Optical system and imaging apparatus

Abstract

To ensure molding stability of lenses in an optical system that is small-sized and has a wide angle of view.SOLUTION: An optical system has a plurality of lenses including a first lens, a second lens, a third lens, a fourth lens, a fifth lens, and a sixth lens, which are arranged in order from an object side to an image side, and an aperture stop SP that is arranged between the first lens and the second lens. The radius of curvature of a surface on the image side of the second lens is defined as R2i, and the radius of curvature of a surface on the object side of the third lens is defined as R3o, wherein S23=(R2i+R3o) / (R2i-R3o). The focal length of the optical system is defined as f, and the focal length of the second lens is defined as f2. Conditions of -0.59≤S23<0.00 and 1.50≤f2 / f≤3.00 are satisfied.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an optical system suitable for an image pickup device or the like. [Background technology]

[0002] Imaging devices such as video cameras, digital still cameras, and smartphone cameras require wide-angle lenses that are small and have good optical performance. In general, in order to shorten the overall length of a wide-angle optical system, it is necessary to reduce the thickness of each lens and the distance between the lenses. However, as the optical system becomes smaller, the impact of manufacturing errors in the lenses located near the aperture on the optical performance increases, making it difficult to correct aberrations. In order to suppress decentering errors between adjacent lenses, there is a method of forming a tapered surface on the edge of each lens and fitting the tapered surfaces of these lenses together. However, when forming a tapered surface on the edge of a lens, if the adjacent lens surfaces are convex, the edge needs to have a constricted shape. As a result, the edge becomes locally thin, and molding stability decreases. Patent Document 1 discloses an optical system having a first lens with negative refractive power, a second lens with positive refractive power, an aperture stop, and a lens group with negative refractive power, arranged in order from the object side to the image side. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6913225 Summary of the Invention [Problem to be solved by the invention]

[0004] In the optical system disclosed in Patent Document 1, the curvature of the second lens and the third lens in particular near the aperture stop is likely to be small, causing the edges to become locally thin, reducing the molding stability of the lenses.

[0005] The present invention provides an optical system that is small and has a wide angle of view, while ensuring lens molding stability. [Means for solving the problem]

[0006] An optical system according to one aspect of the present invention has a plurality of lenses including a first lens, a second lens, a third lens, a fourth lens, a fifth lens, and a sixth lens arranged in this order from the object side to the image side, and an aperture stop arranged between the first lens and the second lens. The radius of curvature of the image side surface of the second lens is R2i, the radius of curvature of the object side surface of the third lens is R3o, and S23=(R2i+R3o) / (R2i-R3o). The focal length of the optical system is f, and the focal length of the second lens is f2. In this case, -0.59≦S23<0.00 1.50≦f2 / f≦3.00 The optical system according to the present invention is characterized in that it satisfies the following conditions: Note that an image pickup apparatus having the above optical system also constitutes another aspect of the present invention. Effect of the Invention

[0007] According to the present invention, it is possible to ensure the stability of lens formation in a compact, wide-angle optical system. [Brief description of the drawings]

[0008] [Figure 1] FIG. 4 is a cross-sectional view of the optical system of the first embodiment (Numerical Example 1). [Diagram 2] FIG. 13 is a longitudinal aberration diagram for Numerical Example 1. [Diagram 3] FIG. 11 is a cross-sectional view of an optical system according to a second embodiment (Numerical Example 2). [Figure 4] FIG. 11 is a longitudinal aberration diagram for Numerical Example 2. [Diagram 5] FIG. 11 is a cross-sectional view of an optical system according to a third embodiment (Numerical Example 3). [Figure 6] FIG. 11 is a longitudinal aberration diagram for Numerical Example 3. [Figure 7] FIG. 11 is a cross-sectional view of an optical system according to a fourth embodiment (Numerical Example 4). [Figure 8] FIG. 11 is a longitudinal aberration diagram for Numerical Example 4. [Figure 9]FIG. 13 is a cross-sectional view of an optical system according to a fifth embodiment (Numerical Example 5). [Figure 10] FIG. 11 is a longitudinal aberration diagram for Numerical Example 5. [Figure 11] FIG. 13 is a cross-sectional view of an optical system according to Example 6 (Numerical Example 6). [Figure 12] FIG. 11 is a longitudinal aberration diagram for Numerical Example 6. [Figure 13] FIG. 4 is a diagram showing the tapered shape of the edge of a lens. [Figure 14] FIG. 4 is a diagram showing the amount of lens sag. [Figure 15] FIG. 1 is a schematic diagram of an imaging device using the optical systems according to Examples 1 to 6. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, embodiments of the present invention will be described with reference to the drawings. First, prior to describing specific embodiments 1 to 6, matters common to the embodiments will be described.

[0010] The optical system of each embodiment is used in various imaging devices such as a digital still camera, a digital video camera, a surveillance camera, and a vehicle-mounted camera.

[0011] 1, 3, 5, 7, 9, and 11 respectively show the configuration of the optical system of Examples 1 to 6. In each figure, the left side is the object side and the right side is the image side. The optical system of each example has a plurality of lenses (six or more) including a first lens, a second lens, a third lens, a fourth lens, a fifth lens, and a sixth lens arranged from the object side to the image side. An aperture stop SP is arranged between the first lens and the second lens.

[0012] FL is an optical block that corresponds to an optical filter, a low-pass filter, an infrared cut filter, etc. IP is an image plane. The image plane IP is where the imaging surface (light receiving surface) of an image sensor, which is a photoelectric conversion element such as a CCD sensor or a CMOS sensor, or the film surface (photosensitive surface) of a silver halide film is located.

[0013] The conditions that the optical system of each embodiment must satisfy and that are preferably satisfied will be described below.

[0014] The radius of curvature of the image side surface of the second lens is R2i, the radius of curvature of the object side surface of the third lens is R3o, and S23=(R2i+R3o) / (R2i-R3o). The focal length of the optical system is f, and the focal length of the second lens is f2. In this case, -0.59≦S23<0.00 (1) 1.50≦f2 / f≦3.00 (2) The following conditions are satisfied.

