Ultra-short back focal length microscopic tube lens

Abstract

The application discloses a kind of ultra-short back focal length microcylinders, by four pieces of spherical lens of isophotal arrangement, no cemented lens;Four pieces of spherical lens are in order from object side to image side: first lens, second lens, third lens and fourth lens;Among them, first lens and third lens are all meniscus lens with positive focal power;Second lens and fourth lens are all meniscus lens with negative focal power;The convex surface of first lens, second lens, third lens and fourth lens all faces object side, the concave surface all faces image side, the curvature radius of first lens, second lens, third lens and fourth lens are all positive value.The application adopts full positive curvature meniscus lens arrangement, four sections gradient dispersion glass combination, can correct spherical aberration and chromatic aberration, can clearly image without focusing under visible light and near infrared light, imaging quality and resolution are high, realize long focal length while compressing total length, focal plane does not deviate within-40 DEG ~80 DEG.

Description

Technical Field

[0001] This invention relates to an ultra-short back focal length microscope tube, belonging to the field of optical lens technology for microscopic imaging and broadband imaging. Background Technology

[0002] The telescopic lens is a core component of an infinity-corrected microscopy system. The infinity objective converts the light emitted from the sample into a parallel beam, which is then converged onto the camera's photosensitive surface by the telescopic lens. Its optical performance directly determines the system's imaging resolution, field-of-view quality, and environmental adaptability, and it is widely used in biomedical microscopy, high-resolution wide-field imaging, laser scanning microscopy, and machine vision inspection. Currently, 200mm focal length telescopic lenses generally follow traditional microscopic optical interface designs. Their back focal length is constrained by the mechanical structure of the microscope tube and the lens arrangement, making it difficult to achieve a short back focal distance. This results in a large overall axial length of the optical system, which is detrimental to the miniaturization of compact self-developed microscopes and integrated laser scanning microscopy equipment.

[0003] To achieve broadband imaging, existing telescopic lenses typically employ designs that increase the number of lenses, introduce aspherical lenses, or use cemented lens groups to correct spherical aberration, chromatic aberration, and especially second-order spectral aberration. However, aspherical lens molds are costly to manufacture; cemented lenses have stringent requirements regarding the bonding process, the spectral transmittance of the adhesive, and temperature resistance, and are prone to delamination and stress birefringence issues under high and low temperature environments; increasing the number of lenses also leads to larger system size, increased assembly difficulty, and higher overall system cost.

[0004] Traditional telescopic lens optical designs do not adequately consider performance retention under wide temperature conditions. Within a wide temperature range of -40℃ to +80℃, the lens assembly experiences focus drift, aberration deterioration, and decreased image sharpness due to thermal drift of the lens material's refractive index and thermal expansion and contraction of the lens barrel structure. Existing solutions for achieving heatless operation often require the introduction of an active focusing mechanism, relying on a motor to compensate for focus shift in real time, which increases system size, power consumption, and control complexity.

[0005] Forcibly compressing the focal length in existing structures would introduce severe spherical and chromatic aberrations, especially in the broad spectral range of 435–1500 nm, making it difficult to guarantee full-field diffraction-limited imaging performance. Furthermore, existing telescopic lens configurations mostly employ biconvex or plano-convex combinations, rarely using multi-element global meniscus lens combinations. While meniscus lens combinations can better correct broad-spectrum chromatic and spherical aberrations, the curvature, material matching, and spacing of multiple meniscus lenses require complex optimization, and current technologies lack mature solutions.

[0006] Therefore, developing a 200mm-class long focal length optical system with an extremely short primary lens barrel and full compatibility with low-cost global surface processing technology is a technical challenge that urgently needs to be solved in the fields of industrial vision and special optical inspection. Summary of the Invention

[0007] To address the shortcomings of existing long-focal-length microscope tubes, such as excessively long back focal length, high cost, and difficulty in correcting chromatic aberration over a wide wavelength range, this invention provides an ultra-short back focal length microscope tube. This invention employs a fully positive curvature meniscus lens arrangement and a four-segment gradient dispersion glass combination, which can correct spherical aberration and chromatic aberration. It enables clear imaging without focusing under visible and near-infrared light, achieving high image quality and resolution. It achieves a long focal length while compressing the overall length, and the focal plane remains unchanged within the temperature range of -40℃ to 80℃. The invention also simplifies the structure, facilitates fabrication, and reduces costs.

