Prime lens

Abstract

The prime lens disclosed by the invention can be used for a full-frame camera, and comprises a first lens group with negative focal power, a second lens group with positive focal power, a third lens group with negative focal power and an aperture diaphragm. During focusing, only the second lens group can move along the central axis. The first lens group and the third lens group in front of and behind the aperture diaphragm are respectively provided with two continuously arranged biconvex spherical positive lenses. In the direction of the central axis, the first lens is a non-spherical object side surface positive lens, the fifteenth lens is a double-aspheric-surface negative lens, and the refractive indexes and abbe numbers of the first lens and the fifteenth lens are consistent. The prime lens adapts to a large aperture.

Description

[0001] This application claims the following priority, the application date of Chinese invention application CN202411609438.X on November 12, 2024. Technical Field

[0002] The present invention relates to the field of photographic lens technology, and more particularly to a fixed-focus lens that can be used for a full-frame camera. Background Art

[0003] The electronic sensor in a full-frame camera has a photosensitive area equivalent to 35mm film in a 135mm camera, and its pixel units are already micron-level, placing high demands on lenses. For existing lenses with apertures larger than F / 1.4, all lenses are typically moved synchronously to achieve focus. If only one lens group is moved to achieve focus, the maximum aperture is typically F / 1.4, as exemplified by Sony's SEL50F1.4GM lens.

[0004] Patent CN115826211A discloses an ultra-large aperture full-frame wide-angle autofocus lens with an aperture of up to F / 1.2 and two movable lens groups. Summary of the Invention

[0005] The technical problem to be solved by this application is how to improve fixed-focus lenses to adapt to full-frame cameras.

[0006] The present application discloses a fixed-focus lens.

[0007] This fixed-focus lens can be used in a full-frame camera. It includes, along the central axis, a first lens group with negative optical power, a second lens group with positive optical power, and a third lens group with negative optical power. It also includes an aperture stop. When focusing, the first lens group, the aperture stop, and the third lens group are fixed relative to the image plane, while the second lens group is movable along the central axis. The first lens group includes, in sequence along the central axis: The first lens is configured as a positive lens, with an aspherical convex surface on the object side and a spherical convex surface on the image side, a refractive index of 1.75 to 1.85, and an Abbe number of 38.0 to 43.0; The second lens is configured as a biconcave spherical negative lens and is cemented to the first lens; The third lens is configured as a biconcave spherical negative lens; The fourth lens is a biconvex spherical positive lens with a refractive index of 1.55 to 1.65 and an Abbe number of 66.0 to 71.0, cemented to the third lens; a fifth lens configured as a biconvex spherical positive lens; and The sixth lens is configured as a negative lens, with a convex spherical surface on the object side and a concave spherical surface on the image side; The second lens group includes, in sequence along the central axis: The seventh lens is configured as a positive lens, with a convex spherical surface on the object side and a concave spherical surface on the image side; an eighth lens configured as a biconcave spherical negative lens; and The ninth lens is a biconvex spherical positive lens with a refractive index of 1.55 to 1.65 and an Abbe number of 66.0 to 71.0, cemented to the eighth lens; The third lens group includes, in sequence along the central axis: a tenth lens configured as a biconcave spherical negative lens; The eleventh lens is a biconvex spherical positive lens with a refractive index of 1.55 to 1.65 and an Abbe number of 66.0 to 71.0, and is cemented with the tenth lens; The twelfth lens is configured as a biconvex spherical positive lens; The thirteenth lens is configured as a positive lens, with a spherical convex object-side surface and a spherical concave image-side surface; A fourteenth lens configured as a negative lens, having a spherical convex object-side surface and a spherical concave image-side surface, cemented to the thirteenth lens; and The fifteenth lens is configured as a negative lens, and both the object-side surface and the image-side surface are aspherical concave surfaces, and have the same refractive index and Abbe number as the first lens.

[0008] In some embodiments of the present application, the focal length of the fixed-focus lens may be 45-50 mm. Furthermore, the first lens element has an object-side curvature radius of +119 mm, an image-side curvature radius of -88 mm, and a central axis thickness of 6.6 mm. The fifteenth lens element has an object-side curvature radius of -189 mm, an image-side curvature radius of +500 mm, and a central axis thickness of 2.0 mm.

[0009] By implementing the technical solution of this application, the following beneficial effects can be achieved.

