JP4186560B2 - Super wide angle lens - Google Patents

Description

【００３６】

【００３７】

【００３８】

【００３９】
【表１】

【００４０】
【発明の効果】
以上説明したように本発明によれば、ガラス球面レンズ８枚構成でありながら固体撮像素子用撮影レンズ系として良好な光学性能と１７０度程度の広い画角を有する、低コストかつコンパクトな超広角レンズを実現することができる。そして、本発明に係る超広角レンズをＴＶ電話用カメラ，ドアホーン用カメラ，監視カメラ，車載カメラ等として用いられるデジタル入力機器(デジタルスチルカメラ，デジタルビデオカメラ等)に撮影レンズ系として用いれば、当該デジタル入力機器の超広角化，高性能化，高機能化，低コスト化及びコンパクト化に寄与することができる。
【図面の簡単な説明】
【図１】第１の実施の形態(実施例１)のレンズ構成図。
【図２】第２の実施の形態(実施例２)のレンズ構成図。
【図３】第３の実施の形態(実施例３)のレンズ構成図。
【図４】第４の実施の形態(実施例４)のレンズ構成図。
【図５】実施例１の収差図。
【図６】実施例２の収差図。
【図７】実施例３の収差図。
【図８】実施例４の収差図。
【符号の説明】
GrF …前群
ST …開口絞り
GrR …後群
L1〜L3 …第１〜第３レンズ(像側に凹面を向けた負レンズ)
L4 …第４レンズ(正レンズ)
L5,L6 …第５，第６レンズ(貼り合わせレンズ)
L7 …第７レンズ
L8 …第８レンズ(単一の正レンズ)
GF …ガラスフィルター
AX …光軸[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ultra-wide-angle lens. For example, a wide image suitable for a digital input device (digital still camera, digital video camera, etc.) used as a camera for a TV phone, a camera for a door horn, a surveillance camera, an in-vehicle camera, etc. The present invention relates to a small super-wide-angle lens for a solid-state imaging device having a small angle (about 170 degrees of view).
[0002]
[Prior art]
Many wide-angle lenses for solid-state imaging devices used for surveillance cameras, vehicle-mounted cameras, and the like have been proposed. For example, the wide-angle lens described in Patent Documents 1 to 3 is an example of a wide-angle lens for a solid-state imaging device having eight lenses.
[0003]
[Patent Document 1]
Japanese Patent Laid-Open No. 7-63986 [Patent Document 2]
JP-A-9-96759 [Patent Document 3]
JP-A-9-127413 [0004]
[Problems to be solved by the invention]
Plastic lenses and aspherical surfaces are used for the wide-angle lenses described in Patent Documents 1 to 3. When a plastic lens is used, back focus fluctuation due to temperature change increases, and it becomes difficult to maintain performance over a wide temperature range. The use of an aspheric surface increases the cost, and is not suitable for equipment that requires low cost. In addition, since the wide angle lenses described in Patent Documents 1 to 3 have an angle of view of 130 degrees or less, the angle of view is not sufficient when it is desired to capture a wide range.
[0005]
The present invention has been made in view of such a situation, and has a good optical performance as a photographing lens system for a solid-state imaging device and a wide angle of view of about 170 degrees, although it has a configuration of eight glass spherical lenses. An object is to provide an ultra-wide-angle lens that is cost-effective and compact.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, the super wide-angle lens of the first invention is a wide-angle lens including a negative front group, an aperture stop, and a positive rear group in order from the object side. It consists of four negative lenses with three concave lenses facing the image side in order from the object side and one positive lens. The rear group includes a single positive lens on the most image side, and the following conditional expression (1 ) And (2) are satisfied.
-0.24 <f / fF <-0.05 (1)
0.17 <f / fR <0.42 (2)
However,
f: focal length of the entire system,
fF: Focal length of the front group,
fR: focal length of rear group,
It is.
[0007]
The super wide-angle lens of the second invention is a wide-angle lens including a negative front group, an aperture stop, and a positive rear group in order from the object side, and the front group is concave on the image side in order from the object side. The four rear lenses are composed of three negative lenses and one positive lens. The rear group includes a single positive lens closest to the image side, and satisfies the following conditional expressions (1) and (3) It is characterized by that.
-0.24 <f / fF <-0.05 (1)
0.54 <f / Y '<0.69 (3)
However,
f: focal length of the entire system,
fF: Focal length of the front group,
Y ': Maximum image height,
It is.
[0008]
A super wide-angle lens according to a third aspect of the invention is a wide-angle lens including a negative front group, an aperture stop, and a positive rear group in order from the object side, and the front group is concave on the image side in order from the object side. The four rear lenses are composed of three negative lenses and one positive lens. The rear group includes a single positive lens closest to the image side, and satisfies the following conditional expressions (2) and (3): It is characterized by that.
0.17 <f / fR <0.42 (2)
0.54 <f / Y '<0.69 (3)
However,
f: focal length of the entire system,
