Ultra-compact lens system for fluorescence imaging

Abstract

The microlens system for fluorescence imaging includes a first lens, a second lens, and a third lens. The first lens has a meniscus shape including a first surface and a second surface facing each other, the first surface being concave, and the first surface and the second surface being aspheric. The second lens includes a third surface and a fourth surface adjacent to the first lens and facing each other, the third surface and the fourth surface being convex and aspheric. The third lens includes a fifth surface and a sixth surface adjacent to the second lens and facing each other, the fifth surface and the sixth surface being concave and aspheric.

Description

[Technical field]

[0001] The present invention relates to an ultra-compact lens system, and more particularly to an ultra-compact lens system for fluorescence imaging that can be applied to a fluorescent molecular imaging endoscope for precise cancer diagnosis based on fluorescence images, and further that can be used in disposable endoscopes and optical imaging diagnostic equipment, etc. [Background technology]

[0002] Recently, particularly due to the increase in gastrointestinal cancers, there has been an increasing trend in the development of endoscopic techniques that enable precise diagnosis of gastrointestinal diseases.

[0003] Meanwhile, conventional general endoscopes rely only on morphological observation of tissues, and therefore, when a precise diagnosis is required, a tissue examination must be performed. However, such a tissue examination requires biopsy of tissues in the suspected area as well as in the surrounding area, which may result in unnecessary damage and bleeding.

[0004] In order to solve these problems with conventional endoscopes, various optical access technologies have been developed recently that can directly diagnose lesions in tissues during endoscopic observation. A representative example is a system that enables such optical diagnosis by combining a miniature camera module with an endoscope, as disclosed in Korean Patent Registration No. 10-1889914.

[0005] However, in the case of an endoscope device to which such an optical module is combined, the performance of the optical lens is the most important factor, since the ability to diagnose lesions depends on the performance of the optical lens.

[0006] In particular, to improve the performance of such optical lenses, it is necessary to properly adjust the F-number and focal length of the optical system and to design the lens with sufficient consideration of resolution. Furthermore, the coating method of the optical lens, the selection of optical filters, and the assembly method must be optimally selected.

[0007] However, up until now, no technology has been developed for the design of such optimized optical lenses.

[0008] Prior art documents on this subject include Korean Patent No. 10-1889914. Summary of the Invention Problem to be solved

[0009] The present invention has been made with this in mind, and an object of the present invention is to provide an ultra-compact lens system for fluorescence imaging that can minimize light loss, provide a low-cost endoscope system, and perform precise cancer diagnosis based on fluorescence images with high resolution. [Means for solving the problem]

[0010] A lens system according to an embodiment for achieving the object of the present invention includes a first lens, a second lens, and a third lens. The first lens has a meniscus shape including a first surface and a second surface facing each other, the first surface being concave, and the first surface and the second surface being aspheric. The second lens includes a third surface and a fourth surface adjacent to the first lens and facing each other, the third surface and the fourth surface being convex and aspheric. The third lens includes a fifth surface and a sixth surface adjacent to the second lens and facing each other, the fifth surface and the sixth surface being concave and aspheric.

[0011] The first lens has a negative refractive power, the second lens has a positive refractive power, and the third lens has a negative refractive power.

[0012] The lens further includes a seventh surface and an eighth surface adjacent to the third lens and facing each other. Glass Department and a diaphragm having a ninth surface between the first lens and the second lens.

[0013] from the first surface of the first lens Glass DepartmentLet the distance to the image plane located outside be TTL and the focal length of the lens system be F.

[0014]

number

[0015] Meet the following.

[0016] If the radius of curvature of the first surface of the first lens is R1 and the radius of curvature of the second surface is R2, then

[0017]

number

[0018] Meet the following.

[0019] If the focal length of the second lens is f2 and the focal length of the lens system is F, then

[0020]

number

[0021] Meet the following.

[0022] If the Abbe number of the first lens is Vd1 and the Abbe number of the third lens is Vd3, then

[0023]

number

[0024] Meet the following.

[0025] If the focal length of the second lens is f2 and the focal length of the third lens is f3, then

[0026]

number

[0027] Meet the following.

