A bi-telecentric lens

Abstract

The present invention belongs to the technical field of optical devices, and specifically relates to a double telecentric lens, comprising an optical device, wherein the optical device is sequentially provided with a first lens G1 with positive focal power and a biconvex structure, a second lens G2 with negative focal power and a meniscus structure, a third lens G3 with positive focal power and a biconvex structure, a fourth lens G4 with negative focal power and a biconcave or plano-concave structure, a beam splitter prism P, a fifth lens G5 with negative focal power and a biconcave structure, a sixth lens G6 with positive focal power and a meniscus structure, and a seventh lens G7 with positive focal power and a meniscus or plano-convex structure from the object side to the image side, wherein the second lens G2, the third lens G3 and the fourth lens G4 form a triplet lens U1. The present invention can correct the chromatic aberration existing in a high-magnification telecentric lens, and at the same time reduce the aberration borne by a single refractive surface of the lens, and effectively reduce the tolerance sensitivity of the optical device.

Description

Technical Field

[0001] The invention belongs to the technical field of optical devices, and in particular relates to a double telecentric lens. Background Art

[0002] In the machine vision precision measurement system, ordinary industrial lenses have problems such as different magnifications, parallax, and large distortion caused by changes in object distance, which makes it difficult to meet high-precision detection requirements. However, within a certain object distance range, the image magnification will not change with changes in object distance. According to the design principle of telecentric optical path, it can be divided into object-side telecentric and image-side telecentric.

[0003] However, some bi-telecentric lenses on the market are too long and have too small numerical apertures. The small numerical aperture will result in low resolution of the telecentric lenses. Existing telecentric lenses can no longer meet the requirements of maintaining a short system length while also having high resolution. Limited by design difficulty and cost control, high-resolution bi-telecentric lenses on the market are currently concentrated on low magnifications, generally below 0.5 times. The resolution of high-magnification bi-telecentric lenses is not high and can no longer meet the requirements of some high-magnification and high-resolution applications. Improving the resolution of high-magnification telecentric lenses will not only increase the design difficulty, but also increase their tolerance sensitivity. Summary of the invention

[0004] The purpose of the present invention is to provide a double telecentric lens to address the deficiencies of the prior art, which can correct the chromatic aberration of a high-magnification telecentric lens and reduce the aberration borne by a single refractive surface of the lens, thereby effectively reducing the tolerance sensitivity of the optical device.

[0005] In order to achieve the above object, the present invention adopts the following technical solution:

[0006] A bi-telecentric lens comprises an optical device, wherein the optical device is sequentially provided with a first lens G1 with positive focal power and a biconvex structure, a second lens G2 with negative focal power and a meniscus structure, a third lens G3 with positive focal power and a biconvex structure, a fourth lens G4 with negative focal power and a biconcave or plano-concave structure, a beam splitter prism P, a fifth lens G5 with negative focal power and a biconcave structure, a sixth lens G6 with positive focal power and a meniscus structure, and a seventh lens G7 with positive focal power and a meniscus or plano-convex structure from the object side to the image side, wherein the second lens G2, the third lens G3 and the fourth lens G4 form a triplet lens U1.

[0007] As an improvement of a double telecentric lens according to the present invention, the first lens G1 and the triplet lens U1 form a front lens group Ga, the focal length of the front lens group Ga is fGa, the fifth lens G5, the sixth lens G6 and the seventh lens G7 form a rear lens group Gb, and the focal length of the rear lens group Gb is fGb.

[0008] As an improvement of a double telecentric lens according to the present invention, the focal length of the first lens G1 is f1, and the focal length f1 of the first lens G1 and the focal length fGa of the front lens group Ga satisfy the relationship: 0.8 < |f1 / fGa| < 1.8.

[0009] As an improvement of a double telecentric lens according to the present invention, the focal length of the triplet lens U1 is fu1, and it satisfies the relationship with the focal length fGa of the front lens group Ga: 3 < |fu1 / fGa| < 5.

