Prime lens

Abstract

The utility model discloses a prime lens, which 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 utility model claims priority to Chinese invention application CN202411609438.X, filed on November 12, 2024. Technical Field

[0002] This utility model belongs to the field of photographic lens technology, specifically relating to a fixed-focus lens that can be used in full-frame cameras. Background Technology

[0003] Full-frame cameras use electronic sensors with a photosensitive area equivalent to 35mm film on a 35mm film camera, and their pixel units are at the micrometer level, placing high demands on the lens. Currently, for such lenses, if the aperture is greater than F / 1.4, all lenses are typically moved simultaneously to focus. If only one set of lenses is moved to focus, the maximum aperture is usually F / 1.4, as seen in Sony's SEL50F1.4GM lens.

[0004] Patent CN115826211A discloses a super-large aperture full-frame wide-angle autofocus lens with an aperture of up to F / 1.2 and two movable lens groups. Utility Model Content

[0005] The technical problem this invention aims to solve is how to improve a fixed-focus lens to adapt it to a full-frame camera.

[0006] This utility model discloses a fixed-focus lens.

[0007] This fixed-focus lens can be used in full-frame cameras. It consists of 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, along the central axis. 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 can move along the central axis.

[0008] The first lens group includes, along the central axis, the following components in sequence:

[0009] 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 1.75~1.85, and an Abbe number of 38.0~43.0;

[0010] The second lens is configured as a biconcave spherical negative lens and is cemented to the first lens;

[0011] The third lens is configured as a double concave spherical negative lens;

[0012] The fourth lens is configured as a biconvex spherical positive lens with a refractive index of 1.55~1.65 and an Abbe number of 66.0~71.0, and is cemented together with the third lens;

[0013] The fifth lens is configured as a biconvex spherical positive lens; and

[0014] 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;

[0015] The second lens group includes, along the central axis, the following components in sequence:

[0016] 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;

[0017] The eighth lens is configured as a biconcave spherical negative lens; and

[0018] The ninth lens is configured as a biconvex spherical positive lens with a refractive index of 1.55~1.65 and an Abbe number of 66.0~71.0, and is cemented with the eighth lens;

[0019] The third lens group includes, along the central axis, the following components in sequence:

[0020] The tenth lens is configured as a biconcave spherical negative lens;

[0021] The eleventh lens is configured as a biconvex spherical positive lens with a refractive index of 1.55~1.65 and an Abbe number of 66.0~71.0, and is cemented with the tenth lens;

[0022] The twelfth lens is configured as a biconvex spherical positive lens;

[0023] The thirteenth 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;

[0024] The fourteenth lens, configured as a negative lens, has a convex spherical surface on the object side and a concave spherical surface on the image side, and is cemented together with the thirteenth lens; and

[0025] The fifteenth lens is configured as a negative lens, with both the object-side and image-side surfaces being aspherical concave surfaces, and it has the same refractive index and Abbe number as the first lens.

[0026] In some embodiments of this utility model, the focal length of the fixed-focus lens can be selected to be 45~50mm. Further, the first lens has an object-side radius of curvature of +119mm, an image-side radius of curvature of -88mm, and a central axis thickness of 6.6mm; the fifteenth lens has an object-side radius of curvature of -189mm, an image-side radius of curvature of +500mm, and a central axis thickness of 2.0mm.

[0027] The following beneficial effects can be obtained by implementing the technical solution of this utility model.

[0028] This utility model discloses a fixed-focus lens. It includes 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. During 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 on the side of an aspherical object, and the fifteenth lens is a negative lens with two aspherical surfaces; both have the same refractive index and Abbe number. This fixed-focus lens is suitable for large apertures and can be used with full-frame cameras. Attached Figure Description

[0029] The accompanying figures should be used in conjunction with the detailed implementation section.

[0030] Figure 1 This is a cross-sectional view of the central axis of the fixed-focus lens in Embodiment 1. The captions represent: IMG - image plane, FIT - filter protector, STO - aperture stop, Z1 - central axis, and T1 - movement range.

[0031] Figure 2 This is the optical path diagram of a fixed-focus lens focusing at infinity in Example 1.

[0032] Figure 3a and Figure 3b These are the two modulation transfer function (MTF) curves of the fixed-focus lens calculated by ZEMAX software in Example 1. Figure 3b and Figure 5 The curve symbols have the same meaning, and the calculation conditions are: incident light mixing range 430~658nm, aperture F / 1.25, and infinity focus state.

