Medium-long-focus fixed-focus photographic lens

Abstract

The invention discloses a medium-long-focus fixed-focus photographic lens. The medium-long-focus fixed-focus photographic lens sequentially comprises a first lens group with positive focal power, an aperture diaphragm, a second lens group with negative focal power and a third lens group with positive focal power from an object side to an image side, in the focusing process, the second lens group moves towards the image side along the optical axis, and the first lens group and the third lens group remain unchanged relative to the position of the image plane. The medium-long fixed-focus photographic lens satisfies the following conditional expressions: F1 / F is greater than or equal to 0.55 and less than or equal to 0.75, (1); -0.65 < = F2 / F < =-0.5, (2); 0.8 < = F3 / F < = 1.304, (3); (4) 0.95 < = F / L < = 1.3; 0.7 < = F21 / F2 < = 1.3 (5). According to the technical scheme, the medium-long-focus fixed-focus photographic lens with a telephoto lens structure is formed through configuration and combination of the lens groups with different focal powers, and the conditional expression met by the medium-long-focus fixed-focus photographic lens is further given, so that a more compact structural design is achieved under the condition that high imaging performance is kept.

Description

Technical Field

[0001] The present application relates to the field of camera technology, and in particular to a medium-long focal length fixed-focus camera lens. Background Art

[0002] The emergence of micro-single cameras has made lightweight lenses the mainstream in the photography market. There are many telephoto lenses on the market, but most of them are large and heavy, which is not conducive to outdoor shooting; while lightweight lenses cannot maintain high imaging effects, seriously affecting the photography experience. As a result, due to the imbalance between volume, quality and imaging effects, users are in a difficult situation when choosing lenses. Summary of the invention

[0003] The present application provides a medium-to-long focal length fixed-focus photographic lens, which aims to solve the problem that existing long focal length lenses are difficult to achieve a balance between lens volume quality and imaging effect.

[0004] To achieve the above-mentioned purpose, the present application provides a medium-long focal length fixed-focus photography lens. The medium-long focal length fixed-focus photography lens comprises, from the object side to the image side, a first lens group with positive focal power, an aperture stop, a second lens group with negative focal power, and a third lens group with positive focal power; during the focusing process, the second lens group moves along the optical axis toward the image side, and the first lens group and the third lens group remain unchanged relative to the image plane; The medium-long focal length fixed focus photography lens meets the following conditions: 0.55≤F1 / F≤0.75, (1); -0.65≤F2 / F≤-0.5, (2); 0.8≤F3 / F≤1.304, (3); 0.95≤F / L≤1.3, (4); 0.7≤|F21 / F2|≤1.3, (5); Among them, F1 represents the composite focal length of the first lens group, F2 represents the composite focal length of the second lens group, F21 represents the focal length of the lens adjacent to the aperture stop in the second lens group, F3 represents the composite focal length of the third lens group, L represents the distance from the object side vertex of the first lens in the lens system to the image plane, and F represents the focal length of the photographic lens.

[0005] In some embodiments, the first lens group includes, from the object side to the image side, a first lens having positive power, a second lens having positive power, a third lens having positive power, a fourth lens having negative power, and a fifth lens having positive power; Wherein, the second lens, the third lens and the fifth lens are all anomalous dispersion lenses, and the third lens and the fourth lens are combined into a first cemented lens.

[0006] In some embodiments, the third lens and the fourth lens satisfy the conditional formula: |Vd3-Vd4|≥30, (6); Wherein, Vd3 is the Abbe number of the third lens in the first lens group with respect to the light with a wavelength of 587.6 nm; Vd4 is the Abbe number of the fourth lens in the first lens group with respect to the light with a wavelength of 587.6 nm.

[0007] In some embodiments, both side surfaces of the first lens and the second lens are spherical surfaces convex toward the object side, and the focal length of the first lens and the focal length of the second lens satisfy the conditional formula: 0.8≤fs1 / fs2≤1.2, (7); Wherein, fs1 is the focal length of the first lens, and fs2 is the focal length of the second lens.

