Optical Department

Abstract

To provide an optical system that satisfies the demand for miniaturization while maintaining excellent optical characteristics. [Solution] The lens is composed of, in order from the object side to the image side, a first lens L1, a second lens L2 with positive refractive power, a third lens L3 with negative refractive power, a fourth lens L4 with negative refractive power, a fifth lens L5 with positive refractive power, a sixth lens L6 with positive refractive power, a seventh lens L7 with positive refractive power, and an eighth lens L8 with negative refractive power. The first lens L1 is a variable-focus lens, the third lens L3 has a concave surface on the image side in the paraxial direction, the fourth lens L4 has a concave surface on the object side in the paraxial direction, the fifth lens L5 has a convex surface on the image side in the paraxial direction, the seventh lens L7 has a convex surface on the image side in the paraxial direction, and the eighth lens L8 has a concave surface on the image side in the paraxial direction.

Description

Technical Field

[0001] The present invention relates to an optical system for forming an image of a subject on a solid-state imaging device such as a CCD sensor or a C-MOS sensor used in an imaging apparatus.

Background Art

[0002] In recent years, camera functions have been mounted on various products such as home appliances, information terminal devices, and automobiles. In particular, multiple cameras are mounted on automobiles, and the safety of automobiles and the convenience of drivers are improved. In the future, it is considered that various product developments that integrate camera functions will proceed. In addition, products are required to have high resolution performance while being small.

[0003] When focusing the lens in an optical system mounted on such a product, one or a plurality of lens focus groups are moved in the optical axis direction to focus from infinity to the shortest shooting distance. At this time, it is necessary to secure a moving space in the optical axis direction of the lens focus group, and the shorter the shortest shooting distance, the larger the moving amount of the focus group and the larger the size.

[0004] As an optical system aiming at conventional high performance, for example, an optical system as described in Patent Document 1 below is known.

[0005] Patent Document 1 discloses an optical system including a first lens group, an aperture, and a second lens group arranged in order from the object side, and among them, the second lens group includes at least one aspherical lens or two cemented lenses, and an optical system using any one of the configurations of two cemented lenses, one aspherical lens and one cemented lens, and one aspherical lens and two lenses is disclosed.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

[0007] When attempting to miniaturize the lens using the lens configuration described in Patent Document 1, correcting aberrations in the peripheral areas becomes extremely difficult, making it impossible to obtain good optical performance.

[0008] This invention has been made in view of the above-mentioned problems, and aims to provide an optical system that satisfies the demand for miniaturization in a balanced manner while possessing high resolution with well-corrected aberrations.

[0009] Furthermore, in relation to the terminology used in this invention, the convex, concave, and planar surfaces of a lens are defined as referring to the paraxial shape. In this specification, refractive power refers to the paraxial refractive power unless otherwise specified. Optical length is defined as the distance along the optical axis from the object-side surface of the optical element located closest to the object to the image sensor. The optical length and back focus are distances obtained by converting the thickness of the IR cut filter, cover glass, etc., placed between the optical system and the image sensor into air equivalent distances. [Means for solving the problem]

[0010] The optical system according to the present invention comprises a first lens, a second lens having positive refractive power, a third lens having negative refractive power, a fourth lens having negative refractive power, a fifth lens having positive refractive power, a sixth lens having positive refractive power, a seventh lens having positive refractive power, and an eighth lens having negative refractive power, all arranged in order from the object side to the image side. The first lens is a variable-focus lens, the third lens has a concave surface on the image side in the paraxial direction, the fourth lens has a concave surface on the object side in the paraxial direction, the fifth lens has a convex surface on the image side in the paraxial direction, the seventh lens has a convex surface on the image side in the paraxial direction, and the eighth lens has a concave surface on the image side in the paraxial direction.

[0011] The first lens is a variable-focus lens to suppress astigmatism, field curvature, and distortion.

[0012] The second lens, possessing positive refractive power, effectively corrects spherical aberration, coma aberration, astigmatism, field curvature, and distortion.

[0013] The third lens has negative refractive power and, by making the image side concave in the paraxial direction, effectively corrects chromatic aberration, coma aberration, astigmatism, field curvature, and distortion.

[0014] The fourth lens has negative refractive power and, by making the object side concave in the paraxial direction, effectively corrects chromatic aberration, astigmatism, field curvature, and distortion.

[0015] The fifth lens has positive refractive power and, by making the image side convex in the paraxial direction, effectively corrects spherical aberration, coma aberration, astigmatism, field curvature, and distortion.

