Optical system

Abstract

The present invention relates to an optical system, comprising a first lens (L1), a second lens (L2), a stop (STOP), a third lens (L3), a fourth lens (L4) and a fifth lens (L5) arranged in sequence from the object side to the image side along an optical axis, wherein the fourth lens (L4) and the fifth lens (L5) form a double-cemented lens group, and the second lens (L2) is a concave-convex type. The optical system of the present invention has a small volume and a large aperture, and the optical system has a large light transmission, so it has both day and night functions and is not out of focus within a temperature range of ‑40° C. to 105° C.

Description

Technical Field

[0001] The present invention relates to the field of optical imaging technology, and in particular to an optical system. Background Art

[0002] With the rapid development of science and technology, people have higher requirements for vehicle-mounted and security, and the demand for surveillance lenses has also emerged. Compared with zoom lenses, fixed-focus lenses are simpler in design and manufacturing. The images of moving objects taken are clear and stable, the pictures are delicate, and they can be shot 24 hours a day. These properties play a very important role in the field of security lenses. However, there is no sunlight at night, so lenses with small apertures can only be used at night with infrared fill light. Summary of the invention

[0003] The object of the present invention is to provide an optical system suitable for a monitoring lens.

[0004] To achieve the above-mentioned purpose of the invention, the present invention provides an optical system, comprising a first lens, a second lens, an aperture, a third lens, a fourth lens and a fifth lens arranged in sequence from the object side to the image side along the optical axis, the fourth lens and the fifth lens form a double-cemented lens group, and the second lens is a concave-convex type.

[0005] According to one aspect of the present invention, the first lens is a negative lens, the second lens is a positive lens or a negative lens, the third lens is a positive lens, the fourth lens is a negative lens, the fifth lens is a positive lens, and the doublet lens group has positive optical power.

[0006] According to one aspect of the present invention, the first lens and the third lens are spherical lenses, and the second lens, the fourth lens and the fifth lens are aspherical lenses.

[0007] According to one aspect of the present invention, the first lens is a convexo-concave type, the third lens is a biconvex type, the fourth lens is a convexo-concave type, and the fifth lens is a biconvex type.

[0008] According to one aspect of the present invention, it also includes a light filter / color filter located on the image side of the fifth lens.

[0009] According to one aspect of the present invention, the focal length fb of the double-cemented lens group and the effective focal length f of the optical system satisfy the relationship: 1.51≤|fb / f|≤19.3.

[0010] According to one aspect of the present invention, the focal length f1 of the first lens and the effective focal length f of the optical system satisfy the relationship: 1.21≤|f1 / f|≤13.1.

[0011] According to one aspect of the present invention, the aspheric surfaces of the second lens, the fourth lens and the fifth lens satisfy the following formula:

[0012]

[0013] Where z is the axial distance from the surface to the vertex at a height h perpendicular to the optical axis along the optical axis; c represents the curvature at the vertex of the aspheric surface; k is the cone coefficient; A4, A6, A8, A 10 , A 12 , A 14 , A 16 ···represent the fourth-order, sixth-order, eighth-order, tenth-order, twelfth-order, fourteenth-order, sixteenth-order···aspheric coefficients respectively.

[0014] According to one aspect of the present invention, the focal length f2 of the second lens, the focal length f3 of the third lens, the focal length f4 of the fourth lens and the focal length f5 of the fifth lens respectively satisfy the following relationship with the effective focal length f of the optical system:

[0015] 3.1≤|f2 / f|≤27.6;

[0016] 1.5≤|f3 / f|≤11.7;

[0017] 1.1≤|f4 / f|≤7.4;

[0018] 1.3≤|f5 / f|≤5.3.

[0019] According to one aspect of the present invention,

[0020] The refractive index Nd of the first lens satisfies: 1.60≤Nd≤1.85, and the Abbe number coefficient Vd satisfies: 35≤Vd≤75;

[0021] The refractive index Nd of the second lens satisfies 1.53≤Nd≤1.70, and the Abbe number coefficient Vd satisfies: 21≤Vd≤35;

[0022] The refractive index Nd of the third lens satisfies 1.43≤Nd≤1.78, and the Abbe number coefficient Vd satisfies: 45≤Vd≤96;

[0023] The refractive index Nd of the fourth lens satisfies 1.50≤Nd≤1.93, and the Abbe number coefficient Vd satisfies: 17≤Vd≤45;

[0024] The refractive index Nd of the fifth lens satisfies 1.43≤Nd≤1.75, and the Abbe number coefficient Vd satisfies: 35≤Vd≤77.

