Prime lens

Abstract

The invention discloses a prime lens. The prime lens comprises three lens groups, in the direction of the central axis, the first lens group with positive focal power sequentially comprises two meniscus positive lenses, a pair of meniscus doublet lenses and another pair of doublet lenses, and the second lens group with negative focal power comprises a pair of doublet lenses. And the third lens group with the positive focal power sequentially comprises a set of triplet lens, three pairs of doublet lenses and an aspheric negative lens. During focusing, only the second lens group moves along the central axis. The prime lens adapts to a large aperture, is small in focusing electric power load, and can be used for a full-frame camera.

Description

Technical Field

[0001] The present application belongs to the technical field of photographic lenses, and in particular relates to a fixed-focus lens for a full-frame camera. Background Art

[0002] The electronic photoreceptor of a full-frame camera has a photosensitive area equivalent to that of a 35mm film in a 135 camera, and its pixel unit reaches the micron level, which places high demands on the lens. For existing lenses of this type, if the aperture can be greater than F / 1.4, all lenses are usually moved when focusing. If only one set of lenses is moved to focus, the maximum aperture is usually F / 1.4, such as the SEL85F1.4GM lens of Sony Corporation of Japan.

[0003] The imaging lens disclosed by Sony Corporation of Japan in patent CN08474925A has a small total number of lenses, and only moves the middle group of lenses when focusing, and has an ultra-low dispersion lens. Summary of the invention

[0004] The technical problem to be solved by this application is how to improve the fixed-focus lens to adapt to the full-frame camera.

[0005] The present application discloses a fixed-focus lens.

[0006] The fixed-focus lens can be used for a full-frame camera, and includes a first lens group with positive focal power, a second lens group with negative focal power, and a third lens group with positive focal power in sequence along the central axis direction, and also includes an aperture stop. When the object is in focus from infinity to a close distance, the first lens group, the aperture stop, and the third lens group are fixed relative to the image plane, and the second lens group moves along the central axis to the image plane. The first lens group includes the following lens groups in sequence along the central axis: The first lens is configured as a positive lens, the object side surface is a spherical convex surface, and the image side surface is a spherical concave surface; The second lens is configured as a positive lens, with a spherical convex surface on the object side and a spherical concave surface on the image side, a refractive index of 1.55~1.65, and an Abbe number of 66~71; The third lens is configured as a positive lens, with a spherical convex surface on the object side and a spherical concave surface on the image side, a refractive index of 1.55~1.65, and an Abbe number of 66~71; The fourth lens is configured as a negative lens, the object side surface is a spherical convex surface, the image side surface is a spherical concave surface, and is cemented with the third lens; A fifth lens is configured as a biconvex spherical positive lens with a refractive index of 1.55 to 1.65 and an Abbe number of 66 to 71; and The sixth lens is configured as a double concave spherical negative lens, the image side curvature radius is 500-600 mm, and is cemented with the fifth lens; The second lens group includes the following in sequence along the central axis: A seventh lens is configured as a positive lens, the object side surface is a concave spherical surface, the absolute value of the radius of curvature is greater than 1000 mm, and the image side surface is a convex spherical surface; and an eighth lens configured as a biconcave spherical negative lens and cemented with the seventh lens; The third lens group includes the following lens groups in sequence along the central axis: The ninth lens is configured as a biconvex spherical positive lens, with a curvature radius of 480~580mm on the object side, a refractive index of 1.55~1.65, and an Abbe number of 66~71; The tenth lens is configured as a double concave spherical negative lens and is cemented with the ninth lens; An eleventh lens is configured as a biconvex spherical positive lens and is cemented with the tenth lens; A twelfth lens is configured as a biconvex spherical positive lens; The thirteenth lens is configured as a double concave spherical negative lens and is cemented with the twelfth lens; A fourteenth lens is configured as a biconvex spherical positive lens; A fifteenth lens is configured as a double concave spherical negative lens and is cemented with the fourteenth lens; A sixteenth lens is configured as a biconvex spherical positive lens; A seventeenth lens is configured as a biconcave spherical negative lens and is cemented with the sixteenth lens; and The eighteenth lens is configured as a negative lens, the object side surface is a non-spherical concave surface with a curvature radius of 450~550mm, and the image side surface is a non-spherical convex surface.

