A medium format dual focal length lens optical system

Abstract

The present application relates to a kind of medium format bifocal lens optical systems, by 13 lenses form optical power in order to be "negative-positive-positive-negative" four groups of architecture, from object side to image side along optical axis in order to be coaxially arranged fixed group, zoom group, compensation group, focusing group, aperture stop is placed in the fixed position between two lenses of compensation group. Zoom group can move along optical axis, for realizing the optical zoom between wide-angle end and long-focus end, compensation group and focusing group can move along optical axis, for compensating the change of image plane position in the optical zoom process of zoom lens. Aperture stop moves with compensation group, so that aperture is substantially unchanged at wide-angle end and long-focus end. The present application realizes the compatibility of high magnification and small volume of bifocal lens, while ensuring that the two focal lengths (wide-angle end and long-focus end) meet high resolution, and give consideration to low distortion imaging performance and large field angle. Through the improvement of the technical scheme of the present application, the demand of medium format optical imaging camera in larger field of view, higher resolution, smaller distortion and the like is met.

Description

Technical Field

[0001] This invention relates to the field of optical design technology, and more specifically to a medium format dual focal length lens optical system. Background Technology

[0002] Optical lenses are one of the core components in machine vision imaging. As imaging requirements become increasingly stringent, the accuracy of optical lens correction in areas such as chromatic aberration and field curvature also increases. The quality of its imaging directly affects the overall performance of the machine.

[0003] Urban pipeline inspection, building damage identification, and road crack identification require the design of medium format dual-focal-length optical lenses to meet the needs of optical imaging cameras in terms of larger field of view, higher resolution, and less distortion. However, in optical design, distortion and field of view are mutually restrictive; image distortion increases with the increase of field of view, resulting in inaccuracies and affecting image recognition and analysis.

[0004] Existing lenses struggle to accommodate medium to high zoom capabilities, wide-angle performance, and low distortion. Current optical imaging lenses generally suffer from small apertures and low resolution, failing to meet the brightness requirements of images in low-light conditions. Mainstream 1080P lenses have a resolution of 2 megapixels, which is insufficient for high-pixel demands. Modern high-resolution lenses require resolutions ranging from tens of millions to hundreds of millions of pixels, necessitating both wide-angle initial scanning and telephoto fine scanning. Currently, this is often achieved using two separate cameras, resulting in high cost and large size.

[0005] In summary, how to effectively solve the problems of insufficient image resolution, distortion, and large field of view in existing optical imaging cameras, which lead to difficulties in image analysis, is an urgent issue that needs to be addressed by those skilled in the art. Summary of the Invention

[0006] To address the aforementioned existing technologies and their problems, this invention proposes a medium format dual-focal-length lens optical system. This system uses a single lens to achieve switching between dual focal length fields of view, simultaneously accommodating wide-angle initial viewing and telephoto fine viewing, thus realizing a compact, high-performance medium format camera. The system as a whole features a four-element zoom structure.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] This invention discloses a medium format dual-focal-length lens optical system, comprising, coaxially arranged from the object side to the image side, a first fixed group with negative optical power, a zoom group with positive optical power, a compensation group with positive optical power, and a focusing group with negative optical power. An aperture stop is fixedly positioned between the two lenses of the compensation group. The zoom group, the compensation group, and the focusing group are movable along the optical axis to achieve switching between the two focal lengths.

[0009] According to one aspect of the present invention, along the optical axis from the object side to the image side, the first fixed group sequentially includes: a first lens having negative optical power, a second lens having positive optical power, and a third lens having negative optical power; the object side and image side of the first lens are convex and concave, respectively; the object side and image side of the second lens are convex and concave, respectively; the object side and image side of the third lens are both concave; and the object side and image side of the first lens are both aspherical.

[0010] According to one aspect of the invention, along the optical axis from the object side to the image side, the zoom group sequentially comprises: a fourth lens with positive optical power, a fifth lens with positive optical power, a sixth lens with negative optical power, and a seventh lens with negative optical power. The object-side and image-side surfaces of the fourth lens are both convex; the object-side and image-side surfaces of the fifth lens are both convex; the object-side and image-side surfaces of the sixth lens are both concave; the object-side and image-side surfaces of the seventh lens are convex and concave, respectively; the object-side surface of the fourth lens is aspherical; the image-side surface of the sixth lens is aspherical; the object-side and image-side surfaces of the seventh lens are both aspherical; the fifth lens, the sixth lens, and the seventh lens are cemented together to form a cemented triplet lens.

