fixed-focus lens

Abstract

The present invention relates to a fixed-focus lens, comprising a first lens (L1), a second lens (L2), a stop (STOP), a third lens (L3), a fourth lens (L4), a fifth lens (L5), and a sixth lens (L6), arranged in sequence along an optical axis from the object side to the image side. The effective focal length f of the fixed-focus lens and the total length (TTL) satisfy the following relationship: f / TTL ≤ 0.26. The fixed-focus lens of the present invention is low-cost and compact, and exhibits no defocusing within a temperature range of -40°C to 80°C.

Description

Technical Field

[0001] The present invention relates to the field of optical imaging technology, and in particular to a fixed-focus lens. Background Art

[0002] With the advancement of science and technology, security surveillance equipment is becoming increasingly popular. Fixed-focus lenses, due to their advantages such as high-definition imaging, wide monitoring field of view, and clear imaging in low-light conditions, are widely used in the security surveillance field. These lenses are collectively referred to as security surveillance lenses. However, at night or in low-light conditions, insufficient brightness can prevent the lens from capturing clear images. Existing technologies often use infrared fill light to achieve this imaging purpose. However, infrared imaging has a limited range and cannot guarantee the capture of true color information, resulting in severe color distortion. Therefore, ensuring clear images at night or in low-light conditions is a pressing issue in the security surveillance field. Summary of the Invention

[0003] The object of the present invention is to provide a fixed-focus lens.

[0004] To achieve the above-mentioned object of the invention, the present invention provides a fixed-focus lens, comprising a first lens, a second lens, an aperture, a third lens, a fourth lens, a fifth lens, and a sixth lens arranged in sequence along the optical axis from the object side to the image side, wherein the effective focal length f and the total length TTL of the fixed-focus lens satisfy the following relationship: f / TTL ≤ 0.26.

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

[0006] According to one aspect of the present invention, the first lens is a convex-concave aspheric lens, the second lens is a concave-convex aspheric lens, the third lens is a convex-concave aspheric lens, the fourth lens is a biconvex spherical lens, the fifth lens is a biconvex aspheric lens, and the sixth lens is a paraxial concave-convex aspheric lens.

[0007] According to one aspect of the present invention, the first lens, the second lens, the third lens, the fifth lens, and the sixth lens are made of plastic.

[0008] According to one aspect of the present invention, the effective focal length f of the fixed-focus lens and the effective focal length f1 of the first lens satisfy the following relationship: -2.2≤f1 / f≤-1.8.

[0009] According to one aspect of the present invention, the effective focal length f of the fixed-focus lens and the effective focal length f2 of the second lens satisfy the following relationship: -162≤f2 / f≤2.5.

[0010] According to one aspect of the present invention, the effective focal length f of the fixed-focus lens and the effective focal length f3 of the third lens satisfy the following relationship: -32≤f3 / f≤-1.5.

[0011] According to one aspect of the present invention, the effective focal length f of the fixed-focus lens and the sum of the effective focal lengths of the fourth lens and the fifth lens (f4+f5) satisfy the following relationship: 2.4≤(f4+f5) / f≤2.65.

[0012] According to one aspect of the present invention, at least one lens is made of low-dispersion glass, and the Abbe value VD satisfies the following condition: VD≥60.

[0013] According to one aspect of the present invention, the FNO number of the fixed-focus lens and the effective focal length f satisfy the following relationship: 0.1≤FNO / f.

[0014] According to one aspect of the present invention, the effective focal length f and the half image height h of the fixed-focus lens satisfy the following relationship: 1.4≤f / h≤1.6.

[0015] According to one aspect of the present invention, the total length TTL, the maximum half image height H, and the maximum field of view DFOV of the fixed-focus lens satisfy the following relationship: TTL / H / DFOV≤0.065.

[0016] According to one aspect of the present invention, the maximum clear aperture D of the first lens on the object side, the total length TTL of the fixed-focus lens, and the maximum half-image height H of the fixed-focus lens satisfy the following relationship: D / TTL / H≤1.3.

[0017] According to one aspect of the present invention, the FNO number of the fixed-focus lens satisfies the following condition: FNO≤1.65.

[0018] According to the concept of the present invention, a low-cost, miniaturized day and night confocal glass-plastic hybrid fixed-focus imaging lens is provided, which does not lose focus in the temperature range of -40°C to 80°C.

[0019] According to one solution of the present invention, plastic is selected as the material of the aspheric lens, which is beneficial to reducing costs and can effectively correct high and low temperature imaging.