[0007] In some embodiments of the present application, the focal length of the fixed-focus lens can be selected to be 80-90 mm. Furthermore, the second lens, the third lens, the fifth lens and the ninth lens are made of the same optical material.

[0008] By implementing the technical solution of this application, the following beneficial effects can be obtained.

[0009] The fixed-focus lens disclosed in the present application includes three lens groups. Along the central axis direction, the first lens group with positive focal power includes two meniscus positive lenses, a pair of meniscus double cemented lenses and another pair of double cemented lenses in sequence, the second lens group with negative focal power includes a pair of double cemented lenses, and the third lens group with positive focal power includes a set of three cemented lenses, three pairs of double cemented lenses and an aspherical negative lens in sequence. When focusing, only the second lens group moves along the central axis. The fixed-focus lens is adapted to a larger aperture, has a small focusing electrical load, and can be used in full-frame cameras. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The following drawings should be used in conjunction with the detailed description.

[0011] Figure 1It is a cross-sectional view of the central axis of the fixed-focus lens in the first embodiment, and the legends represent: IMG-image plane, FIT-filter protector, STO-aperture stop, Z1-central axis, T1-movement range.

[0012] Figure 2a Table 1 shows the data and position relationship of each lens in Example 1.

[0013] Figure 2b The aspheric expressions f1 of the two aspheric surfaces of the first embodiment are listed, as well as Table 2 recording the coefficients of the two aspheric expressions.

[0014] Figure 3 This is a light path diagram of the fixed-focus lens focusing on infinity in the first embodiment.

[0015] Figure 4a and Figure 4b It is a spherical aberration curve diagram and a vertical axis chromatic aberration curve diagram of the fixed focus lens calculated by ZEMAX software in Example 1, and the calculation conditions are: incident light mixing range 430~658nm, incident light pupil radius 34.3090mm, aperture F / 1.25, and infinite focus state.

[0016] Figure 5a and Figure 5b These are two modulation transfer function (MTF) curves of the fixed-focus lens calculated by ZEMAX software in Example 1, and the calculation conditions are as described above.

[0017] Figure 6 and Figure 7 Selected from the official website of Sony's SEL85F1.4GM fixed-focus lens https: / / www.sonystyle.com.cn / products / lenses / sel85f14gm2 / sel85f14gm2_feature.html , Figure 6 is a structural diagram, Figure 7 The method of obtaining the modulation transfer function diagram of is unknown. DETAILED DESCRIPTION

[0018] The embodiments are described below with reference to the accompanying drawings.

[0019] In this specification, unless otherwise specified, one embodiment, some embodiments and other embodiments are used to distinguish different embodiments and do not refer to all embodiments; directions / positions indicated by top, bottom, center, edge, inside, outside, far, near, length, width, vertical, horizontal, up, down, front, back, left, right, etc. are based on the observation angle of the drawings and cannot be understood as a component / device being located at a specific position or facing a specific direction.

[0020] The lens grouping method in this specification is only for the convenience of describing the embodiments. It is understood that other grouping methods can be used during optical design analysis, lens molding and lens assembly.

[0021] Positive lens and positive focal power both refer to the positive focal length of the optical system on the image side, which can make parallel incident light beams converge. Negative lens and negative focal power both refer to the negative focal length of the optical system on the image side, which can make parallel incident light beams diverge. The light-transmitting surface of the lens can be referred to as the "surface". The side of the lens facing the camera's subject is called the "object side", and the side of the lens facing the camera's photosensitive image surface is called the "image side".

[0022] The aperture stop can be referred to as the "stop", and the plane where it is located is numbered together with the light-transmitting surface of the lens.

[0023] Embodiment 1 A fixed-focus lens is disclosed.

[0024] This fixed-focus lens is used for full-frame cameras with autofocus. It has a focal length of 85mm, is compatible with a maximum aperture of F / 1.2~1.3 and an imaging surface of 42~44mm.

