An object-side telecentric optical imaging system with long object distance

Abstract

The invention discloses an object-side telecentric optical imaging system with a long object distance, and relates to the field of optical imaging. The optical system comprises a first lens, a second lens, a third lens, an aperture, a fourth lens, a fifth lens, a sixth lens and a seventh lens in sequence from the object side to the image side along the optical axis; the optical focal lengths of the first lens, the third lens, the fourth lens, the fifth lens and the seventh lens are positive, and the optical focal lengths of the second lens and the sixth lens are negative; and -0.51<f1 / f<-0.36, 0.45<f2 / f<0.63, -0.66<f3 / f<-0.49, -0.18<f4 / f<-0.07, -0.10<f5 / f<-0.05, 0.05<f6 / f<0.06, -0.04<f7 / f<-0.02, wherein: f is the focal length of the object side telecentric optical imaging system; f1, f2, f3, f4, f5, f6, f7 are the focal lengths of the first lens, the second lens, the third lens, the fourth lens, the fifth lens, the sixth lens and the seventh lens in sequence. The invention has the advantages of long object distance, high object telecentricity, low distortion, large depth of field, etc.

Description

Technical Field

[0001] The invention relates to the field of optical imaging, and in particular to an object-side telecentric optical imaging system with a long object distance. Background Art

[0002] With the advancement of optoelectronic technology, machine vision-based inspection systems have been widely used due to their advantages of fast inspection speed, high measurement accuracy, and online real-time monitoring. Among them, imaging lenses are essential components of inspection systems. Since object-side telecentric lenses can maintain almost constant magnification within a certain depth of field, and have the characteristics of large depth of field and low distortion, they are widely used in visual inspection systems.

[0003] The object distances of currently commonly used object-space optical imaging optical systems are relatively small, ranging from tens of millimeters to hundreds of millimeters. However, in some special application scenarios, the imaging system cannot be installed at close range, which requires an object-space telecentric optical system with a long working distance. Summary of the invention

[0004] Technical problem to be solved by the invention

[0005] In view of the above problems existing in the prior art, the present invention provides a long object distance object-side telecentric optical imaging system, which has the advantages of long object distance, high object-side telecentricity, low distortion and large depth of field, and can be applied to long-distance optical morphology measurement.

[0006] Technical Solution

[0007] To solve the above problems, the technical solution provided by the present invention is:

[0008] An object-side telecentric optical imaging system with a long object distance comprises, in order from the object side to the image side along the optical axis, a first lens, a second lens, a third lens, an aperture, a fourth lens, a fifth lens, a sixth lens and a seventh lens;

[0009] The optical power of the first lens, the third lens, the fourth lens, the fifth lens and the seventh lens is positive, and the optical power of the second lens and the sixth lens is negative; and

[0010] -0.51<f1 / f<-0.36, 0.45<f2 / f<0.63, -0.66<f3 / f<-0.49, -0.18<f4 / f<-0.07, -0.10<f5 / f<-0.05, 0.05<f6 / f<0.06, -0.04<f7 / f<-0.02, among which:

[0011] f is the focal length of the object-side telecentric optical imaging system;

[0012] f1, f2, f3, f4, f5, f6, f7 are the focal lengths of the first lens, the second lens, the third lens, the fourth lens, the fifth lens, the sixth lens and the seventh lens respectively.

[0013] Furthermore, the first lens, the second lens, the third lens, the fourth lens, the fifth lens, the sixth lens and the seventh lens are all spherical lenses.

[0014] Further, the first lens, the third lens, the fourth lens and the seventh lens are biconvex lenses, and the second lens, the fifth lens and the sixth lens are meniscus lenses.

[0015] Further, the first lens and the second lens form a first double-cemented lens, the fourth lens and the fifth lens form a second double-cemented lens, and the sixth lens and the seventh lens form a third double-cemented lens.

[0016] Further, the center thicknesses of the first lens, the second lens, the third lens, the fourth lens, the fifth lens, the sixth lens and the seventh lens are 15 mm, 15 mm, 13.3 mm, 4.4 mm, 3.0 mm, 1.0 mm and 4.5 mm respectively;

[0017] The air intervals between the first double-cemented lens, the third lens, the aperture, the second double-cemented lens and the third double-cemented lens are 178.5 mm, 116 mm, 25 mm and 36.2 mm respectively.

[0018] Furthermore, the surface The curvature radii are 211.93mm, -109.29mm, -3239.70mm, 104.10mm, -871.70mm, 2499.77mm, -36.35mm, -10.0mm, 23.33mm, 8.56mm, and -26.87mm respectively.

[0019] Furthermore, the refractive index of the first lens is 1.53, and the dispersion coefficient is 60.16; the refractive index of the second lens is 1.65, and the dispersion coefficient is 33.65; the refractive index of the third lens is 1.52, and the dispersion coefficient is 64.11; the refractive index of the fourth lens is 1.74, and the dispersion coefficient is 28.20; the refractive index of the fifth lens is 1.61, and the dispersion coefficient is 56.40; the refractive index of the sixth lens is 1.85, and the dispersion coefficient is 32.17; the refractive index of the seventh lens is 1.69, and the dispersion coefficient is 54.71.