[0015] The condition of formula (1) indicates an appropriate relationship between the shape of the image side surface of the second lens and the object side surface of the third lens. S23 is also called the shape factor of the air lens between the image side surface of the second lens and the object side surface of the third lens. If the radius of curvature of the image side surface of the second lens becomes small so that S23 falls below the lower limit of formula (1), the edge of the second lens is locally thinned by forming a tapered portion for fitting with the tapered portion of the third lens, which is not preferable. If S23 exceeds the upper limit of formula (1), the radius of curvature of the image side surface of the second lens becomes large, the refractive power becomes weak, and coma aberration occurs significantly and its correction becomes difficult, which is not preferable. By satisfying the condition of formula (1), it is possible to improve the molding stability of the lens arranged near the aperture stop SP (especially a lens having a tapered portion at the edge) and to achieve good correction of coma aberration at the same time.

[0016] The condition of formula (2) shows the appropriate relationship between the axial focal length f in the optical system and the focal length f2 of the second lens. When f2 / f is below the lower limit of formula (2), the refractive power of the second lens becomes strong. In this case, if the lens thickness of the second lens is maintained, the radius of curvature of the lens surface becomes small and the edge portion becomes thin, which is not preferable. When f2 / f is above the upper limit of formula (2), the refractive power of the second lens becomes weak, which results in large spherical aberration that is difficult to correct, which is not preferable.

[0017] By having the above configuration and satisfying the above conditions, it is possible to realize an optical system that is small and has a wide angle of view, yet has high optical performance and ensures lens molding stability.

[0018] It is preferable that the optical system of each embodiment satisfies at least one of the conditions of the following expressions (3) to (8).

[0019] Fig. 13 shows the taper angle θ of a lens. In each embodiment, the tapered portions TS formed on the edge portions E of at least two adjacent lenses are brought into contact (fitted) with each other to avoid relative decentering of these lenses. The edge portions E are the ends of the lenses that are outside the optically effective diameter (described later). The taper angle θ, which is the angle of the tapered portion TS, is the angle that the tapered portion TS makes with a plane perpendicular to the central axis (optical axis AXL) of the lens.

[0020] Fig. 14 shows the sag amount Sag of a lens. The sag amount Sag is the length in the optical axis direction from the apex of the lens surface (e.g., a point on the optical axis AXL) to the point (position) of the optical effective diameter Ea. The optical effective diameter is the radius of the area of ​​the lens surface through which light rays that contribute to image formation pass.

[0021] When the tapered portions provided on the edges of adjacent lenses are brought into contact with each other as described above, it is preferable that the taper angle of the tapered portion with respect to a plane perpendicular to the optical axis be θ, and that the condition of the following formula (3) be satisfied.

[0022] 0.00 <cosθ≦0.77 (3) The condition of formula (3) shows a preferable range of the taper angle θ. When θ is below the lower limit of formula (3), the taper angle θ is 90° or more. As a result, a wedge shape is required at the edge, which is undesirable because it reduces the molding stability of the lens. When θ is above the upper limit of formula (3), the fitting length at the taper portion becomes short, which makes the lens more likely to tilt relative to the plane perpendicular to the optical axis, which is undesirable.

[0023] Furthermore, when the distance on the optical axis between the second lens and the third lens is d23 and the distance in the optical axis direction between the positions of the optical effective diameters of the second lens and the third lens is dE23, it is preferable to satisfy the condition of the following formula (4).

[0024] 1.66≦dE23 / d23≦4.56 (4) The condition of formula (4) shows a preferable relationship between the distance d23 on the optical axis between the second lens and the third lens and the distance dE23 at the position of the optical effective diameter. If dE23 / d23 is below the lower limit of formula (4), the curvature of the second lens or the third lens becomes small, the refractive power becomes weak, and it becomes difficult to correct the spherical aberration, which is not preferable. If dE23 / d23 is above the upper limit of formula (4), the optical effective diameter becomes large relative to the distance on the optical axis between the second and third lenses. As a result, the thickness of the edge portion becomes large compared to the lens thickness within the optical effective diameter, and the lens thickness becomes thin, which is not preferable because it reduces the molding stability of the lens.

[0025] Furthermore, when the distance on the optical axis between the third lens and the fourth lens is d34 and the distance in the optical axis direction at the position of the optical effective diameter of each of the third lens and the fourth lens is dE34, it is preferable to satisfy the condition of the following formula (5).

[0026] 0.40≦dE34 / d34≦2.00 (5) The condition of formula (5) shows a preferable relationship between the distance d34 on the optical axis between the third lens and the fourth lens and the distance dE34 at the position of the optical effective diameter. If dE34 / d34 is below the lower limit of formula (5), the curvature of the third lens or the fourth lens becomes small, the refractive power becomes weak, and it becomes difficult to correct distortion aberration, which is not preferable. If dE34 / d34 is above the upper limit of formula (5), the optical effective diameter becomes large relative to the distance on the optical axis between the third and fourth lenses. As a result, the thickness of the edge portion becomes large compared to the lens thickness within the optical effective diameter, and the lens thickness becomes thin, which is not preferable because it reduces the molding stability of the lens.

[0027] Furthermore, when the maximum image height of the optical system is ImgH and the total length on the optical axis from the surface of the optical system closest to the object side to the image plane is TTL, it is preferable to satisfy the condition of the following formula (6).

[0028] 1.31≦TTL / ImgH≦2.20 (6) The condition of formula (6) shows a preferable relationship between the maximum image height ImgH and the total optical length TTL of the optical system. If TTL / ImgH is below the lower limit of formula (6), the total optical length for the maximum image height becomes short, which is undesirable because it makes it difficult to correct aberrations. If TTL / ImgH is above the upper limit of formula (6), the total optical length becomes too large for the maximum image height, which is undesirable for miniaturizing the optical system.