[0010] This application discloses a fixed-focus lens. It comprises a first lens group with negative optical power, a second lens group with positive optical power, a third lens group with negative optical power, and an aperture stop. When focusing, only the second lens group moves along the central axis. The first and third lens groups before and after the aperture stop each have two consecutively arranged biconvex spherical positive lenses. Along the central axis, the first lens is a positive lens with an aspherical side, and the fifteenth lens is a negative lens with two aspherical surfaces. Both lenses have the same refractive index and Abbe number. This fixed-focus lens is suitable for larger apertures and can be used in full-frame cameras. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The following drawings should be used in conjunction with the detailed description.

[0012] Figure 1This is a cross-sectional view of the central axis of the fixed-focus lens in Example 1. The legends represent: IMG-image plane, FIT-filter protector, STO-aperture stop, Z1-central axis, T1-movement range.

[0013] Figure 2a Table 1 shows the data and position relationship of each lens in Example 1.

[0014] Figure 2b The aspheric surface expressions f1 of the three aspheric surfaces of Example 1 are listed, as well as Table 2 recording the coefficients of the three aspheric surface expressions.

[0015] Figure 3 This is a light path diagram of the fixed-focus lens focusing at infinity in Example 1.

[0016] Figure 4a and Figure 4b : are two modulation transfer function (MTF) curves of the fixed focus lens calculated by ZEMAX software in Example 1, Figure 4b and Figure 6 The curve codes have the same meaning, and the calculation conditions are: incident light mixing range 430~658nm, aperture F / 1.25, and infinity focus state.

[0017] Figure 5 and Figure 6 Selected from the official website of Sony's SEL50F1.4GM fixed-focus lens https: / / www.sonystyle.com.cn / products / lenses / sel50f14gm / sel50f14gm_feature.html , Figure 5 is a structural diagram, Figure 6 The method for obtaining the modulation transfer function diagram of is unknown. DETAILED DESCRIPTION

[0018] The following describes embodiments 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 components / devices being located in specific positions or facing specific directions.

[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 lenses and positive optical power both refer to an optical system with a positive image-side focal length, which converges parallel incident light beams. Negative lenses and negative optical power both refer to an optical system with a negative image-side focal length, which diverges parallel incident light beams. The light-transmitting surface of a lens is referred to as the "side." 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 image plane 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] Example 1 Disclosed is a fixed-focus lens.

[0024] This fixed-focus lens is designed for full-frame cameras with autofocus, has a focal length of 49mm, and is suitable for a maximum aperture of F / 1.2~1.3 and an imaging area 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 shown. The central axis Z1 (also called optical axis, principal axis, or main optical axis) points from left to right to the image plane IMG. 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 denoted as surface S1, and the 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. The image side surface of the fifteenth lens L15 is denoted as surface S26. "Curvature radius R" represents the paraxial curvature radius value of the vertex of a surface. i and the i+1th surface S i+1 For lenses between two adjacent lenses, the "Thickness" is the central axis thickness, and the "Refractive Index Nd" and "Abbe Number Nd" are d-line measurements. The distance between the image-side surface of the preceding lens and the object-side surface of the following lens on central axis Z1 is called the central axis separation between the two lenses.

[0027] The 15 lenses of this fixed-focus lens are all glass lenses and can be divided into three groups, numbered in ascending order along the central axis. Figure 1 In the lens element (not shown), a first lens group G1, an aperture stop STO, a second lens group G2 and a third lens group G3 are arranged in sequence from the object side to the image side along the central axis Z1.

[0028] During focusing (also known as focusing), only the second lens group G2 is driven by a stepper motor to move back and forth along the central axis Z1. The first lens group G1, aperture stop STO, and third lens group G3 are all fixed relative to the image plane IMG. The central axis distance between aperture stop STO and surface S10 of first lens group G1 is 7.353mm, while the central axis distance between surface S26 of third lens group G3 and image plane IMG is approximately 14.9mm.

[0029] The first lens group G1 has negative optical power and consists of six glass lenses, including two consecutively arranged biconvex spherical lenses. These six glass lenses, along the central axis Z1, 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. In the doublet lens pair formed by cementing the first lens L1 and the second lens L2, the object-side surface is an aspherical convex surface, the image-side surface is a concave spherical surface, and the radius of curvature of the cemented surface is negative. In the doublet lens pair formed by cementing the third lens L3 and the fourth lens L4, the object-side surface is a concave spherical surface, the image-side surface is a convex spherical surface, and the radius of curvature of the cemented surface is positive. The fourth lens L4 and the fifth lens L5 are both biconvex spherical positive lenses. The sixth lens L6 is a negative meniscus lens.

