A small-f-number athermal telecentric wide-angle f-theta lens

Abstract

The present application relates to a kind of small F number anastigmatic wide-angle F-theta lens, it is related to the field of optical equipment, first mirror group, third lens, aperture stop, second mirror group, optical filter, protective glass and focal plane are respectively arranged along the light beam propagation path, wherein first mirror group is provided with first lens, second lens along the light beam propagation path, second mirror group is provided with fourth lens, fifth lens, sixth lens, seventh lens and eighth lens along the light beam propagation path, light beam is focused on focal plane by first lens, second lens, third lens, aperture stop, fourth lens, fifth lens, sixth lens, seventh lens, eighth lens, optical filter and protective glass, the present application has the advantages of small F number, low distortion, image far, anastigmatic and athermal.

Description

Technical Field

[0001] This invention relates to the field of optical equipment technology, and in particular to a small F-number thermocentric wide-angle F-Theta lens. Background Technology

[0002] Lens distortion refers to the deviation between the actual position of the off-axis field-of-view rays on the focal plane and the position of their principal rays, used to measure the degree of image and object distortion. Ordinary optical systems follow the object-image similarity imaging criterion, meaning the off-axis field-of-view image point position is the product of the lens focal length F and the tangent of the field-of-view angle θ (Theta). Distortion increases with the field-of-view angle. For lenses with positioning and mapping functions, distortion correction is necessary, or distortion compensation algorithms are used. The off-axis field-of-view image point position of an F-θ (Theta) lens is the product of the lens focal length F and the field-of-view angle θ. If F-θ (Theta) distortion is corrected, the angular coordinates of the object point can be directly calculated based on the object-image projection relationship, without complex inversion calculations. Therefore, low-distortion F-θ (Theta) lenses are widely used in laser scanning, surveillance and reconnaissance, target observation, and identification equipment.

[0003] Furthermore, wide-angle lenses used outdoors or in cabins in low-light conditions with large temperature variations must also meet the requirements of small F-numbers, telecentric image, and thermal asymmetry. Currently, publicly available literature on visible light wide-angle F-θ lenses generally has F-numbers greater than 2, F-θ (Theta) distortion between 1% and 5%, and an anechoic temperature range of -35℃ to 60℃. There is a lack of wide-angle F-θ (Theta) lenses with F-numbers less than 2, F-θ (Theta) distortion less than 1%, and thermal asymmetry between -40℃ and 60℃.

[0004] Therefore, to address the above shortcomings, there is a need to provide a small F-number thermocentric wide-angle F-Theta lens. Summary of the Invention

[0005] (a) Technical problems to be solved

[0006] The technical problem to be solved by this invention is to address the current lack of F-θ lenses with the required parameters.

[0007] (II) Technical Solution

[0008] To address the aforementioned technical problems, this invention provides a small F-number thermocentric wide-angle F-Theta lens. Along the beam propagation path, a first lens group, a third lens, an aperture stop, a second lens group, a filter, a protective glass, and a focal plane are arranged respectively. The first lens group includes a first lens and a second lens along the beam propagation path, and the second lens group includes a fourth lens, a fifth lens, a sixth lens, a seventh lens, and an eighth lens along the beam propagation path. The beam is focused onto the focal plane through the first lens, second lens, third lens, aperture stop, fourth lens, fifth lens, sixth lens, seventh lens, eighth lens, filter, and protective glass. Each lens satisfies the following conditions:

[0009]

[0010]

[0011]

[0012]

[0013] N1 = N2 = N6 = N7 > 1.75

[0014] N3 = N4 = N8 > 1.9

[0015] N5>1.45

[0016] γ1=γ2=γ6=γ7>45

[0017] γ3=γ4=γ8<30

[0018] γ5>80

[0019]

[0020]

[0021]

[0022]

[0023] Where BF is the back focal length; F is the total focal length of the lens; F G1 F is the focal length of the first lens group; G2 F is the focal length of the third lens; G3 γ1 to γ8 are the focal lengths of the second lens group; N1 to N8 are the refractive indices of the first to eighth lenses; γ1 to γ8 are the Abbe numbers of the first to eighth lenses; R2 is the radius of curvature of the second surface of the first lens; R4 is the radius of curvature of the second surface of the second lens; P2 is the half-aperture of the second surface of the first lens; P4 is the half-aperture of the second surface of the second lens.

[0024] As a further explanation of the present invention, preferably, both the first lens and the second lens are negative meniscus colorless spherical optical glass concave to the focal plane.

[0025] As a further explanation of the present invention, preferably, the focal length of the first lens is -23mm and the focal length of the second lens is -14mm.

[0026] As a further explanation of the present invention, preferably, the third lens is a biconvex positive power single-lens spherical lens, and the focal length of the third lens is 19mm.

