JP5421066B2 - Imaging lens - Google Patents

Description

 The present invention relates to a single focus lens used in an imaging apparatus using a solid-state imaging device, such as a digital still camera or a camera for a mobile communication terminal.

 Digital still cameras have been made thinner year by year, such as card types, and there is a demand for miniaturization of imaging devices. Also in mobile phones, downsizing of the imaging device is required in order to reduce the thickness of the terminal itself and to secure a space for mounting multiple functions. As a result, there is an increasing demand for further downsizing the imaging lens mounted on the imaging device.

 Simultaneously with the downsizing of image sensors such as CCD (Charge Coupled Device) and CMOS (Complementary Mental Oxide Semiconductor), the number of pixels is increasing due to the finer pixel pitch of the image sensor. Lenses are also demanding high performance.

 On the surface of these solid-state imaging devices, a microlens for allowing light to enter efficiently is provided. However, when the exit pupil position approaches the image plane, the off-axis light beam emitted from the imaging lens is incident obliquely on the image plane, and a shading phenomenon occurs. Then, the condensing by the microlens becomes insufficient, and there arises a problem that the brightness of the image changes extremely between the central portion of the image and the peripheral portion of the image. In order to solve this problem, a telecentric optical system with a small emission angle is desirable.

 As described above, an imaging lens that forms an image on an imaging element such as a CCD or a CMOS sensor is required to be small first. In addition, it is required to have good imaging performance and distortion characteristics, a sufficient amount of peripheral light, an appropriate back focus, and an exit pupil position as long as possible.

 As an imaging lens that may be able to meet these demands, a single focus lens composed of a total of four lenses (see, for example, Patent Documents 1 and 2), a single lens composed of a total of three lenses. A focus lens (see, for example, Patent Document 3) has been proposed. However, the single focus lenses described in Patent Documents 1 and 2 have a problem that the overall length of the lens system becomes considerably long in order to provide high imaging performance. In addition, the single focus lens described in Patent Document 3 may have insufficient optical performance due to the wide angle demand that has been recently demanded.

JP 2004-184987 A JP 2007-264498 A JP 2004-252312 A

 The present invention has been made in view of the above points, and an object of the present invention is to appropriately set the shape of a lens, the shape of an aspherical surface, etc. while having high optical performance by a three-lens configuration. It is to provide a small and thin imaging lens.

In order to achieve the above object, the lens of the first invention satisfies the following conditional expressions (1) and (2). In order from the object side, the lens has an aperture stop and convex shapes on both sides and has a positive refractive power. Three lenses, a first lens having a concave meniscus shape on the object side and having a negative refractive power, and a third lens having a convex meniscus shape on the object side and having a positive refractive power These lenses are arranged, and satisfy the following conditional expressions (3) to (6).
(1) 1.2 <TL / f <1.5
(2) TL / 2Y <0.9
(3) 0.5 <f1 / f <0.7
(4) -1.2 <f2 / f <-0.8
(5) 4.0 <f3 / f <20.0
(6) −2.00 <R11 / R12 <−0.70
However,
f: focal length of the entire lens system TL: distance from the aperture stop surface to the imaging surface
Y: distance from the center of the optical axis to the maximum image height on the imaging plane f1: focal length of the first lens f2: focal length of the second lens f3: focal length of the third lens
R11: radius of curvature of the object side surface of the first lens
R12: Radius of curvature of the image side surface of the first lens In the lens of the second invention, in the first invention, the three lenses have an aspheric shape on all surfaces, particularly the image side surface of the second lens. And the object side surface of the third lens has a shape in which the positive and negative refractive powers are reversed near and around the optical axis.

According to a third aspect of the present invention, in any one of the first to second aspects, the following conditional expression (7) is satisfied with respect to the refractive index and Abbe number with respect to the d-line of the material constituting the first lens and the second lens. ) And (8) are satisfied.
(7) 0.05 <(Nd1-Nd2) / Nd1 <0.14
(8) 10 <ν1-ν2 <30
However,
Nd1: Refractive index with respect to d-line of the first lens
Nd2: Refractive index for the d-line of the second lens ν1: Abbe number for the d-line of the first lens ν2: Abbe number of the second lens for the d-line Any one of the first to third lenses according to the fourth aspect of the present invention In the invention, the first lens is made of a glass material, and the second lens and the third lens are made of a resin material.