[0020] Furthermore, the first lens, the third lens and the fifth lens are made of crown glass; the second lens is made of heavy flint glass; the fourth lens is made of flint glass; the sixth lens is made of lanthanum flint glass; and the seventh lens is made of lanthanum crown glass.

[0021] Beneficial Effects

[0022] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects:

[0023] (1) The object-side telecentric optical imaging system with a long object distance of the present invention has the advantages of long object distance, high object-side telecentricity, low distortion, and large depth of field, and can be applied to long-distance optical topography measurement;

[0024] (2) The object-side telecentric optical imaging system with a long object distance of the present invention is made of ordinary glass and has a spherical mirror and a double-glued structure, which is easy to process;

[0025] (3) The object-side telecentric optical imaging system with a long object distance of the present invention has a distance from the last surface of the optical system to the image plane of 43.1 mm, which is greater than 17.5 mm, meets the technical requirements of the C-mount of industrial cameras, and can be used with 1 / 3″ CCD or CMOS imaging chips;

[0026] (4) The object-side telecentric optical imaging system of the present invention has an object distance of up to 2 meters, a depth of field of up to 40 mm, and an object-side telecentricity of less than 0.15°;

[0027] (5) The object-side telecentric optical imaging system with a long object distance of the present invention has a small F number and a large field of view, the F number can reach 2.5, the full field of view can reach 40 mm, the magnification is 0.15, the distortion is low, and the maximum distortion is less than 0.1%. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a structural schematic diagram of the object side telecentric optical imaging system of the present invention;

[0029] Figure 2 is the MTF (Modulation Transfer Function) curve of the object-side telecentric optical imaging system of the present invention;

[0030] Figure 3 The field curvature and relative distortion curves of the object-side telecentric optical imaging system of the present invention;

[0031] Figure 4 is the energy concentration curve of the object-side telecentric optical imaging system of the present invention;

[0032] In the accompanying drawings: 1, first lens; 2, second lens; 3, third lens; 4, fourth lens; 5, fifth lens; 6, sixth lens; 7, seventh lens; 8, aperture. DETAILED DESCRIPTION

[0033] The specific implementation methods of the present invention are further explained in detail below by describing the embodiments with reference to the accompanying drawings, with the aim of helping those skilled in the art to have a more complete, accurate and in-depth understanding of the concept and technical solution of the present invention and facilitating its implementation.

[0034] See also Figure 1 In this embodiment, an object-side telecentric optical imaging system with a long object distance includes, from the object side to the image side along the optical axis, a first lens 1, a second lens 2, a third lens 3, an aperture 8, a fourth lens 4, a fifth lens 5, a sixth lens 6 and a seventh lens 7. The aperture 8 is located near the image-side focal plane of the front lens group to ensure the object-side telecentricity requirement.

[0035] The optical power of the first lens 1, the third lens 3, the fourth lens 4, the fifth lens 5 and the seventh lens 7 is positive, and the optical power of the second lens 2 and the sixth lens 6 is negative; and the following conditions are satisfied:

[0036] -0.51<f1 / f<-0.36, 0.45<f2 / f<0.63, -0.66<f3 / f<-0.49, -0.18<f4 / f<-0.07, -0.10<f5 / f<-0.05, 0.05<f6 / f<0.06, -0.04<f7 / f<-0.02, among which:

[0037] f is the focal length of the object-side telecentric optical imaging system;

[0038] f1, f2, f3, f4, f5, f6, f7 are the focal lengths of the first lens 1, the second lens 2, the third lens 3, the fourth lens 4, the fifth lens 5, the sixth lens 6 and the seventh lens 7 respectively.

[0039] Specifically, in this embodiment, the first lens 1, the second lens 2, the third lens 3, the fourth lens 4, the fifth lens 5, the sixth lens 6 and the seventh lens 7 are all spherical lenses. Among them, the first lens 1, the third lens 3, the fourth lens 4 and the seventh lens 7 are biconvex lenses, and the second lens 2, the fifth lens 5 and the sixth lens 6 are meniscus lenses.

[0040] The first lens 1 and the second lens 2 have the same facing surface curvature radius, and the two are glued together to form a first double-glue lens. The fourth lens 4 and the fifth lens 5 have the same facing surface curvature radius, and the two are glued together to form a second double-glue lens. The sixth lens 6 and the seventh lens 7 have the same facing surface curvature radius, and the two are glued together to form a third double-glue lens.

[0041] In addition, the first lens 1, the third lens 3 and the fifth lens 5 are made of crown glass; the second lens 2 is made of heavy flint glass; the fourth lens 4 is made of flint glass; the sixth lens 6 is made of lanthanum flint glass; and the seventh lens 7 is made of lanthanum crown glass.