[0010] As an improvement of a double telecentric lens according to the present invention, the refractive index of the second lens G2 is n2, and the Abbe number is v2, which satisfy the relationship: 1.65 < n2 < 1.75, 50 < v2 < 60; the refractive index of the third lens G3 is n3, and the Abbe number is v3, which satisfy the relationship: 1.48 < n3 < 1.55, 70 < v3 < 85; the refractive index of the fourth lens G4 is n4, and the Abbe number is v4, which satisfy the relationship: 1.70 < n4 < 1.80, 45 < v4 < 55.

[0011] As an improvement of a double telecentric lens according to the present invention, the focal length of the fifth lens G5 is f5, and it satisfies the relationship with the focal length fGb of the rear lens group Gb: 0.25 < |f5 / fGb| < 0.5.

[0012] As an improvement of a double telecentric lens according to the present invention, the focal length of the sixth lens G6 is f6, and it satisfies the relationship with the focal length fGb of the rear lens group Gb: 0.5 < |f6 / fGb| < 1.5.

[0013] As an improvement of a double telecentric lens according to the present invention, the focal length of the seventh lens G7 is f7, and it satisfies the relationship with the focal length fGb of the rear lens group Gb: 0.5 < |f7 / fGb| < 1.5.

[0014] As an improvement of a double telecentric lens according to the present invention, the aperture stop S of the optical device is located in front of the fifth lens G5, and the beam splitter prism P is arranged between the fourth lens G4 and the aperture stop S, and the beam splitter prism P is used to introduce a coaxial illumination light source.

[0015] As an improvement of the bi-telecentric lens described in the present invention, the material of the first lens G1 is a low-dispersion glass material.

[0016] The beneficial effect of the present invention is that the present invention includes an optical device, wherein the optical device is sequentially provided with a first lens G1 with positive focal power and a biconvex structure, a second lens G2 with negative focal power and a meniscus structure, a third lens G3 with positive focal power and a biconvex structure, a fourth lens with negative focal power and a biconcave or plano-concave structure, a beam splitter prism P, a fifth lens G5 with negative focal power and a biconcave structure, a sixth lens G6 with positive focal power and a meniscus structure, and a seventh lens G7 with positive focal power and a meniscus or plano-convex structure from the object side to the image side, and the second lens G2, the third lens G3 and the fourth lens G4 form a triplet lens U1. In the optical device, the use of the low-dispersion first lens and the triplet lens is conducive to correcting the chromatic aberration existing in the high-magnification telecentric lens, and the triplet lens is conducive to reducing the aberration borne by a single refractive surface of the lens, which can effectively reduce the tolerance sensitivity of the optical device. The object-side telecentricity can be less than 0.1°, the image-side telecentricity can be less than 0.2°, the distortion can be less than 0.1%, and the MTF can be greater than 0.3 at 140lp / mm, which meets the requirements of high-resolution dual-telecentric lenses. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a structural schematic diagram of the present invention.

[0018] Figure 2 It is a light path diagram of the optical device of the present invention.

[0019] Figure 3 2 is a distortion diagram of the optical device of the present invention.

[0020] Figure 4 It is the MTF diagram of the optical device of the present invention. DETAILED DESCRIPTION

[0021] For example, certain words are used in the specification and claims to refer to specific components. Those skilled in the art should understand that hardware manufacturers may use different terms to refer to the same component. This specification and claims do not use differences in names as a way to distinguish components, but use differences in the functions of components as the criteria for distinction. For example, "including" mentioned throughout the specification and claims is an open term, so it should be interpreted as "including but not limited to". "Approximately" means that within an acceptable error range, those skilled in the art can solve technical problems within a certain error range and basically achieve technical effects.

[0022] In the description of the present invention, it should be understood that the directions or positional relationships indicated by the terms "upper", "lower", "front", "rear", "left", "right", "horizontal", etc. are based on the directions or positional relationships shown in the drawings, and are 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 direction, be constructed and operate in a specific direction, and therefore cannot be understood as limiting the present invention.