[0016] The sixth lens, possessing positive refractive power, effectively corrects spherical aberration, astigmatism, field curvature, and distortion.

[0017] The seventh lens has positive refractive power and, by making the image side convex in the paraxial direction, effectively corrects spherical aberration, coma aberration, astigmatism, field curvature, and distortion.

[0018] The eighth lens possesses negative refractive power and, by having a concave surface on the image side in the paraxial direction, effectively corrects chromatic aberration, astigmatism, field curvature, and distortion. Furthermore, by having a concave surface on the image side in the paraxial direction, back focus is ensured while maintaining a compact size.

[0019] By adopting the above-described configuration, the optical system of the present invention achieves high resolution with good correction of various aberrations while miniaturizing the device.

[0020] Furthermore, it is desirable that the optical system of the above configuration satisfies the following condition (1). (1) 1.0 < νd6 / (νd7 + νd8) < 1.9 Here, νd6 is the Abbe number of the 6th lens with respect to the d-line, νd7 is the Abbe number of the 7th lens with respect to the d-line, and νd8 is the Abbe number of the 8th lens with respect to the d-line.

[0021] By satisfying the range of the conditional expression (1), good correction of chromatic aberration becomes possible.

[0022] Moreover, it is desirable that the optical system with the above configuration satisfies the following conditional expression (2). (2) 2.5 < (T2 / f2) × 100 < 11.0 Here, T2 is the thickness on the optical axis of the 2nd lens, and f2 is the focal length of the 2nd lens.

[0023] By satisfying the range of the conditional expression (2), miniaturization can be achieved, and good correction of spherical aberration, coma aberration, astigmatism, field curvature, and distortion aberration becomes possible.

[0024] Moreover, it is desirable that the optical system with the above configuration satisfies the following conditional expression (3). (3) 0.25 < f7 / f < 0.95 Here, f7 is the focal length of the 7th lens, and f is the focal length of the entire optical system.

[0025] By satisfying the range of the conditional expression (3), good correction of spherical aberration, coma aberration, astigmatism, field curvature, and distortion aberration becomes possible.

[0026] Moreover, it is desirable that the optical system with the above configuration satisfies the following conditional expression (4). (4) 0.25 < r5 / f < 0.85 Here, r5 is the paraxial curvature radius of the object side surface of the 3rd lens, and f is the focal length of the entire optical system.

[0027] By satisfying the range of the conditional expression (4), good correction of field curvature and distortion aberration becomes possible.

[0028] Furthermore, it is desirable that the optical system of the above configuration satisfies the following condition (5). (5)-0.65 <r10 / f<-0.15 However, r10 is the paraxial radius of curvature of the image-side surface of the fifth lens, and f is the focal length of the entire optical system.

[0029] By satisfying the range of condition (5), good correction of spherical aberration, coma aberration, astigmatism, field curvature, and distortion becomes possible.

[0030] Furthermore, it is desirable that the optical system of the above configuration satisfies the following condition (6). (6)-1.00 <r10 / f5<-0.25 However, r10 is the paraxial radius of curvature of the image-side surface of the fifth lens, and f5 is the focal length of the fifth lens.

[0031] By satisfying the range of condition (6), good correction of spherical aberration, coma aberration, astigmatism, field curvature, and distortion becomes possible.

[0032] Furthermore, it is desirable that the optical system of the above configuration satisfies the following condition (7). (7)-31<(T3 / f3)×100<-6 However, T3 is the thickness of the third lens along its optical axis, and f3 is the focal length of the third lens.

[0033] By satisfying the range of condition (7), the camera's profile can be reduced, and good correction of chromatic aberration, coma aberration, astigmatism, field curvature, and distortion becomes possible.

[0034] Furthermore, it is desirable that the optical system of the above configuration satisfies the following condition (8). (8) 0.3 <f2 / f<1.3 However, f2 is the focal length of the second lens, and f is the focal length of the entire optical system.

[0035] By satisfying the range of condition (8), good correction of spherical aberration, coma aberration, astigmatism, field curvature, and distortion becomes possible.

[0036] Furthermore, it is desirable that the optical system of the above configuration satisfies the following condition (9). (9)-2.30 <f3 / f<-0.45 However, f3 is the focal length of the third lens, and f is the focal length of the entire optical system.

[0037] By satisfying the range of condition (9), good correction of chromatic aberration, coma aberration, astigmatism, field curvature, and distortion becomes possible.

[0038] Furthermore, it is desirable that the optical system of the above configuration satisfies the following condition (10). (10)-0.7 <f4 / f<-0.2 However, f4 is the focal length of the fourth lens, and f is the focal length of the entire optical system.