[0011] According to one aspect of the invention, along the optical axis from the object side to the image side, the compensation group sequentially comprises: an eighth lens having positive optical power and a ninth lens having positive optical power. The object-side and image-side surfaces of the eighth lens are both convex; the object-side and image-side surfaces of the ninth lens are concave and convex, respectively; the object-side surface of the eighth lens is aspherical; and both the object-side and image-side surfaces of the ninth lens are aspherical.

[0012] According to one aspect of the invention, along the optical axis from the object side to the image side, the focusing group sequentially comprises: a tenth lens with negative optical power, an eleventh lens with positive optical power, a twelfth lens with positive optical power, and a thirteenth lens with negative optical power. The object-side and image-side surfaces of the tenth lens are both concave; the object-side and image-side surfaces of the eleventh lens are both convex; the object-side and image-side surfaces of the twelfth lens are convex and concave, respectively; the object-side and image-side surfaces of the thirteenth lens are both convex and concave; both the object-side and image-side surfaces of the twelfth lens are aspherical; and both the object-side and image-side surfaces of the thirteenth lens are aspherical. The tenth and eleventh lenses are cemented together to form a cemented doublet lens; the twelfth and thirteenth lenses are cemented together to form a cemented doublet lens.

[0013] The focal length Fw at the wide-angle end of the dual-focal-length lens, the focal length Ft at the telephoto end of the dual-focal-length lens, and the distance TTL from the first surface of the first fixed group to the imaging surface satisfy the following relationship: 55≤TTL / (Ft / Fw)≤65.

[0014] According to one aspect of the invention, the focal length FG1 of the first fixed group and the focal length Fw of the dual focal length lens at the wide-angle end satisfy the condition: -2.0 ≤ FG1 / Fw ≤ -1.8. The focal length FG2 of the zoom group and the focal length Fw of the dual focal length lens at the wide-angle end satisfy the condition: 1.8 ≤ FG2 / Fw ≤ 2.0. The focal length FG3 of the compensation group and the focal length Fw of the dual focal length lens at the wide-angle end satisfy the condition: 1.1 ≤ FG3 / Fw ≤ 1.3. The focal length FG4 of the focusing group and the focal length Fw of the dual focal length lens at the wide-angle end satisfy the condition: -1.2 ≤ FG4 / Fw ≤ -1.0.

[0015] This solution achieves dual-focal-length field-of-view switching using a single lens. It employs the aforementioned 13 lenses, rationally allocating the optical power and the shapes of their object-side and image-side surfaces. Furthermore, specific lenses utilize materials with specific dispersion coefficients, specific textures, and specific surface shapes. This achieves correction of chromatic aberration and second-order spectral density in the 450–656 nm visible light band at the wide-angle and telephoto ends of the dual-focal-length lens, while also correcting component tolerances and exhibiting excellent assembly and fabrication capabilities. This solution combines excellent imaging performance with medium to high magnification zoom and wide-angle low distortion, while also meeting high image resolution requirements. It effectively solves the problems of insufficient resolution in existing optical cameras and the difficulty of image analysis under large field-of-view and large distortion conditions. Attached Figure Description

[0016] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0017] Figure 1 This is a schematic diagram of the optical system structure at the wide-angle end of an embodiment of the present invention.

[0018] Figure 2 The image-side MTF at the wide-angle end of this invention

[0019] Figure 3 This is a field curvature and distortion curve diagram at the wide-angle end of the present invention.

[0020] Figure 4 This is a schematic diagram of the optical system structure at the telephoto end of an embodiment of the present invention.

[0021] Figure 5 The image-side MTF at the telephoto end of this invention

[0022] Figure 6 This is a field curvature and distortion curve at the telephoto end of the present invention. Detailed Implementation

[0023] The present invention will now be described in detail with reference to specific embodiments and accompanying drawings.