[0033] Figure 4 and Figure 5 Selected from the official website of Sony's SEL50F1.4GM prime lens. https: / / www.sonystyle.com.cn / products / lenses / sel50f14gm / sel50f14gm_feature.html , Figure 4 This is a structural diagram. Figure 5 The method for obtaining the modulation transfer function graph is unknown. Detailed Implementation

[0034] The embodiments are described below with reference to the accompanying drawings.

[0035] 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 in general; the directions / positions indicated by top, bottom, center, edge, inner, outer, far, near, long, wide, vertical, horizontal, up, down, front, back, left, right, etc. are based on the observation angle of the accompanying drawings and should not be understood as the component / device being located in a specific position or facing a specific direction.

[0036] The lens grouping method described in this specification is for the convenience of illustrating the embodiments only. It is understood that other grouping methods may be used in optical design analysis, lens forming, and lens assembly.

[0037] Positive lens and positive optical power both refer to an optical system with a positive image-side focal length, which converges parallel incident light beams. Negative lens 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 can be simply referred to as the "surface." The side of the lens facing the object being photographed by the camera is called the "object-side surface," and the side of the lens facing the camera's image sensor is called the "image-side surface."

[0038] The aperture stop, also known as the "stop," is numbered along with the lens's light-transmitting surface.

[0039] Example 1

[0040] A fixed-focus lens is disclosed.

[0041] This fixed-focus lens is designed for autofocus full-frame cameras, with a focal length of 49mm, and is compatible with a maximum aperture of F / 1.2~1.3 and an image plane of 42~44mm.

[0042] Please see Figure 1 , Figure 1 This is a cross-sectional view of the central axis of the fixed-focus lens. Figure 1 The lens barrel is not shown. The central axis Z1 (also known as the optical axis, principal axis, or principal optical axis) points from left to right towards the image plane IMG, and a filter protector FIT is located in front of the image plane IMG. Tables 1 and 2 and Equation f1 below list the lens data and positional relationships of this fixed-focus lens.

[0043] In Table 1, the object-side surface of the first lens L1 is denoted as surface S1. Other light-transmitting surfaces (including the plane containing the aperture stop STO and the cementing 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. "Radius of curvature R" represents the paraxial radius of curvature at the vertex of a surface. The i-th surface S... i and the (i+1)th surface S i+1 For lenses between two adjacent lenses: their "thickness" is the central axis thickness, and their "refractive index Nd" and "Abbe number Nd" are measured values ​​on the d-line. The distance between the image-side surface of the first lens and the object-side surface of the second lens on the central axis Z1 is called the central axis distance between them.

[0044]

[0045]

[0046] This fixed-focus lens has 15 elements, all of which are glass lenses. These elements are divided into three groups and numbered sequentially along the central axis. The lens barrel of this fixed-focus lens ( Figure 1(Not shown) Along the central axis Z1, from the object side to the image side, the first lens group G1, the aperture stop STO, the second lens group G2, and the third lens group G3 are arranged in sequence.

[0047] During the focusing process of this fixed-focus lens, only the second lens group G2 can be moved back and forth along the central axis Z1 by a stepper motor. The first lens group G1, the aperture stop STO, and the third lens group G3 are all fixed in position relative to the image plane IMG. The distance between the aperture stop STO and the central axis of the surface S10 of the first lens group G1 is 7.353 mm, and the distance between the surface S26 of the third lens group G3 and the central axis of the image plane IMG is approximately 14.9 mm.

[0048] 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, in sequence, lens L1, lens L2, lens L3, lens L4, lens L5, and lens L6. In a cemented doublet formed by cementing lens L1 and lens L2, the object-side surface is a non-spherical convex surface, and the image-side surface is a concave spherical surface; the radius of curvature of the cemented surface is negative. In a cemented doublet formed by cementing lens L3 and lens L4, the object-side surface is a concave spherical surface, and the image-side surface is a convex spherical surface; the radius of curvature of the cemented surface is positive. Lens L4 and lens L5 are both biconvex spherical positive lenses. Lens L6 is a meniscus negative lens.

[0049] The second lens group G2 has positive optical power and consists of three glass lenses. These three lenses, along the central axis Z1, are, in order, the seventh lens L7, the eighth lens L8, and the ninth lens L9. The seventh lens L6 is a meniscus positive lens. In a cemented doublet formed by cementing the eighth lens L8 and the ninth lens L8 together, the object-side surface is concave spherical, the image-side surface is convex spherical, and the radius of curvature of the cemented surface is positive.

