Optical imaging system

Abstract

The invention discloses an optical imaging system which comprises a lens front group, a lens focusing group and a lens rear group which are sequentially arranged from the object side to the image side in the extension direction of an optical axis. The lens front group comprises a first lens with negative focal power, a second lens with positive focal power, a third lens with positive focal power, a fourth lens with negative focal power and an aspheric fifth lens, the first lens, the second lens, the third lens, the fourth lens and the fifth lens are sequentially arranged from the object side to the image side, and the lens front group meets the following conditions:-1.8 lt; fa1 / Flt; and-0.8; wherein Fa1 is the focal length of the first lens; and F is the focal length when the optical imaging system is focused infinitely. Compared with the prior art, the optical system has the advantages that the structure is compact, the size is small, the full field angle changes slightly when the focusing group moves, the optical distortion in all the focusing distance ranges is smaller than 1%, the clear aperture is larger, and high-quality optical performance is provided.

Description

Technical Field

[0001] The present invention relates to the technical field of optical imaging, and particularly to an optical imaging system. Background Art

[0002] In the prior art, with the improvement of photographic equipment and technology level, people's requirements for the optical image quality of interchangeable lenses of cameras are getting higher and higher, and they are more pursuing lenses with small size and light weight. In practical applications, lighter lenses are more conducive to being held by a gimbal or carried by a drone for shooting. However, at present, interchangeable lenses for full-frame cameras with large apertures and high image quality have problems of large volume and weight. Specifically, the change in the full field of view during the movement of the focusing group is too large, and the optical distortion is too large when the shooting distance is relatively short, which cannot meet the application requirements of miniaturized photographic equipment. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide an optical imaging system with higher optical quality, smaller volume and weight, smaller change in the field of view at different focusing positions, and capable of avoiding the visual stretching effect caused by the change in the focal point position, aiming at the deficiencies of the prior art.

[0004] To solve the above technical problem, the present invention adopts the following technical solutions.

[0005] An optical imaging system includes a front lens group, a focusing lens group, and a rear lens group. The front lens group, the focusing lens group, and the rear lens group are sequentially arranged from the object side to the image side along the extension direction of the optical axis. The front lens group includes a first lens with negative optical power, a second lens with positive optical power, a third lens with positive optical power, a fourth lens with negative optical power, and an aspherical fifth lens. The first lens, the second lens, the third lens, the fourth lens, and the fifth lens are sequentially arranged from the object side to the image side. The front lens group satisfies: -1.8 < Fa1 / F < -0.8; where Fa1 is the focal length of the first lens; F is the focal length of the optical imaging system when focused at infinity.

[0006] Preferably, the third lens and the fourth lens form a cemented lens group.

[0007] Preferably, the front lens group satisfies: 20 < Cr3*(Vd3 / Vd4) < 70; where Cr3 is the curvature radius of the surface of the third lens close to the image side; Vd3 is the dispersion coefficient of the third lens at a wavelength of 587.6 nm; Vd4 is the dispersion coefficient of the fourth lens at a wavelength of 587.6 nm.

[0008] Preferably, the lens focusing group includes a sixth lens with a positive optical power, a seventh lens with a negative optical power, and an eighth lens with a positive optical power, and the sixth lens, the seventh lens, and the eighth lens are arranged in sequence from the object side to the image side.

[0009] Preferably, the lens focusing group includes a sixth lens with a negative optical power, a seventh lens with a positive optical power, and an eighth lens with a positive optical power, and the sixth lens, the seventh lens, and the eighth lens are arranged in sequence from the object side to the image side.

[0010] Preferably, the lens focusing group satisfies: |(ET5 - CT5) / CT5| < 0.3; where ET5 is the distance in the optical axis direction of the marginal aperture light of the central field of view passing through the front and rear surfaces of the fifth lens when the optical imaging system has the maximum aperture, and CT5 is the distance in the optical axis direction of the central aperture light of the central field of view passing through the front and rear surfaces of the fifth lens when the optical imaging system has the maximum aperture.

[0011] Preferably, the lens focusing group satisfies: 15 ≤ Fgf / DA ≤ 25; where DA is the moving distance of the lens focusing group when the optical imaging system focuses from infinity to a magnification of 0.05 times, and Fgf is the combined focal length of the lens focusing group.

[0012] Preferably, the lens focusing group satisfies: 0.7 < Fgf / F < 1.1.

