on the image plane becomes too tight. On the other hand, if the lower limit of 1.0 of the condition (4) is not reached, the negative power becomes too weak, the Petzval sum is significantly increased, and good optical performance cannot be obtained.

Instead of this condition (3), it is more desirable if the following condition (3-1) is satisfied.
(3-1) 1.3 <f23 / f <3.0

It is more desirable to satisfy the following condition (3-2) instead of condition (3).
(3-2) 1.7 <f23 / f <2.3

In the imaging optical system of the present invention, a first lens, a second lens, and a third lens are arranged with an aperture stop interposed therebetween. For this reason, off-axis rays pass point-symmetrically around the aperture stop. Therefore, in the optical system of the present invention, it is important to correct lateral chromatic aberration and distortion. In order to correct the lateral chromatic aberration and distortion, it is preferable to satisfy the following condition (4).
(4) -10.0 <f1 / f23 <3.0
Here, f1 is the focal length of the first positive lens, and f23 is the combined focal length of the second negative lens and the third positive lens.

    If the upper limit value of 3.0 in the condition (4) is exceeded or less than the lower limit value of -10.0, the lateral chromatic aberration and distortion will be overcorrected or undercorrected, and the peripheral performance will deteriorate.

In addition, it is more preferable to satisfy the following condition (4-1) instead of condition (4).
(4-1) -1.0 <f1 / f23 <1.0

Furthermore, it is more desirable if the following condition (4-2) is satisfied instead of condition (4).
(4-2) 0.4 <f1 / f23 <0.7

Furthermore, in the imaging optical system of the present invention, it is desirable to satisfy the following condition (5) in order to satisfactorily correct the longitudinal chromatic aberration and to achromatic the entire lens system.
(5) 0.1 < − (ν2−ν1) / (ν3−ν2) <8.0
Here, ν1, ν2, and ν3 are Abbe numbers of the first lens, the second lens, and the third lens, respectively.

    If the upper limit of 8.0 of the condition (5) is exceeded or less than the lower limit of 0.1, the axial chromatic aberration is overcorrected or undercorrected. As a result, it becomes difficult to ensure the central performance of the optical system.

It is more preferable if the following condition (5-1) is satisfied instead of condition (5).
(5-1) 0.3 < − (ν2-ν1) / (ν3-ν2) <3.0

Furthermore, it is more preferable that the following condition (5-2) is satisfied instead of condition (5).
(5-2) 0.5 < − (ν2-ν1) / (ν3-ν2) <1.5

Furthermore, in the imaging optical system of the present invention, it is preferable that the maximum incident angle α of the principal ray on the image plane satisfies the following condition (6).
(6) 10 ° <α <40 °

    When a CCD is used as the image sensor, the brightness of the image differs between the center portion of the image and the peripheral portion of the image when the off-axis light beam emitted from the imaging optical system is incident on the image plane at a very large angle. On the other hand, when the off-axis light beam is incident on the image at a small angle, the problem of the brightness of the image is reduced. However, in this case, the total length of the optical system becomes long, which is not preferable.

    For the above reasons, it is preferable that α satisfies the condition (6).

    If the upper limit of 40 ° of condition (6) is exceeded, the incident angle to the CCD becomes too large and the brightness of the peripheral portion of the image decreases. Further, if the lower limit of 10 ° of the condition (6) is not reached, the total length of the optical system becomes too long, which is not preferable.

It is more preferable if the following condition (6-1) is satisfied instead of the condition (6).
(6-1) 12 ° <α <35 °

Furthermore, it is more preferable that the following condition (6-2) is satisfied instead of condition (6).
(6-2) 15 ° <α <25 °

In the optical system of the present invention, when the imaging element is arranged on the image plane as described above, it is preferable that the following condition (7) is satisfied.
(7) 0.50 [μm] <Fno / P [μm] <2.00 [μm]
Here, Fno is the open F number of the imaging optical system, and P is the pixel interval of the image sensor.