[0029] Furthermore, when the Abbe number based on the d-line of the positive lens Gp closest to the object among the multiple lenses in the optical system that is arranged on the image side of the aperture stop SP is νP_2, it is preferable to satisfy the condition of the following equation (7).

[0030] 35.0≦νP_2≦65.0 (7) The condition of formula (7) indicates a preferable range of the Abbe number vP_2 of the positive lens Gp. In order to satisfactorily correct the axial chromatic aberration, it is preferable to form the positive lens Gp using a low-dispersion material whose vP_2 satisfies the condition of formula (7).

[0031] Furthermore, when the optically effective diameter of the second lens is Ea2 and the sag amount of the image-side surface of the second lens is Sag2, it is preferable to satisfy the condition of the following formula (8).

[0032] -0.20≦Sag2 / Ea2<0.00 (8) Equation (8) shows a preferable relationship between the sag amount Sag2 of the second lens and the optical effective diameter Ea2. If Sag2 / Ea2 is below the lower limit of equation (8), the refractive power of the second lens becomes weak, which makes it difficult to correct spherical aberration, which is not preferable. If Sag2 / Ea2 is above the upper limit of equation (8), the image-side surface of the second lens becomes concave, which makes it difficult to correct spherical aberration and coma, which is not preferable.

[0033] It is more preferable to set the numerical ranges of the formulas (1) to (8) as follows:

[0034] -0.56≦S23≦-0.10 (1a) 1.55≦f2 / f≦2.80 (2a) 0.00 <cosθ≦0.64 (3a) 2.00≦dE23 / d23≦4.40 (4a) 0.42≦dE34 / d34≦1.95 (5a) 1.60≦TTL / ImgH≦2.15 (6a) 40.0≦νP_2≦60.0 (7a) -0.18≦Sag2 / Ea2≦-0.05 (8a) Moreover, it is more preferable to set the numerical ranges of the formulas (1) to (8) as follows:

[0035] -0.53≦S23≦-0.15 (1b) 1.60≦f2 / f≦2.40 (2b) 0.20≦cosθ≦0.50 (3b) 2.30≦dE23 / d23≦4.30 (4b) 0.44≦dE34 / d34≦1.90 (5b) 1.80≦TTL / ImgH≦2.10 (6b) 50.0≦νP_2≦58.0 (7b) -0.16≦Sag2 / Ea2≦-0.06 (8a) By satisfying at least one of the conditions of the formulas (3) to (8) in addition to the conditions of the above formulas (1) and (2), it becomes easier to realize an optical system that is small and has a wide angle of view, yet has high optical performance and ensures lens molding stability.

[0036] Furthermore, to make it easier to realize the above optical system, the multiple lenses of the optical system may include aspheric lenses that have no refractive power on the axis (center) (the curvature on the optical axis is infinite) but have refractive power off the axis (periphery).

[0037] The optical system of each embodiment may include an aspheric surface having an inflection point. The inflection point is a point where the sign of the refractive power of the lens changes. For example, it is preferable that at least one of the multiple lenses is a resin lens, and at least one of the object side surface and the image side surface of the resin lens is an aspheric surface. In particular, it is preferable that the object side surface of the final lens arranged closest to the image side among the multiple lenses is formed so that its center has a convex shape toward the object side and its periphery has a concave shape toward the object side, and that the image side surface of the final lens is formed so that its center has a concave shape toward the image side and its periphery has a convex shape toward the image side.

[0038] The optical systems of Examples 1 to 6 will now be described in detail.

[0039] [Examples 1 to 5] The optical systems of Examples 1 to 5 shown in Figs. 1, 3, 5, 7 and 9 are each composed of a first lens, an aperture stop SP, a second lens, a third lens, a fourth lens, a fifth lens and a sixth lens arranged in this order from the object side to the image side. The second lens corresponds to the positive lens Gp. The fifth and sixth lenses are resin lenses as aspheric lenses having aspheric surfaces with inflection points on the object side and the image side. Furthermore, the object side surface of the sixth lens, which is the final lens, has a central portion convex toward the object side and a peripheral portion concave toward the object side, and the image side surface has a central portion concave toward the image side and a peripheral portion convex toward the image side.

[0040] [Example 6] The optical system of Example 6 shown in FIG. 11 is composed of a first lens, an aperture stop SP, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, and a seventh lens arranged in order from the object side to the image side. The second lens corresponds to a positive lens Gp. The first lens is an aspheric lens having an aspheric surface with an inflection point on its object side, and the seventh lens is an aspheric lens having an aspheric surface with an inflection point on its object side and image side. Furthermore, the object side surface of the seventh lens, which is the final lens, has a central part convex toward the object side and a peripheral part concave toward the object side, and the image side surface has a central part concave toward the image side and a peripheral part convex toward the image side.

[0041] Numerical Examples 1 to 6 corresponding to Examples 1 to 6, respectively, are shown below. In each numerical example, surface number i indicates the order of the surface when counted from the object side. r is the radius of curvature (mm) of the i-th surface from the object side, d is the lens thickness or air space (mm) between the i-th and (i+1)-th surfaces, and nd is the refractive index at the d-line of the optical material between the i-th and (i+1)-th surfaces. νd is the Abbe number based on the d-line of the optical material between the i-th and (i+1)-th surfaces. The Abbe number νd based on the d-line is given by Nd, NF, and NC, respectively, when 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 are Nd, NF, and NC, respectively. νd=(Nd-1) / (NF-NC) It is expressed as:

[0042] In each numerical example, d, focal length [mm], F-number, and half angle of view [°] are all values ​​when the optical system is focused on an object at infinity. BF is back focus (mm). Back focus is the distance on the optical axis from the lens surface (final surface) closest to the image in the optical system to the paraxial image surface, expressed as an air-equivalent length. The total lens length is the distance on the optical axis from the lens surface (foreground) closest to the object in the optical system to the final surface plus the back focus, and corresponds to the total length TTL in the above formula (6).

