Adopting ogive face-type head unit with high image utilization and wide-angle imaging system

Abstract

A wide-angle imaging system using an ogive-shaped head unit with high image plane utilization belongs to the technical field of security monitoring optical systems. Existing image sensors have low utilization rates, with bright images at the center and dark images at the edges. The present invention sequentially arranges a head unit, an aperture, and a subsequent lens group along the imaging optical path. The incident imaging light is reflected once by the head unit and then passes through the aperture and subsequent lens group to form an image on the image plane. The aperture is located at the intersection of each HFOV of incident imaging light after being reflected by the head unit. The head unit is served by an optical element with an ogive surface. The optical element is one of the following two types: an ogive-shaped refractive-reflective lens, whose front mirror surface is a refractive mirror surface and whose rear mirror surface is a reflective mirror surface; or an ogive-shaped reflective mirror. The ogive surface is a rotational curved surface and is the tail portion of a complete ogive surface. The subsequent lens group is capable of converging the imaging light beam and correcting imaging aberrations.

Description

Technical Field

[0001] The invention belongs to the technical field of security monitoring optical systems. Background Art

[0002] Wide-angle imaging optical systems are widely used in the security and surveillance field. In wide-angle imaging optical systems, the field of view (FOV) and resolution determine the amount of information the system can capture. Optical systems with a wide FOV can capture target information across a wider field of view, while high resolution enables the system to capture more target detail within the imaged space. Furthermore, achieving high resolution requires a long focal length and a large aperture, but this makes it difficult to increase the FOV. Furthermore, the geometric aberrations of the optical system increase with increasing aperture and FOV. Large geometric aberrations lead to a larger spot size, which in turn increases image pixel size, reducing resolution. (Physical diffraction can also lead to low resolution, but since the present invention operates in the visible light band, no significant physical diffraction occurs.) This is the interdependent relationship between the FOV and resolution of existing wide-angle imaging optical systems. To achieve a balanced balance between FOV and resolution, it is necessary to find an optimal solution in terms of the optical system's light energy collection capacity, volume, and resolution.

[0003] Under the premise that the wide-angle imaging optical system has the ability to collect light energy, image plane utilization is also a measure to improve imaging resolution. The blind area in the center of the image plane leads to a decrease in image plane utilization, and the use of larger photoelectric detection devices fails to fully utilize the size.

[0004] Furthermore, the popularization of security monitoring also requires that the wide-angle imaging optical system should be low-cost. From the perspective of concealment and installation, it is also required that the wide-angle imaging optical system should be compact in structure and small in size.

[0005] Among existing wide-angle imaging optical systems, there is a solution disclosed in a Chinese patent with the patent number ZL202211032753.1, named "Panoramic Ring Optical System". This solution adopts a catadioptric structure, and the imaging is clear and stable. However, the head unit of this optical system is composed of two lenses, and the subsequent lens group includes at least four lenses. It can be seen that it uses a large number of lenses, has a complex structure, and is costly. Moreover, its total optical length is long and its volume is large. These structural characteristics also make the processing and assembly of the optical system more difficult.

[0006] Among the existing wide-angle imaging optical systems, there is also a solution disclosed in a Chinese patent with the patent number ZL201910802850.6, entitled "A 4K high-resolution panoramic annular optical system". This solution also adopts a catadioptric structure, and the imaging is extremely clear. However, due to the multiple use of the catadioptric (for example, double reflection) structure, the light energy loss is large, the material cost is expensive, and the actual processing is difficult, which cannot meet the requirements of low cost and convenient assembly and adjustment.

[0007] In fact, the wide-angle imaging optical system has two typical defects:

[0008] 1. Since the second reflective surface of the panoramic lens block head unit coincides with the optical axis of the optical system, it blocks the incident light from the front of the optical system, resulting in a circular blind spot in the center of the image plane that cannot be conjugated with the external object point, reducing the utilization rate of the image sensor (such as the optoelectronic device located on the image plane).

