A medium-resolution fisheye lens with no f-θ distortion and a large field of view

Abstract

The present invention discloses a medium-resolution fisheye lens with no f-θ distortion and a large field of view, comprising: a first lens with negative optical power, a second lens with negative optical power, a third lens with positive optical power, a fourth lens with negative optical power, a fifth lens with positive optical power and a protective glass plate arranged in sequence from the object side to the image side along the optical axis; wherein the fourth lens and the fifth lens form a cemented group, and the aperture stop is located between the third lens and the fourth lens. The lens of the present invention has a field of view angle greater than 200° and an f-θ distortion less than 0.1%, which can greatly shorten the delay and occupy less computing power.

Description

Technical Field

[0001] The invention belongs to the technical field of fixed-focus optical systems, and in particular relates to a medium-resolution fisheye lens with no f-θ distortion and a large field of view. Background Art

[0002] With the trend of intelligent automobiles, automobiles need to be equipped with various on-board lenses as sensors. The surround-view lens is composed of 4 wide-angle lenses. However, most of the current on-board surround-view lenses have large distortion, and correcting the deviation through algorithms will bring problems in terms of delay and consumption of computing power.

[0003] In the field of optical lenses, optical distortion-free means that the image size is strictly equal to the focal length multiplied by the tangent of the half field of view. According to the characteristics of the receiver, optical distortion-free is divided into human eye distortion-free, industrial distortion-free, laboratory distortion-free and theoretical distortion-free, etc. Optical distortion-free lenses rarely have a field of view angle of more than 130°.

[0004] f tanθ distortion is usually used to describe the distortion size of a lens. However, when the field of view angle is greater than 180°, tanθ divergence is meaningless. In this case, f-θ distortion is used, and the corresponding lens is called an f-θ lens. The image size of an f-θ lens is linearly related to the half field of view angle. It is mainly used in scanners, optical radars, car navigation, panoramic image synthesis, etc. However, f-θ lenses also have different f-θ distortion sizes. Lenses with f-θ distortion less than 0.1% are usually called industrial-grade distortion-free f-θ lenses. There are almost no distortion-free lenses greater than 180° on the market today. Most fisheye lenses with a field of view angle greater than 180° on the market have an f-θ distortion of more than 5%, which cannot meet high-precision requirements. Summary of the invention

[0005] In order to overcome the above technical defects, the purpose of the present invention is to provide a medium-resolution, f-θ distortion-free, ultra-large field of view fisheye lens in view of the above shortcomings, with one million pixels, a field of view angle greater than 200°, and f-θ distortion less than 0.1%, which can greatly shorten the delay and occupy less computing power.

[0006] To achieve the above object, the present invention provides the following solution: a medium-resolution fisheye lens with no f-θ distortion and a large field of view, comprising:

[0007] A first lens with negative optical power, a second lens with negative optical power, a third lens with positive optical power, a fourth lens with negative optical power, a fifth lens with positive optical power and a protective glass plate are arranged in sequence from the object side to the image side along the optical axis; wherein the fourth lens and the fifth lens form a cemented group, and the aperture stop is located between the third lens and the fourth lens.

[0008] Preferably, the shape of the first lens in the paraxial region is convex-concave, where the first surface of the first lens is convex and the second surface is concave;

[0009] The shape of the second lens in the paraxial region is convex-concave, where the first surface of the second lens is convex and the second surface is concave;

[0010] The shape of the third lens in the paraxial region is convex-convex, where the first surface of the third lens is convex and the second surface is convex;

[0011] The shape of the fourth lens in the paraxial region is convex-concave, where the first surface of the fourth lens is convex and the second surface is concave;

[0012] The shape of the fifth lens in the paraxial region is convex-convex, where the first surface of the fifth lens is convex and the second surface is concave.

[0013] Preferably, the first surface and the second surface of the first lens and the third lens are all spherical lenses;

[0014] The first surface and the second surface of the second lens, the fourth lens, and the fifth lens are all even aspherical lenses.

[0015] Preferably, the aspherical coefficients of the even aspherical lens include a quadratic coefficient, a fourth-order aspherical coefficient, a sixth-order aspherical coefficient, an eighth-order aspherical coefficient, a tenth-order aspherical coefficient, and a twelfth-order aspherical coefficient.

