Pinhole lens

Abstract

The present invention relates to a pinhole lens, comprising a first lens (L1), a second lens (L2), 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 second lens (L2) is a convex-convex lens. The high-definition pinhole lens of the present invention has the characteristics of low cost, large field of view, small aperture and small volume, can work normally at 40°C to 80°C, and realizes day and night confocality.

Description

Technical Field

[0001] The invention relates to the technical field of optical imaging, and in particular to a pinhole lens. Background Art

[0002] With the development of security monitoring, people have higher and higher requirements for scenes and image quality. In addition, for some special scenes, there are also special requirements for the size of the monitoring lens, which is usually required to have high image quality, large field of view, and small size. However, the pinhole lens in the existing technology generally cannot meet this requirement. Summary of the invention

[0003] The object of the present invention is to provide a pinhole lens.

[0004] To achieve the above-mentioned object of the invention, the present invention provides a pinhole lens, comprising a first lens, a second lens, 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, wherein the second lens is a convex-convex lens.

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

[0006] According to one aspect of the present invention, the first lens, the third lens, the fourth lens and the fifth lens are plastic lenses;

[0007] The second lens is a glass spherical lens or a glass aspherical lens.

[0008] According to one aspect of the present invention, the first lens is a convex-concave lens, the third lens is a concave-convex lens, the fourth lens is a convex-convex lens, and the fifth lens is a concave-concave lens or a concave-convex lens.

[0009] According to one aspect of the present invention, a stop is further included, and the stop is located between the first lens and the second lens, or is located on the image side surface of the first lens or the object side surface of the second lens.

[0010] According to one aspect of the present invention, the fourth lens and the fifth lens are cemented together to form a cemented lens group with positive refractive power.

[0011] According to one aspect of the present invention, the relative aperture FNO satisfies the following condition: FNO≤2.2.

[0012] According to one aspect of the present invention, the focal length F1 of the cemented lens group consisting of the fourth lens and the fifth lens and the focal length F of the pinhole lens satisfy the following relationship: 2.00≤F1 / F≤3.0.

[0013] According to one aspect of the present invention, the Abbe number V2 of the second lens satisfies the following condition: V2≥70.

[0014] According to one aspect of the present invention, the field of view FOV satisfies the following condition: FOV ≥ 90°.

[0015] According to one aspect of the present invention, the focal length F2 of the second lens and the focal length F of the pinhole lens satisfy the following relationship: 1.0≤F2 / F≤1.5.

[0016] According to one aspect of the present invention, a thickness TH of a cemented lens group composed of the fourth lens and the fifth lens and a total length TTL of the pinhole lens satisfy the following relationship: 2.0≤10*TH / TTL≤3.

[0017] According to the concept of the present invention, a low-cost, large field of view, small aperture, and small volume high-definition pinhole lens is provided, which can work normally at -40°C to 80°C, has day and night confocal function, and the aperture can be increased to F2.0. At the same time, it has 5M clarity, which can achieve better shooting effects.

[0018] According to one solution of the present invention, by reasonably setting the relationship between the cemented lens group and the focal length of the lens, the sensitivity of high and low temperatures to the back focus can be reduced, so that the ratio of the entrance pupil diameter to the small aperture (2.3) at the front end of the structural component is approximately 1:1, reaching the theoretical design limit of the structural component.

[0019] According to one solution of the present invention, by properly setting the Abbe number of the second lens, chromatic aberration correction and confocalization of visible light and infrared light can be achieved.

[0020] According to one solution of the present invention, the second lens is a glass spherical lens or a glass aspherical lens, so that the aberration at the pupil can be effectively reduced to improve the image quality.

[0021] According to one solution of the present invention, chromatic aberration balance can be achieved by properly setting the relationship between the focal length of the second lens and the focal length of the lens.

[0022] According to one solution of the present invention, by reasonably setting the relationship between the thickness of the cemented lens group and the total length of the lens, the lens can be miniaturized, the processability can be ensured, and the resolution of visible light and infrared light can be balanced. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 A schematic diagram showing the structure of a pinhole lens according to a first embodiment of the present invention;

[0024] Figure 2 Schematically showing an MTF diagram of a pinhole lens according to a first embodiment of the present invention;

[0025] Figure 3 Schematically showing a Through-Focus-MTF diagram of a pinhole lens with a frequency of 125p / mm according to a first embodiment of the present invention;

[0026] Figure 4 A ray fan diagram schematically showing a pinhole lens according to a first embodiment of the present invention;

[0027] Figure 5 A schematic diagram showing the structure of a pinhole lens according to a second embodiment of the present invention;

[0028] Figure 6 Schematically showing an MTF diagram of a pinhole lens according to a second embodiment of the present invention;

