Optical system and imaging device

Abstract

It provides a compact optical system with a short overall length. [Solution] The optical system is 5 or more The lens Furthermore, at least two of the five or more lenses are positive lenses, and five or more The lens closest to the image sensor among the lenses haso This is a negative lens that has an inflection point where the sign of the curvature of the lens surface changes. Furthermore, the five or more lenses are arranged in order from the object side to the image side, with a first lens, a second lens, and a third lens, and an aperture diaphragm is located between any two of the first to third lenses, or adjacent to the first lens on the object side, or adjacent to the third lens on the image side. The focal length of the optical system is f, and the image height is ImgH. fP is the focal length of the lens with the greatest positive refractive power among the first, second, and third lenses, f13 is the combined focal length of the first, second, and third lenses, R1 is the radius of curvature of the object-side lens surface of the negative lens, and R2 is the radius of curvature of the image-side lens surface of the lens adjacent to the negative lens on the object side. When prescribed The conditions are met.

Description

[Technical Field]

[0001] This invention relates to an optical system suitable for imaging. [Background technology]

[0002] Imaging requires an optical system that exhibits good optical performance from the center to the periphery of the field of view, and is also small and lightweight. As such an optical system, as disclosed in Patent Document 1, resin-molded aspherical lenses are sometimes used. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] U.S. Public Gazette No. 2023 / 0168470 [Overview of the project] [Problems that the invention aims to solve]

[0004] There is a need for smaller optical systems with a shorter overall length than conventional ones. [Means for solving the problem]

[0005] One aspect of the present invention is an optical system having a plurality of lenses arranged sequentially from the object side to the image side. The lens closest to the image side among the plurality of lenses is a negative lens having an inflection point where the sign of the curvature of its lens surface changes. When the focal length of the optical system is f, the image height is ImgH, and the effective diameter of the image-side lens surface of the negative lens is EAR, 0.50 ≤ f / ImgH ≤ 0.95 0.40 ≤ EAR / ImgH / 2 ≤ 0.75 It is characterized by satisfying the following conditions.

[0006] Furthermore, as another aspect of the present invention, the optical system is 0.50 ≤ f / ImgH ≤ 0.95 It is characterized by satisfying the following conditions.

[0007] Furthermore, another aspect of the present invention is an optical system having five or more lenses, wherein at least two of the five or more lenses are positive lenses, and the lens closest to the image is a negative lens having an inflection point where the sign of the curvature of its lens surface changes. An imaging device equipped with the above optical system also constitutes another aspect of the present invention. [Effects of the Invention]

[0008] According to the present invention, a compact optical system with a short overall length can be provided. [Brief explanation of the drawing]

[0009] [Figure 1] Cross-sectional view of the optical system of Example 1. [Figure 2] Aberration diagram of the optical system in Example 1. [Figure 3] Cross-sectional view of the optical system in Example 2. [Figure 4] Aberration diagram of the optical system in Example 2. [Figure 5] Cross-sectional view of the optical system of Example 3. [Figure 6] Aberration diagram of the optical system in Example 3. [Figure 7] Cross-sectional view of the optical system of Example 4. [Figure 8] Aberration diagram of the optical system in Example 4. [Figure 9] A diagram showing an imaging device using the optical system of the embodiment. [Modes for carrying out the invention]

[0010] The embodiments of the present invention will be described below with reference to the drawings. First, before describing the specific embodiments 1 to 4, we will explain the matters common to each embodiment. Figures 1, 3, 5, and 7 show cross-sections of the optical systems of embodiments 1, 2, 3, and 4 in a state where they are in focus on an object at infinity (hereinafter referred to as the infinity focus state).

[0011] The optical systems of each embodiment are used as imaging optical systems for various imaging devices such as video cameras, digital still cameras, smartphone cameras, surveillance cameras, night vision cameras, in-vehicle cameras, and silver halide film cameras. Further, the optical system of each embodiment may be used as a projection optical system of an image projection device (projector).

[0012] In each figure, the left side is the object side (front side), and the right side is the image side (rear side). O indicates the optical axis of the optical system. The lenses constituting the optical system are referred to as the i-th lens (i = 1, 2, 3,...) from the object side. SP indicates an aperture stop that determines (limits) the light beam of the open F-number, and IP indicates the image plane. On the image plane IP, the imaging surface (light-receiving surface) of an imaging element such as a CCD sensor or a CMOS sensor or the film surface (photosensitive surface) of a silver halide film is arranged. Further, between the rightmost lens and the image plane IP, an optical block OB having no effective refractive power, such as an optical filter (low-pass filter, infrared cut filter, etc.), a face plate, and a sensor protection glass, is arranged. The optical block OB is not included in the components of the optical system of each embodiment.

[0013] Note that the optical system of each embodiment may include a flare cut stop that cuts unnecessary light (flare light), although not shown in the drawings. Further, the optical system of each embodiment may perform focusing by moving the whole or part of its lenses in the direction along the optical axis O (hereinafter referred to as the optical axis direction).

[0014] Hereinafter, the features of the optical systems of each embodiment will be described. The optical system of each embodiment has a plurality of lenses and has a negative lens with the strongest refractive power on the most image side (hereinafter referred to as the most image-side negative lens). By arranging such an image-side negative lens, the distance on the optical axis from the image plane IP to the exit pupil of the optical system (hereinafter referred to as the pupil distance) can be shortened, and as a result, the overall length of the optical system can be shortened. When the pupil distance is shortened, the incident angle of the light beam from the optical system to the image plane (imaging surface) IP increases, so the diameter of the most image-side negative lens becomes smaller, and miniaturization of the optical system becomes possible.