In condition (7), if the value of Fno / P exceeds the upper limit of 2.00 μm, the imaging optical system becomes too dark or the pixel interval becomes too small, and the amount of light per pixel decreases. For this reason, the shutter speed becomes slow, causing camera shake and increasing noise due to long exposure. On the other hand, if the value of Fno / P is smaller than the lower limit of 0.50 μm, the pixel interval becomes too large and high-pixel imaging data cannot be obtained.

It is more desirable to satisfy the following condition (7-1) instead of the condition (7).
(7-1) 0.60 [μm] <Fno / P [μm] <1.17 [μm]

Furthermore, it is more desirable if the following condition (7-2) is satisfied instead of condition (7) or condition (7-1).
(7-2) 0.65 [μm] <Fno / P [μm] <1.10 [μm]

In the imaging optical system of the present invention, the optical system may be a plastic lens or one or more of the constituent lenses. In that case, when the minimum axial thickness of the plastic lens is ML, it is preferable that the following condition (8) is satisfied.
(8) 0.02 <ML / TL <0.33
However, TL is the total length of the imaging optical system.

    If the value of ML / TL exceeds the upper limit of 0.33 of the condition (8), the minimum axial thickness of the plastic lens with respect to the entire length of the optical system becomes too large. Thickness cannot be secured sufficiently, and the workability of the glass lens is deteriorated. If the ML / TL value becomes smaller than 0.02 which is the lower limit value of the condition (8), the minimum axial thickness of the plastic lens becomes too small, and the resin smoothly flows into the mold when molding the plastic lens. It can not enter, causing stress and causing birefringence, and it takes time to mold and productivity is deteriorated.

It is desirable to satisfy the following condition (8-1) instead of this condition (8).
(8-1) 0.04 <ML / TL <0.23

It is more desirable to satisfy the following condition (8-2) instead of the condition (8) or the condition (8-1).
(8-2) 0.06 <ML / TL <0.17

    According to the present invention, it is possible to realize a high-performance image-forming optical system with little degradation in performance due to manufacturing errors, even if it is downsized.

    Next, embodiments of the optical system of the present invention will be described based on examples.

    Each embodiment of the optical system of the present invention is configured as shown in FIGS. 1 to 3 and has the following data.

Example 1
f = 4.5, F / 2.4, IH = 3.0, ω = 34 °

Surface number Curvature radius Surface spacing Refractive index Abbe number Object surface ∞ ∞
1 Aspherical surface [1] 1.07 1.5256 56.4
2 Aspherical [2] 0.22
3 Diaphragm surface 0.47
4 Aspherical surface [3] 1.08 1.6889 31.1
5 Aspherical [4] 0.10
6 Aspherical surface [5] 2.11 1.5256 56.4
7 Aspherical [6] 1.51
Image plane ∞

Aspherical [1]
Curvature radius 1.55
k 3.5003e × 10 ^-1
a -2.4605 × 10 ^-4

Aspherical [2]
Curvature radius 3.60
k 8.3062
a 8.0001 × 10 ^-3

Aspherical [3]
Radius of curvature -1.43
k 1.0099
a 3.2457 × 10 ^-2

Aspherical [4]
Radius of curvature -2.12
k -6.4049 × 10 ^-1
a 8.6965 × 10 ^-4

Aspherical [5]
Curvature radius 4.87
k -9.9710 × 10 ^-1
a -9.1569 × 10 ^-4

Aspherical [6]
Radius of curvature -25.72
k -3.5117 × 10 ^-4
a -5.0615 × 10 ^-3

Example 2
f = 4.5, F / 2.4, IH = 3.0, ω = 34 °

Surface number Curvature radius Surface spacing Refractive index Abbe number Object surface ∞ ∞
1 Aspherical surface [1] 0.83 1.5831 59.4
2 Aspherical [2] 0.21
3 Diaphragm surface 0.90
4 Aspherical surface [3] 0.41 1.5839 30.2
5 Aspherical [4] 0.10
6 Aspherical surface [5] 2.21 1.5256 56.4
7 Aspherical [6] 1.56
Image plane ∞