The lens of the fifth invention is characterized in that, in any of the first to fourth inventions, the following conditional expression (9) is satisfied.
(9) 0.3 <D12 / D23 <0.7
However,
D12: Axial distance between the first lens image side surface and the second lens object side surface
D23: On-axis distance between the second lens image side surface and the third lens object side surface The lens of the sixth invention satisfies the following conditional expression (10) in any one of the first to fifth inventions. And
(10) 1.0 <D'23 / D23 <2.0
However,
D'23: Distance respective maximum effective diameter position of the second lens image side surface and the third lens object side surface

 According to the present invention, it is possible to provide a bright imaging lens having a short overall length and excellent correction of various aberrations. As a result, a compact imaging lens that can be mounted on a digital camera, a mobile communication terminal camera, or the like can be realized.

It is a figure which shows the basic composition of the imaging lens of this embodiment. 2 is a diagram illustrating a configuration of an imaging lens employed in Example 1. FIG. FIG. 3 is an aberration diagram showing spherical aberration, astigmatism, and distortion in Example 1. 6 is a diagram illustrating a configuration of an imaging lens employed in Example 2. FIG. In Example 2, it is an aberrational figure which shows spherical aberration, astigmatism, and a distortion aberration. 6 is a diagram illustrating a configuration of an imaging lens employed in Example 3. FIG. In Example 3, it is an aberrational figure which shows spherical aberration, astigmatism, and a distortion aberration.

 The best mode for carrying out the present invention will be described below with reference to the drawings. FIG. 1 shows the lens configuration of the embodiment in an optical section. In these embodiments, in order from the object side, the aperture stop 110, the first lens 120, the second lens 130, the third lens 140, a parallel plane glass plate 150, a CCD (Charge Coupled Device), and a CMOS (Complementary Mental-Oxide Semiconductor). a single-focus lens 100 having a three-lens configuration in which an imaging device 160 such as a device) is disposed.

In the imaging lens embodying the present invention, the three lenses satisfy the following conditional expressions (1) and (2), and in order from the object side, the aperture stop 110 and convex shapes on both sides have a positive refractive power. A first lens 120 having a concave meniscus shape on the object side and having a negative refractive power, and a third lens 140 having a convex meniscus shape on the object side and having a positive refractive power. It is arranged like this.
Conditional expressions (1) and (2) are conditions that define the thickness of the optical system and the shooting angle of view, and can be said to be small and wide-angle lenses within this range. By providing an aperture stop in front of the lens, the exit pupil plane can be separated from the imaging plane, and as a result, the light incident angle on the imaging plane can be reduced. By disposing the aperture stop in front of the lens, the symmetry of the optical system with respect to the aperture stop is lost, so distortion becomes large. However, the first lens close to the aperture stop has the main refractive power for imaging, By making the two lenses have negative refractive power, it becomes possible to correct distortion with a good balance. The third lens has a positive refractive power in order to reduce the angle of incidence of the light beam on the image plane. However, if the refractive power is increased too much, negative distortion will increase, so that while correcting aberrations satisfactorily, A meniscus shape is used to reduce the refractive power. In order to remove the curvature of field due to the air space between the second lens and the third lens, the second lens image side surface and the third lens object side surface are convex to each other.
(1) 1.2 <TL / f <1.5
(2) TL / 2Y <0.9
However,
f: focal length of the entire lens system TL: distance from the aperture stop surface to the imaging surface
Y: Distance from the center of the optical axis to the maximum image height on the imaging plane Further, the lens according to the present invention is configured to satisfy the following conditional expressions (3) to (6).
(3) 0.5 <f1 / f <0.7
(4) -1.2 <f2 / f <-0.8
(5) 4.0 <f3 / f <20.0
(6) −2.00 <R11 / R12 <−0.70
However,
f1: Focal length of the first lens f2: Focal length of the second lens f3: Focal length of the third lens
R11: radius of curvature of the object side surface of the first lens
R12: Radius of curvature of the image side surface of the first lens The imaging lens embodying the present invention has a configuration in which the first lens close to the aperture stop has a main imaging force. For this reason, if the upper limit value of the expression (3) is exceeded, the positive refractive power at the front becomes small, and the refractive power of the lens having a large effective diameter arranged at the rear becomes too large, resulting in an increase in distortion. Problems occur. On the other hand, if the lower limit is exceeded, the radius of curvature becomes too small, making it difficult to secure a sufficient edge thickness. Since the second lens corrects aberrations such as distortion and spherical aberration generated in the first lens, if the range of the equation (4) is exceeded, various aberrations are undercorrected or overcorrected. By setting the refractive power of the third lens within the range of the expression (5), it is possible to configure the distortion and the light incident angle on the imaging surface with a good balance. The ratio of the curvature radii of the first lens is set within the range of equation (6). As the distance from the aperture stop increases, the peripheral ray height increases, so the radius of curvature of the object side surface must be reduced. However, if the upper limit of equation (4) is exceeded, the shape becomes difficult to manufacture.

