Internal focusing imaging lens

Abstract

The present invention provides an inner focusing imaging lens, which includes, from the object side to the image side, a first lens group with positive focal power, a second lens group with positive focal power, a third lens group with negative focal power, and a fourth lens group with positive focal power; during the focusing process, the third lens group moves along the optical axis toward the image side, and the positions of the first lens group, the second lens group and the fourth lens group relative to the image plane remain unchanged; the first lens group includes a first lens, a second lens, a third lens and a fourth lens; the second lens group includes a fifth lens, a sixth lens and a seventh lens, and the fifth lens and the sixth lens are combined into a cemented lens group; the third lens group includes an eighth lens; the fourth lens group includes a ninth lens and a tenth lens; the object side surface and the image side surface of the seventh lens and the eighth lens are both aspherical surfaces. The present invention reduces the weight of the focusing group and the overall weight of the imaging lens, and is also conducive to the rapid focusing of the imaging lens and the imaging device.

Description

Technical Field

[0001] The present invention relates to the field of optical imaging technology, and in particular to an inner focusing imaging lens. Background Art

[0002] In recent years, the micro-single camera market has been expanding rapidly. Compared with the large size and poor portability of SLR cameras, the micro-single camera is small, light and portable because the mirror assembly is eliminated. At the same time, thanks to the mature technology of high-precision CCD, the micro-single camera also has excellent high-quality imaging quality. In addition, when shooting sports or landscape images, a shooting field of view from about 40° to 90° and an F number of 2 or less can have a brighter field of view and vision, which can help photography enthusiasts better and more freely shoot large scene images.

[0003] The users of micro-single-lens cameras hope that they have high performance and high image quality, just like SLR cameras. On the one hand, because micro-single-lens cameras are small, the size of their matching lenses needs to be as small as possible compared to SLR lenses. At the same time, since most users are ordinary photography enthusiasts, high cost performance is also sought. It is precisely because of the above points that there are many restrictions on the design of micro-single-lens. Summary of the invention

[0004] The present invention aims at solving the deficiencies in the prior art and provides an internal focusing imaging lens, which is small and light, and the internal focusing component can be composed of only one lens, and has the characteristics of fast focusing speed and excellent imaging performance.

[0005] To achieve the above purpose, the present invention adopts the following technical solutions:

[0006] An imaging lens, comprising, from the object side to the image side, a first lens group with positive focal power, an aperture stop, a second lens group with positive focal power, a third lens group with negative focal power, and a fourth lens group with positive focal power;

[0007] During the focusing process, the third lens group moves along the optical axis toward the image side, and the positions of the first lens group, the second lens group and the fourth lens group relative to the image plane remain unchanged;

[0008] The first lens group includes a first lens with negative power, a second lens with negative power, a third lens with positive power and a fourth lens with positive power; the second lens group includes a fifth lens with negative power, a sixth lens with positive power and a seventh lens with positive power, and the fifth lens and the sixth lens are combined into a cemented lens group; the third lens group includes an eighth lens with negative power; the fourth lens group includes a ninth lens with positive power and a tenth lens with negative power; the object side surface and the image side surface of the seventh lens and the eighth lens are both aspherical surfaces; the first lens group satisfies the following conditional formula:

[0009] 0.3≤L1s / L≤0.5, (1)

[0010] Wherein, L1s represents the on-axis distance from the first lens group to the aperture stop, and L represents the on-axis distance from the vertex of the object side surface of the first lens to the vertex of the image side surface of the tenth lens.

[0011] As a preferred solution, the second lens group satisfies the following conditional formula:

[0012] 3≤(Cvob2-Cvim3) / φ≤4, (2)

[0013] Wherein, Cvob2 represents the curvature of the surface of the sixth lens close to the object side, Cvim3 represents the curvature of the surface of the seventh lens close to the image side, and φ represents the optical power of the imaging lens.