[0020] According to one embodiment of the present invention, by reasonably setting the relationship between the effective focal length of the fixed-focus lens and the focal lengths of the first lens, the second lens, the third lens, and the sum of the focal lengths of the fourth lens and the fifth lens, and by making at least one lens a low-dispersion glass with an Abbe number above a certain value, system chromatic aberration can be effectively corrected, which is conducive to achieving high image quality.

[0021] According to one embodiment of the present invention, by reasonably setting the relationship between the effective focal length and the total length of the fixed-focus lens, the relationship between the FNO number and the effective focal length of the fixed-focus lens, the relationship between the effective focal length and the half-image height of the fixed-focus lens, the relationship between the total length of the fixed-focus lens, the maximum half-image height, and the maximum field of view angle, as well as the relationship between the maximum object-side aperture of the first lens, the total length of the fixed-focus lens, and the maximum half-image height of the fixed-focus lens, it is advantageous to achieve high image quality while ensuring that the fixed-focus lens is compact. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 A diagram schematically showing the structure of a fixed-focus lens according to a first embodiment of the present invention;

[0023] Figure 2 Schematically showing an MTF diagram of a fixed-focus lens according to a first embodiment of the present invention;

[0024] Figure 3 Schematically showing a Through-Focus-MTF diagram of a fixed-focus lens of the first embodiment of the present invention with a frequency of 125 lp / mm;

[0025] Figure 4 Schematically showing a Through-Focus-MTF diagram of the fixed-focus lens of the first embodiment of the present invention at a high temperature of 80°C and a frequency of 125 lp / mm;

[0026] Figure 5 Schematically showing a Through-Focus-MTF diagram of the fixed-focus lens of the first embodiment of the present invention at a low temperature of -40°C and a frequency of 125 lp / mm;

[0027] Figure 6 A diagram schematically showing the structure of a fixed-focus lens according to a second embodiment of the present invention;

[0028] Figure 7 Schematically showing an MTF diagram of a fixed-focus lens according to a second embodiment of the present invention;

[0029] Figure 8 Schematically showing a Through-Focus-MTF diagram of a fixed-focus lens of a second embodiment of the present invention with a frequency of 125 lp / mm;

[0030] Figure 9Schematically showing a Through-Focus-MTF graph of a fixed-focus lens according to a second embodiment of the present invention at a high temperature of 80°C and a frequency of 125 lp / mm;

[0031] Figure 10 Schematically showing a Through-Focus-MTF diagram of a fixed-focus lens according to a second embodiment of the present invention at a low temperature of -40°C and a frequency of 125 lp / mm;

[0032] Figure 11 A diagram schematically showing the structure of a fixed-focus lens according to a third embodiment of the present invention;

[0033] Figure 12 Schematically showing an MTF diagram of a fixed-focus lens according to a third embodiment of the present invention;

[0034] Figure 13 Schematically showing a Through-Focus-MTF diagram of a fixed-focus lens of a third embodiment of the present invention with a frequency of 125 lp / mm;

[0035] Figure 14 Schematically showing a Through-Focus-MTF graph of a fixed-focus lens according to a third embodiment of the present invention at a high temperature of 80°C and a frequency of 125 lp / mm;

[0036] Figure 15 Schematically showing a Through-Focus-MTF diagram of a fixed-focus lens according to a third embodiment of the present invention at a low temperature of -40°C and a frequency of 125 lp / mm;

[0037] Figure 16 A diagram schematically showing the structure of a fixed-focus lens according to a fourth embodiment of the present invention;

[0038] Figure 17 Schematically showing an MTF diagram of a fixed-focus lens according to a fourth embodiment of the present invention;

[0039] Figure 18 Schematically showing a Through-Focus-MTF diagram of a fixed-focus lens of a fourth embodiment of the present invention with a frequency of 125 lp / mm;

[0040] Figure 19 Schematically showing a Through-Focus-MTF graph of a fixed-focus lens according to a fourth embodiment of the present invention at a high temperature of 80°C and a frequency of 125 lp / mm;

[0041] Figure 20 The Through-Focus-MTF diagram of the fixed-focus lens according to the fourth embodiment of the present invention at a low temperature of -40°C and a frequency of 125 lp / mm is schematically shown. DETAILED DESCRIPTION

[0042] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be derived from these drawings without inventive effort.

[0043] When describing the embodiments of the present invention, the orientation or positional relationship expressed by the terms "longitudinal", "transverse", "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 device or element referred to 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.

[0044] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. The embodiments cannot be described one by one here, but the embodiments of the present invention are not limited to the following embodiments.

