Optical Department

Abstract

This provides an optical system that satisfies the requirements for small size and low F-number while possessing excellent optical characteristics. [Solution] The optical system consists of a first lens L1 with positive refractive power, a second lens L2 with negative refractive power, a third lens L3 with positive refractive power, a fourth lens L4 with positive refractive power, and a fifth lens L5 with positive refractive power, arranged in order from the object side to the image side. The first lens L1 has a meniscus shape with a convex surface on the object side in the paraxial direction, the second lens L2 has a convex surface on the object side in the paraxial direction, and the fifth lens L5 has a concave surface on the image side in the paraxial direction. The following condition is satisfied with the paraxial radius of curvature r10 of the image-side surface of the fifth lens L5 and the focal length f of the entire optical system. (1) 0.05

Description

Technical Field

[0001] The present invention relates to an optical system used in an imaging device and a projection display device.

Background Art

[0002] In recent years, camera functions have been installed in various products such as home appliances, information terminal devices, and automobiles. In particular, multiple cameras are installed in automobiles, improving both the safety and convenience of drivers. In addition, the development of VR / AR products is active. For example, AR (Augmented Reality) is provided via devices in the form of goggles, glasses, and head-mounted displays. An AR device overlays and displays virtual images on a transparent or translucent display having the characteristic of showing the actual scene being viewed. It is considered that various product developments integrating camera functions will continue in the future.

[0003] The optical systems installed in such products are required to have high resolution performance while being small and having a low F-number.

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

[0005] Patent Document 1 discloses an optical system composed of, in order from the object side, a first lens with a convex surface facing the object side, a second lens having a negative refractive power, a third lens, a fourth lens, and a fifth lens, configured such that the relationship between the Abbe number and refractive index of the lenses, the viewing angle of the lenses, and the relationship between the effective radius of the object-side surface of the first lens and the effective radius of the image-side surface of the fifth lens satisfy certain conditions.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

[0007] When attempting to miniaturize and reduce the F-number 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 requirements for miniaturization and low F-number in a balanced manner, while also 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. A pole is defined as a point on an aspherical surface other than on the optical axis where the tangent plane intersects the optical axis perpendicularly. The total 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 total 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 is composed of a first lens having positive refractive power, a second lens having negative refractive power, a third lens having positive refractive power, a fourth lens having positive refractive power, and a fifth lens having positive refractive power, arranged in order from the object side to the image side, wherein the first lens has a meniscus shape with a convex surface on the object side in the paraxial direction, the second lens has a convex surface on the object side in the paraxial direction, and the fifth lens has a concave surface on the image side in the paraxial direction.

[0011] The first lens has positive refractive power and a meniscus shape with a convex surface on the object side in the paraxial direction, thereby suppressing spherical aberration, coma aberration, astigmatism, field curvature, and distortion.

[0012] The second lens has negative refractive power and, by making the object side convex in the paraxial direction, effectively corrects chromatic aberration, coma aberration, astigmatism, field curvature, and distortion.

[0013] The third lens, possessing positive refractive power, effectively corrects spherical aberration, coma aberration, astigmatism, and distortion.

[0014] The fourth lens, possessing positive refractive power, effectively corrects spherical aberration, coma aberration, astigmatism, and distortion.

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

[0016] By adopting the above-described configuration, the optical system of the present invention achieves miniaturization while simultaneously achieving a low F-number of 2.6 or less.

[0017] Furthermore, in the optical system with the above configuration, it is desirable that the third lens has a convex surface on the object side in the paraxial direction.

[0018] By making the object-side surface of the third lens a convex surface in the paraxial direction, it becomes possible to effectively correct coma aberration, astigmatism, and distortion.

[0019] Furthermore, in the optical system with the above configuration, it is desirable that the third lens has a concave surface on the image side in the paraxial direction.

[0020] By making the image-side surface of the third lens concave in the paraxial direction, it becomes possible to effectively correct coma aberration, astigmatism, and distortion.

[0021] In the optical system with the above configuration, it is desirable that the fifth lens has a convex surface on the object side in the paraxial region.

[0022] By making the surface on the object side of the fifth lens convex in the paraxial region, it becomes possible to achieve good correction of coma aberration, astigmatism, field curvature, and distortion.

[0023] Also, it is desirable that the optical system with the above configuration satisfies the following conditional expression (1). (1) 0.05 < r10 / f < 0.25 Here, r10 is the paraxial curvature radius of the surface on the image side of the fifth lens, and f is the focal length of the entire optical system.

