A microscope objective for ultra-long working distances

Abstract

The application relates to the technical field of optical elements, in particular to a microscope lens for an ultra-long working distance. The microscope lens comprises a lens barrel, a first lens group, a diaphragm and a second lens group coaxially arranged in the lens barrel; the first lens group is used for collecting and pre-collimating incident light; the diaphragm is used for limiting the incident light angle and light quantity of the incident light entering the second lens group; and the second lens group is used for correcting residual aberration of the light passing through the first lens group and the diaphragm; the first lens group comprises six lenses, which are sequentially arranged from the object side to the image side as lens one, lens two, lens three, lens four, lens five and lens six; the lens two is an asymmetric biconvex positive lens; the lens three to the lens six are all meniscus lenses; the second lens group comprises two lenses, which are sequentially arranged from the object side to the image side as lens seven and lens eight; and the lens seven and the lens eight are both double-concave lenses. The microscope lens provided by the application realizes high-quality imaging of the lens under the premise of realizing ultra-long working distance (600 mm) microscopy.

Description

Technical Field

[0001] This application relates to the field of optical element technology, and more specifically to a microscope head for ultra-long working distances. Background Technology

[0002] For traditional optical systems, higher magnification generally results in a shorter working distance and easier aberration correction. However, for certain specialized applications, such as observing targets in high-temperature or high-concentration dust environments, observing inaccessible high-precision components (e.g., wafers, PCBs), or live-cell imaging in life science research, close-range observation methods are not feasible. Therefore, a microscope objective with high magnification, resolution, and an ultra-long working distance (600 mm) is needed to meet these observation requirements. Summary of the Invention

[0003] The purpose of this application is to provide a microscope lens for ultra-long working distances to solve the performance balance problem of the three core requirements of long working distance, aberration correction and telecentricity.

[0004] To achieve the above objectives, this application provides a microscope head for ultra-long working distances. The microscope head includes a microscope tube and a first lens group, an aperture, and a second lens group coaxially disposed within the microscope tube. The first lens group is used to collect and pre-collimate directly incident light. The aperture is used to limit the incident light angle and light transmission of the second lens group. The second lens group is used to correct residual aberrations of the light rays passing through the first lens group and the aperture. The first lens group includes six lenses, which are lens 1, lens 2, lens 3, lens 4, lens 5, and lens 6 in sequence from the object side to the image side. Among them, lens 1 is a plane lens; lens 2 is an asymmetric biconvex positive lens, with its side with greater curvature facing the object side; lenses 3 to 6 are all meniscus lenses, and their convex surfaces are all facing the object side. The second lens group includes two lenses, which are lens 7 and lens 8 in sequence from the object side to the image side. Lens 7 and lens 8 are both biconcave lenses.

[0005] In the embodiments of this application, the diameters of lenses one through six decrease sequentially.

[0006] In this embodiment of the application, the aperture stop is located on the focal plane of the second lens group.

[0007] In this embodiment of the application, the lens is made of a wear-resistant, high-temperature-resistant, and heat-insulating high-transmittance glass material.

[0008] In the embodiments of this application, lens 2, lens 4, lens 5 and lens 6 are all cemented doublet lenses.

[0009] In this embodiment, the lens seven is a cemented doublet lens, with the side with greater mirror curvature facing the image side.

[0010] In this embodiment of the application, the side with the greater curvature of the two mirror surfaces of the lens eight is positioned facing the object, and the diameter of the lens eight is greater than that of the lens seven.

[0011] In this embodiment of the application, the object-side principal ray incident angle (FOV) of the microscope head satisfies the constraint: 0.2° < FOV < 0.3°.

[0012] In this embodiment of the application, the F-number of the microscope head satisfies the constraint: 8 < F < 10.

[0013] In the embodiments of this application, lens one, lens two, lens three, lens four, lens five, lens six, lens seven and lens eight are all glass spherical lenses.