[0023] In the invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be the internal communication of two elements. For ordinary technicians in this field, the specific meanings of the above terms in the invention can be understood according to specific circumstances.

[0024] The following is combined with Figures 1 to 4 The present invention is further described in detail, but is not intended to limit the present invention.

[0025] A double telecentric lens comprises an optical device, wherein the optical device is sequentially provided with a first lens G1 with positive focal power and a biconvex structure, a second lens G2 with negative focal power and a meniscus structure, a third lens G3 with positive focal power and a biconvex structure, a fourth lens G4 with negative focal power and a biconcave or plano-concave structure, a beam splitter prism P, a fifth lens G5 with negative focal power and a biconcave structure, a sixth lens G6 with positive focal power and a meniscus structure, and a seventh lens G7 with positive focal power and a meniscus or plano-convex structure from an object side to an image side, wherein the second lens G2, the third lens G3 and the fourth lens G4 form a triplet lens U1.

[0026] Preferably, the first lens G1 and the triplet lens U1 form a front lens group Ga, the focal length of the front lens group Ga is fGa, the fifth lens G5, the sixth lens G6 and the seventh lens G7 form a rear lens group Gb, and the focal length of the rear lens group Gb is fGb.

[0027] Preferably, the focal length of the first lens G1 is f1, and the focal length f1 of the first lens G1 and the focal length fGa of the front lens group Ga satisfy the relationship: 0.8<|f1 / fGa|<1.8.

[0028] Preferably, the focal length of the triplet lens U1 is fu1, which satisfies the relationship 3<|fu1 / fGa|<5 with the focal length fGa of the front lens group Ga.

[0029] Preferably, the refractive index of the second lens G2 is n2 and the Abbe number is v2, which satisfy the relational expression: 1.65 < n2 < 1.75, 50 < v2 < 60; the refractive index of the third lens G3 is n3 and the Abbe number is v3, which satisfy the relational expression: 1.48 < n3 < 1.55, 70 < v3 < 85; the refractive index of the fourth lens G4 is n4 and the Abbe number is v4, which satisfy the relational expression: 1.70 < n4 < 1.80, 45 < v4 < 55.

[0030] Preferably, the focal length of the fifth lens G5 is f5, and it satisfies the relational expression with the focal length fGb of the rear lens group Gb: 0.25 < |f5 / fGb| < 0.5.

[0031] Preferably, the focal length of the sixth lens G6 is f6, and it satisfies the relational expression with the focal length fGb of the rear lens group Gb: 0.5 < |f6 / fGb| < 1.5.

[0032] Preferably, the focal length of the seventh lens G7 is f7, and it satisfies the relational expression with the focal length fGb of the rear lens group Gb: 0.5 < |f7 / fGb| < 1.5.

[0033] Preferably, the aperture stop S of the optical device is located in front of the fifth lens G5, and the beam splitter prism P is arranged between the fourth lens G4 and the aperture stop S. The beam splitter prism P is used to introduce a coaxial illumination light source. The coaxial illumination light source or other imaging systems are introduced through the beam splitter prism P.

[0034] Preferably, the material of the first lens G1 is a low-dispersion glass material. In this optical device, the use of the low-dispersion first lens and the cemented triplet lens is beneficial to correcting the chromatic aberration existing in the high-magnification telecentric lens. At the same time, the cemented triplet lens is beneficial to reducing the aberration borne by a single refractive surface of the lens, and can effectively reduce the tolerance sensitivity of the optical device.

[0035] In this embodiment, the data of the optical device are as follows:

[0036]

[0037]

[0038] In this embodiment, fGa = 46.29 mm, fGb = 52.88 mm, f1 = 60.65 mm, fu1 = 193.7 mm, f5 = -18.92 mm, f6 = 54.2 mm, f7 = 48.59 mm; it can be obtained that

[0039] |f1 / fGa| = 1.31, |fu1 / fGa| = 4.18, |f5 / fGb| = 0.36,

[0040] |f6 / fGb| = 1.02, |f7 / fGb| = 0.92.