 In the imaging lens 100, light incident from the object side OBJS is the surface 1 of the aperture stop 110, the object side R1 surface 2 of the first lens 120, the image surface side R2 surface 3, and the object side R3 surface 4 of the second lens 130. The image plane side R4 surface 5, the object side R5 surface 6 of the third lens 140, the image plane side R6 surface 7, the object side surface 8 of the parallel plane glass plate 150, and the image side surface 9 are sequentially passed to the image sensor 160. Lighted.

 Since the three lenses have aspherical surfaces on all surfaces, aberration correction can be facilitated and good resolution performance can be obtained while being small. In particular, since the image side surface of the second lens and the object side surface of the third lens have shapes in which the positive and negative refractive powers are reversed near and around the optical axis, it becomes possible to correct the curvature of field well.

 The aspheric shape of the lens described in the following numerical examples is positive in the direction from the object side to the image plane side, k is a conical coefficient, and A, B, C, and D are aspheric coefficients. , R is the central radius of curvature, h represents the height of the light beam, and c represents the reciprocal of the central radius of curvature. Where Z is the depth from the tangent plane to the surface vertex, A is the fourth-order aspheric coefficient, B is the sixth-order aspheric coefficient, C is the eighth-order aspheric coefficient, and D is the tenth-order aspheric coefficient. Each aspheric coefficient is shown.

The imaging lens embodying the present invention is preferably set so that the following conditional expressions (7) and (8) are satisfied with respect to the refractive index and Abbe number for the d-line of the materials constituting the first lens and the second lens. Is done.
(7) 0.05 <(Nd1-Nd2) / Nd1 <0.14
(8) 10 <ν1-ν2 <30
However,
Nd1: Refractive index with respect to d-line of the first lens
Nd2: Refractive index for the d-line of the second lens ν1: Abbe number for the d-line of the first lens ν2: Abbe number for the d-line of the second lens The third lens has a small refractive power, so the Petzval sum and achromatic conditions Is strongly influenced by the material composition of the first lens and the second lens. Astigmatism and curvature of field can be corrected satisfactorily by selecting a material that satisfies the conditional expression (7) in the refractive power arrangement that satisfies the conditional expressions (3) to (5). It becomes. Similarly, it is possible to satisfactorily correct the chromatic aberration by selecting a material that satisfies the conditional expression (8).

 In the imaging lens embodying the present invention, the first lens is preferably made of a glass material, and the second lens and the third lens are made of a resin material. By forming the first lens with a glass material, it is easy to select a material that satisfies the conditional expressions (7) and (8). Further, by forming the second lens and the third lens from a resin material, it becomes easy to mold an aspherical shape.

The imaging lens embodying the present invention is preferably configured to satisfy the following conditional expression (9).
(9) 0.3 <D12 / D23 <0.7
However,
D12: Axial distance between the first lens image side surface and the second lens object side surface
D23: If the lower limit of the on-axis distance (9) expression between the second lens image side surface and the third lens object side surface is exceeded, it becomes difficult to correct distortion and curvature of field. On the other hand, if the upper limit value of the expression (9) is exceeded, the height of the light beam incident on the second lens becomes large and the lens becomes large.

