extender lens

Abstract

The application provides a wide-angle lens, which comprises, in sequence along an optical axis from an object side to an imaging surface, a first lens with negative optical power, the object side of which is a convex surface and the image side of which is a concave surface; a second lens with positive optical power, the object side of which is a convex surface near the optical axis; a third lens with positive optical power, the image side of which is a convex surface; and a fourth lens with positive optical power, the image side of which is a convex surface; and a mobile phone lens module; wherein the total optical length TTL of the wide-angle lens and the image height IH corresponding to the maximum half field angle of the wide-angle lens satisfy 2.6 < TTL / IH < 3.1. The application realizes the effects of large field of view, large aperture and miniaturization by reasonably matching the lens shapes and optical power combinations between the lenses.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of imaging lens, in particular to an angle expansion lens. BACKGROUND

[0002] In the design process of mobile phone lens, it is difficult to achieve wide-angle lens due to the small size of the lens itself. The design of wide-angle lens is difficult and the production and design cost is high. The angle expansion lens is often used to expand the field of view of the projector lens or the mobile phone lens, so that the projector can project a larger image at a short distance, and the mobile phone lens can be wide-angle shot. However, the chromatic aberration of the existing angle expansion lens is difficult to correct, and the imaging effect is poor. SUMMARY

[0003] In view of the above problems, the purpose of the present application is to provide an angle expansion lens which can solve one or more of the above problems.

[0004] To achieve the above purpose, the present application provides an angle expansion lens, which is sequentially arranged along the optical axis from the object side to the imaging surface: a first lens with negative focal power, the object side surface of which is convex, and the image side surface of which is concave; a second lens with positive focal power, the object side surface of which is convex near the optical axis; a third lens with positive focal power, the image side surface of which is convex; a fourth lens with positive focal power, the image side surface of which is convex; a mobile phone lens module; wherein the total optical length TTL of the angle expansion lens and the image height IH corresponding to the maximum half field angle of the angle expansion lens satisfy: 2.6 < TTL / IH < 3.1.

[0005] Compared with the prior art, the angle expansion lens provided by the present application has the advantages that the focal power distribution, surface type matching, lens thickness and lens spacing are reasonable, so that the angle expansion lens has a compact large aperture structure, and the field of view of the mobile phone lens can be expanded from 84° to 120°, realizing the advantages of large aperture, miniaturization and wide angle. BRIEF DESCRIPTION OF DRAWINGS

[0006] Figure 1 It is a structure schematic diagram of the angle expansion lens of the present application embodiment 1.

[0007] Figure 2 It is an optical distortion curve diagram of the angle expansion lens in the present application embodiment 1.

[0008] Figure 3 It is an MTF curve diagram of the angle expansion lens in the present application embodiment 1.

[0009] Figure 4 It is a curve diagram of the sagittal chromatic aberration of the angle expansion lens in the present application embodiment 1.

[0010] Figure 5 It is a structure schematic diagram of the angle expansion lens of the present application embodiment 2.

[0011] Figure 6 Optical distortion curve graph of the fisheye lens in Embodiment 2 of the present application.

[0012] Figure 7 MTF curve graph of the fisheye lens in Embodiment 2 of the present application.

[0013] Figure 8 Vignetting curve graph of the fisheye lens in Embodiment 2 of the present application.

[0014] Figure 9 Structure diagram of the fisheye lens in Embodiment 3 of the present application.

[0015] Figure 10 Optical distortion curve graph of the fisheye lens in Embodiment 3 of the present application.

[0016] Figure 11 MTF curve graph of the fisheye lens in Embodiment 3 of the present application.

[0017] Figure 12 Vignetting curve graph of the fisheye lens in Embodiment 3 of the present application. DETAILED DESCRIPTION

[0018] For a better understanding of the present application, various aspects of the present application will be described in more detail below with reference to the accompanying drawings. It is to be understood that the detailed description is only a description of embodiments of the present application and is not intended in any way to limit the scope of the present application. Throughout the specification, like reference numerals refer to like elements. The expression "and / or" includes any and all combinations of one or more of the associated listed items.

[0019] It is noted that, in this specification, the expressions first, second, third, etc. are merely used to distinguish one feature from another feature, and do not indicate any limitation on the features. Thus, the first lens discussed below can also be referred to as the second lens or the third lens without departing from the teachings of the present application.