[0009] 2. Since the panoramic annular imaging optical system needs to complete the imaging of an ultra-large field of view on a limited imaging area (image plane), the refractive power required by the imaging lens and the surface shape corresponding to each annular field of view in the ultra-large field of view changes dramatically, causing the relative illumination of the light in each annular field of view to change steeply, and the image brightness decreases rapidly from the center to the edge. Summary of the Invention

[0010] In order to improve the image plane utilization and the uniformity of image plane illumination while ensuring a sufficiently large imaging field of view (panoramic) and high resolution (HD), and at the same time simplify the overall structure of the optical system, making the overall structure of the optical system more compact, smaller in size, and lighter in weight, and further reduce the difficulty of processing, facilitate assembly and adjustment, and achieve low cost, the present invention proposes a solution of "a wide-angle imaging system with high image plane utilization using an ogive face-type head unit".

[0011] The present invention adopts an ogive face-type head unit with high image plane utilization and wide-angle imaging system, which includes a head unit, an aperture, and a subsequent lens group arranged on the same optical axis, and is characterized in that: Figure 1 As shown, a head unit, an aperture 1, and a subsequent lens group 2 are sequentially arranged along the imaging optical path. The incident imaging light is reflected once by the head unit and then passes through the aperture 1 and the subsequent lens group 2 to be imaged on the image plane 3. The aperture 1 is located at the intersection of the incident imaging light of each HFOV (half field of view) after being reflected by the head unit. The head unit is served by an optical element with an ogive surface. The optical element is one of the following two types: one is an ogive surface refractive reflective lens 4, such as Figure 1 As shown, the front mirror surface is a refractive mirror surface 4-1, and the rear mirror surface is a reflective mirror surface 4-2; the second is an ogive surface reflector 5, as shown Figure 2 As shown;

[0012] The ogive surface is a surface of revolution and is the tail portion of a complete ogive surface, such as Figure 3 As shown, its expression is:

[0013] ,

[0014] in:

[0015] ,

[0016] ,

[0017] Where: x, y, and z are the three coordinate values ​​of any point on the surface of revolution in the rectangular coordinate system, the z value is the sag of the surface of revolution, which represents the difference between the coordinate values ​​of any point on the surface of revolution and the vertex in the direction of the optical axis, and r is the radial coordinate of the surface of revolution (the vertical axis distance from the incident point of the incident imaging light on the refracting mirror 4-1 to the optical axis z); is the compensation value, which is the distance between the rotation axis z' of the complete ogive surface and the rotation axis z of the tail ogive surface, such as Figure 3 As shown; c is the curvature of the vertex of the revolution surface; k is the conic coefficient of the revolution surface; Represents the high-order aspheric coefficients (orthogonal polynomial coefficients) of the rotational surface, i = 1, 2, 3, ... ,n,n≤8;

[0018] When the head unit is an ogive-type refractive reflective lens 4, the parameters c of the refractive mirror surface 4-1 and the reflective mirror surface 4-2 are c1 and c2 respectively, as shown in FIG. Figure 3 As shown, the incident angle of aperture 1 is , solving for the parameters:

[0019] ,

[0020] ,

[0021] The parameters r0 of the refractive mirror 4-1 and the reflective mirror 4-2 are respectively 01 、r 02 , and is determined by the following formula:

[0022] ,

[0023] ,

[0024] Where: is the aperture of aperture 1, is the axial distance between the aperture 1 and the refractive mirror 4-1, HFOV m is the minimum half field angle, n is the refractive index of the ogive surface refractive reflective lens 4, is the vertical axis magnification of the ogive surface type refractive reflective lens 4, and t is the thickness of the ogive surface type refractive reflective lens 4;

[0025] The subsequent lens group 2 is capable of converging the imaging light beam and correcting imaging aberrations.

[0026] The technical effects of the present invention are as follows.