[0028] The aspheric surface is defined by the following formula 6:

[0029]

number

[0030] where z is the distance from the vertex of the lens system along the optical axis, h is the distance perpendicular to the optical axis, c is the radius of curvature at the vertex, k is the conic constant, A is a fourth order aspheric coefficient, B is a sixth order aspheric coefficient, C is an eighth order aspheric coefficient, and D is a tenth order aspheric coefficient.

[0031] At least one of the first through sixth surfaces is coated to pass only a specific range of light source wavelengths, and the tangent angle of the coated surface is within ±5°. Effect of the Invention

[0032] According to the present invention, an ultra-compact lens system for fluorescence imaging is configured so that three lenses are arranged in a row, and the shape, structure, and design of each lens are designed as described above, so that at least one surface has a refractive surface that can be coated with a bandpass filter, and coating can be applied depending on the characteristics of the contrast agent used, making it possible to configure a compact optical system and reduce the manufacturing costs of the optical system.

[0033] In addition, for refractive surfaces that can be coated, multi-coating is possible in accordance with the characteristics of not just one contrast agent but two or more contrast agents, expanding the range of use for obtaining fluorescent images.

[0034] In other words, at least one of the refractive surfaces is coated so that only wavelengths of a specific range of light sources can pass through. In this case, by maintaining the tangent angle of the coated surface within ±5°, it is possible to ensure a certain level of transmittance characteristics for each wavelength of incident light.

[0035] In particular, by using three lenses, it is possible to obtain a wide-angle image with a field angle of more than 100°, thereby obtaining a fluorescent image of a relatively wide area inside the living body. Despite being an optical system including an aspheric surface, the inflection point is minimized and the lens shape is designed for ease of production, thereby reducing manufacturing costs. It can be effectively applied not only to fluorescent molecular imaging endoscopes, but also to disposable endoscopes and optical imaging diagnostic devices. [Brief description of the drawings]

[0036] [Figure 1] FIG. 1 is a schematic diagram showing an ultracompact lens system for fluorescence imaging according to one embodiment of the present invention.

[0037] [Diagram 2] FIG. 2 is a graph showing the longitudinal spherical aberration, astigmatism, and distortion of the lens system in FIG.

[0038] [Diagram 3] FIG. 3 is a schematic diagram illustrating a microlens system for fluorescence imaging according to another embodiment of the present invention.

[0039] [Figure 4] FIG. 4 is a schematic diagram showing longitudinal spherical aberration, astigmatism, and distortion of the lens system in FIG.

[0040] [Diagram 5] FIG. 5 is a graph showing the results of a coating simulation in the emission wavelength region of a fluorescein isothiocyanate (FITC) contrast agent for a refractive surface having a tangent angle not exceeding ±5° in the lens system of FIG. 1 or FIG.

[0041] [Figure 6] FIG. 6 is a graph showing the results of a coating simulation in the emission wavelength range of an ICG (indocyanine green) contrast agent for a refractive surface having a tangent angle not exceeding ±5° in the lens system of FIG. 1 or FIG. [Explanation of symbols]

[0042] <Explanation of symbols>

[0043] 1, 2: Lens system 10, 11: First lens

[0044] 20, 21: Second lens 30, 31: Third lens

[0045] 40, 41: Glass Department 50, 51: Aperture

[0046] 60, 61: Image plane DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0047] Specific details for carrying out the invention The present invention can be modified in various ways and can have various forms, and the embodiments will be described in detail in the present specification. However, this is not intended to limit the present invention to the specific disclosed form, and it should be understood that the present invention includes all modifications, equivalents, and alternatives within the spirit and technical scope of the present invention. In describing each drawing, like reference numerals are used to refer to like elements. Terms such as first and second are used to describe various elements, but the elements should not be limited to the terms.

[0048] The above terms are used only for the purpose of distinguishing one component from another. The terms used in this application are merely used to describe a particular embodiment and are not intended to limit the present invention. The singular expression includes the plural expression unless otherwise clearly intended to be different in the context.

