High-performance short-focus lens

Abstract

The invention provides a high-performance short-focal-length lens, which is used for solving the technical problems of high processing requirements, high processing, detection and adjustment difficulty of a visible light high-order aspheric surface, poor manufacturability and poor economical efficiency of the existing short-focal-length lens. The invention provides a high-performance short-focus lens. The high-performance short-focus lens comprises a first lens, an aperture diaphragm, a second lens, a third lens and a glued lens group which are coaxially arranged in sequence, the glued lens group comprises a fourth lens and a fifth lens which are glued; the first lens, the second lens, the third lens, the fourth lens and the fifth lens are spherical mirrors; through the structure of the five spherical mirrors and the focal power design, short-focus imaging is realized. And the five spherical mirrors are only made of two optical materials of ZF7 and ZK6, so that the optical system has relatively good manufacturability and economical efficiency, is good in imaging quality, large in view field, moderate in distortion and compact in structure, and completely meets the use requirements in the fields of commercial monitoring, digital imaging and the like.

Description

Technical Field

[0001] The present invention relates to an optical lens, and particularly to a high-performance short-focus lens. Background Art

[0002] At present, short-focus lenses are widely used in commercial monitoring, digital photography and other fields. In addition to requiring a large field of view (suitable for 1 / 4-inch detectors), a large relative aperture (F2.8), good imaging quality (MTF≥0.4, spatial frequency 30 lp / mm), and moderate distortion (<3% within 0.5 field of view), they also need to have good processability and excellent economy.

[0003] Existing short-focus lenses are mainly realized by combining multiple groups of multi-material lens groups. Among them, each lens group uses multiple high-order aspherical lenses to correct aberrations, thereby reducing the number of lens groups and obtaining better imaging quality. However, this type of short-focus lens has high processing requirements, and the processing, detection and alignment of high-order visible aspherical surfaces are difficult, with poor processability and poor economy. Summary of the Invention

[0004] The purpose of the present invention is to provide a high-performance short-focus lens for the technical problems existing in existing short-focus lenses, such as high processing requirements, difficult processing, detection and alignment of high-order visible aspherical surfaces, poor processability, and poor economy.

[0005] In order to achieve the above purpose, the technical solution provided by the present invention is as follows:

[0006] A high-performance short-focus lens, characterized in that it includes a first lens, an aperture stop, a second lens, a third lens, and a cemented lens group arranged coaxially in sequence;

[0007] The cemented lens group includes a fourth lens and a fifth lens cemented coaxially in sequence;

[0008] The first lens, the second lens, the third lens, the fourth lens, and the fifth lens are all spherical lenses;

[0009] The first lens is a meniscus lens with a negative optical power;

[0010] The second lens is a biconvex lens with a positive optical power;

[0011] The third lens is a convex-concave lens with a positive optical power;

[0012] The second lens is a meniscus lens with a negative optical power;

[0013] The fifth lens is a biconvex lens with a positive optical power;

[0014] The materials of the first lens, the second lens, and the fourth lens are all ZF7, and the materials of the third lens and the fifth lens are both ZK6.

[0015] Further, the aperture stop is disposed on the front surface of the second lens.

[0016] Further, the thickness of the first lens is 0.33 mm, and the distance between the first lens and the aperture stop is 0.15 mm;

[0017] The thickness of the second lens is 0.4 mm, and the distance between the second lens and the third lens is 0.3 mm;

[0018] The thickness of the third lens is 0.63 mm, and the distance between the third lens and the fourth lens is 0.02 mm;

[0019] The thickness of the fourth lens is 0.4 mm, the thickness of the fifth lens is 1.3 mm, and the distance between the fifth lens and the image plane is 1.7 mm.

[0020] Further, the radius of curvature of the front surface of the first lens is 1.449 mm, and the radius of curvature of the rear surface is 0.694 mm;

[0021] The radius of curvature of the front surface of the second lens is 3.1224 mm, and the radius of curvature of the rear surface is -6.6369 mm;

[0022] The radius of curvature of the front surface of the third lens is -2.1436 mm, and the radius of curvature of the rear surface is -1.0 mm;

[0023] The radius of curvature of the front surface of the fourth lens is 7.1963 mm, and the radius of curvature of the rear surface is 1.5734 mm;

[0024] The radius of curvature of the front surface of the fifth lens is 1.5734 mm, and the radius of curvature of the rear surface is -3.4437 mm.

[0025] Further, the target focal length of the short focal length lens formed by the first lens, the aperture stop, the second lens, the third lens, and the cemented lens group is 2.5 mm, the F number is F2.8, the imaging range is Φ4.3 mm, and the total system length is 5.23 mm.

[0026] The beneficial effects of the present invention compared with the prior art are as follows:

[0027] 1. The high-performance short-focus lens provided by the present invention is simpler in structure compared with the existing short-focus lens based on high-order aspherical lenses. It only includes five spherical mirrors, namely a first lens, a second lens, a third lens, a fourth lens, and a fifth lens. Short-focus imaging is achieved through the structural design and optical power of each spherical mirror. Moreover, only two optical materials, ZF7 and ZK6, are used for the five spherical mirrors, which has good processability and economy.