[0016] Preferably, both the fourth lens and the fifth lens are plastic lenses.

[0017] Preferably, the focal length values f1 of the first lens, f2 of the second lens, f3 of the third lens, f4 of the fourth lens, and f5 of the fifth lens are -7mm < f1 < -6mm, -3mm < f2 < -2mm, 3mm < f3 < 4mm, -3mm < f4 < -2mm, 1mm < f5 < 2mm, respectively.

[0018] Preferably, the central thickness of the first lens is 1.22mm, the refractive index is 1.78 < nd1 < 1.82, and the dispersion coefficient is 45 < vd1 < 50;

[0019] The central thickness of the second lens is 1.77mm, the refractive index is 1.78 < nd2 < 1.82, and the dispersion coefficient is 38 < vd2 < 43;

[0020] The central thickness of the third lens is 4.03mm, the refractive index is 1.78 < nd3 < 1.82, and the dispersion coefficient is 30 < vd3 < 35;

[0021] The central thickness of the fourth lens is 1.51 mm, the refractive index satisfies 1.65 < nd4 < 1.7, and the Abbe number satisfies 18 < vd4 < 24;

[0022] The central thickness of the fifth lens is 1.90 mm, the refractive index satisfies 1.5 < nd5 < 1.55, and the Abbe number satisfies 53 < vd5 < 58.

[0023] Preferably, the protective glass plate includes a first parallel plate coated with an IR-CUT film and a second parallel plate serving as a protective sheet;

[0024] The central thickness of the first parallel plate is 0.3 mm, the refractive index nd6 = 1.517, and the Abbe number vd6 = 64.2;

[0025] The central thickness of the second parallel plate is 0.4 mm, the refractive index nd7 = 1.517, and the Abbe number vd7 = 64.2.

[0026] Preferably, the air gap between the first lens and the second lens is 2.01 mm;

[0027] The air gap between the second lens and the third lens is 1.20 mm;

[0028] The air gap between the third lens and the aperture stop is 0.24 mm;

[0029] The air gap between the aperture stop and the cemented group composed of the fourth lens and the fifth lens is 0.21 mm;

[0030] The air gap between the cemented group composed of the fourth lens and the fifth lens and the parallel plate is 0.24 mm.

[0031] Preferably, the combined focal length of the fisheye lens: f = 1.10 mm;

[0032] The maximum aperture: F / NO = 2.0;

[0033] The field of view angle: horizontal 2W ≥ 200°;

[0034] The chief ray angle of incidence: CRA < 23.5°;

[0035] The f-θ distortion < 0.1°;

[0036] The overall optical length: TTL < 15.5 mm;

[0037] The back focal length: 1.4 mm < BFL < 1.7 mm;

[0038] The applicable spectral line range: 430 nm - 670 nm.

[0039] The present invention discloses the following technical effects:

[0040] The present invention provides a medium-resolution fisheye lens with no f-θ distortion and a large field of view.

[0041] The medium-resolution fisheye lens with no f-θ distortion and a large field of view of the present invention is beneficial to the structural design of the lens and effectively reduces the cost. At the same time, the first lens and the second lens use a negative focal meniscus lens bent toward the aperture to achieve a wide angle and reduce the coma and spherical aberration of the system. The third lens is a double convex rear lens to provide a large positive field curvature. The fourth and fifth lenses are aspherical lenses to compensate for aberrations so that the image quality meets the requirements. The fourth and fifth lenses are made of optical plastics to reduce costs. The sixth lens is a parallel plate coated with a bandpass film to intercept unnecessary spectral lines.

[0042] The medium-resolution ultra-wide-angle vehicle-mounted lens without f-θ distortion disclosed by the present invention has a field of view of 200°. Two lenses with a field of view of 200° are symmetrically installed to obtain a 360° full stereoscopic image and provide an overlap area of ​​up to 10°. If both lenses are free of f-θ distortion, the direction angle can be easily obtained when performing panoramic fusion, thereby saving time and cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] 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 will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0044] Figure 1 A schematic diagram of the system structure of an embodiment of the present invention;

[0045] Among them, 1-first lens, 2-second lens, 3-third lens, 4-fourth lens, 5-fifth lens, 6-sixth lens, 7-seventh lens, 8-aperture stop;

