Achromatic prime lens

Abstract

An achromatic fixed-focus lens includes, from the object side to the image side, a first lens with negative optical power, an aperture stop, a second lens group with positive optical power, a third lens with positive optical power, and an imaging surface with an imaging element; the second lens group includes at least three glued lenses. The present invention achieves 4K ultra-high-definition resolution and can be used with image sensors with more than 12 million pixels, greatly improving the imaging quality, and can capture larger scene images, even if the image is enlarged, it is still clear; through a special lens matching method and surface design, and using temperature drift compensation technology, it can achieve infrared confocality from low temperature to high temperature, ensuring 24-hour clear imaging, and can capture high-contrast images even in haze environments; designing multiple glued lenses makes the image restoration extremely high, and there will be no obvious bending and distortion.

Description

Technical Field

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

[0002] The images presented by existing surveillance cameras are not clear enough during monitoring, especially for magnified images of details. Generally speaking, the sharper the image, the more difficult it is to design, and it is more difficult to show it in a high-resolution image. As the pixel of the camera increases, high resolution and high pixel often correspond to large size and high cost, the number of lenses will increase accordingly, and the overall structure of the lens will also become more complex. Therefore, at this stage, it is difficult for fixed-focus lenses for surveillance cameras to take into account many factors that affect lens quality, such as size, cost, imaging quality, infrared confocality, and temperature drift compensation. Summary of the invention

[0003] In view of the above-mentioned deficiencies in the prior art, the present invention proposes an achromatic fixed-focus lens, which can meet 4K ultra-high-definition resolution through a special optical lens combination and optimized surface shape, and at the same time has infrared confocal capability, adopts temperature drift compensation, and can still produce clear images at high temperatures of 80°C and low temperatures of -40°C.

[0004] The present invention is achieved through the following technical solutions:

[0005] The present invention comprises, from the object side to the image side, a first lens with negative optical power, an aperture stop, a second lens group with positive optical power, a third lens with positive optical power and an imaging surface with an imaging element.

[0006] The focal length of the first lens is in the range of (-15, -5) mm.

[0007] The second lens group comprises: at least three cemented lenses, wherein the cemented lens on the near image side is curved toward the image side, and the cemented lens on the near object side is curved toward the object side.

[0008] The overall focal length of the second lens group is in the range of (5, 15) mm.

[0009] The preferred combination of the cemented lenses is: the refractive index range is (1.48, 1.69) and the Abbe number range is (60, 85) or the refractive index range is (1.80, 1.97) and the Abbe number range is (17, 56).

[0010] The focal length of the third lens is in the range of (5, 15) mm.

[0011] Technical Effects

[0012] Compared with the prior art, the technical effects of the present invention include:

[0013] 1) 4K ultra-high-definition resolution: The present invention realizes 4K ultra-high-definition resolution and can be used with image sensors with more than 12 million pixels, which greatly improves the imaging quality and can capture larger scene images. Even if the image is enlarged, it is still clear;

[0014] 2) Full infrared confocal: The present invention achieves full infrared confocal from low temperature to high temperature through a special lens matching method and surface design, ensuring clear imaging 24 hours a day, and can capture high-contrast images even in foggy or dusty environments;

[0015] 3) Temperature drift compensation: The present invention takes into account that the refractive index and surface shape of the lens will change in extreme environments during design, and adopts temperature drift compensation to enable the present invention to achieve clear imaging in extreme environments;

[0016] 4) No distortion: The present invention uses multiple glued lenses to achieve a very high degree of image restoration without obvious bending and distortion. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a structural schematic diagram of Example 1;

[0018] Figure 2 d-line aberration diagrams of Example 1;

[0019] Figure 3 is the MTF diagram of Example 1;

[0020] Figure 4 It is a structural schematic diagram of Example 2;

[0021] Figure 5 d-line aberration diagrams of Example 2;

[0022] Figure 6 is the MTF diagram of Example 2;

[0023] In the figure: the first lens G1, the second lens group G2, the third lens G3, the aperture STP, the imaging surface IMG, the first cemented lens L1, the second cemented lens L2, the third cemented lens L3, the fourth cemented lens L4, the first cemented front lens L1-1, the first cemented rear lens L1-2, the second cemented front lens L2-1, the second cemented rear lens L2-2, the third cemented front lens L3-1, the third cemented rear lens L3-2, the fourth cemented front lens L4-1, and the fourth cemented rear lens L4-2. DETAILED DESCRIPTION

[0024] Example 1

[0025] like Figure 1As shown, in this embodiment, from the object side to the image side, there are a first lens G1 with negative optical power, an aperture stop STP, a second lens group G2 with positive optical power, a third lens G3 with positive optical power, and an imaging surface IMG with an imaging element.