fR: focal length of rear group,
Y ': Maximum image height,
It is.
[0009]
According to a fourth aspect of the present invention, there is provided the super wide-angle lens according to any one of the first to third aspects, wherein the rear group is a bonded lens of a positive lens and a negative lens in order from the object side, or a negative lens. And a positive lens.
[0010]
A super wide-angle lens according to a fifth invention is characterized in that, in the configuration of any one of the first to fourth inventions, an image is formed on a solid-state imaging device.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the super wide-angle lens according to the present invention will be described below with reference to the drawings. 1 to 4 show the lens configurations of the first to fourth embodiments in optical cross sections, respectively. Each of the super wide-angle lenses of each embodiment is a single-focus wide-angle lens for imaging (that is, for a digital input device) that forms an optical image on a solid-state imaging device (for example, a CCD: Charge Coupled Device). On the side, a parallel flat plate-like glass filter (GF) corresponding to an optical low-pass filter or the like is arranged. Each of the super wide-angle lenses constitutes a lens type in which the arrangement of power (a quantity defined by the reciprocal of the focal length) is negative and positive with eight glass spherical lenses. Specifically, it consists of a negative front group (GrF), an aperture stop (ST), and a positive rear group (GrR) in order from the object side, and the front group (GrF) is an image in order from the object side. It consists of four negative lenses (L1 to L3) with a concave surface on the side and one positive lens (L4), and the rear group (GrR) includes bonded lenses (L5, L6). It contains a single positive lens (L8) on the most image side.
[0012]
In the first embodiment (FIG. 1), each group (GrF, GrR) is configured as follows in order from the object side. The front group (GrF) has a negative meniscus first lens (L1) with a concave surface facing the image side, a negative meniscus second lens (L2) with a concave surface facing the image side, and a concave surface on the image side. And a negative meniscus third lens (L3) directed toward the image, and a positive meniscus lens shaped fourth lens (L4) with a convex surface directed toward the image side. The rear group (GrR) consists of a biconcave negative power fifth lens (L5), a biconvex positive power sixth lens (L6), and a biconvex positive power seventh lens (L7). And a biconvex positive power eighth lens (L8).
[0013]
In the second embodiment (FIG. 2), each group (GrF, GrR) is configured as follows in order from the object side. The front group (GrF) has a negative meniscus first lens (L1) with a concave surface facing the image side, a negative meniscus second lens (L2) with a concave surface facing the image side, and a biconcave negative lens. The power third lens (L3) and the biconvex positive power fourth lens (L4) are included. The rear group (GrR) consists of a biconvex positive power fifth lens (L5), a biconcave negative power sixth lens (L6), and a biconvex positive power seventh lens (L7). And a biconvex positive power eighth lens (L8).
[0014]
In the third embodiment (FIG. 3), each group (GrF, GrR) is configured as follows in order from the object side. The front group (GrF) has a negative meniscus first lens (L1) with a concave surface facing the image side, a negative meniscus second lens (L2) with a concave surface facing the image side, and a biconcave negative lens. The power third lens (L3) and the biconvex positive power fourth lens (L4) are included. The rear group (GrR) consists of a biconvex positive power fifth lens (L5), a biconcave negative power sixth lens (L6), and a biconvex positive power seventh lens (L7). And a biconvex positive power eighth lens (L8).
[0015]
In the fourth embodiment (FIG. 4), each group (GrF, GrR) is configured as follows in order from the object side. The front group (GrF) has a negative meniscus first lens (L1) with a concave surface facing the image side, a negative meniscus second lens (L2) with a concave surface facing the image side, and a biconcave negative lens. The power third lens (L3) and the biconvex positive power fourth lens (L4) are included. The rear group (GrR) has a positive meniscus fifth lens (L5) with a convex surface facing the image side, a negative meniscus sixth lens (L6) with a concave surface facing the object side, and a concave surface on the image side. And a negative meniscus seventh lens (L7) and a biconvex positive power eighth lens (L8).