[0020] In the drawings, the thickness, size, and shape of lenses have been slightly exaggerated for ease of explanation. Specifically, the shape of a spherical surface or an aspherical surface shown in the drawings is shown by way of example. That is, the shape of a spherical surface or an aspherical surface is not limited to the shape of a spherical surface or an aspherical surface shown in the drawings. The drawings are merely examples and are not drawn to scale.

[0021] In the present disclosure, the paraxial region refers to a region near the optical axis. If a lens surface is convex and the position of the convex surface is not specified, it means that the lens surface is convex at least in the paraxial region. If a lens surface is concave and the position of the concave surface is not specified, it means that the lens surface is concave at least in the paraxial region. The surface of each lens closest to the object is referred to as the object side surface of the lens, and the surface of each lens closest to the image plane is referred to as the image side surface of the lens.

[0022] It should also be understood that the words "comprise", "comprising", "include", "including", and / or "contain", when used in this specification, specify the presence of stated features, elements, and / or components, but do not preclude the presence or addition of one or more other features, elements, components, and / or groups thereof. Furthermore, when describing the embodiments of the present application, the word "may" is used to mean "one or more embodiments of the present application". Also, the word "exemplary" is used to mean "an example or illustration".

[0023] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. It should also be understood that the terms should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[0024] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The present application will be described in detail below with reference to the accompanying drawings and in conjunction with the embodiments.

[0025] The embodiment of the present application provides an angle expansion lens, which comprises, in sequence from the object side to the image side, a first lens, a second lens, a third lens, a fourth lens, a diaphragm, a mobile phone lens module, and a filter.

[0026] The first lens has a negative focal length, the object side surface thereof is convex, and the image side surface thereof is concave. The second lens has a positive focal length, the object side surface thereof is convex near the optical axis, and the image side surface thereof is concave near the optical axis. The third lens has a positive focal length, the object side surface thereof is convex, and the image side surface thereof is convex. The fourth lens has a positive focal length, the object side surface thereof is concave near the optical axis, and the image side surface thereof is convex. The effective focal length of the mobile phone lens module is 6.7 mm, the field of view is 84°, and the half image height is 6 mm.

[0027] In some embodiments, the diaphragm can be arranged between the fourth lens and the mobile phone lens module to converge the range of light rays exiting the front end of the angle expansion lens into the mobile phone lens module.

[0028] In some embodiments, the effective focal length f of the wide-angle lens and the entrance pupil diameter EPD satisfy: 1.8 < f / EPD < 2.2. Satisfying the above range is conducive to achieving a large aperture characteristic, and ensuring the clarity of an image in a low-light environment or at night.

[0029] In some embodiments, the incident angle CRA of the chief ray of the maximum field angle of the wide-angle lens on the image plane satisfies: 20° < CRA < 40°. Satisfying the above range can make the CRA of the wide-angle lens have a larger allowable error range with the CRA of the photosensitive element of the chip, and improve the adaptation capability of the wide-angle lens to the image sensor.

[0030] In some embodiments, the total track length TTL of the wide-angle lens and the image height IH corresponding to the maximum half field angle of the wide-angle lens satisfy: 2.6 < TTL / IH < 3.1. Satisfying the above range is conducive to achieving a balance between miniaturization and a large image of the wide-angle lens.

[0031] In some embodiments, the effective aperture D1 of the object side of the first lens, the image height IH corresponding to the maximum half field angle of the wide-angle lens, and the maximum half field angle θ of the wide-angle lens satisfy: 1.0 < D1 / (IH x tanθ) < 1.6. Satisfying the above range can reduce the front aperture of the wide-angle lens, and achieve a balance between miniaturization and wide-angle of the wide-angle lens.

[0032] In some embodiments, the effective focal length f1 of the first lens and the effective focal length f2 of the second lens satisfy: -1.0 < f1 / f2 < -0.2. Satisfying the above range can reasonably control the refractive power of the first lens and the second lens, correct the higher-order aberrations of the wide-angle lens, and help shorten the back focal length of the wide-angle lens, and maintain the miniaturization of the wide-angle lens.

[0033] In some embodiments, the effective focal length f2 of the second lens and the effective focal length f of the wide-angle lens satisfy: 5.0 < f2 / f < 7.0; and the radius of curvature R21 of the object side of the second lens and the radius of curvature R22 of the image side of the second lens satisfy: 1.0 < (R22 + R21) / (R22 - R21) < 2.5. Satisfying the above range can reasonably control the refractive power and surface shape of the second lens, adjust the light exit angle, and achieve wide-angle of the wide-angle lens.