[0030] The second lens group G2 has positive optical power and consists of three glass lenses. These three lenses, arranged along central axis Z1, are seventh lens L7, eighth lens L8, and ninth lens L9. Seventh lens L6 is a positive meniscus lens. The cemented doublet, formed by eighth lens L8 and ninth lens L8, has a concave object-side surface and a convex image-side surface, with positive radii of curvature.

[0031] The third lens group G3 has negative optical power and consists of six glass lenses, two of which are biconvex spherical lenses arranged in series. These six glass lenses, arranged along central axis Z1, are, in order: tenth lens L10, eleventh lens L11, twelfth lens L12, thirteenth lens L13, fourteenth lens L14, and fifteenth lens L15. In the doublet formed by cementing tenth lens L10 and eleventh lens L11, the object-side surface is concave, and the image-side surface is convex, with a positive radius of curvature. In the doublet formed by cementing thirteenth lens L13 and fourteenth lens L14, the object-side surface is convex, and the image-side surface is concave, with a positive radius of curvature. Eleventh lens L11 and twelfth lens L12 are both biconvex spherical positive lenses. Fifteenth lens L5 is a biconcave aspherical lens.

[0032] All 15 glass lenses are distributed 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 stepper motor and a power supply interface.

[0033] Figure 1, the second lens group G2 is in the middle of its moving range T1.

[0034] See also Figure 3 The optical path diagram of the fixed-focus lens in the infinity focus state is shown. Figure 3 The second lens group G2 is at the image-side boundary of its moving range T1, and the central axis distance between it and the third lens group G3 is 1.000 mm.

[0035] Each glass lens, each cemented lens and each lens group of this fixed focus lens can be used at a specific focal length Figure 2a and Figure 2b The details of each lens are as follows.

[0036] The first lens L1 is a positive lens with an aspherical convex surface on the object side with a curvature radius of +118.780 mm, a spherical convex surface on the image side with a curvature radius of -87.610 mm, a central axis thickness of 6.600 mm, a refractive index of 1.81, and an Abbe number of 40.7.

[0037] The second lens L2 is a biconcave spherical negative lens with a curvature radius of -87.610mm on the object side and a curvature radius of +41.009mm on the image side. It has a central axis thickness of 1.500mm, a refractive index of 1.49, and an Abbe number of 70.4. It is cemented to the first lens L1.

[0038] The third lens L3 is a biconcave spherical negative lens with a curvature radius of -35.997mm on the object side and a curvature radius of +122.296mm on the image side. It has a central axis thickness of 1.500mm, a refractive index of 1.77, an Abbe number of 29.7, and a central axis spacing of 10.392mm between it and the second lens L2.

[0039] The fourth lens L4 is a biconvex spherical positive lens with a curvature radius of +122.296mm on the object side and a curvature radius of -41.197mm on the image side. It has a central axis thickness of 10.400mm, a refractive index of 1.59, and an Abbe number of 68.3. It is cemented with the third lens L3.

[0040] The fifth lens L5 is a biconvex spherical positive lens with a curvature radius of +197.321mm on the object side and a curvature radius of -77.813mm on the image side. The central axis thickness is 7.300mm, the refractive index is 2.00, the Abbe number is 29.1, and the central axis spacing with the fourth lens L4 is 0.150mm. The sixth lens L6 is a negative lens. Its object-side surface is a convex spherical surface with a curvature radius of +95.683mm, its image-side surface is a concave spherical surface with a curvature radius of +45.506mm, its central axis thickness is 1.000mm, its refractive index is 1.65, its Abbe number is 33.8, its central axis spacing from the fifth lens L5 is 0.150mm, and its central axis spacing from the aperture stop STO is 7.353mm.

[0041] The seventh lens L7 is a positive lens with a convex spherical surface on the object side with a curvature radius of +46.626mm, a concave spherical surface on the image side with a curvature radius of +76.029mm, a central axis thickness of 4.000mm, a refractive index of 1.88, and an Abbe number of 40.8. When focused at infinity, the central axis spacing between it and the aperture stop STO is 15.594mm.