[0039] By satisfying the range of condition (10), good correction of chromatic aberration, astigmatism, field curvature, and distortion becomes possible.

[0040] Furthermore, it is desirable that the optical system of the above configuration satisfies the following condition (11). (11) 0.25 <f5 / f<1.10 However, f5 is the focal length of the fifth lens, and f is the focal length of the entire optical system.

[0041] By satisfying the range of condition (11), good correction of spherical aberration, coma aberration, astigmatism, field curvature, and distortion becomes possible.

[0042] Furthermore, it is desirable that the optical system of the above configuration satisfies the following condition (12). (12)-1.7 <f7 / f8<-0.5 However, f7 is the focal length of the 7th lens, and f8 is the focal length of the 8th lens.

[0043] By satisfying the range of condition (12), good correction of chromatic aberration, spherical aberration, coma aberration, astigmatism, field curvature, and distortion becomes possible.

[0044] Furthermore, it is desirable that the optical system of the above configuration satisfies the following condition (13). (13) 1.0 <f7 / T7<4.5 However, f7 is the focal length of the seventh lens, and T7 is the thickness of the seventh lens along its optical axis.

[0045] By satisfying the range of condition (13), it becomes possible to reduce the profile while also enabling good correction of spherical aberration, coma aberration, astigmatism, field curvature, and distortion.

[0046] Furthermore, it is desirable that the optical system of the above configuration satisfies the following condition (14). (14)-0.85 <f8 / f<-0.25 However, f8 is the focal length of the eighth lens, and f is the focal length of the entire optical system.

[0047] By satisfying the range of condition (14), good correction of chromatic aberration, astigmatism, field curvature, and distortion becomes possible.

[0048] Furthermore, it is desirable that the optical system of the above configuration satisfies the following condition (15). (15) 0.20 <r3 / f<0.75 However, r3 is the paraxial radius of curvature of the object-side surface of the second lens, and f is the focal length of the entire optical system.

[0049] By satisfying the range of condition (15), good correction of coma aberration, astigmatism, field curvature, and distortion becomes possible.

[0050] Furthermore, it is desirable that the optical system of the above configuration satisfies the following condition (16). (16) 4.5 <r3 / T2<16.0 However, r3 is the paraxial radius of curvature of the object-side surface of the second lens, and T2 is the thickness of the second lens along its optical axis.

[0051] By satisfying the range of condition (16), it becomes possible to reduce the profile while also enabling good correction of coma aberration, astigmatism, field curvature, and distortion.

[0052] Furthermore, it is desirable that the optical system of the above configuration satisfies the following condition (17). (17)-10 <r4 / f<-1 However, r4 is the paraxial radius of curvature of the image-side surface of the second lens, and f is the focal length of the entire optical system.

[0053] By satisfying the range of condition (17), good correction of coma aberration, astigmatism, field curvature, and distortion becomes possible.

[0054] Furthermore, it is desirable that the optical system of the above configuration satisfies the following condition (18). (18)-12.5 <r4 / r16<-1.0 However, r4 is the paraxial radius of curvature of the image-side surface of the second lens, and r16 is the paraxial radius of curvature of the image-side surface of the eighth lens.

[0055] By satisfying the range of condition (18), good correction of coma aberration, astigmatism, field curvature, and distortion becomes possible.

[0056] Furthermore, it is desirable that the optical system of the above configuration satisfies the following condition (19). (19) 0.10 <r6 / f<0.45 However, r6 is the paraxial radius of curvature of the image-side surface of the third lens, and f is the focal length of the entire optical system.

[0057] By satisfying the range of condition (19), good correction of coma aberration, astigmatism, field curvature, and distortion becomes possible.

[0058] Furthermore, it is desirable that the optical system of the above configuration satisfies the following condition (20). (20)-1.25 <r6 / r7<-0.30 However, r6 is the paraxial radius of curvature of the image-side surface of the third lens, and r7 is the paraxial radius of curvature of the object-side surface of the fourth lens.

[0059] By satisfying the range of condition (20), good correction of coma aberration, astigmatism, field curvature, and distortion becomes possible.

[0060] Furthermore, it is desirable that the optical system of the above configuration satisfies the following condition (21). (21)-0.60 <r7 / f<-0.15 However, r7 is the paraxial radius of curvature of the object-side surface of the fourth lens, and f is the focal length of the entire optical system.

[0061] By satisfying the range of condition (21), good correction of astigmatism, field curvature, and distortion becomes possible.

