Large field of view high image quality monitoring optical system with compact structure

Abstract

The monitoring optical system with compact structure and large field of view and high image quality belongs to the technical field of monitoring optical system. The prior art cannot meet higher requirements in field of view size, imaging quality, compactness degree, weight and volume. The monitoring optical system comprises, in order from the object side to the image side along the optical axis: a linear polarizing film LP, a front quarter-wave film QWP1, a beam splitting film BP, a turnaround lens with negative focal power, a rear quarter-wave film QWP2, a reflective polarizing film RP, a turnaround compensation lens with negative focal power, and a doublet rear successor lens group; the turnaround compensation lens is separated from the doublet rear successor lens group; the ratio of the total optical length TTL of the monitoring optical system to the tangent tan(HFOV) of the half field of view HFOV satisfies the relationship: 9mm < TTL / tan(HFOV) < 17mm; the ratio of the maximum effective half aperture D of the turnaround lens to the focal length f of the monitoring optical system satisfies the relationship: 0.5 < D / f < 0.9. The total optical length TTL is only 96.4mm; the maximum half field of view HFOV is 96.3°; and the MTF at 60lp / mm can all reach above 0.48. max just 96.3°; the MTF at 60lp / mm can all reach above 0.48.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of monitoring optical systems. BACKGROUND

[0002] Nowadays, monitoring imaging optical systems have both the requirements of large field of view, high image quality, compact structure, light weight and low cost.

[0003] In order to image the scene in a large field of view range to a limited size image plane by reflection and refraction of various mirrors, large field of view optical systems play an important role.

[0004] The existing large field of view optical system applied in the monitoring field is a panoramic ring optical system or a fisheye lens. Due to the large number of lenses, the total optical length is difficult to control, so the assembly is difficult, and the portability is poor. In addition, the image integrity and fidelity are poor.

[0005] For example, a Chinese patent application with application number 201911042582.9 and the name of "a large relative aperture gaze ring scene imaging infrared monitoring mirror" discloses a scheme. The catadioptric panoramic lens used in this scheme belongs to a panoramic ring optical system, which is used as an infrared monitoring mirror to realize high resolution and large field of view imaging. However, this monitoring mirror has a zero field of view blind area, and the image lacks integrity. At the same time, the catadioptric panoramic lens uses a large number of lenses, which is not conducive to processing and adjustment, and the cost is relatively high. In addition, the total optical length reaches 128mm, which makes it difficult to miniaturize the monitoring device.

[0006] The existing VR imaging uses a Pancake optical system because the Pancake optical system has the following characteristics. The Pancake optical system has a short optical total length (TTL), TTL = 18-30 mm, a compact structure, and thus a small volume; the polarizing devices are all optical films; only one lens is needed, and optical plastic can also be used, thus the weight is light. In addition, the field of view (FOV) is large, such as a horizontal design value of 105°, and the real FOV of the current mass-produced Pancake scheme can also be between 60° and 90°. Furthermore, the polarization imaging mode has good image quality, and can obtain an image with high contrast, definition, and delicacy. However, if the existing Pancake optical system is simply copied into a monitoring system, although the compact structure, light weight, and small volume can meet the monitoring requirements, the field of view and image quality cannot fully meet the monitoring requirements. Because, first, VR only requires the Pancake optical system to receive light within the range of the display screen, and the object distance is limited, and a 60°-90° field of view angle is enough, but for a monitoring optical system, it is still too small. Second, VR only needs to meet the requirements of the human eye, and the image quality requirement is relatively low, and the better image quality brought by polarization imaging is enough, but for the dependence of various social activities on the monitoring system, the image quality of the monitoring optical system needs to be greatly improved. SUMMARY

[0007] In order to obtain a compact structure, a small volume, a light weight, and large field of view imaging, and better image quality, we propose a technical scheme named "monitoring optical system with compact structure and large field of view and high image quality".

