Fixed-focus optical system with focal length changing along with view field

Abstract

The invention discloses a fixed-focus optical system with focal length changing along with view field, which belongs to the technical field of optical imaging and comprises a lens group, the lens group is provided with at least one free-form surface lens, so that the focal length of the system continuously changes along with the view field angle under the condition that all lenses and an image surface are kept still, and the central view field of the system is equivalent to a long-focus camera. The edge field of view is equivalent to a short-focus camera, the field of view and the resolution of the system are improved, and large-field-of-view angle detection and small-target high-precision recognition can be met at the same time. According to the fixed-focus optical system with the focal length changing along with the view field, a focusing mechanism does not need to be additionally arranged, capturing and recognition of the system on a target and simplicity, convenience, practicability and light weight of the system can be well considered, and the application requirements of miniaturization, light weight and low cost of modern photoelectric equipment are met.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical imaging, and in particular relates to a fixed-focus optical system whose focal length varies with the field of view. Background Art

[0002] In actual use, some optoelectronic devices prefer a long focal length and a small field of view for target recognition to ensure distance and accuracy. For target capture and observation, a short focal length and a large field of view are preferred. To simultaneously meet the requirements of wide field of view detection and high-precision identification of small targets, a coarse telescope can adopt an optical zoom design from a large field of view with low resolution to a small field of view with high resolution. Alternatively, a combination of a large field of view fixed-focus coarse telescope and a small field of view zoom fine telescope can be used.

[0003] Currently, the only optical systems that can meet these requirements are continuous zoom or two-step zoom systems. Continuous zoom systems present significant challenges in system design, lightweighting, cost reduction, cold screen matching, and cam design and processing. While two-step zoom systems offer a good balance between target capture and recognition and system simplicity, practicality, and lightweighting, they are still inferior to fixed-focus optical systems in terms of structural volume and lightweighting. Summary of the Invention

[0004] In response to one or more of the above-mentioned defects or improvement needs in the prior art, the present invention provides a fixed-focus optical system in which the focal length changes with the field of view, which can well meet the requirements of system miniaturization and lightweighting while achieving large field of view angle detection of targets and high-precision identification of small targets.

[0005] To achieve the above-mentioned objectives, the present invention provides a fixed-focus optical system whose focal length varies with the field of view, comprising a lens group, wherein the lens group includes a plurality of lenses arranged in sequence from the object plane to the image plane, and at least one lens among the plurality of lenses is a free-form surface lens; wherein the free-form surface lens is configured such that, while all the lenses and the image plane remain stationary, the focal length of the fixed-focus optical system continuously varies with the field of view angle, and the central field of view corresponds to a long focal length, and the edge field of view corresponds to a short focal length.

[0006] As a further improvement of the present invention, the field angle of the fixed-focus optical system is not less than 7°×5°.

[0007] As a further improvement of the present invention, the ratio of the focal length of the central field of view to the focal length of the peripheral field of view is between 1.5 and 3, and the amplitude of the focal length change from the central field of view to the peripheral field of view gradually increases.

[0008] As a further improvement of the present invention, the image height corresponding to the edge field of view is between 6 mm and 12 mm.

[0009] As a further improvement of the present invention, the ratio of the entrance pupil diameter corresponding to the central field of view to the entrance pupil diameter corresponding to the edge field of view is between 1.5 and 3.

[0010] As a further improvement of the present invention, the shape of the free-form surface of the free-form surface lens is obtained by calculating and fitting the corresponding entrance pupil diameters of the spherical lens under different field of view angles.

[0011] As a further improvement of the present invention, the lens group is composed of a first free-form surface lens, a second free-form surface lens and a third free-form surface lens arranged in sequence from the object plane to the image plane, and the shapes of the free-form surfaces of the first free-form surface lens, the second free-form surface lens and the third free-form surface are respectively calculated and fitted according to the corresponding entrance pupil diameters of the first spherical lens, the second spherical lens and the third spherical lens under different field of view angles.

[0012] As a further improvement of the present invention, a diffraction optical component is provided between the lens group and the image plane to eliminate chromatic aberration.

[0013] As a further improvement of the present invention, the diffractive optical assembly includes a plurality of diffractive optical elements.

[0014] The above-mentioned improved technical features can be combined with each other as long as they do not conflict with each other.