[0045] See also Figure 1 The fixed-focus lens of the present invention includes, arranged in order from the object side to the image side along the optical axis, a first lens L1, a second lens L2, an aperture stop STOP, a third lens L3, a fourth lens L4, a fifth lens L5, and a sixth lens L6. In the present invention, the effective focal length f and the total length TTL of the fixed-focus lens satisfy the following relationship: f / TTL ≤ 0.26.

[0046] In the present invention, the first lens L1 has negative optical power, the second lens L2 has negative or positive optical power, the third lens L3 has negative optical power, the fourth lens L4 has positive optical power, the fifth lens L5 has positive optical power, and the sixth lens L6 has negative optical power.

[0047] In the present invention, the first lens L1 is a convex-concave aspheric lens, the second lens L2 is a concave-convex aspheric lens, the third lens L3 is a convex-concave aspheric lens, the fourth lens L4 is a biconvex spherical lens, the fifth lens L5 is a biconvex aspheric lens, and the sixth lens L6 is a paraxial concave-convex aspheric lens.

[0048] In the present invention, the first lens L1, the second lens L2, the third lens L3, the fifth lens L5, and the sixth lens L6 are made of plastic, which helps reduce costs and can effectively correct high and low temperature imaging.

[0049] In the present invention, the effective focal length f of the fixed-focus lens and the effective focal length f1 of the first lens L1 satisfy the following relationship: -2.2≤f1 / f≤-1.8. The effective focal length f of the fixed-focus lens and the effective focal length f2 of the second lens L2 satisfy the following relationship: -162≤f2 / f≤2.5. The effective focal length f of the fixed-focus lens and the effective focal length f3 of the third lens L3 satisfy the following relationship: -32≤f3 / f≤-1.5. The effective focal length f of the fixed-focus lens and the sum of the effective focal lengths of the fourth lens L4 and the fifth lens L5 (f4+f5) satisfy the following relationship: 2.4≤(f4+f5) / f≤2.65. At least one lens in the fixed-focus lens is made of low-dispersion glass, and the Abbe value VD satisfies the following condition: VD≥60. Meeting the above-mentioned settings can effectively correct system chromatic aberration, which is conducive to achieving high image quality.

[0050] In the present invention, the fixed-focus lens's FNO number and effective focal length f satisfy the following relationship: 0.1 ≤ FNO / f. The fixed-focus lens's effective focal length f and half-image height h satisfy the following relationship: 1.4 ≤ f / h ≤ 1.6. The fixed-focus lens's total length (TTL), maximum half-image height (H), and maximum field of view (DFOV) satisfy the following relationship: TTL / H / DFOV ≤ 0.065. The object-side maximum clear aperture (D) of the first lens element L1, the fixed-focus lens's total length (TTL), and maximum half-image height (H) satisfy the following relationship: D / TTL / H ≤ 1.3. This, combined with the above-described relationship between the fixed-focus lens's effective focal length and total length, facilitates achieving high image quality while maintaining a compact fixed-focus lens.

[0051] In the present invention, the FNO number of the fixed-focus lens satisfies the following condition: FNO≤1.65.

[0052] In summary, the fixed-focus lens of the present invention can achieve large aperture and high pixels, FNO≤1.65, uniform overall illumination, good brightness, and can achieve confocality during the day and night. By optimizing the positive and negative optical focal lengths of each lens, the aberrations can be effectively corrected. The image plane height of the fixed-focus lens can reach Φ7.6mm, and it can be adapted to sensors such as 1 / 2.5", 1 / 2.7", etc., and has broad application prospects and market competitiveness. In addition, the fixed-focus lens can achieve non-defocusing within the temperature range of -40℃ to 80℃, so it can be used in different environments. The total length of the lens is ≤22.5mm (with protective flat glass CG), so it is relatively small. In addition, the tolerances of single lens components and assembly are also good, thus having good manufacturability.

[0053] The fixed-focus lens of the present invention is described in detail below using four embodiments. In the following embodiments, the surfaces of the optical elements are represented by S1, S2, ..., SN. The aperture stop STOP can also be represented by STO, and the image plane IMAGE can also be represented by IMA.

[0054] Among them, the plastic aspheric lens satisfies the following formula:

[0055]

[0056] 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.

[0057] Parameters of various implementations that specifically meet the above conditional formula are shown in Table 1 below:

[0058]

[0059] Table 1

[0060] First implementation method

[0061] See also Figures 1 to 5 The parameters of the fixed-focus lens of this embodiment are: F#: 1.61; total lens length: 22.275 mm; field of view: 95.6°. Among them, the second lens L2 has negative optical power.