[0014] As a preferred solution, the fourth lens group satisfies the following conditional formula:

[0015] 6≤F4 / F≤13, (3)

[0016] Wherein, F represents the focal length of the imaging lens, and F4 represents the composite focal length of the fourth lens group.

[0017] As a preferred solution, the fourth lens group satisfies the following conditional formula:

[0018] 0.6≤BFL / F≤0.7, (4)

[0019] Wherein, BFL represents the distance between the surface of the tenth lens of the fourth lens group close to the image side and the image plane, and F represents the focal length of the imaging lens.

[0020] As a preferred solution, the imaging lens satisfies the following conditional formula:

[0021] 30≤Vd4a-Vd4b≤50, (5)

[0022] Wherein, Vd4a is the Abbe number of the ninth lens of the fourth lens group with respect to the light with a wavelength of 587.6 nm, and Vd4b is the Abbe number of the tenth lens of the fourth lens group with respect to the light with a wavelength of 587.6 nm.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The imaging lens focusing assembly of the present invention is composed of only one lens, which reduces the weight of the focusing group and the load of the driving motor, and is conducive to the rapid focusing of the imaging lens and the imaging device; the optical power of the two groups before and after the aperture is limited by conditional formula (1) (2), so that they occupy the main part in the optical power distribution, so that the subsequent lens group can better correct the chromatic aberration and make the entrance pupil closer to the first lens to reduce the incident aperture and realize the miniaturization of the system; the focusing lens adopts a glass aspherical surface to ensure the flat field curvature of the imaging surface, balances the large off-axis aberration generated by the front and rear groups during the focusing process, and has a relatively uniform resolution from the edge to the center; the angle of light incident on the image plane is controlled by a reasonable optical structure, effectively improving the brightness of the edge of the picture and reducing the dark corner; the ninth lens of the fourth lens group adopts an ultra-low dispersion weak positive focal lens and a strong negative focal tenth lens to further correct the negative chromatic aberration caused by the front group and reduce the generation of purple edges in the picture.

[0025] In order to more clearly explain the structural features, technical means and specific purposes and functions achieved by the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments: BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 A schematic diagram showing the structure of Embodiment 1 of the present invention is shown;

[0027] Figure 2 A schematic diagram showing spherical aberration of Embodiment 1 of the present invention when in focus at infinity is shown;

[0028] Figure 3 A schematic diagram of field curvature when focusing at infinity is shown in Embodiment 1 of the present invention;

[0029] Figure 4 A schematic diagram showing distortion of Embodiment 1 of the present invention when focusing at infinity;

[0030] Figure 5 A schematic diagram showing spherical aberration of Embodiment 1 of the present invention at the minimum focusing distance is shown;

[0031] Figure 6 A schematic diagram showing the field curvature of Embodiment 1 of the present invention at the minimum focusing distance;

[0032] Figure 7 A schematic diagram showing distortion of Embodiment 1 of the present invention at the closest focusing distance is shown;

[0033] Figure 8 A schematic diagram showing the structure of Embodiment 2 of the present invention is shown;

[0034] Fig. 9 A schematic diagram showing spherical aberration of Embodiment 2 of the present invention when in focus at infinity;

[0035] Fig.10 A schematic diagram showing the field curvature of embodiment 2 of the present invention when in focus at infinity;

[0036] Fig.11 A schematic diagram showing distortion of Embodiment 2 of the present invention when focusing at infinity;

[0037] Fig.12 A schematic diagram showing spherical aberration of Embodiment 2 of the present invention at the closest focusing distance is shown;

[0038] Fig.13 A schematic diagram showing the field curvature of Embodiment 2 of the present invention at the minimum focusing distance;

[0039] Fig.14 A schematic diagram showing the distortion of Embodiment 2 of the present invention at the closest focusing distance;

[0040] Fig.15 A schematic diagram showing the structure of Embodiment 3 of the present invention is shown;

[0041] Fig.16 A schematic diagram showing spherical aberration of Embodiment 3 of the present invention when in focus at infinity is shown;