[0034] In some embodiments, the central thickness CT2 of the second lens and the air space AT23 between the second lens and the third lens on the optical axis satisfy: 2.8 < CT2 / AT23 < 2.9. Satisfying the above range, the light rays passing through the second lens can enter the third lens gently, the aberration, field curvature, etc. of the fisheye lens can be reduced, the imaging quality of the fisheye lens is improved, the total length of the fisheye lens can be shortened to maintain its miniaturization, and the lens manufacturing and shaping requirements can be met to improve the manufacturing yield.

[0035] In some embodiments, the combined focal length f34 of the third lens and the fourth lens and the effective focal length f of the fisheye lens satisfy: 6.0 < f34 / f < 7.5. Satisfying the above range, the optical power of the third lens and the fourth lens can be reasonably distributed, the light ray turning trend can be slowed down, the aberration of the fisheye lens can be corrected, the imaging quality of the fisheye lens is improved, and the total length of the fisheye lens can be reduced.

[0036] In some embodiments, the central thickness CT3 of the third lens and the distance BFL between the image side surface of the fourth lens and the imaging surface on the optical axis and the optical total length TTL of the fisheye lens satisfy: 0.2 < CT3 / (TTL-BFL) < 0.25. Satisfying the above range, the structure of the fisheye lens can be more compact, and the miniaturization of the fisheye lens can be facilitated.

[0037] In some embodiments, the radius of curvature R41 of the object side surface of the fourth lens and the radius of curvature R42 of the image side surface of the fourth lens and the effective focal length f4 of the fourth lens satisfy: 0.3 < (R42-R41) / f4 < 0.4. Satisfying the above range, the off-axis field light ray turning trend can be effectively slowed down, various aberrations of the fisheye lens can be well corrected, and the light rays can be incident to the mobile phone lens module and clearly imaged on the imaging surface.

[0038] In some embodiments, the air space AT45 between the fourth lens and the mobile phone lens module on the optical axis and the optical total length TTL of the fisheye lens satisfy: 0.12 < AT45 / TTL < 0.17; the distance BFL between the image side surface of the fourth lens and the imaging surface on the optical axis and the optical total length TTL of the fisheye lens satisfy: 0.48 < BFL / TTL < 0.55. Satisfying the above range, the fisheye lens can have a longer optical back focus, the assembly of the fisheye lens can be facilitated, the total length of the fisheye lens can be effectively limited, and the miniaturization of the fisheye lens can be achieved.

[0039] In some embodiments, the center thickness CT2 of the second lens, the edge thickness ET2 of the second lens, the center thickness CT3 of the third lens, the edge thickness ET3 of the third lens, the center thickness CT4 of the fourth lens, and the edge thickness ET4 of the fourth lens satisfy: 1.2 < (CT2+CT3+CT4) / (ET2+ET3+ET4) < 1.3. Satisfying the above range can make the second lens to the fourth lens converge light rays of the optical system, assume a specific optical power, reduce the volume of the fisheye lens, increase the imaging surface, and meanwhile ensure the assembly yield of the fisheye lens.

[0040] In order to make the system have better optical performance, a plurality of aspherical lenses are used in the lens, and each aspherical surface shape of the fisheye lens satisfies the following equation:

[0041]

[0042] wherein z is the distance of the curved surface from the vertex of the curved surface in the direction of the optical axis, h is the distance from the optical axis to the curved surface, c is the curvature of the vertex of the curved surface, K is the quadratic surface coefficient, and A, B, C, D, and E are respectively the fourth-order, sixth-order, eighth-order, tenth-order, and twelfth-order curved surface coefficients.

[0043] The application will be further described in the following embodiments. In each embodiment, the thickness, the radius of curvature, and the material selection of each lens in the fisheye lens are different, and the specific differences can be referred to the parameter table of each embodiment. The following embodiments are only preferred embodiments of the application, but the embodiments of the application are not limited to the following embodiments only, and any change, replacement, combination, or simplification made without departing from the innovative points of the application should be regarded as equivalent replacement, and all are included in the protection scope of the application.

[0044] Embodiment 1

[0045] Please refer to Figure 1 , which is a structural schematic diagram of the fisheye lens provided in the embodiment 1 of the application, and the fisheye lens comprises, in sequence along the optical axis from the object side to the imaging surface S12, a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, a diaphragm ST, a mobile phone lens module B1, and a filter G1.