[0026] The first lens G1 is a glass lens.

[0027] The second lens group G2 includes, from the object side to the image side, a first cemented lens L1 with negative focal power and a concave cemented surface facing the image side, an aperture STP, a second cemented lens L2 with positive focal power and a concave cemented surface facing the object side, and a third cemented lens L3 with negative focal power and a concave cemented surface facing the image side.

[0028] The first bonded lens L1 is composed of a first bonded front lens L1-1 with positive power and a first bonded back lens L1-2 with negative power.

[0029] The second bonded lens L2 is composed of a second bonded front lens L2-1 with positive power and a second bonded back lens L2-2 with negative power.

[0030] The third bonded lens L3 is composed of a third bonded front lens L3-1 with negative optical power and a third bonded back lens L3-2 with positive optical power.

[0031] The first glued front lens L1-1, the first glued rear lens L1-2, the second glued front lens L2-1, the second glued rear lens L2-2, the third glued front lens L3-1 and the third glued rear lens L3-2 are all glass spherical lenses.

[0032] The third lens G3 with positive refractive power is a glass lens with positive refractive power.

[0033] The imaging element includes: a charge coupled device (CCD) and a complementary metal oxide semiconductor (CMOS).

[0034] The imaging surface IMG is provided with a filter and a protective lens.

[0035] Various data values ​​of this embodiment are shown below.

[0036] The effective focal length of the lens is EFL=6.1 mm and the numerical aperture is FNO=2.

[0037] Table 1 Lens structure parameters of Example 1 (the unit of curvature radius and thickness is mm)

[0038]

[0039] The image side surface of the first bonded front lens L1-1 is the object side surface of the first bonded rear lens L1-2, the image side surface of the second bonded front lens L2-1 is the object side surface of the second bonded rear lens L2-2, and the image side surface of the third bonded front lens L3-1 is the object side surface of the third bonded rear lens L3-2.

[0040] like Figure 2 FIG. 2 is a diagram showing various aberrations of Example 1 with respect to the d-line, that is, when λ=587.56 nm.

[0041] like Figure 3 As shown, the aberrations corresponding to the meridional image plane and the sagittal image plane of Example 1.

[0042] Example 2

[0043] like Figure 4 As shown, compared with Example 1, this embodiment further includes a fourth cemented lens L4 with negative optical power and a cemented surface concave toward the image side, after the third cemented lens L3 of the second lens group G2.

[0044] The fourth bonded lens L4 is composed of a fourth bonded front lens L4-1 with negative optical power and a fourth bonded rear lens L4-2 with positive optical power.

[0045] The fourth bonded front lens L4-1 and the fourth bonded rear lens L4-2 are both glass spherical lenses.

[0046] Various data values ​​of this embodiment are shown below.

[0047] The effective focal length of the lens is EFL=5.9 mm, and the numerical aperture is FNO=1.8.

[0048] Table 2 Lens structure parameters of Example 2 (radius of curvature and thickness in mm)

[0049]

[0050]

[0051] The image side surface of the first bonded front lens L1-1 is the object side surface of the first bonded rear lens L1-2, the image side surface of the second bonded front lens L2-1 is the object side surface of the second bonded rear lens L2-2, the image side surface of the third bonded front lens L3-1 is the object side surface of the third bonded rear lens L3-2, and the image side surface of the fourth bonded front lens L4-1 is the object side surface of the fourth bonded rear lens L4-2.

[0052] like Figure 5 FIG. 2 is a diagram showing various aberrations of Example 2 with respect to the d-line, that is, when λ=587.56 nm.