[0042] Fig.17 A schematic diagram of field curvature when focusing at infinity is shown in Embodiment 3 of the present invention;

[0043] Fig.18 A schematic diagram showing distortion of Embodiment 3 of the present invention when in focus at infinity is shown;

[0044] Fig.19 A schematic diagram showing spherical aberration of Embodiment 3 of the present invention at the closest focusing distance is shown;

[0045] Fig. 20 A schematic diagram showing the field curvature of Embodiment 3 of the present invention at the minimum focusing distance;

[0046] Fig.21 A schematic diagram showing the distortion of Embodiment 3 of the present invention at the closest focusing distance is shown;

[0047] Fig. 22 A schematic diagram showing the structure of Embodiment 4 of the present invention is shown;

[0048] Fig.23 A schematic diagram showing spherical aberration of Embodiment 4 of the present invention when in focus at infinity is shown;

[0049] Fig.24 A schematic diagram showing the field curvature of Embodiment 4 of the present invention when in focus at infinity;

[0050] Fig.25 A schematic diagram showing the distortion of Embodiment 4 of the present invention when focusing at infinity;

[0051] Fig.26 A schematic diagram showing spherical aberration of Embodiment 4 of the present invention at the closest focusing distance is shown;

[0052] Fig. 27 A schematic diagram showing the field curvature of Embodiment 4 of the present invention at the minimum focusing distance;

[0053] Fig.28 A schematic diagram showing distortion of Embodiment 4 of the present invention at the minimum focusing distance is shown.

[0054] Description of the accompanying drawings: DETAILED DESCRIPTION

[0055] In the description of the present invention, it should be noted that the terms "center", "up", "down", "left", "right", "vertical", "horizontal", "inside" and "outside" etc. indicate directions or positional relationships based on the directions or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the positions or elements referred to must have specific directions, be constructed and operated in specific directions. Therefore, they should not be understood as limitations on the present invention.

[0056] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0057] like Figure 1-28 As shown, an imaging lens comprises, from the object side to the image side, a first lens group G1 having positive focal power, an aperture stop STP, a second lens group G2 having positive focal power, a third lens group G3 having negative focal power, and a fourth lens group G4 having positive focal power; during the focusing process, the third lens group G3 moves along the optical axis toward the image side, and the positions of the first lens group G1, the second lens group G2 and the fourth lens group G4 relative to the image plane IMG remain unchanged;

[0058] The first lens group G1 includes a first lens L11 having negative power, a second lens L12 having negative power, a third lens L13 having positive power, and a fourth lens L14 having positive power. The first lens group G1 satisfies the following conditional formula:

[0059] 0.3≤L1s / L≤0.5, (1)

[0060] Wherein, L1s represents the on-axis distance from the first lens group to the aperture stop, and L represents the on-axis distance from the vertex of the object side surface of the first lens to the vertex of the image side surface of the tenth lens.

[0061] If conditional expression (1) is satisfied, the aperture stop is in a suitable position in the optical system, maintaining the good imaging performance of the system and facilitating the miniaturization of the optical system aperture. If the conditional expression (1) is below its lower limit, the aperture stop gradually approaches the object side, the aperture of the rear lens group close to the image side will increase, and the off-axis aberrations generated by the rear lens group, especially the image curvature, will become particularly significant. If the conditional expression (1) is above its upper limit, the aperture stop gradually approaches the image side, the aperture of the front lens group will be affected and increased, and miniaturization of the optical system becomes difficult.