[0046] The first lens L1 has negative focal power, the object side S1 is a convex surface, and the image side S2 is a concave surface; the second lens L2 has positive focal power, the object side S3 is a convex surface at the near optical axis, and the image side S4 is a concave surface at the near optical axis; the third lens L3 has positive focal power, the object side S5 is a concave surface, and the image side S6 is a convex surface; the fourth lens L4 has positive focal power, the object side S7 is a concave surface at the near optical axis, and the image side S8 is a convex surface; the mobile phone lens module B1 has an effective focal length of 6.7 mm, a field of view of 84°, a half image height of 6 mm, and an optical total length of 6.067 mm from the object side S9 to the image side S10, and the object side S9 is close to the stop ST, and the image side S10 is close to the filter G1; the filter G1 has a flat object side S10 and a flat image side S11.

[0047] The related parameters of the lenses in the wide-angle lens in Example 1 are shown in Table 1-1.

[0048] Table 1-1

[0049]

[0050]

[0051] The curve coefficients of the aspherical lenses in the wide-angle lens in Example 1 are shown in Table 1-2.

[0052] Table 1-2

[0053] Surface No. K A B C D E S3 -1.92E+01 3.82E-04 -3.71E-05 7.93E-07 -1.55E-08 1.85E-10 S4 -1.09E+02 -8.51E-04 -6.91E-06 9.25E-07 -2.74E-08 3.11E-10 S5 3.00E+02 -1.50E-03 2.41E-05 3.44E-07 -2.22E-08 3.01E-10 S6 7.15E+01 -2.59E-04 -7.02E-06 2.46E-08 3.25E-09 2.05E-11 S7 -9.81E+01 7.23E-04 2.18E-06 -5.75E-07 9.77E-09 -1.57E-11 S8 -1.45E-01 6.70E-04 -1.65E-05 1.17E-06 -4.81E-08 5.83E-10

[0054] Figure 2 The optical distortion curve of Example 1 is shown, which represents the distortion at different fields of view on the imaging surface, the horizontal axis represents the percentage, and the vertical axis represents the half field of view (unit: °). As can be seen from the figure, the optical distortion of the present embodiment is controlled within -35%, which shows that the distortion of the wide-angle lens is well corrected.

[0055] Figure 3 The modulation transfer function (MTF) curve of Example 1 is shown, which represents the imaging modulation degree of different spatial frequencies under each field of view, the horizontal axis represents the spatial frequency (unit: lp / mm), and the vertical axis represents the MTF value. As can be seen from the figure, the MTF value of the present embodiment is above 0.6 in the full field of view, and in the range of 0-80 lp / mm, the MTF curve uniformly and smoothly decreases from the center to the edge field of view, and has good imaging quality and good detail resolution ability in low and high frequency cases.

[0056] Figure 4The vertical axis represents the value of the vertical chromatic aberration of each wavelength relative to the central wavelength (0.55 μm) (unit: μm), and the longitudinal axis represents the normalized field angle. As can be seen from the figure, the vertical chromatic aberration of the longest wavelength and the shortest wavelength is controlled within ±2.5 μm, which indicates that the extender lens can correct the chromatic aberration of the edge field and the secondary spectrum of the whole image plane very well.

[0057] Embodiment 2

[0058] Referring to Figure 5 , which is a structural schematic diagram of the extender lens provided in Embodiment 2 of the present application. The extender lens in this embodiment has substantially the same structure and shape as the extender lens in Embodiment 1, and the difference mainly lies in that the curvature radius, the central thickness, the edge thickness and the material of each lens are changed.

[0059] The related parameters of each lens in the extender lens in Embodiment 2 are shown in Table 2-1.

[0060] Table 2-1

[0061]

[0062] The curve coefficients of the aspheric lenses of the extender lens in Embodiment 2 are shown in Table 2-2.