[0008] In some embodiments, the second lens group includes, from the object side to the image side, a sixth lens having negative refractive power and a seventh lens having positive refractive power.

[0009] In some embodiments, the second lens group includes, from the object side to the image side, a sixth lens with negative optical power, a seventh lens with negative optical power, and an eighth lens with positive optical power; wherein the seventh lens and the eighth lens are combined into a second cemented lens.

[0010] In some embodiments, the Abbe number Vd6 of the sixth lens in the second lens group is ≤35.

[0011] In some embodiments, the third lens group includes at least one biconvex lens and one lens with negative optical power from the object side to the image side.

[0012] In some embodiments, the third lens group includes, from the object side to the image side, a ninth lens having positive power and a tenth lens having negative power, the ninth lens being a biconvex lens, and the tenth lens being bent toward the object side; or, The third lens group includes, from the object side to the image side, a ninth lens having positive optical power, a tenth lens having positive optical power, and an eleventh lens having negative optical power, wherein the ninth lens and the tenth lens are both biconvex lenses, and the eleventh lens is a biconcave lens.

[0013] In some embodiments, the refractive index Nd of the lens with negative optical power in the third lens group is ≥ 1.8.

[0014] The technical solution of the present application proposes a medium-long focal length fixed-focus photographic lens. The medium-long focal length fixed-focus photographic lens includes, from the object side to the image side, a first lens group with positive focal length, an aperture stop, a second lens group with negative focal length, and a third lens group with positive focal length; during the focusing process, the second lens group moves along the optical axis toward the image side, and the positions of the first lens group and the third lens group relative to the image plane remain unchanged; and the medium-long focal length fixed-focus photographic lens satisfies the following conditional formulas: 0.55≤F1 / F≤0.75, (1); -0.65≤F2 / F≤-0.5, (2); 2); 0.8≤F3 / F≤1.304, (3); 0.95≤F / L≤1.3, (4); 0.7≤|F21 / F2|≤1.3, (5); wherein, F1 represents the composite focal length of the first lens group, F2 represents the composite focal length of the second lens group, F21 is the focal length of the lens adjacent to the aperture stop in the second lens group, F3 represents the composite focal length of the third lens group, L is the distance from the object side vertex of the first lens in the lens system to the image plane, and F represents the focal length of the photographic lens. The technical solution of the present application forms a medium-long focal fixed-focus photographic lens with a telephoto lens structure by configuring and combining lens groups with different optical focal powers, and further provides a conditional formula satisfied by the medium-long focal fixed-focus photographic lens to achieve a more compact structural design while maintaining high imaging performance. BRIEF DESCRIPTION OF THE DRAWINGS In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the prior art descriptions are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative work, among which: Figure 1 A schematic diagram showing the structure of Embodiment 1 of the present invention is shown; Figure 2 A schematic diagram showing spherical aberration of Embodiment 1 of the present invention when in focus at infinity is shown; Figure 3 A schematic diagram showing field curvature and distortion of embodiment 1 of the present invention when focusing at infinity is shown; Figure 4 A schematic diagram showing spherical aberration of Embodiment 1 of the present invention at the minimum focusing distance is shown; Figure 5 A schematic diagram showing field curvature and distortion of Embodiment 1 of the present invention at the closest focusing distance is shown; Figure 6 A schematic diagram showing the structure of Embodiment 2 of the present invention is shown; Figure 7 A schematic diagram showing spherical aberration of Embodiment 2 of the present invention when in focus at infinity; Figure 8A schematic diagram showing field curvature and distortion of Embodiment 2 of the present invention when focusing at infinity; Fig. 9 A schematic diagram showing spherical aberration of Embodiment 2 of the present invention at the closest focusing distance is shown; Fig.10 A schematic diagram showing field curvature and distortion of Embodiment 2 of the present invention at the closest focusing distance is shown; Fig.11 A schematic diagram showing the structure of Embodiment 3 of the present invention is shown; Fig.12 A schematic diagram showing spherical aberration of Embodiment 3 of the present invention when in focus at infinity is shown; Fig.13 A schematic diagram showing field curvature and distortion of embodiment 3 of the present invention when in focus at infinity is shown; Fig.14 A schematic diagram showing spherical aberration of Embodiment 3 of the present invention at the closest focusing distance is shown; Fig.15 A schematic diagram showing field curvature and distortion of embodiment 3 of the present invention at the closest focusing distance is shown. DETAILED DESCRIPTION