[0049] In this application, terms such as "comprising" or "consisting" are intended to specify the presence of any features, numbers, steps, operations, components, parts, or combinations thereof set forth in the specification, but are to be understood as not precluding the presence or additional possibility of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0050] Unless otherwise defined, all terms used herein, including technical and scientific terms, have the same meaning as commonly understood by a person of ordinary skill in the art to which this invention pertains. Terms as defined in commonly used dictionaries should be interpreted as having a meaning consistent with the meaning they have in the context of the relevant art, and should not be interpreted as having an ideal or overly formal meaning unless expressly defined in this application.

[0051] Hereinafter, preferred embodiments of the present invention will be described in more detail with reference to the accompanying drawings.

[0052] Fig. 1 is a schematic diagram of an ultracompact lens system for fluorescence imaging according to one embodiment of the present invention, and Fig. 2 is a graph showing the longitudinal spherical aberration, astigmatism, and distortion of the lens system of Fig. 1.

[0053] As shown in FIG. 1, the ultra-compact lens system 1 for fluorescence imaging (hereinafter referred to as the lens system) according to this embodiment includes a first lens 10, a second lens 20, a third lens 30, Glass Department 40 and aperture 50.

[0054] In this case, the first lens 10 is disposed adjacent to the object 5 to be photographed, so that the first lens 10, the aperture 50, the second lens 20, the third lens 30, and the Glass Department 40 in order, Glass Department Outside of 40, an image plane 60 is disposed.

[0055] In this case, the image surface 60 is Glass Department The image plane 60 is defined as the outer surface of another structure disposed adjacent to the lens system 1 or the outer surface of the lens system 1, and further, the image plane 60 corresponds to an image sensor such as a CCD or CMOS.

[0056] Also, while FIG. 1 illustrates the lenses being arranged from left to right, this is merely an exemplary arrangement, and it is self-evident that the lenses can be arranged from bottom to top, and that when arranged in a line from the object 5 to be photographed, they can be arranged in various directions.

[0057] More specifically, the first lens 10 is formed to a predetermined thickness, and includes a first surface (S1) and a second surface (S2) facing each other.

[0058] The first surface (S1) is located in a direction toward the object 5, and the second surface (S2) is located in the opposite direction to the first surface (S1).

[0059] In this case, the first surface (S1) and the second surface (S2) are aspheric surfaces, the first surface (S1) is formed concave, and the second surface (S2) is formed convex.

[0060] That is, the first surface (S1) is formed concavely toward the object 5, and the second surface (S2) is formed convexly toward the aperture 50 described later.

[0061] Thus, the first lens 10 has, overall, a meniscus shape.

[0062] Moreover, the first lens 10 has a negative refractive power.

[0063] The diaphragm 50 has a predetermined diaphragm surface (S9), and is disposed between the first lens 10 and the second lens 20.

[0064] The second lens 20 is disposed adjacent to the first lens 10 with the aperture 50 in between, so that the first lens 10 is located between the object 5 and the aperture 50.

[0065] The second lens 20 is formed to a predetermined thickness, and includes a third surface (S3) and a fourth surface (S4) facing each other.

[0066] The third surface (S3) is located in a direction toward the first lens 10, and the fourth surface (S4) is located in the opposite direction to the third surface (S3).

[0067] In this case, the third surface (S3) and the fourth surface (S4) are aspherical, that is, they do not correspond to a part of a sphere, and are all formed to be convex.

[0068] That is, the third surface (S3) is formed to protrude toward the diaphragm 50, and the fourth surface (S4) is formed to be convex toward the outside, that is, toward the third lens 30 described later.

[0069] The second lens 20 has a positive refractive power.

[0070] On the other hand, the third lens 30 is disposed adjacent to the second lens 20 , so that the second lens 20 is located between the aperture 50 and the third lens 30 .

[0071] The third lens 30 is formed to a predetermined thickness, and includes a fifth surface (S5) and a sixth surface (S6) facing each other.

[0072] The fifth surface (S5) is located in a direction toward the second lens 20, and the sixth surface (S6) is located in the opposite direction to the fifth surface (S5).