[0024] By satisfying the range of the conditional expression (1), it becomes possible to achieve good correction of coma aberration, astigmatism, field curvature, and distortion.

[0025] Also, it is desirable that the optical system with the above configuration satisfies the following conditional expression (2). (2) 0.05 < r2 / r1 / f < 0.30 Here, r2 is the paraxial curvature radius of the surface on the image side of the first lens, r1 is the paraxial curvature radius of the surface on the object side of the first lens, and f is the focal length of the entire optical system.

[0026] By satisfying the range of the conditional expression (2), it becomes possible to achieve good correction of spherical aberration, coma aberration, astigmatism, field curvature, and distortion.

[0027] Also, it is desirable that the optical system with the above configuration satisfies the following conditional expression (3). (3) 0.25 < r2 / r5 < 1.20 Here, r2 is the paraxial curvature radius of the surface on the image side of the first lens, and r5 is the paraxial curvature radius of the surface on the object side of the third lens.

[0028] By satisfying the range of the conditional expression (3), it becomes possible to achieve good correction of coma aberration, astigmatism, field curvature, and distortion.

[0029] Furthermore, it is desirable that the optical system of the above configuration satisfies the following condition (4). (4) 0.15 <r2 / f<1.10 However, r2 is the paraxial radius of curvature of the image-side surface of the first lens, and f is the focal length of the entire optical system.

[0030] By satisfying the range of condition (4), good correction of astigmatism, field curvature, and distortion becomes possible.

[0031] Furthermore, it is desirable that the optical system of the above configuration satisfies the following condition (5). (5) 175<|r7| / D45<507 However, r7 is the paraxial radius of curvature of the object-side surface of the fourth lens, and 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.

[0032] By satisfying the range of condition (5), it becomes possible to reduce the profile while also enabling good correction of coma aberration, astigmatism, and distortion aberration.

[0033] Furthermore, it is desirable that the optical system of the above configuration satisfies the following condition (6). (6) 0.05 <r9 / f<0.20 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.

[0034] By satisfying the range of condition (6), good correction of coma aberration, astigmatism, field curvature, and distortion becomes possible.

[0035] Furthermore, it is desirable that the optical system of the above configuration satisfies the following condition (7). (7) 0.50 <f5 / f<2.75 However, f5 is the focal length of the fifth lens, and f is the focal length of the entire optical system.

[0036] By satisfying the range of condition (7), good correction of coma aberration, astigmatism, and distortion becomes possible.

[0037] Furthermore, it is desirable that the optical system of the above configuration satisfies the following condition (8). (8) 11 < νd4 < 26 However, νd4 is the Abbe number for the d line of the fourth lens.

[0038] By satisfying the range of condition (8), good correction of chromatic aberration becomes possible.

[0039] Furthermore, it is desirable that the optical system of the above configuration satisfies the following condition (9). (9) 0.1 <r1 / f<0.6 However, r1 is the paraxial radius of curvature of the object-side surface of the first lens, and f is the focal length of the entire optical system.

[0040] By satisfying the range of condition (9), good correction of spherical aberration, coma aberration, astigmatism, field curvature, and distortion becomes possible.

[0041] Furthermore, it is desirable that the optical system of the above configuration satisfies the following condition (10). (10) 0.25 <r1 / r2<1.20 However, r1 is the paraxial radius of curvature of the object-side surface of the first lens, and r2 is the paraxial radius of curvature of the image-side surface of the first lens.

[0042] By satisfying the range of condition (10), good correction of spherical aberration, coma aberration, astigmatism, field curvature, and distortion becomes possible.

[0043] Furthermore, it is desirable that the optical system of the above configuration satisfies the following condition (11). (11) 0.04 <r2 / r1 / f1<0.25 However, r2 is the paraxial radius of curvature of the image-side surface of the first lens, r1 is the paraxial radius of curvature of the object-side surface of the first lens, and f1 is the focal length of the first lens.

[0044] By satisfying the range of condition (11), good correction of spherical aberration, coma aberration, astigmatism, field curvature, and distortion becomes possible.

[0045] Furthermore, it is desirable that the optical system of the above configuration satisfies the following condition (12). (12) 0.15 <r3 / f<0.70 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.

[0046] By satisfying the range of condition (12), good correction of coma aberration, field curvature, and distortion becomes possible.