[0014] The solution provided in this application has at least the following beneficial effects:

[0015] This application utilizes a first lens group to provide powerful positive optical power, effectively converging light emitted from an object at 600mm, achieving ultra-long working distance microscopy. Furthermore, through the design of up to five cemented lenses and multiple meniscus lenses, it powerfully corrects chromatic aberration, spherical aberration, coma, astigmatism, and field curvature, achieving high resolution and a flat image plane, ensuring high-quality imaging. The object-side principal ray incidence angle (FOV) satisfies the constraint: 0.2° < FOV < 0.3°, making the lens a telecentric lens for precise measurements. Finally, due to the separation of optical power between the front and rear groups, it effectively balances the three core but contradictory requirements of long working distance, aberration correction, and telecentricity, achieving performance equilibrium. In addition, all lenses used in the microscope lens of this application can be glass spherical lenses, resulting in low cost and high cost-effectiveness.

[0016] Other features and advantages of the embodiments of this application will be described in detail in the following detailed description section. Attached Figure Description

[0017] The accompanying drawings are provided to further illustrate the embodiments of this application and form part of the specification. They are used together with the following detailed description to explain the embodiments of this application, but do not constitute a limitation on the embodiments of this application. In the drawings:

[0018] Figure 1 The schematic diagram illustrates the structure and distribution of the lenses in a microscope lens used for ultra-long working distances;

[0019] Figure 2 This is the MTF chart of the microscope lens in this embodiment at a working distance of 600mm;

[0020] Figure 3This is a diffuse image of the microscope lens at a working distance of 600mm in this embodiment.

[0021] Figure 4 This is a color difference distribution diagram of the microscope lens in this embodiment at a working distance of 600mm;

[0022] Figure 5 This is a distortion diagram of the microscope head in this embodiment at a working distance of 600mm.

[0023] Explanation of reference numerals in the attached figures

[0024] 1. Lens One; 2. Lens Two; 3. Lens Three; 4. Lens Four; 5. Lens Five; 6. Lens Six; 7. Lens Seven; 8. Lens Eight. Detailed Implementation

[0025] Example 1

[0026] like Figure 1 As shown, this embodiment provides a microscope lens for ultra-long working distances. The microscope lens includes a microscope tube and a first lens group (referring to the lens group near the object side with the aperture stop as the boundary), an aperture stop, and a second lens group (referring to the lens group near the image side with the aperture stop as the boundary) coaxially disposed within the microscope tube. The first lens group is used to collect and pre-collimate the directly incident light (here, it refers to performing preliminary "adjustment" on the incident light so that it meets the desired incident angle before entering the second lens group, for example, the principal ray on the object side is parallel to the optical axis). The aperture stop is used to limit the incident light angle and the amount of light transmitted into the second lens group. The second lens group is used to... The light rays passing through the first lens group and the aperture stop are subjected to residual aberration correction; the first lens group includes six lenses, from the object side to the image side: lens 1, lens 2, lens 3, lens 4, lens 5, and lens 6; among them, lens 1 is a plane lens; lens 2 is an asymmetrical biconvex positive lens, with its side with greater curvature facing the object side; lenses 3 to 6 are all meniscus lenses, and their convex surfaces are all facing the object side; the second lens group includes two lenses, from the object side to the image side: lens 7 and lens 8, both of which are biconcave lenses.

[0027] Specifically, the aforementioned lens 1 is located on the outermost edge of the lens system and is made of a wear-resistant, high-temperature-resistant, and heat-insulating high-transmittance glass material (such as high borosilicate glass, quartz glass, etc.). It can isolate the internal precision lenses and prevent damage from dust, moisture, or contact. It is placed at the front end and can play a good protective role for other lenses inside the lens system, ensuring that subsequent lens groups work in a controlled environment and effectively providing the entire lens system with environmental adaptability.

[0028] The aforementioned lens 2 is a cemented doublet. Since the working distance of a microscope objective increases with its diameter, the lens in this application has a diameter of 74mm (including the lens barrel). The use of a cemented doublet as the second lens can preliminarily correct chromatic aberration and reduce the angle of incidence of light within the lens, thus reducing the sensitivity of optical elements to eccentricity. By rationally allocating the refractive index and Abbe number, the sensitivity to optical materials is reduced. Specifically, such as... Figure 1 As shown, lens 2 is a cemented lens consisting of a biconvex positive lens and a meniscus negative lens, forming an asymmetrical biconvex positive lens with the side with greater curvature facing the object side. Lens 2 is the first strongly positive lens in the lens system, used to powerfully converge divergent light rays from targets observed at long working distances. Its large curvature facing the object side is for better reception of large-angle light rays. As a cemented lens, it utilizes the dispersive properties of different glass materials (such as crown and flint glass) to effectively correct axial chromatic aberration and spherical aberration; at the same time, the asymmetrical biconvex shape design makes the optical angle of incidence of incident light more gradual and bears a large contribution to spherical aberration correction.