[0015] However, by placing a negative lens on the image-side, the divergence effect causes excessive field curvature of off-axis rays and also generates positive distortion. Therefore, it is necessary to place an aspherical surface to weaken the negative refractive power of off-axis rays. In this case, the image-side lens surface of the negative lens on the image-side will have an aspherical shape with an inflection point such that the region on the optical axis side is concave toward the image side and the region on the peripheral side is convex toward the image side.

[0016] In an aspherical surface, let x be the displacement from the surface vertex in the direction of the optical axis, h be the height from the optical axis in the direction perpendicular to the optical axis (radial direction), and x(h) be the aspherical shape. In this case, the inflection point is the point where the second derivative of x(h) obtained by differentiating it twice with respect to h is zero, and the sign of the second derivative (i.e., the curvature) changes before and after that point (line). Specifically, it means the point where the shape of the lens surface switches from a concave shape to a convex shape, or from a convex shape to a concave shape. Having an inflection point makes it easier to correct image field curvature because the refractive power in the peripheral part can be determined without depending on the refractive power in the paraxial direction. The position of the inflection point can be set at any position radially away from the optical axis, as long as it is within the effective area of ​​the lens surface (the area that contributes to image formation).

[0017] The optical system of each embodiment preferably satisfies at least one of the following conditions.

[0018] 0.50 ≤ f / ImgH ≤ 0.95 (1) 0.40 ≤ EAR / ImgH / 2 ≤ 0.75 (2) In equations (1) and (2), f is the focal length of the optical system, ImgH is the image height, and EAR is the effective diameter (radius of the effective area) of the image-side lens surface of the closest negative lens.

[0019] The conditions in equation (1) indicate an appropriate relationship between the focal length and image height of the optical system. This value becomes smaller because shortening the overall length of the optical system requires shortening the overall focal length accordingly. If f / ImgH exceeds the upper limit of equation (1), the overall focal length becomes too large relative to the image height, making it difficult to shorten the overall length, which is undesirable. If f / ImgH falls below the lower limit of equation (1), the overall focal length becomes too small relative to the image height, i.e., the refractive power becomes too strong, making it difficult to correct field curvature and distortion, which is also undesirable.

[0020] Furthermore, it is more preferable to set the lower limit of equation (1) to 0.60, 0.65, 0.70, or 0.75. Also, it is more preferable to set the upper limit of equation (1) to 0.948, 0.945, or 0.942.

[0021] The conditions in equation (2) indicate an appropriate relationship between the effective diameter on the image side of the image-side negative lens and the image height. Shortening the overall length shortens the interpupillary distance and increases the angle of incidence of light rays to the imaging plane, thus allowing for a smaller effective diameter. A smaller effective diameter of the image-side negative lens reduces the outer diameter of the negative lens, enabling miniaturization of the entire system. It is undesirable if EAR / ImgH exceeds the upper limit of equation (2) and the effective diameter on the image side of the image-side negative lens becomes too large, making it difficult to shorten the overall length. It is also undesirable if EAR / ImgH falls below the lower limit of equation (2) because the effective diameter on the image side of the image-side negative lens becomes too small, increasing the refractive power of the negative lens and making it difficult to correct field curvature and distortion.

[0022] Furthermore, it is more preferable to set the lower limit of equation (2) to 0.42, 0.44, 0.46, or 0.48. Also, it is more preferable to set the upper limit of equation (2) to 0.748, 0.746, or 0.745.

[0023] The optical systems of each embodiment (each numerical example described later) are configured as compact optical systems with shortened overall length by satisfying the conditions of equations (1) and (2).

[0024] Furthermore, it is preferable that the optical system of each embodiment has at least one of the following configurations.

[0025] The optical system of each embodiment has a first lens, a second lens, and a third lens, in order from the object side. These first to third lenses bear the majority of the positive refractive power of the optical system, while the lenses on the image side from the third lens onwards correct field curvature and distortion. Preferably, at least one of the first, second, and third lenses has positive refractive power, and the combined focal length of these first to third lenses is close to the focal length of the entire system. More preferably, by distributing the positive refractive power by using two of these first to third lenses as positive lenses, it becomes easier to correct spherical aberration and coma aberration. By sharing the refractive power among the first to third lenses and sharing the aberration correction among the lenses on the image side from the third lens onwards, high optical performance and a shortened overall length (miniaturization) of the optical system are achieved.

[0026] Furthermore, in order to shorten the interpupillary distance and thus the overall length, a strong negative refractive power is required for the negative lens on the image side. To correct aberrations while sharing the refractive power on both the object side and the image side of this negative lens on the image side, it is preferable that the negative lens on the image side be a biconcave lens. Moreover, if an air lens with negative refractive power is placed adjacent to the negative lens on the object side, field curvature and distortion aberrations can be corrected more effectively. It is preferable that the image-side surface of the air lens, that is, the object-side lens surface of the negative lens on the image side, has a convex shape toward the image side.

[0027] Furthermore, it is preferable that the negative lens on the image-facing side be a resin lens. Using a resin lens increases the degree of freedom in its shape, and allows for better correction of field curvature and distortion.

[0028] Furthermore, it is preferable that the aperture diaphragm SP be positioned between any two of the first to third lenses, either adjacent to the first lens on the object side or adjacent to the third lens on the image side. This increases the height of off-axis rays at the image-side negative lens, thereby enhancing the correction effect for field curvature and distortion.

[0029] The optical system of each embodiment preferably satisfies at least one of the following conditions (3) to (11).

