JP2004302225A - Image pickup lens and imaging apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image pickup lens capable of preventing the occurrence of flare and also obtaining excellent optical characteristic, and an imaging apparatus using the same. <P>SOLUTION: The image pickup lens satisfies respective conditional expressions L≤ 1.7×f, EX ≤1.2×f, 1.3×Φ≤θ≤2.0×Φ and Φ=tan<SP>-1</SP>(y'/EX) (provided that L means the entire length of an optical system, that is, a distance on an optical axis 4 from the object side surface of a lens 2 arranged nearest to the object side to an image surface, f means the focal distance of an entire lens system, EX means a distance between the center of the exit pupil 13 of the lens system and the image surface, θ means a gradient, that is, an inclination angle formed by the inner peripheral surface of a diaphragm 3 to the optical axis 4 of the lens system, Φ means the incident angle of a principal light beam l' on the image pickup surface 6 of a sensor at a maximum viewing angle and y' means the maximum image height of the sensor). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
[Industrial applications]
The present invention relates to an image pickup lens and an image pickup apparatus, and more particularly to an image pickup apparatus using an image pickup device such as a CCD or a CMOS mounted on a portable computer, a videophone or a camera-equipped mobile phone, etc. TECHNICAL FIELD The present invention relates to an imaging lens suitable for an image pickup apparatus and an imaging apparatus using the same.
[0002]
[Prior art]
2. Description of the Related Art In recent years, the progress of multimedia has been remarkable, and for example, the demand for a camera using a solid-state imaging device such as a CCD or a CMOS for mounting on a portable computer, a videophone, a mobile phone, and the like has increased remarkably. Since such a camera needs to be mounted in a limited installation space, it is desired that the camera be small and lightweight.
[0003]
Therefore, the imaging lens used for such a camera is also required to be small and lightweight, and such an imaging lens has conventionally been a CCD or a CCD using one to three lenses. An imaging lens unit for CMOS is widely used.
[0004]
In such an imaging lens unit, in order to prevent the occurrence of image blurring due to light that does not contribute to image formation that arrives at an image plane called a flare, a rear stop may be arranged on the image plane side of the lens. is there.
[0005]
The function of the rear stop is to cover the flange portion formed on the outer periphery of the functional surface of the lens from the image surface side in a state of being disposed behind (image surface side) the lens closest to the image surface side. This prevents harmful light from entering the imaging surface via the flange portion.
[0006]
Such a rear stop is formed by forming an opening in a plate made of a light-shielding material, and a resin material is used as the light-shielding material because of its advantages of low cost and light weight. Often used.
[0007]
As shown in FIG. 4, when the rear stop 3 of the imaging lens 1 does not completely cover the flange 2a of the lens 2, as shown in FIG. 4, the light exits to the image plane through the flange 2a. Is emitted from the end surface of the flange portion 2a on the image plane side, and the diffused light is captured by the sensor on the imaging surface 6 as illumination light, and thus flare occurs.
[0008]
Therefore, it is important that the stop diameter, which is the size of the opening 3a of the rear stop 3, is set to a size that can completely cover and hide the flange portion 2a.
[0009]
Further, the shape of the inner peripheral surface 3b of the opening 3a of the rear stop 3 may be a surface shape parallel to the optical axis 4 in some cases, but at the maximum angle of view from the object side to the image plane side. Some have a slight inclination about the incident angle of the chief ray l 'to the sensor.
[0010]
[Patent Document 1]
JP-A-6-175017 [Patent Document 2]
JP-A-11-44839
[Problems to be solved by the invention]
By the way, recently, further miniaturization of the imaging lens unit has been demanded.
[0012]
In order to further reduce the size of the lens 2 to meet such demands, the distance from the image surface side lens surface of the lens 2 closest to the image surface to the imaging surface 6 must be reduced in optical design. In addition, the incident angle of the principal ray l ′ having the maximum angle of view with respect to the imaging surface 6 must be increased accordingly.