[0073] In this case, the fifth surface (S5) and the sixth surface (S6) are also aspheric and formed concavely.

[0074] That is, the fifth surface (S5) is formed concavely toward the second lens 20, and the sixth surface (S6) faces the outside, i.e., the Glass Department It is formed concavely toward 40.

[0075] The third lens 30 has a negative refractive power.

[0076] The above Glass Department 40 is disposed between the third lens 30 and the image plane 60, and includes a seventh surface (S7) and an eighth surface (S8) facing each other.

[0077] In this case, the cross-sectional shapes of the seventh surface (S7) and the eighth surface (S8) do not have a concave or convex shape as shown in FIG. 1, and the two surfaces facing each other extend parallel to each other.

[0078] Meanwhile, the lens system 1 in this embodiment satisfies the following formulas 1 to 6, and the content and meaning of each formula will be explained below.

[0079] First, the lens system 1 receives the first lens 10 from the first surface (S1) of the first lens 10. Glass Department If the distance to an image plane 60 positioned outside 40 is TTL and the focal length of the entire lens system 1 is F, the following formula (1) is satisfied.

[0080]

number

[0081] Equation 1 defines the overall length of the lens system 1. If the lower limit of Equation 1 is less than 3.5, the overall length becomes shorter and the optical system can be made smaller, but the tolerance control and manufacturability of the lens are significantly reduced.

[0082] In addition, the angle of the chief ray incident on the image surface 60 increases. When the angle of the chief ray increases in this manner, it becomes difficult to correct for the peripheral illumination ratio, and the brightness of the peripheral areas of the image surface 60 decreases compared to the center.

[0083] On the other hand, if the upper limit of 5.0 in the formula 1 is exceeded, the overall length of the lens system 1 becomes long, which causes a problem that it becomes difficult to configure an ultra-compact optical system.

[0084] For this reason, it is necessary to satisfy the condition of the above formula 1.

[0085] Furthermore, the lens system 1 satisfies the following formula 2, where R1 is the radius of curvature of the first surface (S1) of the first lens 10, and R2 is the radius of curvature of the second surface (S2).

[0086]

number

[0087] The formula 2 defines the shape of the first lens 10. If the lower limit of the formula 2 is less than 0.45, the first lens 10 has a reduced refractive power, making it difficult to correct aberrations, and the length of the entire optical system increases.

[0088] On the other hand, if the upper limit value of 0.6 of the formula 2 is exceeded, the first lens 10 is advantageous in ensuring a wide angle of view, but the curvature of the first surface (S1) increases, significantly reducing manufacturability.

[0089] For this reason, it is necessary to satisfy the condition of the above formula 2.

[0090] Furthermore, the lens system 1 satisfies the following formula 3, where the focal length of the second lens 20 is f2 and the focal length of the lens system 1 is F.

[0091]

number

[0092] The formula 3 defines the focal length and shape of the second lens 20. If the formula 3 is less than the lower limit of 0.8, the refractive power of the second lens 20 increases, which is advantageous for miniaturization, but the spherical aberration and coma aberration increase due to the increased curvature. In addition, there is a problem that the manufacturing and tolerance management of the second lens 20 becomes difficult.

[0093] On the other hand, if the upper limit of 1.0 of the formula 3 is exceeded, the refractive power decreases due to an increase in the focal length of the second lens 20, which is disadvantageous for miniaturization of the optical system, and there is a limit to the correction of various aberrations, resulting in a decrease in optical performance.

[0094] For this reason, it is necessary to satisfy the condition of the above formula 3.

[0095] Furthermore, the lens system 1 satisfies the following formula 4, where the Abbe number of the first lens 10 is Vd1 and the Abbe number of the third lens 30 is Vd3.

[0096]

number

[0097] The formula 4 is for correcting aberration and improving performance of the optical system, and the first lens 10 is made of a glass material having the same Abbe number as the second lens 20. Therefore, by maintaining the Abbe numbers of the first lens 10 and the second lens 20 larger than the Abbe number of the third lens 30, it is possible to reduce chromatic aberration, improve resolution, and realize miniaturization.

