High-resolution low-magnification chromatic aberration RGB line scanning camera optical system based on three-color prism

Abstract

The invention discloses a high-resolution low-magnification chromatic aberration RGB (Red, Green and Blue) line scanning camera optical system based on a three-color prism, which is characterized in that light passes through a high-resolution low-magnification chromatic aberration system to be in a convergent state, is split by three spectral band imaging systems containing prisms, and is respectively focused on corresponding detectors; wherein in the spectral band imaging system, the light rays with the spectral band of 420 nm to 500 nm in the light rays are received by a detector 15; in the spectrum imaging system, spectrum light of 500 nm to 580 nm in the light is received by a detector 16; in the spectrum imaging system, the spectrum light of 580 nm to 660 nm in the light is received by a detector 17. According to the invention, lens materials are selected, and chromatic aberration generated by different materials is mutually matched and counteracted, so that the chromatic aberration of the full-field magnification of each color of the whole system is less than 0.5 per ten thousandth, the RGB overlap ratio is excellent, and target color identification is facilitated.

Description

Technical Field

[0001] The present invention belongs to the technical field of RGB line scan camera optical systems, and particularly relates to an RGB line scan camera optical system with high resolution and low magnification chromatic aberration of a three-color prism. Background Art

[0002] With the continuous development of the machinery manufacturing industry, the accuracy requirements for large mechanical inspection equipment are getting higher and higher. CCD and CMOS image sensors with tens of millions of pixels are emerging on the market, and the pixel and distortion requirements for their lenses are also getting higher and higher. Line scan cameras have the advantages of good data acquisition accuracy and high efficiency. Therefore, their applications in measurement become more and more important. Especially when the object is large, continuously moving or requires high-resolution imaging, line scan cameras have irreplaceable advantages. In order to monitor the deformation of large parts and the motion state of objects in a large space in real time, line scan cameras with large fields of view and high precision have emerged. Such cameras can be applied to fields such as aerospace vehicle tests, aircraft structural strength static fatigue tests, and large radar measurements, and meet the requirements of high-precision dynamic measurements. They can also be extended to the measurement applications of large parts in fields such as shipbuilding, power, construction, and transportation.

[0003] When a camera captures an object, the tilt of the camera or the unevenness of the detection surface also has a great impact on imaging. The increase in the tilt angle will cause the object in the image to look distorted. In particular, straight lines will become curved, resulting in "perspective distortion". When photographing a building or a flat object, if the camera is tilted, the part far from the camera will look smaller, while the part close to the camera will look larger, and the proportion and shape of the object will be distorted. Tilt may cause lens distortion, especially in the use of wide-angle lenses. The image edges may be deformed and straight lines will become curved, affecting the realism of the image. On an uneven surface, the direction of light reflection changes, resulting in uneven reflected light. Some areas may be overexposed or underexposed. Surface undulations will cause reflections in different directions, making the details of the object unclear. Especially on highly reflective surfaces (such as metals), light spots and specular reflections may obscure the details. Tilt and surface unevenness often affect the stability of the image. Especially when multiple images need to be stitched into a large image, the tilt angle and the uneven surface will cause obvious misalignment or distortion in the stitching result. In industrial automation inspection and robot vision systems, surface unevenness and camera tilt may greatly reduce the accuracy of the inspection results. Especially when judging the shape or defects of an object by extracting surface features from an image, these problems will lead to incorrect detection and recognition. Summary of the Invention

[0004] The present invention is to solve the deficiencies existing in the above-mentioned prior art, and proposes an RGB line-scan camera optical system with high resolution, low magnification chromatic aberration based on a three-color prism, in order to complete the spectral splitting of three spectral bands by using a combined three-color prism, so that it can perform ultra-high-precision fine particle detection, edge recognition, color recognition, etc. under the condition that the relative position accuracy between the moving speed position, the camera, the lens and the object is not high, so as to meet the high-precision detection requirements of the large-scale industrial inspection industry.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] The RGB line-scan camera optical system with high resolution, low magnification chromatic aberration based on a three-color prism of the present invention is characterized in that it includes: a chromatic aberration system, a first prism, a second prism, a third prism, a first detector, a second detector and a third detector;

[0007] The chromatic aberration system includes: a first lens group, a second lens group and a third lens group arranged in sequence along the optical axis. Among them, the first lens group has a negative optical power and includes: a first lens and a second lens. The second lens group has a positive optical power and includes: a third lens, a fourth lens, a fifth lens, a sixth lens, a seventh lens and an eighth lens. The third lens group has a negative optical power and includes: a ninth lens, a tenth lens and a polarizer; and a diaphragm is arranged between the fifth lens and the sixth lens where the center position of the chromatic aberration system is located.