[0013] Preferably, the optical imaging system satisfies: 0.6 < Fz25 / Fz69 < 1.1; where Fz25 is the combined focal length of the second lens, the third lens, the fourth lens, and the fifth lens, and Fz69 is the combined focal length of the sixth lens, the seventh lens, and the eighth lens.

[0014] Preferably, the rear lens group includes a ninth lens with a negative optical power, a tenth lens with a positive optical power, and an eleventh lens with a negative optical power, and the rear lens group satisfies: 1.7 < Ndrp < 2.1; where Ndrp is the refractive index of the tenth lens at a wavelength of 587.6 nm.

[0015] The optical imaging system disclosed by the present invention is composed of a front lens group with positive optical power, a focusing lens group with positive optical power, and a rear lens group with negative optical power. Along the optical axis, in the order from the object side to the image side, the front lens group is fixed relative to the image plane, and includes a first lens with negative optical power, a second lens with positive optical power, a third lens with positive optical power, a fourth lens with negative optical power, and a fifth lens, wherein the fifth lens is an aspherical surface. At the same time, the front lens group is set to satisfy -1.8 < Fa1 / F < -0.8. Compared with the prior art, the optical imaging system of the present invention realizes a compact structure and a small volume. At the same time, when the focusing group moves, the change of the full field angle is very slight, the optical distortion within all focusing distance ranges is less than 1%, the light passing aperture is larger, and high-quality optical performance is provided. Description of the Drawings

[0016] Figure 1 Schematic structural diagram of the optical imaging system in the first embodiment of the present invention;

[0017] Figure 2 Schematic diagram of spherical aberration when the optical imaging system in the first embodiment of the present invention is focused at infinity;

[0018] Figure 3 Schematic diagram of astigmatism when the optical imaging system in the first embodiment of the present invention is focused at infinity;

[0019] Figure 4 Schematic diagram of distortion when the optical imaging system in the first embodiment of the present invention is focused at infinity;

[0020] Figure 5 Schematic diagram of spherical aberration when the optical imaging system in the first embodiment of the present invention is focused at the nearest shooting distance;

[0021] Figure 6 Schematic diagram of astigmatism when the optical imaging system in the first embodiment of the present invention is focused at the nearest shooting distance;

[0022] Figure 7 Schematic diagram of distortion when the optical imaging system in the first embodiment of the present invention is focused at the nearest shooting distance;

[0023] Figure 8 Schematic structural diagram of the optical imaging system in the second embodiment of the present invention;

[0024] Fig. 9 Schematic diagram of spherical aberration when the optical imaging system in the second embodiment of the present invention is focused at infinity;

[0025] Fig.10 Schematic diagram of astigmatism when the optical imaging system in the second embodiment of the present invention is focused at infinity;

[0026] Fig.11 Schematic diagram of distortion of the optical imaging system when infinity is focused in the second embodiment of the present invention;

[0027] Fig.12 A schematic diagram of spherical aberration of the optical imaging system in the second embodiment of the present invention when focusing at the shortest photographic distance;

[0028] Fig.13 is a schematic diagram of astigmatism of the optical imaging system in the second embodiment of the present invention when focusing at the shortest photographic distance;

[0029] Fig.14 FIG. 4 is a schematic diagram of distortion of the optical imaging system in the second embodiment of the present invention when focusing at the minimum photographic distance. DETAILED DESCRIPTION

[0030] The present invention is described in more detail below with reference to the accompanying drawings and embodiments.

[0031] Embodiment 1

[0032] This embodiment proposes an optical imaging system, see Figure 1 , which includes a front lens group GA, a focus lens group GF and a back lens group GB, the front lens group GA, the focus lens group GF and the back lens group GB are arranged in sequence from the object side to the image side along the extension direction of the optical axis, the front lens group GA includes a first lens L11 with negative focal power, a second lens L12 with positive focal power, a third lens L13 with positive focal power, a fourth lens L14 with negative focal power and an aspherical fifth lens L15, the first lens L11, the second lens L12, the third lens L13, the fourth lens L14 and the fifth lens L15 are arranged in sequence from the object side to the image side, and the front lens group GA satisfies:

[0033] -1.8 <Fa1 / F<-0.8;

[0034] Wherein, Fa1 is the focal length of the first lens L11; F is the focal length of the optical imaging system when focusing at infinity.