[0063] Table 2-2

[0064] Surface No. K A B C D E S3 -1.92E+01 3.82E-04 -3.71E-05 7.93E-07 -1.55E-08 1.85E-10 S4 -1.09E+02 -8.51E-04 -6.91E-06 9.25E-07 -2.74E-08 3.11E-10 S5 3.00E+02 -1.50E-03 2.41E-05 3.44E-07 -2.22E-08 3.01E-10 S6 7.15E+01 -2.59E-04 -7.02E-06 2.47E-08 3.25E-09 2.08E-11 S7 -9.81E+01 7.23E-04 2.18E-06 -5.75E-07 9.76E-09 -1.62E-11 S8 -1.45E-01 6.70E-04 -1.65E-05 1.17E-06 -4.80E-08 5.85E-10

[0065] Figure 6 to Figure 8 The distortion curve diagram, the modulation transfer function (MTF) curve diagram and the vertical chromatic aberration curve diagram of Embodiment 2 are shown respectively. As can be seen from the figures, the optical distortion is controlled within -35%, which indicates that the distortion of the extender lens is well corrected; the MTF value of the extender lens is above 0.65 in the whole field of view, and in the range of 0-80 lp / mm, the MTF curve uniformly and smoothly decreases from the center to the edge field of view, and the extender lens has good imaging quality and good detail resolution ability in the case of low frequency and high frequency; the vertical chromatic aberration of the longest wavelength and the shortest wavelength is controlled within ±1.3 μm, which indicates that the extender lens can correct the chromatic aberration of the edge field and the secondary spectrum of the whole image plane very well.

[0066] Embodiment 3

[0067] Referring to Figure 9 , which is a structural schematic diagram of the extender lens provided in Embodiment 3 of the present application. The extender lens in this embodiment has substantially the same structure and shape as the extender lens in Embodiment 1, and the difference mainly lies in that the curvature radius, the central thickness and the edge thickness of each lens are changed.

[0068] The relevant parameters of each lens in the wide-angle lens in Example 3 are shown in Table 3-1.

[0069] Table 3-1

[0070]

[0071] The surface coefficients of the aspherical lenses of the wide-angle lens in Example 3 are shown in Table 3-2.

[0072] Table 3-2

[0073] Surface No. K A B C D E S3 -1.92E+01 3.87E-04 -3.70E-05 7.94E-07 -1.55E-08 1.86E-10 S4 -1.09E+02 -8.54E-04 -6.91E-06 9.25E-07 -2.74E-08 3.09E-10 S5 3.00E+02 -1.50E-03 2.41E-05 3.42E-07 -2.22E-08 3.00E-10 S6 7.15E+01 -2.59E-04 -6.96E-06 2.61E-08 3.28E-09 1.94E-11 S7 -9.81E+01 7.31E-04 2.17E-06 -5.80E-07 9.63E-09 -1.35E-11 S8 -1.45E-01 6.70E-04 -1.65E-05 1.17E-06 -4.81E-08 5.70E-10

[0074] Figure 10 to Figure 12 The distortion curve, the modulation transfer function (MTF) curve, and the axial chromatic aberration curve of Example 3 are shown respectively. As can be seen from the figures, the optical distortion is controlled within-35%, which indicates that the distortion of the wide-angle lens is well corrected; the MTF value of the wide-angle lens is above 0.65 in the full field of view, and in the range of 0-80 lp / mm, the MTF curve is uniformly and smoothly decreased from the center to the edge of the field of view, and has good imaging quality and good detail resolution ability in low and high frequency conditions; the axial chromatic aberration of the longest wavelength and the shortest wavelength is controlled within ±1.2 μm, which indicates that the wide-angle lens can well correct the chromatic aberration of the edge of the field of view and the secondary spectrum of the entire image plane.

[0075] Please refer to Table 4 for the optical properties corresponding to each of the above examples, including the effective focal length f, the maximum half field angle θ, the entrance pupil diameter EPD, the total optical length TTL, the aperture value FNO, the true half image height IH, and the numerical value corresponding to each conditional expression in the examples.

[0076] Table 4

[0077] Parameter and Condition Formula Example 1 Example 2 Example 3 f (mm) 5.258 5.270 5.264 θ (°) 60 60 60 EPD (mm) 2.673 2.677 2.676 TTL (mm) 17.720 18.147 17.778 FNO 2.0 2.0 2.0 IH (mm) 6.0 6.0 6.0 CRA (°) 37.2 37.1 37.4 TTL / IH 2.916 2.952 3.002 D1 / (IH x tan θ) 1.376 1.292 1.423 f1 / f2 -0.459 -0.460 -0.455 f2 / f 5.850 5.836 5.991 (R22+R21) / (R22-R21) 1.759 1.763 1.846 CT2 / AT23 2.880 2.880 2.83 f34 / f 6.808 6.796 6.698 CT3 / (TTL-BFL) 0.234 0.222 0.237 (R42-R41) / f4 0.333 0.333 0.356 AT45 / TTL 0.131 0.151 0.154 BFL / TTL 0.522 0.517 0.518 (CT2+CT3+CT4) / (ET2+ET3+ET4) 1.239 1.238 1.255

[0078] In summary, the wide-angle lens of the embodiments of the present application has the advantages of large aperture, miniaturization, light weight, and large wide-angle by reasonably matching the lens shape and optical power combination between each lens, and can meet the diversified use requirements in the field of mobile phones.