[0043] An asterisk (*) next to a surface number indicates that the surface has an aspheric shape. The aspheric shape is expressed by the following formula, where X is the displacement from the apex of the surface in the optical axis direction, h is the height from the optical axis in a direction perpendicular to the optical axis, the light traveling direction is positive, R is the paraxial radius of curvature, K is the conic constant, and A4, A6, A8, A10, and A12 are aspheric coefficients.

[0044] 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 The conic constant and aspheric coefficient "e±XX" are expressed as "×10 ±XX " means.

[0045] The values ​​of formulas (1) to (8) in each numerical example are shown in Table 1.

[0046] 2, 4, 6, 8, 10, and 12 respectively show longitudinal aberrations (spherical aberration, astigmatism, distortion, and chromatic aberration) of the optical systems of Numerical Examples 1 to 6 when focused on an object at infinity. In the spherical aberration diagrams, Fno indicates the F-number, the solid line indicates the spherical aberration for the d-line (wavelength 587.6 nm), and the two-dot chain line indicates the spherical aberration for the g-line (wavelength 435.8 nm). The horizontal axis indicates the amount of defocus, which is −0.100 to +0.100 [mm]. In the astigmatism diagrams, the solid line S indicates the astigmatism (amount of field curvature) on the sagittal image surface, and the dashed line M indicates the astigmatism on the meridional image surface. The horizontal axis is the same as the spherical aberration.