[0041] Satisfies the relationship:

[0042] 0.8<|f1 / fGa|<1.8, 3<|fu1 / fGa|<5, 0.25<|f5 / fGb|<0.5,

[0043] 0.5<|f6 / fGb|<1.5, 0.5<|f7 / fGb|<1.5.

[0044] In this example, the working distance of the double telecentric lens optical device is 114 mm, the object-image conjugate distance is 255 mm, the half image height is 5.5 mm, the effective aperture value is 6.5, and the magnification is 1 times.

[0045] The optical device according to the embodiment of the present invention can achieve: object-side telecentricity less than 0.1°, image-side telecentricity less than 0.2°; distortion less than 0.1%; MTF greater than 0.3 at 140lp / mm, meeting the requirements of a high-resolution dual-telecentric lens.

[0046] According to the disclosure and teaching of the above description, those skilled in the art to which the present invention belongs can also change and modify the above embodiment. Therefore, the present invention is not limited to the above specific embodiment, and any obvious improvement, replacement or modification made by those skilled in the art on the basis of the present invention belongs to the protection scope of the present invention. In addition, although some specific terms are used in this specification, these terms are only for the convenience of description and do not constitute any limitation to the present invention.

Claims

1. A bi-telecentric lens, characterized in that: It includes an optical device, which is successively provided with a first lens G1 having a positive optical power and a biconvex structure, a second lens G2 having a negative optical power and a meniscus structure, a third lens G3 having a positive optical power and a biconvex structure, a fourth lens G4 having a negative optical power and a biconcave or plano-concave structure, a beam splitter prism P, a fifth lens G5 having a negative optical power and a biconcave structure, a sixth lens G6 having a positive optical power and a meniscus structure, and a seventh lens G7 having a positive optical power and a meniscus or plano-convex structure from the object side to the image side. The second lens G2, the third lens G3 and the fourth lens G4 form a triple cemented lens U1; Among them, the first lens G1 and the triple cemented lens U1 form a front lens group Ga, the focal length of the front lens group Ga is fGa, the fifth lens G5, the sixth lens G6 and the seventh lens G7 form a rear lens group Gb, and the focal length of the rear lens group Gb is fGb; The focal length of the first lens G1 is f1, and the focal length f1 of the first lens G1 and the focal length fGa of the front lens group Ga satisfy the relationship: 0.8 < |f1 / fGa| < 1.8; The focal length of the triple cemented lens U1 is fu1, and it satisfies the relationship with the focal length fGa of the front lens group Ga: 3 < |fu1 / fGa| < 5; The refractive index of the second lens G2 is n2, and the Abbe number is v2, which satisfies the relationship: 1.65 < n2 < 1.75, 50 < v2 < 60; the refractive index of the third lens G3 is n3, and the Abbe number is v3, which satisfies the relationship: 1.48 < n3 < 1.55, 70 < v3 < 85; the refractive index of the fourth lens G4 is n4, and the Abbe number is v4, which satisfies the relationship: 1.70 < n4 < 1.80, 45 < v4 < 55; The focal length of the fifth lens G5 is f5, and it satisfies the relationship with the focal length fGb of the rear lens group Gb: 0.25 < |f5 / fGb| < 0.5; The focal length of the sixth lens G6 is f6, and it satisfies the relationship with the focal length fGb of the rear lens group Gb: 0.5 < |f6 / fGb| < 1.5; The focal length of the seventh lens G7 is f7, and it satisfies the relationship with the focal length fGb of the rear lens group Gb: 0.5 < |f7 / fGb| < 1.5; The aperture stop S of the optical device is located in front of the fifth lens G5, and the beam splitter prism P is arranged between the fourth lens G4 and the aperture stop S. The beam splitter prism P is used to introduce a coaxial illumination light source.

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