[0013]
As described above, when the angle of incidence of the principal ray 1 ′ having the maximum angle of view with respect to the imaging surface 6 increases, even if the rear diaphragm 3 completely covers the flange portion 2a, as shown in FIG. In the case where the inclination angle of the inner peripheral surface 3b of the portion 3a is only an inclination angle about the incident angle of the principal ray l 'at the maximum angle of view with respect to the sensor (for example, the maximum angle of view 64 ° (that is, the half angle of view 32 °) In this case, the light 1 outside the effective angle of view is incident on the inner peripheral surface 3b. Then, the incident light is irregularly reflected by the inner peripheral surface 3b, thereby causing flare.
[0014]
Further, even if a matting material is adopted as the material of the rear stop 3 and the inner peripheral surface 3b of the opening 3a of the rear stop 3 is roughened, it is still insufficient.
[0015]
FIG. 6 schematically shows an image in which a so-called high-luminance object is present at a high luminance in the peripheral portion of the screen and in the vicinity of the screen. As shown in FIG. Is incident on the inner peripheral surface 3b of the opening 3a, the inner peripheral surface 3b becomes glossy, so that the flare 9 also occurs.
[0016]
Therefore, with the shape of the conventional rear stop 3, the occurrence of flare 9 cannot be effectively prevented, and there has been a problem that a good image cannot be obtained as the imaging lens 1.
[0017]
The present invention has been made in view of such a problem, and an image pickup lens capable of preventing the occurrence of flare by improving the shape of the rear diaphragm and consequently obtaining good optical characteristics, and It is an object of the present invention to provide an imaging device used.
[0018]
[Means for Solving the Problems]
In order to achieve the above object, a feature of the imaging lens according to the present invention is that an imaging lens provided with at least one lens and an aperture in order from the object side to the image plane side has L ≦ 1.7 × f, EX ≦ 1.2 × f, 1.3 × Φ ≦ θ ≦ 2.0 × Φ and Φ = tan ⁻¹ (y ′ / EX) (where L is the total length of the optical system, that is, The distance on the optical axis from the object-side surface to the image plane of the lens disposed closest to the object side, f is the focal length of the entire lens system, and EX is the distance between the center of the exit pupil of the lens system and the image plane. Is the gradient, that is, the inclination angle formed by the inner peripheral surface of the stop with respect to the optical axis of the lens system, Φ is the incident angle of the principal ray on the sensor imaging surface at the maximum angle of view, and y ′ is the sensor angle. (Maximum image height).
[0019]
According to such a configuration, by satisfying each of the conditional expressions (1) and (2), it becomes possible to reduce the total length of the lens system. By satisfying each conditional expression, it is possible to effectively prevent the occurrence of flare while ensuring sufficient manufacturability.
[0020]
Further, a feature of the imaging apparatus according to the present invention is that, in the order from the object side to the image plane side, at least one lens, an imaging lens provided with an aperture, and an imaging device having an imaging element, When the imaging lens is L ≦ 1.7 × f, EX ≦ 1.2 × f, 1.3 × Φ ≦ θ ≦ 2.0 × Φ and Φ = tan ⁻¹ (y ′ / EX) Here, L is the total length of the optical system, that is, the distance on the optical axis from the object side surface to the image plane of the lens disposed closest to the object side, f is the focal length of the entire lens system, and EX is the lens system. The distance between the center of the exit pupil and the image plane, θ is a gradient, that is, the inclination angle formed by the inner peripheral surface of the diaphragm with respect to the optical axis of the lens system, and Φ is the sensor imaging plane of the principal ray at the maximum angle of view. Is the point at which the maximum image height of the sensor is satisfied.
[0021]
According to such a configuration, when the imaging lens satisfies the conditional expressions (1) and (2), the overall length of the lens system can be shortened. Further, (3) and (3) By satisfying the conditional expressions of 4), it is possible to effectively prevent the occurrence of flare while ensuring sufficient manufacturability, and to realize a small-sized imaging device having good optical performance.
[0022]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of an imaging lens and an imaging device according to the present invention will be described with reference to FIGS.
