A short-focus lens

Abstract

The present invention discloses a short-focus lens, which includes, successively arranged from the object side to the image side: a first lens with a positive optical power; a second lens with a negative optical power; a third lens with a negative optical power; a fourth lens with a negative optical power; a fifth lens with a positive optical power and forming a doublet lens with the fourth lens; a sixth lens with a positive optical power; a seventh lens with a positive optical power and spaced from the sixth lens; a stop STO spaced from the seventh lens and used to limit the beam aperture; an eighth lens with a positive optical power; a ninth lens with a positive optical power and spaced from the eighth lens; a tenth lens with a negative optical power and forming a doublet lens with the ninth lens. By reasonably distributing the optical powers of the lenses, reasonably selecting materials, and using all-glass spherical lenses, the present technical solution achieves high pixel count, low distortion, and relative illumination. At the same time, by using a smaller number of lenses and a simple structure, the volume of the lens is miniaturized.

Description

Technical Field

[0001] The present invention relates to the technical field of optical lenses, and particularly to a short-focus lens. Background Art

[0002] In the field of machine vision, as the "eyeglasses" for machine vision to obtain target images, the performance of optical lenses determines whether the machine vision system can meet the applications. At the same time, with the continuous development of machine vision, the requirements for optical lenses are getting higher and higher. Generally, it is required that optical lenses take into account factors such as high resolution, good aberration correction, low distortion, and large field of view. However, short-focus lenses on the market usually have difficulty in simultaneously meeting the requirements of low distortion, small volume, and low cost. Summary of the Invention

[0003] The present invention aims to at least solve one of the technical problems existing in the prior art. For this purpose, the present invention provides a short-focus lens that can simultaneously meet the requirements of low distortion, small volume, and low cost.

[0004] A short-focus lens according to an embodiment of the present invention includes, sequentially arranged from the object side to the image side: a first lens having a positive optical power, where the dispersion coefficient Vd1 of the first lens ≥ 40; a second lens having a negative optical power and spaced from the first lens, where the dispersion coefficient Vd2 of the second lens ≥ 60; a third lens having a negative optical power and spaced from the second lens, where the dispersion coefficient Vd3 of the third lens ≤ 60; a fourth lens having a negative optical power and spaced from the third lens, where the dispersion coefficient Vd4 of the fourth lens ≤ 30; a fifth lens having a positive optical power and forming a doublet with the fourth lens, where the dispersion coefficient Vd5 of the fifth lens ≥ 50, and |Vd4 - Vd5| ≥ 30; a sixth lens having a positive optical power and spaced from the fifth lens, where the dispersion coefficient Vd6 of the sixth lens ≤ 30; a seventh lens having a positive optical power and spaced from the sixth lens, where the dispersion coefficient Vd7 of the seventh lens ≤ 30; a diaphragm STO spaced from the seventh lens and used to limit the beam aperture; an eighth lens having a positive optical power and spaced from the diaphragm STO, where the dispersion coefficient Vd8 of the eighth lens ≥ 60; a ninth lens having a positive optical power and spaced from the eighth lens, where the dispersion coefficient Vd9 of the ninth lens ≥ 80; a tenth lens having a negative optical power and forming a doublet with the ninth lens, where the dispersion coefficient Vd 10 ≤ 30, and |Vd9 - Vd 10 | ≥ 50.

[0005] A short-focus lens according to an embodiment of the present invention has at least the following beneficial effects:

[0006] This technical solution realizes high pixel, low distortion and relative illumination by reasonably distributing the lens optical power, reasonably selecting materials, and using all-glass spherical lenses. At the same time, the lens volume is miniaturized by using fewer lenses and a simple structure.

[0007] According to some embodiments of the present invention, one surface of the first lens facing the object side is convex, and the surface facing the image side is concave; one surface of the second lens facing the object side is convex, and the surface facing the image side is concave; one surface of the third lens facing the object side is convex, and the surface facing the image side is concave; both surfaces of the fourth lens are concave; both surfaces of the fifth lens are convex; one surface of the sixth lens facing the object side is convex, and the surface facing the image side is concave; both surfaces of the seventh lens are convex; both surfaces of the eighth lens are convex; both surfaces of the ninth lens are convex; one surface of the tenth lens facing the object side is concave, and the surface facing the image side is convex.