[0016]
As described above, the front group (GrF) is composed of three negative lenses (L1 to L3) with concave surfaces facing the image side in order from the object side, so that off-axis rays incident at a tight angle can be effectively prevented. Since it can be led to the rear group (GrR) and correction of each aberration can be carried out in three parts, very effective correction can be performed. Further, by correcting the residual aberration generated by the three negative lenses (L1 to L3) with the positive lens (L4), further improvement in performance can be achieved. Further, by configuring the most image side of the rear group (GrR) with a single positive lens (L8), it is possible to achieve high performance by correcting each aberration while ensuring telecentricity. Therefore, as in the embodiments, in the wide-angle lens including the negative front group (GrF), the aperture stop (ST), and the positive rear group (GrR) in order from the object side, the front group (GrF) Is composed of four negative lenses (L1 to L3) and one positive lens (L4) with the concave surface facing the image side in order from the object side, and the most image side of the rear group (GrR) is single. The positive lens (L8) is composed of eight glass spherical lenses, but has good optical performance as a photographing lens system for a solid-state imaging device, and is low in cost and compact at an angle of view of about 170 degrees. Enables realization of ultra-wide-angle lenses. The conditions for effectively realizing this will be described below.
[0017]
Here, a conditional expression that the super-wide-angle lens of each embodiment should satisfy, that is, a conditional expression that should be satisfied in the super-wide-angle lens of the type as in each embodiment will be described. However, it is not necessary to satisfy all the conditional expressions described below at the same time, and it is possible to achieve the corresponding actions and effects as long as each conditional expression is satisfied independently according to the optical configuration. Needless to say, satisfying a plurality of conditional expressions is more desirable from the viewpoint of optical performance, miniaturization, assembly, and the like.
[0018]
It is desirable that the following conditional expression (1) is satisfied.
-0.24 <f / fF <-0.05 (1)
However,
f: focal length of the entire system,
fF: focal length of front group (GrF),
It is.
[0019]
Conditional expression (1) defines a condition range regarding the power of the front group (GrF). If the upper limit of conditional expression (1) is exceeded, the total length of the optical system and the diameter of the front lens become large, leading to an increase in size in the optical axis (AX) direction and radial direction of the imaging lens device. On the other hand, if the lower limit of conditional expression (1) is exceeded, the total length of the optical system and the front lens diameter will be reduced, but the spherical aberration, coma aberration, and lateral chromatic aberration will be significantly increased and performance will be reduced.
[0020]
It is desirable to satisfy the following conditional expression (2), and it is more desirable to satisfy the conditional expression (1).
0.17 <f / fR <0.42 (2)
However,
f: focal length of the entire system,
fR: focal length of rear group (GrR),
It is.
[0021]
Conditional expression (2) defines a condition range regarding the power of the rear group (GrR). If the lower limit of conditional expression (2) is exceeded, the total length of the optical system increases, leading to an increase in the size of the imaging lens device in the optical axis (AX) direction. On the contrary, if the upper limit of conditional expression (2) is exceeded, the total length of the optical system becomes small, but the spherical aberration, coma aberration, and lateral chromatic aberration become remarkably large and the performance deteriorates.
[0022]
It is preferable that the following conditional expression (3) is satisfied, and it is further preferable that the conditional expression (3) is satisfied together with at least one of the conditional expressions (1) and (2).
0.54 <f / Y '<0.69 (3)
However,
f: focal length of the entire system,
Y ': Maximum image height,
It is.
[0023]