[0046] Figure 2 It is an mtf vs field image quality evaluation curve diagram of an embodiment of the present invention;

[0047] Figure 3 This is an MTF image quality evaluation curve diagram of an embodiment of the present invention;

[0048] Figure 4 is an f-θ distortion curve diagram of an embodiment of the present invention;

[0049] Figure 5 FIG. 4 is a relative illumination curve diagram of an embodiment of the present invention. DETAILED DESCRIPTION

[0050] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0051] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0052] like Figure 1 As shown, the present invention provides a medium-resolution fisheye lens with no f-θ distortion and a large field of view, comprising:

[0053] A first lens 1 with negative optical power, a second lens 2 with negative optical power, a third lens 3 with positive optical power, a fourth lens 4 with negative optical power, a fifth lens 5 with positive optical power and a protective glass plate are arranged in sequence from the object side to the image side along the optical axis. The fourth lens 4 and the fifth lens 5 form a cemented group, and the aperture stop 8 is located between the third lens 3 and the fourth lens 4.

[0054] Further, according to one aspect of the present invention, along the direction from the object side to the image side of the optical axis,

[0055] The shape of the first lens 1 in the paraxial region is convex-concave;

[0056] The shape of the second lens 2 in the paraxial region is convex-concave;

[0057] The shape of the third lens 3 in the paraxial region is convex-convex;

[0058] The shape of the fourth lens 4 in the paraxial region is convex-concave;

[0059] The shape of the fifth lens 5 in the paraxial region is convex-convex.

[0060] The first lens 1 and the third lens 3 are both spherical lenses;

[0061] Further, according to one aspect of the present invention, the second lens 2, the fourth lens 4 and the fifth lens 5 are all aspherical lenses, specifically even-order aspherical lenses.

[0062] Further, according to one aspect of the present invention, the fourth lens 4 and the fifth lens 5 are both plastic lenses.

[0063] Further, the medium-resolution f-θ distortion-free ultra-wide-field-of-view fisheye lens satisfies: -7 mm < f1 < -6 mm, -3 mm < f2 < -2 mm, 3 mm < f3 < 4 mm, -3 mm < f4 < -2 mm, 1 mm < f5 < 2 mm. Herein, f1, f2, f3, f4, and f5 are the focal lengths of the first lens 1, the second lens 2, the third lens 3, the fourth lens 4, and the fifth lens 5, respectively.

[0064] Further, the combined focal length of the medium-resolution f-θ distortion-free ultra-wide-field-of-view fisheye lens satisfies f = 1.10 mm.

[0065] Further, the medium-resolution f-θ distortion-free ultra-wide-field-of-view fisheye lens satisfies: 1.78 < nd1 < 1.82, 45 < vd1 < 50, 1.78 < nd2 < 1.82, 38 < vd2 < 43, 1.78 < nd3 < 1.82, 30 < vd3 < 35, 1.65 < nd4 < 1.7, 18 < vd4 < 24, 1.5 < nd5 < 1.55, 53 < vd5 < 58. Herein, nd1, nd2, nd3, nd4, and nd5 are the refractive indices of the first lens 1, the second lens 2, the third lens 3, the fourth lens 4, and the fifth lens 5, respectively, and vd1, vd2, vd3, vd4, and vd5 are the dispersion coefficients of the first lens 1, the second lens 2, the third lens 3, the fourth lens 4, and the fifth lens 5, respectively.

[0066] For a further optimization solution, the basic lens data of the medium-resolution f-θ distortion-free ultra-wide-field-of-view fisheye lens in this embodiment is shown in Table 1.

[0067]

[0068]

[0069] The aspheric coefficients of the aspheric lenses in this embodiment, including the quadratic coefficient K value, the fourth-order aspheric coefficient A4, the sixth-order aspheric coefficient A6, the eighth-order aspheric coefficient A8, the tenth-order aspheric coefficient A10, and the twelfth-order aspheric coefficient A12, are shown in Table 2 below.

[0070] Table 2

[0071]

[0072] Specifically, for the first lens 1, the first surface is convex, the second surface is concave, the central thickness is 1.22 mm, nd = 1.804, vd = 46.57, and both surfaces are spherical.