[0029] Figure 7 Schematically showing a Through-Focus-MTF diagram of a pinhole lens with a frequency of 125p / mm according to a second embodiment of the present invention;

[0030] Figure 8 A ray fan diagram schematically showing a pinhole lens according to a second embodiment of the present invention;

[0031] Fig. 9 A schematic diagram showing the structure of a pinhole lens according to a third embodiment of the present invention;

[0032] Fig.10 Schematically showing an MTF diagram of a pinhole lens according to a third embodiment of the present invention;

[0033] Fig.11 Schematically showing a Through-Focus-MTF diagram of a pinhole lens with a frequency of 125p / mm according to a third embodiment of the present invention;

[0034] Fig.12 A ray fan diagram schematically showing a pinhole lens according to a third embodiment of the present invention;

[0035] Fig.13 A schematic diagram showing the structure of a pinhole lens according to a fourth embodiment of the present invention;

[0036] Fig.14 Schematically showing an MTF diagram of a pinhole lens according to a fourth embodiment of the present invention;

[0037] Fig.15 Schematically showing a Through-Focus-MTF diagram of a pinhole lens with a frequency of 125p / mm according to a fourth embodiment of the present invention;

[0038] Fig.16A ray fan diagram schematically showing a pinhole lens according to a fourth embodiment of the present invention. DETAILED DESCRIPTION

[0039] 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.

[0040] 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.

[0041] 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.

[0042] See also Figure 1 The pinhole lens of the present invention comprises a first lens L1, a second lens L2, 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. The first lens L1 and the fifth lens L5 are negative power lenses, the second lens L2 and the fourth lens L4 are positive power lenses, and the third lens L3 is a positive power or negative power lens. The first lens L1, the third lens L3, the fourth lens L4 and the fifth lens L5 are plastic lenses. The second lens L2 is a glass spherical lens or a glass aspherical lens, so that the aberration at the pupil can be reduced to improve the image quality.

[0043] In the present invention, the first lens L1 is a convex-concave lens, the second lens L2 is a convex-convex lens, the third lens L3 is a concave-convex lens, the fourth lens L4 is a convex-convex lens, and the fifth lens L5 is a concave-concave lens or a concave-convex lens.

[0044] The present invention further includes a stop STO, which is located between the first lens L1 and the second lens L2, or on the image side surface (ie, L1R2) of the first lens L1 or on the object side surface (ie, L2R1) of the second lens L2.

[0045] In some embodiments, the fourth lens L4 and the fifth lens L5 are cemented together to form a cemented lens group with positive refractive power.

[0046] In the present invention, the relative aperture FNO satisfies the following condition: FNO≤2.2.

[0047] In the present invention, the focal length F1 of the cemented lens group composed of the fourth lens L4 and the fifth lens L5 and the focal length F of the pinhole lens satisfy the following relationship: 2.00≤F1 / F≤3.0. In this way, by reasonably allocating the optical power, the sensitivity of the back focus to high and low temperatures can be reduced, so that the ratio of the entrance pupil diameter to the small aperture (2.3) at the front end of the structural component is approximately 1:1, reaching the theoretical design limit of the structural component.

[0048] In the present invention, the Abbe number V2 of the second lens L2 satisfies the following condition: V2 ≥ 70. Satisfying the above condition can correct chromatic aberration and make visible light and infrared light confocal.

[0049] In the present invention, the field of view FOV satisfies the following condition: FOV ≥ 90°.

[0050] In the present invention, the focal length F2 of the second lens L2 and the focal length F of the pinhole lens satisfy the following relationship: 1.0≤F2 / F≤1.5. When the above relationship is satisfied, chromatic aberration can be balanced.

[0051] In the present invention, the thickness TH of the cemented lens group composed of the fourth lens L4 and the fifth lens L5 and the total length TTL of the pinhole lens satisfy the following relationship: 2.0≤10*TH / TTL≤3. Satisfying the above relationship can miniaturize the lens, ensure processability, and balance the resolution of visible light and infrared light.

[0052] In summary, the pinhole lens of the present invention adopts a glass-plastic hybrid structure, thereby reducing production costs. The lens can achieve a front-end aperture of 3 mm, and the entrance pupil diameter reaches the limit of the front-end aperture while meeting the standard requirements of the 5M lens resolution. In addition, it can also achieve no defocusing in the temperature range of -40°C to 80°C, thereby overcoming the difficulty of plastic aspheric lenses that are prone to focus drift in high and low temperature environments due to their large expansion coefficient. In addition, the present invention optimizes the configuration of the positive and negative optical powers of each lens by gluing plastic lenses, so that the aberrations are effectively corrected. The lens has good tolerances for single components and assembly, thus having good manufacturability.