Conditional expression (3) defines a condition range for balancing the total lens length and the front lens diameter. If the lower limit of conditional expression (3) is exceeded, the diameter of the front lens will increase, leading to an increase in the radial direction of the imaging lens device and making it difficult to correct distortion. On the contrary, if the upper limit of conditional expression (3) is exceeded, the total length of the optical system increases, leading to an increase in the size of the imaging lens device in the optical axis (AX) direction.
[0024]
In the first embodiment (FIG. 1), the rear group (GrR) includes a cemented lens of a negative power fifth lens (L5) and a positive power sixth lens (L6). In the fourth embodiment (FIGS. 2 to 4), the rear group (GrR) includes a cemented lens of a positive power fifth lens (L5) and a negative power sixth lens (L6). By including a bonded lens in the rear group (GrR), it is possible to easily correct the lateral chromatic aberration caused by widening the angle, and it is also possible to effectively shorten the total lens length. Therefore, it is desirable that the rear group (GrR) includes, in order from the object side, a cemented lens of a positive lens and a negative lens or a cemented lens of a negative lens and a positive lens.
[0025]
As described above, all the lenses (L1 to L8) used in the first to fourth embodiments are glass lenses, and all the lens surfaces (r1, r2,...) Are spherical surfaces. It is. If the lens surface is formed of an aspherical surface, the cost increases, and it becomes difficult to meet the demand for cost reduction. Therefore, it is desirable that all the lens surfaces be formed of a spherical surface. In addition, when a glass lens is used, it is possible to reduce back focus fluctuation due to temperature change and maintain performance in a wide temperature range. Therefore, it is desirable that all the lenses are configured with glass lenses.
[0026]
The ultra-wide-angle lens of each embodiment is composed only of a refractive lens that deflects incident light by refraction (that is, a lens that is deflected at the interface between media having different refractive indexes). Not limited to. For example, a diffractive lens that deflects incident light by diffraction, a refractive / diffractive hybrid lens that deflects incident light by a combination of diffraction and refraction, and a refractive index distribution type that deflects incident light according to the refractive index distribution in the medium A lens or the like may be used. However, since these lenses are expensive due to their complicated manufacturing method, it is desirable to use a glass spherical lens made of a homogeneous material in the super-wide-angle lens according to the present invention.
[0027]
In each embodiment, a surface that does not have optical power (for example, a reflective surface, a refracting surface, or a diffractive surface) is disposed in the optical path, so that the optical path is bent before, after, or in the middle of the super-wide-angle lens. Also good. The folding position can be set as required, and by appropriately bending the optical path, it is possible to achieve an apparently thin and compact digital input device (such as a digital camera) equipped with an ultra-wide-angle lens. is there.
[0028]
The super-wide-angle lens of each embodiment is suitable for use as a small photographic lens system for digital input devices, and by combining this with an optical low-pass filter or a solid-state image sensor, the subject image is optically captured. Thus, an imaging lens device that outputs an electrical signal can be configured. The imaging lens device is a camera used for still image shooting and moving image shooting of a subject (for example, a digital camera; a video camera; a surveillance camera; an in-vehicle camera; a digital video unit, a personal computer, a mobile computer, a scanner, a mobile phone, a TV phone, A main component of a door horn, a camera incorporated in or externally attached to a personal digital assistant (PDA), etc., for example, a photographing lens system that forms an optical image of an object in order from the object (subject) side; And an optical low-pass filter and a solid-state imaging device that converts an optical image formed by the photographing lens system into an electrical signal.
[0029]
Accordingly, each of the above-described embodiments includes the inventions {circle around (1)} and {circle around (2)} having the following configurations, and with these configurations, imaging having a good optical performance, a low cost, a compact, and a wide angle of view. A lens device can be realized. If the imaging lens device is applied to a digital input device such as a digital camera, it can contribute to an ultra wide angle, high performance, high functionality, low cost, and compactness of the digital input device.