[0008] Among them, the first prism and the second prism are closely attached, and a first spectral splitting film is provided at the contact surface between the two. The second prism and the third prism are closely attached, and a second spectral splitting film is provided at the contact surface between the two;

[0009] After the light passes through each lens in the chromatic aberration system in sequence, the light in the spectral band of 420nm - 500nm is perpendicularly incident on the front surface of the first prism at an angle of 90°, is incident and reflected at an angle of 45° at the contact surface between the first prism and the second prism, and finally exits from the surface of the first prism near the first detector, and forms a first spectral splitting and is received by the first detector;

[0010] The light in the spectral band of 500nm - 580nm is perpendicularly incident on the front surface of the second prism at an angle of 90°, is incident and transmitted at an angle of 45° at the contact surface between the first prism and the second prism, is incident and reflected at an angle of 45° at the contact surface between the second prism and the third prism, and finally exits from the surface of the second prism near the second detector, and forms a second spectral splitting and is received by the second detector;

[0011] The light in the spectral range of 580nm - 660nm in the light beam is perpendicularly incident on the front surface of the prism at an angle of 90°, incident and transmitted at an angle of 45° on the contact surface between the first prism and the second prism, incident and transmitted at an angle of 45° on the contact surface between the second prism and the third prism, and finally exits from the surface of the third prism near the third detector, and forms the third spectral separation and is received by the third detector;

[0012] After the three spectral separations are processed by the three detectors respectively, red, green, and blue three-channel digital signals are obtained and combined into a complete color image.

[0013] The design method of an RGB line-scan camera optical system with high resolution and low magnification chromatic aberration based on a three-color prism according to the present invention is characterized in that it includes the following steps:

[0014] Step 1. Obtain the focal length of the chromatic aberration system by using Equation (1) :

[0015] (1)

[0016] In Equation (1), L represents the conjugate distance of the chromatic aberration system, F1 represents the F-number of the chromatic aberration system, and β represents the lateral magnification of the chromatic aberration system;

[0017] Step 2. Obtain the optical power of the chromatic aberration system by using Equation (2) :

[0018] (2)

[0019] Step 3. Use Equation (3) to construct the optical power relationship between the first lens group, the second lens group, and the third lens group and the chromatic aberration system respectively:

[0020] (3)

[0021] In Equation (3), , , are the optical powers of the first lens group, the second lens group, and the third lens group respectively, , are the thicknesses between the first lens group and the second lens group, and between the second lens group and the third lens group respectively;

[0022] Step 4: Given , , and determine , , , the positive and negative and the ratio of , , ;

[0023] Step 5: Determine that the structure of the second lens group is a double Gauss structure. Select the lens group in the typical double Gauss reference lens library that is closest to the F-number and has the smallest magnification chromatic aberration, and perform focal length scaling on the structure of the selected lens group to obtain the initial structure of the second lens group;

[0024] Step 6: Select flint glass H-ZF6 for the first lens and crown glass H-K9L for the second lens in the first lens group. Among them, the curvature radius of the lens surface of the first lens close to the object surface , and the curvature of the other lens surface of the first lens is negative. The structure of the second lens is a biconvex structure, and the curvature radii of the two surfaces ;

[0025] Given the ratio of the optical powers between the first lens and the second lens ;

[0026] Use Equation (4) to obtain the optical power of the first lens and the optical power of the second lens;

[0027] (4)

[0028] In Equation (4), represents the distance between the first lens and the second lens;

[0029] Step 7: Determine the initial structure of the first lens according to , including: the curvature radius of the lens surface of the first lens close to the object surface, and the curvature radius of the other lens surface of the first lens, which is obtained from Equation (5):

[0030] (5)

[0031] In Equation (5), is the refractive index of the first lens, is the central thickness of the first lens;

[0032] According to , determine that the initial structure of the second lens is a biconvex structure, and the curvature radii of the two surfaces , and use Equation (6) to obtain:

[0033] (6)

[0034] In Equation (6), among them, is the refractive index of the second lens, is the central thickness of the second lens;

[0035] Step 9: Select crown glass H-K9L for the ninth lens and flint glass H-ZF6 for the tenth lens in the third lens group;

[0036] Step 10: Taking the optical power of the third lens group as a reference, obtain the optical power of the ninth lens and the optical power of the tenth lens in accordance with the process of Step 6, and determine that the initial structure of the ninth lens includes: the curvature radius of the lens surface of the ninth lens close to the object surface and the curvature radius of the other lens surface of the ninth lens which is obtained from Equation (7),

[0037] (7)

[0038] In Equation (7), is the refractive index of the ninth lens, is the central thickness of the ninth lens;

[0039] Determine that the initial structure of the tenth lens is a meniscus convex lens structure, and the curvature radii of the two surfaces are and are obtained from Equation (8);

[0040] (8)

[0041] In Equation (8), where is the refractive index of the tenth lens, is the central thickness of the tenth lens;

