A glass aspheric wide-spectrum imaging lens

Abstract

The application discloses a glass aspheric wide-spectrum imaging lens to solve the imaging requirement of a wide waveband. The lens comprises four glass aspheric lenses and a protective glass coaxially arranged in sequence from an object side to an image side, wherein the first lens is a positive lens; the second lens is a negative lens; the third lens is a positive lens; and the fourth lens is a negative lens. The total length of the lens is 5.98 mm, the F# is 3.11, and the lens satisfies the requirement of the axial aberration being less than 50 microns in the confocal imaging in the waveband range of 340 nm-1550 nm. The lens system effectively corrects various aberrations in the waveband range of 340 nm-1550 nm by using the mode of matching the high-Abbe-number positive lens with the low-Abbe-number negative lens.

Description

Technical Field

[0001] This invention relates to the field of mobile phone lens imaging, and more particularly to a glass aspherical broadband mobile phone imaging lens system. Background Technology

[0002] With the widespread adoption and development of smartphones, in addition to the basic function of distortion-free high-definition imaging, people's pursuit and requirements for mobile phone lenses are constantly increasing, and they are beginning to try out new functions of mobile phone lenses. Mobile phone lenses that can simultaneously image in the ultraviolet, visible light, and near-infrared bands are often favored by lens enthusiasts. In recent years, various plastic-based mobile phone lenses have appeared on the market, but their imaging range is limited to the visible light band. Therefore, they have obvious shortcomings, one of which is listed below:

[0003] 1. A search of published patents reveals Chinese patent application number 201610866753.X, entitled "A Mobile Phone Imaging Lens," filed on September 30, 2016. This patent describes the lens as "comprising, sequentially arranged along the optical axis from the object end to the image end: a first positive lens with a first refractive index, a second negative lens with a second refractive index, a third positive lens with a third refractive index, and a fourth negative lens with a fourth refractive index. All lenses are aspherical resin lenses. The refractive indices of the first, third, and fourth positive lenses are all less than or equal to 1.60, and the Abbe values ​​are greater than or equal to 40. The refractive index of the second negative lens is greater than or equal to 1.60, and the Abbe value is less than or equal to 40." Furthermore, according to the patent description, the lens only corrects aberrations within the 470nm-650nm range. The shortcomings of the lens mentioned in the patent are that it uses plastic as the lens material and only corrects various aberrations in the extremely narrow visible light band of 470nm-650nm, making it impossible to achieve imaging in a wider visible light band as well as ultraviolet and near-infrared bands. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a glass aspherical wide-spectrum imaging lens that enables image sensors with a single pixel size of 5μm×5μm to achieve confocal imaging in a wide spectral band of 340nm-1550nm.

[0005] A glass aspherical broadband imaging lens includes four lenses and a protective glass G1 arranged sequentially along the optical axis from the subject to the image plane IMA. The four lenses are, in order: first lens L1, second lens L2, third lens L3 and fourth lens L4.

[0006] Preferably, the object-end optical surface and image-end optical surface of the four lenses arranged in sequence are both aspherical surfaces, namely S11, S12, S21, S22, S31, S32, S41 and S42 respectively, and the aspherical surfaces satisfy the following surface shape equation in the xoz plane of the o-xyz coordinate system:

[0007]

[0008] Where c represents the curvature at the vertex of the aspherical surface of the lens, x represents the x-coordinate of each point on the aspherical surface of the lens, z is the sag corresponding to the x-coordinate of each point on the aspherical surface of the lens, k is the coefficient of the quadratic conic section, and a i These are the coefficients of higher-order terms, all of which are even-order, with a maximum order of 8. The aspherical surface is radially symmetric about the z-axis.

[0009] Preferably, the lens material is glass.

[0010] Preferably, the refractive index of the first lens L1 is less than 1.50 and the Abbe number is greater than 88; the material of the third lens L3 is the same as that of the first lens L1.

[0011] Preferably, the materials of the first lens, the second lens, and the fourth lens have requirements for transmittance. When the material thickness is within the range of 25mm, the transmittance of the materials is greater than 0.7 when electromagnetic waves in the 340nm-1550nm band irradiate the materials.

[0012] Preferably, the transmittance of the protective glass material is greater than 0.1 in the 340nm-1550nm wavelength range within a thickness of 25mm.

[0013] Preferably, the distance between the center of the object optical surface of the first lens L1 and the center of the image plane IMA is less than 6.5 mm.

[0014] Preferably, the center thickness d1 of the first lens L1 satisfies: 0.8mm < d1 < 1.2mm; the center thickness d2 of the second lens L2 satisfies: 0.35mm < d2 < 0.45mm; the center thickness d3 of the third lens L3 satisfies: 1.1mm < d3 < 1.4mm; and the center thickness d4 of the fourth lens L4 satisfies: 0.5mm < d4 < 0.8mm.