[0015] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0016] See also Figure 1 As shown, the present application provides a medium-long focal length fixed-focus photography lens. The medium-long focal length fixed-focus photography lens includes, from the object side to the image side, a first lens group G1 with positive focal length, an aperture stop STP, a second lens group G2 with negative focal length, and a third lens group G3 with positive focal length; during the focusing process, the second lens group G2 moves along the optical axis toward the image side, and the first lens group G1 and the third lens group G3 remain unchanged relative to the image plane; The medium-long focal length fixed focus photography lens meets the following conditions: 0.55≤F1 / F≤0.75, (1); -0.65≤F2 / F≤-0.5, (2); 0.8≤F3 / F≤1.304, (3); 0.95≤F / L≤1.3, (4); 0.7≤|F21 / F2|≤1.3, (5); Among them, F1 represents the composite focal length of the first lens group G1, F2 represents the composite focal length of the second lens group G2, F21 is the focal length of the lens adjacent to the aperture stop STP in the second lens group G2, F3 represents the composite focal length of the third lens group G3, L is the distance from the object side vertex of the first lens in the lens system to the image plane, and F represents the focal length of the photographic lens.

[0017] The technical solution of the present application configures lens groups with different optical focal lengths and limits the divergence and convergence capabilities of each lens group on light through conditional expressions, so that the refraction and focusing of light can be effectively controlled when the light passes through each lens group, thereby achieving high-quality imaging. In particular, conditional expression (5) proposes a ratio range between the focal length of the lens adjacent to the aperture stop STP in the second lens group G2 and the synthetic focal length of the second lens group G2, which helps to optimize the optical design in the second lens group G2 and improve the lens aberration correction capability.

[0018] Furthermore, the miniaturization of the medium-long focal length fixed-focus photography lens is achieved through conditional expressions. Among them, conditional expression (1) indicates that the first lens group G1 occupies a large proportion of the total focal length of the photography lens, thereby reducing the length of the rear lens group; and conditional expression (4) limits the ratio of the focal length of the lens to the distance from the object side vertex of the first lens in the lens system to the image plane. A smaller ratio makes the lens more compact, which is conducive to the miniaturization design of the lens.

[0019] In some embodiments, the first lens group G1 includes, from the object side to the image side, a first lens L01 with positive power, a second lens L02 with positive power, a third lens L03 with positive power, a fourth lens L04 with negative power, and a fifth lens L05 with positive power; wherein the second lens L02, the third lens L03, and the fifth lens L05 are all anomalous dispersion lenses, and the third lens L03 and the fourth lens L04 are combined into a first cemented lens.

[0020] In this embodiment, a specific lens configuration of the first lens group G1 is proposed, and its positive-positive-positive-negative-positive optical power combination helps to control the refraction and focusing of light to form a clear image.

[0021] Among them, the second lens L02, the third lens L03 and the fifth lens L05 are all set as anomalous dispersion lenses, which can effectively correct the chromatic aberration in the medium-telephoto photography lens based on the different refractive powers of the anomalous dispersion lenses to light of different wavelengths. The third lens L03 and the fourth lens L04 are further combined into a first cemented lens; the cemented lens can simplify the lens structure to reduce weight, and because different lens materials in the cemented lens have different dispersion characteristics, it can also correct chromatic aberration.

[0022] Therefore, the anomalous dispersion lens and the cemented lens are simultaneously provided in the first lens group G1, and their cooperation can more effectively reduce the influence of chromatic aberration in the medium-to-telephoto photography lens.