(1) An imaging lens apparatus comprising: an imaging super-wide-angle lens that forms an optical image; and a solid-state imaging device that converts an optical image formed by the super-wide-angle lens into an electrical signal, The super wide-angle lens includes, in order from the object side, a negative front group, an aperture stop, and a positive rear group, and the front group has three negative lenses with a concave surface facing the image side in order from the object side and a positive lens. The rear group includes a single positive lens on the most image side and satisfies at least one of the conditional expressions (1), (2), and (3). An imaging lens device characterized by the above.
(2) The imaging lens device according to (1), wherein all the lenses are made of glass lenses and all the lens surfaces are made of spherical surfaces.
[0030]
As the solid-state image sensor, for example, a CCD or a complementary metal oxide semiconductor (CMOS) sensor composed of a plurality of pixels is used, and an optical image formed by the super wide-angle lens is converted into an electrical signal by the solid-state image sensor. An optical image to be formed by an ultra-wide-angle lens is generated when it is converted into an electrical signal by passing through an optical low-pass filter having a predetermined cutoff frequency characteristic determined by the pixel pitch of the solid-state image sensor. The spatial frequency characteristic is adjusted so that the so-called aliasing noise is minimized. The signal generated by the solid-state image sensor is subjected to predetermined digital image processing, image compression processing, etc. as necessary, and is recorded as a digital video signal in a memory (semiconductor memory, optical disk, etc.). Or is converted into an infrared signal and transmitted to another device.
[0031]
The optical low-pass filter arranged between the final surface of the super-wide-angle lens and the solid-state image sensor is composed of a glass filter (GF) in each embodiment, but it depends on the digital input device used. Anything can be used. For example, a birefringent low-pass filter made of quartz or the like with a predetermined crystal axis direction adjusted, or a phase-type low-pass filter that achieves the required optical cutoff frequency characteristics by the diffraction effect can be applied. is there.
[0032]
【Example】
Hereinafter, the super wide-angle lens embodying the present invention will be described more specifically with reference to construction data and the like. Examples 1 to 4 listed here correspond to the first to fourth embodiments described above, and the lens configuration diagrams (FIGS. 1 to 4) representing the first to fourth embodiments are as follows. The lens configurations of corresponding Examples 1 to 4 are respectively shown.
[0033]
In the construction data of each example, ri (i = 1, 2, 3, ...) is the radius of curvature (mm) of the i-th surface counted from the object side, di (i = 1, 2, 3,. ..) indicates the i-th axis upper surface distance (mm) counted from the object side, and Ni (i = 1,2,3, ...), νi (i = 1,2,3, ...). .) Shows the refractive index (Nd) and Abbe number (νd) of the i-th optical element counted from the object side with respect to the d-line. Further, f is the focal length (mm) of the entire system, ω is the half angle of view (°), and FNO is the F number. Table 1 shows values corresponding to parameters defined by each conditional expression for each example.
[0034]
5 to 8 are aberration diagrams corresponding to Examples 1 to 4. FIG. 5 to 8, (A) shows spherical aberration, etc., (B) shows astigmatism, and (C) shows distortion aberration {FNO: F number, Y ′: maximum image height (mm)}. In the spherical aberration diagram, the solid line (d) represents the d line, the alternate long and short dash line (g) represents the g line, the alternate long and two short dashes line (c) represents the amount of spherical aberration (mm) with respect to the c line, and the broken line (SC) represents the sine. The amount of unsatisfied conditions (mm). In the astigmatism diagram, a broken line (DM) represents each astigmatism (mm) with respect to the d-line on the meridional surface and a solid line (DS) on the sagittal surface. In the distortion diagram, the solid line represents the distortion (%) with respect to the d-line.
[0035]