[0062] The relevant parameters of each lens of the fixed-focus lens of this embodiment, including surface type, curvature radius, thickness, refractive index of the material, and Abbe number, are shown in Table 2 below:

[0063]

[0064]

[0065] Table 2

[0066] The aspheric coefficients of the aspheric lenses in this embodiment are shown in Table 3 below:

[0067]

[0068] Table 3

[0069] Among them, K is the quadratic constant of the surface, A4, A6, A8, A 10 、A 12 、A 14 、A 16 They are the aspheric coefficients of the fourth, sixth, eighth, tenth, twelfth, fourteenth and sixteenth orders respectively.

[0070] Second implementation method

[0071] See also Figures 6 to 10 The parameters of the fixed-focus lens of this embodiment are: F#: 1.61; total lens length: 22.499 mm; field of view: 94°. The second lens L2 has positive refractive power.

[0072] The relevant parameters of each lens of the fixed-focus lens of this embodiment, including surface type, curvature radius, thickness, refractive index of the material, and Abbe number, are shown in Table 4 below:

[0073] Surface number Surface type R-value thickness Refractive index Abbe number S1 Aspheric 3.798 1.408 1.54 55.99 S2 Aspheric 1.994 2.181 S3 Aspheric -5.859 2.708 1.66 20.38 S4 Aspheric -4.055 0.028 S5(STO) spherical surface Infinity 0.372 S6 Aspheric 8.522 1.500 1.66 20.38 S7 Aspheric 3.435 0.651 S8 spherical surface 6.434 3.644 1.44 95.10 S9 spherical surface -6.095 0.100 S10 Aspheric 7.893 2.432 1.54 55.71 S11 Aspheric -5.151 0.326 S12 Aspheric -2.388 1.067 1.66 20.38 S13 Aspheric -3.793 5.082 S14 spherical surface Infinity 0.7 1.52 64.21 S15 spherical surface Infinity 0.3 S16(IMA) spherical surface Infinity - - -

[0074] Table 4

[0075] The aspheric coefficients of the aspheric lenses in this embodiment are shown in Table 5 below:

[0076]

[0077] Table 5

[0078] Among them, K is the quadratic constant of the surface, A4, A6, A8, A 10 、A 12 、A 14 、A 16 They are the aspheric coefficients of the fourth, sixth, eighth, tenth, twelfth, fourteenth and sixteenth orders respectively.

[0079] Third implementation method

[0080] See also Figures 11 to 15 The parameters of the fixed-focus lens of this embodiment are: F#: 1.61; total lens length: 22.485 mm; field of view: 97°. The second lens L2 has negative refractive power.

[0081] The relevant parameters of each lens of the fixed-focus lens of this embodiment, including surface type, curvature radius, thickness, refractive index of the material, and Abbe number, are shown in Table 6 below:

[0082] Surface number Surface type R-value thickness Refractive index Abbe number S1 Aspheric 3.490 1.615 1.54 55.71 S2 Aspheric 1.918 2.158 S3 Aspheric -5.838 2.604 1.54 55.71 S4 Aspheric -7.657 0.100 S5(STO) spherical surface Infinity 1.135 S6 Aspheric 6.171 2.305 1.64 23.53 S7 Aspheric 4.994 0.206 S8 spherical surface 6.277 2.838 1.44 95.10 S9 spherical surface -6.881 0.100 S10 Aspheric 6.945 2.383 1.54 55.71 S11 Aspheric -5.454 0.293 S12 Aspheric -2.836 0.976 1.64 23.53 S13 Aspheric -5.488 4.772 S14 spherical surface Infinity 0.7 1.52 64.21 S15 spherical surface Infinity 0.3 S16(IMA) spherical surface Infinity - - -

[0083] Table 6

[0084] The aspheric coefficients of the aspheric lenses in this embodiment are shown in Table 7 below:

[0085]

[0086]

[0087] Table 7

[0088] Among them, K is the quadratic constant of the surface, A4, A6, A8, A 10、A 12 、A 14 、A 16 They are the aspheric coefficients of the fourth, sixth, eighth, tenth, twelfth, fourteenth and sixteenth orders respectively.

[0089] Fourth implementation method

[0090] See also Figures 16 to 20 The parameters of the fixed-focus lens of this embodiment are: F#: 1.60; total lens length: 22.445 mm; field of view: 96.6°. The second lens L2 has negative refractive power.