[0023]
As shown in FIG. 1, the imaging lens 1 according to the present embodiment includes, in order from the object side to the image surface side, at least one lens 2 having a flange 2 a formed on the outer periphery of a functional surface, and an opening 3 a. The optical systems 2 and 3 are formed in an axially symmetric shape with the optical axis 4 as the center.
[0024]
The stop diameter, which is the diameter of the opening 3a of the rear stop 3, is set so that the rear stop 3 can completely cover the flange portion 2a from the image surface side.
[0025]
Further, on the image surface side of the rear stop 3, an imaging surface 6 which is a light receiving surface of a sensor of an imaging device such as a CCD or a CMOS is provided.
[0026]
In FIG. 1, only one lens 2 is shown in the drawing, but it goes without saying that one or more other lenses may be arranged on the object side of the lens 2.
[0027]
In the present embodiment, the following conditional expressions (1) to (4) are satisfied.
[0028]
L ≦ 1.7 × f (1)
EX ≦ 1.2 × f (2)
1.3 × Φ ≦ θ ≦ 2.0 × Φ (3)
Φ = tan ⁻¹ (y ′ / EX) (4)
Here, L in the expression (1) is the light from the object-side surface to the image plane of the entire length of the optical system, that is, the lens (the lens 2 shown in FIG. 1 in the case of a single lens) disposed closest to the object. The distance on the axis. f is a focal length of the entire lens system, and EX is an exit pupil (indicated by reference numeral 13 in FIG. 2), that is, a light amount aperture (a front aperture 10 in FIG. ) Is the distance between the center of the image and the image plane. The image plane may be an ideal image plane or a nominal image plane. θ is a gradient, that is, an inclination angle formed by the inner peripheral surface of the rear stop 3 with respect to the optical axis 4 of the lens system. Φ is the angle of incidence of the principal ray l ′ at the maximum angle of view on the sensor. y ′ is the maximum image height of the sensor.
[0029]
Here, the value of L exceeds the value (1.7 × f) shown in the equation (1), or the value of EX exceeds the value (1.2f) shown in the equation (2). When the size is large, the overall length of the lens system becomes too long, which is against the demand for miniaturization.
[0030]
When the value of θ is smaller than the value (1.3 × Φ) shown in the equation (3), the light beam l outside the effective angle of view enters the inner peripheral surface 3b of the opening 3a of the rear stop 3, The reflected light generated by the incident light is incident on the imaging surface 6 as harmful light, so that a flare 9 is generated.
[0031]
On the other hand, when the value of θ becomes larger than the value (2.0 × Φ) shown in the equation (3), the tip of the inner peripheral surface 3b of the opening 3a (the tip on the optical axis 4 side and the lens 2 side) ) Becomes too thin, and it is difficult to form the resin material by the injection molding method.
[0032]
Note that Φ in equation (3) is defined as in equation (4) using y ′ and EX.
[0033]
Therefore, in the present embodiment, the value of L satisfies the conditional expression (1), the value of EX satisfies the conditional expression (2), and the value of θ is the conditional expression (3). Is satisfied, and the value of Φ satisfies the conditional expression (4), thereby shortening the overall length of the lens system and responding to the demand for miniaturization, while ensuring sufficient manufacturability. In addition, it is possible to effectively prevent the adverse effects (the occurrence of flare) due to downsizing.
[0034]
Preferably, the rear stop 3 is formed of a resin material such as plastic, and the inner peripheral surface 3b of the opening 3a of the rear stop 3 is subjected to a matting process by roughening or a process using a matting material. It is desirable to have been.
[0035]
Next, the operation of the present embodiment will be described with reference to FIG.
[0036]
FIG. 2 shows a case where the imaging lens 1 is constituted by two lenses as an example.
[0037]
The imaging lens 1 according to the present embodiment is housed in a cylindrical body 11 on which a front diaphragm 10 is formed, together with another one of the lenses 5 arranged on the object side of the lens 2, so that the camera 12 ( Imaging device).
[0038]
When an image of an object is taken by using the camera 12, the light beam l that has entered the body 11 from the object side via the front stop 10 is condensed by the two lenses 5 and 2, Pass.