[0025] See also Figure 1 , Figure 2a and Figure 2b , Figure 1 is the central axis cross-section of the fixed-focus lens. Figure 1 The lens barrel is not drawn. The central axis Z1 (also called optical axis, principal axis, main optical axis) points from left to right to the image plane IMG, and a filter protector FIT is provided in front of the image plane IMG. Figure 2a and Figure 2b In the figure, the lens data and position relationship of the fixed-focus lens are listed in Table 1, Table 2 and Formula f1.

[0026] exist Figure 2a In Table 1, the object side surface of the first lens L1 is represented as surface S1, and other light-transmitting surfaces (including the plane where the aperture stop STO is located and the cemented surface of the cemented lens) are numbered in ascending order along the central axis Z1 direction. The image side surface of the eighteenth lens L18 is represented as surface S29. "Curvature radius R" represents the paraxial curvature radius value of the vertex of a surface. i and the i+1th surface S i+1 Lenses between: their "thickness" is the central axis thickness, and their "refractive index Nd" and "Abbe number Nd" are d-line measurement values. In two adjacent lenses, the distance between the image side of the front lens and the object side of the rear lens on the central axis Z1 is called the central axis distance between the two.

[0027] The 18 lenses of this fixed-focus lens are all glass lenses, which can be divided into three groups and numbered in ascending order along the central axis. Figure 1 In the lens element (not shown), a first lens group G1, a second lens group G2, an aperture stop STO and a third lens group G3 are arranged in sequence from the object side to the image side along the central axis Z1.

[0028] In the process of focusing (also called focusing, focusing), only the second lens group G2 can be driven by the stepping motor to move forward and backward along the central axis Z1, and the first lens group G1, the aperture stop STO and the third lens group G3 are all fixed relative to the image plane IMG. The central axis spacing between the aperture stop STO and the surface S15 of the third lens group G3 is about 2.5mm, and the central axis spacing between the image plane IMG and the surface S29 of the third lens group G3 is about 20.3mm.

[0029] The first lens group G1 has positive power and is composed of six glass lenses, including two positive meniscus lenses, a pair of meniscus doublets and another pair of doublets. The six glass lenses are the first lens L1, the second lens L2, the third lens L3, the fourth lens L4, the fifth lens L5 and the sixth lens L6, which are arranged in sequence along the central axis Z1. The third lens L3 and the fourth lens L4 are glued together to form a pair of meniscus doublets, and the radius of curvature of the glued surface is positive. In another pair of doublets formed by the fifth lens L5 and the sixth lens L6, the object side surface is a convex spherical surface, the image side surface is a concave spherical surface close to a plane, and the radius of curvature of the glued surface is negative.

[0030] The second lens group G2 has negative power and is composed of two glass lenses. The two glass lenses are the seventh lens L7 and the eighth lens L8 arranged in sequence along the central axis Z1. In a pair of doublets composed of the two glass lenses cemented together, both the object side and the image side are concave spherical surfaces, the object side is close to a plane, and the curvature radius of the cemented surface is a negative value.

[0031] The third lens group G3 has positive power and is composed of ten glass lenses, including a set of three cemented lenses, three pairs of double cemented lenses and an aspherical negative lens. The ten glass lenses are the ninth lens L9, the tenth lens L10, the eleventh lens L11, the twelfth lens L12, the thirteenth lens L13, the fourteenth lens L14, the fifteenth lens L15, the sixteenth lens L16, the seventeenth lens L17 and the eighteenth lens L18 arranged in sequence along the central axis Z1. The tenth lens L10 is a double concave spherical negative lens, which is cemented with the ninth lens L9 and the eleventh lens L11 to form a set of three cemented lenses. The object side surface of the three cemented lenses is a convex spherical surface close to a plane, and the image side surface is a convex spherical surface. The twelfth lens L12 is cemented with the thirteenth lens L13, the fourteenth lens L14 is cemented with the fifteenth objective lens L15, and the sixteenth lens L16 is cemented with the seventeenth lens L17. In the three double cemented lenses, the object side surfaces are all convex spherical surfaces, the image side surfaces are all concave spherical surfaces, and the curvature radii of the cemented surfaces are all negative values.