[0030] 0.7 ≤ TTL / ImgH ≤ 1.3 (3) 0 <skd / ImgH≦0.3 (4) 0.8 ≤ fP / f ≤ 1.5 (5) 0.6 ≤ f13 / f ≤ 1.1 (6) -1.1 ≤ fR / f ≤ -0.5 (7) -3.00 ≤ R1 / |R2| ≤ -0.05 (8) 0.05 ≤ TR / EAR ≤ 0.40 (9) -1.5 ≤ sagmax / sagmin < 0 (10) -0.60 ≤ Tk / ImgH ≤ -0.20 (11) In equations (3) to (11), TTL is the total length along the optical axis from the lens surface with the greatest object-side refractive power in the optical system to the image plane, skd is the air-converted value (back focus) of the distance along the optical axis from the lens surface with the greatest image-side refractive power to the image plane. fP is the focal length of the lens with the greatest positive refractive power among the first, second, and third lenses, f13 is the combined focal length of the first, second, and third lenses, and fR is the focal length of the negative lens on the image side.

[0031] The object-side lens surface of the image-side negative lens has a concave shape toward the object, and an air gap (air lens) is formed between the image-side negative lens and the lens adjacent to it on the object side. In this case, R1 is the radius of curvature of the object-side lens surface of the image-side negative lens, and R2 is the radius of curvature of the image-side lens surface of the lens adjacent to the image-side negative lens on the object side. TR is the distance along the optical axis between the object-side lens surface of the image-side negative lens and the image-side lens surface of the lens adjacent to it on the object side (length along the optical axis of the air lens), and Tk is the pupil distance. sagmax and sagmin are the maximum and minimum sag amounts of the image-side lens surface of the image-side negative lens, respectively. The sag amount corresponds to x (displacement from the vertex of the surface in the optical axis direction) in the formula for the aspherical shape described later.

[0032] The conditions in equation (3) indicate an appropriate relationship between the total length of the optical system and the image height, and are conditions related to the size of the optical system. If TTL / ImgH exceeds the upper limit of equation (3), the total length becomes too large relative to the image height, which is undesirable. If TTL / ImgH falls below the lower limit of equation (3), the total length becomes too small relative to the image height, making it difficult to correct field curvature and distortion, which is also undesirable.

[0033] Furthermore, it is more preferable to set the lower limit of equation (3) to 0.75, 0.80, 0.85, or 0.90. Also, it is more preferable to set the upper limit of equation (3) to 1.28, 1.26, or 1.24.

[0034] The conditions in equation (4) indicate an appropriate relationship between back focus and image height. If skd / ImgH exceeds the upper limit of (4), the back focus becomes too large, hindering the reduction of the overall length, which is undesirable. If skd / ImgH falls below the lower limit of equation (4), the back focus becomes too small, causing dust adhering to the cover glass and filters to appear in the image, which is also undesirable.

[0035] Furthermore, it is more preferable to set the lower limit of equation (4) to 0.10, 0.15, or 0.17. Also, it is more preferable to set the upper limit of equation (4) to 0.29 or 0.28.

[0036] The conditions in equation (5) indicate an appropriate relationship between the lens with the greatest positive refractive power among the first, second, and third lenses and the overall focal length of the system. If fP / f exceeds the upper limit of equation (5), the overall focal length of the system becomes too long, making it difficult to shorten the distance to the image plane IP and thus the overall length, which is undesirable. If fP / f falls below the lower limit of equation (5), the refractive power of the lens with the greatest positive refractive power becomes too strong, making it difficult to correct spherical aberration and coma aberration, which is also undesirable.

[0037] Furthermore, it is more preferable to set the lower limit of equation (5) to 0.85, 0.90, 0.95, or 1.00. Also, it is more preferable to set the upper limit of equation (5) to 1.40, 1.35, or 1.3.

[0038] The conditions in equation (6) indicate an appropriate relationship between the combined focal length of the first, second, and third lenses and the focal length of the entire system. If f13 / f exceeds the upper limit of equation (6), the focal length of the entire system becomes too long, making it difficult to shorten the distance to the image plane IP and thus difficult to shorten the overall length, which is undesirable. If f13 / f falls below the lower limit of equation (6), even if the refractive power is dispersed by the first, second, and third lenses, the spherical aberration and coma aberration generated in these lenses become too large, which is also undesirable.

[0039] Furthermore, it is more preferable to set the lower limit of equation (6) to 0.70, 0.75, or 0.80. Also, it is more preferable to set the upper limit of equation (6) to 1.05, 1.04, or 1.03.

[0040] The conditions in equation (7) indicate an appropriate relationship between the focal length of the negative lens on the image side and the focal length of the entire system. If fR / f exceeds the upper limit of equation (7), the interpupillary distance cannot be shortened and the overall length increases, which is undesirable. If fR / f falls below the lower limit of equation (7), the refractive power of the negative lens on the image side becomes too strong, making it difficult to correct field curvature and distortion even when using an aspherical lens, which is also undesirable.

[0041] Furthermore, it is more preferable to set the lower limit of equation (7) to -1.00, -0.95, or -0.90. Also, it is more preferable to set the upper limit of equation (7) to -0.60, -0.65, or -0.70.

[0042] The conditions in equation (8) indicate the appropriate shape of the air lens formed on the object side of the image-side negative lens. If R1 / |R2| exceeds the upper limit of equation (8), the curvature of the image-side surface of the air lens becomes too strong, making it difficult to correct field curvature and distortion, which is undesirable. If R1 / |R2| falls below the lower limit of equation (8), the curvature of the image-side surface of the air lens becomes too gentle, weakening the negative refractive power of the air lens, making it difficult to shorten the interpupillary distance and thus difficult to shorten the overall length, which is also undesirable.

[0043] Furthermore, it is more preferable to set the lower limit of equation (8) to -2.5, -2.0, -1.8, or -1.7. Also, it is more preferable to set the upper limit of equation (8) to -0.1, -0.2, or -0.25.