[0062] Furthermore, it is desirable that the optical system of the above configuration satisfies the following condition (22). (22) 0.5 <r9 / f<5.5 However, r9 is the paraxial radius of curvature of the object-side surface of the fifth lens, and f is the focal length of the entire optical system.

[0063] By satisfying the range of condition (22), good correction of astigmatism and distortion becomes possible.

[0064] Furthermore, it is desirable that the optical system of the above configuration satisfies the following condition (23). (23)-6.5 <r10 / (D56+T6)<-1.0 However, r10 is the radius of paraxial curvature of the image-side surface of the fifth lens, D56 is the distance along the optical axis from the image-side surface of the fifth lens to the object-side surface of the sixth lens, and T6 is the thickness of the sixth lens along the optical axis.

[0065] By satisfying the range of condition (23), the profile can be reduced, and good correction of spherical aberration, coma aberration, astigmatism, field curvature, and distortion can be achieved.

[0066] Furthermore, it is desirable that the optical system of the above configuration satisfies the following condition (24). (24) 0.3 <r13 / f<1.3 However, r13 is the paraxial radius of curvature of the object-side surface of the seventh lens, and f is the focal length of the entire optical system.

[0067] By satisfying the range of condition (24), good correction of astigmatism, field curvature, and distortion becomes possible.

[0068] Furthermore, it is desirable that the optical system of the above configuration satisfies the following condition (25). (25)17 <r13 / D78<144 However, r13 is the paraxial radius of curvature of the object-side surface of the seventh lens, and D78 is the distance along the optical axis from the image-side surface of the seventh lens to the object-side surface of the eighth lens.

[0069] By satisfying the range of condition (25), the profile can be reduced, and good correction of astigmatism, field curvature, and distortion can be achieved.

[0070] Furthermore, it is desirable that the optical system of the above configuration satisfies the following condition (26). (26) 1.0 <r13 / (D45+T5+D56)<5.5 However, r13 is the radius of paraxial curvature of the object-side surface of the seventh lens, D45 is the distance along the optical axis from the image-side surface of the fourth lens to the object-side surface of the fifth lens, T5 is the thickness along the optical axis of the fifth lens, and D56 is the distance along the optical axis from the image-side surface of the fifth lens to the object-side surface of the sixth lens.

[0071] By satisfying the range of condition (26), the height can be reduced, and good correction of astigmatism, field curvature, and distortion becomes possible.

[0072] Furthermore, it is desirable that the optical system of the above configuration satisfies the following condition (27). (27)-1.3 <r14 / f<-0.3 However, r14 is the paraxial radius of curvature of the image-side surface of the seventh lens, and f is the focal length of the entire optical system.

[0073] By satisfying the range of condition (27), good correction of coma aberration, astigmatism, field curvature, and distortion becomes possible.

[0074] Furthermore, it is desirable that the optical system of the above configuration satisfies the following condition (28). (28) 0.35 <r16 / f<1.20 However, r16 is the paraxial radius of curvature of the image-side surface of the eighth lens, and f is the focal length of the entire optical system.

[0075] By satisfying the range of condition (28), good correction of astigmatism, field curvature, and distortion becomes possible.

[0076] The present invention provides a high-resolution optical system with well-corrected aberrations while simultaneously satisfying the demands for miniaturization in a balanced manner. Furthermore, because aberrations are well corrected in the optical system according to the present invention, the number of lenses can be reduced, thereby contributing to environmental protection by reducing the amount of lens material used. [Brief explanation of the drawing]

[0077] [Figure 1] This figure shows a schematic configuration of the optical system of Embodiment 1 of the present invention. [Figure 2] This figure shows the spherical aberration, astigmatism, and distortion of the optical system of Embodiment 1 of the present invention when the object distance OBJ is 74 mm. [Figure 3] This figure shows the spherical aberration, astigmatism, and distortion of the optical system of Embodiment 1 of the present invention when the object distance OBJ is 100 mm. [Figure 4] This figure shows the spherical aberration, astigmatism, and distortion of the optical system of Embodiment 1 of the present invention when the object distance OBJ is 42 mm. [Figure 5] This figure shows a schematic configuration of the optical system in Embodiment 2 of the present invention. [Figure 6] This figure shows the spherical aberration, astigmatism, and distortion of the optical system of Embodiment 2 of the present invention when the object distance OBJ is 170 mm. [Figure 7] This figure shows a schematic configuration of the optical system according to Embodiment 3 of the present invention. [Figure 8] This figure shows the spherical aberration, astigmatism, and distortion of the optical system of Embodiment 3 of the present invention when the object distance OBJ is 160 mm. [Figure 9] This is a cross-sectional view showing the schematic configuration of a variable-focus lens included in the lens configuration of the present invention. [Modes for carrying out the invention]

[0078] Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings.