[0027] As a further explanation of the present invention, preferably, the fourth lens is a biconcave negative spherical mirror, the fifth, sixth and seventh lenses are all biconvex positive spherical mirrors, and the eighth lens is a plano-concave negative spherical mirror, with the plane of the eighth lens facing the focal plane of the image.

[0028] As a further explanation of the present invention, preferably, the fourth lens and the fifth lens are cemented together, and the seventh lens and the eighth lens are cemented together.

[0029] As a further explanation of the present invention, preferably, the filter is made of quartz glass, the center thickness of the filter is 2 mm, and the bandpass is 480 nm to 660 nm.

[0030] As a further explanation of the present invention, preferably, the protective glass is optical glass with a thickness of 0.55 mm.

[0031] (III) Beneficial Effects

[0032] The above-described technical solution of the present invention has the following advantages:

[0033] This invention solves the problems of large distortion, low sensitivity, short observation distance and small thermal aberration range of wide-angle lenses by designing multiple sets of lenses. The lens has the characteristics of large field of view, low distortion, high sensitivity, telecentric image side and large thermal aberration range, and does not use an aspherical structure, so the processing cost is low. Attached Figure Description

[0034] Figure 1 This is the lens optical path diagram of the present invention;

[0035] Figure 2 These are the field curvature and F-θ distortion diagrams of this invention;

[0036] Figure 3 This is the MTF curve of the lens of the present invention at room temperature;

[0037] Figure 4 This is the MTF curve of the lens of the present invention at -40°C;

[0038] Figure 5This is the MTF curve of the lens of the present invention at 60°C.

[0039] In the diagram: 1. First lens group; 11. First lens; 12. Second lens; 2. Third lens; 3. Aperture stop; 4. Third lens group; 41. Fourth lens; 42. Fifth lens; 43. Sixth lens; 44. Seventh lens; 45. Eighth lens; 5. Filter; 6. Protective glass; 7. Focal plane. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0041] A type of small F-number thermocentric wide-angle F-Theta lens, such as... Figure 1 As shown, the first mirror group 1, the third lens 2, the aperture stop 3, the second mirror group 4, the filter 5, the protective glass 6, and the focal plane 7 are arranged along the beam propagation path.

[0042] like Figure 1 As shown, the first lens group 1 includes a first lens 11 and a second lens 12 along the beam propagation path. Both the first lens 11 and the second lens 12 are negative meniscus colorless spherical optical glass concave to the focal plane. The focal length of the first lens 11 is -23mm, and the focal length of the second lens 12 is -14mm. The refractive indices N1=N2>1.75 and the Abbe numbers γ1=γ2>45 of the first lens 11 and the second lens 12 are respectively. The ratio of the second concave surface aperture P2 of the first lens 11 to the second surface radius of curvature R2 is <0.9, and the ratio of the second concave surface aperture P4 of the second lens 12 to the second surface radius of curvature R4 is <0.7.

[0043] like Figure 1As shown, the third lens 2 is a biconvex positive power single-lens spherical mirror with a focal length of 19 mm, a refractive index N3 > 1.9, and an Abbe number γ3 < 30. The aperture stop 3 is positioned between the third lens 2 and the second lens group 4, 1.24 mm from the third lens 2 and 4 mm from the second lens group 4. The second lens group 4 includes a fourth lens 41, a fifth lens 42, a sixth lens 43, a seventh lens 44, and an eighth lens 45 along the beam propagation path. The fourth lens 41 is a biconcave negative power spherical mirror with a refractive index N4 = N1 > 1.9 and an Abbe number γ4 = γ3 < 30. The fifth lens 42, sixth lens 43, and seventh lens 44 are all biconvex positive power spherical mirrors. The refractive index N5 of the fifth lens 42 is > 1.45, and the refractive indices N6 and N7 of the sixth and seventh lenses 44 are the same as N1 and N2, all > 1.75. The Abbe number γ5 of the fifth lens 42 is greater than 80. The Abbe numbers γ6 and γ7 of the sixth lens 43 and the seventh lens 44 are the same as γ1 and γ2, all greater than 45. The eighth lens 45 is a plano-concave negative-transmission spherical mirror. The plane of the eighth lens 45 faces the focal plane 7 of the image. The refractive index of the eighth lens 45 is N8 = N3 = N4 > 1.9, and the Abbe number γ8 = γ3 = γ4 < 30. The fourth lens 41 and the fifth lens 42 are cemented together, and the seventh lens 44 and the eighth lens 45 are cemented together.