[0047] The distortion diagram shows distortion at the d-line. The horizontal axis is -20.000 to +20.000%. The chromatic aberration diagram shows lateral chromatic aberration at the g-line. The horizontal axis is -0.020 to +0.020 mm. ω is the half angle of view (°). [Numerical example 1] Unit: mm Surface Data Surface number rd nd νd 1* 20.191 0.40 1.53500 56.0 2* 2.079 0.54 3 (Aperture) ∞ (Variable) 4* 15.407 0.64 1.53500 56.0 5* -3.228 (variable) 6∞0.11 7* 4.903 0.88 1.53500 56.0 8* -2.328 0.10 9* -1.441 0.40 1.67070 19.3 10* -2.844 0.10 11* 4.626 0.79 1.53500 56.0 12* -2.262 0.09 13* 1.433 0.50 1.67070 19.3 14* 0.845 (variable) 15 ∞ 0.50 1.51633 64.1 16 ∞ (variable) Image plane ∞ Aspheric Data Front page K = 9.90002e+01 A 4= 2.69929e-01 A 6=-2.62395e-01 A 8= 3.26642e-01 A10=-2.83439e-01 A12= 1.57972e-01 A14=-4.41437e-02 A16= 3.03934e-03 2nd side K = 3.57596e+00 A 4= 4.04469e-01 A 6=-2.95327e-01 A 8= 5.10817e-01 A10= 1.58440e+00 A12=-7.91944e+00 A14= 1.54251e+01 A16=-1.08170e+01 Side 4 K = 0.00000e+00 A 4=-4.42968e-02 A 6= 1.95834e-02 A 8=-1.55123e-01 A10=-5.40909e-02 5th page K = 0.00000e+00 A 4=-1.70883e-01 A 6= 7.37522e-02 A 8=-9.92577e-02 A10= 1.34773e-01 A12=-1.51087e-01 Side 7 K = 0.00000e+00 A 4=-1.20111e-01 A 6= 8.85577e-02 A 8=-3.04424e-02 A10= 2.91164e-02 A12=-1.16655e-02 Page 8 K = 0.00000e+00 A 4= 6.45329e-02 A 6=-2.48897e-01 A 8= 1.47799e-01 A10=-1.45545e-02 Page 9 K = 0.00000e+00 A 4= 3.26282e-01 A 6=-2.86700e-01 A 8= 1.66888e-01 A10=-4.42501e-02 A12= 3.79471e-03 Page 10 K = 0.00000e+00 A 4= 1.20327e-01 A 6=-2.60615e-02 A 8=-3.35844e-03 A10= 2.18625e-03 A12=-3.03343e-04 Page 11 K = 0.00000e+00 A 4= 5.11198e-02 A 6=-3.95871e-02 A 8= 9.72543e-03 A10=-1.66003e-03 Page 12 K = 0.00000e+00 A 4= 1.80852e-01 A 6=-5.21144e-02 A 8= 7.15455e-03 A10=-4.47579e-04 Page 13 K =-9.27669e-01 A 4=-1.83614e-01 A 6= 3.26856e-02 A 8=-4.27438e-03 A10 = 3.17448e-04 Page 14 K =-2.72910e+00 A 4=-9.91445e-02 A 6= 3.21312e-02 A 8=-7.34233e-03 A10= 1.04723e-03 A12=-8.68265e-05 A14= 3.16248e-06 Various data Focal length 2.30 F-number 2.50 Half angle of view (°) 55.12 Image height 3.30 Lens length 6.21 BF 0.41 [Numerical example 2] Unit: mm Surface Data Surface number rd nd νd 1* 17.515 0.40 1.53500 56.0 2* 1.678 0.47 3 (Aperture) ∞ (Variable) 4* 6.366 0.74 1.53500 56.0 5* -3.550 (variable) 6∞0.10 7* 4.399 0.81 1.53500 56.0 8* -2.323 0.10 9* -1.465 0.40 1.67070 19.3 10* -2.778 0.10 11* 5.525 0.75 1.53500 56.0 12* -2.000 0.09 13* 1.610 0.50 1.67070 19.3 14* 0.912 (variable) 15 ∞ 0.50 1.51633 64.1 16 ∞ (variable) Image plane ∞ Aspheric Data Front page K = 9.67841e+01 A 4= 3.34490e-01 A 6=-3.10866e-01 A 8= 3.59136e-01 A10=-3.18637e-01 A12= 1.93437e-01 A14=-6.23518e-02 A16= 5.52754e-03 2nd side K = 3.63450e+00 A 4= 4.35880e-01 A 6= 3.43973e-01 A 8=-1.19595e+00 A10= 1.36672e+00 A12=-2.92109e+00 A14= 1.80170e+01 A16=-2.08068e+01 Page 4 K = 0.00000e+00 A 4= 2.02238e-02 A 6=-8.72034e-02 A 8= 2.34233e-01 A10=-1.41787e-01 Page 5 K = 0.00000e+00 A 4=-2.40854e-01 A 6= 1.48514e-01 A 8=-1.08695e-02 A10=-1.78754e-01 A12= 1.46635e-01 Page 7 K = 0.00000e+00 A 4=-1.96604e-01 A 6= 1.24591e-01 A 8=-1.35871e-02 A10= 1.81806e-02 A12=-8.74667e-03 Page 8 K = 0.00000e+00 A 4= 2.94802e-02 A 6=-2.14856e-01 A 8= 1.31962e-01 A10 = 2.03303e-03 Page 9 K = 0.00000e+00 A 4= 2.86654e-01 A 6=-2.09965e-01 A 8= 1.07292e-01 A10=-2.07780e-02 A12=-8.14649e-04 Page 10 K = 0.00000e+00 A 4= 9.79067e-02 A 6= 1.30777e-03 A 8=-2.06164e-02 A10= 7.25192e-03 A12=-1.02729e-03 Page 11 K = 0.00000e+00 A 4= 2.95807e-02 A 6=-3.94769e-02 A 8= 8.36568e-03 A10=-1.32300e-03 Side 12 K = 0.00000e+00 A 4= 1.83636e-01 A 6=-5.50412e-02 A 8= 7.34860e-03 A10=-4.13531e-04 Page 13 K =-8.86595e-01 A 4=-1.90092e-01 A 6= 3.55751e-02 A 8=-5.23180e-03 A10= 4.05644e-04 Side 14 K =-2.92138e+00 A 4=-1.02409e-01 A 6= 3.44602e-02 A 8=-8.15530e-03 A10= 1.20272e-03 A12=-1.03365e-04 A14= 3.95304e-06 Various data Focal length 2.19 F-number 2.50 Half angle of view(°) 57.54 Image height 3.45 Lens length 6.10 BF 0.40 [Numerical example 3] Unit: mm Surface Data Surface number rd nd νd 1* 25.798 0.40 1.53500 56.0 2* 2.030 0.50 3 (Aperture) ∞ (Variable) 4* 11.821 0.67 1.53500 56.0 5* -3.019 (variable) 6 ∞ 0.06 7* 4.853 0.78 1.53500 56.0 8* -2.374 0.12 9* -1.429 0.40 1.67070 19.3 10* -2.800 0.10 11* 5.161 0.77 1.53500 56.0 12* -2.235 0.09 13* 1.446 0.50 1.67070 19.3 14* 0.851 (variable) 15 ∞ 0.50 1.51633 64.1 16 ∞ (variable) Image plane ∞ Aspheric Data Front page K = 9.89999e+01 A 4= 2.96570e-01 A 6=-2.74326e-01 A 8= 3.33396e-01 A10=-2.85924e-01 A12= 1.58728e-01 A14=-4.06374e-02 A16= 1.03894e-03 2nd side K = 4.51982e+00 A 4= 4.32042e-01 A 6=-2.20712e-01 A 8= 4.27436e-01 A10= 1.31593e+00 A12=-7.15287e+00 A14= 1.65575e+01 A16=-1.29020e+01 Side 4 K = 0.00000e+00 A 4=-4.43698e-02 A 6=-1.36464e-02 A 8=-5.31461e-02 A10=-2.55892e-01 5th page K = 0.00000e+00 A 4=-2.14168e-01 A 6= 9.47346e-02 A 8=-9.82462e-02 A10= 1.34655e-01 A12=-1.97190e-01 Side 7 K = 0.00000e+00 A 4=-1.40585e-01 A 6= 1.11879e-01 A 8=-1.44115e-02 A10= 2.91427e-02 A12=-1.83949e-02 Page 8 K = 0.00000e+00 A 4= 5.58113e-02 A 6=-2.51752e-01 A 8= 1.55751e-01 A10 = 3.81027e-05 Page 9 K = 0.00000e+00 A 4= 3.08237e-01 A 6=-2.87325e-01 A 8= 1.67972e-01 A10=-4.05462e-02 A12=-9.04188e-04 Page 10 K = 0.00000e+00 A 4= 1.20140e-01 A 6=-2.79746e-02 A 8=-3.54032e-03 A10= 2.08016e-03 A12=-3.56861e-04 Page 11 K = 0.00000e+00 A 4= 5.21962e-02 A 6=-4.07358e-02 A 8= 1.02293e-02 A10=-1.78847e-03 Page 12 K = 0.00000e+00 A 4= 1.83311e-01 A 6=-5.30339e-02 A 8= 7.26012e-03 A10=-4.55350e-04 Page 13 K =-8.93058e-01 A 4=-1.81266e-01 A 6= 3.26088e-02 A 8=-4.15078e-03 A10 = 2.76107e-04 Page 14 K =-2.74514e+00 A 4=-9.92078e-02 A 6= 3.22442e-02 A 8=-7.37018e-03 A10= 1.04751e-03 A12=-8.66091e-05 A14= 3.15905e-06 Various data Focal length 2.30 F-number 2.50 Half angle of view(°) 56.31 Image height 3.45 Lens length 6.11 BF 0.41 [Numerical