[0032] All 18 glass lenses are distributed in sequence along the central axis Z1 to form the above three lens groups, which are installed in the lens barrel. The lens barrel is equipped with a stepping motor and a power supply interface.

[0033] Figure 1 The second lens group G2 is at the object boundary of its moving range T1, and the distance between it and the central axis of the aperture stop STO is about 21.5mm. At this time, the fixed-focus lens is in the infinity focus state. For the optical path diagram, please refer to Figure 3 When the fixed-focus lens focuses on a close-up object, the second lens group G2 moves along the central axis toward the image plane IMG without exceeding the image-side boundary of its moving range T1. Because only the two glued lenses are moved, the focusing electric power load of the fixed-focus lens is low, which can reduce the energy consumption of the camera.

[0034] Each glass lens, each pair (set) of cemented lenses and three lens groups of this fixed focus lens can be used with specific focal lengths Figure 2a and Figure 2b The details of each lens are as follows.

[0035] The first lens L1 is configured as a positive lens, with a spherical convex surface on the object side with a curvature radius of +76.011 mm, a spherical concave surface on the image side with a curvature radius of 215.365 mm, a central axis thickness of 10.300 mm, a refractive index of 1.85, and an Abbe number of 23.8.

[0036] The second lens L2 is configured as a positive lens, with a spherical convex surface on the object side with a curvature radius of +61.477 mm, a spherical concave surface on the image side with a curvature radius of +78.556 mm, a central axis thickness of 5.600 mm, a refractive index of 1.59, an Abbe number of 68.3, and a central axis spacing of 0.150 mm from the first lens L1.

[0037] The third lens L3 is configured as a positive lens, with a spherical convex surface on the object side with a curvature radius of +47.222mm, a spherical concave surface on the image side with a curvature radius of +82.800mm, a central axis thickness of 8.200mm, a refractive index of 1.59, an Abbe number of 68.3, and a central axis spacing of 0.150mm from the second lens L2.

[0038] The fourth lens L4 is configured as a negative lens, with a spherical convex surface on the object side with a curvature radius of +82.800 mm, a spherical concave surface on the image side with a curvature radius of +35.941 mm, a central axis thickness of 1.500 mm, a refractive index of 1.85, and an Abbe number of 25.2, and is cemented with the third lens L3.

[0039] The fifth lens L5 is configured as a biconvex spherical positive lens, with an object side curvature radius of +53.336 mm, an image side curvature radius of -174.338 mm, a central axis thickness of 9.50 mm, a refractive index of 1.59, an Abbe number of 68.3, and a central axis distance of 3.946 mm from the fourth lens L4.

[0040] The sixth lens L6 is configured as a biconcave spherical negative lens, with an object side curvature radius of -174.338 mm, an image side curvature radius of +568.332 mm, a central axis thickness of 1.500 mm, a refractive index of 2.00, and an Abbe number of 25.5, and is cemented with the fifth lens L5.

[0041] The seventh lens L7 is configured as a positive lens, with a concave spherical surface on the object side with a curvature radius of -1204.786 mm, a convex spherical surface on the image side with a curvature radius of -163.974 mm, a central axis thickness of 3.400 mm, a refractive index of 1.92, an Abbe number of 20.9, and a central axis spacing of 2.138 mm with the sixth lens L6 when focusing at infinity.

[0042] The eighth lens L8 is configured as a double concave spherical negative lens, with a curvature radius of -163.974mm on the object side, a curvature radius of +46.971mm on the image side, a central axis thickness of 1.00mm, a refractive index of 1.70, an Abbe number of 55.5, and is cemented with the seventh lens L7. When focusing at infinity, the central axis spacing between it and the aperture stop STO is 21.473mm.

[0043] The ninth lens L9 is configured as a biconvex spherical positive lens, with a curvature radius of +533.957 mm on the object side, a curvature radius of -35.626 mm on the image side, a central axis thickness of 7.500 mm, a refractive index of 1.59, and an Abbe number of 68.3; the central axis spacing with the aperture stop STO is 2.489 mm.