[0008] The monitoring optical system with compact structure and large field of view and high image quality is characterized in that, Figures 1-3As shown, sequentially arranged along the direction of the optical axis from the object side to the image side: a linear polarizing film LP, a front quarter-wave film QWP1, a beam splitting film BP, a turnaround lens 1 with negative optical power, a rear quarter-wave film QWP2, a reflective polarizing film RP, a turnaround compensation lens 2 with negative optical power, and a doublet successor lens group 3; the entrance mirror surface of the linear polarizing film LP, the entrance mirror surface of the front quarter-wave film QWP1, the entrance mirror surface of the beam splitting film BP, and the entrance mirror surface of the turnaround lens 1 are mutually adhered; the exit mirror surface of the turnaround lens 1, the entrance mirror surface of the rear quarter-wave film QWP2, the entrance mirror surface of the reflective polarizing film RP, and the entrance mirror surface of the turnaround compensation lens 2 are mutually adhered; the turnaround compensation lens 2 is separated from the doublet successor lens group 3; the entrance mirror surface and the exit mirror surface of the turnaround lens 1, and the entrance mirror surface and the exit mirror surface of the turnaround compensation lens 2 are all even aspheric surfaces; the ratio of the total optical length TTL of the monitoring optical system to the tangent tan(HFOV) of the half field of view HFOV satisfies the relationship: 9mm < TTL / tan(HFOV) < 17mm; the ratio of the maximum effective half aperture D of the turnaround lens 1 to the focal length f of the monitoring optical system satisfies the relationship: 0.5 < D / f < 0.9; and a diaphragm 4 is arranged in front of the doublet successor lens group 3.

[0009] The technical effects achieved by the present application can be illustrated by the polarized imaging process of the present application in the form of a companion matrix.

[0010] The optical axis direction of the monitoring optical system of the present application is defined as the x-axis, and the y-axis is perpendicular to the x-axis. As shown in the figure, Figures 1-4 As shown, the natural light from a large field of view range becomes linearly polarized light with the vibration direction perpendicular to the optical axis after passing through the linear polarizing film LP, and its matrix form is The linearly polarized light becomes left-handed circularly polarized light after passing through the front quarter-wave film QWP1, and its matrix form becomes The left-handed circularly polarized light transmits the turnaround lens 1 after passing through the beam splitting film BP, and becomes linearly polarized light parallel to the optical axis after passing through the rear quarter-wave film QWP2, and its matrix form becomes The vibration direction of the linearly polarized light is perpendicular to the tangent plane of the intersection point of the reflective polarizing film RP and the optical axis, and the linearly polarized light is S-polarized light (transverse wave); when the reflective polarizing film RP is a reflective S-polarized P-polarizing film, the S-polarized light is reflected and reversely passes through the rear quarter-wave film QWP2, and becomes left-handed circularly polarized light again, and its matrix form is The left-handed circularly polarized light reversely transmits the turnaround lens 1 and is reflected by the beam splitting film BP, and thirdly transmits the turnaround lens 1, and the phase of the left-handed circularly polarized light changes by Π at this time, and becomes right-handed circularly polarized light, and its matrix form is The right-handed circularly polarized light thirdly passes through the rear quarter-wave film QWP2 and becomes linearly polarized light perpendicular to the optical axis, and its matrix form is The vibration direction of the linear polarized light is perpendicular to the tangent plane of the intersection of the reflective polarizing film RP and the optical axis, and the linear polarized light is P polarized light (longitudinal wave); when the reflective polarizing film RP is a reflective S polarizing film, the P polarized light transmits the reflective S polarizing film and is incident on the return compensation lens 2, the spherical aberration is compensated by the return compensation lens 2; the P polarized light is emitted from the return compensation lens 2, passes through the diaphragm 4, is incident on the double-cemented subsequent lens group 3, the chromatic aberration is corrected by the double-cemented subsequent lens group 3, and finally is focused on the image plane 5.

[0011] The following advantages are summarized from the structural features, polarization imaging process and specific embodiments of the application.