[0073] For the second lens 2, the first surface is convex, the second surface is concave, the central thickness is 1.77 mm, nd = 1.809, vd = 40.97, and both surfaces are even-order aspheric surfaces.

[0074] The third lens 3 has a convex first surface and a convex second surface, a center thickness of 4.03 mm, nd=1.806, vd=33.29, and both surfaces are spherical.

[0075] The fourth lens 4 has a convex first surface and a concave second surface, a center thickness of 1.51 mm, nd=1.661, vd=20.41, and both surfaces are even-order aspheric surfaces.

[0076] The fifth lens 5 has a convex first surface and a concave second surface, a center thickness of 1.90 mm, nd=1.535, vd=55.71, and both surfaces are even-order aspheric surfaces.

[0077] Further, the protective glass plate includes a first parallel plate coated with an IR-CUT film and a second parallel plate as a protective sheet;

[0078] The first parallel flat plate coated with the IR-CUT film is used as the sixth lens 6, with a central material thickness of 0.3, nd=1.517, and vd=64.2.

[0079] The second parallel flat plate used for the protective sheet serves as the seventh lens 7, with a central material thickness of 0.4, nd=1.517, and vd=64.2.

[0080] In this embodiment, the air gap between the first lens 1 and the second lens 2 is 2.01 mm, the air gap between the second lens 2 and the third lens 3 is 1.20 mm, the air gap between the third lens 3 and the aperture stop 8 is 0.24 mm, the air gap between the aperture stop 8 and the cemented group consisting of the fourth lens 4 and the fifth lens 5 is 0.21 mm, and the air gap between the cemented group consisting of the fourth lens 4 and the fifth lens 5 and the first parallel plate is 0.24 mm.

[0081] In this embodiment, the optical system composed of the above lenses achieves the following optical indicators:

[0082] Focal length: f = 1.10 mm;

[0083] Relative aperture: F / NO=2.0;

[0084] Field of view: horizontal 2W ≥ 200°;

[0085] Chief ray incident angle: CRA<23.5°;

[0086] f-θ distortion <0.1°;

[0087] Total optical length: TTL<15.3mm;

[0088] Optical back focus: 1.4mm <BFL<1.7mm;

[0089] Resolution: can match 1 million pixel CMOS or CCD;

[0090] Applicable spectral line range: 430nm-670nm;

[0091] The mtf vs field image quality evaluation curve, mtf image quality evaluation curve, f-θ distortion curve, and relative illumination curve calculated by the system are as follows: Figure 2-5 As shown in the figure, the performance is good. At a half field angle below 90°, MTF>0.4@100lp / mm, fθ distortion is only 0.1%, and relative illumination>40% at full field of view.

[0092] The medium-resolution fisheye lens with no f-θ distortion and a large field of view of the present invention is beneficial to the structural design of the lens and effectively reduces the cost. At the same time, the first lens 1 and the second lens 2 use a negative focal meniscus lens bent toward the aperture to achieve a wide angle and reduce the coma and spherical aberration of the system. The third lens 3 is a double convex rear lens to provide a large positive field curvature. The fourth and fifth lenses 5 are aspherical lenses to compensate for aberrations so that the image quality meets the requirements. The fourth and fifth lenses 5 are made of optical plastics to reduce costs. The sixth lens is a parallel plate coated with a bandpass film to intercept unnecessary spectral lines.

[0093] The medium-resolution ultra-wide-angle vehicle-mounted lens without f-θ distortion of the present invention has a field of view of 200°. Two lenses with a field of view of 200° are symmetrically installed to obtain a 360° full stereoscopic image and provide an overlap area of ​​up to 10°. If both lenses are free of f-θ distortion, the direction angle can be easily obtained when performing panoramic fusion, thereby saving time and cost.