[0042] Step 11: Determine the optimization variables, including: the curvature radii of each surface in the initial structure of the chromatic aberration system, the thicknesses of the ten lenses, the air thickness between the lenses, and the thickness from the object surface to the first lens;

[0043] Construct focal length constraints, lens length constraints, conjugate distance constraints, spherical aberration correction, magnification chromatic aberration, and boundary condition constraints, and use them to optimize the initial structure of the chromatic aberration system to obtain a preliminary optimization result;

[0044] Step 12: According to the preliminary optimization result of the chromatic aberration system, insert a prism equivalent plate at the position between the tenth lens and the image surface, and determine the length of the prism equivalent plate, where is the clear aperture diameter of the prism;

[0045] Step 13: Optimize the RGB line scan camera optical system in accordance with the process of Step 11 to obtain a final optimization result;

[0046] According to the final optimization result and the three optical paths formed by light in the prism, a triple structure composed of a chromatic aberration system, a first prism, a second prism, and a third prism is constructed;

[0047] In the first structure, the equivalent flat plate of the prism is converted into two parts. The isosceles right triangle region formed by the front surface of the first prism as a right-angled side and the contact surface between the first prism and the second prism as the hypotenuse is set as the second part, and the remaining region of the first prism is set as the first part;

[0048] In the second structure, the equivalent flat plate of the prism is converted into two parts, namely the second part in the first prism and the second prism;

[0049] In the third structure, the equivalent flat plate of the prism is converted into two parts, namely the second part in the first prism and the part composed of the second prism and the third prism;

[0050] Step 13: The two contact surfaces between the three prisms are respectively coated with a beam-splitting film composed of alternating stacks of high-refractive-index materials with n>2.3 and low-refractive-index materials with n<1.46, and the optical thickness of each layer of material in the beam-splitting film is λ / 4, so that the wavelengths that satisfy the condition in the prism are reflected, and the wavelengths that do not satisfy the condition directly penetrate the prism, where λ is the target wavelength, m is an integer, d is the thickness of the beam-splitting film, is the incident angle of light on the beam-splitting film.

[0051] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0052] 1. The advantage of the present invention is that the incident light is divided into the required bands by means of a three-beam-splitting prism, imaged on different sensors, and then transmitted to the digital signal processor (DSP) of the camera. In the DSP, these electrical signals are digitized and processed through algorithms to enhance the image quality. The processed red, green, and blue digital signals are recombined into a complete color image in the DSP. Before the prism beam splitting, the optical paths of different bands are completely the same, and the optical paths after the prism beam splitting are also the same, so that the prism camera will not have a halo effect, overcoming the problems of incorrect detection and recognition caused by the tilt of the camera installation or the unevenness of the detection surface.

[0053] 2. The advantage of the present invention is that the polarizer is located between the achromatic system and the first prism. After passing through the polarizer, the light becomes polarized light. An adjustable polarizer is used to select and control the direction of the polarized light, so as to perform a more precise and specific polarization direction analysis on the spectral splitting spectrum after passing through the prism. The polarizer and the three-color prism are combined to form a polarization spectral splitting system. Compared with the traditional energy spectral splitting system, the advantage of the polarization spectral splitting system lies in its high resolution, multi-dimensional information acquisition, wide application fields, strong adaptability, and the ability to analyze the detailed characteristics of substances. It can provide richer and more precise optical analysis and is suitable for various complex experimental and application scenarios.

[0054] 3. The spectral splitting of the present invention provides the spectral information of the light source or the substance, which can help to understand the composition and structure of the substance. The polarization splitting, on the other hand, provides additional information when light interacts with the surface or structure of the substance, such as surface roughness, molecular orientation, etc. When the two are used in combination, a more comprehensive analysis of the optical characteristics can be carried out. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 It is a schematic diagram of the overall structure of the multi-spectral camera optical system based on a three-color prism according to the present invention;

[0056] Figure 2 It is a modulation transfer function diagram of the image formed in the spectral range of 420nm - 500nm in the RGB line scan camera optical system based on a three-color prism with high resolution and low magnification chromatic aberration according to the present invention;

[0057] Figure 3 It is a modulation transfer function diagram of the image formed in the spectral range of 500nm - 580nm in the RGB line scan camera optical system based on a three-color prism with high resolution and low magnification chromatic aberration according to the present invention;

[0058] Figure 4 It is a modulation transfer function diagram of the image formed in the spectral range of 580nm - 660nm in the RGB line scan camera optical system based on a three-color prism with high resolution and low magnification chromatic aberration according to the present invention;

[0059] Figure 5 It is a full-field magnification chromatic aberration diagram of the RGB line scan camera optical system based on a three-color prism with high resolution and low magnification chromatic aberration according to the present invention;