[0012] 1. Compared with the existing panoramic ring optical system or fisheye lens and other large field optical systems, the Pancake optical system is introduced into the monitoring optical system, and more optical functional films are adopted to compress the imaging light path in a return manner, so that the structure becomes more compact, the exit mirror surface of the return lens 1 is attached to the entrance mirror surface of the return compensation lens 2, and the total optical length TTL is further shortened. Finally, the total optical length TTL (the axial distance from the entrance mirror surface of the return lens 1 to the image plane 5) of the monitoring optical system is only 96.4 mm, and the overall weight and volume are greatly reduced.

[0013] 2. Similarly, compared with the existing panoramic ring optical system or fisheye lens and other large field optical systems, there is no zero field blind area in the imaging process of the application, the information search capability is strong, and at the same time, there is no image distortion caused by the imaging system, and the required monitoring picture is obtained.

[0014] 3. The return lens 1 in the application adopts a large-aperture convex aspheric entrance mirror surface to receive object side light rays, and object side light rays from various angles in a large field of view can be well incident on the beam splitter film BP attached to the convex aspheric entrance mirror surface, and then incident on the return lens 1. The scene in the large field of view is imaged at the image plane 5 at one time, and the image brightness is high. The real FOV of the existing mass-produced Pancake scheme is between 60° and 90°, and the maximum half field of view HFOV of the application is max 96.3°, as shown in Figure 1 .

[0015] 4. The relationship 9mm < TTL / tan (HFOV) < 17mm takes into account the relationship between the total optical length TTL and the field of view FOV, and a small size monitoring optical system has a large imaging field of view.

[0016] 5. The relationship 0.5 < D / f < 0.9 makes it possible to reduce the aperture of the return lens 1 as much as possible under the premise of setting the required focal length of the monitoring optical system, so as to control the radial size of the entire monitoring optical system.

[0017] 6、The present application adopts polarization imaging mode, the introduced foldback compensation lens 2 and double-cemented subsequent lens group 3 can reduce aberration, optimize image quality, greatly improve the imaging quality, and MTF can reach above 0.48 at 60 lp / mm; the anti-S polarization film can filter non-imaging light, eliminate stray light, improve the imaging clarity, and the imaging quality is improved again.

[0018] 7、Although the existing Pancake optical system has multiple pieces, the single-piece Pancake optical system is combined with the foldback compensation lens 2 and the double-cemented subsequent lens group 3, so that large field of view, high image quality imaging can be realized, and the structure of the monitoring optical system is relatively simple and compact.

[0019] 8、The foldback lens 1 incident mirror surface and the foldback compensation lens 2 incident mirror surface respectively bear three layers and two layers of optical function films, so that the film process can be simplified;

[0020] 9、With a full-system coaxial structure, the difficulty of assembly and adjustment is low. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 It is the whole structure of the present application and the schematic diagram of the imaging process of the zero to maximum half field of view incident light beam, and the figure is also the abstract drawing.

[0022] Figure 2 is Figure 1 A local enlarged schematic view of the area in the

[0023] Figure 3 is Figure 1 A local enlarged schematic view of the B area in the

[0024] Figure 4 It is the whole structure of the present application and the schematic diagram of the simple light path.

[0025] Figure 5 It is the root mean square spot radius curve of the present application.

[0026] Figure 6 It is the field curvature curve of the present application.

[0027] Figure 7 It is the distortion curve of the present application.

[0028] Figure 8 It is the MTF curve of the present application.

[0029] Figure 9 It is the standard point column diagram of the present application. DETAILED DESCRIPTION

[0030] The present application needs to be further limited as follows.

[0031] The linear polarization film LP, the front quarter-wave film QWP1 and the beam splitting film BP are attached on the incident mirror surface of the fold return lens 1, and the rear quarter-wave film QWP2 and the reflective polarization film RP are attached on the incident mirror surface of the fold return compensation lens 2.

[0032] The beam splitting film BP is selected from a semi-transmissive and semi-reflective film, and the reflective polarization film RP is selected from a reverse S polarization film or a reverse P polarization film.