[0008] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: An ultra-short back focal length microscope tube lens is composed of four spherical lenses arranged coaxially, without cemented lenses; the four spherical lenses are arranged from the object side to the image side as follows: first lens, second lens, third lens, and fourth lens; wherein, the first lens and the third lens are both meniscus lenses with positive optical power; the second lens and the fourth lens are both meniscus lenses with negative optical power; the convex surfaces of the first lens, the second lens, the third lens, and the fourth lens all face the object side, and the concave surfaces all face the image side, and the radii of curvature of the first lens, the second lens, the third lens, and the fourth lens are all positive.

[0009] In the aforementioned ultra-short back focal length microscope tube, the radii of curvature of the first to fourth lenses are all positive from the object side to the image side. This meniscus lens group configuration, which uses positive radii of curvature throughout, can effectively stretch the focal length of the system by accumulating the refractive power of each lens surface without the need for cementing.

[0010] The aforementioned ultra-short back focal length microscope tube is a global surface design, with all lens surfaces having positive radii of curvature, and each lens having spherical surfaces on both sides, without aspherical surfaces, diffraction surfaces, or cemented lenses, resulting in low cost.

[0011] To further improve wide temperature adaptability and ensure imaging quality, the first lens satisfies: 1.4 < Nd1 < 1.5, 80 < Vd1 < 83, where Nd 1、 Vd1 and Vd2 are the refractive index and Abbe number of the first positive lens, respectively; the second lens satisfies: 1.8 < Nd2 < 1.9, 22 < Vd2 < 25, where Nd2 < Vd2 < 25. 2、 Vd2 are the refractive index and Abbe number of the second negative lens, respectively; the third lens satisfies: 1.8 < Nd3 < 1.9, 22 < Vd3 < 25, where Nd 3、 Vd3 represents the refractive index and Abbe number of the third positive lens, respectively; the fourth lens satisfies: 1.6 < Nd4 < 1.7, 51 < Vd4 < 55, where Nd... 4、 Vd4 represents the refractive index and Abbe number of the fourth negative lens, respectively.

[0012] This application effectively eliminates second-order spectral chromatic aberration in the visible spectrum by selecting and matching the refractive index and Abbe number of each lens.

[0013] From the object side to the image side, the two sides of the first lens are the first object side and the first image side, the two sides of the second lens are the second object side and the second image side, the two sides of the third lens are the third object side and the third image side, and the two sides of the fourth lens are the fourth object side and the fourth image side.

[0014] To further improve imaging performance, the radius of curvature of the first object-side surface is 18.992±0.010mm, and the radius of curvature of the first image-side surface is 105.059±0.050mm; the radius of curvature of the second object-side surface is 27.869±0.050mm, and the radius of curvature of the second image-side surface is 13.582±0.010mm; the radius of curvature of the third object-side surface is 18.850±0.010mm, and the radius of curvature of the third image-side surface is 34.679±0.010mm; the radius of curvature of the fourth object-side surface is 85.598±2.000mm, and the radius of curvature of the fourth image-side surface is 20.762±0.100mm.

[0015] To further ensure image quality, the center-to-center distance between the first and second lenses is 0.300±0.030mm; the center-to-center distance between the second and third lenses is 6.139±0.050mm; and the center-to-center distance between the third and fourth lenses is 11.693±0.100mm.

[0016] To balance cost, quality, and imaging performance, the center thickness of the first lens is 5.00±0.03mm; the center thickness of the second lens is 3.00±0.02mm; the center thickness of the third lens is 4.50±0.05mm; and the center thickness of the fourth lens is 3.00±0.10mm.

[0017] This invention, through a special air gap distribution and an extremely short main lens barrel, highlights the low-cost manufacturing and ultra-high modular integration performance of the global surface.

