Optical system of large-aperture half-frame prime lens
By designing three objective lens groups and combining lenses, the refraction and convergence of light are optimized, aberrations are suppressed, and the aberration problem of large-aperture APS-C prime lenses during focusing is solved, achieving high-quality imaging.
Patent Information
- Application Number
- CN202511715119.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-21
- Publication Date
- 2026-01-23
AI Technical Summary
Large-aperture APS-C prime lenses are prone to introducing aberrations when focusing, affecting image quality. Furthermore, lens movement causes aberration fluctuations, making it difficult to meet the high image quality demands of photography enthusiasts.
It adopts a three-objective-lens design: the first objective-lens group GR1 is fixed, the second objective-lens group GR2 is floating for focusing, and the third objective-lens group GR3 balances aberrations. By optimizing the ratio of positive and negative optical power and focal length of the lens groups, light refraction and convergence are optimized. Combined with the use of cemented lenses and aspherical lenses, aberrations and chromatic aberrations are suppressed.
At a large aperture of F1.2, it effectively suppresses spherical aberration, coma, and chromatic aberration, improves edge image quality, reduces the weight of the focusing group, ensures image plane stability during focusing, and achieves high-quality imaging.
Smart Images
Figure CN121386147A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The application belongs to the technical field of optical lenses, and relates to an optical system of a large-aperture half-frame fixed focus lens. BACKGROUND
[0002] In the field of photography, a picture taken by a 25mm focal length combined with a half-frame camera has a "small wide-angle" view angle and is called a "human mirror king", which can retain the environment around the subject; F1.2 large aperture has the unique charm of shallow depth of field, large light quantity and consideration of the demand for shooting in a weak light environment, can highlight the subject, blur the background and create a dreamy atmosphere, and enhance the picture level. Therefore, its unique advantages are gradually favored by the majority of photography enthusiasts.
[0003] Large aperture is easy to introduce spherical aberration, magnification chromatic aberration and other aberrations, which affect the picture quality, and the movement of the lens group during focusing will cause aberration fluctuation, affecting the imaging quality. With the increasing demand of photography enthusiasts for photography quality, the imaging quality of the large-aperture half-frame fixed focus lens needs to be improved. SUMMARY
[0004] The application aims to provide an optical system of a large-aperture half-frame fixed focus lens, which solves the above problems.
[0005] The technical scheme adopted by the application is as follows: An optical system of a large-aperture half-frame fixed focus lens, comprising a first objective group GR1, a second objective group GR2 and a third objective group GR3, the first objective group GR1, the second objective group GR2 and the third objective group GR3 are sequentially arranged along the optical axis direction from the object side to the image side, and an aperture stop STOP is located in the third objective group GR3. During focusing, the second objective group GR2 moves to the object side along the optical axis, and the first objective group GR1, the aperture stop STOP and the third objective group GR3 remain unchanged relative to the image plane position. The optical system satisfies the following conditional formula: 10.024≤|FG1 / F|≤12.134, 1.526≤|FG2 / F|≤2.134, 0.732≤FG3 / F≤1.134; Wherein, FGR1 represents the total focal length of the first objective group, FGR2 represents the total focal length of the second objective group, FGR3 represents the total focal length of the third objective group, and F represents the total focal length of the optical system.
[0006] Further, the first objective group GR1 comprises a first lens, a second lens, a third lens, a fourth lens and a fifth lens; the second lens and the third lens form a cemented lens, and the fourth lens and the fifth lens form a cemented lens. The second objective group GR2 comprises a sixth lens; The third lens group GR3 comprises: an aperture stop STOP, a seventh lens, an eighth lens, a ninth lens, a tenth lens, an eleventh lens, a twelfth lens, a thirteenth lens, a fourteenth lens; the eighth lens, the ninth lens and the tenth lens constitute a cemented lens, and the twelfth lens and the thirteenth lens constitute a cemented lens.
[0007] Further, the first lens and the fifth lens are both meniscus negative lenses, and the first lens and the fifth lens satisfy the following conditional expression: 0.986≤Ф5 / Ф1≤1.214; Wherein, Ф1 is the focal power of the first lens, and Ф5 is the focal power of the fifth lens.