[0027] First, it can achieve high-quality imaging at all angles with a large field of view. Regardless of whether the head unit is served by the ogive surface-shaped refractive reflective lens 4 or the ogive surface-shaped reflective mirror 5, the ogive surface can achieve high-quality imaging at all angles within the HFOV (half field of view) range of 27° to 105°. This is because the ogive surface is formed by re-fitting the remaining part of the complete ogive surface after removing the central area, or in other words, removing the remaining tail part of the head part of the complete ogive surface, which is the tail ogive surface mentioned above. Figure 3 As shown in the figure, the figure represents half of the complete ogive surface with its rotation axis z' as the boundary. However, the tail ogive surface is half of the complete ogive surface and then removes the remaining part between the rotation axis z' of the complete ogive surface and the rotation axis z of the tail ogive surface. The tail ogive surface makes the imaging light surface coefficients at different angles different and all protrude toward the direction of the light. Such an ogive surface head unit has negative optical focal length and can achieve rapid convergence. That is, the light beam emitted from the ogive surface head unit is significantly contracted compared with the light beam incident on the ogive surface head unit. While achieving high-quality imaging at all angles, it also brings a direct effect, that is, the axial length (total optical length) of the wide-angle imaging system can be designed to be shorter, such as 12mm. Due to the structural characteristics of the tail ogive surface, the refractive power required by the head unit and the surface corresponding to each annular field of view in the wide-angle field of view is relatively consistent, so that the relative illumination of the imaging light from each annular field of view on the image plane does not change much, the image brightness appears almost the same from the center to the edge, and the uniformity of the image plane illumination is improved.

[0028] Secondly, although the object plane has a central blind spot, such as ±27°, the image plane does not have a central blind spot. The front and rear mirror surfaces of the ogive surface refractive reflective lens 4 are formed by rotating the tail of the complete ogive surface around the z-axis (the optical axis of the wide-angle imaging system). The vertex of the complete ogive surface (located on the z' axis) is separated from the optical axis (z-axis) of the wide-angle imaging system. r0 is the distance from the rotation axis of the complete ogive surface to the optical axis of the wide-angle imaging system, as shown in Figure 2. Figure 3 As shown, if a complete ogive surface is used, with the vertex located on the z-axis, light incident at that vertex at a certain incident angle ultimately does not reach the center of the image plane, resulting in the center of the image plane not being utilized. However, the head unit of the present invention has good controllability of the light reflection angle near the z-axis, strong controllability of deflection and reflection, and controllable deflection direction. Through the cooperation of the subsequent lens group 2, imaging light incident on the vertex of the head unit and its vicinity ultimately illuminates the center of the image plane and its vicinity, improving image plane utilization and ensuring that the image plane completely covers the photosensitive surface of the photosensitive device.

[0029] The central blind spot of the object plane can be completely compensated by another matching non-wide-angle monitoring imaging system without central blind spot.

[0030] Third, the overall structure of the wide-angle imaging system of the present invention is simplified, more compact, smaller in size, lighter in weight, less difficult to process, easy to assemble and adjust, and low in cost. The head element is only composed of one optical element, such as an ogive surface-type refractive reflective lens 4, or an ogive surface-type reflective mirror 5, and the ogive surface-type refractive reflective lens 4 can be injection-molded by optical plastic, and the ogive surface-type reflective mirror 5 can be stamped by metal sheet, which is easy to manufacture and has low material and processing costs. The incident angle of light entering the subsequent lens group 2 is small, and a simple subsequent lens group can also obtain the required image quality. Therefore, the subsequent lens group 2 is composed of only three lenses, and all mirror surfaces are either flat or spherical, all of which are injection-molded by optical plastic, and are also easy to manufacture and low in cost.

[0031] The two head unit designs each have their strengths. When using an ogive-shaped refractive-reflective lens 4, its reflective mirror surface 4-2 is coated with an imaging light reflective film to achieve reflected imaging of the incident imaging light. During this process, the incident imaging light is also refracted twice at the refractive mirror surface 4-1. This process corrects image distortion and improves image quality. When using an ogive-shaped reflector 5, the head unit can directly reflect the image. If image quality requirements are not high, this solution is sufficient and does not require redesigning the subsequent lens assembly.