[0098] For this reason, it is necessary to satisfy the condition of the above formula 4.

[0099] Furthermore, the lens system 1 satisfies the following formula 5, where the focal length of the second lens 20 is f2 and the focal length of the third lens 30 is f3.

[0100]

number

[0101] The above formula 5 satisfies the focal lengths of the second lens 20 and the third lens 30. If the lower limit of the formula 5 is less than 0.4, it becomes difficult to correct the field curvature, and the overall performance of the optical system deteriorates.

[0102] Furthermore, if the upper limit of 0.65 of the formula 5 is exceeded, the angle of the chief ray incident on the image surface 60 increases, and the peripheral illumination ratio decreases. Furthermore, although the field curvature and performance correction are advantageous, the manufacturability of the second lens 20 decreases, and tolerance control of the second lens 20 and the third lens 30 becomes difficult.

[0103] For this reason, it is necessary to satisfy the condition of the above formula 5.

[0104] Furthermore, as mentioned above, the first surface (S1) and the second surface (S2) of the first lens 10 included in the lens system 1 are aspheric, the third surface (S3) and the fourth surface (S4) of the second lens 20 are also aspheric, and the fifth surface (S5) and the sixth surface (S6) of the third lens 30 are also aspheric.

[0105] In this case, the aspheric surface is defined by the following formula 6.

[0106]

number

[0107] Here, z is the distance from the vertex of the lens system 1 in the optical axis direction, h is the distance in a direction perpendicular to the optical axis, c is the radius of curvature at the vertex, k is the conic constant, A is a fourth-order aspheric coefficient, B is a sixth-order aspheric coefficient, C is an eighth-order aspheric coefficient, and D is a tenth-order aspheric coefficient.

[0108] Meanwhile, as an example of an actual design of the lens system 1 of FIG. 1, design values ​​of a lens system satisfying the conditional expressions 1 to 6 are as shown in Tables 1 and 2 below, and the longitudinal spherical aberration, astigmatism, and distortion of the lens system 1 designed according to Tables 1 and 2 below are as shown in FIG. 2.

[0109] In this case, in the lens system 1 designed exemplarily according to Tables 1 and 2 below, the F-number (aperture value) is 4, the angle of view (FOV) is 100°, the effective focal length (EFL) of the entire lens system 1 is 0.615 mm, the focal length (f1) of the first lens 10 is -1.832 mm, the focal length (f2) of the second lens 20 is 0.571 mm, the focal length (f3) of the third lens 30 is -1.241 mm, and the distance (TTL) from the first surface (S1) of the first lens 10 to the image plane 60 is 2.553 mm.

[0110] On the other hand, the longitudinal spherical aberration and astigmatism in FIG. 2 are shown for light having wavelengths of 656.27 nm, 546.07 nm, and 486.13 nm, respectively, and the astigmatism and distortion are shown for light having a wavelength of 546.07 nm.

[0111] As described above, the lens system 1 satisfying the conditional expressions 1 to 6 can be designed as shown in Tables 1 and 2 below, thereby realizing an ultra-compact lens system for fluorescence imaging.

[0112] [Table 1]

[0113] [Table 2]

[0114] Fig. 3 is a schematic diagram showing a microlens system for fluorescence imaging according to another embodiment of the present invention, and Fig. 4 is a schematic diagram showing the longitudinal spherical aberration, astigmatism, and distortion of the lens system in Fig. 3.

[0115] The lens system 2 in this embodiment includes a configuration similar to that of the lens system 1 described with reference to FIG. 1, and therefore a duplicated description of the configuration of the lens system 2 will be omitted.

[0116] That is, as shown in FIG. 3, the lens system 2 in this embodiment includes a first lens 11, a second lens 21, a third lens 31, Glass Department 41, the aperture 51, and the image plane 61 correspond to the first lens 10, the second lens 20, the third lens 30, Glass Department 40, aperture 50, and image plane 60 are substantially identical.

[0117] As a result, the lens system 2 also satisfies the conditions explained in Equations 1 to 6 above.