[0025] According to the present invention, a day and night optical system is provided which has a small volume, is not out of focus in the temperature range of -40°C to 105°C, has a large aperture, a large amount of light, and is infrared confocal, thus being suitable for wide-angle vehicle-mounted security lenses.

[0026] According to one solution of the present invention, the fourth lens and the fifth lens are glued together using high and low dispersion coefficient materials to eliminate chromatic aberration.

[0027] According to one solution of the present invention, the first lens has negative optical power and can control the incident angle of light to reduce distortion.

[0028] According to one solution of the present invention, the second lens has positive refractive power and can control the angle of light bending, so that the third lens can better converge the light.

[0029] According to the solution of the present invention, the optical system can achieve large aperture and high pixels, Fno≤1.2, large aperture, large amount of light passing through, relatively uniform overall illumination, and good brightness (relative illumination above 50%). By optimizing the positive and negative optical focal lengths of each lens, the aberration can be effectively corrected. And the image plane height of the optical system can reach Φ4.6mm, which can be adapted to a variety of sensors, with broad application prospects and improved market competitiveness. It can also achieve non-defocusing within the temperature range of -40℃~105℃, and can be used in different environments. In addition, the optical system can also achieve image capture with a maximum field of view angle Fov≥110°, with a total length TTL≤22mm and a small size, which also makes the single component and assembly tolerances better and has good manufacturability. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 A schematic diagram showing a structure of an optical system according to a first embodiment of the present invention;

[0031] Figure 2 Schematically showing an MTF diagram of an optical system according to a first embodiment of the present invention when the object distance is 2 m;

[0032] Figure 3 Schematically showing an MTF diagram of an optical system according to a first embodiment of the present invention with an object distance of 0.2 m;

[0033] Figure 4 Schematically showing the MTF diagram of the optical system according to the first embodiment of the present invention at an object distance of 2 m and a high temperature of 105° C.;

[0034] Figure 5 Schematically showing the MTF diagram of the optical system according to the first embodiment of the present invention with an object distance of 2m and a low temperature of -40°C;

[0035] Figure 6Schematically showing the MTF diagram of the infrared band at an object distance of 2 m for the optical system according to the first embodiment of the present invention;

[0036] Figure 7 A schematic diagram showing a structure of an optical system according to a second embodiment of the present invention;

[0037] Figure 8 Schematically showing an MTF diagram of an optical system according to a second embodiment of the present invention when the object distance is 2 m;

[0038] Fig. 9 Schematically showing an MTF diagram of an optical system according to a second embodiment of the present invention when the object distance is 0.2 m;

[0039] Fig.10 Schematically showing the MTF diagram of the optical system according to the second embodiment of the present invention at an object distance of 2 m and a high temperature of 105° C.;

[0040] Fig.11 Schematically showing the MTF diagram of the optical system according to the second embodiment of the present invention with an object distance of 2m and a low temperature of -40°C;

[0041] Fig.12 Schematically showing the MTF diagram of the infrared band at an object distance of 2 m for the optical system according to the second embodiment of the present invention;

[0042] Fig.13 A schematic diagram showing a structure of an optical system according to a third embodiment of the present invention;

[0043] Fig.14 Schematically showing an MTF diagram of an optical system according to a third embodiment of the present invention when the object distance is 2 m;

[0044] Fig.15 Schematically showing an MTF diagram of an optical system according to a third embodiment of the present invention when the object distance is 0.2 m;

[0045] Fig.16 Schematically showing the MTF diagram of the optical system according to the third embodiment of the present invention at an object distance of 2 m and a high temperature of 105° C.;

[0046] Fig.17 Schematically showing the MTF diagram of the optical system according to the third embodiment of the present invention with an object distance of 2m and a low temperature of -40°C;

[0047] Fig.18 The MTF diagram in the infrared band is schematically shown when the object distance of the optical system according to the third embodiment of the present invention is 2 m. DETAILED DESCRIPTION

[0048] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0049] When describing the embodiments of the present invention, the orientation or positional relationship expressed by the terms "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside" and "outside" are based on the orientation or positional relationship shown in the relevant drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operate in a specific orientation. Therefore, the above terms should not be understood as limiting the present invention.

[0050] The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments. The embodiments cannot be described one by one here, but the embodiments of the present invention are not therefore limited to the following embodiments.