[0060] Figure 6 It is a spectral image fitted from the data collected by detector 15 when the spectrum in the wavelength range of 420nm - 660nm is incident on the RGB line scan camera optical system based on a three-color prism with high resolution and low magnification chromatic aberration according to the present invention;

[0061] Figure 7It is the spectral image fitted from the data collected by detector 16 when the spectrum in the 420nm - 660nm band is incident in the RGB line scan camera optical system with high resolution and low magnification chromatic aberration based on a three - color prism of the present invention;

[0062] Figure 8 It is the spectral image fitted from the data collected by detector 17 when the spectrum in the 420nm - 660nm band is incident in the RGB line scan camera optical system with high resolution and low magnification chromatic aberration based on a three - color prism of the present invention;

[0063] Reference numerals in the figure: 1, first lens; 2, second lens; 3, third lens; 4, fourth lens; 5, fifth lens; 6, sixth lens; 7, seventh lens; 8, eighth lens; 9, ninth lens; 10, tenth lens; 11, polarizer; 12, prism; 13, prism; 14, prism; 15, detector; 16, detector; 17, detector. Detailed implementation mode

[0064] In this embodiment, as Figure 1 shown, an RGB line scan camera optical system with high resolution and low magnification chromatic aberration based on a three - color prism includes: a chromatic aberration system L1, a first prism L2, a second prism L3, a third prism L4, a first detector 15, a second detector 16, and a third detector 17;

[0065] The chromatic aberration system L1 includes: a first lens group, a second lens group, and a third lens group arranged in sequence along the optical axis. Among them, the first lens group has a negative focal power and includes: the first lens 1, the second lens 2; the second lens group has a positive focal power and includes: the third lens 3, the fourth lens 4, the fifth lens 5, the sixth lens 6, the seventh lens 7, the eighth lens 8; the third lens group has a negative focal power and includes: the ninth lens 9, the tenth lens 10, and the polarizer 11; and a diaphragm is arranged between the fifth lens 5 and the sixth lens 6 where the center position of the chromatic aberration system L1 is located.

[0066] After the light passes through each lens in the chromatic aberration system L1 in sequence, the light in the 420nm - 500nm spectral band in the light is incident perpendicularly at a 90° angle on the front surface of the first prism 12. The 90° perpendicular incidence minimizes the surface reflection loss and avoids the influence of beam distortion on the result. It is incident and reflected at a 45° angle on the contact surface between the first prism 12 and the second prism 13. The 45° incidence and reflection make the incident light and the reflected light form a 90° right angle, which is convenient for simplifying the system and compacting the space. Finally, it exits from the surface near the detector 15 and is received by it;

[0067] Light in the spectral range of 500 nm - 580 nm is incident perpendicularly on the front surface of the second prism 12 at an angle of 90°, is incident and transmitted at an angle of 45° on the contact surface between the first prism 12 and the second prism 13, is incident and reflected at an angle of 45° on the contact surface between the second prism 13 and the third prism 14, and finally exits from the surface near the detector 16 and is received by it;

[0068] Light in the spectral range of 580 nm - 660 nm is incident perpendicularly on the front surface of the prism 12 at an angle of 90°, is incident and transmitted at an angle of 45° on the contact surface between the first prism 12 and the second prism 13, is incident and transmitted at an angle of 45° on the contact surface between the second prism 13 and the third prism 14, and finally exits from the surface near the detector 17 and is received by it.

[0069] The first prism 12 and the second prism 13 are closely attached, and a spectral splitting film is provided at the contact surface. The light with a wavelength of 420 nm - 500 nm is reflected here, and the light with a wavelength of 500 nm - 660 nm is transmitted. The second prism 13 and the third prism 14 are closely attached, and a spectral splitting film is provided at the contact surface. The light with a wavelength of 500 nm - 580 nm is reflected here, and the light with a wavelength of 580 nm - 660 nm is transmitted. The two contact surfaces of the three prisms are respectively coated with a splitting film composed of alternating stacks of high refractive index materials with n > 2.3 and low refractive index materials with n < 1.46, and the optical thickness of each layer of material is λ / 4, where λ is the target wavelength, so that the wavelengths that satisfy are reflected, and the wavelengths that do not meet the conditions directly penetrate the prism. Where m is an integer, d is the thickness of the splitting film, is the incident angle of the light on the splitting film;

[0070] The light is in a converging state and is split by three prisms. The three beams of light after color separation are respectively irradiated on three detectors. Each detector contains millions of tiny photosensitive elements, which can convert the received optical signal into an electrical signal. Each sensor only processes information of one color. The electrical signals generated by the photosensitive elements on each detector are read out and amplified, and then transmitted to the digital signal processor DSP of the camera. In the DSP, these electrical signals are digitized and processed through algorithms to enhance the image quality. The processed red, green, and blue three-channel digital signals are recombined into a complete color image in the DSP.