[0008] According to some embodiments of the present invention, the short-focus lens satisfies the following relationships:

[0009] 6 < f1 / f < 7;

[0010] -5 < f2 / f < -3.5;

[0011] -2 < f3 / f < -0.8;

[0012] -3.5 < f 4-5 / f < -2;

[0013] 5.6 < f6 / f < 7;

[0014] 1.8 < f7 / f < 3;

[0015] 2 < f8 / f < 3.2;

[0016] 7 < f 9-10 / f < 8.4;

[0017] 6.8 < TTL / f < 8.2;

[0018] Wherein, f is the focal length of the short-focus lens, f1 is the focal length of the first lens, f2 is the focal length of the second lens, f3 is the focal length of the third lens, f 4-5 is the combined focal length of the fourth lens and the fifth lens, f6 is the focal length of the sixth lens, f7 is the focal length of the seventh lens, f8 is the focal length of the eighth lens, f 9-10 is the combined focal length of the ninth lens and the tenth lens, and TTL is the overall length of the short-focus lens.

[0019] According to some embodiments of the present invention, it further includes an image sensor chip, which is located on the image side and is spaced apart from the tenth lens, and is used to capture imaging signals and form images.

[0020] According to some embodiments of the present invention, there is protective glass between the image sensor chip and the tenth lens.

[0021] According to some embodiments of the present invention, the short-focus lens satisfies the following relational expressions:

[0022] Nd1≥1.7;

[0023] Nd2≥1.5;

[0024] Nd3≤1.8;

[0025] Nd4≥1.8;

[0026] Nd5≤1.7;

[0027] |Nd4 - Nd5|≥0.18;

[0028] Nd6≥1.8;

[0029] Nd7≤1.9;

[0030] Nd8≤1.6;

[0031] Nd9≤1.6;

[0032] Nd 10 ≥1.8;

[0033] |Nd9 - Nd 10 |≥0.3;

[0034] Wherein, Nd1 is the refractive index of the first lens, Nd2 is the refractive index of the second lens, Nd3 is the refractive index of the third lens, Nd4 is the refractive index of the fourth lens, Nd5 is the refractive index of the fifth lens, Nd6 is the refractive index of the sixth lens, Nd7 is the refractive index of the seventh lens, Nd8 is the refractive index of the eighth lens, Nd9 is the refractive index of the ninth lens, and Nd 10 is the refractive index of the tenth lens.

[0035] According to some embodiments of the present invention, the first lens, the second lens, the third lens, the fourth lens, the fifth lens, the sixth lens, the seventh lens, the eighth lens, the ninth lens, and the tenth lens are all made of glass material lenses.

[0036] According to some embodiments of the present invention, the focal length f of the short-focus lens is 8 mm, FNO = 2.4, and the total length TL of the short-focus lens is 54.7 mm.

[0037] Additional aspects and advantages of the present invention will be given in part in the following description, become apparent in part from the following description, or be learned through the practice of the present invention. Description of the Drawings

[0038] The present invention will be further described below in conjunction with the drawings and embodiments, where:

[0039] Figure 1 Schematic diagram of the short-focus lens structure of an embodiment of the present invention;

[0040] Figure 2 MTF curve graph of an embodiment of the present invention when the object distance is 400 mm;

[0041] Figure 3 Defocus MTF curve graph of an embodiment of the present invention when the object distance is 400 mm;

[0042] Figure 4 Distortion curve graph of an embodiment of the present invention when the object distance is 400 mm;

[0043] Figure 5 Relative illumination curve graph of an embodiment of the present invention when the object distance is 400 mm;

[0044] Figure 6 Ray aberration curve graph of an embodiment of the present invention when the object distance is 400 mm;

[0045] Figure 7 Axial chromatic aberration curve graph of an embodiment of the present invention when the object distance is 400 mm;

[0046] Figure 8 Lateral chromatic aberration curve graph of an embodiment of the present invention when the object distance is 400 mm;

[0047] Figure 9 MTF curve graph of an embodiment of the present invention when the object distance is infinity.