[0042] The eighth lens L8 is a biconcave spherical negative lens with a curvature radius of -72.262mm on the object side and a curvature radius of +44.759mm on the image side. The central axis thickness is 1.500mm, the refractive index is 1.61, the Abbe number is 37.0, and the central axis spacing between it and the seventh lens L7 is 5.492mm. The ninth lens L9 is a biconvex spherical positive lens with a curvature radius of +44.759mm on the object side and a curvature radius of -56.999mm on the image side. It has a central axis thickness of 9.700mm, a refractive index of 1.59, and an Abbe number of 68.3. It is cemented with the eighth lens L8.

[0043] The tenth lens L10 is a biconcave spherical negative lens with a curvature radius of -109.274mm on the object side and a curvature radius of +46.003mm on the image side. The central axis thickness is 1.500mm, the refractive index is 1.77, and the Abbe number is 29.7. When focused at infinity, the central axis spacing between it and the ninth lens L9 is 1.000mm.

[0044] The eleventh lens L11 is a biconvex spherical positive lens with a curvature radius of +46.003mm on the object side and a curvature radius of -88.756mm on the image side. The central axis thickness is 9.00mm, the refractive index is 1.59, and the Abbe number is 68.3. It is cemented with the tenth lens L10.

[0045] The twelfth lens L12 is a biconvex spherical positive lens with a curvature radius of +61.323 mm on the object side and a curvature radius of -243.144 mm on the image side. The central axis thickness is 7.112 mm, the refractive index is 1.92, the Abbe number is 20.9, and the central axis spacing between the twelfth lens L11 and the lens is 0.150 mm.

[0046] The thirteenth lens L13 is a positive lens with a spherical convex surface on the object side with a curvature radius of +42.029 mm, a spherical concave surface on the image side with a curvature radius of +184.079 mm, a central axis thickness of 6.100 mm, a refractive index of 1.88, an Abbe number of 40.8, and a central axis spacing of 0.150 mm from the twelfth lens L12.

[0047] The fourteenth lens L14 is a negative lens with a spherical convex surface on the object side with a curvature radius of +184.079mm, a spherical concave surface on the image side with a curvature radius of +26.468mm, a central axis thickness of 1.500mm, a refractive index of 1.85, and an Abbe number of 23.8. It is cemented with the thirteenth lens L13.

[0048] The fifteenth lens L15 is a negative lens. Both the object-side and image-side surfaces are aspherical concave surfaces. The radius of curvature of the object-side surface is -188.696 mm, the radius of curvature of the image-side surface is +500.00 mm, the central axis thickness is 2.000 mm, the refractive index is 1.81, the Abbe number is 40.7, the central axis spacing between it and the fourteenth lens L14 is 7.921 mm, and the central axis spacing between it and the image plane IMG is approximately 14.9 mm.

[0049] The first lens L1 and the fifteenth lens L15 of the fixed-focus lens have the same refractive index and Abbe number, and are two aspherical lenses with coupled optical properties. Specifically, the first lens L1 and the fifteenth lens L15 are made of the same brand of optical glass.

[0050] Figure 2a As shown in Table 1, the specific shapes of the three aspheric surfaces S1, S25 and S26 are Figure 2b The aspheric expression f1 and the coefficients in Table 2 are used to characterize the aspheric surface. 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 conic constant; and Ai is the i-th order aspheric coefficient.

[0051] The calculated modulation transfer function (MTF) curve of this fixed-focus lens is shown in the following figure under the conditions of incident light mixing range of 430~658nm, aperture F / 1.25, and infinity focus state. Figure 4a and Figure 4b .Depend on Figure 4a It can be seen that the MTF values of the six curves decrease basically evenly in the frequency range of 0~30lp / mm. The four curves on the top almost overlap with each other and are distributed in a narrow vertical coordinate range. Only the 21mm-sagittal curve finally drops below 0.5. Figure 4b and Figure 6As we can see, at an aperture of F / 1.25, the image quality of this fixed-focus lens approaches the maximum aperture of F / 1.4 of the Japanese Sony SEL50F1.4GM fixed-focus lens. Therefore, this fixed-focus lens can be used on full-frame cameras, and the maximum aperture it can accommodate is F / 1.2-1.3.