[0079] In the description of the present specification, the description of the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0080] The above-described embodiments only express several implementation manners of the present application, which are described in a more specific and detailed manner, but cannot be understood as a limitation on the patent scope of the present application. It should be noted that, for those of ordinary skill in the art, several modifications and improvements can be made without departing from the concept of the present application, which are all within the protection scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. A retrofocus lens, in total four lenses, characterized in that, In order from the object side to the imaging surface along the optical axis, there are: a first lens with negative refractive power, an object side surface of the first lens being convex, an image side surface of the first lens being concave; a second lens with positive refractive power, an object side surface of the second lens being convex at the near optical axis; a third lens with positive refractive power, an image side surface of the third lens being convex; a fourth lens with positive refractive power, an image side surface of the fourth lens being convex; a mobile phone lens module; wherein the total optical length TTL of the corner-expanding lens and the image height IH corresponding to the maximum half field angle of the corner-expanding lens satisfy: 2.6 < TTL / IH < 3.1; the effective aperture D1 of the object side surface of the first lens, the image height IH corresponding to the maximum half field angle of the corner-expanding lens, and the maximum half field angle θ of the corner-expanding lens satisfy: 1.0 < D1 / (IH x tanθ) < 1.

6.

2. The extender lens according to claim 1, characterized in that, the total optical length TTL of the corner-expanding lens and the image height IH corresponding to the maximum half field angle of the corner-expanding lens satisfy: 2.916 ≤ TTL / IH ≤ 3.002; the effective aperture D1 of the object side surface of the first lens, the image height IH corresponding to the maximum half field angle of the corner-expanding lens, and the maximum half field angle θ of the corner-expanding lens satisfy: 1.292 ≤ D1 / (IH x tanθ) ≤ 1.

423.

3. The extender lens of claim 1, wherein the effective focal length f1 of the first lens and the effective focal length f2 of the second lens satisfy: -1.0 < f1 / f2 < -0.

2.

4. The extender lens of claim 1, wherein the effective focal length f2 of the second lens and the effective focal length f of the corner-expanding lens satisfy: 5.0 < f2 / f < 7.0; the curvature radius R21 of the object side surface of the second lens and the curvature radius R22 of the image side surface of the second lens satisfy: 1.0 < (R22+R21) / (R22-R21) < 2.

5.

5. The extender lens of claim 1, wherein the center thickness CT2 of the second lens and the air gap AT23 between the second lens and the third lens on the optical axis satisfy: 2.8 < CT2 / AT23 < 2.

9.

6. The extender lens of claim 1, wherein the combined focal length f34 of the third lens and the fourth lens and the effective focal length f of the corner-expanding lens satisfy: 6.0 < f34 / f < 7.

5.

7. The extender lens of claim 1, wherein the center thickness CT3 of the third lens and the interval BFL between the image side surface of the fourth lens and the imaging surface on the optical axis and the total optical length TTL of the corner-expanding lens satisfy: 0.2 < CT3 / (TTL-BFL) < 0.

25.

8. The extender lens of claim 1, wherein, the curvature radius R41 of the object side surface of the fourth lens, the curvature radius R42 of the image side surface of the fourth lens, and the effective focal length f4 of the fourth lens satisfy: 0.3 < (R42-R41) / f4 < 0.

4.

9. The extender lens of claim 1, wherein, the air gap AT45 between the fourth lens and the mobile phone lens module on the optical axis and the total optical length TTL of the corner-expanding lens satisfy: 0.12 < AT45 / TTL < 0.17; the interval BFL between the image side surface of the fourth lens and the imaging surface on the optical axis and the total optical length TTL of the corner-expanding lens satisfy: 0.48 < BFL / TTL < 0.

55.

10. The extender lens of claim 1, wherein, The center thickness CT2 of the second lens, the edge thickness ET2 of the second lens, the center thickness CT3 of the third lens, the edge thickness ET3 of the third lens, the center thickness CT4 of the fourth lens, and the edge thickness ET4 of the fourth lens satisfy: 1.2 < (CT2 + CT3 + CT4) / (ET2 + ET3 + ET4) < 1.3.

Images