[0079] Figures 1, 5, and 7 show the schematic configurations of the optical systems according to Examples 1 to 3 of this embodiment, respectively. The details of the optical system according to this embodiment will be described below with reference to Figure 1.

[0080] As shown in Figure 1, the optical system according to the present invention is composed of a first lens L1, a second lens L2 having positive refractive power, a third lens L3 having negative refractive power, a fourth lens L4 having negative refractive power, a fifth lens L5 having positive refractive power, a sixth lens L6 having positive refractive power, a seventh lens L7 having positive refractive power, and an eighth lens L8 having negative refractive power, all arranged in order from the object side to the image side. The first lens L1 is a variable-focus lens, the third lens L3 has a concave surface on the image side in the paraxial direction, the fourth lens L4 has a concave surface on the object side in the paraxial direction, the fifth lens L5 has a convex surface on the image side in the paraxial direction, the seventh lens L7 has a convex surface on the image side in the paraxial direction, and the eighth lens L8 has a concave surface on the image side in the paraxial direction.

[0081] Furthermore, an infrared cut filter (IR) and a cover glass (CG) are placed between the eighth lens (L8) and the image sensor (IMG). Note that these IR and cover glass components can be omitted.

[0082] The aperture diaphragm ST is positioned in front of the first lens L1 to facilitate the correction of various aberrations and to easily control the angle at which high-image-height light rays enter the image sensor. Note that the position of the aperture diaphragm ST is not limited to in front of the first lens L1. It can be positioned appropriately according to the specifications of the image sensor.

[0083] The first lens L1 is a variable-focus lens consisting of a film Me, a liquid polymer resin layer PL, and a glass substrate Gs. By making the first lens L1 a variable-focus lens, miniaturization is achieved while suppressing an increase in the diameter of the first lens L1, and astigmatism, field curvature, and distortion are suppressed.

[0084] Here, the variable focus lens will be explained with reference to Figure 9. As shown in Figure 9, the variable focus lens according to this embodiment consists of an actuator Act, the film Me, a liquid polymer resin layer PL, and a glass substrate Gs, arranged in order from the object side toward the imaging surface IMG side, on the surface of the film Me toward the imaging surface IMG side. The film Me changes its surface shape by applying a voltage to the actuator Act placed on its surface, thereby changing the focal length of the lens. The surface of the liquid polymer resin layer PL that is in contact with the glass substrate Gs (the surface toward the imaging surface IMG in this embodiment 1) is always kept flat, while the surface that is in contact with the film Me (the surface toward the object in this embodiment 1) changes its surface shape in accordance with the change in the shape of the film Me. By changing the shape of the surface that is in contact with the film Me, it plays a role in preventing gaps from forming between the film Me and the layer. The glass substrate Gs plays a role in supporting the structure of the variable focus lens.

[0085] Variable focus lenses allow for adjustment of the focal point without moving the lens itself, resulting in advantages such as miniaturization of the optical system, extremely fast focusing speed, and reduced power consumption during focusing. They also offer the advantage of minimal variation in the angle of view across the entire range from the shortest focusing distance to infinity.

[0086] Furthermore, the variable focus lens according to this embodiment is not limited to the configuration described above, and may also have a configuration in which the object side and the imaging surface IMG side are reversed, that is, a configuration in which the glass substrate Gs, the liquid polymer resin layer PL, and the film Me are arranged in order from the object side toward the imaging surface IMG side. The actuator Act is positioned on the imaging surface IMG side of the film Me.

[0087] The variable focus lens according to this embodiment is not limited to the configuration described above, and may be other liquid lenses, film lenses, or liquid crystal lenses.

[0088] The second lens, L2, has positive refractive power and a biconvex shape in the paraxial direction. As a result, coma aberration, astigmatism, field curvature, and distortion are well corrected.

[0089] The third lens, L3, has negative refractive power and a meniscus shape with a concave image side in the paraxial direction. As a result, chromatic aberration, coma aberration, astigmatism, field curvature, and distortion are well corrected.

[0090] The fourth lens, L4, has negative refractive power and a biconcave shape in the paraxial direction. As a result, chromatic aberration, astigmatism, field curvature, and distortion are well corrected.