The imaging lens embodying the present invention is preferably configured to satisfy the following conditional expression (10).
(10) 1.0 <D'23 / D23 <2.0
However,
D'23: Distance between the maximum effective diameter positions of the second lens image side surface and the third lens object side surface If the lower limit of equation (10) is exceeded, a sufficient optical path difference between the center and the periphery cannot be secured. Astigmatism or curvature of field becomes difficult to correct. On the other hand, when the upper limit is exceeded, the shape of the second lens or the third lens becomes complicated, making it difficult to manufacture.

 Examples 1 to 3 according to specific numerical values of the imaging lens are shown below. In the numerical examples 1 to 3, the focal length, F number, angle of view, image height, total lens length, and back focus (Bf) are as shown in Table 1 below. Similarly, in the numerical examples of 1 to 3, the numerical data of the conditional expressions (1) to (10) are values shown in the following Table 2.

 The basic configuration of the lens system in Embodiment 1 is shown in FIG. 2, each numerical data (setting value) is shown in Tables 3 and 4, and aberration diagrams showing spherical aberration, astigmatism, and distortion are shown in FIG. Each is shown.

 As shown in FIG. 2, the first lens has a biconvex shape, the second lens has a meniscus shape with a concave surface facing the object side, and the third lens has a meniscus shape with a convex surface facing the object side. Each of the first lens to the third lens has an aspheric surface on both sides. As shown in the figure, the distance between the diaphragm surface 1 and the R1 surface 2 of the first lens is D1, the distance between the R1 surface 2 and the R2 surface 3 which is the thickness of the first lens is D2, and the first lens The distance between the R2 surface 3 and the R3 surface 4 of the second lens is D3, the distance between the R3 surface 4 and the R4 surface 5 that is the thickness of the second lens is D4, the R4 surface 5 of the second lens and the R5 of the third lens. The distance between the surfaces 6 is D5, the distance between the R5 surface 6 and the R6 surface 7 which is the thickness of the third lens is D6, the distance between the R6 surface 7 of the third lens and the surface 8 of the flat glass is D7, parallel plane glass The distance between the surface 8 and the surface 9 having a thickness of is D8, and the distance between the plane parallel glass and the imaging surface is D9.

 Table 3 shows the stop corresponding to each surface number of the imaging lens in Example 1, the radius of curvature R, the interval D, the refractive index Nd, and the dispersion value νd of each lens. Table 4 shows the aspheric coefficient of the predetermined surface.

 <Numerical example 1>

3A and 3B show spherical aberration, FIG. 3B shows astigmatism, and FIG. 3C shows distortion aberration in Example 1, respectively. The vertical axis in FIG. 3A represents the pupil coordinates, and each line of the graph indicates the values of the C line, d line, and g line. The vertical axis in FIG. 3B represents the real image height on the imaging plane. In FIG. 3B, the solid line S is the value of the d-line on the sagittal image plane, and the broken line T is the value of the d-line on the tangential image plane. (The same applies to FIGS. 5 and 7). The vertical axis in FIG. 3C represents the real image height on the imaging plane, and the value represents the value of the d line. As can be seen from FIG. 3, according to Example 1, various aberrations such as spherical, astigmatism, and distortion are satisfactorily corrected, and an imaging lens excellent in imaging performance can be obtained.

 The basic configuration of the lens system according to Embodiment 2 is shown in FIG. 4, each numerical data (setting value) is shown in Tables 5 and 6, and aberration diagrams showing spherical aberration, astigmatism and distortion are shown in FIG. Indicated.

 As shown in FIG. 4, the first lens has a biconvex shape, the second lens has a meniscus shape with a concave surface facing the object side, and the third lens has a meniscus shape with a convex surface facing the object side. Each of the first lens to the third lens has an aspheric surface on both sides.

 Table 5 shows the diaphragm corresponding to each surface number of the imaging lens in Example 2, the radius of curvature R, the interval D, the refractive index Nd, and the dispersion value νd of each lens. Table 6 shows the aspheric coefficient of the predetermined surface.