[0008] Further, the second lens is a negative lens, which is a double-concave lens; the third lens is a positive lens, which is a double-convex lens; the second lens and the third lens constitute a cemented lens, and satisfy the following conditional expression: 0.157<|ФGR1 / Ф23|<0.213; Wherein, ФGR1 is the focal power of the first objective group GR1, and Ф23 is the focal power of the cemented lens composed of the second lens and the third lens.
[0009] Further, the fourth lens is a positive lens, which is a meniscus lens, and both the spherical centers of the two sides are on the object side, and the fourth lens and the fifth lens constitute a cemented lens, and satisfy the following conditional expression: 0.648<|ФGR1 / Ф45|<0.762; Wherein, ФGR1 is the focal power of the first objective group GR1, and Ф45 is the focal power of the cemented lens composed of the fourth lens and the fifth lens.
[0010] Further, the sixth lens is a negative lens, and satisfies the following conditional expression: 1.699<|Ф / Ф6|<2.054; Wherein, Ф is the total focal power of the optical system, and Ф6 is the focal power of the sixth lens.
[0011] Further, the seventh lens is a non-spherical lens, and the fourteenth lens is a non-spherical lens, and satisfy the following conditional expression: 1.524<|R141 / R71|<|R142 / R72|<2.045; Wherein, R71 is the object side vertex curvature radius of the seventh lens, R72 is the image side vertex curvature radius of the seventh lens, R141 is the object side vertex curvature radius of the fourteenth lens, and R142 is the image side vertex curvature radius of the fourteenth lens.
[0012] Further, the eighth lens, the tenth lens, the eleventh lens and the twelfth lens are all positive lenses and belong to biconvex lenses, and satisfy the following conditional expressions: N8=N10, 1.76<N12<N11<2.0007; Wherein, N8 is the refractive index of the eighth lens relative to D light, N10 is the refractive index of the tenth lens relative to D light, N11 is the refractive index of the eleventh lens relative to D light, and N12 is the refractive index of the twelfth lens relative to D light.
[0013] Further, the ninth lens and the thirteenth lens are both negative lenses and belong to biconcave lenses, and satisfy the following conditional expressions: 1.72<N13<N9<2.0007, V9<V13<35; Wherein, N9 is the refractive index of the ninth lens relative to D light, N13 is the refractive index of the thirteenth lens relative to D light, V9 is the Abbe number of the ninth lens relative to D light, and V13 is the Abbe number of the thirteenth lens relative to D light. Further, the twelfth lens and the thirteenth lens form a cemented lens, and satisfy the following conditional expressions: 2.315<|ФGR3 / Ф1213|<2.551; Wherein, ФGR3 is the focal power of the third objective lens group GR3, and Ф1213 is the focal power of the cemented lens formed by the twelfth lens and the thirteenth lens.
[0014] Further, the eighth lens, the ninth lens and the tenth lens form a cemented lens, and satisfy the following conditional expressions: 3.564<|ФGR3 / Ф8910|<3.842; Wherein, ФGR3 is the focal power of the third objective lens group GR3, and Ф8910 is the focal power of the cemented lens formed by the eighth lens, the ninth lens and the tenth lens.