[0091] The fifth lens, L5, has positive refractive power and a biconvex shape in the paraxial direction. As a result, spherical aberration, coma aberration, astigmatism, field curvature, and distortion are well corrected.

[0092] The sixth lens, L6, has positive refractive power and a meniscus shape with a convex image side in the paraxial direction. As a result, spherical aberration, astigmatism, field curvature, and distortion are well corrected.

[0093] Furthermore, the shape of the sixth lens L6 may be biconvex in the paraxial direction, as in Examples 2 and 3. In this case, the positive refractive power on both sides is advantageous for miniaturization.

[0094] The seventh lens, L7, has positive refractive power and a biconvex shape in the paraxial direction. As a result, spherical aberration, coma aberration, astigmatism, field curvature, and distortion are well corrected.

[0095] The eighth lens, L8, has negative refractive power and a biconcave shape in the paraxial direction. Therefore, chromatic aberration, astigmatism, field curvature, and distortion are effectively corrected. Furthermore, by making the image-side concave in the paraxial direction, back focus is ensured while maintaining a compact size.

[0096] In this embodiment, the optical system consists of a second lens L2, a third lens L3, a fourth lens L4, a fifth lens L5, a sixth lens L6, a seventh lens L7, and an eighth lens L8, each composed of a single lens. By using single lenses, it is possible to form aspherical surfaces on the object-side and image-side surfaces that are effective in correcting aberrations. In this embodiment, good correction of various aberrations is achieved by forming appropriate aspherical surfaces on each lens surface of the second lens L2, third lens L3, fourth lens L4, fifth lens L5, sixth lens L6, seventh lens L7, and eighth lens L8. Furthermore, since the number of steps can be reduced compared to using cemented lenses, manufacturing costs can be suppressed.

[0097] While it is preferable to form the lens surfaces of the second lens L2, third lens L3, fourth lens L4, fifth lens L5, sixth lens L6, seventh lens L7, and eighth lens L8 aspherical surfaces, spherical surfaces may be used depending on the required performance, as they are easier to manufacture.

[0098] The optical system in this embodiment achieves desirable effects by satisfying the following conditions (1) to (28). (1) 1.0 < νd6 / (νd7+νd8) < 1.9 (2) 2.5 < (T2 / f2) × 100 < 11.0 (3) 0.25 <f7 / f<0.95 (4) 0.25 <r5 / f<0.85 (5)-0.65 <r10 / f<-0.15 (6)-1.00 <r10 / f5<-0.25 (7)-31<(T3 / f3)×100<-6 (8) 0.3 <f2 / f<1.3 (9)-2.30 <f3 / f<-0.45 (10)-0.7 <f4 / f<-0.2 (11) 0.25 <f5 / f<1.10 (12)-1.7 <f7 / f8<-0.5 (13) 1.0 <f7 / T7<4.5 (14)-0.85 <f8 / f<-0.25 (15) 0.20 <r3 / f<0.75 (16) 4.5 <r3 / T2<16.0 (17)-10 <r4 / f<-1 (18)-12.5 <r4 / r16<-1.0 (19) 0.10 <r6 / f<0.45 (20)-1.25 <r6 / r7<-0.30 (21)-0.60 <r7 / f<-0.15 (22) 0.5 <r9 / f<5.5 (23)-6.5 <r10 / (D56+T6)<-1.0 (24) 0.3 <r13 / f<1.3 (25)17 <r13 / D78<144 (26) 1.0 <r13 / (D45+T5+D56)<5.5 (27)-1.3 <r14 / f<-0.3 (28) 0.35 <r16 / f<1.20 however, νd6: Abbe number for the d line of the 6th lens L6, νd7: Abbe number for the d line of lens L7, νd8: Abbe number for the d line of lens L8 (8th lens), T2: Thickness of the second lens L2 on the optical axis X, T3: Thickness of the third lens L3 on the optical axis X, T5: Thickness of the 5th lens L5 on the optical axis X, T6: Thickness of the 6th lens L6 on the optical axis X, T7: Thickness of the 7th lens L7 on the optical axis X, D45: Distance along the optical axis X from the image-side surface of the fourth lens L4 to the object-side surface of the fifth lens L5. D56: Distance along the optical axis X from the image-side surface of the 5th lens L5 to the object-side surface of the 6th lens L6. D78: The distance along the optical axis X from the image-side surface of the 7th lens L7 to the object-side surface of the 8th lens L8. f: focal length of the entire optical system, f2: Focal length of the second lens L2, f3: Focal length of the third lens L3, f4: Focal length of the 4th lens L4, f5: Focal length of the 5th lens L5, f7: Focal length of the 7th lens L7, f8: Focal length of the 8th lens L8, r3: Paraxial radius of curvature of the object-side surface of the second lens L2, r4: Paraxial radius of curvature of the image-side surface of the second lens L2, r5: The paraaxial radius of curvature of the object-side surface of the third lens L3. r6: Paraxial radius of curvature of the image-side surface of the third lens L3. r7: The paraaxial radius of curvature of the object-side surface of the fourth lens L4. r9: Paraxial radius of curvature of the object-side surface of the fifth lens L5. r10: The paraxial radius of curvature of the image-side surface of the fifth lens L5. r13: The paraaxial radius of curvature of the object-side surface of the seventh lens L7. r14: The paraxial radius of curvature of the image-side surface of the seventh lens L7. r16: The paraxial radius of curvature of the image-side surface of the 8th lens L8. It is not necessary to satisfy all of the above conditions; the effects corresponding to each condition can be obtained by satisfying each condition individually.