[0023] Furthermore, the third lens L03 and the fourth lens L04 satisfy the conditional formula: |Vd3-Vd4|≥30, (6); Wherein, Vd3 is the Abbe number of the third lens L03 in the first lens group G1 with respect to the light with a wavelength of 587.6 nm; Vd4 is the Abbe number of the fourth lens L04 in the first lens group G1 with respect to the light with a wavelength of 587.6 nm.

[0024] Thus, the conditional expression (6) specifies that the difference (absolute value) between the Abbe numbers of the third lens L03 and the fourth lens L04 must be greater than or equal to 30. The dispersion characteristics of different lens materials are used to complement each other to more effectively correct chromatic aberration and improve image quality.

[0025] In some embodiments, both side surfaces of the first lens L01 and the second lens L02 are spherical surfaces convex toward the object side, and the focal length of the first lens L01 and the focal length of the second lens L02 satisfy the conditional formula: 0.8≤fs1 / fs2≤1.2, (7); Wherein, fs1 is the focal length of the first lens L01, and fs2 is the focal length of the second lens L02.

[0026] In this embodiment, conditional formula (7) limits the ratio of the focal length of the first lens L01 to the focal length of the second lens L02 to be close, which can avoid fluctuations in imaging quality caused by excessive focal length differences. In addition, both side surfaces of the first lens L01 and the second lens L02 are spherical surfaces convex to the object side, which can better control the incident and refractive power of light, reduce light scattering and aberrations, and improve the clarity and stability of imaging.

[0027] In some embodiments, the second lens group G2 includes, from the object side to the image side, a sixth lens L06 with negative power and a seventh lens L07 with positive power. Alternatively, in some embodiments, the second lens group G2 includes, from the object side to the image side, a sixth lens L06 with negative power, a seventh lens L07 with negative power and an eighth lens L08 with positive power; wherein the seventh lens L07 and the eighth lens L08 are combined into a second cemented lens.

[0028] In this embodiment, two specific lens configurations of the second lens group G2 are proposed. In these two lens configurations, the number of lenses included in the second lens group G2 does not exceed 3, thereby reducing the complexity and manufacturing cost of the second lens group G2, realizing a lightweight design of the second lens group G2, and further realizing fast focusing during the focusing process. In addition, each lens configuration involves a combination of positive and negative optical power lenses, so as to better control the propagation path of light, reduce the scattering and reflection of light in the second lens group G2, optimize the imaging quality, and improve the clarity and contrast of the image.

[0029] In one of the lens configurations, a second cemented lens is further provided to replace the single lens. Compared with the single lens, the cemented lens is more stable and can further reduce chromatic aberration and aberration, thereby improving the imaging quality.

[0030] Furthermore, the Abbe number Vd6 of the sixth lens L06 in the second lens group G2 is ≤35.

[0031] In this embodiment, the Abbe number Vd6 of the sixth lens L06 is ≤35, which is a low Abbe number lens. Although a low Abbe number means that the dispersion ability of the lens is relatively weak, at the same time, the manufacturing cost of the low Abbe number lens is low. In this embodiment, the sixth lens L06 can be matched with a high refractive index lens to effectively control chromatic aberration, and balance and optimize optical performance and manufacturing cost.

[0032] In some embodiments, the third lens group G3 includes at least one biconvex lens and one lens with negative optical power in sequence from the object side to the image side.

[0033] In this embodiment, the lens of the third lens group G3 disposed near the object side is a biconvex lens, which has a strong light convergence ability and can effectively converge the light onto the image plane. Further disposing a lens with negative optical power can correct the residual aberration generated by the front lens, further improving the clarity and color reproduction of the image.