[0015] Preferably, for the focal length f1 of the first lens L1, 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 f of the entire lens group, the following relationships are satisfied: 3.5 mm < f < 4.5 mm, 0.6 < f1 / f < 0.8, -0.6 < f2 / f < -0.4, 0.4 < f3 / f < 0.5, -0.7 < f4 / f < -0.6. Preferably, the full field angle of the lens is greater than or equal to 60°, and F# satisfies: 2.5 < F# < 3.5.

[0016] Preferably, the lens can correct aberrations in the wavelength range of 340 nm - 1550 nm and satisfy the confocal condition, that is, the axial aberration is less than 50 μm, enabling clear imaging.

[0017] The protective glass includes an object-side optical surface S51 and an image-side optical surface S52, and both optical surfaces are flat surfaces.

[0018] Compared with the prior art, the present invention has the following advantages: By using a combination of a high Abbe number positive lens and a low Abbe number negative lens, various aberrations of the lens system are effectively corrected within the wavelength range of 340 nm - 1550 nm. Finally, the lens system satisfies a chromatic focal shift less than 20 μm and an axial aberration less than 50 μm, thereby achieving confocal imaging within the wavelength range of 340 nm - 1550 nm. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a structural diagram of the optical imaging lens system of Embodiment 1 of the present invention.

[0020] Figure 2 It is the image-side spot diagram of the optical imaging lens system of Embodiment 1 of the present invention.

[0021] Figure 3 It is the chromatic light color MTF curve graph of the optical imaging lens system of Embodiment 1 of the present invention.

[0022] Figure 4 It is the F-Tan(Theta) distortion curve of the optical imaging lens system of Embodiment 1 of the present invention.

[0023] Figure 5 It is the lateral chromatic aberration curve of the optical imaging lens system of Embodiment 1 of the present invention.

[0024] Figure 6 It is the axial aberration curve of the optical imaging lens system of Embodiment 1 of the present invention.

[0025] Figure 7 It is the focal shift curve of the optical imaging lens system of Embodiment 1 of the present invention.

[0026] Figure 8This is the field curvature curve of the optical imaging lens system in Embodiment 1 of the present invention. Detailed Implementation

[0027] The present invention will be further explained and described below with reference to the accompanying drawings and embodiments.

[0028] like Figure 1 The diagram illustrates the structure of a glass aspherical broadband imaging lens provided by this invention. The glass aspherical broadband imaging lens comprises, along the optical axis, a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, a protective glass G1, and an image plane IMA. Specifically, the first lens L1 is a positive glass lens, the second lens L2 is a negative glass lens, the third lens L3 is a positive glass lens, and the fourth lens L4 is a negative glass lens. During imaging, light passes through the first lens L1, then the second lens L2, and then sequentially through the third lens L3, the fourth lens L4, and the protective glass G1, ultimately forming an image on the image plane IMA.

[0029] The first lens L1 has a refractive index of less than 1.50 and an Abbe number greater than 88. The third lens L3 is made of the same material as the first lens L1. The total length of the lens is 5.98 mm, which is the distance from the center of the optical plane at the object end of the first lens to the image plane IMA, less than 6.5 mm. The full field of view is not less than 60°, the focal shift is less than 20 μm, and the axial aberration is less than 50 μm. It can perform optical imaging in an extremely wide wavelength range of 340 nm to 1550 nm.

[0030] Example 1

[0031] This embodiment provides a glass aspherical broadband imaging lens with a total length of 5.98 mm, a focal length of 4.06 μm, and a full field of view of not less than 60°. The first lens L1 and the third lens L3 are both made of H-FK71 with an F# of 3.11. It corrects various aberrations in the 340nm-1550nm wavelength range, with a chromatic focus shift of 7.6 μm and an axial aberration of 29.0 μm. The specific parameters of each lens and optical surface are detailed in Table 1.

[0032] Table 1

[0033]

[0034]

[0035] In Table 1, OBJ represents the object plane of the all-glass aspherical broadband imaging lens. Stop represents the lens aperture, located at the S11 plane. * in the table indicates that the surface is aspherical. The aspherical surfaces of the four lenses satisfy the following surface shape equations in the xoz plane of the o-xyz coordinate system:

[0036]

[0037] Where c represents the curvature at the vertex of the aspherical surface of the lens, x represents the x-coordinate of each point on the aspherical surface of the lens, z is the sag corresponding to the x-coordinate of each point on the aspherical surface of the lens, k is the coefficient of the quadratic conic section, and a i These are the coefficients of higher-order terms, all of which are even-order, with a maximum order of 8. The aspherical surface is radially symmetric about the z-axis. The coefficients of the quadratic conic sections and the coefficients of higher-order terms for each aspherical surface are shown in Table 2.