[0033] The fold return lens 1 is made of quartz glass, and the small specific gravity of the fold return lens 1 is beneficial to the miniaturization and lightening of the monitoring optical system, the small thermal expansion coefficient of the fold return lens 1 is beneficial to the stable imaging of the monitoring optical system under different environmental temperatures, the good chemical stability of the fold return lens 1 is beneficial to the anti-erosion of water vapor and corrosive gas of the monitoring optical system used outdoors, and the good electrical insulation of the fold return lens 1 is beneficial to the lens processing. The central thickness of the fold return lens 1 is determined in the range of 25mm to 30mm, and the refractive index of the fold return lens 1 is determined in the range of 1.5 to 1.6.

[0034] The fold return compensation lens 2 is made of optical plastic. The central thickness of the fold return compensation lens 2 is determined in the range of 6mm to 10mm, the refractive index of the fold return compensation lens 2 is determined in the range of 1.5 to 1.6, and the central curvature radius of the fold return compensation lens 2 is determined in the range of 25mm to 40mm.

[0035] The double-cemented subsequent lens group 3 is cemented by a meniscus thick lens 6 with positive refractive power and a positive lens 7 with positive refractive power, as shown in the formula (1), the refractive power is 0.08, and the meniscus thick lens 6 and the positive lens 7 are spherical lenses. Figure 4

[0036] An embodiment of the present application is described as follows.

[0037] The focal length f of the monitoring optical system is 1.546mm, the F number is 1.553, the half field of view HFOV is in the range of 0° to 96.3°, and the working wavelength is 0.588μm. The other technical parameters of the monitoring optical system are given in the following table.

[0038]

[0039]

[0040] The even aspheric surface is determined by the following aspheric surface formula:

[0041]

[0042] In the formula, z is the sag of the aspheric surface, which represents the difference between the coordinate value of any point on the aspheric surface and the coordinate value of the vertex in the optical axis direction, r is the radial coordinate of the aspheric surface, c is the curvature of the vertex of the aspheric surface, k is the conic coefficient of the aspheric surface, a1 is the quadratic term coefficient, a2 is the quartic term coefficient, and a3 is the sextic term coefficient.​

[0043] The conic coefficient k, the quadratic term coefficient a1, the fourth order term coefficient a2 and the sixth order term coefficient a3 of each even aspherical surface are given in the following table.

[0044]

[0045] Figures 5-9 It is shown that the imaging quality of the application is high.

[0046] As shown in the figure, Figure 5 the spherical aberration of the imaging light beam of the application is well compensated.

[0047] As shown in the figure, Figure 6 the field curvature of the imaging light beam of the application is well compensated.

[0048] As shown in the figure, Figure 7 the distortion of the imaging light beam of the application is well corrected.

[0049] As shown in the figure, Figure 8 the line pair is represented by the horizontal coordinate with unit of mm, and the MTF value is represented by the vertical coordinate, and the MTF value is not less than 0.69.

[0050] As shown in the figure, Figure 9 the reference wavelength is 0.588 μm, the relative field of view is represented by the horizontal coordinate, and the root mean square spot radius is represented by the vertical coordinate with unit of mm, and the spot radius of the application under multiple fields of view is not much different from the Airy spot radius 1.114 μm, and the spherical aberration of the imaging light beam of the application is well compensated.

Claims

1. A large field of view high image quality monitoring optical system having a compact structure, characterized by, In order from the object side to the image side along the optical axis: a linear polarizing film LP, a front quarter-wave film QWP1, a beam splitting film BP, a turning lens (1) with negative optical power, a rear quarter-wave film QWP2, a reflective polarizing film RP, a turning compensation lens (2) with negative optical power, a double-cemented subsequent lens group (3); the incident mirror surface of the turning lens (1), the exit mirror surface of the turning lens (1), the incident mirror surface of the rear quarter-wave film QWP2, the incident mirror surface of the reflective polarizing film RP and the incident mirror surface of the turning compensation lens (2) are mutually attached; the turning compensation lens (2) is separated from the double-cemented subsequent lens group (3); the incident mirror surface and the exit mirror surface of the turning lens (1) and the incident mirror surface and the exit mirror surface of the turning compensation lens (2) are all even aspheric surfaces; the ratio of the total optical length TTL of the monitoring optical system to the tangent tan(HFOV) of the half field of view HFOV satisfies the relationship: 9mm < TTL / tan(HFOV) < 17mm; the ratio of the maximum effective half aperture D of the turning lens (1) to the focal length f of the monitoring optical system satisfies the relationship: 0.5 < D / f < 0.9; a diaphragm (4) is arranged in front of the double-cemented subsequent lens group (3); The double-cemented subsequent lens group (3) is formed by cementing a meniscus thick lens (6) with positive optical power and a positive lens (7) with positive optical power, the optical power is 0.08, and the meniscus thick lens (6) and the positive lens (7) are both spherical lenses.