[0042] Specific parameters of the optical system of this embodiment are shown in the following table:

[0043]

[0044] The object-side telecentric optical imaging system in this embodiment forms a real erect image, the image diameter is 6 mm, and the angle between the main ray and the optical axis is no greater than 0.15°; Figure 2 As shown in , the cutoff frequency of all field rays is greater than 100lp / mm, and the average MTF value is greater than 0.25 at 50lp / mm; Figure 3 As shown in , the maximum distortion does not exceed 0.1%; Figure 4 As shown in the figure, the relative illumination is greater than 97% within the image field of 6mm. The following technical indicators can be achieved:

[0045] Image side F number: 3.5;

[0046] Maximum field of view of object space: 40 mm;

[0047] Object working distance: 2000 mm;

[0048] Magnification: 0.15;

[0049] Object telecentricity: <0.15°.

[0050] This solution solves the aberration correction problem of the object telecentric optical path under large field of view and large object distance, which ensures the design requirements of object telecentricity while ensuring excellent image quality and small distortion.

[0051] The present invention and its embodiments are described schematically above, and the description is not restrictive. The drawings show only one embodiment of the present invention, and the actual structure is not limited thereto. Therefore, if a person skilled in the art is inspired by it and designs a structural method and an embodiment similar to the technical solution without creativity without departing from the purpose of the invention, they shall all fall within the protection scope of the present invention.

Claims

1. An object-side telecentric optical imaging system with a long object distance, comprising, in order from the object side to the image side along the optical axis, a first lens (1), a second lens (2), a third lens (3), an aperture (8), a fourth lens (4), a fifth lens (5), a sixth lens (6) and a seventh lens (7); characterized in that: The angle between the principal ray and the optical axis is no greater than 0.15°; The optical focal powers of the first lens (1), the third lens (3), the fourth lens (4), the fifth lens (5) and the seventh lens (7) are positive values, and the optical focal powers of the second lens (2) and the sixth lens (6) are negative values; and -0.51< f 1 / f <-0.36,0.45< f 2 / f <0.63,-0.66< f 3 / f <-0.49,-0.18< f 4 / f <-0.07,-0.10< f 5 / f <-0.05,0.05< f 6 / f <0.06,-0.04< f 7 / f <-0.02, where: f is the focal length of the object-side telecentric optical imaging system; f 1. f 2. f 3. f 4. f 5. f 6. f 7 are the focal lengths of the first lens (1), the second lens (2), the third lens (3), the fourth lens (4), the fifth lens (5), the sixth lens (6) and the seventh lens (7) respectively.

2. The object-side telecentric optical imaging system with a long object distance according to claim 1, characterized in that: The first lens (1), the second lens (2), the third lens (3), the fourth lens (4), the fifth lens (5), the sixth lens (6) and the seventh lens (7) are all spherical lenses.

3. The object-side telecentric optical imaging system with a long object distance according to claim 2, characterized in that: The first lens (1), the third lens (3), the fourth lens (4) and the seventh lens (7) are biconvex lenses, and the second lens (2), the fifth lens (5) and the sixth lens (6) are meniscus lenses.

4. The object-side telecentric optical imaging system with a long object distance according to claim 3, characterized in that: The first lens (1) and the second lens (2) form a first double-cemented lens, the fourth lens (4) and the fifth lens (5) form a second double-cemented lens, and the sixth lens (6) and the seventh lens (7) form a third double-cemented lens.

5. The object-side telecentric optical imaging system with a long object distance according to claim 4, characterized in that: The center thicknesses of the first lens (1), the second lens (2), the third lens (3), the fourth lens (4), the fifth lens (5), the sixth lens (6) and the seventh lens (7) are 15 mm, 15 mm, 13.3 mm, 4.4 mm, 3.0 mm, 1.0 mm and 4.5 mm respectively; The air intervals between the first double-cemented lens, the third lens (3), the aperture (8), the second double-cemented lens and the third double-cemented lens are 178.5 mm, 116 mm, 25 mm and 36.2 mm respectively.

6. The object-side telecentric optical imaging system with a long object distance according to claim 4, characterized in that: The refractive index of the first lens (1) is 1.53, and the dispersion coefficient is 60.16; The refractive index of the second lens (2) is 1.65, and the dispersion coefficient is 33.65; The refractive index of the third lens (3) is 1.52, and the dispersion coefficient is 64.11; The refractive index of the fourth lens (4) is 1.74 and the dispersion coefficient is 28.20; The refractive index of the fifth lens (5) is 1.61, and the dispersion coefficient is 56.40; The refractive index of the sixth lens (6) is 1.85 and the dispersion coefficient is 32.17; The refractive index of the seventh lens (7) is 1.69 and the dispersion coefficient is 54.

71.

7. The object-side telecentric optical imaging system with a long object distance according to any one of claims 1 to 6, characterized in that: The first lens (1), the third lens (3) and the fifth lens (5) are made of crown glass; the second lens (2) is made of heavy flint glass; the fourth lens (4) is made of flint glass; the sixth lens (6) is made of lanthanum flint glass; and the seventh lens (7) is made of lanthanum crown glass.

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