[0018] The coefficients of thermal expansion of the first, second, third, and fourth lenses mentioned above satisfy the following conditions within the temperature range of -40℃ to +80℃: the coefficient of thermal expansion of the first lens is 12.3-14.2×10⁻⁶. -6 mm / (mm·℃); the coefficient of thermal expansion of the second lens is 8.1-8.8×10 -6 mm / (mm·℃); the coefficient of thermal expansion of the third lens is 8.1-8.8×10 -6 mm / (mm·℃); the coefficient of thermal expansion of the fourth lens is 6.8-7.5×10. -6 mm / (mm·℃).

[0019] The aforementioned ultra-short back focal length microscope tube is characterized by: further comprising a lens barrel located outside the optical lens, the lens barrel being adapted to the lens assembly (first lens, second lens, third lens, and fourth lens), and the thermal expansion coefficient of the lens barrel satisfying the following condition within the temperature range of -40℃ to 80℃: 19.2-20.9×10⁻⁶. -6 mm / (mm·℃).

[0020] As one preferred implementation, the ultra-short back focal length microscope tube of the present invention has a focal length of 200mm, a back focal length of 102.35mm, a total optical length of 205.99mm, and a working wavelength range of 435nm~1500nm.

[0021] As one preferred implementation, the ultra-short back focal length microscope tube of the present invention has a full field of view of 7.4°, an entrance pupil diameter of 8mm, and a relative aperture of F#25.

[0022] The ultra-short back focal length microscope tube of this application does not shift its focal plane within the temperature range of -40℃ to 80℃.

[0023] The aforementioned optical lens features four meniscus spherical lenses arranged sequentially along the optical axis from the object side to the image side. One lens is convex towards the object side, and the other concave towards the image side, all with positive radii of curvature. The entire lens structure is free of cementation, aspherical surfaces, and diffraction surfaces. Furthermore, through precise matching of four segments of differentiated dispersive glass, apochromatic aberration is achieved across a wide wavelength range from 435nm to 1500nm (visible to near-infrared) within a minimalist four-element architecture. Passive calorimetry is achieved over a wide temperature range from -40℃ to +80℃ through coordinated compensation of the lens's thermal expansion coefficient and the lens barrel's thermal expansion coefficient.

[0024] The lens group of the aforementioned optical lens is only 33.6mm long, with an effective focal length of 200mm and a back focal length compressed to 102.35mm. It also has multiple advantages such as low-cost global surface processing, long focal length and compact size, and wide temperature environment adaptability. It solves the technical pain points of existing long focal length lenses, such as complex structure, high cost, large size and large temperature drift. It is suitable for industrial machine vision, microscopic imaging, wide spectrum special monitoring and other scenarios.

[0025] Any techniques not mentioned in this invention are based on existing technologies.

[0026] Compared with the prior art, the present invention has at least the following advantages and beneficial effects: 1. This application, by employing a combination of four meniscus lenses with positive radii of curvature, can effectively stretch the focal length of the system to 200mm by accumulating the refractive power of each lens surface without the need for cementation, aspherical surfaces, or diffraction surfaces.

[0027] 2. This application successfully achieved excellent apochromatic effect in a wide spectral range of 435nm to 1500nm by combining three glass materials with different refractive indices and dispersion coefficients, ensuring high image clarity and color reproduction.

[0028] 3. This application features a long focal length and extreme compactness, achieving an effective focal length of 200mm and an ultra-short back focal length of 102.35mm. The lens group length is only 33.6mm, providing a large mechanical margin for various additional modules such as beam splitters, large-size filters, and front-mounted folding optical paths, giving the lens a strong modular expansion and system integration capability.

[0029] 4. The optical system of this application does not shift the focal plane within the temperature range of -40℃ to 80℃, achieving passive calorification over a wide temperature range of -40℃ to +80℃. It has a wide range of applications, small size, light weight, and low cost.