[0094] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A medium-resolution, f-θ distortion-free, ultra-wide-field-of-view fisheye lens, characterized in that, it includes: A first lens with a negative focal power, a second lens with a negative focal power, a third lens with a positive focal power, a fourth lens with a negative focal power, a fifth lens with a positive focal power, and a protective glass plate arranged in sequence along the optical axis from the object side to the image side; wherein, the fourth lens and the fifth lens form a cemented group, and the aperture stop is located between the third lens and the fourth lens; The number of lenses with focal power in the lens is five; The focal length values f1 of the first lens, f2 of the second lens, f3 of the third lens, f4 of the fourth lens, and f5 of the fifth lens are respectively -7mm < f1 < -6mm, -3mm < f2 < -2mm, 3mm < f3 < 4mm, -3mm < f4 < -2mm, 1mm < f5 < 2mm; The central thickness of the first lens is 1.22mm, the refractive index is 1.78 < nd1 < 1.82, and the dispersion coefficient is 45 < vd1 < 50; The central thickness of the second lens is 0.77mm, the refractive index is 1.78 < nd2 < 1.82, and the dispersion coefficient is 38 < vd2 < 43; The central thickness of the third lens is 4.03mm, the refractive index is 1.78 < nd3 < 1.82, and the dispersion coefficient is 30 < vd3 < 35; The central thickness of the fourth lens is 1.51mm, the refractive index is 1.65 < nd4 < 1.7, and the dispersion coefficient is 18 < vd4 < 24; The central thickness of the fifth lens is 1.90mm, the refractive index is 1.5 < nd5 < 1.55, and the dispersion coefficient is 53 < vd5 < 58.

2. The medium-resolution, f-θ distortion-free, ultra-wide-field-of-view fisheye lens according to claim 1, characterized in that, The shape of the first lens in the paraxial region is convex-concave, wherein the object side surface of the first lens is convex and the image side surface is concave; The shape of the second lens in the paraxial region is convex-concave, wherein the object side surface of the second lens is convex and the image side surface is concave; The shape of the third lens in the paraxial region is convex-convex, wherein the object side surface of the third lens is convex and the image side surface is convex; The shape of the fourth lens in the paraxial region is convex-concave, wherein the object side surface of the fourth lens is convex and the image side surface is concave; The shape of the fifth lens in the paraxial region is convex-convex, wherein the object side surface of the fifth lens is convex and the image side surface is concave.

3. The medium-resolution, f-θ distortion-free, ultra-wide-field-of-view fisheye lens according to claim 1, characterized in that, The object side surface and the image side surface of the first lens and the third lens are all spherical lenses; The object side surface and the image side surface of the second lens, the fourth lens, and the fifth lens are all even aspherical lenses.

4. The medium-resolution, f-θ distortion-free, ultra-wide-field-of-view fisheye lens according to claim 3, characterized in that, The aspheric coefficients of the even aspheric lens include the quadratic coefficient, the fourth-order aspheric coefficient, the sixth-order aspheric coefficient, the eighth-order aspheric coefficient, the tenth-order aspheric coefficient, and the twelfth-order aspheric coefficient.

5. The medium-resolution f-θ distortion-free ultra-wide field-of-view fisheye lens according to claim 1, wherein, both the fourth lens and the fifth lens are plastic lenses.

6. The medium-resolution f-θ distortion-free ultra-wide field-of-view fisheye lens according to claim 1, wherein, the protective glass plate includes a first parallel plate coated with an IR-CUT film and a second parallel plate as a protective sheet; the central thickness of the first parallel plate is 0.3 mm, the refractive index nd6 = 1.517, and the dispersion coefficient vd6 = 64.2; the central thickness of the second parallel plate is 0.4 mm, the refractive index nd7 = 1.517, and the dispersion coefficient vd7 = 64.

2.

7. The medium-resolution f-θ distortion-free ultra-wide field-of-view fisheye lens according to claim 1, wherein, the air gap between the first lens and the second lens is 2.01 mm; the air gap between the second lens and the third lens is 1.20 mm; the air gap between the third lens and the aperture stop is 0.24 mm; the air gap between the aperture stop and the cemented group composed of the fourth lens and the fifth lens is 0.21 mm; the air gap between the cemented group composed of the fourth lens and the fifth lens and the parallel plate is 0.24 mm.

8. The medium-resolution f-θ distortion-free ultra-wide field-of-view fisheye lens according to claim 1, wherein, the combined focal length of the fisheye lens: f = 1.10 mm; the maximum aperture: F / NO = 2.0; the field of view angle: horizontal 2W ≥ 200°; the chief ray angle of incidence: CRA < 23.5°; f-θ distortion < 0.1°; the overall optical length: TTL < 15.5 mm; the back focal length: 1.4 mm < BFL < 1.7 mm; the applicable spectral line range: 430 nm - 670 nm.

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