[0029] Lens 3, described above, is a meniscus positive lens with its convex surface facing the object side. Through its specific curvature, lens 3 can pre-adjust the angle at which light enters the subsequent negative lens group (the second lens group), allowing it to enter at a more "gentle" and "friendly" angle. This significantly reduces the correction burden on the subsequent second lens group, allowing them to focus more effectively on their primary tasks (i.e., further field flattening and correction of chromatic aberration). Within the entire first lens group, the distribution of optical power is carefully designed, in the following sequence: strong positive (lens 2) - positive (lens 3) - negative (lens 4) - positive (lens 5) - negative (lens 6). Lens 3 ensures the continuity of positive optical power, preventing abrupt changes in optical power caused by jumping directly from the first positive lens to the negative lens (such abrupt changes would make aberration control difficult and could lead to excessively large angles of incidence on the lens surface). It acts as a smooth transition, maintaining the total positive optical power of the entire first lens group while creating conditions for introducing negative optical power internally for aberration correction. Although Lens 3 is a single lens, by choosing its material (for example, using a glass with a medium refractive index and Abbe number), it can be matched with the glass materials in the front and rear cemented lenses to fine-tune the overall axial chromatic aberration and magnification chromatic aberration correction status, ensuring a smooth transition of the chromatic aberration correction curve.

[0030] Lenses 4, 5, and 6 are all cemented doublets, and all are meniscus-shaped. Using three consecutive meniscus-shaped cemented doublets in the same direction can gradually eliminate field curvature and astigmatism, ensuring clear imaging across the entire image plane, not just the center. Furthermore, by using multiple cemented doublets composed of different dispersive materials, chromatic aberration can be perfectly corrected at multiple wavelengths, achieving apochromatic correction. The microscope lens provided in this application, as an apochromatic microscope objective, has chromatic aberration at only half the diffraction limit. Specifically, lenses 4, 5, and 6 are a negative lens, a positive lens, and a negative lens, respectively, forming a "negative-positive-negative" aberration correction structure. Based on this structure, field curvature, astigmatism, and chromatic aberration can be finely and synergistically corrected without significantly changing the total optical power of the system.

[0031] Lens 4, as the first negative lens in the system, has the core mission of strongly correcting the positive field curvature and positive astigmatism produced by the two preceding positive lenses (the first cemented lens and the meniscus lens). The meniscus negative lens is an effective tool for correcting astigmatism, its shape balancing the tangential and sagittal focal planes. As a cemented lens, it utilizes the dispersion difference between the two types of glass to correct axial chromatic aberration and can provide preliminary correction for magnification chromatic aberration. However, this strong correction (introducing negative optical power) may be "overdone," leading to overcorrection tendencies in a certain intermediate image plane or beam pattern, or introducing new imbalances, such as coma or distortion in a specific field of view or aperture. Lens 4 also reduces the system's total positive optical power. If left unchecked, the system's effective focal length will increase, resulting in a decrease in magnification. Therefore, this solution introduces lens 5 to provide an appropriate amount of positive optical power to partially offset the potential "overcorrection" effect of the preceding negative lens, bringing the field curvature and astigmatism correction curves back to an ideal state. Simultaneously, it promptly compensates for the loss of positive optical power in the system, ensuring that the total optical power and predetermined magnification of the entire first lens group are maintained. Lens 6 is used to achieve the final fine-tuning of the field-flat effect, ensuring that the image plane is completely flat until the edge of the field of view; it is also used to lock the telecentrism, contributing to achieving strict image-side telecentrism and ensuring that light rays are directed at the rear aperture and the second lens group at the optimal angle.

[0032] The diameters of lenses 1 through 6 decrease sequentially, which can gradually shrink and converge the incident light. In this embodiment, the beam diameter can be reduced from 64mm to 6mm, a shrinkage ratio of approximately 11:1. This effectively improves image quality and resolution, achieving excellent image-side telecentrism.