[0050] The third lens group G3 has negative optical power and consists of six glass lenses, including two consecutive biconvex spherical lenses. These six glass lenses, along the central axis Z1, are, in order: the tenth lens L10, the eleventh lens L11, the twelfth lens L12, the thirteenth lens L13, the fourteenth lens L14, and the fifteenth lens L15. In the cemented doublet formed by the cemented tenth lens L10 and the eleventh lens L11, the object-side surface is concave spherical, the image-side surface is convex spherical, and the radius of curvature of the cemented surface is positive. In the cemented doublet formed by the cemented thirteenth lens L13 and the fourteenth lens L14, the object-side surface is convex spherical, the image-side surface is concave spherical, and the radius of curvature of the cemented surface is positive. The eleventh lens L11 and the twelfth lens L12 are both biconvex spherical positive lenses. The fifteenth lens L5 is a biconcave aspherical lens.

[0051] All 15 glass lenses are arranged sequentially along the central axis Z1 to form the three lens groups mentioned above, and are installed inside the lens barrel. The lens barrel is equipped with a stepper motor and a power input interface.

[0052] Figure 1 In the middle, the second lens group G2 is located in the middle of its movement range T1.

[0053] Please see Figure 2 The diagram illustrates the optical path of the fixed-focus lens in its infinity-focused state. Figure 2 The second lens group G2 is located at the image-side boundary of its movement range T1, and the distance between its central axis and the third lens group G3 is 1.000mm.

[0054] The specific focal length of each glass lens, each cemented lens, and each lens group of this fixed-focus lens can be calculated using the data in the table above. Details of each lens are as follows.

[0055] The first lens L1 is a positive lens with an object-side surface that is a non-spherical convex surface with a radius of curvature of +118.780 mm, an image-side surface that is a spherical convex surface with a radius of curvature 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.

[0056] The second lens L2 is a biconcave spherical negative lens with an object-side radius of curvature of -87.610 mm, an image-side radius of curvature 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. It is cemented together with the first lens L1.

[0057] The third lens L3 is a biconcave spherical negative lens with an object-side radius of curvature of -35.997 mm, an image-side radius of curvature of +122.296 mm, a central axis thickness of 1.500 mm, a refractive index of 1.77, an Abbe number of 29.7, and a central axis distance of 10.392 mm from the second lens L2.

[0058] The fourth lens, L4, is a biconvex spherical positive lens with an object-side radius of curvature of +122.296 mm, an image-side radius of curvature 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. It is cemented together with the third lens, L3.

[0059] The fifth lens, L5, is a biconvex spherical positive lens with an object-side radius of curvature of +197.321 mm, an image-side radius of curvature of -77.813 mm, a central axis thickness of 7.300 mm, a refractive index of 2.00, an Abbe number of 29.1, and a central axis distance of 0.150 mm from the fourth lens, L4.

[0060] The sixth lens, L6, is a negative lens. Its object side is a convex spherical surface with a radius of curvature of +95.683 mm, and its image side is a concave spherical surface with a radius of curvature of +45.506 mm. Its central axis thickness is 1.000 mm, its refractive index is 1.65, and its Abbe number is 33.8. The distance between its central axis and that of the fifth lens, L5, is 0.150 mm, and the distance between its central axis and that of the aperture stop, STO, is 7.353 mm.

[0061] The seventh lens, L7, is a positive lens with a convex spherical object side with a radius of curvature of +46.626 mm and a concave spherical image side with a radius of curvature of +76.029 mm. It has a central axis thickness of 4.000 mm, a refractive index of 1.88, and an Abbe number of 40.8. When focused at infinity, its central axis distance from the aperture stop STO is 15.594 mm.

[0062] The eighth lens, L8, is a biconcave spherical negative lens with an object-side radius of curvature of -72.262 mm, an image-side radius of curvature of +44.759 mm, a central axis thickness of 1.500 mm, a refractive index of 1.61, an Abbe number of 37.0, and a central axis distance of 5.492 mm from the seventh lens, L7.

[0063] The ninth lens, L9, is a biconvex spherical positive lens with an object-side radius of curvature of +44.759 mm, an image-side radius of curvature 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. It is cemented together with the eighth lens, L8.

[0064] The tenth lens, L10, is a biconcave spherical negative lens with an object-side radius of curvature of -109.274 mm, an image-side radius of curvature 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. When focused at infinity, its central axis distance from that of the ninth lens, L9, is 1.000 mm.