[0015] In summary, due to the adoption of the above technical solutions, the present application has the following advantages: 1. An optical system of a large-aperture half-frame fixed focus lens achieves the purposes of optimizing the refraction and convergence of light, balancing aberration and improving imaging quality by setting the positive and negative focal powers of each lens group and the ratio between the synthetic focal length of each lens group and the synthetic focal length of the entire lens, and further makes the lens achieve high image quality; 2. The present application effectively suppresses spherical aberration, coma and chromatic dispersion under F1.2 large aperture through the collaborative design of three objective lens groups, GR1 fixedly bears the main focal power, GR2 is floating focus, and GR3 balances aberration; 3. The dispersion compensation design of the cemented lens (the second lens and the third lens, the fourth lens and the fifth lens) in the first objective group GR1 and the cemented lens (the eighth lens, the ninth lens and the tenth lens) in the third objective group GR3 in the application significantly reduces the magnification chromatic aberration and improves the edge image quality; 4. In the application, only the second objective group GR2 (the sixth lens) moves during focusing, effectively reducing the weight of the focusing group and making the focusing more rapid; the focal ratio (|D6 / Ф6|∈[1.524, 1.841]) and the optical power condition (0.4251<|Ф / Ф6|<0.6874) of GR2 ensure the stability of the image surface during focusing; 5. In the application, the seventh lens and the fourteenth lens of the third objective group GR3 are both aspherical lenses, which can effectively compensate for the spherical aberration, coma and distortion of the system; 6. In the application, the eighth lens, the ninth lens and the tenth lens form a cemented lens, and the eighth lens and the tenth lens are made of the same material, which can achieve the effect of complex achromatism. BRIEF DESCRIPTION OF DRAWINGS
[0016] In order to more clearly illustrate the technical solutions of the embodiments of the application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some embodiments of the application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor on the basis of these drawings, wherein: Figure 1 It is a schematic diagram of the optical system structure of the application; Figure 2 It is a schematic diagram of the field curvature distortion of the application embodiment 1 when focusing at infinity; Figure 3 It is a schematic diagram of the axial chromatic aberration of the application embodiment 1 when focusing at infinity; Figure 4 It is a schematic diagram of the field curvature distortion of the application embodiment 1 when focusing at 0.25m; Figure 5 It is a schematic diagram of the axial chromatic aberration of the application embodiment 1 when focusing at 0.25m; Markings in the figure: 1-first lens, 2-second lens, 3-third lens, 4-fourth lens, 5-fifth lens, 6-sixth lens, 7-seventh lens, 8-eighth lens, 9-ninth lens, 10-tenth lens, 11-eleventh lens, 12-twelfth lens, 13-thirteenth lens, 14-fourteenth lens. DETAILED DESCRIPTION
[0017] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention; that is, the described embodiments are merely some embodiments of the invention, and not all embodiments. The components of the embodiments of the invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.
[0018] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.
[0019] It should be noted that relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.
[0020] The features and performance of the present invention will be further described in detail below with reference to embodiments.
[0021] Example 1:
[0022] like Figures 1-5 As shown, the preferred embodiment of the present invention provides an optical system for a large aperture APS-C fixed focal length lens, including a first objective lens group GR1, a second objective lens group GR2, and a third objective lens group GR3. The first objective lens group GR1, the second objective lens group GR2, and the third objective lens group GR3 are arranged sequentially from the object side to the image side along the optical axis, and the aperture stop STOP is located in the third objective lens group GR3. During the focusing process, the second objective group GR2 moves along the optical axis to the object side, while the positions of the first objective group GR1, the aperture stop STOP, and the third objective group GR3 relative to the image plane remain unchanged. The optical system satisfies the following condition: 10.024≤|FG1 / F|≤12.134, 1.526≤|FG2 / F|≤2.134, 0.732≤FG3 / F≤1.134; Wherein, FGR1 represents the total focal length of the first objective group, FGR2 represents the total focal length of the second objective group, FGR3 represents the total focal length of the third objective group, and F represents the total focal length of the optical system.
[0023] The first objective group GR1 comprises a first lens 1, a second lens 2, a third lens 3, a fourth lens 4, and a fifth lens 5; the second lens 2 and the third lens 3 form a cemented lens, and the fourth lens 4 and the fifth lens 5 form a cemented lens. The second objective group GR2 comprises a sixth lens 6. The third lens group GR3 comprises an aperture stop STOP, a seventh lens 7, an eighth lens 8, a ninth lens 9, a tenth lens 10, an eleventh lens 11, a twelfth lens 12, a thirteenth lens 13, and a fourteenth lens 14; the eighth lens 8, the ninth lens 9, and the tenth lens 10 form a cemented lens, and the twelfth lens 12 and the thirteenth lens 13 form a cemented lens.
[0024] The first lens 1 and the fifth lens 5 are both meniscus negative lenses, and the first lens 1 and the fifth lens 5 satisfy the following conditional expression: 0.986≤Ф5 / Ф1≤1.214; Wherein, Ф1 is the optical power of the first lens 1, and Ф5 is the optical power of the fifth lens 5.
[0025] The second lens 2 is a negative lens and belongs to a double-concave lens; the third lens 3 is a positive lens and belongs to a double-convex lens; the second lens 2 and the third lens 3 form a cemented lens and satisfy the following conditional expression: 0.157<|ФGR1 / Ф23|<0.213; Wherein, ФGR1 is the optical power of the first objective group GR1, and Ф23 is the optical power of the cemented lens formed by the second lens 2 and the third lens 3.