[0033] In this embodiment, the (aperture) stop functions to control light rays: defining the system's F-number (8-10) determines the image-side focal length (NA) and resolution; placing it between the first and second lens groups allows complex aberrations (such as distortion) to be distributed to the front and rear groups for separate correction, facilitating optimization. Positioning the stop on the object-side focal plane ensures the principal ray is parallel to the optical axis on the image side, achieving image-side telecentricity; furthermore, to achieve a double telecentric lens design, in this embodiment, the stop is located where the object-side focal plane coincides with the image-side focal plane.

[0034] In this embodiment, lens 7 is a cemented doublet lens (composed of a positive lens and a negative lens cemented together, forming a biconcave structure). The negative lens can introduce distortion opposite to that of the positive lens, thereby correcting the distortion of the entire system and ensuring that the image is distortion-free. By cooperating with the first lens group in front, it completes field flatness and uses the cemented structure to correct the remaining magnification chromatic aberration.

[0035] In this embodiment, lens 8 is also a biconcave lens, with the side of its two mirror surfaces having a larger curvature facing the object side. As the final element, it performs final fine adjustments to aberrations. Its specific position and optical power help ensure that the incident principal ray exits parallel to the image plane (image-side sensor), reinforcing the image-side telecentric characteristics. Furthermore, since lens 7, located in front of it, is a concave lens, it has a diverging effect on light. Therefore, lens 8 must have a sufficiently large aperture to receive this diverged light beam; otherwise, vignetting (darkening of image edges) or even cutting off light rays from the edge field of view will occur.

[0036] Specifically, the object-side principal ray incident angle (FOV) of the microscope head satisfies the constraint: 0.2° < FOV < 0.3° (approximately parallel to the optical axis), that is, the microscope head is an object-side telecentric lens. Combined with the aforementioned image-side telecentric design, the microscope head provided in this application is actually a double telecentric lens.

[0037] Specifically, the F-number of the microscope lens satisfies the constraint: 8 < F < 10. This means it is a "slow-motion" lens, suitable for the high-resolution application scenarios required in this application.

[0038] All lenses in this embodiment, including lens 1, lens 2, lens 3, lens 4, lens 5, lens 6, lens 7, and lens 8, can be glass spherical lenses, which can effectively reduce the manufacturing cost of the lens.

[0039] Example 2

[0040] For example, the basic parameters of each lens in the ultra-long working distance microscope lens provided in this embodiment are shown in Table 1, where the unit of radius of curvature and air gap is millimeters (mm). Note: All radii of curvature (the larger the radius of curvature, the smaller the curvature), lens center thickness, and air gap are normalized values, and the positive or negative value only indicates the direction, not the magnitude. The value is positive when the lens is bent towards the object side and negative when the lens is bent towards the image side.

[0041] Table 1

[0042] Lens surface serial number radius of curvature Air gap / glass center thickness Refractive index Abbe number S1 -0.594200 0.024000 1.804000 46.574 S2 0.454700 0.136872 1.000000 0.000 (air) S3 -0.755860 0.058200 1.784720 25.720 S4 -0.160860 0.024000 1.804000 46.574 S5 2.518200 0.500000 1.000000 0.000 (air) S6 (aperture stop) INFINITY 0.091553 1.000000 0.000 (air) S7 -0.887600 0.050000 1.834810 42.725 S8 2.135400 0.075200 1.922860 18.895 S9 -1.480000 0.161188 1.000000 0.000 (air) S10 -1.159400 0.070000 1.804000 46.574 S11 3.988000 0.165400 1.592800 68.342 S12 -0.689200 0.050000 1.000000 0.000 (air) S13 -0.594120 0.080000 1.806105 33.286 S14 -2.401200 0.133000 1.497000 81.605 S15 -0.858600 0.020000 1.000000 0.000 (air) S16 -3.792600 0.176400 1.592800 68.342 S17 -0.928000 0.020000 1.000000 0.000 (air) S18 8.698600 0.224200 1.592800 68.342 S19 -1.108900 0.120000 1.806105 33.286 S20 -1.903600 0.040000 1.000000 0.000 (air) S21 INFINITY 0.060000 1.516800 64.198 S22 INFINITY / 1.000000 0.000 (air)