[0039]
At this time, the inclination angle of the inner peripheral surface 3b of the opening 3a in the rear stop 3 is larger than the incident angle of the principal ray l 'on the sensor light receiving surface at the maximum angle of view, as shown in the conditional expression (3). (For example, in the case of a maximum angle of view of 64 ° (that is, a half angle of view of 32 °), the inclination angle θ is 45 ° to 60 °).
[0040]
Accordingly, it is possible to prevent the light beam l outside the effective angle of view from being incident on the inner peripheral surface 3b of the opening 3a, and to prevent the generation of harmful light due to the incident light on the inner peripheral surface 3b. Can be.
[0041]
Therefore, a good light beam from which harmful light has been removed enters the imaging surface 6.
[0042]
As a result, for example, as shown in FIG. 3, even when an image in which the high-luminance object 7 is present is captured, a good image with reduced flare 9 can be captured.
[0043]
The present invention is not limited to the above-described embodiment, but can be variously modified as needed.
[0044]
【The invention's effect】
As described above, according to the imaging lens and the imaging apparatus using the same according to the present invention, it is possible to realize a small and lightweight imaging lens and an imaging apparatus having excellent optical characteristics while ensuring manufacturability.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram illustrating an embodiment of an imaging lens according to the present invention. FIG. 2 is a schematic configuration diagram illustrating a camera (imaging apparatus) equipped with an imaging lens in an embodiment of the imaging lens according to the present invention. FIG. 4 is an explanatory view schematically showing an imaging state in the embodiment of the imaging lens according to the present invention. FIG. 4 is an explanatory view showing a problem of the imaging lens which has been conventionally used. FIG. 5 has been conventionally used. FIG. 6 is an explanatory view different from FIG. 4 showing a problem of the imaging lens. FIG. 6 is an explanatory view schematically showing an imaging state by a conventional imaging lens.
DESCRIPTION OF SYMBOLS 1 Imaging lens 2 Lens 3 Rear stop 3a Opening 3b Inner peripheral surface 4 Optical axis 6 Imaging surface 9 Flare 10 Front stop 13 Exit pupil of lens system l Ray outside effective field angle l 'Principal ray at maximum field angle

Claims (2)

In order from the object side to the image plane side, at least one lens and an imaging lens provided with an aperture,
The following conditional expressions (1) to (4),
L ≦ 1.7 × f (1)
EX ≦ 1.2 × f (2)
1.3 × Φ ≦ θ ≦ 2.0 × Φ (3)
Φ = tan ⁻¹ (y ′ / EX) (4)
Here, L is the total length of the optical system, that is, the distance on the optical axis from the object side surface to the image plane of the lens disposed closest to the object side, f: the focal length of the entire lens system EX: the center of the exit pupil of the lens system Distance from the image plane θ: Slope, that is, the inclination angle Φ formed by the inner peripheral surface of the stop with respect to the optical axis of the lens system: Angle of incidence of the principal ray on the sensor imaging surface at the maximum angle of view y ′: Maximum of the sensor An imaging lens characterized by satisfying an image height. In an imaging apparatus having at least one lens, an imaging lens provided with an aperture, and an imaging device in order from the object side to the image plane side, the imaging lens includes the following (1) to (4) ),
L ≦ 1.7 × f (1)
EX ≦ 1.2 × f (2)
1.3 × Φ ≦ θ ≦ 2.0 × Φ (3)
Φ = tan ⁻¹ (y ′ / EX) (4)
Here, L is the total length of the optical system, that is, the distance on the optical axis from the object side surface to the image plane of the lens disposed closest to the object side, f: the focal length of the entire lens system EX: the center of the exit pupil of the lens system Distance from the image plane θ: Slope, that is, the inclination angle Φ formed by the inner peripheral surface of the stop with respect to the optical axis of the lens system: Angle of incidence of the principal ray on the sensor imaging surface at the maximum angle of view y ′: Maximum of the sensor An imaging device characterized by satisfying an image height.

Images