[0044] The tenth lens L10 is configured as a double concave spherical negative lens, with a curvature radius of -35.626 mm on the object side, a curvature radius of +35.626 mm on the image side, a central axis thickness of 2.000 mm, a refractive index of 1.77, and an Abbe number of 29.7, and is cemented with the ninth lens L9.

[0045] The eleventh lens L11 is configured as a biconvex spherical positive lens, with an object side curvature radius of +35.626 mm, an image side curvature radius of -135.604 mm, a central axis thickness of 8.600 mm, a refractive index of 1.73, and an Abbe number of 54.7, and is cemented with the tenth lens L10.

[0046] The twelfth lens L12 is configured as a biconvex spherical positive lens, with an object side curvature radius of +46.752 mm, an image side curvature radius of -181.209 mm, a central axis thickness of 6.500 mm, a refractive index of 1.73, an Abbe number of 54.7, and a central axis spacing of 0.150 mm from the eleventh lens L11.

[0047] The thirteenth lens L13 is configured as a double concave spherical negative lens, with an object side curvature radius of -181.209 mm, an image side curvature radius of +50.080 mm, a central axis thickness of 1.500 mm, a refractive index of 1.77, and an Abbe number of 29.7, and is cemented with the twelfth lens L12.

[0048] The fourteenth lens L14 is configured as a biconvex spherical positive lens, with an object side curvature radius of +62.431 mm, an image side curvature radius of -71.562 mm, a central axis thickness of 6.700 mm, a refractive index of 2.00, an Abbe number of 29.1, and a central axis spacing of 0.893 mm from the thirteenth lens L11.

[0049] The fifteenth lens L15 is configured as a double concave spherical negative lens, with an object side curvature radius of -71.562 mm, an image side curvature radius of +46.084 mm, a central axis thickness of 1.500 mm, a refractive index of 1.62, and an Abbe number of 36.3, and is cemented with the fourteenth lens L14.

[0050] The sixteenth lens L16 is configured as a biconvex spherical positive lens, with an object side curvature radius of +56.199 mm, an image side curvature radius of -97.979 mm, a central axis thickness of 6.400 mm, a refractive index of 2.00, an Abbe number of 25.5, and a central axis spacing of 0.903 mm from the fifteenth lens L15.

[0051] The seventeenth lens L17 is configured as a double concave spherical negative lens, with an object side curvature radius of -97.979 mm, an image side curvature radius of +43.506 mm, a central axis thickness of 4.000 mm, a refractive index of 1.49, and an Abbe number of 70.4, and is cemented with the sixteenth lens L16.

[0052] The eighteenth lens L18 is configured as a negative lens, with an object side surface being a non-spherical concave surface with a curvature radius of -119.605 mm, an image side surface being a non-spherical convex surface with a curvature radius of -500.00 mm, a central axis thickness of 2.500 mm, a refractive index of 1.81, an Abbe number of 40.7, a central axis spacing between the lens L17 and the image plane IMG of 5.208 mm, and a central axis spacing between the lens L18 and the image plane IMG of approximately 20.3 mm.

[0053] The second lens L2, the third lens L3, the fifth lens L5 and the ninth lens L9 of the fixed-focus lens have consistent refractive index and Abbe number and are made of the same brand of optical glass.

[0054] Figure 2a As shown in Table 1, the specific shapes of the two aspheric surfaces S28 and S29 are Figure 2bThe aspheric expression f1 in the figure and the coefficients in Table 2 are used to characterize the aspheric expression f1. In the aspheric expression f1, Y is the radial coordinate, that is, the distance from the central axis in the direction perpendicular to the central axis; Z(Y) is the axial coordinate, that is, the distance from the vertex of the lens surface in the direction parallel to the central axis; R is the paraxial curvature radius at the vertex of the lens surface; K is the cone constant; Ai is the i-th order aspheric coefficient.