[0047] Furthermore, it is desirable that the optical system of the above configuration satisfies the following condition (13). (13) 0.1 <r3 / |r7|<0.6 However, r3 is the paraxial radius of curvature of the object-side surface of the second lens, and r7 is the paraxial radius of curvature of the object-side surface of the fourth lens.

[0048] By satisfying the range of condition (13), good correction of coma aberration, field curvature, and distortion becomes possible.

[0049] Furthermore, it is desirable that the optical system of the above configuration satisfies the following condition (14). (14) 0.10 <r4 / f<0.45 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.

[0050] By satisfying the range of condition (14), good correction of astigmatism and distortion becomes possible.

[0051] Furthermore, it is desirable that the optical system of the above configuration satisfies the following condition (15). (15) 0.80 <r5 / r2<2.75 However, r5 is the paraxial radius of curvature of the object-side surface of the third lens, and r2 is the paraxial radius of curvature of the image-side surface of the first lens.

[0052] By satisfying the range of condition (15), good correction of coma aberration, astigmatism, field curvature, and distortion becomes possible.

[0053] Furthermore, it is desirable that the optical system of the above configuration satisfies the following condition (16). (16) 0.2 <r5 / |r7|<1.5 However, r5 is the paraxial radius of curvature of the object-side surface of the third lens, and r7 is the paraxial radius of curvature of the object-side surface of the fourth lens.

[0054] By satisfying the range of condition (16), good correction of coma aberration, astigmatism, and distortion becomes possible.

[0055] Furthermore, it is desirable that the optical system of the above configuration satisfies the following condition (17). (17) 1.15 <r6 / r2<25.00 However, r6 is the paraxial radius of curvature of the image-side surface of the third lens, and r2 is the paraxial radius of curvature of the image-side surface of the first lens.

[0056] By satisfying the range of condition (17), good correction of coma aberration, astigmatism, field curvature, and distortion becomes possible.

[0057] Furthermore, it is desirable that the optical system of the above configuration satisfies the following condition (18). (18) 0.5 < |r7| / f < 2.7 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.

[0058] By satisfying the range of condition (18), good correction of coma aberration, astigmatism, and distortion becomes possible.

[0059] Furthermore, it is desirable that the optical system of the above configuration satisfies the following condition (19). (19) 1.25 < |r7| / r3 < 7.50 However, r7 is the paraxial radius of curvature of the object-side surface of the fourth lens, and r3 is the paraxial radius of curvature of the object-side surface of the second lens.

[0060] By satisfying the range of condition (19), good correction of coma aberration, astigmatism, field curvature, and distortion becomes possible.

[0061] Furthermore, it is desirable that the optical system of the above configuration satisfies the following condition (20). (20) 0.85 < |r8| / f < 4.75 However, r8 is the paraxial radius of curvature of the image-side surface of the fourth lens, and f is the focal length of the entire optical system.

[0062] By satisfying the range of condition (20), good correction of coma aberration, astigmatism, and distortion becomes possible.

[0063] Furthermore, it is desirable that the optical system of the above configuration satisfies the following condition (21). (21) 4.5 < |r8| / r9 < 35.0 However, r8 is the paraxial radius of curvature of the image-side surface of the fourth lens, and r9 is the paraxial radius of curvature of the object-side surface of the fifth lens.

[0064] By satisfying the range of condition (21), good correction of coma aberration, astigmatism, field curvature, and distortion becomes possible.

[0065] Furthermore, it is desirable that the optical system of the above configuration satisfies the following condition (22). (22) 0.05 <r10 / r5<0.35 However, r10 is the paraxial radius of curvature of the image-side surface of the fifth lens, and r5 is the paraxial radius of curvature of the object-side surface of the third lens.

[0066] By satisfying the range of condition (22), good correction of coma aberration, astigmatism, field curvature, and distortion becomes possible.

[0067] Furthermore, it is desirable that the optical system of the above configuration satisfies the following condition (23). (23) 1.00 < (T3 / f3) × 100 < 4.55 However, T3 is the thickness of the third lens along its optical axis, and f3 is the focal length of the third lens.

[0068] By satisfying the range of condition (23), it becomes possible to reduce the profile while also achieving good correction of spherical aberration, coma aberration, astigmatism, and distortion.

[0069] Furthermore, it is desirable that the optical system of the above configuration satisfies the following condition (24). (24) 0.5 <f3 / f<5.0 However, f3 is the focal length of the third lens, and f is the focal length of the entire optical system.

[0070] By satisfying the range of condition (24), good correction of spherical aberration, coma aberration, astigmatism, and distortion becomes possible.