[0118] However, the lens system 2 can be modified and designed in the same manner as in Tables 3 and 4 below, and the lens system 2 designed in this way satisfies the conditional expressions 1 to 6.

[0119] The longitudinal spherical aberration, astigmatism, and distortion of the lens system 2 designed according to the following Tables 3 and 4 are as shown in FIG.

[0120] In this case, in the lens system 2 designed exemplarily according to Tables 3 and 4 below, the F-number (aperture value) is 4, the angle of view (FOV) is 100°, the effective focal length (EFL) of the entire lens system 2 is 0.603 mm, the focal length (f1) of the first lens 11 is -2.007 mm, the focal length (f2) of the second lens 21 is 0.503 mm, the focal length (f3) of the third lens 31 is -0.850 mm, and the distance (TTL) from the first surface (S1) of the first lens 11 to the image plane 61 is 2.503 mm.

[0121] On the other hand, the longitudinal spherical aberration and astigmatism in FIG. 4 are shown for light having wavelengths of 656.27 nm, 546.07 nm, and 486.13 nm, respectively, and the astigmatism and distortion are shown for light having a wavelength of 546.07 nm.

[0122] [Table 3]

[0123] As described above, the lens system 2 satisfying the conditional expressions 1 to 6 can be designed as shown in Tables 3 and 4, thereby realizing an ultra-compact wide-angle lens system for endoscopes.

[0124] [Table 4]

[0125] Furthermore, the actual design values ​​of the lens systems 1 and 2 described with reference to FIGS. 1 and 3 satisfy all of the above formulas 1 and 5 as shown in Table 5 below.

[0126] [Table 5]

[0127] In this case, the lens systems 1 and 2 shown in Tables 1 to 5 below and the design values ​​confirmed by FIGS. 2 and 4 are merely examples, and it is obvious that various designs are possible within the range that satisfies Equations 1 to 6.

[0128] Meanwhile, in the case of the lens systems 1 and 2 according to the present embodiment, the first to eighth surfaces, i.e., the refractive surfaces, of each of the first to third lenses may be coated so that only wavelengths of a light source within a specific range pass through.

[0129] In this case, the refractive surface on which the coating is applied is at least one of the first to eighth surfaces in each of the lens systems 1 and 2. By applying the coating to the refractive surface in this manner, it is possible to allow only a specific range of wavelengths of the light source to pass, i.e., to function as a band pass filter.

[0130] However, when coating the refractive surface in this manner, the tangent angle of the coated surface should be within ±5°. In this case, the tangent angle is defined as the gradient at the contact point depending on the height of the lens surface with respect to a plane perpendicular to the optical axis of the optical system constituted by the lens systems 1 and 2.

[0131] As described above, by applying a coating to the refractive surface so as to satisfy the tangent angle condition, the lens systems 1 and 2 allow only light of a specific range of wavelengths from a light source to pass therethrough.

[0132] FIG. 5 is a graph showing the results of a coating simulation in the emission wavelength region of a fluorescein isothiocyanate (FITC) contrast agent for a refractive surface having a tangent angle not exceeding ±5° in the lens system of FIG. 1 or FIG.

[0133] That is, in the lens systems 1 and 2, the refractive surfaces may be coated to limit the emission wavelength range of a fluorescein isothiocyanate (FITC) contrast agent to a specific range.

[0134] For example, as in FIG. 5, when the lens systems 1 and 2 limit the emission wavelength region range of the FITC contrast agent, the blocking ranges are 400 nm to 490 nm and 570 nm to 700 nm, the central wavelength, i.e., maximum transmittance of the bandpass filter is 530 nm, and the bandwidth, i.e., wavelength range, is determined to be approximately 50 nm.

[0135] FIG. 6 is a graph showing the results of a coating simulation in the emission wavelength range of an ICG (indocyanine green) contrast agent for a refractive surface having a tangent angle not exceeding ±5° in the lens system of FIG. 1 or FIG.

[0136] Similarly, the lens systems 1, 2 may have coatings on their refractive surfaces to limit the emission wavelength range of the ICG (indocyanine green) contrast agent to a particular range.