[0055] For the spherical aberration curve of this fixed-focus lens in the vertical axis direction (i.e. radial, Y-axis direction) calculated under the conditions of incident light mixing range 430~658nm, incident light pupil radius 34.309mm, aperture F / 1.25, and infinite focus state, please refer to Figure 5a , please refer to the calculated vertical axis color difference curve Figure 5b . Figure 5a The spherical aberration of all curves is in the range of -0.03~0.03mm. Figure 5b The color difference of all curves is in the range of -2.5~5 microns.

[0056] See also Figure 5a and Figure 5b The modulation transfer function (MTF) curve of the fixed focal length lens calculated under the above conditions is shown in the figure. Figure 5a It can be seen that the MTF values ​​of each curve decreases basically evenly in the frequency range of 0~30lp / mm. The upper curves (curve a, curve b, ... and curve k) are distributed in a narrow vertical coordinate range, and only the 21mm-sagittal curve (curve p) eventually drops below 0.4. Figure 5b and Figure 7 It can be seen that the image quality of this fixed-focus lens at an aperture of F / 1.25 is close to the maximum aperture F / 1.4 of the SEL85F1.4GM fixed-focus lens of Sony Corporation of Japan. Therefore, this fixed-focus lens can be used for full-frame cameras, and the maximum aperture it is adapted to is F / 1.2~1.3.

[0057] In the fixed-focus lens, the first lens group includes two positive meniscus lenses, a pair of meniscus doublet lenses and another pair of doublet lenses in sequence, the second lens group is a pair of doublet lenses, and the third lens group includes a set of triplet lenses, three pairs of doublet lenses and an aspherical negative lens in sequence. When focusing, only the second lens group moves along the central axis. The fixed-focus lens has good resolution and low optical distortion under the condition of large light flux, that is, aperture F / 1.2~1.3, which can improve the lens vignetting problem of large aperture lenses, and has a compact structure and a small focusing electric load.

[0058] The fixed-focus lens is equipped with seven pairs (sets) of cemented lenses. The dispersion coefficients of the positive and negative lenses are greatly different, which can correct axial chromatic aberration, spherical aberration and distortion aberration, and also reduce the tolerance sensitivity of imaging quality, making it easier to manufacture and assemble. By adding cemented lenses, the axial length, the number of aspherical surfaces and the number of ultra-low dispersion lenses can be controlled.

[0059] The fixed-focus lens is a replaceable component of a full-frame camera. For other aspects of its structure and function, please refer to paragraphs 0110 to 0122 on pages 10 to 11 of the specification of patent CN10847825A, or refer to commercially available fixed-focus lenses for cameras.

[0060] In other embodiments, the above-mentioned lens may be made of other types of lens materials, the stepper motor may be replaced by a voice coil motor or an ultrasonic motor, and the total focal length of the fixed-focus lens may be any value within the range of 80 to 90 mm. Based on the lens data of the first embodiment, the surface shape, central axis thickness and central axis spacing of each lens may be adaptively adjusted to achieve clear imaging and other technical requirements of the camera. Specifically: The first lens L1 has a refractive index of 1.80 to 1.90 and an Abbe number of 21 to 26; The second lens L2, the third lens L3, the fifth lens L5 and the ninth lens L9 have refractive indices of 1.55 to 1.65 and Abbe numbers of 66 to 71, respectively, and may be made of the same optical material; The fourth lens L4 has a refractive index of 1.80 to 1.90 and an Abbe number of 22.5 to 27.5; The sixth lens L6 has an image side curvature radius of 500 to 600 mm, a refractive index of 1.95 to 20.5, and an Abbe number of 23 to 28; The seventh lens L7 has an object side curvature radius of 480~580mm, a refractive index of 1.87~1.97, and an Abbe number of 18~23; The eighth lens L8 has a refractive index of 1.65 to 1.75 and an Abbe number of 53 to 58; The tenth lens L10 and the thirteenth lens L13 have a refractive index of 1.72 to 1.82 and an Abbe number of 27 to 32, and may be made of the same optical material; The eleventh lens L11 and the twelfth lens L12 have refractive indices of 1.65 to 1.75 and Abbe numbers of 50 to 60, respectively, and may be made of the same optical material; A fourteenth lens L14 has a refractive index of 1.95 to 2.05 and an Abbe number of 26.5 to 31.5; The fifteenth lens L15 has a refractive index of 1.57 to 1.67 and an Abbe number of 33.5 to 38.5; The sixteenth lens L16 has a refractive index of 1.95 to 2.05 and an Abbe number of 23 to 28; The seventeenth lens L17 has a refractive index of 1.45 to 1.55 and an Abbe number of 68 to 73; The eighteenth lens L18 has a refractive index of 1.75 to 1.85 and an Abbe number of 38 to 43; In addition, the image side surface of the sixth lens L6 has a curvature radius of 500-600 mm, the object side surface of the seventh lens L7 has a curvature radius greater than 1000 mm, the object side surface of the ninth lens L9 has a curvature radius of 480-580 mm, and the object side surface of the eighteenth lens L18 has a curvature radius of 450-550 mm. That is, these four lenses each have one side (S in Table 1) 10 , S 11 , S 15 and S 29 ) is approximately flat relative to the lens itself.