[0071] Furthermore, it is desirable that the optical system of the above configuration satisfies the following condition (25). (25) 0.05 <f3 / f1 / f<0.35 However, f3 is the focal length of the third lens, f1 is the focal length of the first lens, and f is the focal length of the entire optical system.

[0072] By satisfying the range of condition (25), good correction of spherical aberration, coma aberration, astigmatism, field curvature, and distortion becomes possible.

[0073] Furthermore, it is desirable that the optical system of the above configuration satisfies the following condition (26). (26) 0.4 <f1 / f5<1.7 However, f1 is the focal length of the first lens, and f5 is the focal length of the fifth lens.

[0074] By satisfying the range of condition (26), good correction of spherical aberration, coma aberration, astigmatism, field curvature, and distortion becomes possible.

[0075] Furthermore, it is desirable that the optical system of the above configuration satisfies the following condition (27). (27)-1.3 <f2 / f5<-0.3 However, f2 is the focal length of the second lens, and f5 is the focal length of the fifth lens.

[0076] By satisfying the range of condition (27), good correction of chromatic aberration, spherical aberration, coma aberration, astigmatism, field curvature, and distortion becomes possible. [Effects of the Invention]

[0077] The present invention provides a high-resolution optical system with well-corrected aberrations while maintaining a good balance between miniaturization and a low F-number. 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]

[0078] [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. [Figure 3] This figure shows a schematic configuration of the optical system in Embodiment 2 of the present invention. [Figure 4] This figure shows the spherical aberration, astigmatism, and distortion of the optical system of Embodiment 2 of the present invention. [Figure 5] This figure shows a schematic configuration of the optical system according to Embodiment 3 of the present invention. [Figure 6] This figure shows the spherical aberration, astigmatism, and distortion of the optical system of Embodiment 3 of the present invention. [Modes for carrying out the invention]

[0079] Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings.

[0080] Figures 1, 3, and 5 are diagrams showing 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.

[0081] As shown in Figure 1, the optical system according to the present invention is composed of a first lens L1 having positive refractive power, a second lens L2 having negative refractive power, a third lens L3 having positive refractive power, a fourth lens L4 having positive refractive power, and a fifth lens L5 having positive refractive power, arranged in order from the object side to the image side. The first lens L1 has a meniscus shape with a convex surface on the object side in the paraxial direction, the second lens L2 has a convex surface on the object side in the paraxial direction, and the fifth lens L5 has a concave surface on the image side in the paraxial direction.

[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 has positive refractive power and a meniscus shape with a convex surface on the object side in the paraxial direction. As a result, spherical aberration, coma aberration, astigmatism, field curvature, and distortion are suppressed.

[0084] The second lens, L2, has negative refractive power and a meniscus shape with a convex surface on the object side in the paraxial direction. As a result, chromatic aberration, coma aberration, astigmatism, field curvature, and distortion are well corrected.

[0085] The third lens, L3, has positive refractive power and a meniscus shape with a convex surface on the object side in the paraxial direction. As a result, spherical aberration, coma aberration, astigmatism, and distortion are well corrected.

[0086] The fourth lens, L4, has a meniscus shape with a concave surface on the object side in the paraxial direction. As a result, spherical aberration, coma aberration, astigmatism, and distortion are well corrected.

[0087] Furthermore, the shape of the fourth lens L4 may be a meniscus shape with a convex surface on the object side in the paraxial direction, as in Examples 2 and 3. In this case, it is advantageous for correcting coma aberration, astigmatism, and distortion.

[0088] The fifth lens, L5, has a meniscus shape with a concave image side in the paraxial direction. As a result, spherical aberration, coma aberration, astigmatism, field curvature, and distortion are well corrected.

[0089] The prism PR is positioned on the image side of an optical system consisting of five optical elements. The inclined surface of the prism PR functions as a reflective surface that bends the optical path at approximately a right angle. As shown in Figure 1, by adding the prism PR closest to the image side and employing a bent optical system that bends the optical path at approximately a right angle, it is possible to incorporate it into thinner devices. Furthermore, if a material with a high refractive index is used for the prism PR, the prism PR itself can be miniaturized, making it even easier to adapt to the thinning of devices. In addition, by making the reflective surface of the prism PR flat, the occurrence of asymmetric distortion and image field curvature can be suppressed. The bent optical system can also be constructed using mirrors or other means instead of the prism PR, and the configuration of the bent optical system is arbitrary as long as it bends the optical path at approximately a right angle.