[0099] Furthermore, the optical system in this embodiment exhibits more favorable effects by satisfying the following conditions (1a) to (28a). (1a) 1.2 < νd6 / (νd7 + νd8) < 1.7 (2a) 4 < (T2 / f2) × 100 < 9 (3a) 0.4 <f7 / f<0.8 (4a) 0.35 <r5 / f<0.70 (5a)-0.50 <r10 / f<-0.25 (6a)-0.85 <r10 / f5<-0.35 (7a)-25.5<(T3 / f3)×100<-9.5 (8a) 0.5 <f2 / f<1.0 (9a)-1.90 <f3 / f<-0.65 (10a)-0.6 <f4 / f<-0.3 (11a) 0.45 <f5 / f<0.90 (12a)-1.40 <f7 / f8<-0.75 (13a) 1.65 <f7 / T7<3.50 (14a)-0.70 <f8 / f<-0.40 (15a) 0.3 <r3 / f<0.6 (16a)6.5 <r3 / T2<13.5 (17a)-8.0 <r4 / f<-1.7 (18a)-10 <r4 / r16<-2 (19a) 0.20 <r6 / f<0.35 (20a)-1.0 <r6 / r7<-0.5 (21a)-0.50 <r7 / f<-0.25 (22a) 1.0 <r9 / f<4.4 (23a)-5.5 <r10 / (D56+T6)<-2.0 (24a) 0.5 <r13 / f<1.0 (25a)25 <r13 / D78<120 (26a)2.0 <r13 / (D45+T5+D56)<4.5 (27a)-1.1 <r14 / f<-0.5 (28a) 0.5 <r16 / f<1.0 However, the signs of each conditional expression are the same as explained in the previous paragraph. Alternatively, only the lower limit or only the upper limit of each conditional expression (1a) to (28a) may be applied to the corresponding conditional expressions (1) to (28).

[0100] In this embodiment, the aspherical shape adopted for the aspherical surface of the lens is expressed by Equation 1, where Z is the axis in the direction of the optical axis, H is the height in the direction perpendicular to the optical axis, R is the radius of paraxial curvature, k is the conicity coefficient, and An is the nth aspherical coefficient.

[0101]

number

[0102] Next, examples of the optical system according to this embodiment are shown. In each example, f is the focal length of the entire optical system, Fno is the F number, ω is the half-angle of view, ih is the maximum image height, and TTL is the total optical length. i is the surface number counted from the object side, r is the radius of paraxial curvature, d is the distance between lens surfaces on the optical axis X (interplanar spacing), Nd is the refractive index of the d line (reference wavelength), and νd is the Abbe number for the d line. Aspherical surfaces are indicated by adding the sign * (asterisk) after the surface number i.

[0103] (Example 1)

[0104] Basic lens data is shown in Table 1 below.

[0105] [Table 1]

[0106] Table 2 shows the focal length (f) of the entire optical system and the values ​​of the paraxial radius of curvature (MeR) of surfaces 2 and 3 of the variable-focus lens for the object distance OBJ of Example 1 when it is 100 mm, 74 mm, and 42 mm. [Table 2]

[0107] The optical system of Example 1 satisfies conditions (1) to (28) as shown in Table 7.

[0108] Figures 2, 3, and 4 show the spherical aberration (mm), astigmatism (mm), and distortion (%) for each object distance OBJ of the optical system of Example 1. The spherical aberration diagram shows the amount of aberration for each wavelength of the F line (486 nm), d line (588 nm), and C line (656 nm). The astigmatism diagram shows the amount of d line aberration at the sagittal image plane S (solid line) and the amount of d line aberration at the tangential image plane T (dashed line), respectively (the same applies to Figures 6 and 8). As shown in Figures 2, 3, and 4, each aberration is well corrected at each object distance OBJ.