[0061] All the above embodiments, application examples and technical analysis are intended to introduce the technical concept and features of the present application so that those skilled in the art can implement the technical solution of the present application, and do not constitute any limitation on the protection scope of the present application. Simple modifications and equivalent transformations of the above embodiments are within the protection scope of the claims of the present application.

Claims

1. A fixed-focus lens, which can be used for a full-frame camera, which includes a first lens group with positive focal power, a second lens group with negative focal power, and a third lens group with positive focal power in sequence along the central axis direction, and further includes an aperture stop. When the object is in focus from infinity to close distance, the first lens group, the aperture stop, and the third lens group are fixed relative to the image plane, and the second lens group moves along the central axis toward the image plane; It is characterized in that The first lens group includes, in sequence along the central axis direction: The first lens is configured as a positive lens, the object side surface is a spherical convex surface, and the image side surface is a spherical concave surface; The second lens is configured as a positive lens, with a spherical convex surface on the object side and a spherical concave surface on the image side, a refractive index of 1.55~1.65, and an Abbe number of 66~71; The third lens is configured as a positive lens, with a spherical convex surface on the object side and a spherical concave surface on the image side, a refractive index of 1.55~1.65, and an Abbe number of 66~71; The fourth lens is configured as a negative lens, the object side surface is a spherical convex surface, the image side surface is a spherical concave surface, and is cemented with the third lens; A fifth lens is configured as a biconvex spherical positive lens with a refractive index of 1.55 to 1.65 and an Abbe number of 66 to 71; and The sixth lens is configured as a double concave spherical negative lens, the image side curvature radius is 500-600 mm, and is cemented with the fifth lens; The second lens group includes the following in sequence along the central axis: A seventh lens is configured as a positive lens, the object side surface is a concave spherical surface, the absolute value of the radius of curvature is greater than 1000 mm, and the image side surface is a convex spherical surface; and an eighth lens configured as a biconcave spherical negative lens and cemented with the seventh lens; The third lens group includes the following lens groups in sequence along the central axis: The ninth lens is configured as a biconvex spherical positive lens, with a curvature radius of 480~580mm on the object side, a refractive index of 1.55~1.65, and an Abbe number of 66~71; The tenth lens is configured as a double concave spherical negative lens and is cemented with the ninth lens; An eleventh lens is configured as a biconvex spherical positive lens and is cemented with the tenth lens; A twelfth lens is configured as a biconvex spherical positive lens; The thirteenth lens is configured as a double concave spherical negative lens and is cemented with the twelfth lens; A fourteenth lens is configured as a biconvex spherical positive lens; A fifteenth lens is configured as a double concave spherical negative lens and is cemented with the fourteenth lens; A sixteenth lens is configured as a biconvex spherical positive lens; A seventeenth lens is configured as a biconcave spherical negative lens and is cemented with the sixteenth lens; and The eighteenth lens is configured as a negative lens, the object side surface is a non-spherical concave surface with a curvature radius of 450~550mm, and the image side surface is a non-spherical convex surface.

2. The fixed-focus lens according to claim 1, characterized in that: The focal length is 80~90mm.

3. The fixed-focus lens according to claim 2, characterized in that: The second lens, the third lens, the fifth lens and the ninth lens are made of the same optical material.