[0090] It should be noted that the optical system according to the present invention is not limited to a configuration using a prism PR. Embodiment 3 shown in Figure 5 is an example of a configuration that does not include a prism PR.

[0091] In the embodiment 3 shown in Figure 5, an infrared cut filter or cover glass (IR) is placed between the fifth lens L5 and the imaging surface IMG (i.e., the imaging surface of the image sensor). This IR filter can be omitted.

[0092] In the optical system according to this embodiment, it is preferable that all of the first lens L1 to the fifth lens L5 are composed of single lenses. A configuration consisting only of single lenses allows for the extensive use of aspherical surfaces. In this embodiment, good correction of various aberrations is achieved by forming appropriate aspherical surfaces on the lens surfaces. Furthermore, since the number of manufacturing steps can be reduced compared to the case where cemented lenses are used, it is possible to manufacture the system at a low cost.

[0093] Furthermore, the lens material used is not limited to plastic. In this embodiment, the optical system employs a glass material for the first lens L1, thereby achieving an optical system with good temperature characteristics.

[0094] The optical system in this embodiment achieves desirable effects by satisfying the following conditions (1) to (27). (1) 0.05 <r10 / f<0.25 (2) 0.05 <r2 / r1 / f<0.30 (3) 0.25 <r2 / r5<1.20 (4) 0.15 <r2 / f<1.10 (5) 175<|r7| / D45<507 (6) 0.05 <r9 / f<0.20 (7) 0.50 <f5 / f<2.75 (8) 11 < νd4 < 26 (9) 0.1 <r1 / f<0.6 (10) 0.25 <r1 / r2<1.20 (11) 0.04 <r2 / r1 / f1<0.25 (12) 0.15 <r3 / f<0.70 (13) 0.1 <r3 / |r7|<0.6 (14) 0.10 <r4 / f<0.45 (15) 0.80 <r5 / r2<2.75 (16) 0.2 <r5 / |r7|<1.5 (17) 1.15 <r6 / r2<25.00 (18) 0.5 < |r7| / f < 2.7 (19) 1.25 < |r7| / r3 < 7.50 (20) 0.85 < |r8| / f < 4.75 (21) 4.5 < |r8| / r9 < 35.0 (22) 0.05 <r10 / r5<0.35 (23) 1.00 < (T3 / f3) × 100 < 4.55 (24) 0.5 <f3 / f<5.0 (25) 0.05 <f3 / f1 / f<0.35 (26) 0.4 <f1 / f5<1.7 (27)-1.3 <f2 / f5<-0.3 however, νd4: Abbe number for the d line of the fourth lens L4, T3: Thickness of the third lens L3 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. f: focal length of the entire optical system, f1: Focal length of the first lens L1, f2: Focal length of the second lens L2, f3: Focal length of the third lens L3, f5: Focal length of the 5th lens L5, r1: The paraaxial radius of curvature of the object-side surface of the first lens L1. r2: Paraxial radius of curvature of the image-side surface of the first lens L1, 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: Paraxial radius of curvature of the object-side surface of the third lens L3. r6: The 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. r8: The paraaxial radius of curvature of the image-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. 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.

[0095] Furthermore, the optical system in this embodiment exhibits more favorable effects by satisfying the following conditions (1a) to (27a). (1a) 0.09 <r10 / f<0.19 (2a) 0.10 <r2 / r1 / f<0.25 (3a) 0.45 <r2 / r5<1.00 (4a) 0.25 <r2 / f<0.90 (5a)200<|r7| / D45<420 (6a) 0.09 <r9 / f<0.17 (7a) 0.9 <f5 / f<2.3 (8a) 14 < νd4 < 22 (9a) 0.2 <r1 / f<0.5 (10a) 0.4 <r1 / r2<1.0 (11a) 0.07 <r2 / r1 / f1<0.20 (12a) 0.25 <r3 / f<0.55 (13a) 0.15 <r3 / |r7|<0.50 (14a) 0.15 <r4 / f<0.35 (15a) 1.0 <r5 / r2<2.2 (16a) 0.35 <r5 / |r7|<1.25 (17a) 1.75 <r6 / r2<20.5 (18a) 0.9 < |r7| / f < 2.3 (19a) 1.95 < |r7| / r3 < 6.20 (20a) 1.0 < |r8| / f < 3.9 (21a) 6.5 < |r8| / r9 < 29.0 (22a) 0.09 <r10 / r5<0.25 (23a) 1.75 < (T3 / f3) × 100 < 3.75 (24a)1.5 <f3 / f<4.0 (25a) 0.10 <f3 / f1 / f<0.29 (26a) 0.6 <f1 / f5<1.4 (27a)-1.0 <f2 / f5<-0.5 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 (27a) may be applied to the corresponding conditional expressions (1) to (27).