[0035] The above system is composed of a front lens group GA with a positive optical power, a focusing lens group GF with a positive optical power, and a rear lens group GB with a negative optical power. Along the optical axis in the order from the object side to the image side, the front lens group GA is fixed relative to the image plane, and includes a first lens L11 with a negative optical power, a second lens L12 with a positive optical power, a third lens L13 with a positive optical power, a fourth lens L14 with a negative optical power, and a fifth lens L15, wherein the fifth lens L15 is an aspherical lens. At the same time, the front lens group GA is set to satisfy -1.8 < Fa1 / F < -0.8. Compared with the prior art, the optical imaging system of the present invention achieves a compact structure and a small volume. At the same time, when the focusing group moves, the change in the full field of view angle is very slight, the optical distortion within all focusing distances is less than 1%, the clear aperture is larger, and high-quality optical performance is provided.

[0036] In this embodiment, please refer to Figure 1 , the third lens L13 and the fourth lens L14 form a cemented lens group. Further, the front lens group GA satisfies:

[0037] 20 < Cr3*(Vd3 / Vd4) < 70;

[0038] wherein, Cr3 is the radius of curvature of the surface of the third lens L13 close to the image side; Vd3 is the dispersion coefficient of the third lens L13 at a wavelength of 587.6 nm; Vd4 is the dispersion coefficient of the fourth lens L14 at a wavelength of 587.6 nm.

[0039] Regarding the specific composition of the focusing lens group GF, please refer to Figure 1 , the focusing lens group GF includes a sixth lens L21 with a positive optical power, a seventh lens L22 with a negative optical power, and an eighth lens L23 with a positive optical power. The sixth lens L21, the seventh lens L22, and the eighth lens L23 are arranged in sequence from the object side to the image side.

[0040] On this basis, the focusing lens group GF satisfies:

[0041] |(ET5 - CT5) / CT5| < 0.3;

[0042] wherein, ET5 is the distance in the optical axis direction of the marginal aperture light of the central field of view passing through the front and rear surfaces of the fifth lens L15 when the optical imaging system has the maximum aperture; CT5 is the distance in the optical axis direction of the central aperture light of the central field of view passing through the front and rear surfaces of the fifth lens L15 when the optical imaging system has the maximum aperture.

[0043] At the same time, the focusing lens group GF satisfies:

[0044] 15≤Fgf / DA≤25;

[0045] Wherein, DA is the moving distance of the lens focus group GF when the optical imaging system focuses from infinity to 0.05 times magnification; Fgf is the composite focal length of the lens focus group GF.

[0046] Furthermore, the lens focus group GF satisfies: 0.7 <Fgf / F<1.1。

[0047] The above-mentioned optical imaging system also satisfies:

[0048] 0.6 <Fz25 / Fz69<1.1;

[0049] Wherein, Fz25 is the combined focal length of the second lens L12, the third lens L13, the fourth lens L14 and the fifth lens L15; Fz69 is the combined focal length of the sixth lens L21, the seventh lens L22 and the eighth lens 23.

[0050] See also Figure 1 In this embodiment, the rear lens group GB includes a ninth lens L31 with negative power, a tenth lens L32 with positive power, and an eleventh lens L33 with negative power, and the rear lens group GB satisfies:

[0051] 1.7 <Ndrp<2.1;

[0052] Wherein, Ndrp is the refractive index of the tenth lens L32 at a wavelength of 587.6 nm.

[0053] Based on the above structure of the optical imaging system, Figure 1 The numerical data of various parameters are shown in Table 1, Table 2 and Table 3.

[0054] Please refer to Table 1 for surface data:

[0055]

[0056]

[0057] Aspheric surface data please see Table 2:

[0058]

[0059] Please refer to Table 3 for optical imaging system data:

[0060] Focus status Infinity closest focal length 51 45.7 Aperture FNO 1.88 2.11 Total optical length 78 78 Field of view 2ω 45.8° 45.1° <![CDATA[D0]]> Inf 420 <![CDATA[D1]]> 8.98 3.97 <![CDATA[D2]]> 0.91 5.92

[0061] In the above data, the surface number indicates the number of the lens surfaces arranged in sequence from the object side to the image side along the optical axis, the surface type indicates the type of the lens surface corresponding to the surface number. In this embodiment, the lens surface types involve spherical surfaces and aspherical surfaces, the radius of curvature R indicates the radius of curvature of the surface corresponding to the surface number, the thickness indicates the distance from the center point of the lens surface corresponding to the surface number to the center point of the next lens surface along the optical axis, the refractive index Nd indicates the refractive index of the lens at a wavelength of 587.6nm, the Abbe number Vd indicates the Abbe number of the dispersion coefficient of the lens at a wavelength of 587.6nm, Object indicates that the surface corresponding to the number is the object surface, STOP indicates that the surface corresponding to the number is the aperture stop, IMAGE indicates that the surface corresponding to the number is the image surface, and the aspherical surface data indicates the aspherical surface coefficients of each aspherical surface.