[0048] Reference numerals in the drawings:

[0049] First lens 1, second lens 2, third lens 3, fourth lens 4, fifth lens 5, sixth lens 6, seventh lens 7, aperture STO, eighth lens 8, ninth lens 9, tenth lens 10, photosensitive chip 11, protective glass 12. Detailed Embodiments

[0050] Embodiments of the present invention will be described in detail below. Examples of the embodiments are shown in the accompanying drawings, where like or similar reference numerals denote like or similar elements or elements having like or similar functions throughout. The embodiments described below by referring to the accompanying drawings are exemplary and are only used to explain the present invention and should not be construed as limiting the present invention.

[0051] In the description of the present invention, it should be understood that with respect to the orientation description, such as up, down, etc., the orientation or positional relationship indicated is based on the orientation or positional relationship shown in the accompanying drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as limiting the present invention.

[0052] In the description of the present invention, "plurality" means more than two. If there is a description of first and second, it is only for the purpose of distinguishing technical features and should not be construed as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features or implicitly indicating the sequence relationship of the indicated technical features.

[0053] In the description of the present invention, unless otherwise clearly defined, words such as "set", "install", "connect", etc. should be understood in a broad sense, and those skilled in the art can reasonably determine the specific meanings of the above words in the present invention in combination with the specific content of the technical solution.

[0054] Refer to Figure 1As shown in the figure, a short-focus lens according to an embodiment of the present invention includes, sequentially arranged from the object side to the image side: a first lens 1 with a positive optical power, and the dispersion coefficient Vd1 of the first lens 1 ≥ 40; a second lens 2 with a negative optical power and spaced from the first lens 1, and the dispersion coefficient Vd2 of the second lens 2 ≥ 60; a third lens 3 with a negative optical power and spaced from the second lens 2, and the dispersion coefficient Vd3 of the third lens 3 ≤ 60; a fourth lens 4 with a negative optical power and spaced from the third lens 3, and the dispersion coefficient Vd4 of the fourth lens 4 ≤ 30; a fifth lens 5 with a positive optical power and forming a doublet lens with the fourth lens 4, and the dispersion coefficient Vd5 of the fifth lens 5 ≥ 50, and satisfying |Vd4 - Vd5| ≥ 30; a sixth lens 6 with a positive optical power and spaced from the fifth lens 5, and the dispersion coefficient Vd6 of the sixth lens 6 ≤ 30; a seventh lens 7 with a positive optical power and spaced from the sixth lens 6, and the dispersion coefficient Vd7 of the seventh lens 7 ≤ 30; a stop STO, spaced from the seventh lens 7 and used to limit the beam aperture; an eighth lens 8 with a positive optical power and spaced from the stop STO, and the dispersion coefficient Vd8 of the eighth lens 8 ≥ 60; a ninth lens 9 with a positive optical power and spaced from the eighth lens 8, and the dispersion coefficient Vd9 of the ninth lens 9 ≥ 80; a tenth lens 10 with a negative optical power and forming a doublet lens with the ninth lens 9, and the dispersion coefficient Vd 10 ≤ 30, and satisfying |Vd9 - Vd 10 | ≥ 50.

[0055] Each lens in this lens has a reasonable optical power distribution and material combination. Among them, the first lens has a positive optical power, which can converge off-axis beams at a large angle, thereby reducing the light-passing aperture of the rear optical path and facilitating the miniaturization of the optical path structure; the second lens 2 and the third lens 3 have a high Abbe number, which can directly reduce the chromatic aberration correction of the beam passing through the first lens 1; the fourth lens 4 and the fifth lens 5 have an Abbe number difference of more than 30 after being closely bonded, which can well correct chromatic aberration and secondary spectrum; the sixth lens and the seventh lens 7 have a positive optical power and a high refractive index, and effectively focus the divergent beam after passing through the bonded lens of the fourth lens 4 and the fifth lens 5, and the light aperture passing through the stop; after the light propagates for a long distance before and after passing through the stop, the chromatic aberration accumulation becomes larger. Therefore, the eighth lens 8 uses a low-dispersion material to reduce the difference between different wavelengths, thereby reducing chromatic aberration. The ninth lens 9 and the tenth lens 10 have an Abbe number difference of more than 50 after being closely bonded, and can well correct chromatic aberration and secondary spectrum for the beam focused on the photosensitive chip.