Aspherical [1]
Curvature radius 1.84
k 4.0305 × 10 ^-1
a 1.0299 × 10 ^-5 b -6.1723 × 10 ^-4

Aspherical [2]
Curvature radius 4.36
k -4.0146 × 10 ^-1
a 8.8825 × 10 ^-3 b 1.8630 × 10 ^-3

Aspherical [3]
Radius of curvature -0.82
k -6.3680 × 10 ^-1
a 1.7662 × 10 ^-1 b -9.4120 × 10 ^-3

Aspherical [4]
Radius of curvature -1.29
k -6.8734 × 10 ^-1
a 3.7877 × 10 ^-2 b 2.7515 × 10 ^-2

Aspherical [5]
Curvature radius 2.53
k -1.1928 × 10 ^-1
a 3.9115 × 10 ^-3 b -2.2073 × 10 ^-4

Aspherical [6]
Radius of curvature -22.59
k -9.5216 × 10 ^-3
a -6.1641 × 10 ^-3 b -7.7722 × 10 ^-5

Example 3
f = 4.5, F / 2.4, IH = 3.0, ω = 34 °

Surface number Curvature radius Surface spacing Refractive index Abbe number Object surface ∞ ∞
1 Aspherical surface [1] 0.92 1.5163 64.1
2 Aspherical [2] 0.17
3 Diaphragm surface 1.03
4 Aspherical surface [3] 0.50 1.5839 30.2
5 Aspherical [4] 0.10
6 Aspherical [5] 2.45 1.5891 61.2
7 Aspherical [6] 1.51
Image plane ∞

Aspherical [1]
Curvature radius 1.75
k -7.8407 × 10 ^-1
a 2.2435 × 10 ^-2 b 7.7442 × 10 ^-3

Aspherical [2]
Curvature radius 4.61
k 6.7021
a -3.4841 × 10 ^-3 b -1.1327 × 10 ^-2

Aspherical [3]
Radius of curvature -0.75
k -8.2755 × 10 ^-1
a 1.2962 × 10 ^-1 b -2.9707 × 10 ^-1 c 1.9988 × 10 ^-1
d -9.5096 × 10 ^-2

Aspherical [4]
Radius of curvature -1.30
k -1.1964
a -5.1736 × 10 ^-2 c -9.9580 × 10 ^-3 d 9.0645 × 10 ^-3

Aspherical [5]
Curvature radius 2.36
k -1.2943 × 10 ^-1
a 3.2511 × 10 ^-3 b -1.6528 × 10 ^-4

Aspherical [6]
Radius of curvature -32.41
k -2.6405 × 10 ^-4
a -4.4808 × 10 ^-3 b -2.8346 × 10 ^-5

In the above data, f is the focal length of the entire system, F is the F number, IH is the image height, and ω is the half field angle. Further, the radius of curvature is the radius of curvature of the surfaces r ₁ , r ₂ ,... In the figure, and the surface interval is the value of d ₁ , d ₂ .

With these values, the unit of length such as focal length f, radius of curvature r ₁ , r ₂ ,..., Surface spacing d ₁ , d ₂ .

In the above-described examples, the optical system of Example 1 has a lens configuration as shown in FIG. 1, and in order from the object side, a double-sided aspherical first positive meniscus lens (r ₁ to r ₂₎ with the convex surface facing the object side. r ₂ ), an aperture stop S (r ₃ ), a double-sided aspherical second negative meniscus lens (r _{4 to} r ₅ ) with a convex surface facing the image side, and a biconvex third-sided aspherical surface. It consists of a positive lens.

    In the optical system of Example 1, the first lens and the third lens are made of plastic, and the second lens is made of glass. Of these, the first lens and the third lens made of plastic are both made of polyolefin ZEONEX.

    In the imaging optical system of the first embodiment, an image pickup device having 1/3 inch and 1.3 million pixels (pixel spacing 3.6 μm) is arranged on the image plane.