[0030] 5. The optical system of this application has a simple lens surface shape and the same bending direction, which improves compactness, simplifies the structure and manufacturing, reduces costs, and at the same time ensures imaging quality. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the structure of the ultra-short back focal length microscope tube of the present invention; Figure 2 This is a dot plot of the ultra-short back focal length microscope tube lens of the present invention at an ambient temperature of 20°C. Figure 3 This is a dot plot of the ultra-short back focal length microscope tube lens of the present invention at an ambient temperature of -40℃. Figure 4 This is a dot plot of the ultra-short back focal length microscope tube lens of the present invention at an ambient temperature of 80°C. Figure 5 This is the MTF curve of the ultra-short back focal length microscope tube of the present invention at an ambient temperature of 20°C; Figure 6 This is the MTF curve of the ultra-short back focal length microscope tube of the present invention at an ambient temperature of -40℃; Figure 7 This is the MTF curve of the ultra-short back focal length microscope tube of the present invention at an ambient temperature of 80°C. Figure 8 This is a diagram showing the relative illumination curve of the entire field of view of the ultra-short back focal length microscope tube of this invention. In the diagram, L1 is the first lens, L2 is the second lens, L3 is the third lens, L4 is the fourth lens, R1 is the first object-side surface, R2 is the first image-side surface, R3 is the second object-side surface, R4 is the second image-side surface, R5 is the third object-side surface, R6 is the third image-side surface, R7 is the fourth object-side surface, R8 is the fourth image-side surface, and X is the imaging plane. Detailed Implementation

[0032] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0033] It should be noted that, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the specification of this application is for the purpose of describing particular embodiments only and is not intended to limit the scope of this application.

[0034] like Figure 1 As shown, an ultra-short back focal length microscope tube lens consists of four spherical lenses arranged coaxially, without cemented lenses, aspherical surfaces, or diffraction surfaces. The four spherical lenses from the object side to the image side are, in order: a first lens, a second lens, a third lens, and a fourth lens. The first and third lenses are both meniscus lenses with positive optical power; the second and fourth lenses are both meniscus lenses with negative optical power. The convex surfaces of the first, second, third, and fourth lenses all face the object side, and the radii of curvature of the first, second, third, and fourth lenses are all positive.

[0035] From the object side to the image side, the first lens has two surfaces that are, in sequence, the first object-side surface and the first image-side surface; the second lens has two surfaces that are, in sequence, the second object-side surface and the second image-side surface; the third lens has two surfaces that are, in sequence, the third object-side surface and the third image-side surface; and the fourth lens has two surfaces that are, in sequence, the fourth object-side surface and the fourth image-side surface. The first, second, third, and fourth object-side surfaces are all convex, while the first, second, third, and fourth image-side surfaces are all concave. The radius of curvature of the first object-side surface is 18.992 mm, and the radius of curvature of the first image-side surface is 105.059 mm; the radius of curvature of the second object-side surface is 27.869 mm, and the radius of curvature of the second image-side surface is 13.582 mm; the radius of curvature of the third object-side surface is 18.850 mm, and the radius of curvature of the third image-side surface is 34.679 mm; the radius of curvature of the fourth object-side surface is 85.598 mm, and the radius of curvature of the fourth image-side surface is 20.762 mm. The center-to-center distance between the first and second lenses is 0.300 mm; the center-to-center distance between the second and third lenses is 6.139 mm; and the center-to-center distance between the third and fourth lenses is 11.693 mm. The center thickness of the first lens is 5.00 mm; the center thickness of the second lens is 3.00 mm; the center thickness of the third lens is 4.50 mm; and the center thickness of the fourth lens is 3.00 mm.

[0036] The first lens satisfies: 1.4 < Nd1 < 1.5, 80 < Vd1 < 83, where Nd1 and Vd1 are the refractive index and Abbe number of the first positive lens, respectively. In this example, Nd1 is 1.497 and Vd1 is 81.613. The second lens satisfies: 1.8 < Nd2 < 1.9, 22 < Vd2 < 25, where Nd1 < Vd2 < 83. 2、 Vd2 and Nd3 are the refractive index and Abbe number of the second negative lens, respectively. In this example, Nd2 is 1.847 and Vd2 is 23.784. The third lens satisfies: 1.8 < Nd3 < 1.9, 22 < Vd3 < 25, where Nd2 < Vd3 < 25. 3、 Vd3 and Nd4 are the refractive index and Abbe number of the third positive lens, respectively. In this example, Nd3 is 1.847 and Vd3 is 23.784. The fourth lens satisfies: 1.6 < Nd4 < 1.7, 51 < Vd4 < 55, where Nd4 < Vd3 < Vd4 < Vd4. 4、 Vd4 represents the refractive index and Abbe number of the fourth negative lens, respectively. In this example, Nd4 is 1.670 and Vd4 is 51.738.