[0053] like Figure 6 The aberrations corresponding to the meridional image plane and the sagittal image plane of Example 2 are shown.

[0054] Depend on Figure 2 and Figure 3 and Figure 5 and Figure 6 By comparison, it can be seen that the addition of a cemented lens in Example 2 makes the chromatic aberration better and the image sharper.

[0055] The above-mentioned specific implementation can be partially adjusted in different ways by those skilled in the art without departing from the principle and purpose of the present invention. The protection scope of the present invention shall be based on the claims and shall not be limited by the above-mentioned specific implementation. Each implementation scheme within its scope shall be subject to the constraints of the present invention.

Claims

1. An achromatic fixed-focus lens, characterized in that: The lens system includes, from the object side to the image side, a first lens with negative power, an aperture stop, a second lens group with positive power, a third lens with positive power, and an imaging surface with an imaging element; the second lens group includes at least three cemented lenses, wherein the cemented lens near the image side is bent toward the image side, and the cemented lens near the object side is bent toward the object side; Use any of the following structures to implement it: ① The object side of the first lens is a spherical surface with a curvature radius of 21.55mm, the thickness of the first lens is 1.5mm, the refractive index is 1.81, and the Abbe number is 40.

2. The image side of the first lens is a spherical surface with a curvature radius of 5.47mm. The distance from the image side of the first lens to the object side of the first cemented lens is 3.93mm. The object side of the first cemented lens is a spherical surface with a curvature radius of 8.51mm. The thickness of the first cemented front lens is 0.76mm, the refractive index is 1.53, and the Abbe number is 56. The cemented surface of the first cemented lens is a spherical surface with a curvature radius of 24.88mm. The distance from the cemented surface of the cemented lens to the image side surface is 0.6mm, the refractive index is 1.45, and the Abbe number is 89. The image side surface of the first cemented lens is a spherical surface with a curvature radius of 4.36mm. The distance from the image side surface of the first cemented lens to the aperture is 2.94mm, the aperture is a spherical surface with an infinite curvature radius. The distance from the aperture to the object side surface of the second cemented lens is 0.01mm. The object side surface of the second cemented lens is a spherical surface with a curvature radius of 8.85mm. The thickness of the second cemented front lens is 0.9mm, the refractive index is 1.87, the Abbe number is 19.8, and the cemented surface of the second cemented lens is a spherical surface. The radius of curvature is -3.02mm, the distance from the bonding surface of the second bonded lens to the image side is 0.5mm, the refractive index is 1.45, the Abbe number is 89.5, the image side of the second bonded lens is a spherical surface, and the radius of curvature is -19.14mm, the distance from the image side of the second bonded lens to the object side of the third bonded lens is 1.93mm, the object side of the third bonded lens is a spherical surface, and the radius of curvature is -4.43mm, the thickness of the third bonded front lens is 0.14mm, the refractive index is 1.77, the Abbe number is 49.5, the bonding surface of the third bonded lens is a spherical surface, and the radius of curvature is 4.78 mm, the distance from the cemented surface of the third cemented lens to the image side surface is 0.98 mm, the refractive index is 1.5, the Abbe number is 91.8, the image side surface of the third cemented lens is a spherical surface with a curvature radius of -4.98 mm, the distance from the image side surface of the third cemented lens to the object side surface of the third lens is 0.1 mm, the object side surface of the third lens is a spherical surface with a curvature radius of 6.3 mm, the thickness of the third lens is 1.75 mm, the refractive index is 1.63, the Abbe number is 56, the image side surface of the third lens is a spherical surface with a curvature radius of -8.77 mm, and the distance from the image side surface of the third lens to the imaging plane is 2.06 mm; ②The object side of the first lens is a spherical surface with a curvature radius of 17.55mm, the thickness of the first lens is 2.1mm, the refractive index is 1.81, and the Abbe number is 40.