[0028] 2. For the high-performance short-focus lens provided by the present invention, when the spatial frequency is 30 lp / mm, MTF ≥ 0.4, the distortion is ≤ 3% within 0.5 field of view and ≤ 8% in the full field of view. It has good imaging quality, a large field of view, moderate distortion, and a compact structure, fully meeting the usage requirements in fields such as commercial monitoring and digital imaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic optical path diagram of an embodiment of the high-performance short-focus lens of the present invention;

[0030] Figure 2 It is an MTF curve graph of an embodiment of the high-performance short-focus lens of the present invention under different fields of view.

[0031] Figure 3 It is a distortion curve graph of an embodiment of the high-performance short-focus lens of the present invention under different fields of view.

[0032] The specific reference numerals are as follows:

[0033] 1. First lens; 2. Aperture stop; 3. Second lens; 4. Third lens; 5. Fourth lens; 6. Fifth lens; 7. Image plane. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0034] To make the advantages and features of the present invention clearer, the following further describes the present invention in detail with reference to the accompanying drawings and specific embodiments.

[0035] As Figure 1 shown, a high-performance short-focus lens adopts a four-group five-element structure, and the lens surface shapes are all spherical. Specifically, the high-performance short-focus lens includes a first lens 1, an aperture stop 2, a second lens 3, a third lens 4, and a cemented lens group arranged coaxially in sequence.

[0036] The first lens 1 is composed of a single meniscus lens made of ZF7 (heavy flint glass) with a negative optical power, and is mainly used for correcting most of the axial spherical aberration, chromatic aberration, and off-axis aberrations (coma, astigmatism, field curvature, and distortion). The aperture stop 2 is arranged between the first lens 1 and the second lens 3 for dimming. The second lens 3 is composed of a single biconvex lens made of ZF7 with a positive optical power, and is mainly used for correcting some of the remaining off-axis aberrations (astigmatism, field curvature, and distortion) and assisting in correcting the spherical aberration and chromatic aberration of the axial aberration. The third lens 4 is composed of a single meniscus-convex lens made of ZK6 (heavy crown glass) with a positive optical power, and is mainly used for assisting in correcting most of the remaining axial spherical aberration, chromatic aberration, and off-axis aberrations (coma, astigmatism, field curvature, and distortion).

[0037] The cemented lens group includes a fourth lens 5 and a fifth lens 6 arranged coaxially. The front surface of the fourth lens 5 is arranged close to the third lens 4, and the rear surface is cemented to the front surface of the fifth lens 6. The fourth lens 5 is a meniscus lens made of ZF7 with a negative optical power, and the fifth lens 6 is a biconvex lens made of ZK6 with a positive optical power. The fourth lens 5 and the fifth lens 6 work together mainly for correcting all the remaining off-axis aberrations (coma, astigmatism, field curvature, and distortion) and assisting in correcting the spherical aberration and chromatic aberration of the axial aberration to achieve system aberration balance, and finally form an image at the image plane 7.

[0038] In this embodiment, the aperture stop 2 is arranged on the front surface of the second lens 3. The target focal length of the high-performance short focal length lens is 2.5 mm, the F-number is F2.8, the imaging range is Φ4.3 mm, the total system length is 5.23 mm, the field of view can reach ±43.23°, and the relative aperture D / f′ = 2.8, which can be used for detectors of 1 / 4 inch and below. The optical element parameters of the five lenses are shown in Table 1:

[0039] Table 1 Optical Element Parameter Table

[0040]

[0041] The radius of curvature of the front surface of the first lens 1 is 1.449 mm, the radius of curvature of the rear surface is 0.694 mm, the thickness is 0.33 mm, and the distance between the first lens 1 and the aperture stop 2 is 0.15 mm; the radius of curvature of the front surface of the second lens 3 is 3.1224 mm, the radius of curvature of the rear surface is -6.6369 mm, the thickness is 0.4 mm, and the distance between the second lens 3 and the third lens 4 is 0.3 mm; the radius of curvature of the front surface of the third lens 4 is -2.1436 mm, the radius of curvature of the rear surface is -1.0 mm, the thickness is 0.63 mm, and the distance between the third lens 4 and the fourth lens 5 is 0.02 mm; the radius of curvature of the front surface of the fourth lens 5 is 7.1963 mm, the radius of curvature of the rear surface is 1.5734, the thickness is 0.4 mm; the radius of curvature of the front surface of the fifth lens 6 is 1.5734, the radius of curvature of the rear surface is -3.4437 mm, the thickness is 1.3 mm, and the distance between the fifth lens 6 and the image plane 7 is 1.7 mm. Among them, the front surface of each lens refers to the surface that receives the light beam, and the rear surface is the opposite surface of the front surface.