2. The monitoring optical system with a compact structure and a large field of view and high image quality according to claim 1, characterized in that, The polarization imaging process of the monitoring optical system is that natural light from a large field of view range becomes linearly polarized light with vibration direction perpendicular to the optical axis through a linear polarization film LP, and its matrix form is The linearly polarized light becomes left-handed circularly polarized light through a front quarter-wave film QWP1, and its matrix form becomes The left-handed circularly polarized light transmits a fold mirror (1) and becomes linearly polarized light parallel to the optical axis through a rear quarter-wave film QWP2, and its matrix form becomes The vibration direction of the linearly polarized light is perpendicular to the tangent plane of the intersection of the reflective polarizing film RP and the optical axis, and the linearly polarized light is S-polarized light; when the reflective polarizing film RP is an anti-S transmission P polarizing film, the S-polarized light is reflected and reversely transmitted through the rear quarter-wave film QWP2, and becomes left-handed circularly polarized light again, and its matrix form is The left-handed circularly polarized light is reflected by the beam splitter film BP and is transmitted through the fold mirror (1) for the third time, and the phase of the left-handed circularly polarized light changes by Π, and becomes right-handed circularly polarized light, and its matrix form is The right-handed circularly polarized light is transmitted through the rear quarter-wave film QWP2 for the third time, and becomes linearly polarized light perpendicular to the optical axis, and its matrix form is The vibration direction of the linearly polarized light is perpendicular to the tangent plane of the intersection of the reflective polarizing film RP and the optical axis, and the linearly polarized light is P-polarized light; when the reflective polarizing film RP is an anti-S transmission P polarizing film, the P-polarized light transmits the anti-S transmission P polarizing film and is incident on a fold compensation lens (2), and the spherical aberration is compensated by the fold compensation lens (2); the P-polarized light is emitted from the fold compensation lens (2), passes through an aperture (4), and is incident on a double-cemented subsequent lens group (3), and the chromatic aberration is corrected by the double-cemented subsequent lens group (3), and finally focused on an image plane (5).

3. The monitoring optical system with a compact structure and a large field of view and high image quality according to claim 1, characterized in that, The linear polarizing film LP, the front quarter-wave film QWP1 and the beam splitting film BP are attached to the incident mirror surface of the turning lens (1), and the rear quarter-wave film QWP2 and the reflective polarizing film RP are attached to the incident mirror surface of the turning compensation lens (2).

4. The monitoring optical system with a compact structure and a large field of view and high image quality according to claim 1, characterized in that, The beam splitting film BP is selected from a semi-transparent and semi-reflective film, and the reflective polarizing film RP is selected from a reflective S polarizing film or a reflective P polarizing film.

5. The monitoring optical system with a compact structure and a large field of view and high image quality according to claim 1, characterized in that, The material of the turning lens (1) is quartz glass; the central thickness of the turning lens (1) is determined in the range of 25mm-30mm, and the refractive index is determined in the range of 1.5-1.

6.

6. The monitoring optical system with a compact structure and a large field of view and high image quality according to claim 1, characterized in that, The material of the turning compensation lens (2) is optical plastic; the central thickness of the turning compensation lens (2) is determined in the range of 6mm-10mm, the refractive index is determined in the range of 1.5-1.6, and the central curvature radius is determined in the range of 25mm-40mm.

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