example 4] Unit: mm Surface Data Surface number rd nd νd 1* 27.285 0.40 1.53500 56.0 2* 2.771 0.50 3 (Aperture) ∞ (Variable) 4* 32.282 0.71 1.53500 56.0 5* -2.637 (variable) 6 ∞ 0.06 7* 6.982 0.67 1.53500 56.0 8* -2.680 0.21 9* -1.297 0.40 1.67070 19.3 10* -2.288 0.11 11* 6.045 0.76 1.53500 56.0 12* -2.160 0.12 13* 1.508 0.50 1.67070 19.3 14* 0.861 (variable) 15 ∞ 0.50 1.51633 64.1 16 ∞ (variable) Image plane ∞ Aspheric Data Front page K = 9.90091e+01 A 4= 2.74957e-01 A 6=-2.13253e-01 A 8= 2.07576e-01 A10=-1.03873e-01 A12= 1.36720e-03 A14= 3.48376e-02 A16=-1.32523e-02 Page 2 K = 9.88411e+00 A 4= 4.21547e-01 A 6=-2.23705e-01 A 8=-4.50773e-01 A10= 4.44887e+00 A12=-1.24000e+01 A14= 1.87107e+01 A16=-1.13162e+01 Page 4 K = 0.00000e+00 A 4=-4.77872e-02 A 6=-2.69298e-01 A 8= 9.53964e-01 A10=-1.77358e+00 Page 5 K = 0.00000e+00 A 4=-3.41695e-01 A 6= 2.51110e-01 A 8=-2.35164e-01 A10= 2.89013e-01 A12=-3.02640e-01 Page 7 K = 0.00000e+00 A 4=-2.81367e-01 A 6= 1.55669e-01 A 8=-4.50000e-02 A10= 1.27961e-01 A12=-6.29497e-02 Page 8 K = 0.00000e+00 A 4=-1.78289e-02 A 6=-1.83697e-01 A 8= 2.24181e-02 A10 = 7.72461e-02 Page 9 K = 0.00000e+00 A 4= 3.46661e-01 A 6=-2.18654e-01 A 8= 1.40550e-03 A10= 9.53493e-02 A12=-2.71074e-02 Page 10 K = 0.00000e+00 A 4= 1.65416e-01 A 6=-3.93858e-02 A 8=-2.04161e-02 A10= 1.62875e-02 A12=-3.15256e-03 Page 11 K = 0.00000e+00 A 4= 5.82279e-02 A 6=-4.12553e-02 A 8= 1.07833e-02 A10=-1.84058e-03 Side 12 K = 0.00000e+00 A 4= 1.92018e-01 A 6=-5.31327e-02 A 8= 7.13338e-03 A10=-3.84994e-04 Page 13 K =-7.99601e-01 A 4=-1.68649e-01 A 6= 3.35701e-02 A 8=-4.98014e-03 A10= 3.13064e-04 Side 14 K =-2.86337e+00 A 4=-9.36456e-02 A 6= 3.11706e-02 A 8=-7.33434e-03 A10= 1.07299e-03 A12=-9.16239e-05 A14= 3.41945e-06 Various data Focal length 2.50 F-number 2.50 Half angle of view (°) 54.07 Image height 3.45 Lens length 6.13 BF 0.41 [Numerical example 5] Unit: mm Surface Data Surface number rd nd νd 1* -28.113 0.40 1.53500 56.0 2* 2.708 0.52 3 (Aperture) ∞ 0.05 4* 12.454 0.71 1.53500 56.0 5* -3.149 -0.01 6 ∞ 0.13 7* 4.994 0.90 1.53500 56.0 8* -2.490 0.11 9* -1.454 0.40 1.67070 19.3 10* -3.158 0.11 11* 4.751 0.80 1.53500 56.0 12* -2.288 0.10 13* 1.404 0.50 1.67070 19.3 14* 0.881 (variable) 15 ∞ 0.50 1.51633 64.1 16 ∞ (variable) Image plane ∞ Aspheric Data Front page K =-9.90000e+01 A 4= 2.44842e-01 A 6=-2.49793e-01 A 8= 3.07521e-01 A10=-2.70426e-01 A12= 1.45740e-01 A14=-4.17283e-02 A16= 4.62671e-03 2nd side K = 2.58517e+00 A 4= 3.77741e-01 A 6=-3.27268e-01 A 8= 6.17591e-01 A10= 9.02188e-01 A12=-5.88191e+00 A14= 9.63382e+00 A16=-5.23792e+00 Side 4 K = 0.00000e+00 A 4=-2.95271e-02 A 6=-4.40647e-02 A 8=-4.39331e-02 A10= 2.39323e-02 5th page K = 0.00000e+00 A 4=-1.72101e-01 A 6= 1.11261e-01 A 8=-5.04755e-02 A10=-1.24475e-01 A12= 1.26349e-01 Page 7 K = 0.00000e+00 A 4=-1.32679e-01 A 6= 1.07538e-01 A 8=-6.98770e-02 A10= 2.44056e-02 A12=-3.03499e-03 Page 8 K = 0.00000e+00 A 4= 7.10477e-02 A 6=-2.47000e-01 A 8= 1.41996e-01 A10=-3.23519e-02 Page 9 K = 0.00000e+00 A 4= 3.08539e-01 A 6=-2.73380e-01 A 8= 1.58813e-01 A10=-4.59732e-02 A12= 4.58404e-03 Page 10 K = 0.00000e+00 A 4= 9.49834e-02 A 6=-2.36609e-02 A 8=-6.77300e-04 A10= 2.35794e-03 A12=-5.37719e-04 Page 11 K = 0.00000e+00 A 4= 6.23075e-02 A 6=-4.25202e-02 A 8= 1.03858e-02 A10=-1.91516e-03 Page 12 K = 0.00000e+00 A 4= 1.87618e-01 A 6=-5.52500e-02 A 8= 7.35950e-03 A10=-4.29992e-04 Page 13 K =-9.08692e-01 A 4=-1.78329e-01 A 6= 3.14907e-02 A 8=-4.44126e-03 A10= 3.22297e-04 Page 14 K =-2.87538e+00 A 4=-9.73192e-02 A 6= 3.19685e-02 A 8=-7.30878e-03 A10= 1.04469e-03 A12=-8.75248e-05 A14= 3.21185e-06 Various data Focal length 2.30 F Number 1 1.80 Half angle of view(°) 54.72 Image height 3.25 Lens length 6.31 BF 0.41 [Numerical example 6] Unit: mm Surface Data Surface number rd nd νd 1* -3.391 0.40 1.53500 56.0 2* 4.467 0.74 3 (Aperture) ∞ 0.05 4* 5.190 0.62 1.53500 56.0 5* -3.124 -0.01 6 ∞ 0.13 7* 10.000 0.81 1.53500 56.0 8* -1.782 0.20 9* -1.173 0.40 1.67070 19.3 10* -1.712 0.11 11* -7.867 0.80 1.53500 56.0 12* -1.835 0.10 13* 142.205 0.40 1.63560 23.9 14* -3.618 0.10 15* 4.298 0.40 1.67070 19.3 16* 1.009 (variable) 17 ∞ 0.50 1.51633 64.1 18 ∞ (variable) Image plane ∞ Aspheric Data Front page K =-2.85341e+01 A 4= 3.03177e-01 A 6=-3.20876e-01 A 8= 2.97182e-01 A10=-1.96677e-01 A12= 8.52122e-02 A14=-2.12615e-02 A16= 2.22315e-03 2nd side K =-1.68364e+02 A 4= 6.83211e-01 A 6=-6.35808e-01 A 8= 5.15567e-01 A10= 6.79769e-01 A12=-2.63820e+00 A14= 3.72581e+00 A16=-1.96605e+00 Side 4 K = 0.00000e+00 A 4= 1.82483e-02 A 6=-2.87274e-01 A 8= 7.53900e-01 A10=-7.66303e-01 5th page K = 0.00000e+00 A 4= 4.98478e-02 A 6=-4.48516e-01 A 8= 7.17536e-01 A10=-2.20127e-01 A12=-8.46379e-02 Side 7 K = 0.00000e+00 A 4= 6.48390e-02 A 6=-3.19105e-01 A 8= 3.42700e-01 A10=2.71052e-02 A12=-8.43733e-02 Side 8 K = 0.00000e+00 A 4= 1.12560e-01 A 6=-2.11901e-01 A 8=-5.04672e-02 A10 = 1.29264e-01 Page 9 K = 0.00000e+00 A 4= 3.88130e-01 A 6=-2.80342e-01 A 8= 4.60709e-02 A10= 1.02443e-01 A12=-2.54533e-02 Page 10 K = 0.00000e+00 A 4= 2.16787e-01 A 6=-6.12781e-02 A 8= 2.03115e-03 A10= 4.08690e-03 A12=-9.45404e-04 Page 11 K = 0.00000e+00 A 4= 6.44323e-02 A 6=-6.02014e-02 A 8= 5.28765e-03 A10 = 5.71006e-05 Page 12 K = 0.00000e+00 A 4= 2.23087e-02 A 6=-7.59855e-03 A 8=-3.71058e-03 A10 = 3.10301e-03 Page 13 K =-6.46661e+23 A 4=-1.23483e-01 A 6= 4.31916e-02 A 8=-7.76464e-03 A10=-4.30659e-04 A12= 2.62888e-04 Page 14 K =-5.10184e+01 A 4=-2.22487e-02 A 6= 2.01134e-02 A 8=-8.72629e-03 A10= 1.51142e-03 A12=-1.09551e-04 Page 15 K = 1.04774e+00 A 4=-1.09534e-01 A 6= 2.12363e-02 A 8=-2.82349e-03 A10= 1.76150e-04 A12=-5.94746e-06 Page 16 K =-4.30910e+00 A 4=-8.63616e-02 A 6= 3.03324e-02 A 8=-7.21624e-03 A10= 1.01020e-03 A12=-7.75406e-05 A14= 2.52645e-06 Various data Zoom ratio 1.00 Focal length 2.30 F-number 2.50 Half angle of view(°) 56.31 Image height 3.45 Lens length 6.71 BF 0.41