[0015] In general, the above technical solutions conceived by the present invention have the following beneficial effects compared with the prior art: (1) The present invention provides a fixed-focus optical system with a focal length that varies with the field of view, comprising a lens assembly. By providing at least one free-form surface lens, the focal length of the system continuously varies with the field of view angle while all lenses and the image plane remain stationary. The central field of view is equivalent to that of a telephoto camera, and the peripheral field of view is equivalent to that of a short-focus camera. This improves the field of view and resolution of the system, thereby simultaneously meeting the requirements for wide field of view detection and high-precision identification of small targets. The present invention provides a fixed-focus optical system with a focal length that varies with the field of view, without requiring a separate focusing mechanism, and can effectively balance the system's capture and identification of targets with the system's simplicity, practicality, and lightweightness, thereby meeting the application requirements of modern optoelectronic devices for miniaturization, lightweightness, and low cost.

[0016] (2) The fixed-focus optical system of the present invention, in which the focal length varies with the field of view, can improve the overall performance of the system by controlling the ratio of the focal length values ​​of the central field of view and the edge field of view and the trend of the focal length varying with the field of view angle.

[0017] (3) The fixed-focus optical system of the present invention, in which the focal length varies with the field of view, can effectively correct the system chromatic aberration and broaden the imaging band by arranging a diffractive optical element between the lens group and the image plane. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0019] Figure 1 is an overall schematic diagram of a fixed-focus optical system in which the focal length varies with the field of view in an embodiment of the present invention; Figure 2 It is a structural diagram of an initial fixed-focus optical system.

[0020] In all the drawings, the same reference numerals represent the same technical features, specifically: 1. Lens group; 11. First free-form surface lens; 12. Second free-form surface lens; 13. Third free-form surface lens; 2. Diffractive optical component; 3. Curve; 4. Image plane; 10. First spherical lens; 20. Second spherical lens; 30. Third spherical lens. DETAILED DESCRIPTION

[0021] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only intended to illustrate the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0022] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like to indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying 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 orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0023] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "plurality" means at least two, such as two, three, etc., unless otherwise specifically defined.

[0024] In the present invention, unless otherwise specified or limited, the terms "installed," "connected," "connect," "fixed," etc. should be understood in a broad sense. For example, they can refer to fixed connection, detachable connection, or integration; mechanical connection, electrical connection; direct connection, or indirect connection through an intermediate medium; internal communication between two components, or interaction between two components, unless otherwise specified. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0025] In the present invention, unless otherwise expressly specified or limited, when a first feature is "above" or "below" a second feature, it may mean that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediary. Furthermore, when a first feature is "above," "above," or "above" a second feature, it may mean that the first feature is directly above or diagonally above the second feature, or simply means that the first feature is at a higher level than the second feature. When a first feature is "below," "below," or "below" a second feature, it may mean that the first feature is directly below or diagonally below the second feature, or simply means that the first feature is at a lower level than the second feature.

[0026] See also Figure 1 The fixed-focus optical system with a focal length that varies with the field of view in a preferred embodiment of the present invention is suitable for small laser equipment, and includes a lens group 1, wherein the lens group 1 includes a plurality of lenses arranged in sequence from the object plane to the image plane 4, and at least one lens among the plurality of lenses is a free-form surface lens; wherein the free-form surface lens is configured so that the focal length of the fixed-focus optical system continuously changes with the field of view angle while all the lenses and the image plane remain stationary, and the central field of view corresponds to a long focal length and the edge field of view corresponds to a short focal length.

[0027] Free-form surfaces lack rotational symmetry, resulting in more degrees of freedom and greater aberration correction capabilities. The fixed-focus optical system in this embodiment utilizes a specific free-form lens to design a new imaging system. By continuously varying the focal length with the field of view angle, the central field of view is equivalent to that of a telephoto camera, while the peripheral field of view is equivalent to that of a short-focus camera. This reduces the number of components required, the system's size, and weight, while also improving the system's field of view and resolution. This effectively achieves the goal of miniaturization and lightweighting while simultaneously enabling wide-angle target detection and high-precision recognition of small targets.

[0028] Further preferably, a diffraction optical component 2 is provided between the lens group 1 and the image plane 4 to eliminate chromatic aberration.

[0029] Preferably, the diffractive optical assembly 2 includes several diffractive optical elements. Diffractive optical elements have unique dispersion characteristics, temperature stability, and excellent aberration correction capabilities. The dispersion characteristics of diffractive optical elements are independent of the material and have a negative orientation, which is very beneficial for achromatic aberration. They can be combined with refractive optical elements to form a hybrid achromatic system with better overall performance.