2. The image side of the first lens is a spherical surface with a curvature radius of 7.54mm. The distance from the image side of the first lens to the object side of the first cemented lens is 3.93mm. The object side of the first cemented lens is a spherical surface with a curvature radius of 10.75mm. The thickness of the first cemented front lens is 1.25mm, the refractive index is 1.53, and the Abbe number is 56. The cemented surface of the first cemented lens is a spherical surface with a curvature radius of 18.75mm. The distance from the cemented surface of the first cemented lens to the image side is 1.34mm, the refractive index is 1.45, and the Abbe number is 89. The image side surface is a spherical surface with a radius of curvature of 6.54mm. The distance from the image side surface of the first cemented lens to the aperture is 2.51mm. The aperture is a spherical surface with an infinite radius of curvature. The distance from the aperture to the object side surface of the second cemented lens is 0.01mm. The object side surface of the second cemented lens is a spherical surface with a radius of curvature of 12.65mm. The thickness of the second cemented front lens is 1.29mm, the refractive index is 1.87, and the Abbe number is 19.

8. The cemented surface of the second cemented lens is a spherical surface with a radius of curvature of -4.31mm. The distance from the cemented surface of the second cemented lens to the image side surface is 0.5mm, the refractive index is 1.45, and the Abbe number is 89.

5. The image side surface of the second cemented lens is a spherical surface with a radius of curvature of -27.3 ... The distance from the image side surface to the object side surface of the third cemented lens is 2.76mm, the object side surface of the third cemented lens is a spherical surface with a curvature radius of -6.33mm, the thickness of the third cemented front lens is 0.5mm, the refractive index is 1.77, and the Abbe number is 49.

5. The cemented surface of the third cemented lens is a spherical surface with a curvature radius of 6.82mm. The distance from the cemented surface of the third cemented lens to the image side surface is 1.41mm, the refractive index is 1.5, and the Abbe number is 91.

8. The image side surface of the third cemented lens is a spherical surface with a curvature radius of -7.12mm. The distance from the image side surface of the third cemented lens to the object side surface of the fourth cemented lens is 1mm, the object side surface of the fourth cemented lens is a spherical surface with a curvature radius of -7.5mm, and the thickness of the fourth cemented front lens is 0.6mm, the refractive index is 1.77, the Abbe number is 49.5, the cemented surface of the fourth cemented lens is a spherical surface, the radius of curvature is 7.58mm, the distance from the cemented surface of the fourth cemented lens to the image side surface is 1.6mm, the refractive index is 1.5, the Abbe number is 91.8, the image side surface of the fourth cemented lens is a spherical surface, the radius of curvature is -6.8mm, the distance from the image side surface of the fourth cemented lens to the object side surface of the third lens is 0.1mm, the object side surface of the third lens is a spherical surface, the radius of curvature is 6.3mm, the thickness of the third lens is 1.75mm, the refractive index is 1.63, the Abbe number is 56, the image side surface of the third lens is a spherical surface, the radius of curvature is -8.77mm, and the distance from the image side surface of the third lens to the imaging plane is 2.06mm; The first glued front lens, the first glued back lens, the second glued front lens, the second glued back lens, the third glued front lens and the third glued back lens are all glass spherical lenses.

2. The achromatic fixed-focus lens according to claim 1, characterized in that: The ratio of the focal length of the first lens to the overall focal length of the fixed-focus lens satisfies (-15, -5) mm.

3. The achromatic fixed-focus lens according to claim 1, characterized in that: The ratio of the overall focal length of the second lens group to the overall focal length of the fixed-focus lens satisfies (5, 15) mm.

4. The achromatic fixed-focus lens according to claim 1, characterized in that: The ratio of the focal length of the third lens to the overall focal length of the fixed-focus lens satisfies (5, 15) mm.

5. The achromatic fixed-focus lens according to claim 1, characterized in that: The combination of the cemented lenses is: the refractive index ranges from (1.48, 1.69) and the Abbe number ranges from (60, 85) or the refractive index ranges from (1.80, 1.97) and the Abbe number ranges from (17, 56).

6. The achromatic fixed-focus lens according to claim 1, characterized in that: A filter and a protective lens for filtering out stray light are arranged on the imaging surface.

7. The achromatic fixed-focus lens according to claim 1, characterized in that: The imaging element comprises: a charge coupled device and a complementary metal oxide semiconductor.

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