[0037] The optical lens has a matching lens barrel. In this example, the lens barrel is made of HPB59-1 material.

[0038] The specific optical parameters of the lens in this example are shown in Table 1, and the physical properties are shown in Table 2.

[0039] Table 1 shows the specific optical parameters of the ultra-short back focal length microscope tube in this embodiment.

[0040] In Table 1, the radius of curvature refers to the radius of curvature of the object side and image side surfaces of each lens; thickness or spacing refers to the lens thickness or the distance between adjacent lens surfaces; material refers to the material used for the corresponding lens; and the medium between two lenses is air.

[0041] Table 2 shows the physical properties of the ultra-short back focal length microscope tube in this embodiment.

[0042] The ultra-short back focal length microscope tube of this embodiment does not shift its focal plane within the temperature range of -40℃ to 80℃.

[0043] Figure 2 The image shows a dot plot of the ultra-short back focal length microscope tube in this embodiment at room temperature (20°C). It can be seen that the RMS radius of the blur spot is less than 7.3 μm at each field of view, indicating that the optical system aberrations are well corrected and the imaging quality is good.

[0044] Figure 3 The image shows a dot plot of the ultra-short back focal length microscope tube in this embodiment at a low temperature of -40℃. It can be seen that the RMS radius of the blur spot is less than 7 μm at each field of view, indicating that the optical system aberrations are well corrected and the imaging quality is good.

[0045] Figure 4 The image shows a dot plot of the ultra-short back focal length microscope tube in this embodiment at a high temperature of 80°C. It can be seen that the RMS radius of the blur spot is less than 8.3 μm at each field of view, indicating that the optical system aberrations are well corrected and the imaging quality is good. Figure 5 The image shows the optical modulation transfer function (MTF) of the ultra-short back focal length microscope tube in this embodiment at a normal temperature of 20°C. It can be seen that the MTF of each field of view at 36 lp / mm is greater than 0.3.

[0046] Figure 6 The image shows the optical modulation transfer function (MTF) of the ultra-short back focal length microscope tube in this embodiment at a low temperature of -40℃. It can be seen that the MTF of each field of view at 36 lp / mm is greater than 0.3.

[0047] Figure 7 The image shows the optical modulation transfer function (MTF) of the ultra-short back focal length microscope tube in this embodiment under a high temperature environment of 80°C. It can be seen that the MTF of each field of view at 36 lp / mm is greater than 0.3.

[0048] Figure 8 The image shows the relative illumination of the ultra-short back focal length microscope tube in this embodiment. It can be seen that the relative illumination across the entire field of view is ≥95%, and the image plane uniformity is good.

[0049] As can be seen, the ultra-short back focal length microscope tube of this embodiment achieves good aberration correction under operating conditions of 20℃ (normal temperature), -40℃ (low temperature), and 80℃ (high temperature), with a small blur spot size across the entire field of view. Within a wide temperature range of -40℃ to 80℃, the MTF (Mean Transmission Factor) of each field of view is higher than 0.3 at a characteristic frequency of 36 lp / mm, indicating that the imaging resolution is minimally affected by temperature. Furthermore, the lens achieves a relative illumination of ≥95% across the entire field of view, with excellent image plane illumination uniformity. This lens does not require aspherical elements; it achieves excellent imaging based on its global aspherical configuration and possesses outstanding wide-temperature operating stability. It also eliminates the need for cemented lenses, resulting in a simple structure, small size, light weight, and low cost.

Claims

1. A microscope tube with an ultra-short back focal length, characterized in that: It consists of four spherical lenses arranged coaxially, without cemented lenses; the four spherical lenses, from object side to image side, are: first lens, second lens, third lens, and fourth lens; among them, the first lens and the third lens are both meniscus lenses with positive optical power; the second lens and the fourth lens are both meniscus lenses with negative optical power; the convex surfaces of the first lens, the second lens, the third lens, and the fourth lens all face the object side, and the concave surfaces all face the image side, and the radii of curvature of the first lens, the second lens, the third lens, and the fourth lens are all positive.