[0044] The conditions in equation (9) indicate an appropriate relationship between the length of the air lens formed on the object side of the image-side negative lens and the effective diameter of the lens surface on the image side of the image-side negative lens. If TR / EAR exceeds the upper limit of equation (9), the length of the air lens becomes too large, making it difficult to shorten the overall length, which is undesirable. If TR / EAR falls below the lower limit of equation (9), the length of the air lens becomes too small, weakening the negative refractive power of the air lens, making it difficult to shorten the interpupillary distance and thus difficult to shorten the overall length, which is also undesirable.

[0045] Furthermore, it is more preferable to set the lower limit of equation (9) to 0.06 or 0.07. Also, it is more preferable to set the upper limit of equation (9) to 0.35, 0.30, or 0.28.

[0046] The conditions in equation (10) indicate the appropriate shape of the image-side lens surface in the image-side negative lens, i.e., the amount of sag. If sagmax / sagmin exceeds the upper limit of equation (10), the refractive power of the image-side negative lens becomes too weak, or the curvature of the object-side lens surface of the image-side negative lens becomes too strong, making it difficult to achieve both overall length reduction and aberration correction, which is undesirable. If sagmax / sagmin falls below the lower limit of equation (10), the waviness of the image-side lens surface of the image-side negative lens becomes too large, making it difficult to shape the image-side negative lens, which is also undesirable.

[0047] Furthermore, it is more preferable to set the lower limit of equation (10) to -1.4, -1.3, or -1.25.

[0048] The conditions in equation (11) indicate the appropriate relationship between the pupil distance and image height of the optical system. If Tk / ImgH exceeds the upper limit of equation (11), the pupil distance becomes too short, making it difficult to correct field curvature and distortion aberrations with the negative lens on the image side, which is undesirable. If Tk / ImgH falls below the lower limit of equation (11), the pupil distance becomes too long, making it difficult to shorten the overall length, which is also undesirable.

[0049] Furthermore, it is more preferable to set the lower limit of equation (11) to -0.57, 0.55, or -0.53. Also, it is more preferable to set the upper limit of equation (11) to -0.30, -0.32, or -0.34.

[0050] Examples 1 to 4 will be described in detail below. Following Example 4, numerical examples 1 to 4 corresponding to each of Examples 1 to 4 are shown. [Examples]

[0051] The optical system of Embodiment 1 (Numerical Example 1) shown in Figure 1 has a focal length of 3.322 mm, an F-number of 1.798, and a half-angle of view of 46.736°. The optical system of this embodiment consists of six lenses with positive-negative-positive-negative-positive refractive powers arranged in order from the object side to the image side. All six lenses are aspherical lenses formed with aspherical surfaces on both sides. The aperture diaphragm SP is positioned between the first lens and the second lens.

[0052] Figure 2 shows the longitudinal aberrations (spherical aberration, astigmatism, distortion, and chromatic aberration) of the optical system in numerical example 1. In the spherical aberration diagram, Fno indicates the F number, the solid line shows the spherical aberration at the d line (wavelength 587.6 nm), and the dashed line shows the spherical aberration at the g line (wavelength 435.8 nm). In the astigmatism diagram, the solid line S shows the astigmatism at the sagittal image plane, and the dashed line M shows the astigmatism at the meridional image plane. The distortion diagram shows the distortion at the d line. The chromatic aberration diagram shows the lateral chromatic aberration at the g line. ω is the half-angle of view (°). The explanation of the above aberration diagrams is the same for other numerical examples described later. [Examples]

[0053] The optical system of Embodiment 2 (Numerical Example 2) shown in Figure 3 has a focal length of 2.718 mm, an F-number of 1.798, and a half-angle of view of 52.401°. The optical system of this embodiment consists of six lenses with positive-negative-positive-negative-positive refractive powers arranged in order from the object side to the image side. All six lenses are aspherical lenses formed with aspherical surfaces on both sides. The aperture diaphragm SP is positioned between the first lens and the second lens.

[0054] Figure 4 shows the longitudinal aberration of the optical system in numerical example 2. [Examples]

[0055] The optical system of Embodiment 3 (Numerical Example 3) shown in Figure 5 has a focal length of 3.025 mm, an F-number of 2.785, and a half-angle of view of 49.404°. The optical system of this embodiment consists of six lenses with positive-negative-positive-negative-negative refractive powers arranged in order from the object side to the image side. All six lenses are aspherical lenses formed with aspherical surfaces on both sides. The aperture diaphragm SP is positioned between the first lens and the second lens.

[0056] Figure 6 shows the longitudinal aberration of the optical system in numerical example 3. [Examples]

[0057] The optical system of Embodiment 4 shown in Figure 7 has a focal length of 2.997 mm, an F-number of 2.782, and a half-angle of view of 49.671°. The optical system of this embodiment consists of five lenses with positive-negative-positive-negative refractive powers arranged in order from the object side to the image side. All five lenses are aspherical lenses with aspherical surfaces on both sides. The aperture diaphragm SP is positioned between the third and fourth lenses. By positioning the aperture diaphragm SP in the middle of the optical system, it becomes possible to share the correction of field curvature and distortion aberrations with the first lens.

[0058] Figure 8 shows the longitudinal aberration of the optical system in numerical example 4.

[0059] The following shows Numerical Examples 1 to 4. The surface number i of each numerical example indicates the order of the optical surfaces counted from the object side, r represents the paraxial curvature radius (mm) of the i-th optical surface, which is the i-th surface, and d represents the lens thickness or air gap (mm) on the optical axis between the i-th surface and the (i + 1)-th surface. nd represents the refractive index at the d-line of the optical material between the i-th surface and the (i + 1)-th surface, and νd represents the Abbe number based on the d-line of the optical material between the i-th surface and the (i + 1)-th surface. The Abbe number νd based on the d-line is expressed as νd = (Nd - 1) / (NF - NC), where Nd, NF, and NC are the refractive indices at the d-line (587.6 nm), F-line (486.1 nm), and C-line (656.3 nm) of the Fraunhofer lines. As described above, the effective diameter is the diameter (mm) of the effective area through which the light rays contributing to imaging pass on the i-th lens surface.