[0071] In this embodiment, a design method of an RGB line-scan camera optical system with high resolution and low magnification chromatic aberration based on a three-color prism includes the following steps:

[0072] Step 1. Obtain the focal length of the chromatic aberration system L1 using Equation (1) :

[0073] (1)

[0074] In formula (1), L represents the conjugate distance of the chromatic aberration system L1, F1 represents the F-number of the chromatic aberration system L1, and β represents the lateral magnification of the chromatic aberration system L1.

[0075] Step 2. Obtain the optical power of the chromatic aberration system L1 using formula (2) :

[0076] (2)

[0077] Step 3. Construct the optical power relationship between the first lens group, the second lens group, and the third lens group and the chromatic aberration system L1 using formula (3):

[0078] (3)

[0079] In formula (3), , , are the optical powers of the first lens group, the second lens group, and the third lens group respectively, , are the thicknesses between the first lens group and the second lens group, and the thickness between the second lens group and the third lens group respectively.

[0080] Step 4: Given , , and determine , , the positive and negative and the ratio of , , ;

[0081] Step 5: Determine that the structure of the second lens group is a double Gauss structure. Select the lens group in the typical double Gauss reference lens library that is closest to the F-number and has the smallest magnification chromatic aberration, and perform focal length scaling on the structure of the selected lens group to obtain the initial structure of the second lens group. One of the characteristics of the double Gauss lens structure is its relatively compact design. Due to the combination of two groups of lenses, the volume and weight of the system can be effectively controlled. Compared with other optical systems with the same performance, the double Gauss structure design can be more lightweight and is suitable for devices that require portability. Among them, the fourth lens 4 and the fifth lens 5 are a double cemented lens composed of lanthanum crown glass and heavy flint glass. The combination of lanthanum crown glass and heavy flint glass is commonly used for chromatic aberration correction. Lanthanum crown glass usually has a low refractive index and low dispersion, while heavy flint glass has a high refractive index and high dispersion. Through the combination of these two glasses, the dispersion of light with different wavelengths in the lens can be effectively corrected, reducing chromatic aberration and improving the color accuracy and image quality of imaging. This combination is often used in high-precision optical systems. The sixth lens 6 and the seventh lens 7 are a double cemented lens composed of heavy phosphate crown glass and heavy flint glass. The combination of heavy phosphate crown glass and heavy flint glass is also very suitable for chromatic aberration correction and is also very excellent in correcting the spherical aberration of the system. Since heavy flint glass has a high refractive index and dispersion, it is suitable for optical systems that require high refractive index materials to achieve small focal lengths. The lower refractive index of heavy phosphate crown glass can maintain relatively good transparency and low absorption while reducing chromatic aberration, ensuring that the lens can work in a wide wavelength range. Minimize the system volume without reducing the system spectral range.

[0082] Step 6: Select flint glass H-ZF6 for the first lens 1 in the first lens group and crown glass H-K9L for the second lens 2. Among them, the curvature radius of the lens surface of the first lens close to the object surface , and the curvature of the other surface takes a negative value to bear a large optical power and is responsible for increasing the system field of view. The structure of the second lens is a double convex structure, and the curvature radii of both surfaces , which is responsible for correcting the aberration generated by the first lens. The combination of high refractive index flint glass and low refractive index crown glass in the first lens group is a classic method in optical design to eliminate chromatic aberration. The dispersion characteristics of the two glasses are complementary and cancel each other out, but the total optical power is retained. And both materials are available, and the lens processing technology is mature.

[0083] Given the ratio of the optical powers between the first lens 1 and the second lens 2 .

[0084] Use equation (4) to obtain the optical power of the first lens 1 and the optical power of the second lens 2 :

[0085] (4)

[0086] In formula (4), represents the distance between the first lens 1 and the second lens 2.

[0087] Step 7: According to determine the initial structure of the first lens 1, including: the curvature radius of the lens surface of the first lens 1 close to the object surface , and the curvature radius of the other surface obtained from formula (5):

[0088] (5)

[0089] In formula (5), is the refractive index of the first lens 1, is the central thickness of the first lens 1.

[0090] According to determine the initial structure of the second lens 2 as a biconvex structure, and the curvature radii of the two surfaces , and obtain from formula (6):

[0091] (6)

[0092] In formula (6), where is the refractive index of the second lens 2, is the central thickness of the second lens 2.

[0093] Step 9: Select crown glass H-K9L for the ninth lens 9 in the third lens group, and flint glass H-ZF6 for the tenth lens 10;

[0094] Step 10: Taking the optical power of the third lens group as a reference, obtain the optical power of the ninth lens 9 and the optical power of the tenth lens 10 according to the process of Step 6, and determine the initial structure of the ninth lens 9 including: the curvature radius of the lens surface of the ninth lens 9 close to the object surface , and the curvature radius of the other surface obtained from formula (7);

[0095] (7)

[0096] In formula (7), where is the refractive index of the ninth lens 9, is the central thickness of the ninth lens 9.