[0043] In Table 1, the lens surface serial numbers S1~S22 and Figure 1 The numbers S1 to S22 correspond to the following: S6 represents the aperture stop; the air gap / glass center thickness value corresponding to S1 indicates the interval between S1 and S2, i.e., the (center) thickness of lens 8; the refractive index corresponding to S1 is the refractive index of the object between S1 and S2, i.e., the refractive index of lens 8; the Abbe number corresponding to S1 is the Abbe number of the object between S1 and S2, i.e., the Abbe number of lens 8. The air gap / glass center thickness value corresponding to S2 indicates the interval between S2 and S3, i.e., the air gap between lens 8 and lens 7; the corresponding refractive index and Abbe number for S2 are the refractive index and Abbe number of air. The explanations of the values ​​corresponding to the other lens surface numbers in the table can be found in the [reference needed]. Figure 1 And so on, without going into further detail here.

[0044] This embodiment also verifies the imaging effect of the microscope head provided above. A standardized test image was imaged while maintaining a working distance of 600mm for the microscope head. Imaging analysis yielded the following results: Figure 2 The MTF chart shown is as follows: Figure 3 The image point diffusion pattern shown is as follows: Figure 4 The color difference distribution diagram shown and as follows Figure 5 The distortion diagram shown.

[0045] Figure 2The MTF plot shown has the horizontal axis representing spatial frequency (Hz / mm) and the vertical axis representing OTF modulus. It visually demonstrates the microscope lens's limiting resolution and contrast characteristics at a working distance of 600mm. Different colored curves represent MTF curves measured at different locations in the image field (sensor plane). The black straight line represents the theoretical upper limit of the performance of an ideal optical system (limited only by physical diffraction) in the meridional (and sagittal) directions (actually there are two lines; due to the ideal state, the black straight line (meridian direction) and the black dashed line (sagittal direction) coincide). The distance from the center of the image plane to the field of view corresponding to the green, red, blue, and yellow curves gradually increases, with the yellow curve (the dashed and solid curves corresponding to the MTF curves measured along the sagittal and meridional directions respectively) located at the edge of the image plane. Figure 2 As can be seen, the microscope lens provided in this embodiment, at a working distance of 600mm, has an MTF value of over 0.9 at all measuring points at low frequency (10 lp / mm) (overall contrast and transparency), and an MTF value of over 0.7 at all measuring points at high frequency (30 lp / mm) (characterizing detail resolution). All color curves fit the black curve, which is close to the ideal state.

[0046] Figure 3 The four image point diffusion patterns shown have units of μm for both the horizontal and vertical axes (with a maximum scale of 20 μm), representing the size of the image point diffusion patterns. Figure 3 (a) shows the image point diffusion pattern measured at the sensor imaging center (center of the image plane). The view shows a compact, uniform, and nearly circular spot, indicating that the imaging effect at the center of the microscope lens is excellent, sharp, and without chromatic aberration. Figure 3 (b) shows the image point blur pattern measured at a distance of 2.118 mm from the center of the sensor imaging (image plane center). The image point blur pattern here has "wings" and a halo, indicating that there is a point of spherical aberration, but the overall spot is small and still within the error range. Figure 3 (c) represents the image point blur pattern measured at a distance of 2.546 mm from the center of the sensor imaging (center of the image plane). The image point blur pattern is larger here, indicating that the problems such as spherical aberration and astigmatism are more serious here. Figure 3(d) shows the image point blur pattern measured at a distance of 2.993 mm from the sensor imaging center (image plane center). Compared to the previous images, the image point blur pattern here occupies a significantly larger area and is more irregular, indicating that spherical aberration and astigmatism are more severe at this location. Although the microscope lens provided in this application inevitably has some spherical aberration and astigmatism at locations other than the sensor imaging center, the diameter of the image point blur patterns in (b), (c), and (d) above does not exceed 20 μm. Therefore, it can be proven that the microscope lens provided in this application still possesses sharp and high-resolution imaging capabilities.