[0052] This fixed-focus lens has two consecutive biconvex spherical lenses arranged before and after the aperture stop STO. The first lens L1 and the fifteenth lens L15 are large-diameter aspherical lenses and are optically coupled to each other. This can improve the lens vignetting problem of large aperture lenses under conditions of large aperture F / 1.2-1.3.

[0053] This fixed-focus lens utilizes five cemented lens elements with significantly different positive and negative aberration coefficients, correcting axial chromatic aberration, spherical aberration, and distortion while also reducing the tolerance sensitivity of image quality. By adding cemented lens elements, the axial length, number of aspherical surfaces, and number of ultra-low dispersion lenses can be controlled.

[0054] This fixed-focus lens is a replaceable component for a full-frame camera. For other aspects of its structure and function, please refer to paragraphs 0110 to 0122 on pages 10-11 of the specification of patent CN10847825A, or refer to commercially available fixed-focus lenses for cameras with standard focal lengths.

[0055] In other embodiments, the above-mentioned lenses may be made of other types of lens materials, the stepper motor may be replaced with 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 45 to 55 mm. Based on the lens data of Example 1, 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 and the fifteenth lens L15 are made of the same optical material, and have a refractive index of 1.75 to 1.85 and an Abbe number of 38.0 to 43.0. The second lens L2 has a refractive index of 1.45 to 1.55 and an Abbe number of 68.0 to 73.0. The third lens L3 and the tenth lens are made of the same optical material, with a refractive index of 1.75 to 1.85 and an Abbe number of 27.0 to 32.0. The fourth lens element L4, the ninth lens element L9, and the eleventh lens element L11 all have a refractive index of 1.55 to 1.65 and an Abbe number of 66.0 to 71.0, and may be made of the same brand of optical glass. The fifth lens L5 has a refractive index of 1.95 to 2.05 and an Abbe number of 26.5 to 31.5. The sixth lens L6 has a refractive index of 1.65 to 1.75 and an Abbe number of 31.0 to 36.0. The seventh lens L7 and the thirteenth lens L13 both have a refractive index of 1.85 to 1.95 and an Abbe number of 38.0 to 43.0, and can be made of the same brand of optical glass. The eighth lens L8 has a refractive index of 1.55 to 1.65 and an Abbe number of 34.5 to 39.5. The twelfth lens L12 has a refractive index of 1.85 to 1.95 and an Abbe number of 18.5 to 23.5; The refractive index of the fourteenth lens L14 is 1.80-1.90, and the Abbe number is 21.0-26.0.

[0056] All of the above embodiments, application examples, and technical analyses are intended to introduce the technical concepts and features of this application and enable those skilled in the art to implement the technical solutions of this application. They do not constitute any limitation on the scope of protection of this application. Simple modifications and equivalent transformations of the above embodiments are within the scope of protection of the claims of this application.

Claims

1. A fixed-focus lens for use with a full-frame camera, comprising, along a central axis, a first lens group with negative optical power, a second lens group with positive optical power, and a third lens group with negative optical power, and an aperture stop. When focusing, the first lens group, the aperture stop, and the third lens group are fixed relative to the image plane, while the second lens group is movable along the central axis. It is characterized in that The first lens group includes, in order along the central axis: The first lens is configured as a positive lens, with an aspherical convex surface on the object side and a spherical convex surface on the image side, a refractive index of 1.75 to 1.85, and an Abbe number of 38.0 to 43.0; The second lens is configured as a biconcave spherical negative lens and is cemented to the first lens; The third lens is configured as a biconcave spherical negative lens; The fourth lens is a biconvex spherical positive lens with a refractive index of 1.55 to 1.65 and an Abbe number of 66.0 to 71.0, cemented to the third lens; a fifth lens configured as a biconvex spherical positive lens; and The sixth lens is configured as a negative lens, with a convex spherical surface on the object side and a concave spherical surface on the image side; The second lens group includes, in sequence along the central axis: The seventh lens is configured as a positive lens, with a convex spherical surface on the object side and a concave spherical surface on the image side; an eighth lens configured as a biconcave spherical negative lens; and The ninth lens is a biconvex spherical positive lens with a refractive index of 1.55 to 1.65 and an Abbe number of 66.0 to 71.0, cemented to the eighth lens; The third lens group includes, in sequence along the central axis: a tenth lens configured as a biconcave spherical negative lens; The eleventh lens is a biconvex spherical positive lens with a refractive index of 1.55 to 1.65 and an Abbe number of 66.0 to 71.0, and is cemented with the tenth lens; The twelfth lens is configured as a biconvex spherical positive lens; The thirteenth lens is configured as a positive lens, with a spherical convex object-side surface and a spherical concave image-side surface; A fourteenth lens configured as a negative lens, having a spherical convex object-side surface and a spherical concave image-side surface, cemented to the thirteenth lens; and The fifteenth lens is configured as a negative lens, and both the object-side surface and the image-side surface are aspherical concave surfaces, and have the same refractive index and Abbe number as the first lens.