[0051] See also Figure 1 The glass-plastic hybrid infrared confocal high and low temperature confocal optical system of the present invention comprises a first lens L1, a second lens L2, an aperture STOP, a third lens L3, a fourth lens L4, a fifth lens L5 and a filter IR or a color filter CG arranged in sequence along the optical axis from the object side to the image side. The fourth lens L4 and the fifth lens L5 form a double-cemented lens group. The first lens L1 is a negative lens, the second lens L2 is a positive lens or a negative lens, the third lens L3 is a positive lens, the fourth lens L4 is a negative lens, the fifth lens L5 is a positive lens, and the double-cemented lens group has positive focal length. The first lens L1 and the third lens L3 are spherical lenses, and the second lens L2, the fourth lens L4 and the fifth lens L5 are aspherical lenses. The first lens L1 is a convex-concave type; the second lens L2 is a concave-convex type, with the concave surface on the object side and the convex surface on the image side, which can effectively adjust the system tolerance and correct the high and low temperature of the system; the third lens L3 is a biconvex type; the fourth lens L4 is a convex-concave type; the fifth lens L5 is a biconvex type. The fourth lens L4 and the fifth lens L5 are made of high and low dispersion coefficient materials and glued together to eliminate chromatic aberration. The first lens L1 has a negative optical power that can control the incident angle of light and play a role in reducing distortion. The second lens L2 has a positive optical power that can control the angle of light bending, so that the third lens L3 (i.e., the positive lens) can better converge light.

[0052] In the present invention, the focal length of the double cemented lens group (i.e., the combined focal length of the fourth lens L4 and the fifth lens L5) fb and the effective focal length f of the optical system satisfy the relationship: 1.51≤|fb / f|≤19.3. The focal length f1 of the first lens L1 and the effective focal length f of the optical system satisfy the relationship: 1.21≤|f1 / f|≤13.1. The focal length f2 of the second lens L2, the focal length f3 of the third lens L3, the focal length f4 of the fourth lens L4, and the focal length f5 of the fifth lens L5 satisfy the following relationship:

[0053] 3.1≤|f2 / f|≤27.6;

[0054] 1.5≤|f3 / f|≤11.7;

[0055] 1.1≤|f4 / f|≤7.4;

[0056] 1.3≤|f5 / f|≤5.3.

[0057] In the present invention, the refractive index Nd of the first lens L1 satisfies: 1.60≤Nd≤1.85, and the Abbe number coefficient Vd satisfies: 35≤Vd≤75. The refractive index Nd of the second lens L2 satisfies: 1.53≤Nd≤1.70, and the Abbe number coefficient Vd satisfies: 21≤Vd≤35. The refractive index Nd of the third lens L3 satisfies: 1.43≤Nd≤1.78, and the Abbe number coefficient Vd satisfies: 45≤Vd≤96. The refractive index Nd of the fourth lens L4 satisfies: 1.50≤Nd≤1.93, and the Abbe number coefficient Vd satisfies: 17≤Vd≤45. The refractive index Nd of the fifth lens L5 satisfies: 1.43≤Nd≤1.75, and the Abbe number coefficient Vd satisfies: 35≤Vd≤77.

[0058] In the present invention, the aspheric surfaces of the second lens L2, the fourth lens L4 and the fifth lens L5 satisfy the following formula:

[0059]

[0060] In the formula, z is the axial distance from the curved surface to the vertex at a height h perpendicular to the optical axis along the optical axis; c represents the curvature at the vertex of the aspheric surface; k is the cone coefficient; A4, A6, A8, A10, A12, A14, A16... represent the fourth-order, sixth-order, eighth-order, tenth-order, twelfth-order, fourteenth-order, sixteenth-order... aspheric coefficients respectively.

[0061] In summary, the optical system that meets the above settings can achieve large aperture and high pixels, Fno≤1.2, large aperture, large amount of light, relatively uniform overall illumination, and good brightness (relative illumination of more than 50%). In addition, the present invention effectively corrects the aberrations by optimizing the positive and negative optical focal lengths of each lens. The image plane height of the optical system of the present invention can reach Φ4.6mm, which can be adapted to a variety of sensors, has broad application prospects, and enhances market competitiveness. In addition, the optical system of the present invention can achieve non-defocusing in the temperature range of -40℃~105℃, and can be used in different environments. It can also achieve image capture with a maximum field of view angle Fov≥110°, with a total length TTL≤22mm and a small size. The single component and assembly tolerances of the optical system are good, and it has good manufacturability.