[0030] Preferably, the field of view of the fixed-focus optical system is no less than 7° × 5°. That is, the maximum horizontal angle of the system is no less than 7°, and the maximum vertical angle of the system is no less than 5°. Alternatively, the field of view of the system can be 7° × 7°, 16° × 10°, or other suitable angles.

[0031] Further preferably, the field of view angle of the fixed-focus optical system is not less than 16°×16°, that is, the maximum range of angles that can be observed by the system in the horizontal and / or vertical directions to both sides is not less than 8°.

[0032] Preferably, the ratio of the focal length of the central field of view to the focal length of the peripheral field of view is between 1.5 and 3, and the amplitude of the focal length change gradually increases from the central field of view to the peripheral field of view.

[0033] In a specific preferred embodiment, the focal length corresponding to the central field of view is 70 mm, and the focal length of the edge field of view is 35 mm. The focal length gradually decreases from 70 mm to 35 mm from the central field of view to the edge field of view, and the reduction rate gradually increases. For example, the field of view angle of the fixed-focus optical system is 16°×16°. When the field of view angles are 0°, 4°, 8°, 12°, and 16°, respectively, the corresponding field of view focal lengths are 70 mm, 67.8 mm, 61.3 mm, 50.4 mm, and 35 mm, respectively.

[0034] Preferably, the image height corresponding to the edge field of view is between 6 mm and 12 mm.

[0035] In a specific preferred embodiment, the field of view angle of the fixed-focus optical system is 16°×16°, and the image height corresponding to the edge field of view is 8.26mm. The image height gradually decreases from the edge field of view to the center field of view. Specifically, when the field of view angles are 4°, 8°, 12°, and 16°, respectively, the corresponding image heights are 2.42mm, 4.7mm, 6.69mm, and 8.26mm, respectively.

[0036] Preferably, the ratio of the entrance pupil diameter corresponding to the central field of view to the entrance pupil diameter corresponding to the edge field of view is between 1.5 and 3.

[0037] In a specific preferred embodiment, the entrance pupil diameter is 25.0 mm in the central field of view and 8.79 mm in the peripheral field of view, with the entrance pupil diameter gradually decreasing from 25 mm to 8.8 mm from the central field of view to the peripheral field of view. For example, if the field of view angle of this fixed-focus optical system is 16°×16°, when the field of view angles are 0°, 4°, 8°, 12°, and 16°, respectively, the corresponding entrance pupil diameters are 25.0 mm, 17.5 mm, 16.95 mm, 15.32 mm, and 8.79 mm.

[0038] Preferably, the shape of the free-form surface of the free-form surface lens is a spherical lens obtained by calculating the corresponding entrance pupil size under different field of view angles.

[0039] Specifically preferably, the lens group consists of a first free-form surface lens 11, a second free-form surface lens 12 and a third free-form surface lens 13, which are arranged in sequence from the object plane to the image plane, and the shapes of the free-form surfaces of the first free-form surface lens 11, the second free-form surface lens 12 and the third free-form surface lens 13 are respectively calculated and fitted according to the corresponding entrance pupil diameters of the first spherical lens, the second spherical lens and the third spherical lens under different field of view angles.

[0040] The lens group 1 is composed of a first free-form surface lens 11 , a second free-form surface lens 12 and a third free-form surface lens 13 arranged in sequence from the object plane to the image plane 4 . The F number of the fixed-focus optical system is 4.

[0041] In a specific preferred embodiment, Figure 2 The structure diagram of the initial fixed-focus optical system shown is a schematic diagram of the structure of the initial fixed-focus optical system, which consists of a first spherical lens 10, a second spherical lens 20, and a third spherical lens 30, wherein the first spherical lens 10, the second spherical lens 20, and the third spherical lens 30 are respectively a first doublet lens, a second meniscus lens, and a third doublet lens. The focal length of the initial fixed-focus optical system is 70mm, the F number is 4, and it can image visible light to achieve a rough search of the target. The following conditions were set in ZEMAX software: the field of view angle was 16°×16°, the focal length of the central field of view was 70mm, the focal length of the edge field of view was 35mm, and the F number was 4; when the field of view angles were 4°, 8°, 12°, and 16°, the focal lengths were 67.8mm, 61.3mm, 50.4mm, and 35mm, respectively; the entrance pupil diameters were 17.5mm, 16.95mm, 15.32mm, and 8.79mm, respectively; the image heights were 2.42mm, 4.7mm, 6.69mm, and 8.26mm, respectively. Figure 2The initial optical system in is adjusted, and the first spherical lens 10, the second spherical lens 20, and the third spherical lens 30 are respectively optimized to a first free-curved surface lens 11, a second free-curved surface lens 12, and a third free-curved surface lens 13 with free-curved surfaces, so as to obtain one of the fixed-focus optical systems provided in the present application with a focal length that varies with the field of view.