[0032] The object and image of the present invention are on the same side, the structure is compact, and the maximum semi-aperture of the head unit is =8mm, and the total optical length is 12mm. It can be seen that the present invention is smaller in size; only 5 optical elements, as well as optical plastic and aluminum sheet materials make it lighter in weight.

[0033] Fourth, it can achieve panoramic and high-definition imaging.

[0034] The optical system disclosed in the present invention utilizes the advantages of the Ogive aspheric surface in the Ogive head unit to make the overall system structure compact and easy to miniaturize, achieving the effect of both lightweight and high image quality. Due to the simple optical path, the light energy loss is small; BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a schematic cross-sectional diagram of the overall structure and imaging optical path when the head unit of the present invention is performed by an ogive surface-type refractive-reflective lens, and also serves as an abstract drawing.

[0036] Figure 2 This is a schematic cross-sectional diagram of the overall structure and imaging optical path when the head unit of the present invention is served by an ogive surface reflector.

[0037] Figure 3 This is a schematic diagram of the structure and optical path analysis when the head unit is served by an ogive surface-type refractive-reflective lens.

[0038] Figure 4 It is an enlarged cross-sectional diagram of the subsequent lens assembly structure and imaging optical path of the present invention.

[0039] Figure 5 This is the MTF diagram of polychromatic light diffraction of an example of the present invention.

[0040] Figure 6 This is a spot diagram of an example of the present invention.

[0041] Figure 7 This is a relative illumination diagram of an example of the present invention.

[0042] Figure 8 This is a relative distortion diagram of an example of the present invention. DETAILED DESCRIPTION

[0043] The present invention needs to be further defined as follows.

[0044] The ogive surface-type refractive reflective lens 4 is injection-molded with optical plastic, the refractive mirror surface 4-1 is plated with an imaging light anti-reflection film, and the reflective mirror surface 4-2 is plated with an imaging light reflective film, and the optical plastic is PMMA.

[0045] The ogive surface reflector 5 is formed by stamping a metal sheet, and the metal sheet is an aluminum sheet.

[0046] In the subsequent lens group 2, a plano-convex lens 2-1, a biconvex lens 2-2, and a concave-planar lens 2-3 are coaxially arranged in sequence along the imaging optical path, as shown in FIG. Figure 4 As shown, the imaging light reflected from the head unit is limited by the aperture 1, and then converged by the plano-convex lens 2-1, the biconvex lens 2-2, and the concave-planar lens 2-3 to form an image on the image plane 3.

[0047] The following is an example of the present invention, in which the head unit adopts an ogive surface-type refractive reflective lens 4.

[0048] The head unit is an ogive surface refractive reflective lens 4, whose thickness t is 2mm and made of PMMA; About the refractive mirror surface 4-1: curvature radius =21.15mm, cone coefficient k1=1.87, =3.97mm, maximum semi-diameter =8mm (7.3mm for clean mouth mirror); high-order aspheric coefficient Take i = 1, 2, 3, and =0, =-3.22-E05, =1.36-E07; About the reflective mirror surface 4-2: its curvature radius curvature radius =9.65mm, cone coefficient k2=-0.36, =1.743mm, maximum semi-diameter =5mm (4.3mm for clean mouth mirror), high-order aspheric coefficient Take i = 1, 2, 3, and =0, =-4.71-E07, =3.39-E07.

[0049] The specific parameters of the subsequent lens group 2 are given in the following table, where the length values ​​are in millimeters.

[0050]

[0051] The half field of view (HFOV) range of the example is 27° to 105°, and the total length of the optical system is 12 mm.

[0052] The present invention has good imaging quality, such as Figure 5 As shown, when the spatial frequency is cut off at 60lp / mm, the MTF modulus value reaches above 0.5 in the entire field of view.

[0053] The aberration of the present invention is better compensated, such as Figure 6 As shown in the figure, this is the point diagram corresponding to the imaging light beams with wavelengths of 0.486133μm, 0.587562μm, and 0.656273μm, respectively. The RMS radii (root mean square radii) corresponding to the five fields of view with incident angles from small to large (27°, 45°, 68°, 88°, and 105°) are 5.956μm, 2.923μm, 2.525μm, 2.675μm, and 2.608μm, respectively, which are all better than or close to the Airy disk value.