Example 2 has a configuration as shown in FIG. 2, and in order from the object side, a double-sided aspherical first positive lens (r _{1 to} r ₂ ) having a convex surface facing the object side, and an aperture stop S (r _3). ), A double-sided aspherical second negative meniscus lens (r _{4 to} r ₅ ) with a convex surface facing the image side, and a biconvex third-sided aspherical positive lens. In the optical system of Example 2, the first lens is made of glass, and the second and third lenses are both made of plastic. The second lens is made of polycarbonate, and the third lens is made of amorphous polyolefin ZEONEX.

    In the image forming optical system of Example 2, an image pickup device having 1/3 inch and 2 million pixels (pixel spacing: 3.0 μm) is arranged on the image plane.

    Further, the optical system of Example 3 includes, in order from the object side, a double-sided aspheric first positive meniscus lens having a convex surface facing the object side, and a double-sided aspherical second negative meniscus lens having a convex surface facing the image side. And a third positive lens having a biconvex shape and a double-sided aspheric surface. In Example 3, the first lens and the third lens are made of glass, and the second lens is made of plastic. The plastic of this second lens is polycarbonate. In the imaging optical system of Example 3, an image pickup device having 1/3 inch and 3 million pixels (pixel spacing of 2.4 μm) is arranged on the image plane.

Values corresponding to conditions (1) to (8) in these examples are as shown in the following table.

    As is apparent from this table, each example satisfies each condition.

    In these embodiments, some lenses are made of plastic, but the plastic may be made of glass. For example, if a glass having a refractive index higher than that of the material used in the examples is used, a higher performance optical system can be obtained. Use of special low dispersion glass is effective for correcting chromatic aberration. Further, when the lens is made of plastic, the use of a low moisture absorption material can reduce performance degradation due to environmental changes.

    In addition to a brightness stop, a flare stop may be used in order to cut unnecessary light such as ghosts and flares. This flare stop is located before the first lens, between the first lens and the brightness stop, between the brightness stop and the second lens, between the second lens and the third lens, and between the third lens and the image plane. You may arrange | position in any between. In order to provide the function as a flare stop, a method of cutting flare light by a frame may be used. Further, any method may be used in which a flare ray is cut by providing another member. Alternatively, the flare stop may be configured by printing directly on an optical system (an optical element such as a lens), painting, or adhering a seal or the like. Further, the shape of the diaphragm may be any shape such as a circle, an ellipse, a rectangle, a polygon, or a range surrounded by a function curve. Further, not only harmful light but also light beams such as coma flare around the screen may be cut.

    Further, each lens may be provided with an antireflection coating to reduce ghosts and flares. A multi-coat can effectively reduce ghosts and flares. Moreover, you may perform an infrared cut coat on a lens surface, a cover glass, etc.

    Further, focusing may be performed for focus adjustment. As a focusing method, there is a drawing out of the entire lens system, a drawing out of a part of the lens, or a retraction.

    Further, the decrease in brightness at the periphery of the image may be reduced by shifting the CCD microlens. For example, it is possible to prevent a decrease in brightness at the periphery of the image by changing the design of the CCD microlens according to the incident angle of the light beam at each image height. Moreover, you may correct | amend the fall of the brightness of an image peripheral part by image processing.

    The shape of the aspherical surface used in each example is expressed by the following equation, where the direction in which the light on the optical axis travels is the x axis and the direction orthogonal to the optical axis is the y axis. .

x = (y ² / r) / [1+ {1- (1 + k) (y / r) ² } ^1/2 ]
+ Ay ⁴ + by ⁶ + cy ⁸ + dy ¹⁰ +...
Where r is the radius of curvature of the reference sphere, k is the conical coefficient, and a, b, c, d... Are aspherical coefficients.

    The imaging optical system of the present invention is used in various optical devices such as digital still cameras, digital video cameras, mobile phones, small cameras mounted on personal computers, and surveillance cameras.