[0060] skd represents the back focus (mm). The back focus is the distance on the optical axis from the most image-side lens surface (the final surface) of the optical system to the paraxial image plane, expressed in terms of the air-equivalent length. The overall lens length is the length obtained by adding the back focus to the distance on the optical axis from the most object-side lens surface (the frontmost surface) of the optical system to the final surface.

[0061] The "*" attached to the surface number means that the surface has an aspherical shape. The aspherical shape is expressed by the following formula when x is the displacement amount from the vertex of the surface in the optical axis direction, h is the height from the optical axis in the direction perpendicular to the optical axis, the direction of light propagation is positive, R is the paraxial curvature radius, K is the conic constant, and A4, A6, A8, A10, A12 are the aspherical coefficients. "e±M" of the conic constant and the aspherical coefficients means ×10 ±M is meant.

[0062] x=(h 2 / R) / [1+{1-(1+K)(h / R) 2} 1 / 2 +A4·h 4 +A6·h 6 +A8·h 8 +A10·h 10 +A12·h 12 ​Furthermore, Table 1 summarizes the values ​​related to equations (1) to (11) in numerical examples 1 to 4. Each numerical example satisfies all the conditions of equations (1) to (11). [Numerical Example 1] Unit: mm Surface data Face number rd nd νd Effective diameter 1* 2.1540 0.537 1.53500 55.73 1.85 2* 52.0828 0.019 1.89 3 (aperture) ∞ 0.019 1.84 4* -4.5286 0.200 1.68040 18.10 1.84 5* -3541.7250 0.130 1.74 6* 4.9065 0.342 1.53500 55.73 1.72 7* -3.5224 0.434 1.75 8* -1.1938 0.446 1.53500 55.73 2.19 9* -1.3349 0.050 2.50 10* 1.9889 0.507 1.53500 55.73 2.81 11* 7.1738 0.403 3.48 12* -1.8433 0.237 1.53500 55.73 3.50 13* 4.6774 0.224 5.25 14 ∞ 0.150 1.56300 51.30 6.20 15 ∞ 0.647 6.20 Image plane ∞ Aspherical data Front page K = 0.00000e+00 A 4=-8.14108e-02 A 6=-2.58854e-02 A 8=-1.29269e-01 A10 = 6.16829e-02 2nd side K = 0.00000e+00 A 4=-1.53706e-01 Page 4 K = 0.00000e+00 A 4= 1.30697e-01 Page 5 K = 0.00000e+00 A 4= 1.65609e-01 A 6=-7.88063e-02 Page 6 K = 0.00000e+00 A 4=-5.72367e-02 A 6=-1.12574e-01 A 8=-8.06172e-02 Page 7 K = 0.00000e+00 A 4= 8.44583e-03 A 6=-4.89279e-02 A 8=-1.40782e-01 A10 = 6.24752e-02 Page 8 K = 0.00000e+00 A 4= 4.47776e-01 A 6=-3.60718e-01 A 8= 2.29893e-01 A10 = -2.68004e-02 Page 9 K = 0.00000e+00 A 4= 1.48357e-01 A 6=-7.27908e-02 A 8= 2.54562e-02 A10 = 1.53782e-02 Page 10 K = 0.00000e+00 A 4=-2.18130e-01 A 6= 6.23217e-02 A 8=-6.71843e-02 A10= 1.38505e-02 A12= 2.06156e-03 Page 11 K = 0.00000e+00 A 4=-9.22420e-02 A 6= 3.13727e-02 A 8=-4.12448e-02 A10= 2.05818e-02 A12=-3.04928e-03 Page 12 K = 0.00000e+00 A 4= 3.90588e-02 A 6=-1.61074e-02 A 8= 7.22856e-03 Page 13 K = 0.00000e+00 A 4=-2.57105e-02 A 6= 1.63764e-03 A 8=-1.04485e-04 Various data Focal length 3.322 F-number 1.798 Half-angle (°): 46.736 Image height 3.530 Lens length: 4.345 skd(inair) 0.967 Entrance pupil position 0.406 Exit pupil position -1.786 Front principal point position -0.807 Back principal point position -2.675 Single lens data Lens starting plane, focal length 1 1 4.184 2 4 -6.664 3 6 3.888 4 8 207.272 5 10 4.974 6 12 -2.441 [Numerical Example 2] Unit: mm Surface data Face number rd nd νd Effective diameter 1* 2.7815 0.321 1.53500 55.73 1.52 2* 10.7662 0.095 1.52 3 (aperture) ∞ 0.141 1.48 4* 1.8256 0.150 1.67070 19.30 1.42 5* 1.6388 0.080 1.49 6* 5.3353 0.422 1.53500 55.73 1.61 7* -2.4970 0.180 1.83 8* -1.0432 0.209 1.67070 19.30 1.82 9* -3.3981 0.121 2.05 10* 1.5395 0.448 1.61550 25.80 2.92 11* -2.3821 0.421 3.65 12* -3.8540 0.416 1.67070 19.30 3.76 13* 2.6357 0.271 4.88 14 ∞ 0.150 1.56300 51.30 6.20 15 ∞ 0.500 6.20 Image plane ∞ Aspherical data Front page K = 0.00000e+00 A 4=-1.10520e-01 A 6=-1.54797e-02 A 8=-9.67059e-02 A10 = 3.11710e-02 2nd side K = 0.00000e+00 A 4=-1.96247e-01 Side 4 K = 0.00000e+00 A 4=-3.53892e-01 A 6= 6.75138e-02 5th page K = 0.00000e+00 A 4=-2.92276e-01 A 6= 3.39016e-02 Side 6 K = 0.00000e+00 A 4= 6.88524e-03 A 6=-1.33536e-02 A 8=-1.36976e-02 Side 7 K = 0.00000e+00 A 4=-1.67506e-03 A 6=-1.37711e-02 A 8= 5.94318e-02 Side 8 K = 0.00000e+00 A 4=-6.44818e-02 A 6= 5.55446e-01 A 8=-4.89780e-01 A10 = 3.95026e-01 9th page K = 0.00000e+00 A 4=-6.55469e-01 A 6= 