[0097] Determine the initial structure of the tenth lens 10 as a meniscus convex lens structure, and the curvature radii of the two surfaces are ​​, responsible for increasing the system focal length and correcting the system aberration, and the specific values are obtained from Equation (8);

[0098] (8)

[0099] In Equation (8), where is the refractive index of the tenth lens 10, is the central thickness of the tenth lens 10.

[0100] The third lens group also uses the combination of flint glass with high refractive index and crown glass with low refractive index, and the overall optical power is negative. The negative power lens (concave lens) can effectively reduce the aberration in the optical system. When the negative focal lens is placed closer to the image plane, it can effectively adjust the propagation path of light, thereby optimizing the clarity and accuracy of the image and improving the imaging quality. Dense flint glass has low dispersion characteristics. Placing the dense flint glass with negative optical power near the image plane helps to correct and reduce chromatic aberration.

[0101] Step 11: Determine the optimization variables, including: the curvature radius of each surface in the initial structure of the chromatic aberration system L1, the thickness of the ten lenses, the air thickness between the lenses, and the thickness from the object plane to the first lens;

[0102] Construct the focal length constraint, lens length constraint, conjugate distance constraint, spherical aberration correction, magnification chromatic aberration, and boundary condition constraints, and use them to optimize the initial structure of the chromatic aberration system L1. Among them, the optimization evaluation function uses the RMS wavefront aberration to optimize the system. The TTHI operand is used to constrain the lens length and conjugate distance respectively; the SPHA is used for spherical aberration correction; the REAY operand is used for the wavelengths of 420nm and 660nm respectively to obtain REAY1 and REAY2, and the OPLT operand is used to control the result of (REAY1 - REAY2) / REAY2 to optimize the magnification chromatic aberration; the conventional operand is used to constrain the boundary conditions. The system is optimized to obtain the preliminary optimization result.

[0103] Step 12: According to the preliminary optimization result of the chromatic aberration system L1, insert a prism equivalent flat plate at the position between () and the image plane, and determine the length of the prism equivalent flat plate , where is the clear aperture diameter of the prism. Due to the compact system structure, without losing the system energy as much as possible and wasting materials. The value of D can be the same as the clear aperture of the back surface of lens 10 in the preliminary optimization result.

[0104] Step 13: Optimize the RGB line scan camera optical system according to the process of Step 11 to obtain the final optimization result;

[0105] According to the final optimization result and the fact that light is divided into three optical paths in the prism, a triple structure of the chromatic aberration system L1, the first prism 12, the second prism 13, and the third prism 14 is constructed.

[0106] In the first structure, the equivalent flat plate of the prism is converted into the first prism 12, and an isosceles right triangle region with the front surface of the first prism in the first prism 12 as the right-angle side and the contact surface between the first prism 12 and the second prism 13 as the hypotenuse is set as the second part ②, and the remaining region of the first prism 12 is the first part ①;

[0107] In the second structure, the equivalent flat plate of the prism is converted into the prism in the second structure, and the prism in the second structure is composed of the second part ② in the first prism 12 and the third part ③ represented by the second prism 13;

[0108] In the third structure, the equivalent flat plate of the prism is converted into the prism in the third structure, and the prism in the third structure is jointly composed of the second part ② in the first prism 12, the third part ③ represented by the second prism 13, and the fourth part ④ represented by the third prism 14; In the three prism structures, the distance from the front surface of the prism to the rear surface of the tenth lens must be kept equal.

[0109] Step 13: The two contact surfaces of the three prisms are respectively coated with a beam-splitting film composed of alternating stacks of high refractive index materials with n > 2.3 and low refractive index materials with n < 1.46, and the optical thickness of each layer of material is λ / 4, where λ is the target wavelength, so that wavelengths satisfying are reflected, and wavelengths not satisfying the conditions directly penetrate the prism. Where m is an integer, d is the thickness of the beam-splitting film, is the incident angle of light on the beam-splitting film.

[0110] According to the above steps, an initial structure of an RGB line-scan camera optical system with high resolution and low magnification chromatic aberration based on a three-color prism is obtained, and then the initial structure is optimized to obtain the final initial structure of the RGB line-scan camera optical system with high resolution and low magnification chromatic aberration. Among them, the optimization steps are as follows: 1) Determine the mechanical aperture of the component; 2) Perform template matching and process rounding processing. 3) Conduct tolerance analysis and temperature analysis on the system:

[0111] As shown in Table 1, the main parameters of a specific embodiment of an RGB line-scan camera optical system with high resolution and low magnification chromatic aberration designed according to this embodiment are presented.