2. The fixed-focus lens according to claim 1, wherein: The focal length is 45~55mm.

3. The fixed-focus lens according to claim 2, wherein: The first lens has an object side curvature radius of +119 mm, an image side curvature radius of -88 mm, and a central axis thickness of 6.6 mm; The fifteenth lens has an object side curvature radius of -189 mm, an image side curvature radius of +500 mm, and a central axis thickness of 2.0 mm.

4. The fixed-focus lens according to claim 3, wherein: The first lens has an object side curvature radius of +118.780 mm, an image side curvature radius of -87.610 mm, a central axis thickness of 6.600 mm, a refractive index of 1.81, and an Abbe number of 40.7; The second lens has an object side curvature radius of -87.610 mm, an image side curvature radius of +41.009 mm, a central axis thickness of 1.500 mm, a refractive index of 1.49, and an Abbe number of 70.4; The third lens has an object side curvature radius of -35.999 mm, an image side curvature radius of +122.296 mm, a central axis thickness of 1.500 mm, a refractive index of 1.77, and an Abbe number of 29.7; The fourth lens has an object-side curvature radius of +122.296 mm, an image-side curvature radius of +41.197 mm, a central axis thickness of 10.400 mm, a refractive index of 1.59, and an Abbe number of 68.3; The fifth lens has an object side curvature radius of +197.321 mm, an image side curvature radius of -77.813 mm, a central axis thickness of 7.300 mm, a refractive index of 2.00, and an Abbe number of 29.1; The sixth lens has an object side curvature radius of +95.683 mm, an image side curvature radius of +45.506 mm, a central axis thickness of 1.000 mm, a refractive index of 1.65, and an Abbe number of 33.

8.

5. The fixed-focus lens according to claim 4, wherein: The tenth lens has an object side curvature radius of -109.274 mm, an image side curvature radius of +46.003 mm, a central axis thickness of 1.500 mm, a refractive index of 1.77, and an Abbe number of 29.7; The eleventh lens has an object side curvature radius of +46.003 mm, an image side curvature radius of -88.756 mm, a central axis thickness of 9.000 mm, a refractive index of 1.59, and an Abbe number of 68.3; The twelfth lens has an object side curvature radius of +61.323 mm, an image side curvature radius of -243.144 mm, a central axis thickness of 7.112 mm, a refractive index of 1.92, and an Abbe number of 20.9; The thirteenth lens has an object side curvature radius of +42.029 mm, an image side curvature radius of +184.079 mm, a central axis thickness of 6.100 mm, a refractive index of 1.88, and an Abbe number of 40.8; The fourteenth lens has an object side curvature radius of +184.079 mm, an image side curvature radius of +26.468 mm, a central axis thickness of 1.500 mm, a refractive index of 1.85, and an Abbe number of 23.8; The fifteenth lens has an object side curvature radius of -188.696 mm, an image side curvature radius of +500.00 mm, and a central axis thickness of 2.000 mm.

6. The fixed-focus lens according to claim 5, wherein: The seventh lens has an object side curvature radius of +46.626 mm, an image side curvature radius of +76.029 mm, a central axis thickness of 4.000 mm, a refractive index of 1.88, and an Abbe number of 40.8; The eighth lens has an object side curvature radius of -72.262 mm, an image side curvature radius of +44.759 mm, a central axis thickness of 1.500 mm, a refractive index of 1.61, and an Abbe number of 37.0; The ninth lens has an object side curvature radius of +44.759 mm, an image side curvature radius of -56.999 mm, a central axis thickness of 9.700 mm, a refractive index of 1.59, and an Abbe number of 68.

3.

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

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