[0026] The fourth lens 4 is a positive lens and belongs to a meniscus lens, both of whose spherical centers are on the object side, and forms a cemented lens with the fifth lens 5, which satisfies the following conditional expression: 0.648<|ФGR1 / Ф45|<0.762; Wherein, ФGR1 is the optical power of the first objective group GR1, and Ф45 is the optical power of the cemented lens formed by the fourth lens 4 and the fifth lens 5.
[0027] The sixth lens 6 is a negative lens and satisfies the following conditional expression: 1.699<|Ф / Ф6|<2.054; wherein Ф is the total optical power of the optical system, and Ф6 is the optical power of the sixth lens 6.
[0028] The seventh lens 7 is an aspherical lens, and the fourteenth lens 14 is an aspherical lens, satisfying the following conditional expressions: 1.524<|R141 / R71|<|R142 / R72|<2.045; wherein R71 is the object-side vertex curvature radius of the seventh lens 7, R72 is the image-side vertex curvature radius of the seventh lens 7, R141 is the object-side vertex curvature radius of the fourteenth lens 14, and R142 is the image-side vertex curvature radius of the fourteenth lens 14.
[0029] The eighth lens 8, the tenth lens 10, the eleventh lens 11, and the twelfth lens 12 are all positive lenses and belong to biconvex lenses, satisfying the following conditional expressions: N8=N10, 1.76<N12<N11<2.0007; wherein N8 is the refractive index of the eighth lens 8 with respect to D light, N10 is the refractive index of the tenth lens 10 with respect to D light, N11 is the refractive index of the eleventh lens 11 with respect to D light, and N12 is the refractive index of the twelfth lens 12 with respect to D light.
[0030] The ninth lens 9 and the thirteenth lens 13 are both negative lenses and belong to biconcave lenses, satisfying the following conditional expressions: 1.72<N13<N9<2.0007, V9<V13<35; wherein N9 is the refractive index of the ninth lens 9 with respect to D light, N13 is the refractive index of the thirteenth lens 13 with respect to D light, V9 is the Abbe number of the ninth lens 9 with respect to D light, and V13 is the Abbe number of the thirteenth lens 13 with respect to D light. Further, the twelfth lens 12 and the thirteenth lens 13 form a cemented lens, satisfying the following conditional expressions: 2.315<|ФGR3 / Ф1213|<2.551; wherein ФGR3 is the optical power of the third objective lens group GR3, and Ф1213 is the optical power of the cemented lens formed by the twelfth lens 12 and the thirteenth lens 13.
[0031] The eighth lens 8, the ninth lens 9, and the tenth lens 10 form a cemented lens, satisfying the following conditional expressions: 3.564<|ФGR3 / Ф8910|<3.842; Wherein, ΦGR3 is the optical power of the third objective group GR3, and Φ8910 is the optical power of the cemented lens composed of the eighth lens 8, the ninth lens 9 and the tenth lens 10.
[0032] In combination Figures 1-5 As shown in the figures, the optical system given in Embodiment 1 can achieve good imaging quality, and realizes high-performance design.
[0033] Table 1 shows the radius of curvature, thickness, refractive index and Abbe number of each lens of the optical system in the range of Embodiment 1; Table 2 shows the aspheric lens parameters; the position state of the second objective group when focusing at different shooting distances is shown in Table 3, corresponding to D1 and D2 in Table 1; the physical parameters of the optical system in the range of Embodiment 1 are shown in Table 4.
[0034] The radius of curvature column shows the radius of curvature of a certain lens, and the positive radius of curvature indicates that the surface is curved in the object side direction, and the negative radius of curvature indicates that the surface is curved in the image side direction; the thickness column shows the surface spacing on the optical axis between each surface and the surface adjacent to it on the image side; the refractive index column shows the refractive index of a certain lens; and the Abbe number column shows the Abbe number of a certain lens.