8.53273e-01 A 8=-5.99959e-01 A10 = 2.35025e-01 Side 10 K = 0.00000e+00 A 4=-1.53816e-01 A 6= 1.75684e-01 A 8=-2.08703e-01 A10= 7.89850e-02 A12=-1.25776e-02 Page 11 K = 0.00000e+00 A 4= 7.29221e-01 A 6=-6.04810e-01 A 8= 2.35636e-01 A10=-4.53760e-02 A12= 3.40406e-03 Side 12 K = 0.00000e+00 A 4= 1.58466e-01 A 6=-2.14184e-01 A 8= 1.22155e-01 A10=-3.08379e-02 A12= 2.81198e-03 Page 13 K = 0.00000e+00 A 4=-1.06563e-01 A 6= 1.92478e-02 A 8=-1.74094e-03 Various data Focal length 2.718 F-number 1.798 Half-angle (°): 52.401 Image height 3.530 Lens length 3.925 skd(inair) 0.867 Entrance pupil position 0.322 Exit pupil position -1.848 Front principal point position -0.107 Back principal point position -2.218 Single lens data Lens starting plane, focal length 1 1 6.913 2 4 -35.244 3 6 3.240 4 8 -2.327 5 10 1.588 6 12 -2.275 [Numerical Example 3] Unit: mm Surface data Face number rd nd νd Effective diameter 1* 1.5570 0.264 1.53500 55.73 1.48 2* 6.8551 0.019 1.30 3 (aperture) ∞ 0.019 1.22 4* -7.9597 0.150 1.68040 18.10 1.17 5* 6.6916 0.094 1.02 6* 3.7356 0.471 1.53500 55.73 1.01 7* -4.7547 0.224 1.40 8* -4.4005 0.489 1.53500 55.73 1.60 9* -1.1384 0.050 2.01 10* 3.5594 0.213 1.53500 55.73 2.12 11* 1.7930 0.403 3.06 12* -1.8293 0.333 1.53500 55.73 3.21 13* 3.9086 0.303 4.27 14 ∞ 0.150 1.56300 51.30 6.20 15 ∞ 0.500 6.20 Image plane ∞ Aspherical data Front page K = 0.00000e+00 A 4=-1.34200e-01 A 6=-1.88171e-01 A 8=-3.36325e-01 A10 = 3.82815e-01 2nd side K = 0.00000e+00 A 4=-1.99344e-01 Page 4 K = 0.00000e+00 A 4= 1.40615e-01 Page 5 K = 0.00000e+00 A 4= 1.57500e-01 A 6=-1.43797e-01 Page 6 K = 0.00000e+00 A 4=-1.93695e-01 A 6= 6.99704e-02 A 8=-8.17960e-01 Page 7 K = 0.00000e+00 A 4=-2.00303e-01 A 6=-3.01398e-01 A 8=-5.83509e-02 A10 = -5.69628e-01 Page 8 K = 0.00000e+00 A 4= 9.61061e-03 A 6=-3.30501e-01 A 8= 2.49984e-01 A10 = -5.61774e-01 Page 9 K = 0.00000e+00 A 4= 1.25070e-01 A 6= 1.50515e-01 A 8=-1.83233e-01 A10 = 1.40005e-01 Page 10 K = 0.00000e+00 A 4=-4.82125e-01 A 6= 2.43761e-01 A 8=-4.34741e-01 A10= 2.90344e-01 A12=-3.66902e-02 Page 11 K = 0.00000e+00 A 4=-3.08245e-01 A 6= 9.27313e-02 A 8=-1.59675e-02 A10= 5.00974e-03 A12=-1.71245e-03 Page 12 K = 0.00000e+00 A 4= 8.44218e-02 Page 13 K = 0.00000e+00 A 4=-1.00078e-01 A 6= 2.99480e-02 A 8=-4.98787e-03 A10 = 3.26481e-04 Various data Focal length 3.025 F-number 2.785 Half-angle (°): 49.404 Image height 3.530 Lens length: 3.682 skd(inair) 0.899 Entrance pupil position 0.204 Exit pupil position -1.627 Front principal point position -1.073 Back principal point position -2.525 Single lens data Lens starting plane, focal length 1 1 3.701 2 4 -5.321 3 6 3.987 4 8 2.728 5 10 -7.050 6 12 -2.283 [Numerical Example 4] Unit: mm Surface data Face number rd nd νd Effective diameter 1* 1.2026 0.400 1.53500 55.73 1.92 2* 3.7886 0.100 1.69 3* 26.4153 0.200 1.68040 18.10 1.52 4* 2.6002 0.100 1.24 5* 1.8750 0.209 1.53500 55.73 1.02 6* -16.9570 0.000 0.85 7 (aperture) ∞ 0.150 0.85 8* -2.7130 0.200 1.68040 18.10 1.07 9* -2.0055 0.941 1.31 10* -1.4169 0.200 1.53500 55.73 2.36 11* 48.8756 0.150 3.50 12 ∞ 0.150 1.56300 51.30 6.20 13 ∞ 0.400 6.20 Image plane ∞ Aspherical data Front page K = 0.00000e+00 A 4=-9.46581e-02 A 6=-7.29938e-03 A 8=-3.68665e-01 A10 = 1.91235e-01 2nd side K = 0.00000e+00 A 4=-1.09360e-01 3rd page K = 0.00000e+00 A 4=-2.80556e-02 Side 4 K = 0.00000e+00 A 4=-2.71697e-02 A 6=-1.56441e-01 A 8=-6.41411e-01 A10 = 1.52047e+00 5th page K = 0.00000e+00 A 4= 1.52000e-01 Page 6 K = 0.00000e+00 A 4= 1.70206e-01 A 6= 7.44171e-02 A 8=-4.32500e-01 A10 = -3.29782e + 00 Side 8 K = 0.00000e+00 A 4= 1.19178e-01 A 6= 3.16565e-01 A 8=-5.79887e-01 A10=-8.64080e+00 A12= 1.08679e+01 9th page K = 0.00000e+00 A 4= 2.62555e-01 A 6=-3.68056e-01 A 8= 3.56426e+00 A10=-1.11272e+01 A12= 1.05768e+01 Side 10 K = 0.00000e+00 A 4=-2.62822e-01 A 6= 1.72009e-01 Page 11 K = 0.00000e+00 A 4=-1.38702e-01 A 6= 7.03018e-02 A 8=-1.95097e-02 A10 = 2.01158e-03 Various data Focal length 2.997 F-number 2.782 Half-angle (°): 49.671 Image height 3.530 Lens length 3.200 skd(inair) 0.646 Entrance pupil position 0.981 Exit pupil position -1.206 Front principal point position -1.612 Back principal point position -2.596 Single lens data Lens starting plane, focal length 1 1 3.125 2 3 -4.253 3 5 3.168 4 8 10.142 5 10 -2.570