    As an example of these optical devices, an electronic camera (digital camera) and a mobile phone using the imaging optical system of the present invention will be described.

    7 and 8 show an electronic camera (digital camera) using the imaging optical system of the present invention. FIG. 7 is a perspective view seen from the front, and FIG. 8 is a perspective view seen from the rear.

    In these drawings, reference numeral 10 denotes an electronic camera, which includes an imaging optical system 12 having a photographing optical path 11, a shutter 13, a flash 14, a liquid crystal display monitor 15, and the like. In this camera 10, when a shutter 13 disposed on the upper part thereof is pressed, photographing is performed through the imaging optical system 12 of the present invention in conjunction therewith. That is, an object image is formed on the imaging element chip such as a CCD (not shown) by the imaging optical system 12 via the infrared cut filter.

    An image formed on the image sensor chip is displayed on a liquid crystal display monitor.

    9 and 10 show a mobile phone incorporating the imaging optical system of the present invention. FIG. 9 is a front view and FIG. 10 is a rear view.

    As shown in FIGS. 9 and 10, the mobile phone 20 includes a microphone unit 21 for inputting the voice of the operator, a speaker unit 22 for outputting the voice of the other party, and an operation unit for inputting information by the operator. 23, for example, a display unit 24 of a liquid crystal display element for displaying information such as a photographed image of the operator himself or the other party, a telephone number, etc., an imaging device unit 25 including the imaging optical system of the present invention, and a call radio wave Are provided with an antenna 26 for transmitting and receiving, a rear display unit 27, a battery 28, and the like.

    The imaging optical system of the present invention has a configuration as described in detail above. Therefore, in addition to the optical system having the configuration described in the claims, what is described in the following items is also the object of the present invention. Can be achieved.

(1) An imaging optical system according to claim 1, 2, or 3, wherein the following condition (3) is satisfied.
(3) 1.0 <f23 / f <4.0
Here, f23 is the combined focal length of the second lens and the third lens, and f is the focal length of the entire system.

(2) An imaging optical system according to claim 1, 2, or 3, wherein the following condition (3-1) is satisfied.
(3-1) 1.3 <f23 / f <3.0
Here, f23 is the combined focal length of the second lens and the third lens, and f is the focal length of the entire system.

(3) An imaging optical system according to claim 1, 2 or 3, wherein the following condition (3-2) is satisfied.
(3-2) 1.7 <f23 / f <2.3
Here, f23 is the combined focal length of the second lens and the third lens, and f is the focal length of the entire system.

(4) The optical system described in claim 1, 2 or 3 of the claims or the item (1), (2) or (3) satisfies the following condition (4): An imaging optical system.
(4) -10.0 <f1 / f23 <3.0
Here, f1 is the focal length of the first positive lens, and f23 is the combined focal length of the second negative lens and the third positive lens.

(5) The following condition (4-1) is satisfied in the optical system described in claim 1, 2 or 3 of the claims or the item (1), (2) or (3). An imaging optical system characterized by the above.
(4-1) -1.0 <f1 / f23 <1.0
Here, f1 is the focal length of the first positive lens, and f23 is the combined focal length of the second negative lens and the third positive lens.

(6) The following condition (4-2) is satisfied in the optical system described in claim 1, 2 or 3 of the claims or the item (1), (2) or (3). An imaging optical system characterized by the above.
(4-2) 0.4 <f1 / f23 <0.7
Here, f1 is the focal length of the first positive lens, and f23 is the combined focal length of the second negative lens and the third positive lens.

(7) The optical system according to claim 1, 2 or 3 of the claims or the item (1), (2), (3), (4), (5) or (6), An imaging optical system characterized by satisfying the following condition (5):
(5) 0.1 < − (ν2−ν1) / (ν3−ν2) <8.0
Here, ν1, ν2, and ν3 are Abbe numbers of the first lens, the second lens, and the third lens, respectively.