[0038] Table 2

[0039] k <![CDATA[a1]]> <![CDATA[a2]]> <![CDATA[a3]]> <![CDATA[a4]]> S11 -5.287 0 -0.013 8.404-E3 -0.093 S12 -5.681 0 -0.136 -0.128 0.101 S21 -2.856 0 -0.149 0.038 0.053 S22 -5.261 0 0.012 0.015 -8.489E-3 S31 -7.115 0 -7.355E-3 7.862E-3 -3.730E-3 S32 -1.408 0 0.029 7.420E-3 -1.281E-3 S41 -0.839 0 0.020 9.820E-3 -1.203E-3 S42 -1.757 0 -0.025 9.175E-3 -1.143E-3

[0040] Example 2

[0041] This embodiment provides a glass aspherical broadband imaging lens with a total length of 5.98 mm, a focal length of 3.94 mm, and a full field of view of not less than 60°. The first lens L1 and the third lens L3 are both H-FK95N with an F# of 3.01. It corrects various aberrations in the 340nm-1550nm wavelength range, with a chromatic focus shift of 7.6 μm and an axial aberration of 32.0 μm. The specific parameters of each lens and optical surface are detailed in Table 3.

[0042] Table 3

[0043]

[0044]

[0045] In Table 3, OBJ represents the object plane of the all-glass aspherical broadband imaging lens. Stop represents the lens aperture, which is located at the S11 plane. * in the table indicates that the surface is aspherical. The aspherical surfaces of the four lenses satisfy the following surface shape equations in the xoz plane of the o-xyz coordinate system:

[0046]

[0047] Where c represents the curvature at the vertex of the aspherical surface of the lens, x represents the x-coordinate of each point on the aspherical surface of the lens, z is the sag corresponding to the x-coordinate of each point on the aspherical surface of the lens, k is the coefficient of the quadratic conic section, and a i These are the coefficients of higher-order terms, all of which are even-order, with a maximum order of 8. The aspherical surface is radially symmetric about the z-axis.

[0048] The aspherical coefficients of each lens are detailed in Table 4.

[0049] Table 4

[0050]

[0051] Example 3

[0052] This embodiment provides a glass aspherical broadband imaging lens with a total length of 5.98 mm, a focal length of 3.93 μm, and a full field of view of not less than 60°. The first lens L1 and the third lens L3 are both D-FK95 with an F# of 3.01. It corrects various aberrations in the 340 nm-1550 nm wavelength range, with a chromatic focus shift of 7.2 μm and an axial aberration of 32.4 μm. The specific parameters of each lens and optical surface are detailed in Table 5.

[0053] Table 5

[0054]

[0055] In Table 5, OBJ represents the object plane of the all-glass aspherical broadband imaging lens. Stop represents the lens aperture, located at the S11 plane. * in the table indicates that the surface is aspherical. The aspherical surfaces of the four lenses satisfy the following surface shape equations in the xoz plane of the o-xyz coordinate system:

[0056]

[0057] Where c represents the curvature at the vertex of the aspherical surface of the lens, x represents the x-coordinate of each point on the aspherical surface of the lens, z is the sag corresponding to the x-coordinate of each point on the aspherical surface of the lens, k is the coefficient of the quadratic conic section, and a i These are the coefficients of higher-order terms, all of which are even-order, with a maximum order of 8. The aspherical surface is radially symmetric about the z-axis.

[0058] For details of the aspherical coefficients of each lens, please refer to Table 6.

[0059]

[0060]

[0061] Since the parameter curves of the lens assemblies in the above three embodiments are similar across the various fields of view of the image plane IMA, the performance parameters of the lens are described here using Embodiment 1. These performance parameters include: dot plot, polychromatic color MTF curve, transverse chromatic aberration curve, field curvature curve, F-Tan (Theta) distortion curve, axial aberration curve, and focus shift curve, as detailed below:

[0062] Figure 2 This is a dot plot of the IMA (Integrated Motion Area) of the lens image plane. The figure shows the dot plots for the center (0.00deg), 15-degree (15.00deg), 25-degree (25.00deg), and edge (30.00deg) fields of view. The Airy disk radius is 3.575μm. The root mean square radius (RMS Radius) of the diffuse spots in all fields of view is comparable to the Airy disk radius of the lens, indicating that the lens is close to the diffraction limit.