[0062] The second lens group G2 includes a fifth lens L21 having negative refractive power, a sixth lens L22 having positive refractive power, and a seventh lens L23 having positive refractive power, and the second lens group G2 satisfies the following conditional formula:

[0063] 3≤(Cvob2-Cvim3) / φ≤4, (2)

[0064] Wherein, Cvob2 represents the curvature of the surface of the sixth lens close to the object side, Cvim3 represents the curvature of the surface of the seventh lens L23 close to the image side, and φ represents the optical power of the imaging lens. The lens group satisfying conditional formula (2) can correct spherical aberration well, and the off-axis chromatic aberration also converges toward the optical axis; if it is lower than the lower limit in conditional formula (2), the angle of the light emitted from the cemented lens group increases, and the corresponding spherical aberration coma will increase. If it is higher than the upper limit in conditional formula (2), the optical power of the second lens group G2 is reduced, and the overall length of the imaging lens tends to increase.

[0065] The third lens group G3 includes an eighth lens L31 having negative refractive power.

[0066] The fourth lens group G4 includes a ninth lens L41 having positive refractive power and a tenth lens L42 having negative refractive power. The fourth lens group G4 satisfies the following conditional formula:

[0067] 6≤F4 / F≤13, (3)

[0068] 0.6≤BFL / F≤0.7, (4)

[0069] 30≤Vd4a-Vd4b≤50, (5)

[0070] Wherein, F represents the focal length of the imaging lens, F4 represents the composite focal length of the fourth lens group G4, BFL represents the distance between the surface of the tenth lens of the fourth lens group close to the image side and the image plane, Vd4a represents the Abbe number of the ninth lens of the fourth lens group with respect to the light with a wavelength of 587.6nm, and Vd4b represents the Abbe number of the tenth lens of the fourth lens group with respect to the light with a wavelength of 587.6nm. If the conditional formulas (3), (4), and (5) are satisfied, the fourth lens group has a suitable optical power, can well correct the positive and negative chromatic aberrations outside the axis, and there is a suitable margin between the lens and the camera image plane CCD for photography enthusiasts to match with other photography accessories. If the conditional formulas (3), (4), and (5) are below the lower limit, the optical power of the fourth lens group is enhanced, the spherical aberration and coma will increase, and the distance from the camera lens to the image plane CCD will be shortened, the lens close to the image plane will be compressed in outer diameter, and the brightness of the image will be affected. If the value in conditional expressions (3), (4) and (5) is higher than the upper limit, the optical power of the fourth lens group will decrease, the image curvature, coma and off-axis chromatic aberration will increase, the overall length of the imaging lens will increase, and the F value of the imaging lens will tend to increase. At the same time, the back focal length will also increase to a certain extent.

[0071] In the present invention, a parallel glass plate GL configured by a filter is arranged between the negative lens L42 of the fourth lens group G4 and the image surface IMG. The back focus is the distance from the image side surface of L42 to the image surface IMG, where the parallel glass plate GL can be transformed into air.

[0072] Example 1

[0073] Figure 1 The figure shows a schematic diagram of the structure of the imaging lens of Example 1. The numerical data of the imaging lens are shown in Table 1, Table 2 and Table 3:

[0074] Table 1

[0075]

[0076]

[0077] Table 2

[0078]

[0079] Table 3

[0080] Surface number k A4 A6 A8 A10 13 0 -7.55E-06 3.58E-09 -1.28E-11 1.11E-13 14 0 1.05E-05 -5.18E-09 -2.37E-11 3.64E-14 15 0 9.27E-05 -5.08E-07 1.65E-09 -2.56E-12 16 0 1.03E-04 -4.96E-07 1.57E-09 -2.41E-12

[0081] The surface number indicates the surface number of each lens from the object side to the image side;

[0082] In Example 1, the object side surface and image side surface of L23 and L31 are formed as aspherical surfaces. In the following table, the fourth, sixth, eighth, and tenth order aspherical coefficients A4, A6, A8, A10 and the cone constant k of the aspherical surface are shown together.

[0083] The definition of aspherical shape is explained below, and the definition of aspherical shape is not repeated in the following embodiments:

[0084] y: radial coordinate from the optical axis.

[0085] z: The offset in the direction of the optical axis starting from the intersection point of the aspherical surface and the optical axis.

[0086] r: The radius of curvature of the reference sphere of the aspheric surface.