[0024] Figure 1This invention relates to a medium format dual-focal-length optical lens. This embodiment features a four-element zoom-transmissive structure. From the object side to the image side, along the optical axis, are coaxially arranged a first fixed group G1 with negative optical power, a zoom group G2 with positive optical power, a compensation group G3 with positive optical power, a focusing group G4 with negative optical power, a protective glass plate, and a CMOS sensor. The aperture stop STO is fixedly positioned between the two lenses of the compensation group. The zoom group G2 is movable along the optical axis to achieve optical zoom between the wide-angle and telephoto ends of the dual-focal-length lens. The compensation group G3 and the focusing group G4 are also movable along the optical axis to compensate for changes in the image plane position during optical zoom. The aperture stop STO moves with the compensation group, resulting in apertures of F#=4.80 at the wide-angle end and F#=4.83 at the telephoto end. By using the above settings and employing four lens groups with optical powers of negative, positive, positive, and negative in sequence, the dual-focal-length lens achieves compatibility between high magnification and small size. At the same time, it ensures high resolution at both focal lengths (wide-angle and telephoto ends) and also satisfies good performance in terms of low distortion imaging and large field of view. This solves the problems of low resolution and large distortion at large field of view that make image analysis difficult in existing optical cameras.

[0025] In this embodiment of the invention, along the optical axis from the object side to the image side, the first fixed group sequentially includes G1: a first lens L1 with negative optical power, a second lens L2 with positive optical power, and a third lens L3 with negative optical power; the object side S1 and the image side S2 of the first lens L1 are convex and concave, respectively; the object side S3 and the image side S4 of the second lens L2 are convex and concave, respectively; the object side S5 and the image side S6 of the third lens L3 are both concave; the object side S1 and the image side S2 of the first lens L1 are both aspherical.

[0026] In this embodiment of the invention, along the optical axis from the object side to the image side, the zoom group G2 sequentially includes: a fourth lens L4 with positive optical power, a fifth lens L5 with positive optical power, a sixth lens L6 with negative optical power, and a seventh lens L7 with negative optical power. The object-side surface S7 and image-side surface S8 of the fourth lens L4 are both convex; the object-side surface S9 and image-side surface S10 of the fifth lens L5 are both convex; the object-side surface S10 and image-side surface S11 of the sixth lens L6 are both concave; the object-side surface S11 and image-side surface S12 of the seventh lens L7 are convex and concave, respectively; the object-side surface S7 of the fourth lens L4 is aspherical; the image-side surface S11 of the sixth lens L6 is aspherical; the object-side surface S11 and image-side surface S12 of the seventh lens L7 are both aspherical; the fifth lens L5, the sixth lens L6, and the seventh lens L7 are cemented together to form a cemented triplet lens. The radius of curvature R of the cemented surfaces of the fifth and sixth lenses is... L5L6 The focal length FG2 of the zoom group satisfies the condition: -1.8 ≤ R L5L6 / FG2≤-1.5. The radius of curvature R of the cemented surface of the sixth lens and the seventh lens. L6L7 The focal length FG2 of the zoom group satisfies the condition: 0.2 ≤ R L6L7 / FG2≤0.5.

[0027] In this embodiment of the invention, along the optical axis from the object side to the image side, the compensation group G3 sequentially includes: an eighth lens L8 with positive optical power and a ninth lens L9 with positive optical power. The object-side surface S13 and the image-side surface S14 of the eighth lens L8 are both convex; the object-side surface S16 and the image-side surface S17 of the ninth lens L9 are concave and convex, respectively; the object-side surface S13 of the eighth lens L8 is aspherical; and the object-side surface S16 and the image-side surface S17 of the ninth lens L9 are both aspherical.