[0056] In some embodiments of the present invention, one side of the first lens 1 facing the object side is convex, and the side facing the image side is concave; one side of the second lens 2 facing the object side is convex, and the side facing the image side is concave; one side of the third lens facing the object side is convex, and the side facing the image side is concave; both sides of the fourth lens 4 are concave;; both sides of the fifth lens 5 are convex; one side of the sixth lens 6 facing the object side is convex, and the side facing the image side is concave; both sides of the seventh lens 7 are convex; both sides of the eighth lens 8 are convex; both sides of the ninth lens 9 are convex; one side of the tenth lens 10 facing the object side is concave, and the side facing the image side is convex. The above lens shapes are only one embodiment of the present technical solution and are not the only limitation. They can be replaced by lenses with other shapes that can achieve the same parameter performance.

[0057] In some embodiments of the present invention, the short focal length lens satisfies the following relationship:

[0058] 6 < f1 / f < 7;

[0059] -5 < f2 / f < -3.5;

[0060] -2 < f3 / f < -0.8;

[0061] -3.5 < f 4-5 / f < -2;

[0062] 5.6 < f6 / f < 7;

[0063] 1.8 < f7 / f < 3;

[0064] 2 < f8 / f < 3.2;

[0065] 7 < f 9-10 / f < 8.4;

[0066] 6.8 < TTL / f < 8.2;

[0067] Wherein, f is the focal length of the short focal length lens, f1 is the focal length of the first lens, f2 is the focal length of the second lens, f3 is the focal length of the third lens, f 4-5 is the combined focal length of the fourth lens and the fifth lens, f6 is the focal length of the sixth lens, f7 is the focal length of the seventh lens, f8 is the focal length of the eighth lens, f 9-10 is the combined focal length of the ninth lens and the tenth lens, and TTL is the overall length of the short focal length lens.

[0068] In this embodiment, the lens combination structure that satisfies the above relationship is beneficial to realizing a reasonable distribution of optical power, can better balance spherical aberration, coma, and field curvature, and at the same time, with a reasonable material combination, is beneficial to correcting chromatic aberration, thereby generating a high-resolution and color-true high-quality imaging picture.

[0069] As Figure 1 shown, in some embodiments of the present invention, it further includes a photosensitive chip 11. The photosensitive chip 11 is located on the image side and is spaced apart from the tenth lens 10, and is used to capture imaging signals and form images.

[0070] Furthermore, in some embodiments of the present invention, there is a protective glass 12 between the photosensitive chip 11 and the tenth lens 10, which can protect the chip from direct damage by external forces.

[0071] In some embodiments of the present invention, a short-focus lens has a focal length f = 8 mm, FNO = 2.4, and the total optical system length TL = 54.7 mm, and can be paired with a photosensitive chip for 1 / 1.7".

[0072] Specifically, in some embodiments of the present invention, the first lens 1, the second lens 2, the third lens 3, the fourth lens 4, the fifth lens 5, the sixth lens 6, the seventh lens 7, the eighth lens 8, the ninth lens 9, and the tenth lens 10 are all made of glass material lenses. Compared with plastic materials, they have higher transmittance, less final light energy loss, better imaging transparency, and at the same time, glass materials are not easily aged and deformed, and have a longer service life; compared with glass aspherical lenses, the cost is lower.

[0073] In some embodiments of the present invention, by setting as little vignetting as possible or no vignetting, the peripheral field light is made to pass through the lens to the chip surface as much as possible, so that the lens obtains a higher relative illuminance, ensuring the overall uniformity and transparency of the image plane brightness.

[0074] The specific parameters of the lens in this embodiment are shown in Table 1 below:

[0075]

[0076]

[0077] Table 1

[0078] In Table 1 above, the units of the radius R and the thickness are both millimeters.