[0063] [Table 1]

[0064] [Imaging device] Figure 9 shows a digital still camera as an imaging device using the optical systems of Examples 1 to 4. 20 is the camera body, and 21 is the imaging optical system composed of one of the optical systems from Examples 1 to 4. 22 is an image sensor, such as a CCD sensor or CMOS sensor, built into the camera body 20, which converts the subject image formed by the imaging optical system 21 into photoelectric data (images of the subject through the optical system). 23 is a memory that records image data generated from the signal from the image sensor 22. 24 is an electronic viewfinder composed of a display element such as a liquid crystal display panel, which displays image data and enables observation of the subject.

[0065] By using the optical systems of each embodiment in an imaging device, a compact imaging device with a shortened overall length can be provided.

[0066] The above embodiments include the following configuration.

[0067] (Composition 1) An optical system having multiple lenses arranged in order from the object side to the image side, Of the aforementioned multiple lenses, the lens closest to the image is a negative lens having an inflection point where the sign of the curvature of its lens surface changes. When the focal length of the optical system is f, the image height is ImgH, and the effective diameter of the image-side lens surface of the negative lens is EAR, 0.50 ≤ f / ImgH ≤ 0.95 0.40 ≤ EAR / ImgH / 2 ≤ 0.75 An optical system characterized by satisfying the following conditions. (Configuration 2) When TTL is the distance along the optical axis from the lens surface with the strongest refractive power on the object side to the image plane in the aforementioned optical system, 0.7 ≤ TTL / ImgH ≤ 1.3 The optical system according to configuration 1, characterized by satisfying the following conditions. (Composition 3) When skd is the air-equivalent value of the distance along the optical axis from the lens surface with the greatest refractive power on the image side to the image plane in the aforementioned optical system, 0 <skd / ImgH≦0.3 The optical system according to configuration 1 or 2, characterized by satisfying the following conditions. (Composition 4) The optical system has, in order from the object side, a first lens, a second lens, and a third lens, and when the focal length of the lens with the largest positive refractive power among the first, second, and third lenses is fP, 0.8 ≤ fP / f ≤ 1.5 An optical system according to any one of configurations 1 to 3, characterized by satisfying the following conditions. (Composition 5) The optical system has, in order from the object side, a first lens, a second lens, and a third lens, and when the combined focal length of the first, second, and third lenses is f13, 0.6 ≤ f13 / f ≤ 1.1 An optical system according to any one of configurations 1 to 4, characterized by satisfying the following conditions. (Composition 6) The negative lens is a biconcave lens, and when the focal length of the negative lens is fR, -1.1 ≤ fR / f ≤ -0.5 An optical system according to any one of configurations 1 to 5, characterized by satisfying the following conditions. (Composition 7) The object-side lens surface of the negative lens has a concave shape toward the object, and there is an air gap between the negative lens and the lens adjacent to it on the object side. When R1 is the radius of curvature of the object-side lens surface of the negative lens, and R2 is the radius of curvature of the image-side lens surface of the lens adjacent to the negative lens on the object side, -3.00 ≤ R1 / |R2| ≤ -0.05 An optical system according to any one of configurations 1 to 6, characterized by satisfying the following conditions. (Composition 8) When TR is the distance on the optical axis between the negative lens and the lens adjacent to it on the object side, 0.05 ≤ TR / EAR ≤ 0.40 An optical system according to any one of configurations 1 to 7, characterized by satisfying the following conditions. (Composition 9) The optical system according to any one of configurations 1 to 8, characterized in that the negative lens has the image-side lens surface having the inflection point. (Composition 10) When the maximum and minimum sag amounts of the image-side lens surface of the negative lens are denoted as sagmax and sagmin, respectively, -1.5 ≤ sagmax / sagmin < 0 An optical system according to any one of configurations 1 to 9, characterized by satisfying the following conditions. (Composition 11) When Tk is the distance along the optical axis from the image plane to the exit pupil of the optical system, -0.60 ≤ Tk / ImgH ≤ -0.20 An optical system according to any one of configurations 1 to 10, characterized by satisfying the following conditions. (Composition 12) The optical system has, in order from the object side, a first lens, a second lens, and a third lens. The optical system according to any one of configurations 1 to 11, characterized in that it has an aperture diaphragm positioned between any two of the first to third lenses or adjacent to the first lens on the object side. (Composition 13) The optical system according to any one of configurations 1 to 12, characterized by being composed of six lenses with positive-negative-positive-negative-positive refractive powers arranged in order from the object side to the image side. (Composition 14) The optical system according to any one of configurations 1 to 12, characterized by being composed of six lenses with positive-negative-positive-negative-positive refractive powers arranged in order from the object side to the image side. (Composition 15) The optical system according to any one of configurations 1 to 12, characterized by being composed of six lenses with positive, negative, positive, positive, negative refractive powers arranged in order from the object side to the image side. (Composition 16) The optical system according to any one of configurations 1 to 12, characterized by being composed of five lenses with positive, negative, positive, positive, negative refractive powers arranged in order from the object side to the image side. (Composition 17) An optical system having five or more lenses, Of the five or more lenses mentioned above, at least two are positive lenses. An optical system characterized in that the lens closest to the image among the five or more lenses is a negative lens having an inflection point where the sign of the curvature of its lens surface changes. (Composition 18) The optical system described in any one of configurations 1 to 17, An imaging device characterized by having an image sensor that captures an image of a subject through the optical system.