[0042] As Figure 2 、 Figure 3 shown, they are respectively the modulation transfer function (MTF) curve graph and the distortion curve graph of the high-performance short focal length lens of this embodiment at different fields of view. Figure 2 In it, the abscissa represents the spatial frequency (unit: lp / mm), the ordinate represents the modulation transfer function. The two blue curves respectively represent the MTF curves of the meridional plane and the sagittal plane at a field of view of 0.00 degrees. The two green curves respectively represent the MTF curves of the meridional plane and the sagittal plane at a field of view of 21.62 degrees. The two red curves respectively represent the MTF curves of the meridional plane and the sagittal plane at a field of view of 30.69 degrees. The two yellow curves respectively represent the MTF curves of the meridional plane and the sagittal plane at a field of view of 37.44 degrees. The two pink curves respectively represent the MTF curves of the meridional plane and the sagittal plane at a field of view of 43.23 degrees. Figure 3 In it, the abscissa represents the percentage, the ordinate represents the distortion. The blue curve, the green curve, the red curve, and the yellow curve respectively represent the distortion at a field of view of 0.00 degrees, 21.62 degrees, 30.69 degrees, and 37.44 degrees. It can be seen that for the high-performance short focal length lens of this embodiment, when the spatial frequency is 30 lp / mm, MTF≥0.4, the distortion is ≤3% within 0.5 field of view and ≤8% in the full field of view. That is, the four-group and five-element structure of the present invention fully meets the performance requirements of the high-performance short focal length lens.

[0043] Compared with the prior art, the structure of the present invention is simple, only includes five spherical lenses, and only two optical materials, ZF7 and ZK6, are used for the five spherical lenses. It has good processability and economy, and has good imaging quality, large field of view, moderate distortion, and compact structure, fully meeting the use requirements in the fields of commercial monitoring and digital imaging, etc.

[0044] As described above, it is only used to illustrate the technical solution of the present invention, rather than to limit it. For those of ordinary skill in the art, the specific technical solution recorded in the above embodiments can be modified, or some of the technical features can be equivalently replaced, and these modifications or replacements do not make the essence of the corresponding technical solution deviate from the scope of the technical solution protected by the present invention.

Claims

1. A high performance short focal length lens, characterized in that: It comprises a first lens (1), an aperture stop (2), a second lens (3), a third lens (4) and a cemented lens group which are coaxially arranged in sequence; The cemented lens group comprises a fourth lens (5) and a fifth lens (6) which are coaxially cemented in sequence; The first lens (1), the second lens (3), the third lens (4), the fourth lens (5) and the fifth lens (6) are all spherical lenses; The first lens (1) is a meniscus lens with negative optical power; The second lens (3) is a biconvex lens with positive optical power; The third lens (4) is a concave-convex lens with positive optical power; The second lens (3) is a meniscus lens, and its optical power is negative; The fifth lens (6) is a biconvex lens with positive optical power; The materials of the first lens (1), the second lens (3) and the fourth lens (5) are all ZF7, and the materials of the third lens (4) and the fifth lens (6) are all ZK6.

2. A high performance short focal length lens according to claim 1, characterized in that: The aperture stop (2) is arranged on the front surface of the second lens (3).

3. A high performance short focal length lens according to claim 1 or 2, characterized in that: The thickness of the first lens (1) is 0.33 mm, and the distance between the first lens (1) and the aperture stop (2) is 0.15 mm; The thickness of the second lens (3) is 0.4 mm, and the distance between the second lens (3) and the third lens (4) is 0.3 mm; The thickness of the third lens (4) is 0.63 mm, and the distance between the third lens (4) and the fourth lens (5) is 0.02 mm; The thickness of the fourth lens (5) is 0.4 mm, the thickness of the fifth lens (6) is 1.3 mm, and the distance between the fifth lens (6) and the image plane (7) is 1.7 mm.

4. A high performance short focal length lens according to claim 3, characterized in that: The curvature radius of the front surface of the first lens (1) is 1.449 mm, and the curvature radius of the rear surface is 0.694 mm; The curvature radius of the front surface of the second lens (3) is 3.1224 mm, and the curvature radius of the rear surface is -6.6369 mm; The radius of curvature of the front surface of the third lens (4) is -2.1436 mm, and the radius of curvature of the rear surface is -1.0 mm; The curvature radius of the front surface of the fourth lens (5) is 7.1963 mm, and the curvature radius of the rear surface is 1.5734 mm; The curvature radius of the front surface of the fifth lens (6) is 1.5734 mm, and the curvature radius of the rear surface is -3.4437 mm.

5. A high performance short focal length lens according to claim 4, characterized in that: The short focal length lens composed of the first lens (1), the aperture stop (2), the second lens (3), the third lens (4) and the cemented lens group has a target focal length of 2.5 mm, an F number of F2.8, an imaging range of Φ4.3 mm and a total length of 5.23 mm.

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