[0044] like Figure 1 As shown, filter 5 is made of quartz glass with a center thickness of 2mm and a bandpass of 480nm to 660nm. Protective glass 6 is optical glass with a thickness of 0.55mm. Focal plane 7 is the photosensitive surface of the detector, used to receive optical signals. The light beam is focused onto focal plane 7 through the first lens 11, the second lens 112, the third lens 2, the aperture stop 3, the fourth lens 41, the fifth lens 42, the sixth lens 43, the seventh lens 44, the eighth lens 45, filter 5, and protective glass 6. The lens satisfies the following conditions:

[0045]

[0046] also,

[0047]

[0048]

[0049]

[0050]

[0051]

[0052] Where BF is the back focal length; F is the total focal length of the lens; F G1 F is the focal length of the first lens group 1;G2 F is the focal length of the third lens 2; G3 R1 is the focal length of the second lens group 4; R2 is the radius of curvature of the second surface of the first lens 11; R4 is the radius of curvature of the second surface of the second lens 12.

[0053] Combination Figures 2-5 Through the above settings, the wide-angle lens of this application can achieve a working wavelength of 0.481μm to 0.656μm, a field of view of 85°, a focal length of 5.9mm, an F-number of 1.6, an image-side telecentric angle of less than 1°, an F-θ distortion of less than 0.1%, and an athermalization temperature range of -40℃ to 60℃. Wide-angle lenses have short focal lengths, small entrance pupils, low detection sensitivity, and short observation distances. Reducing the F-number of the lens can improve detection sensitivity and observation distance. Using image-side telecentricity ensures uniform illumination on the focal plane and relatively stable illumination on the focal plane during target movement. The thermal ablation within the working temperature range ensures image plane stability and clear imaging when the lens experiences temperature changes, meeting design requirements. Furthermore, it does not employ an aspherical structure, resulting in low manufacturing costs. This effectively solves the current problem of a lack of wide-angle F-θ (Theta) lenses with an F-number of less than 2, F-θ (Theta) distortion of less than 1%, and thermal ablation within the -40℃ to 60℃ temperature range.

[0054] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A small F-number thermocentric wide-angle F-Theta lens, characterized in that: A first lens group (1), a third lens (2), an aperture stop (3), a second lens group (4), a filter (5), a protective glass (6), and a focal plane (7) are arranged along the beam propagation path. The first lens group (1) has a first lens (11) and a second lens (12) along the beam propagation path. The second lens group (4) has a fourth lens (41), a fifth lens (42), a sixth lens (43), a seventh lens (44), and an eighth lens (45) along the beam propagation path. The beam is focused onto the focal plane (7) by the first lens (11), the second lens (12), the third lens (2), the aperture stop (3), the fourth lens (41), the fifth lens (42), the sixth lens (43), the seventh lens (44), the eighth lens (45), the filter (5), and the protective glass (6). Each lens satisfies the following: N1 = N2 = N6 = N7 > 1.75 N3 = N4 = N8 > 1.9 N5>1.45 γ1=γ2=γ6=γ7>45 γ3=γ4=γ8<30 γ5>80 Where BF is the back focal length; F is the total focal length of the lens; F G1 F is the focal length of the first lens group (1); G2 F is the focal length of the third lens (2); G3 γ1 to γ8 are the focal lengths of the second lens group (4); N1 to N8 are the refractive indices of the first lens (11) to the eighth lens (45); γ1 to γ8 are the Abbe numbers of the first lens (11) to the eighth lens (45); R2 is the radius of curvature of the second surface of the first lens (11); R4 is the radius of curvature of the second surface of the second lens (12); P2 is the half-aperture of the second surface of the first lens (11); P4 is the half-aperture of the second surface of the second lens (12).

2. The small F-number thermocentric wide-angle F-Theta lens according to claim 1, characterized in that: Both the first lens (11) and the second lens (12) are negative meniscus colorless spherical optical glass concave to the focal plane.

3. The small F-number thermally aberration-corrected telecentric wide-angle F-Theta lens according to claim 2, characterized in that: The first lens (11) has a focal length of -23mm, and the second lens (12) has a focal length of -14mm.

4. A small F-number thermally aberration-corrected telecentric wide-angle F-Theta lens according to claim 3, characterized in that: The third lens (2) is a biconvex positive power single-lens spherical lens with a focal length of 19mm.

5. A small F-number thermally aberration-corrected telecentric wide-angle F-Theta lens according to claim 4, characterized in that: The fourth lens (41) is a biconcave negative spherical mirror, the fifth lens (42), the sixth lens (43) and the seventh lens (44) are all biconvex positive spherical mirrors, and the eighth lens (45) is a plano-concave negative spherical mirror with the plane of the eighth lens (45) facing the focal plane (7) of the image.

6. A small F-number thermocentric wide-angle F-Theta lens according to claim 5, characterized in that: The fourth lens (41) and the fifth lens (42) are cemented together, and the seventh lens (44) and the eighth lens (45) are cemented together.

7. A small F-number thermocentric wide-angle F-Theta lens according to claim 6, characterized in that: The filter (5) is made of quartz glass, with a center thickness of 2 mm and a bandpass of 480 nm to 660 nm.

8. A small F-number thermocentric wide-angle F-Theta lens according to claim 7, characterized in that: The protective glass (6) is optical glass with a thickness of 0.55 mm.

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