[0048] [Table 1]

[0049] [Imaging device] 15 shows a digital still camera (imaging device) using the optical system of Examples 1 to 6 as an imaging optical system. In camera 10, 13 is a camera body, and 11 is an imaging optical system constituted by any of the optical systems of Examples 1 to 6. 12 is an imaging element such as a CCD sensor or a CMOS sensor that is built into camera body 13 and receives a subject image formed by imaging optical system 11 (captures the subject).

[0050] By using an imaging optical system configured with any one of the optical systems in the first to sixth embodiments, it is possible to realize a compact camera capable of obtaining images with a wide angle of view and good image quality.

[0051] The optical system of each embodiment can be applied to various imaging devices such as a digital video camera, a silver halide film camera, etc., and is not limited to the camera 10 shown in Fig. 15. The camera may be an integrated lens type or an interchangeable lens type, and may be a single-lens reflex camera or a mirrorless camera.

[0052] The above embodiment includes the following configurations.

[0053] (Configuration 1) An optical system having a plurality of lenses including a first lens, a second lens, a third lens, a fourth lens, a fifth lens, and a sixth lens arranged in order from an object side to an image side, and an aperture stop arranged between the first lens and the second lens, When the radius of curvature of the image-side surface of the second lens is R2i, the radius of curvature of the object-side surface of the third lens is R3o, S23=(R2i+R3o) / (R2i-R3o), the focal length of the optical system is f, and the focal length of the second lens is f2, -0.59≦S23<0.00 1.50≦f2 / f≦3.00 An optical system characterized by satisfying the following conditions.