[0034] In some embodiments, the third lens group G3 includes, from the object side to the image side, a ninth lens L09 with positive power and a tenth lens L10 with negative power, the ninth lens L09 is a biconvex lens, and the tenth lens L10 is bent toward the object side; or, the third lens group G3 includes, from the object side to the image side, a ninth lens L09 with positive power, a tenth lens L10 with positive power, and an eleventh lens L11 with negative power, the ninth lens L09 and the tenth lens L10 are both biconvex lenses, and the eleventh lens L11 is a biconcave lens.

[0035] This embodiment proposes two specific lens configurations of the third lens group G3. Whether a combination of two lenses or a combination of three lenses is used, the purpose is to correct aberrations and improve imaging clarity and color reproduction by precisely controlling the refraction and reflection of light.

[0036] Among them, in the first lens configuration, the double convex lens can enhance the ability to converge light and help focus the light onto the image plane, while the tenth lens L10 bent toward the object side can correct the over-convergence effect formed in the system, thereby helping to control the focal length and aberration of the imaging.

[0037] In the second lens configuration, the two biconvex lenses further enhance the ability to converge light, allowing for a smaller focal length and a larger aperture, helping to overcome the problem of light divergence caused by wide-angle shooting and improve image clarity and contrast. The biconcave lens has a stronger ability to diverge light and is also used to correct the over-convergence effect, balance optical performance, and improve image quality.

[0038] In some embodiments, the refractive index Nd of the lens with negative power in the third lens group G3 is ≥ 1.8.

[0039] That is, when the third lens group G3 is configured to include, in order from the object side to the image side, a ninth lens L09 having positive power and a tenth lens L10 having negative power, the refractive index Nd10 of the tenth lens L10 is ≥ 1.8. Or when the third lens group G3 is configured to include, in order from the object side to the image side, a ninth lens L09 having positive power, a tenth lens L10 having positive power and an eleventh lens L11 having negative power, the refractive index Nd11 of the eleventh lens L11 is ≥ 1.8.

[0040] In this embodiment, a negative optical focal length lens with a high refractive index can more strongly diverge light, thereby playing a better correction role in the optical system and improving the imaging quality.

[0041] In the present application, a parallel glass plate GL configured by a filter is arranged between the last lens of the third lens group G3 and the image plane IMG. The parallel glass plate GL is used to filter light to improve the image quality. Specifically, the parallel glass plate GL can absorb or reflect light of certain wavelengths to eliminate or reduce interference factors such as chromatic aberration and stray light, thereby improving the contrast and clarity of the image.

[0042] Example 1 Figure 1 FIG. 1 is a schematic diagram of the structure of a medium-long focal length fixed-focus photographic lens according to Embodiment 1. Figure 1As shown, in this embodiment, the first lens group G1 includes, from the object side to the image side, a first lens L01 with positive power, a second lens L02 with positive power, a third lens L03 with positive power, a fourth lens L04 with negative power, and a fifth lens L05 with positive power; wherein the second lens L02, the third lens L03, and the fifth lens L05 are all anomalous dispersion lenses, and the third lens L03 and the fourth lens L04 are combined into a first cemented lens. The second lens group G2 includes, from the object side to the image side, a sixth lens L06 with negative power, a seventh lens L07 with negative power, and an eighth lens L08 with positive power; wherein the Abbe number Vd6 of the sixth lens L06 is 29.507, and the seventh lens L07 and the eighth lens L08 are combined into a second cemented lens. The third lens group G3 includes, from the object side to the image side, a ninth lens L09 with positive refractive power and a tenth lens L10 with negative refractive power, the ninth lens L09 is a biconvex lens, the tenth lens L10 is bent toward the object side, and the refractive index Nd10 of the tenth lens L10 is 1.8467.

[0043] In this embodiment, the numerical data of the medium-long focal length fixed-focus photographic lens are shown in Table 1 and Table 2: Table 1

[0044] Table 2

[0045] The surface number indicates the surface number of each lens from the object side to the image side.

[0046] Figure 2 and Figure 3 The spherical aberration, field curvature and distortion curves of Example 1 when the image is in focus at infinity are shown. Figure 4 and Figure 5 The spherical aberration, field curvature and distortion curves of Example 1 when the lens is in focus at the closest distance are shown.