[0062] Three groups of implementations are given below to specifically illustrate the optical system of the present invention according to the above-mentioned configuration of the present invention. In the following implementations, S1, S2, ..., SN are used to represent the surfaces of each lens, wherein the cemented surface of the cemented lens group is recorded as one surface, and the aperture is recorded as STO. The parameter settings of each implementation meet the following Table 1:

[0063]

[0064] Table 1

[0065] The first implementation method:

[0066] See also Figure 1 , the optical system parameters of this embodiment are: F# = 1.2; total lens length = 20.09 mm; field of view = 112°. Other related parameters such as surface type, radius of curvature, thickness, refractive index of the material and Abbe number are shown in Table 2 below:

[0067] Surface number Surface type R-Value thickness Refractive Index Abbe number S0(OBJ) Spherical Infinity 2000 S1 Spherical 14.1227 1.9945 1.80 48.6 S2 Spherical 3.2772 3.6340 S3 Aspheric -5.4471 1.8536 1.64 23.5 S4 Aspheric -5.1001 0.1809 S5(STO) Spherical Infinity 0.3839 S6 Spherical 9.4046 2.0196 1.70 50.7 S7 Spherical -9.4046 1.3968 S8 Aspheric 31.9642 1.6227 1.64 23.5 S9 Aspheric 2.8720 2.8089 1.54 56.0 S10 Aspheric -5.5475 1.0000 S11 Spherical Infinity 0.85 1.52 64.2 S12 Spherical Infinity 2.3453 S13(IMA) Spherical Infinity - - -

[0068] Table 2

[0069] Table 3 shows the aspheric coefficients of each aspheric lens in this embodiment, K is the quadratic constant of the surface, A, B, C, D, E are the aspheric coefficients of the fourth order, sixth order, eighth order, tenth order, and twelfth order respectively:

[0070]

[0071] Table 3

[0072] Combination Figures 2 to 6 As shown, the optical system of this embodiment can achieve a picture capture range with a maximum field of view angle of 112°, no out-of-focus in the temperature range of -40°C to 105°C, a large aperture, infrared confocality, and good manufacturability in a small volume.

[0073] The second implementation method:

[0074] See also Figure 7 , the optical system parameters of this embodiment are: F# = 1.19; total lens length = 19.63mm; field of view = 112°. Other related parameters such as surface type, radius of curvature, thickness, refractive index of the material and Abbe number are shown in Table 4 below:

[0075] Surface number Surface type R-Value thickness Refractive Index Abbe number S0(OBJ) Spherical Infinity 2000 S1 Spherical 13.1225 1.3945 1.80 48.6 S2 Spherical 2.456 5.6824 S3 Aspheric -4.9456 2.4335 1.64 23.5 S4 Aspheric -5.1110 0.2547 S5(STO) Spherical Infinity -0.1245 S6 Spherical 8.9045 2.0196 1.70 50.7 S7 Spherical -8.1486 0.4563 S8 Aspheric 20.2145 1.1234 1.64 23.5 S9 Aspheric 4.5678 3.3045 1.54 56.0 S10 Aspheric -6.2456 1.0000 S11 Spherical Infinity 0.85 1.52 64.2 S12 Spherical Infinity 1.2348 S13(IMA) Spherical Infinity - - -

[0076] Table 4

[0077] Table 5 shows the aspheric coefficients of each aspheric lens in this embodiment, K is the quadratic constant of the surface, A, B, C, D, E are the aspheric coefficients of the fourth order, sixth order, eighth order, tenth order, and twelfth order respectively:

[0078]

[0079] Table 5

[0080] Combination Figures 8 to 12 As shown, the optical system of this embodiment can achieve a picture capture range with a maximum field of view angle of 112°, no out-of-focus in the temperature range of -40°C to 105°C, a large aperture, infrared confocality, and good manufacturability in a small volume.