[0137] For example, as in FIG. 6, when the lens systems 1 and 2 limit the emission wavelength region range of the ICG contrast agent, the blocking ranges are 350 nm to 790 nm, 880 nm to 1050 nm, the central wavelength, i.e., maximum transmittance of the bandpass filter is 832 nm, and the bandwidth, i.e., wavelength range, is confirmed to be approximately 50 nm.

[0138] As described above, the lens systems 1 and 2 can function as bandpass filters that allow only wavelengths in a specific range to pass by applying a coating to the refractive surfaces.

[0139] According to the embodiment of the present invention as described above, the ultra-compact lens system for fluorescence imaging is configured so that three lenses are arranged in a row, and the shape, structure, and design of each lens are designed as described above, and the lens has at least one refractive surface that can be coated with a bandpass filter. Coatings are applied depending on the characteristics of the contrast agent used, making it possible to configure a compact optical system and reduce the manufacturing costs of the optical system.

[0140] In addition, for refractive surfaces that can be coated, multi-coating is possible to match the characteristics of not just one contrast agent but two or more contrast agents, expanding the range of use for obtaining fluorescent images.

[0141] In other words, at least one of the refractive surfaces is coated so that only wavelengths of a specific range of light sources can pass through. In this case, by maintaining the tangent angle of the coated surface within ±5°, it is possible to ensure a certain level of transmittance characteristics for each wavelength of incident light.

[0142] In particular, by using three lenses, it is possible to obtain a wide-angle image with a field angle of more than 100°, thereby obtaining a fluorescent image of a relatively wide area inside the living body. Despite being an optical system including an aspheric surface, it is possible to reduce manufacturing costs by minimizing the inflection point and designing the lens shape for ease of production, and it can be effectively applied not only to fluorescent molecular imaging endoscopes but also to disposable endoscopes and optical imaging diagnostic devices.

[0143] Although the present invention has been described above with reference to preferred embodiments, those skilled in the art will understand that various modifications and variations of the present invention can be made without departing from the spirit and scope of the present invention as set forth in the following claims.

Claims

1. a first lens having a meniscus shape including a first surface and a second surface opposed to each other, the first surface being concave, and the first surface and the second surface being aspheric; a second lens adjacent to the first lens and including a third surface and a fourth surface facing each other, the third surface and the fourth surface being convex and aspherical; a third lens adjacent to the second lens and including a fifth surface and a sixth surface facing each other, the fifth surface and the sixth surface being concave and aspherical; a glass portion adjacent to the third lens and including a seventh surface and an eighth surface opposed to each other; a diaphragm having a ninth surface between the first lens and the second lens; Let TTL be the distance from the first surface of the first lens to an image plane located outside the glass portion, and F be the focal length of the lens system. [0010] Fulfilling If the focal length of the second lens is f2 and the focal length of the lens system is F, then [0030] Fulfilling If the focal length of the third lens is f3, [0050] A lens system characterized by satisfying the above.

2. the first lens has a negative refractive power; the second lens has a positive refractive power; The lens system of claim 1 , wherein the third lens has negative refractive power.

3. If the radius of curvature of the first surface of the first lens is R1 and the radius of curvature of the second surface is R2, then [0025] 2. The lens system according to claim 1, wherein:

4. If the Abbe number of the first lens is Vd1 and the Abbe number of the third lens is Vd3, then [0045] 2. The lens system according to claim 1, wherein:

5. The aspheric surface is defined by the following formula 6: [006] 2. The lens system of claim 1, wherein z is the distance from the vertex of the lens system in the optical axis direction, h is the distance in a direction perpendicular to the optical axis, c is the radius of curvature at the vertex, k is a conic constant, A is a fourth-order aspheric coefficient, B is a sixth-order aspheric coefficient, C is an eighth-order aspheric coefficient, and D is a tenth-order aspheric coefficient.

6. At least one of the first to sixth surfaces is coated so as to pass only a specific range of light source wavelengths; 2. The lens system of claim 1, wherein the tangent angle of the coated surface is less than or equal to ±5 degrees.

Images