[0068] The embodiments described above are merely representative examples, and various modifications and changes can be made to each embodiment when implementing the present invention. [Explanation of symbols]

[0069] O optical axis SP aperture diaphragm IP image plane

Claims

1. An optical system having multiple lenses arranged in order from the object side to the image side, Of the aforementioned multiple lenses, the lens closest to the image is a negative lens having an inflection point where the sign of the curvature of its lens surface changes. When the focal length of the optical system is f, the image height is ImgH, and the effective diameter of the image-side lens surface of the negative lens is EAR, 0.50 ≤ f / ImgH ≤ 0.95 0.40≦EAR / ImgH / 2≦0.75 An optical system characterized by satisfying the following conditions.

2. When TTL is the distance along the optical axis from the lens surface with the greatest refractive power on the object side to the image plane in the aforementioned optical system, 0.7 ≤ TTL / ImgH ≤ 1.3 The optical system according to claim 1, characterized in that it satisfies the following conditions.

3. When skd is the air-equivalent value of the distance along the optical axis from the lens surface with the strongest refractive power on the image side to the image plane in the aforementioned optical system, 0<skd / ImgH≦0.3 The optical system according to claim 1, characterized in that it satisfies the following conditions.

4. The optical system has, in order from the object side, a first lens, a second lens, and a third lens, and when the focal length of the lens with the largest positive refractive power among the first, second, and third lenses is fP, 0.8 ≤ fP / f ≤ 1.5 The optical system according to claim 1, characterized in that it satisfies the following conditions.

5. The optical system has, in order from the object side, a first lens, a second lens, and a third lens, and when the combined focal length of the first, second, and third lenses is f13, 0.6 ≤ f13 / f ≤ 1.1 The optical system according to claim 1, characterized in that it satisfies the following conditions.

6. The negative lens is a biconcave lens, and when the focal length of the negative lens is fR, -1.1 ≤ fR / f ≤ -0.5 The optical system according to claim 1, characterized in that it satisfies the following conditions.

7. The object-side lens surface of the negative lens has a concave shape toward the object, and there is an air gap between the negative lens and the lens adjacent to it on the object side. When R1 is the radius of curvature of the object-side lens surface of the negative lens, and R2 is the radius of curvature of the image-side lens surface of the lens adjacent to the negative lens on the object side, -3.00≦R1 / |R2|≦-0.05 The optical system according to claim 1, characterized in that it satisfies the following conditions.

8. When TR is the distance on the optical axis between the negative lens and the lens adjacent to the negative lens on the object side, 0.05 ≤ TR / EAR ≤ 0.40 The optical system according to claim 1, characterized in that it satisfies the following conditions.

9. The optical system according to claim 1, characterized in that the negative lens has the inflection point on its image-side lens surface.

10. When the maximum and minimum sag amounts of the image-side lens surface of the negative lens are denoted as sagmax and sagmin, respectively, -1.5≦sagmax / sagmin<0 The optical system according to claim 1, characterized in that it satisfies the following conditions.

11. When Tk is the distance along the optical axis from the image plane to the exit pupil of the optical system, -0.60 ≤ Tk / ImgH ≤ -0.20 The optical system according to claim 1, characterized in that it satisfies the following conditions.

12. The optical system has, in order from the object side, a first lens, a second lens, and a third lens. The optical system according to claim 1, characterized in that it has an aperture diaphragm positioned between any two of the first to third lenses, at a position adjacent to the first lens on the object side or adjacent to the third lens on the image side.

13. The optical system according to claim 1, characterized in that it is composed of six lenses with positive, negative, positive, positive, positive, and negative refractive powers, arranged in order from the object side to the image side.

14. The optical system according to claim 1, characterized in that it is composed of six lenses with positive-negative-positive-negative-positive refractive powers arranged in order from the object side to the image side.

15. The optical system according to claim 1, characterized in that it is composed of six lenses with positive, negative, positive, positive, negative refractive powers arranged in order from the object side to the image side.

16. The optical system according to claim 1, characterized in that it is composed of five lenses with positive, negative, positive, positive, negative refractive powers arranged in order from the object side to the image side.

17. An optical system having five or more lenses, Of the five or more lenses mentioned above, at least two are positive lenses. An optical system characterized in that the lens closest to the image among the five or more lenses is a negative lens having an inflection point where the sign of the curvature of its lens surface changes.

18. An optical system according to any one of claims 1 to 17, An imaging device characterized by having an image sensor that captures an image of a subject through the optical system.

Images