[0054] (Configuration 2) In the case where the tapered portions provided on the edges of the adjacent lenses among the plurality of lenses are brought into contact with each other, the taper angle of the tapered portions with respect to a plane perpendicular to the optical axis is defined as θ, 0.00 <cosθ≦0.77 2. The optical system according to claim 1, wherein the following condition is satisfied: (Configuration 3) When the distance between the second lens and the third lens on the optical axis is d23, and the distance between the positions of the optical effective diameters of the second lens and the third lens in the optical axis direction is dE23, 1.66≦dE23 / d23≦4.56 3. The optical system according to configuration 1 or 2, which satisfies the following condition: (Configuration 4) When the distance between the third lens and the fourth lens on the optical axis is d34, and the distance between the positions of the optical effective diameters of the third lens and the fourth lens in the optical axis direction is dE34, 0.40≦dE34 / d34≦2.00 4. The optical system according to any one of configurations 1 to 3, wherein the following condition is satisfied: (Configuration 5) Let ImgH be the maximum image height of the optical system, and TTL be the total length on the optical axis from the surface of the optical system closest to the object to the image plane. 1.31≦TTL / ImgH≦2.20 5. The optical system according to any one of configurations 1 to 4, wherein the following condition is satisfied: (Configuration 6) When the Abbe number of the positive lens closest to the object among the lenses arranged on the image side of the aperture stop among the plurality of lenses is νP_2, the Abbe number based on the d-line of the positive lens is 35.0≦νP_2≦65.0 6. The optical system according to any one of configurations 1 to 5, wherein the following condition is satisfied: (Configuration 7) The optical system according to configuration 6, wherein the second lens is the positive lens. (Configuration 8) When the optical effective diameter of the second lens is Ea2 and the sag amount of the image side surface of the second lens is Sag2, -0.20≦Sag2 / Ea2<0.00 8. The optical system according to any one of configurations 1 to 7, wherein the following condition is satisfied: (Configuration 9) 9. The optical system described in any one of configurations 1 to 8, wherein at least one of the plurality of lenses is a plastic lens, and at least one of the object side surface and the image side surface of the plastic lens has an aspheric shape. (Configuration 10) a surface of a final lens arranged closest to the image side among the plurality of lenses on the object side has a central portion convex toward the object side and a peripheral portion concave toward the object side, 10. The optical system according to any one of configurations 1 to 9, wherein the image-side surface of the final lens has a central portion having a concave shape toward the image side and a peripheral portion having a convex shape toward the image side. (Configuration 11) The optical system described in any one of configurations 1 to 10, characterized in that the optical system comprises, arranged in order from the object side to the image side, the first lens, the aperture stop, the second lens, the third lens, the fourth lens, the fifth lens, and a sixth lens as a final lens. (Configuration 12) The optical system described in any one of configurations 1 to 10, characterized in that the optical system comprises, arranged in order from the object side to the image side, the first lens, the aperture stop, the second lens, the third lens, the fourth lens, the fifth lens, a sixth lens, and a seventh lens as a final lens. (Configuration 13) An optical system according to any one of configurations 1 to 12, and an image sensor for capturing an image of a subject via the optical system.

[0055] The embodiments described above are merely representative examples, and various modifications and alterations are possible for each embodiment when implementing the present invention. [Explanation of symbols]

[0056] SP aperture stop Gp positive lens IP image plane

Claims

1. An optical system having a plurality of lenses including a first lens, a second lens, a third lens, a fourth lens, a fifth lens, and a sixth lens arranged in order from an object side to an image side, and an aperture stop arranged between the first lens and the second lens, When the radius of curvature of the image side surface of the second lens is R2i, the radius of curvature of the object side surface of the third lens is R3o, S23=(R2i+R3o) / (R2i-R3o), the focal length of the optical system is f, and the focal length of the second lens is f2, −0.59≦S23<0.00 1.50≦f2 / f≦3.00 An optical system characterized by satisfying the following conditions.

2. In the case where the tapered portions provided on the edges of the adjacent lenses among the plurality of lenses are brought into contact with each other, the taper angle of the tapered portions with respect to a plane perpendicular to the optical axis is defined as θ, 0.00<cosθ≦0.77 2. The optical system according to claim 1, which satisfies the following condition:

3. When the distance between the second lens and the third lens on the optical axis is d23, and the distance between the positions of the optical effective diameters of the second lens and the third lens in the optical axis direction is dE23, 1.66≦dE23 / d23≦4.56 2. The optical system according to claim 1, which satisfies the following condition:

4. When the distance between the third lens and the fourth lens on the optical axis is d34, and the distance between the positions of the optical effective diameters of the third lens and the fourth lens in the optical axis direction is dE34, 0.40≦dE34 / d34≦2.00 2. The optical system according to claim 1, which satisfies the following condition:

5. Let ImgH be the maximum image height of the optical system, and TTL be the total length on the optical axis from the surface of the optical system closest to the object to the image plane. 1.31≦TTL / ImgH≦2.20 2. The optical system according to claim 1, which satisfies the following condition:

6. When the Abbe number based on the d-line of the positive lens closest to the object among the lenses arranged on the image side of the aperture stop in the plurality of lenses is νP_2, 35.0≦νP_2≦65.0 2. The optical system according to claim 1, which satisfies the following condition:

7. The optical system according to claim 6 , wherein the second lens is the positive lens.

8. When the optical effective diameter of the second lens is Ea2 and the sag amount of the image side surface of the second lens is Sag2, -0.20≦Sag2 / Ea2<0.00 2. The optical system according to claim 1, which satisfies the following condition:

9. 2. The optical system according to claim 1, wherein at least one of the plurality of lenses is a plastic lens, and at least one of an object side surface and an image side surface of the plastic lens has an aspheric shape.

10. a surface of a final lens arranged closest to the image side among the plurality of lenses on the object side has a central portion convex toward the object side and a peripheral portion concave toward the object side, 2. The optical system according to claim 1, wherein the image-side surface of the final lens has a central portion that is concave toward the image side and a peripheral portion that is convex toward the image side.

11. 2. The optical system according to claim 1, comprising, arranged in order from the object side to the image side, the first lens, the aperture stop, the second lens, the third lens, the fourth lens, the fifth lens, and a sixth lens as a final lens.

12. 2. The optical system according to claim 1, comprising, arranged in order from the object side to the image side, the first lens, the aperture stop, the second lens, the third lens, the fourth lens, the fifth lens, a sixth lens, and a seventh lens as the final lens.

13. An optical system according to any one of claims 1 to 12; and an image sensor for capturing an image of a subject via the optical system.

Images