[0065] The eleventh lens, L11, is a biconvex spherical positive lens with an object-side radius of curvature of +46.003 mm, an image-side radius of curvature of -88.756 mm, a central axis thickness of 9.00 mm, a refractive index of 1.59, and an Abbe number of 68.3. It is cemented together with the tenth lens, L10.

[0066] The twelfth lens, L12, is a biconvex spherical positive lens with an object-side radius of curvature of +61.323 mm, an image-side radius of curvature of -243.144 mm, a central axis thickness of 7.112 mm, a refractive index of 1.92, an Abbe number of 20.9, and a central axis distance of 0.150 mm from the eleventh lens, L11.

[0067] The thirteenth lens, L13, is a positive lens with a convex spherical surface on the object side and a radius of curvature of +42.029 mm, a concave spherical surface on the image side and a radius of curvature 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 distance of 0.150 mm from that of the twelfth lens, L12.

[0068] The fourteenth lens, L14, is a negative lens with a convex spherical surface on the object side and a radius of curvature of +184.079 mm, a concave spherical surface on the image side and a radius of curvature 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. It is cemented together with the thirteenth lens, L13.

[0069] 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 distance between it and the fourteenth lens, L14, is 7.921 mm, and the central axis distance between it and the image plane, IMG, is approximately 14.9 mm.

[0070] The first lens L1 and the fifteenth lens L15 of this fixed-focus lens have the same refractive index and Abbe number, and are two aspherical lenses with coupled optical performance. Specifically, the first lens L1 and the fifteenth lens L15 use the same grade of optical glass.

[0071] The specific shapes of the three aspherical surfaces S1, S25, and S26 in Table 1 are characterized by the aspherical expression f1 and the coefficients in Table 2. In the aspherical expression f1, Y is the radial coordinate, i.e., the distance from the central axis in the direction perpendicular to the central axis; Z(Y) is the axial coordinate, i.e., the distance from the vertex of the lens surface in the direction parallel to the central axis; R is the paraxial radius of curvature at the vertex of the lens surface; K is the conic constant; and Ai is the i-th order aspherical coefficient.

[0072] For the modulation transfer function (MTF) curve of this fixed-focus lens under the conditions of incident light mixing range of 430~658nm, aperture of F / 1.25, and infinity focus, please refer to [link to MTF curve]. Figure 3a and Figure 3b .Depend on Figure 3a It can be seen that the MTF values ​​of the six curves decrease almost uniformly within the frequency range of 0~30 lp / mm. The four upper curves almost overlap in pairs and are distributed within a relatively narrow range of the vertical axis. Only the 21 mm-sagittal curve eventually drops below 0.5. (Comparison) Figure 3b and Figure 5It can be seen that at an aperture of F / 1.25, the image quality of this prime lens is close to that of the Sony SEL50F1.4GM prime lens with a maximum aperture of F / 1.4. Therefore, this prime lens can be used with full-frame cameras, and its maximum aperture range is F / 1.2 to F / 1.3.

[0073] This fixed-focus lens has two continuously arranged biconvex spherical lenses before and after the aperture stop STO. The first lens L1 and the fifteenth lens L15 use large-diameter aspherical lenses and are coupled to each other in optical design, which can improve the lens vignetting problem of large aperture lenses under the condition of large aperture F / 1.2~1.3.

[0074] This fixed-focus lens is equipped with five cemented lenses, whose positive and negative lenses have significantly different dispersion coefficients. This corrects axial chromatic aberration, spherical aberration, and distortion aberration, and also reduces the tolerance sensitivity of image quality. By adding cemented lenses, the axial length, the number of aspherical lenses, and the number of ultra-low dispersion lenses can be controlled.

[0075] As a replaceable component of a full-frame camera, for other aspects of the structure and function of this fixed-focus lens, 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 standard focal length cameras.

[0076] In other embodiments, the lenses described above can be made of other types of lens materials, the stepper motor can be replaced by a voice coil motor or an ultrasonic motor, and the total focal length of the fixed-focus lens can be any value within the range of 45~55mm. Based on the lens data of Embodiment 1, the surface shape, central axis thickness, and central axis spacing of each lens can be adaptively adjusted to achieve clear imaging and other technical requirements of the camera. Specifically:

[0077] The first lens L1 and the fifteenth lens L15 use the same optical material, with a refractive index of 1.75~1.85 and an Abbe number of 38.0~43.0;

[0078] The refractive index of the second lens L2 is 1.45~1.55, and the Abbe number is 68.0~73.0;

[0079] The third lens L3 and the tenth lens use the same optical material with a refractive index of 1.75~1.85 and an Abbe number of 27.0~32.0;

[0080] The fourth lens L4, the ninth lens L9, and the eleventh lens L11 all have a refractive index of 1.55~1.65 and an Abbe number of 66.0~71.0, and can use the same grade of optical glass.