[0035] Table 1 - Parameters of each lens Surface number Radius of curvature Thickness / interval Refractive index Abbe number 1 77.128 1.500 1.8040 46.5745 2 26.018 7.155 3 -77.387 1.200 1.4875 70.4405 4 25.737 8.593 1.8830 39.2182 5 -90.762 3.201 6 -40.792 4.695 1.8830 40.8475 7 -22.354 1.200 1.6989 30.0505 8 -92.553 D1 9 -25.539 1.300 1.6204 60.3393 10 -293.723 D2 Stop Infinite 2.000 12* 41.323 8.871 1.8456 40.0943 13* -44.348 0.100 14 69.418 9.722 1.4970 81.6128 15 -24.175 1.200 1.8467 23.7845 16 27.743 7.667 1.4970 81.6128 17 -81.559 0.100 18 53.769 6.399 1.9460 17.9420 19 -50.693 0.100 20 71.420 7.475 1.8040 46.5745 21 -22.710 1.200 1.7408 27.7601 22 21.159 4.753 23* -66.668 2.000 1.8456 40.0943 24* -71.192 - Table 2 - Aspheric lens parameters 12 13 23 24 K -2.436781 -4.182355 28.58324 18.08421 A2 0 0 0 0 A4 -2.5442845E-06 6.9523868E-07 -4.5230881E-05 -1.9355785E-05 A6 -2.8513017E-10 -1.4852283E-09 -1.7359220E-07 -1.6914365E-07 A8 6.0230151E-11 2.9995189E-11 5.3698258E-09 6.5332950E-09 A10 -4.9357866E-13 -3.0414794E-13 -5.5430514E-11 -7.2925186E-11 A12 1.8610934E-15 1.2409000E-15 3.2088162E-13 4.6323164E-13 A14 -2.8070336E-18 -2.0976940E-18 -6.7576029E-16 -1.1603102E-15 A16 0 0 0 0 Table 3 - Position state of the second objective group Conjugate distance Infinity 0.25m D1 8.393 4.094 D2 2.755 7.054 Table 4 - Physical parameters of the optical system Focal length 25.62 Relative aperture F# 1.2 Field of view angle 2w 58.08° Optical total length 106.8 The present application achieves the purposes of optimizing the refraction and convergence of light, reducing aberration and improving imaging quality by setting the positive and negative optical powers of each lens group and the ratio between the synthetic focal length of each lens group and the synthetic focal length of the entire lens, and further makes the lens achieve higher image quality.
[0036] The above only describes the preferred embodiments of the present application and should not be used to limit the protection scope of the present application, and any modifications, equivalent replacements and improvements made by any person skilled in the art within the spirit and principles of the present application should be included in the protection scope of the present application.
Claims
1. An optical system of a large aperture half-frame fixed focus lens, characterized by: The optical system comprises a first objective group GR1, a second objective group GR2, and a third objective group GR3, the first objective group GR1, the second objective group GR2, and the third objective group GR3 are sequentially arranged along the optical axis direction from the object side to the image side, and the aperture stop STOP is located in the third objective group GR3; During the focusing process, the second objective group GR2 moves to the object side along the optical axis, and the first objective group GR1, the aperture stop STOP, and the third objective group GR3 remain unchanged relative to the image plane position; The optical system satisfies the following conditional expressions: 10.024≤|FG1 / F|≤12.134, 1.526≤|FG2 / F|≤2.134, 0.732≤FG3 / F≤1.134; Wherein, FGR1 represents the total focal length of the first objective group, FGR2 represents the total focal length of the second objective group, FGR3 represents the total focal length of the third objective group, and F represents the total focal length of the optical system.
2. The optical system of a large aperture half frame fixed focus lens according to claim 1, wherein: The first objective group GR1 comprises a first lens (1), a second lens (2), a third lens (3), a fourth lens (4), and a fifth lens (5); the second lens (2) and the third lens (3) form a cemented lens, and the fourth lens (4) and the fifth lens (5) form a cemented lens. The second objective group GR2 comprises a sixth lens (6). The third lens group GR3 comprises an aperture stop STOP, a seventh lens (7), an eighth lens (8), a ninth lens (9), a tenth lens (10), an eleventh lens (11), a twelfth lens (12), a thirteenth lens (13), and a fourteenth lens (14); the eighth lens (8), the ninth lens (9), and the tenth lens (10) form a cemented lens, and the twelfth lens (12) and the thirteenth lens (13) form a cemented lens.