(8) In the optical system according to claim 1, 2 or 3, or (1), (2), (3), (4), (5) or (6), An imaging optical system characterized by satisfying the following condition (5-1):
(5-1) 0.3 < − (ν2-ν1) / (ν3-ν2) <3.0
Here, ν1, ν2, and ν3 are Abbe numbers of the first lens, the second lens, and the third lens, respectively.

(9) The optical system according to claim 1, 2 or 3 of the claims or the item (1), (2), (3), (4), (5) or (6), An imaging optical system characterized by satisfying the following condition (5-2).
(5-2) 0.5 < − (ν2-ν1) / (ν3-ν2) <1.5
Here, ν1, ν2, and ν3 are Abbe numbers of the first lens, the second lens, and the third lens, respectively.

(10) Claims 1, 2 or 3 of the claims or (1), (2), (3), (4), (5), (6), (7), (8) or An imaging optical system according to the item (9), which satisfies the following condition (6):
(6) 10 ° <α <40 °
Where α is the maximum incident angle of the chief ray on the image plane.

(11) Claims 1, 2 or 3 of the claims or (1), (2), (3), (4), (5), (6), (7), (8) or An imaging optical system according to the item (9), which satisfies the following condition (6-1):
(6-1) 12 ° <α <35 °
Where α is the maximum incident angle of the chief ray on the image plane.

(12) Claims 1, 2 or 3 of the claims or (1), (2), (3), (4), (5), (6), (7), (8) or An imaging optical system according to the item (9), which satisfies the following condition (6-2):
(6-2) 15 ° <α <25 °
Where α is the maximum incident angle of the chief ray on the image plane.

(13) Claims 1, 2 or 3 of the claims or (1), (2), (3), (4), (5), (6), (7), (8), (9) An imaging optical system that satisfies the following condition (7) in the optical system described in the item (10), (11), or (12):
(7) 0.50 [μm] <Fno / P [μm] <2.00 [μm]
Here, Fno is the open F number of the imaging optical system, and P is the pixel interval of the image sensor.

(14) Claims 1, 2 or 3 of the claims or (1), (2), (3), (4), (5), (6), (7), (8), (9) An imaging optical system which satisfies the following condition (7-1) in the optical system described in the item (10), (11) or (12).
(7-1) 0.60 [μm] <Fno / P [μm] <1.17 [μm]
Here, Fno is the open F number of the imaging optical system, and P is the pixel interval of the image sensor.

(15) Claims 1, 2 or 3 of the claims or (1), (2), (3), (4), (5), (6), (7), (8), (9) An imaging optical system which satisfies the following condition (7-2) in the optical system described in the item (10), (11) or (12).
(7-2) 0.65 [μm] <Fno / P [μm] <1.10 [μm]
Here, Fno is the open F number of the imaging optical system, and P is the pixel interval of the image sensor.

(16) Claims 1, 2 or 3 of the claims or (1), (2), (3), (4), (5), (6), (7), (8), (9), (10), (11) or (12), wherein the lens constituting the optical system includes a plastic lens and satisfies the following condition (8): An imaging optical system.
(8) 0.02 <ML / TL <0.33
Where ML is the minimum axial thickness of the plastic lens, and TL is the total length of the imaging optical system.

(17) Claims 1, 2 or 3 of the claims or (1), (2), (3), (4), (5), (6), (7), (8), (9) In the optical system described in the item (10), (11) or (12), the lens constituting the optical system includes a plastic lens, and satisfies the following condition (8-1): Characteristic imaging optical system.
(8-1) 0.04 <ML / TL <0.23
Where ML is the minimum axial thickness of the plastic lens, and TL is the total length of the imaging optical system.

(18) Claims 1, 2 or 3 of the claims or (1), (2), (3), (4), (5), (6), (7), (8), (9) In the optical system described in the item (10), (11) or (12), the lens constituting the optical system includes a plastic lens and satisfies the following condition (8-2): Characteristic imaging optical system.
(8-2) 0.06 <ML / TL <0.17
Where ML is the minimum axial thickness of the plastic lens, and TL is the total length of the imaging optical system.