[0081] The refractive index of the fifth lens L5 is 1.95~2.05, and the Abbe number is 26.5~31.5;

[0082] The refractive index of the sixth lens L6 is 1.65~1.75, and the Abbe number is 31.0~36.0.

[0083] The seventh lens L7 and the thirteenth lens L13 both have a refractive index of 1.85~1.95 and an Abbe number of 38.0~43.0, and can use the same grade of optical glass;

[0084] The refractive index of the eighth lens L8 is 1.55~1.65, and the Abbe number is 34.5~39.5.

[0085] The refractive index of the twelfth lens L12 is 1.85~1.95, and the Abbe number is 18.5~23.5;

[0086] The refractive index of the fourteenth lens L14 is 1.80~1.90, and the Abbe number is 21.0~26.0.

[0087] All the embodiments, application examples, and technical analyses described above are intended to introduce the technical concept and features of this utility model, enabling those skilled in the art to implement the technical solution of this utility model, and do not constitute any limitation on the scope of protection of this utility model. Simple modifications and equivalent transformations to the above embodiments are all within the scope of protection of the claims of this utility model.

Claims

1. A fixed-focus lens for use in a full-frame camera, comprising, in sequence 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 further comprising an aperture stop, wherein, when in focus, the first lens group, the aperture stop, and the third lens group are fixed relative to the image plane, and the second lens group is movable along the central axis. Its features are, The first lens group includes, sequentially 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 1.75~1.85, and an Abbe number of 38.0~43.0; 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 double concave spherical negative lens; The fourth lens is configured as a biconvex spherical positive lens with a refractive index of 1.55~1.65 and an Abbe number of 66.0~71.0, and is cemented together with the third lens; The fifth lens is 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, along the central axis, the following components in sequence: 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; The eighth lens is configured as a biconcave spherical negative lens; and The ninth lens is configured as a biconvex spherical positive lens with a refractive index of 1.55~1.65 and an Abbe number of 66.0~71.0, and is cemented with the eighth lens; The third lens group includes, along the central axis, the following components in sequence: The tenth lens is configured as a biconcave spherical negative lens; The eleventh lens is configured as a biconvex spherical positive lens with a refractive index of 1.55~1.65 and an Abbe number of 66.0~71.0, 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 surface on the object side and a spherical concave surface on the image side; The fourteenth lens, configured as a negative lens, has a convex spherical surface on the object side and a concave spherical surface on the image side, and is cemented together with the thirteenth lens; and The fifteenth lens is configured as a negative lens, with both the object-side and image-side surfaces being aspherical concave surfaces, and it has the same refractive index and Abbe number as the first lens.

2. The fixed-focus lens according to claim 1, characterized in that, The focal length is 45~55mm.

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

4. The fixed-focus lens according to claim 3, characterized in that, The first lens has an object-side radius of curvature of +118.780 mm, an image-side radius of curvature 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 radius of curvature of -87.610 mm, an image-side radius of curvature 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 radius of curvature of -35.999 mm, an image-side radius of curvature 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 radius of curvature of +122.296 mm, an image-side radius of curvature 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 radius of curvature of +197.321 mm, an image-side radius of curvature 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 radius of curvature of +95.683 mm, an image-side radius of curvature 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, characterized in that, The tenth lens has an object-side radius of curvature of -109.274 mm, an image-side radius of curvature 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 radius of curvature of +46.003 mm, an image-side radius of curvature 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 radius of curvature of +61.323 mm, an image-side radius of curvature 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 radius of curvature of +42.029 mm, an image-side radius of curvature 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 radius of curvature of +184.079 mm, an image-side radius of curvature 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 radius of curvature of -188.696 mm, an image-side radius of curvature of +500.00 mm, and a central axis thickness of 2.000 mm.

6. The fixed-focus lens according to claim 5, characterized in that, The seventh lens has an object-side radius of curvature of +46.626 mm, an image-side radius of curvature 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 radius of curvature of -72.262 mm, an image-side radius of curvature 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 radius of curvature of +44.759 mm, an image-side radius of curvature 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, characterized in that, The aperture stop is positioned between the first lens group and the second lens group.

Images