3. The optical system of a large aperture half frame format fixed focus lens according to claim 2, characterized in that: The first lens (1) and the fifth lens (5) are both meniscus negative lenses, and the first lens (1) and the fifth lens (5) satisfy the following conditional expressions: 0.986≤Ф5 / Ф1≤1.214; Wherein, Ф1 is the optical power of the first lens (1), and Ф5 is the optical power of the fifth lens (5).
4. The optical system of a large aperture half frame format fixed focus lens according to claim 2, wherein: The second lens (2) is a negative lens and belongs to a double-concave lens; the third lens (3) is a positive lens and belongs to a double-convex lens; the second lens (2) and the third lens (3) form a cemented lens and satisfy the following conditional expressions: 0.157<|ФGR1 / Ф23|<0.213; Wherein, ФGR1 is the optical power of the first objective group GR1, and Ф23 is the optical power of the cemented lens formed by the second lens (2) and the third lens (3).
5. The optical system of a large aperture half frame format fixed focus lens according to claim 2, wherein: The fourth lens (4) is a positive lens and belongs to a meniscus lens, both of which are on the object side, and forms a cemented lens with the fifth lens (5) and satisfies the following conditional expressions: 0.648<|ФGR1 / Ф45|<0.762; Wherein, ФGR1 is the optical power of the first objective group GR1, and Ф45 is the optical power of the cemented lens formed by the fourth lens (4) and the fifth lens (5).
6. The optical system of a large-aperture half-frame fixed focus lens according to claim 2, wherein: The sixth lens (6) is a negative lens and satisfies the following conditional expressions: 1.699<|Ф / Ф6|<2.054; wherein Ф is the total optical power of the optical system, and Ф6 is the optical power of the sixth lens (6).
7. The optical system of a large aperture half frame format fixed focus lens according to claim 2, wherein: The seventh lens (7) is an aspherical lens, and the fourteenth lens (14) is an aspherical lens, satisfying the following conditional expressions: 1.524 < |R141 / R71| < |R142 / R72| < 2.045; wherein R71 is the object-side vertex curvature radius of the seventh lens (7), R72 is the image-side vertex curvature radius of the seventh lens (7), R141 is the object-side vertex curvature radius of the fourteenth lens (14), and R142 is the image-side vertex curvature radius of the fourteenth lens (14).
8. The optical system of a large aperture half frame format fixed focus lens according to claim 2, wherein: The eighth lens (8), the tenth lens (10), the eleventh lens (11), and the twelfth lens (12) are all positive lenses and belong to biconvex lenses, satisfying the following conditional expressions: N8 = N10, 1.76 < N12 < N11 < 2.0007; wherein N8 is the refractive index of the eighth lens (8) relative to D light, N10 is the refractive index of the tenth lens (10) relative to D light, N11 is the refractive index of the eleventh lens (11) relative to D light, and N12 is the refractive index of the twelfth lens (12) relative to D light.
9. The optical system of a large-aperture half-frame fixed focus lens according to claim 8, characterized in that: The ninth lens (9) and the thirteenth lens (13) are both negative lenses and belong to biconcave lenses, satisfying the following conditional expressions: 1.72 < N13 < N9 < 2.0007, V9 < V13 < 35; wherein N9 is the refractive index of the ninth lens (9) relative to D light, N13 is the refractive index of the thirteenth lens (13) relative to D light, V9 is the Abbe number of the ninth lens (9) relative to D light, and V13 is the Abbe number of the thirteenth lens (13) relative to D light; and the twelfth lens (12) and the thirteenth lens (13) form a cemented lens, satisfying the following conditional expressions: 2.315 < |ФGR3 / Ф1213| < 2.551; wherein ФGR3 is the optical power of the third objective lens group GR3, and Ф1213 is the optical power of the cemented lens formed by the twelfth lens (12) and the thirteenth lens (13).
10. The optical system of a large aperture half frame format fixed focus lens according to claim 2, wherein: The eighth lens (8), the ninth lens (9), and the tenth lens (10) form a cemented lens, satisfying the following conditional expressions: 3.564 < |ФGR3 / Ф8910| < 3.842; wherein ФGR3 is the optical power of the third objective lens group GR3, and Ф8910 is the optical power of the cemented lens formed by the eighth lens (8), the ninth lens (9), and the tenth lens (10).