[0053] The pinhole lens of the present invention is described in detail below using four specific implementations. In the following implementations, S1, S2, ..., SN are used to represent the surfaces of each optical element, wherein the cemented surface of the cemented lens group is recorded as one surface. The aspheric surface formula is as follows:

[0054]

[0055] 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 They represent the fourth-order, sixth-order, eighth-order, twelfth-order, fourteenth-order, and sixteenth-order aspheric coefficients respectively.

[0056] Parameters of various implementations that specifically meet the above conditional formula are shown in Table 1 below:

[0057]

[0058] Table 1

[0059] First Implementation Method

[0060] See also Figure 1 In this embodiment, the aperture FNO=2.0; the refractive power of the third lens L3 is positive.

[0061] The relevant parameters of each lens in the pinhole lens of this embodiment include surface type, radius of curvature, thickness, refractive index of the material, and Abbe number, as shown in Table 2 below:

[0062] Surface number Surface type R-Value thickness Refractive Index Abbe number S1 Aspheric 2.472 0.431 1.54 56.2 S2 Aspheric 1.325 1.041 S3(STO) Spherical Infinity 0.651 S4 Spherical 6.065 1.280 1.46 91.2 S5 Spherical -4.63 0.605 S6 Aspheric -1.967 0.892 1.54 56 S7 Aspheric -1.984 0.1 S8 Aspheric 3.396 2.083 1.54 55.7 S9 Aspheric -8.775 0.41 1.66 20.4 S10 Aspheric 7.33 3.458 S11 Spherical Infinity 0.8 1.52 64.2 S12 Spherical Infinity 0.05 S13(IMA) Spherical Infinity

[0063] Table 2

[0064] The aspheric coefficients of each aspheric lens in this embodiment are shown in Table 3 below:

[0065]

[0066]

[0067] Table 3

[0068] Among them, K is the quadratic surface constant of the surface, and A, B, C, D, and E are the fourth-order, sixth-order, eighth-order, tenth-order, and twelfth-order aspheric coefficients respectively.

[0069] Combination Figures 2 to 4 It can be seen that the pinhole lens of this embodiment has a large field of view angle, a small front-end aperture, and can ensure a small overall volume. It can work normally at -40℃ ~ 80℃, has day and night confocal function, and the aperture can be increased to F2.0. At the same time, it has 5M clarity, which can achieve better shooting effects.

[0070] Second implementation method

[0071] See also Figure 5 In this embodiment, the aperture FNO=2.05; the refractive power of the third lens L3 is positive.

[0072] The relevant parameters of each lens in the pinhole lens of this embodiment include surface type, radius of curvature, thickness, refractive index of the material, and Abbe number, as shown in Table 4 below:

[0073]

[0074]

[0075] Table 4

[0076] The aspheric coefficients of each aspheric lens in this embodiment are shown in Table 5 below:

[0077]

[0078] Table 5

[0079] Among them, K is the quadratic surface constant of the surface, and A, B, C, D, and E are the fourth-order, sixth-order, eighth-order, tenth-order, and twelfth-order aspheric coefficients respectively.

[0080] Combination Figures 6 to 8 It can be seen that the pinhole lens of this embodiment has a large field of view angle, a small front-end aperture, and can ensure a small overall volume. It can work normally at -40℃ ~ 80℃, has day and night confocal function, and the aperture can be increased to F2.05. At the same time, it has 5M clarity, which can achieve better shooting effects.

[0081] The third implementation method

[0082] See also Fig. 9 In this embodiment, the aperture FNO=2.1; the refractive power of the third lens L3 is negative.

[0083] The relevant parameters of each lens in the pinhole lens of this embodiment include surface type, radius of curvature, thickness, refractive index of the material, and Abbe number, as shown in Table 6 below:

[0084] Surface number Surface type R-Value thickness Refractive Index Abbe number S1 Aspheric 2.557 0.409 1.53 56 S2 Aspheric 1.309 1.173 S3(STO) Spherical Infinity 0.1 S4 Spherical 14.057 1.491 1.50 81 S5 Spherical -2.767 0.423 S6 Aspheric -1.841 0.921 1.53 55.6 S7 Aspheric -2.232 0.1 S8 Aspheric 4.395 2.657 1.54 55.7 S9 Aspheric -4.435 0.151 S10 Aspheric -3.987 0.509 1.66 20.4 S11 Aspheric -353.80 3.637 S12 Spherical Infinity 0.8 1.52 64.2 S13 Spherical Infinity 0.05 S13(IMA) Spherical Infinity

[0085] Table 6

[0086] The aspheric coefficients of each aspheric lens in this embodiment are shown in Table 7 below:

[0087]

[0088] Table 7

[0089] Among them, K is the quadratic surface constant of the surface, and A, B, C, D, and E are the fourth-order, sixth-order, eighth-order, tenth-order, and twelfth-order aspheric coefficients respectively.