[0036]

[0037]

[0038]

[0039]
[Table 1]

[0040]
【The invention's effect】
As described above, according to the present invention, a low-cost and compact super wide-angle lens having a good optical performance and a wide field angle of about 170 degrees as a photographic lens system for a solid-state imaging device while having a configuration of eight glass spherical lenses. A lens can be realized. If the super wide-angle lens according to the present invention is used as a photographing lens system in a digital input device (digital still camera, digital video camera, etc.) used as a camera for a video phone, a camera for a door phone, a surveillance camera, an in-vehicle camera, etc. It can contribute to ultra wide angle, high performance, high functionality, low cost and compactness of digital input devices.
[Brief description of the drawings]
FIG. 1 is a lens configuration diagram of a first embodiment (Example 1).
FIG. 2 is a lens configuration diagram of a second embodiment (Example 2).
FIG. 3 is a lens configuration diagram of a third mode for embodying the present invention (embodiment 3);
FIG. 4 is a lens configuration diagram of a fourth embodiment (Example 4).
FIG. 5 is an aberration diagram of Example 1.
6 is an aberration diagram of Example 2. FIG.
FIG. 7 is an aberration diagram of Example 3.
FIG. 8 is an aberration diagram of Example 4.
[Explanation of symbols]
GrF… front group
ST… Aperture stop
GrR: Rear group
L1 to L3 ... 1st to 3rd lens (negative lens with concave surface facing the image side)
L4 ... Fourth lens (positive lens)
L5, L6 ... Fifth and sixth lenses (bonded lenses)
L7 ... 7th lens
L8 ... 8th lens (single positive lens)
GF ... Glass filter
AX… Optical axis

Claims (5)

A wide-angle lens composed of, in order from the object side, a negative front group, an aperture stop, and a positive rear group, wherein the front group has three negative lenses with a concave surface facing the image side in order from the object side and a positive lens An ultra-wide-angle lens that is composed of one lens and four lenses, and the rear group includes a single positive lens closest to the image side and satisfies the following conditional expressions (1) and (2):
-0.24 <f / fF <-0.05 (1)
0.17 <f / fR <0.42 (2)
However,
f: focal length of the entire system,
fF: Focal length of the front group,
fR: focal length of rear group,
It is. A wide-angle lens composed of, in order from the object side, a negative front group, an aperture stop, and a positive rear group, wherein the front group has three negative lenses with a concave surface facing the image side in order from the object side and a positive lens An ultra-wide-angle lens comprising four lenses, one lens and the rear lens group including a single positive lens closest to the image side and satisfying the following conditional expressions (1) and (3):
-0.24 <f / fF <-0.05 (1)
0.54 <f / Y '<0.69 (3)
However,
f: focal length of the entire system,
fF: Focal length of the front group,
Y ': Maximum image height,
It is. A wide-angle lens composed of, in order from the object side, a negative front group, an aperture stop, and a positive rear group, wherein the front group has three negative lenses with a concave surface facing the image side in order from the object side and a positive lens An ultra-wide-angle lens that is composed of four lenses, one lens and the rear lens group includes a single positive lens closest to the image side and satisfies the following conditional expressions (2) and (3):
0.17 <f / fR <0.42 (2)
0.54 <f / Y '<0.69 (3)
However,
f: focal length of the entire system,
fR: focal length of rear group,
Y ': Maximum image height,
It is. The rear group includes, in order from the object side, a cemented lens of a positive lens and a negative lens, or a cemented lens of a negative lens and a positive lens. The described ultra wide-angle lens. The super-wide-angle lens according to claim 1, wherein the super-wide-angle lens is configured to form an image on a solid-state imaging device.

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