[0109] (Example 2)

[0110] Basic lens data is shown in Table 3 below.

[0111] [Table 3]

[0112] Table 4 shows the focal length (f) of the entire optical system and the values ​​of the paraxial radius of curvature (MeR) of surfaces 2 and 3 of the variable-focus lens for the object distance OBJ of Example 2 when it is 200 mm, 170 mm, and 51 mm. [Table 4]

[0113] The optical system of Example 2 satisfies conditions (1) to (28), as shown in Table 7.

[0114] Figure 6 shows the spherical aberration (mm), astigmatism (mm), and distortion (%) for the optical system of Example 2 when the object distance OBJ is 170 mm. As shown in Figure 6, each aberration is well corrected.

[0115] (Example 3)

[0116] Basic lens data is shown in Table 5 below.

[0117] [Table 5]

[0118] Table 6 shows the focal length (f) of the entire optical system and the values ​​of the paraxial radius of curvature (MeR) of surfaces 2 and 3 of the variable-focus lens for the object distance OBJ of Example 3 when it is 200 mm, 160 mm, and 51 mm. [Table 6]

[0119] The optical system of Example 3 satisfies conditions (1) to (28) as shown in Table 7.

[0120] Figure 8 shows the spherical aberration (mm), astigmatism (mm), and distortion (%) for the optical system of Example 3 when the object distance OBJ is 160 mm. As shown in Figure 8, each aberration is well corrected.

[0121] Table 7 shows the values ​​of conditional expressions (1) to (28) related to Examples 1 to 3.

[0122] [Table 7] [Industrial applicability]

[0123] When the optical system according to the present invention is applied to a product equipped with a camera function, it can contribute to miniaturizing the camera and improving its performance. [Explanation of Symbols]

[0124] X optical axis ST aperture diaphragm L1 First Lens L2 Second Lens L3 3rd lens L4 4th lens L5 5th lens L6 6th lens L7 7th lens L8 8th lens Me film PL liquid polymer resin layer Gs glass substrate IR filter CG cover glass IMG imaging plane Act Actuator

Claims

1. Arranged sequentially from the object side towards the image side, The first lens, A second lens having positive refractive power, A third lens having negative refractive power, A fourth lens having negative refractive power, A fifth lens having positive refractive power, A sixth lens having positive refractive power, A seventh lens having positive refractive power, It consists of an eighth lens having negative refractive power, The first lens is a variable-focus lens, The third lens has a concave surface on the image side in the paraxial direction. The fourth lens has a concave surface on the object side in the paraxial direction. The fifth lens has a convex surface on the image side in the paraxial direction. The seventh lens has a convex surface on the image side in the paraxial direction. The eighth lens is an optical system characterized in that the image side is concave in the paraxial direction.

2. The optical system according to claim 1, characterized in that it satisfies the following condition (1). (1) 1.0<νd6 / (νd7+νd8)<1.9 however, νd6: Abbe number for the d line of the sixth lens, νd7: Abbe number for the d line of the 7th lens, νd8: Abbe number for the d line of the 8th lens, Let's assume that.

3. The optical system according to claim 1, characterized in that it satisfies the following condition (2). (2) 2.5<(T2 / f2)×100<11.0 however, T2: Thickness of the second lens along the optical axis, f2: Focal length of the second lens, Let's assume that.

4. The optical system according to claim 1, characterized in that it satisfies the following condition (3). (3) 0.25<f7 / f<0.95 however, f7: Focal length of the 7th lens, f: Focal length of the entire optical system, Let's assume that.

5. The optical system according to claim 1, characterized in that it satisfies the following condition (4). (4) 0.25<r5 / f<0.85 however, r5: Paraxial radius of curvature of the object-side surface of the third lens. f: Focal length of the entire optical system, Let's assume that.

6. The optical system according to claim 1, characterized in that it satisfies the following condition (5). (5) -0.65<r10 / f<-0.15 however, r10: The paraxial radius of curvature of the image-side surface of the fifth lens. f: Focal length of the entire optical system, Let's assume that.

7. The optical system according to claim 1, characterized in that it satisfies the following condition (6). (6) -1.00<r10 / f5<-0.25 however, r10: The paraxial radius of curvature of the image-side surface of the fifth lens. f5: Focal length of the fifth lens, Let's assume that.

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