 <Numerical Example 2>

5A and 5B, in Example 2, FIG. 5A shows spherical aberration, FIG. 5B shows astigmatism, and FIG. 5C shows distortion. As can be seen from FIG. 5, according to Example 2, various aberrations such as spherical surface, astigmatism, and distortion are favorably corrected, and an imaging lens excellent in imaging performance can be obtained.

 The basic configuration of the lens system according to Embodiment 3 is shown in FIG. 6, numerical data (setting values) are shown in Tables 7 and 8, and aberration diagrams showing spherical aberration, astigmatism and distortion are shown in FIG. Indicated.

 As shown in FIG. 6, the first lens has a biconvex shape, the second lens has a meniscus shape with a concave surface facing the object side, and the third lens has a meniscus shape with a convex surface facing the object side. Each of the first lens to the third lens has an aspheric surface on both sides.

 Table 7 shows the stop corresponding to each surface number of the imaging lens in Example 3, the radius of curvature R, the interval D, the refractive index Nd, and the dispersion value νd of each lens. Table 8 shows the aspheric coefficient of the predetermined surface.

 <Numerical Example 3>

7A and 7B, in Example 3, FIG. 7A shows spherical aberration, FIG. 7B shows astigmatism, and FIG. 7C shows distortion. As can be seen from FIG. 7, according to the third embodiment, various aberrations such as spherical surface, astigmatism, and distortion are satisfactorily corrected, and an imaging lens excellent in imaging performance can be obtained.

DESCRIPTION OF SYMBOLS 100,100A-100C ... Imaging lens 110 ... Aperture stop part 120 ... 1st lens 130 ... 2nd lens 140 ... 3rd lens 150 ... Parallel plane glass 160 ... Imaging surface

Claims (6)

In order from the object side, an aperture stop, a first lens having a convex shape on both sides and having a positive refractive power, a second lens having a concave meniscus shape on the object side and having a negative refractive power, and an object An imaging lens comprising three lenses, a third lens having a convex meniscus shape and a positive refractive power, satisfying the following conditional expressions (1) to (6).
(1) 1.2 <TL / f <1.5
(2) TL / 2Y <0.9
(3) 0.5 <f1 / f <0.7
(4) -1.2 <f2 / f <-0.8
(5) 4.0 <f3 / f <20.0
(6) −2.00 <R11 / R12 <−0.70
However,
f: focal length of the entire lens system TL: distance from the aperture stop surface to the imaging surface
Y: distance from the center of the optical axis to the maximum image height on the imaging plane f1: focal length of the first lens f2: focal length of the second lens f3: focal length of the third lens
R11: radius of curvature of the object side surface of the first lens
R12: radius of curvature of the image side surface of the first lens The three lenses have aspherical shapes on all surfaces, and in particular, the image side surface of the second lens and the object side surface of the third lens have shapes in which the positive and negative refractive powers are reversed near and around the optical axis. The imaging lens according to claim 1. The following conditional expressions (7) and (8) are satisfied with respect to the refractive index and Abbe number for the d-line of the material constituting the first lens and the second lens: The imaging lens described.
(7) 0.05 <(Nd1-Nd2) / Nd1 <0.14
(8) 10 <ν1-ν2 <30
However,
Nd1: Refractive index with respect to d-line of the first lens
Nd2: Refractive index for the d-line of the second lens ν1: Abbe number for the d-line of the first lens ν2: Abbe number of the second lens for the d-line The imaging lens according to claim 1, wherein the first lens is made of a glass material, and the second lens and the third lens are made of a resin material. The imaging lens according to claim 1, wherein the following conditional expression (9) is satisfied.
(9) 0.3 <D12 / D23 <0.7
However,
D12: Axial distance between the first lens image side surface and the second lens object side surface
D23: Axial distance between the second lens image side surface and the third lens object side surface The imaging according to claim 1, wherein the following conditional expression (10) is satisfied:
lens.
(10) 1.0 <D'23 / D23 <2.0
However,
D'23: Distance between the maximum effective diameter positions of the second lens image side surface and the third lens object side surface