[0091] The relevant parameters of each lens of the fixed-focus lens of this embodiment, including surface type, curvature radius, thickness, refractive index of the material, and Abbe number, are shown in Table 8 below:

[0092] Surface number Surface type R-value thickness Refractive index Abbe number S1 Aspheric 3.560 1.569 1.54 55.71 S2 Aspheric 1.919 2.107 S3 Aspheric -6.211 2.559 1.54 55.71 S4 Aspheric -7.906 0.095 S5(STO) spherical surface Infinity 0.952 S6 Aspheric 6.152 2.064 1.64 23.53 S7 Aspheric 5.004 0.279 S8 spherical surface 7.021 3.165 1.46 90.19 S9 spherical surface -7.021 0.100 S10 Aspheric 6.965 2.354 1.54 55.71 S11 Aspheric -5.359 0.257 S12 Aspheric -2.858 0.860 1.64 23.53 S13 Aspheric -5.546 5.084 S14 spherical surface Infinity 0.7 1.52 64.21 S15 spherical surface Infinity 0.3 S16(IMA) spherical surface Infinity - - -

[0093] Table 8

[0094] The aspheric coefficients of the aspheric lenses in this embodiment are shown in Table 9 below:

[0095]

[0096] Table 9

[0097] Among them, K is the quadratic constant of the surface, A4, A6, A8, A 10 、A 12 、A 14 、A 16 They are the aspheric coefficients of the fourth, sixth, eighth, tenth, twelfth, fourteenth and sixteenth orders respectively.

[0098] The above description is merely one embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that the present invention is susceptible to various modifications and variations. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A fixed-focus lens comprising a first lens (L1), a second lens (L2), a stop (STOP), a third lens (L3), a fourth lens (L4), a fifth lens (L5) and a sixth lens (L6) arranged in sequence along the optical axis from the object side to the image side, totaling six lenses, characterized in that: The effective focal length f of the fixed-focus lens and the total length TTL satisfy the following relationship: 0.24≤f / TTL≤0.26; The first lens (L1) has negative optical power, the second lens (L2) has negative optical power or positive optical power, the third lens (L3) has negative optical power, the fourth lens (L4) has positive optical power, the fifth lens (L5) has positive optical power, and the sixth lens (L6) has negative optical power; The effective focal length f of the fixed-focus lens and the effective focal length f1 of the first lens (L1) satisfy the following relationship: -2.2≤f1 / f≤-1.8; The effective focal length f and the half-image height h of the fixed-focus lens satisfy the following relationship: 1.4≤f / h≤1.

6.

2. The fixed-focus lens according to claim 1, wherein: The first lens (L1) is a convex-concave aspheric lens, the second lens (L2) is a concave-convex aspheric lens, the third lens (L3) is a convex-concave aspheric lens, the fourth lens (L4) is a biconvex spherical lens, the fifth lens (L5) is a biconvex aspheric lens, and the sixth lens (L6) is a paraxial concave-convex aspheric lens.

3. The fixed-focus lens according to claim 2, wherein: The first lens (L1), the second lens (L2), the third lens (L3), the fifth lens (L5) and the sixth lens (L6) are made of plastic.

4. The fixed-focus lens according to any one of claims 1 to 3, wherein: The effective focal length f of the fixed-focus lens and the effective focal length f2 of the second lens (L2) satisfy the following relationship: -162≤f2 / f≤2.

5.

5. The fixed-focus lens according to any one of claims 1 to 3, wherein: The effective focal length f of the fixed-focus lens and the effective focal length f3 of the third lens (L3) satisfy the following relationship: -32≤f3 / f≤-1.

5.

6. The fixed-focus lens according to any one of claims 1 to 3, wherein: The effective focal length f of the fixed-focus lens and the sum of the effective focal lengths of the fourth lens (L4) and the fifth lens (L5) (f4+f5) satisfy the following relationship: 2.4≤(f4+f5) / f≤2.

65.

7. The fixed-focus lens according to any one of claims 1 to 3, wherein: At least one lens is made of low-dispersion glass, and the Abbe value VD satisfies the following conditions: VD ≥ 60.

8. The fixed-focus lens according to any one of claims 1 to 3, wherein: The FNO number of the fixed-focus lens and the effective focal length f satisfy the following relationship: 0.1≤FNO / f≤0.

3.

9. The fixed-focus lens according to any one of claims 1 to 3, wherein: The total length TTL, the maximum half image height H, and the maximum field of view DFOV of the fixed-focus lens satisfy the following relationship: 0.063≤TTL / H / DFOV≤0.

065.

10. The fixed-focus lens according to any one of claims 1 to 3, wherein: The maximum clear aperture D of the object side of the first lens (L1), the total length TTL of the fixed-focus lens, and the maximum half-image height H of the fixed-focus lens satisfy the following relationship: 1.23≤D / TTL / H≤1.

3.

11. The fixed-focus lens according to any one of claims 1 to 3, wherein: The FNO number of the fixed-focus lens satisfies the following condition: 1.60≤FNO≤1.65.

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