[0047] The spherical aberration curve shows the spherical aberration curve when the aperture number is 2.09, where the F line, D line, and C line represent the spherical aberration at a wavelength of 486nm, a wavelength of 587nm, and a wavelength of 656nm, respectively. The horizontal axis represents the spherical aberration value, and the vertical axis represents the field of view. When the focus is infinity, the field curvature curve shows the field curvature curve when the half field angle ω is 14.5°, where the dotted line S represents the value of the chief ray D line on the sagittal image plane, the solid line T represents the value of the chief ray D line on the meridional image plane, the horizontal axis represents the field curvature value, and the vertical axis represents the field of view; the distortion curve shows the distortion curve when the half field angle ω is 14.5°, where the horizontal axis represents the distortion value, and the vertical axis represents the field of view. When focusing at the minimum distance, the field curvature curve graph represents the field curvature curve when the half field angle ω is 12.4°, wherein the dotted line S represents the value of the chief ray D on the sagittal image plane, the solid line T represents the value of the chief ray D on the meridian image plane, the abscissa represents the field curvature value, and the ordinate represents the field of view; the distortion curve graph represents the distortion curve when the half field angle ω is 12.4°, wherein the abscissa represents the distortion value, and the ordinate represents the field of view.

[0048] Depend on Figure 2-Figure 5 It can be seen from the figure that the photographic lens of this embodiment 1 has a good imaging effect.

[0049] Example 2 Figure 6 FIG. 2 is a schematic diagram of the structure of a medium-long focal length fixed-focus photographic lens according to Embodiment 2. Figure 6 As shown, in this embodiment, the first lens group G1 includes, from the object side to the image side, a first lens L01 with positive power, a second lens L02 with positive power, a third lens L03 with positive power, a fourth lens L04 with negative power, and a fifth lens L05 with positive power; wherein the second lens L02, the third lens L03, and the fifth lens L05 are all anomalous dispersion lenses, and the third lens L03 and the fourth lens L04 are combined into a first cemented lens. The second lens group G2 includes, from the object side to the image side, a sixth lens L06 with negative power, a seventh lens L07 with negative power, and an eighth lens L08 with positive power; wherein the Abbe number Vd6 of the sixth lens L06 is 29.507, and the seventh lens L07 and the eighth lens L08 are combined into a second cemented lens. The third lens group G3 includes, from the object side to the image side, a ninth lens L09 with positive refractive power and a tenth lens L10 with negative refractive power, the ninth lens L09 is a biconvex lens, the tenth lens L10 is curved toward the object side, and the refractive index Nd10 of the tenth lens L10 is 1.8467. This embodiment is different from Embodiment 1 only in the data of some lenses.

[0050] In this embodiment, the numerical data of the medium-long focal length fixed-focus photographic lens are shown in Table 3 and Table 4: Table 3

[0051] Table 4

[0052] Figure 7 and Figure 8 The spherical aberration, field curvature and distortion curves of Example 2 when in focus at infinity are shown. Fig. 9 and Fig.10 The spherical aberration, field curvature and distortion curves of Example 2 are shown when the image is in focus at the closest distance.

[0053] The spherical aberration curve shows the spherical aberration curve when the aperture number is 2.26, where the F line, D line, and C line represent the spherical aberration at a wavelength of 486nm, a wavelength of 587nm, and a wavelength of 656nm, respectively. The horizontal axis represents the spherical aberration value, and the vertical axis represents the field of view. When the focus is infinity, the field curvature curve shows the field curvature curve when the half field angle ω is 9.3°, where the dotted line S represents the value of the chief ray D line on the sagittal image plane, the solid line T represents the value of the chief ray D line on the meridional image plane, the horizontal axis represents the field curvature value, and the vertical axis represents the field of view; the distortion curve shows the distortion curve when the half field angle ω is 9.3°, where the horizontal axis represents the distortion value, and the vertical axis represents the field of view. When focusing at the minimum distance, the field curvature curve graph represents the field curvature curve when the half field angle ω is 7.8°, wherein the dotted line S represents the value of the chief ray D on the sagittal image plane, the solid line T represents the value of the chief ray D on the meridional image plane, the abscissa represents the field curvature value, and the ordinate represents the field of view; the distortion curve graph represents the distortion curve when the half field angle ω is 7.8°, wherein the abscissa represents the distortion value, and the ordinate represents the field of view.