[0087] K, 4th, 6th, 8th, 10th, 12th aspheric coefficients

[0088]

[0089] Figure 2-4 The spherical aberration, field curvature, and distortion curves of Example 1 when the image is in focus at infinity are shown. Figure 5-7 The graphs show spherical aberration, field curvature, and distortion of Example 1 when the lens is in focus at the closest distance.

[0090] The spherical aberration curve shows the spherical aberration curve when the aperture number is 1.4, where the F line, D line, and C line represent the spherical aberration at wavelengths of 486nm, 587nm, and 656nm, respectively. 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 half field angle ω is 31.6 0 The field curvature curve is shown in Figure 1, where the solid line S represents the value of the principal ray d on the sagittal image plane, the solid line T represents the value of the principal ray d 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 value of the field curvature when the half field angle ω is 31.6 0 The distortion curve when the horizontal axis represents the distortion value and the vertical axis represents the field of view. The above description of various spherical aberrations, field curvatures, and distortion curves is the same as that of other embodiments, and will not be repeated below. It can be seen from Figures 2-7 that the imaging lens of this embodiment 1 has a good imaging effect.

[0091] Example 2

[0092] like Figure 8 As shown, the difference between this embodiment and Embodiment 1 is that the lens parameters of the imaging lens are different. Below, Table 4, Table 5 and Table 6 show various numerical data about the imaging lens of this embodiment.

[0093] Table 4

[0094]

[0095]

[0096] Table 5

[0097]

[0098] Table 6

[0099] Surface number k A4 A6 A8 A10 13 0 -9.70E-06 -5.74E-11 -3.14E-12 7.01E-14 14 0 8.29E-06 -3.69E-09 -3.97E-11 5.52E-14 15 0 8.61E-05 -4.12E-07 1.11E-09 -1.41E-12 16 0 9.59E-05 -4.02E-07 1.05E-09 -1.30E-12

[0100] The surface number indicates the surface number of each lens from the object side to the image side;

[0101] In Example 2, the object side surface and image side surface of L23 and L31 are formed as aspherical surfaces. In the following table, the fourth, sixth, eighth, and tenth order aspherical coefficients A4, A6, A8, A10 and the cone constant k of the aspherical surface are shown together.

[0102] Figure 9-11 The spherical aberration, field curvature, and distortion curves of Example 2 when the image is in focus at infinity are shown. Figure 12-14 The spherical aberration, field curvature and distortion curves of Example 2 at the closest focusing distance are shown. As can be seen from Figures 9-14, the imaging lens of this embodiment has a good imaging effect.

[0103] Example 3

[0104] like Fig.15 As shown, the difference between this embodiment and Embodiment 1 is that the lens parameters of the imaging lens are different. Below, Table 7, Table 8 and Table 9 show various numerical data about the imaging lens of this embodiment.

[0105] Table 7

[0106]

[0107]

[0108] Table 8

[0109]

[0110] Table 9

[0111] Surface number k A4 A6 A8 A10 13 0 -1.14E-05 -2.00E-08 1.52E-10 -6.26E-13 14 0 9.43E-06 -2.65E-08 1.26E-10 -6.58E-13 15 0 8.50E-05 -3.59E-07 7.89E-10 -8.25E-13 16 0 9.57E-05 -3.34E-07 6.44E-10 -5.51E-13

[0112] The surface number indicates the surface number of each lens from the object side to the image side;

[0113] In Example 3, the object side surface and image side surface of L23 and L31 are formed as aspherical surfaces. In the following table, the fourth, sixth, eighth, and tenth order aspherical coefficients A4, A6, A8, A10 and the cone constant k of the aspherical surface are shown together.

[0114] Figure 16-18 The spherical aberration, field curvature, and distortion curves of Example 3 when the image is in focus at infinity are shown. Figure 19-21 The spherical aberration, field curvature and distortion curves of Example 3 at the closest focusing distance are shown. As can be seen from Figures 16-21, the imaging lens of this embodiment has a good imaging effect.