[0063] Figure 3 This is the MTF curve of the polychromatic light from the lens. This lens is designed for IMA image sensors with individual pixel sizes greater than 5 μm × 5 μm. The pixel size of the image sensor requires the lens's polychromatic light MTF curve to be greater than 0.2 at a spatial frequency of 100 lp / mm. This lens has a value of 0.23 at 100 lp / mm, which meets the imaging requirements.

[0064] Figure 4 The figure shows the F-Tan (Theta) distortion curve of the lens. The maximum F-Tan (Theta) distortion of each wavelength within the half field of view is 1.2%. The lens design requires F-Tan (Theta) distortion to be less than 2%, and the design meets the requirements.

[0065] Figure 5 The figure shows the transverse chromatic aberration curve of the lens. The solid line in the figure represents the transverse chromatic aberration curve of the lens at different wavelengths within the half field of view, while the dashed line represents the transverse chromatic aberration curve of the Airy disk. As can be seen from the figure, the transverse chromatic aberration curves at all wavelengths are smaller than the transverse chromatic aberration curve of the Airy disk, and the transverse chromatic aberration curve of the lens design meets the requirements.

[0066] Figure 6 The figure shows the axial aberration curves for the lens. The curves represent the axial aberrations at different wavelengths under different pupils. The maximum axial aberration of this lens is 29 μm, and the maximum axial aberration requirement is less than 50 μm, which meets the design requirements.

[0067] Figure 7 This is the lens focal shift curve. The figure shows the focal shift at different wavelengths, with the maximum focal shift being 7.6 μm at each wavelength.

[0068] Figure 8 The figure shows the field curvature curves of the lens. The solid lines represent the field curvature curves of different wavelengths within the half-field of view on the meridional plane, with a maximum field curvature of 105 μm. The dashed lines represent the field curvature curves of different wavelengths within the half-field of view on the sagittal plane, with a maximum field curvature of 75 μm. The combined maximum field curvature is 105 μm, and the actual field curvature requirement is less than 150 μm, which meets the design requirements.

[0069] The above are merely three embodiments of the present invention, and these embodiments are not intended to limit the present invention. Any equivalent substitutions made within the spirit and essence of the present invention are within the protection scope of the present invention.

Claims

1. A glass aspherical broadband imaging lens, characterized in that: The lens has four lenses and a protective glass arranged coaxially from the subject to the image plane. The four lenses are: the first lens, the second lens, the third lens and the fourth lens. All lenses are made of glass, and the first lens is made of the same material as the third lens. The transmittance of the materials used in the first, second, and fourth lenses is greater than 0.7 in the 340nm-1550nm wavelength range within a thickness of 25 mm. Each of the lenses includes an object-end optical surface and an image-end optical surface, and both the object-end optical surface and the image-end optical surface of the four lenses are aspherical. The first lens is a positive lens, including a first object end optical surface and a first image end optical surface. The refractive index n1 of the first lens material is required to be n1 < 1.50, and the Abbe number v1 is required to be v1 > 88. The second lens is a negative lens, including a second object end optical surface and a second image end optical surface. The refractive index n2 of the second lens material is required to be n2 > 1.55, and the Abbe number v2 is required to be v2 < 55. The third lens is a positive lens, including a third object end optical surface and a third image end optical surface, and the material of the third lens is the same as that of the first lens. The fourth lens is a negative lens, including a fourth object-end optical surface and a fourth image-end optical surface; The total length of the lens, i.e. the distance between the center of the optical plane of the first lens object end and the center of the image plane of the lens group, TOTR, satisfies the following relationship: TOTR < 6.5 mm; The center thickness d1 of the first lens satisfies: 0.8 mm < d1 < 1.2 mm; the center thickness d2 of the second lens satisfies: 0.35 mm < d2 < 0.45 mm; the center thickness d3 of the third lens satisfies: 1.1 mm < d3 < 1.4 mm; and the center thickness d4 of the fourth lens satisfies: 0.5 mm < d4 < 0.8 mm. The focal lengths f1 of the first lens, f2 of the second lens, f3 of the third lens, f4 of the fourth lens, and the focal length f of the entire lens group satisfy the following relationship: 3.5 mm <f<4.5 mm,0.6<f1 / f<0.8,-0.6<f2 / f<-0.4,0.4<f3 / f<0.5,-0.7<f4 / f<-0.6; Define F# = f / D, where f is the focal length and D is the entrance pupil diameter. F# determines the difficulty of lens design and the light throughput of the lens. F# satisfies: 2.5 <F#<3.5; The lens corrects aberrations in the 340 nm-1550 nm band to meet the confocal condition, that is, to achieve clear imaging with axial aberration less than 50 μm.

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