[0079] For this fixed-focus lens, a floating focusing method is adopted to meet the requirement of good imaging for different object distances. One embodiment of the present invention is divided into three groups (where the first lens 1 and the second lens 2 are one group, the third lens 3 to the seventh lens 7 are the second group, and the aperture STO to the tenth lens 10 are the third group), and this purpose is achieved by adjusting the distance between the first group and the second group (i.e., the S4 thickness) and the back focus. The specific adjustment amounts are shown in Table 2 below:

[0080] Object distance (mm) 100 200 500 2000 Infnity S4 thickness (mm) 5.0447 5.2609 5.6176 5.8450 5.9346 Back focal length (mm) 11.9936 11.6913 11.4935 11.3897 11.3532

[0081] Table 2

[0082] The present invention will be described in detail below with reference to the accompanying drawings. However, the embodiments of the present invention are not limited to the following embodiments.

[0083] Figures 2 to 9 It is the optical performance diagram of the embodiment of the present invention, where:

[0084] Figure 2 It is the MTF curve of the optical system under the condition that the object distance is 400 mm, which is used to evaluate the resolution ability of the optical system. It can be seen from the curve in the figure that the MTF of the full field of view is greater than 0.6 at 100 lp / mm, having excellent resolution ability, and the trends of the on-axis and off-axis MTF curves are basically the same;

[0085] Figure 3 It is the defocus MTF curve of the optical system under the condition that the object distance is 400 mm, which is used to analyze the overall uniformity and sharpness of the image formed after the light passes through the system. It can be seen from the figure that the coincidence of the best image planes of each field of view is very good, ensuring the imaging consistency of the peripheral field of view and the central field of view, and it can be used for high-pixel chips;

[0086] Figure 4 It is the distortion curve of the optical system under the condition that the object distance is 400 mm. The distortion is only -1.9% at the full field of view.

[0087] For a short-focus lens, the distortion is small;

[0088] Figure 5 It is the relative illumination curve of the optical system under the condition that the object distance is 400 mm. The relative illumination of the full field of view is above 80%. The relatively high relative illumination can ensure the uniformity of the overall picture brightness.

[0089] Figure 6 It is the ray aberration curve of the optical system under the condition that the object distance is 400 mm. The spherical aberration and chromatic aberration of the central field of view have been corrected well, and the performance of the off-axis field of view is basically the same;

[0090] Figure 7 It is the axial chromatic aberration curve of the optical system under the condition that the object distance is 400 mm. The on-axis and off-axis aberrations are well corrected;

[0091] Figure 8 It is the lateral chromatic aberration of the optical system under the condition that the object distance is 400 mm. The lateral chromatic aberration in the wavelength range of 436 - 656 nm is all corrected within the diffraction limit;

[0092] Figure 9 It is the MTF curve of the optical system under the condition that the object distance is infinity. Except for the meridional direction of the 1st field of view, the MTF of the other fields of view can reach greater than 0.6 at 100 lp / mm, indicating that the lens also has excellent imaging quality at a long distance.

[0093] The embodiments of the present invention have been described in detail above in conjunction with the accompanying drawings. However, the present invention is not limited to the above embodiments, and various changes can be made without departing from the spirit of the present invention within the scope of knowledge possessed by those of ordinary skill in the art.