[0112] Table 1. Main parameters of a specific embodiment

[0113] Parameter Value Parameter Value Wavelength 420~660 nm Entrance pupil diameter 18.357mm F-number 2.91 Chromatic difference of magnification 0.5 per ten thousand Focal length 51.4mm Object-image conjugate distance 700mm

[0114] As Figure 2The MTF image of the first multi-structure (420nm - 500nm band) is shown as follows. Figure 3 The MTF image of the second multi-structure (500nm - 580nm band) is shown as follows. Figure 4 The MTF image of the third multi-structure (580nm - 660nm band) is shown as follows. It shows that for this specific embodiment, whether in the central field of view (0, 0) or the edge field of view (at the object height of 150mm), the MTF is greater than 0.3 at 100lp / mm. The image plane height is as high as 14mm. The entire system can be matched with a CCD with a pixel size of 5μm and a target plane size of 28mm * 28mm. Figure 5 This is the longitudinal chromatic aberration image of the system. Using the method in step 11, the longitudinal chromatic aberration of the system is calculated to be less than 0.5 per ten thousand, and the optimization result is excellent, belonging to the category of ultra-precision optical systems. Figure 6 , Figure 7 and Figure 8 As shown by , the spectra received by detectors 15, 16, and 17 are very close to the theoretical spectra of the detectors, indicating that the three-color prism beam splitting system can divide the spectra in the 420nm - 660nm band into three bands of 420nm - 500nm, 500nm - 580nm, and 580nm - 660nm, and the spectral energy loss is minimized.

Claims

1. An RGB line-scan camera optical system based on a three-color prism with high resolution and low magnification chromatic aberration, characterized in that, Including: A color difference system (L1), a first prism (12), a second prism (13), a third prism (14), a first detector (15), a second detector (16), and a third detector (17); The color difference system (L1) includes: a first lens group, a second lens group, and a third lens group arranged in sequence along the optical axis. Among them, the first lens group has a negative optical power and includes: a first lens (1), a second lens (2). The second lens group has a positive optical power and includes: a third lens (3), a fourth lens (4), a fifth lens (5), a sixth lens (6), a seventh lens (7), an eighth lens (8). The third lens group has a negative optical power and includes: a ninth lens (9), a tenth lens (10), and a polarizing plate (11); and an aperture is provided between the fifth lens (5) and the sixth lens (6) where the center position of the color difference system (L1) is located; Among them, the first prism (12) and the second prism (13) are closely attached, and a first spectral splitting film is provided at the contact surface between the two. The second prism (13) and the third prism (14) are closely attached, and a second spectral splitting film is provided at the contact surface between the two; After the light passes through each lens in the color difference system (L1) in sequence, the light in the spectral range of 420nm - 500nm in the light is perpendicularly incident on the front surface of the first prism (12) at an angle of 90°, is incident and reflected at an angle of 45° on the contact surface between the first prism (12) and the second prism (13), and finally exits from the surface of the first prism (12) near the first detector (15), and forms a first spectral splitting and is received by the first detector (15); The light in the spectral range of 500nm - 580nm in the light is perpendicularly incident on the front surface of the second prism (12) at an angle of 90°, is incident and transmitted at an angle of 45° on the contact surface between the first prism (12) and the second prism (13), is incident and reflected at an angle of 45° on the contact surface between the second prism (13) and the third prism (14), and finally exits from the surface of the second prism (13) near the second detector (16), and forms a second spectral splitting and is received by the second detector (16); The light in the spectral range of 580nm - 660nm in the light is perpendicularly incident on the front surface of the prism (12) at an angle of 90°, is incident and transmitted at an angle of 45° on the contact surface between the first prism (12) and the second prism (13), is incident and transmitted at an angle of 45° on the contact surface between the second prism (13) and the third prism (14), and finally exits from the surface of the third prism (14) near the third detector (17), and forms a third spectral splitting and is received by the third detector (17); After the three spectral splittings are processed by the three detectors respectively, red, green, and blue three - channel digital signals are obtained and form a complete color image.