[0062] In this embodiment, x is used as the displacement of the optical axis direction relative to the vertex of the surface, and the aspheric surface is defined by the following formula:

[0063]

[0064] In the above formula, h represents the height relative to the optical axis, c represents the reciprocal of the paraxial curvature radius R, K represents the cone coefficient, and An represents the n-order aspheric coefficient. In addition, "E±XX" in Table 2 represents an index mark, that is, *10±XX.

[0065] In the above data of this embodiment, D0 represents the distance between the photographed object (object plane) and the center point of the object side lens of the optical system, and D1 and D2 represent the position of the focus group in different focus states.

[0066] In this example, see Figures 2 to 4 , which shows the spherical aberration, astigmatism and distortion curves of this embodiment when the focus is infinity; please refer to Figures 5 to 7 , which shows the spherical aberration, astigmatism, and distortion curves of this embodiment when focusing at a close distance.

[0067] Specifically, the spherical aberration curve shows the spherical aberration curve when the image side aperture number is 1.88, where the horizontal axis represents the spherical aberration value and the vertical axis represents the field of view; the field curvature curve shows the spherical aberration curve when the wavelength of 546nm light is 22.9 0 The field curvature curve is shown in Figure 1, where the solid line represents the value of the main ray at the sagittal image plane at a wavelength of 546nm, the dotted line represents the value of the main ray at the meridional image plane at a wavelength of 546nm, the horizontal axis represents the field curvature value, and the vertical axis represents the field of view; the distortion curve shows that the half field angle ω is 22.9 when the wavelength is 546nm 0 The time-distortion curve is shown in Figure 1, where the horizontal axis represents the distortion value and the vertical axis represents the field of view. Figures 2 to 7 It can be seen that the optical imaging system of this embodiment has a good imaging effect.

[0068] Example 2

[0069] See also Figure 8 The difference between this embodiment and the first embodiment is that the lens focus group GF includes a sixth lens L21 with negative optical power, a seventh lens L22 with positive optical power and an eighth lens L23 with positive optical power, and the sixth lens L21, the seventh lens L22 and the eighth lens L23 are arranged in sequence from the object side to the image side.

[0070] correspond Figure 8 Various numerical data about the optical imaging system in this embodiment are shown in Table 4, Table 5 and Table 6.

[0071] Please refer to Table 4 for surface data:

[0072]

[0073]

[0074] Please refer to Table 5 for aspheric surface data:

[0075]

[0076] Please refer to Table 6 for optical imaging system data:

[0077]

[0078]

[0079] In this embodiment, Figures 9 to 11 The spherical aberration, field curvature and distortion curves of the optical imaging system when the optical imaging system is in focus at infinity are shown; Figure 12 to Figure 14 The graphs show the spherical aberration, field curvature and distortion of the optical imaging system when it is in close focus.

[0080] Based on the above-mentioned embodiment 1 and embodiment 2, the present invention further provides a statistical table of calculated values ​​of the conditional formulas of the above two embodiments:

[0081]

[0082] Based on the above embodiment 1 and embodiment 2, it can be seen that the optical imaging system disclosed in the present invention includes, starting from the object side along the optical axis, a front lens group GA, an aperture S, a focus lens group GF and a back lens group GB, wherein the front lens group GA has positive optical power, and includes a first lens L11, a second lens L12, a third lens L13, a fourth lens L14 and a fifth lens L15, wherein the third lens and the fourth lens form a cemented lens group, and the fifth lens is an aspherical lens; the focus lens group GF has positive optical power, and includes a sixth lens L21, a seventh lens L22 and an eighth lens L23, wherein the sixth lens and the seventh lens form a cemented lens group; the back lens group GB has negative optical power, and includes a ninth lens L31, a tenth lens L32 and an eleventh lens L33, and when focusing from infinity to a close object, the focus lens group GF moves along the optical axis from the image side to the object side, and when focusing, the front and rear lenses of the entire system are fixed relative to the image plane.