[0054] Depend on Figure 7-Figure 10 It can be seen from the figure that the photographic lens of the second embodiment has a good imaging effect.

[0055] Example 3 Fig.11 FIG. 1 is a schematic diagram of the structure of a medium-long focal length fixed-focus photographic lens according to Embodiment 3. Fig.11As shown, in this embodiment, the first lens group G1 includes, from the object side to the image side, a first lens L01 with positive power, a second lens L02 with positive power, a third lens L03 with positive power, a fourth lens L04 with negative power, and a fifth lens L05 with positive power; wherein the second lens L02, the third lens L03, and the fifth lens L05 are all anomalous dispersion lenses, and the third lens L03 and the fourth lens L04 are combined into a first cemented lens. The second lens group G2 includes, from the object side to the image side, a sixth lens L06 with negative power, a seventh lens L07 with negative power, and an eighth lens L08 with positive power; wherein the Abbe number Vd6 of the sixth lens L06 is 29.507, and the seventh lens L07 and the eighth lens L08 are combined into a second cemented lens. The third lens group G3 includes, from the object side to the image side, a ninth lens L09 having positive refractive power, a tenth lens L10 having positive refractive power, and an eleventh lens L11 having negative refractive power. The ninth lens L09 and the tenth lens L10 are both biconvex lenses, the eleventh lens L11 is a biconcave lens, and the refractive index Nd11 of the eleventh lens L11 is 1.8467.

[0056] In this embodiment, the numerical data of the medium-long focal length fixed-focus photographic lens are shown in Table 5 and Table 6: Table 5

[0057] Table 6

[0058] Fig.12 and Fig.13 The spherical aberration, field curvature and distortion curves of Example 3 when in infinity focus are shown. Fig.14 and Fig.15 The spherical aberration, field curvature and distortion curves of Example 3 are shown when the image is in focus at the closest distance.

[0059] The spherical aberration curve shows the spherical aberration curve when the aperture number is 1.88, where the F line, D line, and C line represent the spherical aberration at a wavelength of 486nm, a wavelength of 587nm, and a wavelength of 656nm, respectively. The horizontal axis represents the spherical aberration value, and the vertical axis represents the field of view. When the focus is infinity, the field curvature curve shows the field curvature curve when the half field angle ω is 10.7°, where the dotted line S represents the value of the chief ray D line on the sagittal image plane, the solid line T represents the value of the chief ray D line on the meridional image plane, the horizontal axis represents the field curvature value, and the vertical axis represents the field of view; the distortion curve shows the distortion curve when the half field angle ω is 10.7°, where the horizontal axis represents the distortion value, and the vertical axis represents the field of view. When focusing at the minimum distance, the field curvature curve graph represents the field curvature curve when the half field angle ω is 9.0°, wherein the dotted line S represents the value of the chief ray D on the sagittal image plane, the solid line T represents the value of the chief ray D on the meridional image plane, the abscissa represents the field curvature value, and the ordinate represents the field of view; the distortion curve graph represents the distortion curve when the half field angle ω is 9.0°, wherein the abscissa represents the distortion value, and the ordinate represents the field of view.

[0060] Depend on Figure 12-Figure 15 It can be seen from the figure that the photographic lens of the present embodiment 3 has a good imaging effect.

[0061] The above description is only a partial or preferred embodiment of the present application. Neither the text nor the drawings can limit the scope of protection of the present application. All equivalent structural changes made using the contents of the present application specification and drawings under the overall concept of the present application, or direct / indirect application in other related technical fields are included in the scope of protection of the present application.