2. The design method of an RGB line-scan camera optical system with high resolution and low magnification chromatic aberration based on a three-color prism according to claim 1, characterized in that, Including the following steps: Step 1. Obtain the focal length of the color difference system (L1) using Equation (1) :[[-END]] (1) In formula (1), L represents the conjugate distance of the color difference system (L1), F1 represents the F - number of the color difference system (L1), and β represents the lateral magnification of the color difference system (L1); Step 2. Obtain the optical power of the color difference system (L1) using Equation (2) :[[-END]] (2) Step 3. Use Equation (3) to construct the optical power relationship formulas between the first lens group, the second lens group, and the third lens group and the chromatic aberration system (L1): (3) In Equation (3), , , are the optical powers of the first lens group, the second lens group, and the third lens group, respectively, , are the thicknesses between the first lens group and the second lens group, and between the second lens group and the third lens group, respectively; Step 4: Given , , and determine , , the positive / negative and ratio of , , ; thus, calculate the optical powers of the three lens groups according to Equation (3), and obtain the focal lengths of the three lens groups as , , respectively according to Equation (2); Step 5: Determine that the structure of the second lens group is a double-Gauss structure. Select the lens group in the typical double-Gauss reference lens library that is closest to the F-number and has the smallest magnification chromatic aberration, and perform focal length scaling on the structure of the selected lens group to obtain the initial structure of the second lens group; Step 6: Select flint glass H-ZF6 for the first lens (1) in the first lens group and crown glass H-K9L for the second lens (2). Among them, the curvature radius of the lens surface of the first lens (1) close to the object surface , the curvature of the other lens surface of the first lens (1) is negative. The structure of the second lens (2) is a biconvex structure, and the curvature radii of both surfaces ; Given the ratio of the optical power between the first lens (1) and the second lens (2) ; Obtain the optical power of the first lens (1) using Equation (4) and the optical power of the second lens (2) ; (4) In formula (4), represents the distance between the first lens (1) and the second lens (2); Step 7: According to determine the initial structure of the first lens (1), including: the curvature radius of the lens surface of the first lens (1) close to the object surface , the curvature radius of the other lens surface of the first lens (1) obtained from Equation (5): (5) In formula (5), is the refractive index of the first lens (1), is the central thickness of the first lens (1); According to it is determined that the initial structure of the second lens (2) is a biconvex structure, and the curvature radii of both surfaces , and the following is obtained by using Equation (6): (6) In formula (6), where is the refractive index of the second lens (2), is the central thickness of the second lens (2); Step 9: Select crown glass H-K9L for the ninth lens (9) in the third lens group, and flint glass H-ZF6 for the tenth lens (10); Step 10: Taking the optical power of the third lens group as a reference, obtain the optical power of the ninth lens (9) and the optical power of the tenth lens (10) according to the process of Step 6 , and determine that the initial structure of the ninth lens (9) includes: the curvature radius of the lens surface of the ninth lens (9) close to the object surface , the curvature radius of the other lens surface of the ninth lens (9) , which is obtained from Equation (7). ​ (7) In formula (7), is the refractive index of the ninth lens (9), is the central thickness of the ninth lens (9); The initial structure of the tenth lens (10) is determined to be a meniscus convex lens structure, and the curvature radii of the two surfaces are , and are obtained from Equation (8); (8) In Equation (8), where is the refractive index of the tenth lens (10), is the central thickness of the tenth lens (10); Step 11: Determine the optimization variables, including: the curvature radii of each surface in the initial structure of the chromatic aberration system (L1), the thicknesses of the ten lenses, the air thickness between the lenses, and the thickness from the object surface to the first lens (1); Construct focal length constraints, lens length constraints, conjugate distance constraints, spherical aberration correction, magnification chromatic aberration, and boundary condition constraints, and use them to optimize the initial structure of the chromatic aberration system (L1) to obtain a preliminary optimization result; Step 12: According to the preliminary optimization result of the color difference system (L1), insert a prism equivalent flat plate at the position between the tenth lens (10) and the image plane, and determine the length of the prism equivalent flat plate , where is the clear aperture diameter of the prism Step 13: Optimize the RGB line-scan camera optical system according to the process in Step 11 to obtain the final optimization result; According to the final optimization result and the three optical paths formed by the light rays in the prism, construct a triple structure composed of the chromatic aberration system (L1), the first prism (12), the second prism (13), and the third prism (14); In the first triple structure, convert the prism equivalent flat plate into two parts. Set the isosceles right triangle region formed by the front surface of the first prism (12) as the right-angle side and the contact surface between the first prism (12) and the second prism (13) as the hypotenuse as the second part, and set the remaining region of the first prism (12) as the first part; In the second triple structure, convert the prism equivalent flat plate into two parts, namely the second part in the first prism (12) and the second prism (13); In the third triple structure, convert the prism equivalent flat plate into two parts, namely the second part in the first prism (12), and the part composed of the second prism (13) and the third prism (14); Step 13: Two contact surfaces between the three prisms are respectively coated with a beam-splitting film composed of alternating stacks of high-refractive-index materials with n > 2.3 and low-refractive-index materials with n < 1.46, and the optical thickness of each layer of material in the beam-splitting film is λ / 4, so that the wavelengths satisfying the condition in the prism are reflected, and the wavelengths not satisfying the condition directly penetrate the prism, where λ is the target wavelength, m is an integer, d is the thickness of the beam-splitting film, is the incident angle of the light on the beam-splitting film.

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