4. The fixed-focus lens according to claim 3, characterized in that: The first lens has an object side curvature radius of +76.011 mm, an image side curvature radius of +215.365 mm, a central axis thickness of 10.300 mm, a refractive index of 1.85, and an Abbe number of 23.8; The second lens has an object side curvature radius of +61.477mm, an image side curvature radius of +78.556mm, a central axis thickness of 5.600mm, a refractive index of 1.59, and an Abbe number of 68.3; The third lens has an object side curvature radius of +47.222mm, an image side curvature radius of +82.800mm, a central axis thickness of 8.200mm, a refractive index of 1.59, and an Abbe number of 68.3; The fourth lens has an object side curvature radius of +82.800 mm, an image side curvature radius of +35.941 mm, a central axis thickness of 1.500 mm, a refractive index of 1.85, and an Abbe number of 25.2; The fifth lens has an object side curvature radius of +53.336 mm, an image side curvature radius of -174.338 mm, a central axis thickness of 9.50 mm, a refractive index of 1.59, and an Abbe number of 68.3; The sixth lens has an object side curvature radius of -174.338 mm, an image side curvature radius of +568.332 mm, a central axis thickness of 1.500 mm, a refractive index of 2.00, and an Abbe number of 25.

5.

5. The fixed-focus lens according to claim 4, characterized in that: The ninth lens has an object side curvature radius of +533.957 mm, an image side curvature radius of -35.626 mm, a central axis thickness of 7.500 mm, a refractive index of 1.59, and an Abbe number of 68.3; The tenth lens has an object side curvature radius of -35.626 mm, an image side curvature radius of +35.626 mm, a central axis thickness of 2.000 mm, a refractive index of 1.77, and an Abbe number of 29.7; The eleventh lens has an object side curvature radius of +35.626 mm, an image side curvature radius of -135.604 mm, a central axis thickness of 8.600 mm, a refractive index of 1.73, and an Abbe number of 54.7; The twelfth lens has an object side curvature radius of +46.752 mm, an image side curvature radius of -181.209 mm, a central axis thickness of 6.500 mm, a refractive index of 1.73, and an Abbe number of 54.7; The thirteenth lens has an object side curvature radius of -181.209 mm, an image side curvature radius of +50.080 mm, a central axis thickness of 1.500 mm, a refractive index of 1.77, and an Abbe number of 29.7; The fourteenth lens has an object side curvature radius of +62.431 mm, an image side curvature radius of -71.562 mm, a central axis thickness of 6.700 mm, a refractive index of 2.00, and an Abbe number of 29.1; The fifteenth lens has an object side curvature radius of -71.562 mm, an image side curvature radius of +46.084 mm, a central axis thickness of 1.500 mm, a refractive index of 1.62, and an Abbe number of 36.3; The sixteenth lens has an object side curvature radius of +56.199 mm, an image side curvature radius of -97.979 mm, a central axis thickness of 6.400 mm, a refractive index of 2.00, and an Abbe number of 25.5; The seventeenth lens has an object side curvature radius of -97.979 mm, an image side curvature radius of +43.506 mm, a central axis thickness of 4.000 mm, a refractive index of 1.49, and an Abbe number of 70.4; The eighteenth lens has an object side curvature radius of -119.605 mm, an image side curvature radius of -500.00 mm, a central axis thickness of 2.50 mm, a refractive index of 1.81, and an Abbe number of 40.

7.

6. The fixed-focus lens according to claim 5, characterized in that: The seventh lens has an object side curvature radius of -1204.786 mm, an image side curvature radius of -163.974 mm, a central axis thickness of 3.400 mm, a refractive index of 1.92, and an Abbe number of 20.9; The eighth lens has an object side curvature radius of -163.974 mm, an image side curvature radius of +46.971 mm, a central axis thickness of 1.00 mm, a refractive index of 1.70, and an Abbe number of 55.

5.

7. The fixed-focus lens according to claim 6, wherein: The aperture stop is disposed between the second lens group and the third lens group.

Images