[0054] The brightness of the image formed by the present invention is uniform within the imaging field of view of HFOV27°~105°, such as Figure 7 As shown in the figure, we can see that the relative illumination values ​​are all higher than 0.7, and the curve is relatively smooth.

[0055] The distortion of the present invention is well compensated, and the imaging quality is high. Figure 8 As shown in the figure, it can be seen that the distortion is small within the normalized field of view.

Claims

1. The ogive surface-type head unit high image plane utilization wide-angle imaging system includes a head unit, an aperture, and a subsequent lens group arranged on the same optical axis, characterized in that: A head unit, an aperture (1), and a subsequent mirror group (2) are sequentially arranged along the imaging optical path. The incident imaging light is reflected once by the head unit and then passes through the aperture (1) and the subsequent mirror group (2) to be imaged on the image plane (3). The aperture (1) is located at the intersection of the incident imaging light of each HFOV after being reflected by the head unit. The head unit is served by an optical element with an ogive surface shape. The optical element is one of the following two types: one is an ogive surface type refractive reflective lens (4), the front mirror surface of which is a refractive mirror surface (4-1) and the rear mirror surface of which is a reflective mirror surface (4-2); the other is an ogive surface type reflector (5); The ogive surface is a surface of revolution and is the tail portion of the complete ogive surface. Its expression is: ， in: ， ， Where: x, y, and z are the three coordinate values ​​of any point on the surface of revolution in the rectangular coordinate system, the z value is the sag of the surface of revolution, which represents the difference between the coordinate values ​​of any point on the surface of revolution and the vertex in the direction of the optical axis, and r is the radial coordinate of the surface of revolution; is the compensation value, which is the distance between the rotation axis z' of the complete ogive surface and the rotation axis z of the tail ogive surface; c is the curvature of the vertex of the revolution surface; k is the conic coefficient of the revolution surface; Represents the high-order aspheric coefficients of the rotational surface, i=1,2,3, ... ,n,n≤8; When the head unit is an ogive-type refractive-reflective lens (4), the parameters c of its refractive mirror (4-1) and reflective mirror (4-2) are c1 and c2 respectively, and the incident angle of the aperture (1) is , solving for the parameters: ， ， The parameters r0 of the refractive mirror (4-1) and the reflective mirror (4-2) are respectively 01 、r 02 , and is determined by the following formula: ， ， Where: is the diameter of the aperture (1), is the axial distance between the aperture (1) and the refractive mirror (4-1), HFOV m is the minimum half-field angle, n is the refractive index of the ogive surface-type refractive-reflective lens (4), is the vertical axis magnification of the ogive surface type refractive reflective lens (4), and t is the thickness of the ogive surface type refractive reflective lens (4); The subsequent lens group (2) is capable of converging the imaging light beam and correcting imaging aberrations.

2. The high image plane utilization and wide-angle imaging system using the ogive face-type head unit according to claim 1 is characterized in that: The ogive surface-type refractive reflective lens (4) is formed by optical plastic injection molding, the refractive mirror surface (4-1) is plated with an imaging light anti-reflection film, and the reflective mirror surface (4-2) is plated with an imaging light reflective film.

3. The high image plane utilization and wide-angle imaging system using the ogive face-type head unit according to claim 1, characterized in that: The ogive surface reflector (5) is formed by stamping a metal sheet.

4. The high image surface utilization and wide-angle imaging system using the ogive face-type head unit according to claim 1, characterized in that: In the subsequent lens group (2), a plano-convex lens (2-1), a biconvex lens (2-2), and a concave-planar lens (2-3) are coaxially arranged in sequence along the imaging light path. The imaging light reflected from the head unit is limited by the aperture (1) and then converged by the plano-convex lens (2-1), the biconvex lens (2-2), and the concave-planar lens (2-3) in sequence to form an image on the image plane (3).

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