[0096] 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.

[0097]

number

[0098] 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 (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 an asterisk (*) after the surface number i.

[0099] (Example 1)

[0100] Basic lens data is shown in Table 1 below.

[0101] [Table 1]

[0102] The optical system of Example 1 achieves an F-number of 2.30. Furthermore, it satisfies conditions (1) through (27) as shown in Table 4.

[0103] Figure 2 shows the spherical aberration (mm), astigmatism (mm), and distortion (%) for the optical system of Example 1. The spherical aberration diagram shows the aberration amounts for each wavelength of the F line (486 nm), d line (588 nm), and C line (656 nm). The astigmatism diagram shows the aberration amount of the d line at the sagittal image plane S (solid line) and the aberration amount of the d line at the tangential image plane T (dashed line), respectively (the same applies to Figures 4 and 6). As shown in Figure 2, each aberration is well corrected.

[0104] (Example 2)

[0105] Basic lens data is shown in Table 2 below.

[0106] [Table 2]

[0107] The optical system of Example 2 achieves an F-number of 2.30. Furthermore, it satisfies conditions (1) through (27) as shown in Table 4.

[0108] Figure 4 shows the spherical aberration (mm), astigmatism (mm), and distortion (%) for the optical system of Example 2. As shown in Figure 4, each aberration is well corrected.

[0109] (Example 3)

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

[0111] [Table 3]

[0112] The optical system of Example 3 achieves an F-number of 2.40. Furthermore, it satisfies conditions (1) through (27) as shown in Table 4.

[0113] Figure 6 shows the spherical aberration (mm), astigmatism (mm), and distortion (%) for the optical system of Example 3. As shown in Figure 6, each aberration is well corrected.

[0114] Table 4 shows the values ​​of conditional expressions (1) to (27) related to Examples 1 to 3.

[0115] [Table 4] [Industrial applicability]

[0116] When the optical system according to the present invention is applied to a product equipped with a camera function, it contributes to miniaturization and a lower F-number of the camera, as well as improving its performance. [Explanation of symbols]

[0117] X optical axis ST aperture diaphragm L1 First Lens L2 Second Lens L3 3rd lens L4 4th lens L5 5th lens PR Prism IR filter IMG imaging plane

Claims

1. Arranged sequentially from the object side towards the image side, A first lens having positive refractive power, A second lens having negative refractive power, A third lens having positive refractive power, A fourth lens having positive refractive power, It consists of a fifth lens having positive refractive power, The first lens has a meniscus shape with a convex surface on the object side in the paraxial direction. The second lens has a convex surface on the object side in the paraxial direction. The fifth lens has a concave surface on the image side in the paraxial direction, An optical system characterized by satisfying the following condition (1). (1) 0.05 <r10 / f<0.25 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.

2. The optical system according to claim 1, characterized in that it satisfies the following condition (2). (2) 0.05<r2 / r1 / f<0.30 however, r2: Paraxial radius of curvature of the image-side surface of the first lens, r1: The paraaxial radius of curvature of the object-side surface of the first lens. f: Focal length of the entire optical system, Let's assume that.

3. The optical system according to claim 1, characterized in that it satisfies the following condition (3). (3) 0.25<r2 / r5<1.20 however, r2: Paraxial radius of curvature of the image-side surface of the first lens, r5: Paraxial radius of curvature of the object-side surface of the third lens. Let's assume that.

4. The optical system according to claim 1, characterized in that it satisfies the following condition (4). (4) 0.15<r2 / f<1.10 however, r2: Paraxial radius of curvature of the image-side surface of the first 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 (5). (5) 175<|r7| / D45<507 however, r7: The paraaxial radius of curvature of the object-side surface of the fourth lens. D45: Distance along the optical axis from the image-side surface of the fourth lens to the object-side surface of the fifth lens. Let's assume that.

6. The optical system according to claim 1, characterized in that it satisfies the following condition (6). (6) 0.05<r9 / f<0.20 however, r9: Paraxial radius of curvature of the object-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 (7). (7) 0.50<f5 / f<2.75 however, f5: Focal length of the fifth lens, f: Focal length of the entire optical system, Let's assume that.

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