[0042] A diffractive optical component 2 is further provided between the third free-form surface lens 13 and the image plane 4 to eliminate chromatic aberration. In the fixed-focus optical system in which the focal length varies with the field of view, light rays with different field-of-view entrance pupil diameters are imaged on the image plane 4 after passing through the first free-form surface lens 11, the second free-form surface lens 12, the third free-form surface lens 13 and the diffractive optical component 2. The range between two points parallel to the image plane 4 in each group on the curve 3 corresponds to the image size on the image plane 4 of light rays with different fields of view after passing through the fixed-focus optical system in which the focal length varies with the field of view. Among them, the range between the two points on the curve 3 farthest from the image plane 4 is the image size on the image plane 4 when the field of view angle is maximum (16°).

[0043] In specific applications, the fixed-focus optical system whose focal length changes with the field of view can be set on the detector of the laser equipment, so that the laser equipment can be small and light while achieving target capture and recognition, and is easy to carry and use.

[0044] The fixed-focus optical system with a focal length that varies with the field of view of the present invention utilizes at least one free-form surface lens, allowing the system's focal length to continuously vary with the field of view angle while all lenses and the image plane remain stationary. The central field of view is equivalent to that of a telephoto camera, while the peripheral fields of view are equivalent to those of a short-focus camera. This simultaneously improves the system's field of view and resolution, enabling both wide-angle detection and high-precision identification of small targets. The fixed-focus optical system with a focal length that varies with the field of view of the present invention eliminates the need for a separate focusing mechanism for the coarse-grained image sensor, effectively balancing the system's ability to capture and identify targets with its simplicity, practicality, and lightweight design, meeting the application requirements of modern optoelectronic devices for miniaturization, lightweighting, and low cost.

[0045] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A fixed-focus optical system whose focal length varies with the field of view, characterized in that: The invention comprises a lens group, wherein the lens group comprises a plurality of lenses arranged in sequence from the object plane to the image plane, and at least one lens among the plurality of lenses is a free-form surface lens; wherein the free-form surface lens is configured so that when all the lenses and the image plane remain stationary, the focal length of the fixed-focus optical system continuously changes with the field of view angle, and the central field of view corresponds to a long focal length and the edge field of view corresponds to a short focal length.

2. The fixed-focus optical system with a focal length that varies with the field of view according to claim 1, wherein: The field of view of the fixed-focus optical system shall not be less than 7°×5°.

3. The fixed-focus optical system with a focal length that varies with the field of view according to claim 2, wherein: The ratio of the focal length of the central field of view to the focal length of the peripheral field of view is between 1.5 and 3, and the amplitude of the focal length change from the central field of view to the peripheral field of view gradually increases.

4. The fixed-focus optical system with a focal length that varies with the field of view according to claim 2, wherein: The image height corresponding to the edge field of view is between 6mm and 12mm.

5. The fixed-focus optical system with a focal length that varies with the field of view according to claim 2, wherein: The ratio of the entrance pupil diameter corresponding to the central field of view to the entrance pupil diameter corresponding to the edge field of view is between 1.5 and 3.

6. The fixed-focus optical system with a focal length that varies with the field of view according to claim 5, wherein: The shape of the free-form surface of the free-form surface lens is obtained by calculating and fitting the corresponding entrance pupil diameters of the spherical lens under different field of view angles.

7. The fixed-focus optical system with a focal length that varies with the field of view according to claim 6, wherein: The lens group consists of a first free-form surface lens, a second free-form surface lens, and a third free-form surface lens, which are arranged in sequence from the object plane to the image plane, and the shapes of the free-form surfaces of the first free-form surface lens, the second free-form surface lens, and the third free-form surface are respectively obtained by calculating and fitting the first spherical lens, the second spherical lens, and the third spherical lens according to the corresponding entrance pupil diameters under different field of view angles.

8. The fixed-focus optical system with a focal length that varies with the field of view according to any one of claims 1 to 7, wherein: A diffraction optical component is provided between the lens group and the image plane to eliminate chromatic aberration.

9. The fixed-focus optical system with focal length varying with field of view according to claim 8, wherein: The diffractive optical assembly includes a plurality of diffractive optical elements.

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