Claims

1. A medium-long focal length fixed-focus photographic lens, characterized in that: The lens system includes, from the object side to the image side, a first lens group with positive power, an aperture stop, a second lens group with negative power, and a third lens group with positive power; during the focusing process, the second lens group moves along the optical axis toward the image side, and the positions of the first lens group and the third lens group relative to the image plane remain unchanged; The medium-long focal length fixed focus photography lens meets the following conditions: 0.55≤F1 / F≤0.75, (1); -0.65≤F2 / F≤-0.5, (2); 0.8≤F3 / F≤1.304, (3); 0.95≤F / L≤1.3, (4); 0.7≤|F21 / F2|≤1.3, (5); Among them, F1 represents the composite focal length of the first lens group, F2 represents the composite focal length of the second lens group, F21 represents the focal length of the lens adjacent to the aperture stop in the second lens group, F3 represents the composite focal length of the third lens group, L represents the distance from the object side vertex of the first lens in the lens system to the image plane, and F represents the focal length of the photographic lens.

2. The medium-long focal length fixed focus photographic lens according to claim 1, characterized in that: The first lens group includes, from the object side to the image side, a first lens with positive refractive power, a second lens with positive refractive power, a third lens with positive refractive power, a fourth lens with negative refractive power, and a fifth lens with positive refractive power; Wherein, the second lens, the third lens and the fifth lens are all anomalous dispersion lenses, and the third lens and the fourth lens are combined into a first cemented lens.

3. The medium-long focal length fixed focus photographic lens according to claim 2, characterized in that: The third lens and the fourth lens satisfy the conditional formula: |Vd3-Vd4|≥30, (6); Wherein, Vd3 is the Abbe number of the third lens in the first lens group with respect to the light with a wavelength of 587.6 nm; Vd4 is the Abbe number of the fourth lens in the first lens group with respect to the light with a wavelength of 587.6 nm.

4. The medium-long focal length fixed focus photographic lens according to claim 2, characterized in that: Both side surfaces of the first lens and the second lens are spherical surfaces convex toward the object side, and the focal length of the first lens and the focal length of the second lens satisfy the conditional formula: 0.8≤fs1 / fs2≤1.2, (7); Wherein, fs1 is the focal length of the first lens, and fs2 is the focal length of the second lens.

5. The medium-long focal length fixed focus photographic lens according to any one of claims 1 to 4, characterized in that: The second lens group includes, from the object side to the image side, a sixth lens having negative refractive power and a seventh lens having positive refractive power.

6. The medium-long focal length fixed focus photographic lens according to any one of claims 1 to 4, characterized in that: The second lens group includes, from the object side to the image side, a sixth lens with negative optical power, a seventh lens with negative optical power and an eighth lens with positive optical power; wherein the seventh lens and the eighth lens are combined into a second cemented lens.

7. The medium-long focal length fixed-focus photographic lens according to claim 6, characterized in that: The Abbe number Vd6 of the sixth lens in the second lens group is ≤35.

8. The medium-long focal length fixed focus photographic lens according to any one of claims 1 to 4, characterized in that: The third lens group includes at least one biconvex lens and one lens with negative optical power in sequence from the object side to the image side.

9. The medium-long focal length fixed focus photography lens according to claim 8, characterized in that: The third lens group includes, from the object side to the image side, a ninth lens having positive power and a tenth lens having negative power, wherein the ninth lens is a biconvex lens, and the tenth lens is bent toward the object side; or, The third lens group includes, from the object side to the image side, a ninth lens having positive optical power, a tenth lens having positive optical power, and an eleventh lens having negative optical power, wherein the ninth lens and the tenth lens are both biconvex lenses, and the eleventh lens is a biconcave lens.

10. The medium-long focal length fixed focus photography lens according to claim 9, characterized in that: The refractive index Nd of the lens with negative power in the third lens group is ≥1.8.

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