[0081] The third implementation method:

[0082] See also Fig.13 , the optical system parameters of this embodiment are: F# = 1.15; total lens length = 22mm; field of view = 112°. Other related parameters such as surface type, radius of curvature, thickness, refractive index of the material and Abbe number are shown in Table 6 below:

[0083] Surface number Surface type R-Value thickness Refractive Index Abbe number S0(OBJ) Spherical Infinity 2000 S1 Spherical 15.1226 2.3945 1.80 48.6 S2 Spherical 6.9772 3.6487 S3 Aspheric -3.9471 3.4358 1.64 23.5 S4 Aspheric -6.6054 0.6805 S5(STO) Spherical Infinity 0.183917 S6 Spherical 10.9057 3.0147 1.70 50.7 S7 Spherical -12.1585 0.8921 S8 Aspheric 25.9645 1.3245 1.64 23.5 S9 Aspheric 4.3478 3.0145 1.54 56.0 S10 Aspheric -6.0156 1.0000 S11 Spherical Infinity 0.80 1.52 64.2 S12 Spherical Infinity 1.3547 S13(IMA) Spherical Infinity - - -

[0084] Table 6

[0085] Table 7 shows the aspheric coefficients of each aspheric lens in this embodiment, K is the quadratic constant of the surface, A, B, C, D, E are the aspheric coefficients of the fourth order, sixth order, eighth order, tenth order, and twelfth order respectively:

[0086]

[0087] Table 7

[0088] Combination Figures 14 to 18 As shown, the optical system of this embodiment can achieve a picture capture range with a maximum field of view angle of 112°, no out-of-focus in the temperature range of -40°C to 105°C, a large aperture, infrared confocality, and good manufacturability in a small volume.

[0089] The above is only one solution of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An optical system, comprising a first lens (L1), a second lens (L2), a stop (STOP), a third lens (L3), a fourth lens (L4) and a fifth lens (L5), which are arranged in sequence from the object side to the image side along the optical axis, a total of five lenses, wherein the fourth lens (L4) and the fifth lens (L5) form a doublet lens group, characterized in that: The second lens (L2) is of concave-convex type; The relative aperture Fno of the optical system satisfies the relationship: Fno≤1.2; The first lens (L1) is a negative lens, the second lens (L2) is a positive lens or a negative lens, the third lens (L3) is a positive lens, the fourth lens (L4) is a negative lens, the fifth lens (L5) is a positive lens, and the doublet lens group has positive optical power.

2. The optical system according to claim 1, characterized in that The first lens (L1) and the third lens (L3) are spherical lenses, and the second lens (L2), the fourth lens (L4) and the fifth lens (L5) are aspherical lenses.

3. The optical system according to claim 1, characterized in that The first lens (L1) is of a convex-concave type, the third lens (L3) is of a biconvex type, the fourth lens (L4) is of a convex-concave type, and the fifth lens (L5) is of a biconvex type.

4. The optical system according to any one of claims 1 to 3, characterized in that: The focal length fb of the double-cemented lens group and the effective focal length f of the optical system satisfy the relationship: 1.51≤|fb / f|≤19.

3.

5. The optical system according to any one of claims 1 to 3, characterized in that: The focal length f1 of the first lens (L1) and the effective focal length f of the optical system satisfy the relationship: 1.21≤|f1 / f|≤13.

1.

6. The optical system according to any one of claims 1 to 3, characterized in that: The focal length f2 of the second lens (L2), the focal length f4 of the fourth lens (L4) and the focal length f5 of the fifth lens (L5) respectively satisfy the following relationship with the effective focal length f of the optical system: 3.1≤|f2 / f|≤27.6; 1.1≤|f4 / f|≤7.4; 1.3≤|f5 / f|≤5.

3.

7. The optical system according to any one of claims 1 to 3, characterized in that: The focal length f3 of the third lens (L3) and the effective focal length f of the optical system satisfy the following relationship: 1.5≤|f3 / f|≤11.

7.

8. The optical system according to any one of claims 1 to 3, characterized in that: The refractive index Nd of the first lens (L1) satisfies: 1.60≤Nd≤1.85, and the Abbe number coefficient Vd satisfies: 35≤Vd≤75; The refractive index Nd of the second lens (L2) satisfies 1.53≤Nd≤1.70, and the Abbe number coefficient Vd satisfies: 21≤Vd≤35; The refractive index Nd of the fourth lens (L4) satisfies 1.50≤Nd≤1.93, and the Abbe number coefficient Vd satisfies: 17≤Vd≤45; The refractive index Nd of the fifth lens (L5) satisfies 1.43≤Nd≤1.75, and the Abbe number coefficient Vd satisfies: 35≤Vd≤77.

9. The optical system according to any one of claims 1 to 3, characterized in that: The refractive index Nd of the third lens (L3) satisfies 1.43≤Nd≤1.78, and the Abbe number coefficient Vd satisfies: 45≤Vd≤96.

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