[0083] In practical applications, in order to reduce the length of the system, the second lens L12 uses a larger focal length to quickly shrink and focus the light, the first lens L11 has a negative focal length and has an opposite aberration to the second lens L12, the first and second lenses form a lens group with positive and negative compensation, the fifth lens L15 is an aspheric surface, and is burdened with a very large spherical aberration, which can compensate for the huge spherical aberration generated by the second lens L12, and at the same time, because the focal length of the fifth lens L15 is very small, it does not generate too many other aberrations except for providing spherical aberration, the front lens group GA, the lens focusing group GF and the ninth lens L31 in the rear lens group GB form a nearly symmetrical structure relative to the aperture of the aperture, and compensate for various aberrations, so that the entire optical imaging system can ensure very small aberrations while reducing the length. Compared with the prior art, the present invention provides an optical imaging system with high performance and a relative aperture greater than F2 while meeting the requirements of compact structure and small volume, and better meets the application requirements.

[0084] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the technical scope of the present invention should be included in the scope of protection of the present invention.

Claims

1. An optical imaging system, characterized in that: The invention comprises a front lens group, a focusing lens group and a rear lens group, wherein the front lens group, the focusing lens group and the rear lens group are arranged in sequence from the object side to the image side along the extension direction of the optical axis, the front lens group comprises a first lens with negative optical power, a second lens with positive optical power, a third lens with positive optical power, a fourth lens with negative optical power and an aspherical fifth lens, the first lens, the second lens, the third lens, the fourth lens and the fifth lens are arranged in sequence from the object side to the image side, and the front lens group satisfies: -1.8 <Fa1 / F<-0.8; Wherein, Fa1 is the focal length of the first lens; F is the focal length of the optical imaging system when focusing at infinity.

2. The optical imaging system according to claim 1, wherein: The third lens and the fourth lens form a cemented lens group.

3. The optical imaging system according to claim 2, wherein: The front lens group satisfies: 20 <Cr3*(Vd3 / Vd4)<70; Wherein, Cr3 is the curvature radius of the third lens close to the image side; Vd3 is the dispersion coefficient of the third lens at a wavelength of 587.6 nm; and Vd4 is the dispersion coefficient of the fourth lens at a wavelength of 587.6 nm.

4. The optical imaging system according to claim 1, wherein: The lens focusing group includes a sixth lens with positive power, a seventh lens with negative power and an eighth lens with positive power, and the sixth lens, the seventh lens and the eighth lens are arranged in sequence from the object side to the image side.

5. The optical imaging system according to claim 1, wherein: The lens focusing group includes a sixth lens with negative optical power, a seventh lens with positive optical power and an eighth lens with positive optical power, and the sixth lens, the seventh lens and the eighth lens are arranged in sequence from the object side to the image side.

6. The optical imaging system according to claim 4 or 5, characterized in that: The lens focusing group satisfies: |(ET5-CT5) / CT5|<0.3; Among them, ET5 is the distance in the direction of the optical axis between the edge aperture light of the central field of view and the front and back surfaces of the fifth lens when the optical imaging system has a maximum aperture; CT5 is the distance in the direction of the optical axis between the center aperture light of the central field of view and the front and back surfaces of the fifth lens when the optical imaging system has a maximum aperture.

7. The optical imaging system according to claim 4 or 5, characterized in that: The lens focusing group satisfies: 15≤Fgf / DA≤25; Wherein, DA is the moving distance of the lens focus group when the optical imaging system focuses from infinity to 0.05 times magnification; Fgf is the composite focal length of the lens focus group.

8. The optical imaging system according to claim 7, wherein: The lens focus group meets: 0.7 <Fgf / F<1.1。 9. The optical imaging system according to claim 4 or 5, characterized in that: The optical imaging system satisfies: 0.6 <Fz25 / Fz69<1.1; Among them, Fz25 is the combined focal length of the second lens, the third lens, the fourth lens and the fifth lens; Fz69 is the combined focal length of the sixth lens, the seventh lens and the eighth lens.

10. The optical imaging system according to claim 1, wherein: The rear lens group includes a ninth lens having negative power, a tenth lens having positive power, and an eleventh lens having negative power, and the rear lens group satisfies: 1.7 <Ndrp<2.1; Wherein, Ndrp is the refractive index of the tenth lens at a wavelength of 587.6 nm.

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