[0115] Example 4

[0116] like Fig. 22 As shown, the difference between this embodiment and Embodiment 1 is that the lens parameters of the imaging lens are different. Below, Table 10, Table 11 and Table 12 show various numerical data about the imaging lens of this embodiment.

[0117] Table 10

[0118]

[0119]

[0120] Table 11

[0121]

[0122] Table 12

[0123]

[0124]

[0125] The surface number indicates the surface number of each lens from the object side to the image side;

[0126] In Example 4, the object side surface and image side surface of L23 and L31 are formed as aspherical surfaces. In the following table, the fourth, sixth, eighth, and tenth order aspherical coefficients A4, A6, A8, A10 and the cone constant k of the aspherical surface are shown together.

[0127] Figure 23-25 The spherical aberration, field curvature, and distortion curves of Example 4 when in focus at infinity are shown. Figure 26-28 The spherical aberration, field curvature and distortion curves of Example 4 at the closest focusing distance are shown. As can be seen from Figures 23-28, the imaging lens of this embodiment has a good imaging effect.

[0128] Table 9 shows a list of calculated values ​​of conditional formulas 1-6 of various embodiments:

[0129] Table 9

[0130]

[0131] The above shows and describes the basic principles and main features of the present invention and the advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. An inner focusing imaging lens, characterized in that: From the object side to the image side, it is composed of a first lens group with positive power, an aperture stop, a second lens group with positive power, a third lens group with negative power, and a fourth lens group with positive power; During the focusing process, the third lens group moves along the optical axis toward the image side, and the positions of the first lens group, the second lens group and the fourth lens group relative to the image plane remain unchanged; The first lens group is composed of a first lens with negative power, a second lens with negative power, a third lens with positive power and a fourth lens with positive power in sequence; the second lens group is composed of a fifth lens with negative power, a sixth lens with positive power and a seventh lens with positive power in sequence, and the fifth lens and the sixth lens are combined into a cemented lens group; The third lens group is composed of an aspherical eighth lens with negative power; the fourth lens group is composed of a ninth lens with positive power and a tenth lens with negative power in sequence; the object side surface and the image side surface of the seventh lens and the eighth lens are both aspherical surfaces; the first lens group satisfies the following conditional formula: 0.3≤L1s / L≤0.5, (1); Wherein, L1s represents the on-axis distance from the first lens group to the aperture stop, and L represents the on-axis distance from the vertex of the object side surface of the first lens to the vertex of the image side surface of the tenth lens.

2. The inner focusing imaging lens according to claim 1, characterized in that: The second lens group satisfies the following conditional formula: 3≤(Cvob2-Cvim3) / φ≤4, (2); Wherein, Cvob2 represents the curvature of the surface of the sixth lens close to the object side, Cvim3 represents the curvature of the surface of the seventh lens close to the image side, and φ represents the optical power of the imaging lens.

3. The inner focusing imaging lens according to claim 1, wherein: The fourth lens group satisfies the following conditional formula: 6≤F4 / F≤13, (3); Wherein, F represents the focal length of the imaging lens, and F4 represents the composite focal length of the fourth lens group.

4. The inner focusing imaging lens according to claim 1, wherein: The fourth lens group satisfies the following conditional formula: 0.6≤BFL / F≤0.7, (4); Wherein, BFL represents the distance between the surface of the tenth lens of the fourth lens group close to the image side and the image plane, and F represents the focal length of the imaging lens.

5. The inner focusing imaging lens according to any one of claims 1 to 4, characterized in that: The fourth lens group satisfies the following conditional formula: 30≤Vd4a-Vd4b≤50, (5); Wherein, Vd4a is the Abbe number of the ninth lens of the fourth lens group with respect to the light with a wavelength of 587.6 nm, and Vd4b is the Abbe number of the tenth lens of the fourth lens group with respect to the light with a wavelength of 587.6 nm.

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