Claims

1. A short-focus lens, the number of lenses of the short-focus lens being 10, characterized in that, Including, sequentially arranged from the object side to the image side: A first lens with a positive focal power, where the dispersion coefficient Vd1 of the first lens ≥ 40; A second lens with a negative focal power and spaced from the first lens, where the dispersion coefficient Vd2 of the second lens ≥ 60; A third lens with a negative focal power and spaced from the second lens, where the dispersion coefficient Vd3 of the third lens ≤ 60; A fourth lens with a negative focal power and spaced from the third lens, where the dispersion coefficient Vd4 of the fourth lens ≤ 30; A fifth lens with a positive focal power and forming a doublet lens with the fourth lens, where the dispersion coefficient Vd5 of the fifth lens ≥ 50 and |Vd4 - Vd5| ≥ 30; A sixth lens with a positive focal power and spaced from the fifth lens, where the dispersion coefficient Vd6 of the sixth lens ≤ 30; A seventh lens with a positive focal power and spaced from the sixth lens, where the dispersion coefficient Vd7 of the seventh lens ≤ 30; A stop STO, spaced from the seventh lens and used to limit the beam aperture; An eighth lens with a positive focal power and spaced from the stop STO, where the dispersion coefficient Vd8 of the eighth lens ≥ 60; A ninth lens with a positive focal power and spaced from the eighth lens, where the dispersion coefficient Vd9 of the ninth lens ≥ 80; The tenth lens, having a negative optical power and forming a doublet lens with the ninth lens, the Abbe number Vd of the tenth lens 10 ≤ 30, and satisfying |Vd9 - Vd 10 | ≥ 50; The surface of the first lens facing the object side is convex, and the surface facing the image side is concave; the surface of the second lens facing the object side is convex, and the surface facing the image side is concave; the surface of the third lens facing the object side is convex, and the surface facing the image side is concave; both surfaces of the fourth lens are concave; both surfaces of the fifth lens are convex; the surface of the sixth lens facing the object side is convex, and the surface facing the image side is concave; both surfaces of the seventh lens are convex; both surfaces of the eighth lens are convex; both surfaces of the ninth lens are convex; the surface of the tenth lens facing the object side is concave, and the surface facing the image side is convex; The short - focus lens satisfies the following relationships: 6 < f1 / f < 7; - 5 < f2 / f < - 3.5; - 2 < f3 / f < - 0.8; -3.5 < f 4-5 / f < -2; 5.6 < f6 / f < 7; 1.8 < f7 / f < 3; 2 < f8 / f < 3.2; 7 < f 9-10 / f < 8.4; 6.8 < TTL / f < 8.2; where f is the focal length of the short-focus lens, f1 is the focal length of the first lens, f2 is the focal length of the second lens, f3 is the focal length of the third lens, f 4-5 is the combined focal length of the fourth and fifth lenses, f6 is the focal length of the sixth lens, f7 is the focal length of the seventh lens, f8 is the focal length of the eighth lens, f 9-10 is the combined focal length of the ninth and tenth lenses, and TTL is the overall length of the short-focus lens.

2. A short-focus lens according to claim 1, characterized in that: It further includes an image - sensing chip, which is located on the image side and spaced from the tenth lens, and is used to capture imaging signals and form images.

3. The short-focus lens according to claim 2, wherein: There is a protective glass between the image - sensing chip and the tenth lens.

4. A short-focus lens according to claim 1, characterized in that: The short - focus lens satisfies the following relationships: Nd1 ≥ 1.7; Nd2 ≥ 1.5; Nd3 ≤ 1.8; Nd4 ≥ 1.8; Nd5 ≤ 1.7; |Nd4 - Nd5| ≥ 0.18; Nd6 ≥ 1.8; Nd7 ≤ 1.9; Nd8 ≤ 1.6; Nd9 ≤ 1.6; Nd 10 ≥1.8; |Nd9-Nd 10 |≥0.3; Among them, Nd1 is the refractive index of the first lens, Nd2 is the refractive index of the second lens, Nd3 is the refractive index of the third lens, Nd4 is the refractive index of the fourth lens, Nd5 is the refractive index of the fifth lens, Nd6 is the refractive index of the sixth lens, Nd7 is the refractive index of the seventh lens, Nd8 is the refractive index of the eighth lens, Nd9 is the refractive index of the ninth lens, and Nd 10 is the refractive index of the tenth lens.

5. A short-focus lens according to claim 1, characterized in that: The first lens, the second lens, the third lens, the fourth lens, the fifth lens, the sixth lens, the seventh lens, the eighth lens, the ninth lens, and the tenth lens are all made of glass - material lenses.

6. A short-focus lens according to claim 1, characterized in that: The focal length f of the short - focus lens = 8 mm, FNO = 2.4, and the total length TL of the short - focus lens = 54.7 mm.

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