[0090] Combination Figures 10 to 12It can be seen that the pinhole lens of this embodiment has a large field of view angle, a small front-end aperture, and can ensure a small overall volume. It can work normally at -40℃ ~ 80℃, has day and night confocal function, and the aperture can be increased to F2.1. At the same time, it has 5M clarity, which can achieve better shooting effects.

[0091] Fourth Implementation Method

[0092] See also Fig.13 In this embodiment, the aperture FNO=2.2; the refractive power of the third lens L3 is negative.

[0093] The relevant parameters of each lens in the pinhole lens of this embodiment include surface type, radius of curvature, thickness, refractive index of the material, and Abbe number, as shown in Table 8 below:

[0094] Surface number Surface type R-Value thickness Refractive Index Abbe number S1 Aspheric 2.458 0.42 1.54 56.2 S2 Aspheric 1.261 1.095 S3(STO) Spherical Infinity 0.1 S4 Aspheric 36.586 1.441 1.51 82 S5 Aspheric -2.598 0.449 S6 Aspheric -1.792 0.985 1.54 56 S7 Aspheric -2.161 0.1 S8 Aspheric 4.167 2.843 1.54 55.7 S9 Aspheric -4.695 0.460 1.66 20.4 S10 Aspheric 72.018 3.661 S11 Spherical Infinity 0.8 1.52 64.2 S12 Spherical Infinity 0.05 S13(IMA) Spherical Infinity

[0095] Table 8

[0096] The aspheric coefficients of each aspheric lens in this embodiment are shown in Table 9 below:

[0097]

[0098]

[0099] Table 9

[0100] Among them, K is the quadratic surface constant of the surface, and A, B, C, D, and E are the fourth-order, sixth-order, eighth-order, tenth-order, and twelfth-order aspheric coefficients respectively.

[0101] Combination Figures 14 to 16 It can be seen that the pinhole lens of this embodiment has a large field of view angle, a small front-end aperture, and can ensure a small overall volume. It can work normally at -40℃ ~ 80℃, has day and night confocal function, and the aperture can be increased to F2.2. At the same time, it has 5M clarity, which can achieve better shooting effects.

[0102] The above is only one embodiment 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. A pinhole lens, comprising a first lens (L1), a second lens (L2), 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, characterized in that: The second lens (L2) is a convex-convex lens; The first lens (L1) and the fifth lens (L5) are negative power lenses, the second lens (L2) and the fourth lens (L4) are positive power lenses, and the third lens (L3) is a positive power or negative power lens; The focal length F1 of the cemented lens group composed of the fourth lens (L4) and the fifth lens (L5) and the focal length F of the pinhole lens satisfy the following relationship: 2.00≤F1 / F≤3.0; The focal length F2 of the second lens (L2) and the focal length F of the pinhole lens satisfy the following relationship: 1.0≤F2 / F≤1.

5.

2. The pinhole lens according to claim 1, characterized in that: The first lens (L1), the third lens (L3), the fourth lens (L4) and the fifth lens (L5) are plastic lenses; The second lens (L2) is a glass spherical lens or a glass aspherical lens.

3. The pinhole lens according to claim 1, characterized in that: The first lens (L1) is a convex-concave lens, the third lens (L3) is a concave-convex lens, the fourth lens (L4) is a convex-convex lens, and the fifth lens (L5) is a concave-concave lens or a concave-convex lens.

4. The pinhole lens according to claim 1, characterized in that: It also includes an aperture stop (STO), which is located between the first lens (L1) and the second lens (L2), or located on the image side surface of the first lens (L1) or the object side surface of the second lens (L2).

5. The pinhole lens according to claim 1, characterized in that: The fourth lens (L4) and the fifth lens (L5) are cemented together to form a cemented lens group with positive refractive power.

6. The pinhole lens according to any one of claims 1 to 5, characterized in that: The relative aperture FNO satisfies the following condition: FNO≤2.

2.

7. The pinhole lens according to any one of claims 1 to 5, characterized in that: The Abbe number V2 of the second lens (L2) satisfies the following condition: V2≥70.

8. The pinhole lens according to any one of claims 1 to 5, characterized in that: The field of view FOV meets the following conditions: FOV ≥ 90°.

9. The pinhole lens according to any one of claims 1 to 5, characterized in that: The thickness TH of the cemented lens group composed of the fourth lens (L4) and the fifth lens (L5) and the total length TTL of the pinhole lens satisfy the following relationship: 2.0≤10*TH / TTL≤3.

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