[0047] Figure 4 The chromatic aberration distribution diagram shown can intuitively display the axial chromatic aberration of the microscope lens of this application. Its horizontal axis represents the focal offset (unit: μm), and the vertical axis represents the wavelength (unit: μm). The curve in the diagram is the focal line; each point on this line represents the physical position where light of a corresponding wavelength is most clearly imaged. Figure 4 It can be seen that within the wavelength range of 0.486μm to 0.6μm, the focal line has a relatively low coverage area on the horizontal axis, indicating better control of axial chromatic aberration when facing light within this wavelength range. The wavelength range of 0.486μm to 0.6μm covers cyan, green, and yellow-green light, which is a region that the human eye is very sensitive to, and is also the core band of some important fluorescent dyes and naturally reflected light.

[0048] Figure 5 The distortion diagram of the microscope lens provided in this embodiment at a working distance of 600mm is shown, with the abscissa representing the distortion rate and the ordinate representing the field of view. The distortion rate is calculated using the formula: Distortion rate = [(Actual image height - Ideal image height) / Ideal image height] × 100%. A positive value indicates pincushion distortion (image convex), while a negative value indicates barrel distortion (image concave). Figure 5 It can be seen that its maximum distortion is -0.24%, which is much smaller than the industrial testing lens standard (within ±1.5%), and meets the expected standard.

[0049] The above are merely embodiments of this application and are not intended to limit the scope of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of the claims of this application.

Claims

1. A microscope lens for ultra-long working distances, characterized in that, The microscope head includes a microscope tube and a first mirror group, an aperture, and a second mirror group coaxially disposed within the microscope tube; the first mirror group is used to collect and pre-collimate directly incident light, the aperture is used to limit the incident light angle and light transmission of the second mirror group, and the second mirror group is used to correct residual aberrations of light passing through the first mirror group and the aperture; the first mirror group consists of six lenses, which are arranged from the object side to the image side as lens one (1), lens two (2), lens three (3), lens four (4), lens five (5), and lens six (6); among which lens one (1) ) is a plane lens; lens 2 (2) is an asymmetrical biconvex positive lens, with the side with greater surface curvature facing the object; lenses 3 (3) to 6 (6) are all meniscus lenses, and their convex surfaces are all facing the object; among them, lens 3 (3) is a positive lens, lens 4 is a negative lens, lens 5 (5) is a positive lens, and lens 6 (6) is a negative lens; the second lens group consists of two lenses, which are lens 7 (7) and lens 8 (8) from the object side to the image side. Both lens 7 (7) and lens 8 (8) are biconcave lenses.

2. The microscope lens for ultra-long working distance according to claim 1, characterized in that, The diameters of lenses 1 (1) to 6 (6) decrease sequentially.

3. The microscope lens for ultra-long working distance according to claim 1, characterized in that, The aperture stop is located on the focal plane of the second lens group.

4. The microscope lens for ultra-long working distance according to claim 1, characterized in that, The lens (1) is made of a wear-resistant, high-temperature resistant and heat-insulating high-transmittance glass material.

5. The microscope lens for ultra-long working distance according to claim 1, characterized in that, Lens 2 (2), lens 4 (4), lens 5 (5) and lens 6 (6) are all cemented doublet lenses.

6. The microscope lens for ultra-long working distance according to claim 1, characterized in that, The lens seven (7) is a cemented doublet lens, with the side with greater mirror curvature facing the image side.

7. The microscope lens for ultra-long working distance according to claim 6, characterized in that, The side with the greater curvature of the two mirror surfaces of the lens eight (8) is positioned facing the object side, and the diameter of the lens eight (8) is greater than that of the lens seven (7).

8. The microscope lens for ultra-long working distance according to claim 1, characterized in that, The object-side principal ray incident angle (FOV) of the microscope lens satisfies the constraint: 0.2° < FOV < 0.3°.

9. The microscope lens for ultra-long working distance according to claim 1, characterized in that, The F-number of the microscope lens satisfies the constraint: 8 < F < 10.

10. The microscope lens for ultra-long working distance according to any one of claims 1 to 9, characterized in that, Lens 1 (1), Lens 2 (2), Lens 3 (3), Lens 4 (4), Lens 5 (5), Lens 6 (6), Lens 7 (7) and Lens 8 (8) are all glass spherical lenses.

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