  (19) Claims 1, 2 or 3 of the claims or (1), (2), (3), (4), (5), (6), (7), (8), (9), (10), (11), (12), (13), (14), (15), (16), (17), or an optical system comprising the optical system described in (18) apparatus.

Sectional drawing of Example 1 of this invention Sectional drawing of Example 2 of this invention Sectional drawing of Example 3 of this invention Aberration curve diagram of Example 1 of the present invention Aberration curve diagram of Example 2 of the present invention Aberration curve diagram of Example 3 of the present invention The perspective view of the digital camera provided with the imaging optical system of this invention The perspective view seen from the back side of the digital camera shown in FIG. Front view of a mobile phone provided with the imaging optical system of the present invention Rear view of the mobile phone shown in FIG.

Claims (7)

In order from the object side, the third lens includes a first positive meniscus lens having a convex surface directed toward the object side, an aperture stop, a second negative meniscus lens having a convex surface directed toward the image side, and a third positive lens. The object-side surface is an aspheric surface whose curvature decreases toward the periphery, and the image-side surface thereof is an aspheric surface whose curvature increases toward the periphery, and the following condition ( 3-2 ) is satisfied : An imaging optical system characterized by being satisfied.
( 3-2 ) 1. 7 <f23 / f <4.0
Here, f23 is the combined focal length of the second lens and the third lens, and f is the focal length of the entire system. In order from the object side, the third lens includes a first positive meniscus lens having a convex surface directed toward the object side, an aperture stop, a second negative meniscus lens having a convex surface directed toward the image side, and a third positive lens. The object-side surface is an aspheric surface whose curvature decreases toward the periphery, and the image-side surface is an aspheric surface whose curvature increases toward the periphery, and the following conditions (1) , (3 ) imaging optical system, characterized by satisfying the.
(1) −100 <(r1r ² / f1) / (r2f ² / f2) <− 1
(3) 1.0 <f23 / f <4.0
Where r1r is the radius of curvature of the image side surface of the first positive lens, r2f is the radius of curvature of the object side surface of the second negative lens, f1 is the focal length of the first positive lens, and f2 is the focal point of the second negative lens. The distance , f23 is the combined focal length of the second lens and the third lens, and f is the focal length of the entire system . The imaging optical system according to claim 1 or 2, wherein the following condition (2) is satisfied.
(2) 0.1 <f1 / f <3.0
Here, f1 is the focal length of the first positive lens, and f is the focal length of the entire system. The imaging optical system according to claim 1, 2 or 3, wherein the following condition (4) is satisfied.
(4) 0.48 ≦ f1 / f23 <3.0
Here, f1 is the focal length of the first positive lens, and f23 is the combined focal length of the second negative lens and the third positive lens. In order from the object side, the third lens includes a first positive meniscus lens having a convex surface directed toward the object side, an aperture stop, a second negative meniscus lens having a convex surface directed toward the image side, and a third positive lens. The object-side surface is an aspheric surface whose curvature decreases toward the periphery, and the image-side surface thereof is an aspheric surface whose curvature increases toward the periphery, and the following conditions (3), (5 ) An imaging optical system characterized by satisfying
(3) 1.0 <f23 / f <4.0
(5) 0.1 <-(ν2-ν1) / (ν3-ν2) <8.0
Here, f23 is a combined focal length of the second lens and the third lens, f is a focal length of the entire system, and ν1, ν2, and ν3 are Abbe numbers of the first lens, the second lens, and the third lens, respectively. 6. An imaging optical system for forming an object image on an image sensor disposed on an imaging surface, wherein the following condition (7) is satisfied: Imaging optical system.
(7) 0.50 [μm] <Fno / P [μm] <2.00 [μm]
Here, Fno is the open F number of the imaging optical system, and P is the pixel interval of the image sensor. An optical device comprising the imaging optical system according to claim 1, 2, 3, 4, 5 or 6.

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