2. The ultra-short back focal length microscope tube according to claim 1, characterized in that: The first lens satisfies: 1.4 < Nd1 < 1.5, 80 < Vd1 < 83, where Nd 1、 Vd1 represents the refractive index and Abbe number of the first positive lens, respectively; The second lens satisfies: 1.8 < Nd² < 1.9, 2² < Vd² < 25, where Nd... 2、 Vd2 represents the refractive index and Abbe number of the second negative lens, respectively. The third lens satisfies: 1.8 < Nd³ < 1.9, 22 < Vd³ < 25, where Nd... 3、 Vd3 represents the refractive index and Abbe number of the third positive lens, respectively. The fourth lens satisfies: 1.6 < Nd⁴ < 1.7, 51 < Vd⁴ < 55, where Nd 4、 Vd4 represents the refractive index and Abbe number of the fourth negative lens, respectively.

3. The ultra-short back focal length microscope tube according to claim 1 or 2, characterized in that: From the object side to the image side, the two sides of the first lens are the first object side and the first image side, the two sides of the second lens are the second object side and the second image side, the two sides of the third lens are the third object side and the third image side, and the two sides of the fourth lens are the fourth object side and the fourth image side. The radius of curvature of the side surface of the first object is 18.992±0.010mm, and the radius of curvature of the side surface of the first image is 105.059±0.050mm. The radius of curvature of the second object's side surface is 27.869±0.050mm, and the radius of curvature of the second image's side surface is 13.582±0.010mm. The radius of curvature of the third object's side surface is 18.850±0.010mm, and the radius of curvature of the third image's side surface is 34.679±0.010mm. The radius of curvature of the fourth object's side surface is 85.598±2.000mm, and the radius of curvature of the fourth image's side surface is 20.762±0.100mm.

4. The ultra-short back focal length microscope tube according to claim 1 or 2, characterized in that: The center-to-center distance between the first and second lenses is 0.300±0.030mm; the center-to-center distance between the second and third lenses is 6.139±0.050mm; and the center-to-center distance between the third and fourth lenses is 11.693±0.100mm.

5. The ultra-short back focal length microscope tube according to claim 1 or 2, characterized in that: The center thickness of the first lens is 5.00±0.03mm; the center thickness of the second lens is 3.00±0.02mm; the center thickness of the third lens is 4.50±0.05mm; and the center thickness of the fourth lens is 3.00±0.10mm.

6. The ultra-short back focal length microscope tube according to claim 1 or 2, characterized in that: The coefficients of thermal expansion of the first, second, third, and fourth lenses satisfy the following conditions within the temperature range of -40℃ to +80℃: the coefficient of thermal expansion of the first lens is 12.3-14.2×10⁻⁶. -6 mm / (mm·℃); the coefficient of thermal expansion of the second lens is 8.1-8.8×10 -6 mm / (mm·℃); the coefficient of thermal expansion of the third lens is 8.1-8.8×10 -6 mm / (mm·℃); the coefficient of thermal expansion of the fourth lens is 6.8-7.5×10. -6 mm / (mm·℃).

7. The ultra-short back focal length microscope tube according to claim 1 or 2, characterized in that: It also includes the lens barrel located outside the optical lens, whose coefficient of thermal expansion is 19.2-20.9×10⁻⁶ at temperatures ranging from -40℃ to 80℃. -6 mm / (mm·℃).

8. The ultra-short back focal length microscope tube according to claim 1 or 2, characterized in that: Its focal length is 200mm, back focal length is 102.35mm, total optical length is 205.99mm, and operating wavelength is 435nm~1500nm.

9. The ultra-short back focal length microscope tube according to claim 1 or 2, characterized in that: Its full field of view is 7.4°, entrance pupil diameter is 8mm, and relative aperture is F#25.

10. The ultra-short back focal length microscope tube according to claim 1 or 2, characterized in that: The inner focal plane does not shift within the temperature range of -40℃ to 80℃.

Images