[0028] In this embodiment of the invention, along the optical axis from the object side to the image side, the focusing group G4 sequentially includes: a tenth lens L10 with negative optical power, an eleventh lens L11 with positive optical power, a twelfth lens L12 with positive optical power, and a thirteenth lens L13 with negative optical power. The object-side surface S18 and image-side surface S19 of the tenth lens L10 are both concave; the object-side surface S19 and image-side surface S20 of the eleventh lens L11 are both convex; the object-side surface S21 and image-side surface S22 of the twelfth lens L12 are convex and concave, respectively; the object-side surface S22 and image-side surface S23 of the thirteenth lens L13 are both convex and concave; the object-side surface S21 and image-side surface S22 of the twelfth lens L12 are both aspherical; and the object-side surface S22 and image-side surface S23 of the thirteenth lens L13 are both aspherical. The tenth lens L10 and the eleventh lens L11 are cemented together to form a cemented doublet lens; the twelfth lens L12 and the thirteenth lens L13 are cemented together to form a cemented doublet lens. The radius of curvature R of the cementing surface of the tenth lens and the eleventh lens is... L10L11 The focal length FG4 of the focusing group satisfies the condition: -0.6 ≤ R L10L11 / FG4≤-0.4. The radius of curvature R of the cemented surface of the twelfth and thirteenth lenses. L12L13 The focal length FG4 of the focusing group satisfies the condition: -15≤R L12L13 / FG4≤-10.

[0029] The focal length Fw at the wide-angle end of the dual-focal-length lens, the focal length Ft at the telephoto end of the dual-focal-length lens, and the distance TTL from the first surface of the front fixed group to the imaging surface satisfy the following relationship: 55≤TTL / (Ft / Fw)≤65.

[0030] According to one aspect of the invention, the focal length FG1 of the first fixed group and the focal length Fw of the dual focal length lens at the wide-angle end satisfy the condition: -2.0 ≤ FG1 / Fw ≤ -1.8. According to one aspect of the invention, the focal length FG2 of the zoom group and the focal length Fw of the dual focal length lens at the wide-angle end satisfy the condition: 1.8 ≤ FG2 / Fw ≤ 2.0. According to one aspect of the invention, the focal length FG3 of the compensation group and the focal length Fw of the dual focal length lens at the wide-angle end satisfy the condition: 1.1 ≤ FG3 / Fw ≤ 1.3. According to one aspect of the invention, the focal length FG4 of the focusing group and the focal length Fw of the dual focal length lens at the wide-angle end satisfy the condition: -1.2 ≤ FG4 / Fw ≤ -1.0.

[0031] In the embodiments of the present invention, the equivalent parameters of the wide-angle optical system and the equivalent parameters of the telephoto optical system of the medium format dual focal length optical lens are shown in Table 1 and Table 2, respectively.

[0032] Table 1. Parameters of Medium Format Bifocal Lenses

[0033] Surface serial number Surface type Radius of curvature R (mm) Thickness (mm) Refractive index Abbe number S0 spherical Infinity Infinity S1 aspherical 291.030 5.000 1.80 46.6 S2 aspherical 96.410 5.930 S3 spherical 173.020 11.780 1.92 20.9 S4 spherical 388.200 12.330 S5 spherical -206.770 5.000 1.71 53.9 S6 spherical 89.820 T1 S7 aspherical 62.490 22.190 1.62 63.4 S8 spherical -175.170 0.500 S9 spherical 41.760 19.110 1.62 63.4 S10 spherical -115.010 4.000 1.81 33.3 S11 aspherical 23.750 10.640 1.55 45.8 S12 aspherical 41.420 T2 S13 aspherical 178.130 8.900 1.85 23.8 S14 spherical -63.400 0.500 STOP spherical Infinity 0.850 S16 aspherical -197.150 8.300 1.62 63.4 S17 aspherical -61.750 T3 S18 spherical -243.750 2.500 1.81 33.3 S19 spherical 20.500 12.454 1.50 81.6 S20 spherical -86.000 6.400 S21 aspherical 688.220 5.040 1.49 70.1 S22 aspherical 500.000 4.770 1.71 53.9 S23 aspherical 62.400 T4 S24 spherical Infinity 2.800 S25 spherical Infinity 1.000 1.52 64.2 S26 spherical Infinity 2.000 S27 spherical Infinity 0.000

[0034] Table 1 lists the relevant parameters of each lens in the dual-focal-length lens of this embodiment, including: surface type, radius of curvature R, thickness, refractive index of the material, and Abbe number.

[0035] Table 2 Aspherical parameters of medium format dual-focal-length optical lenses

[0036] Surface serial number K <![CDATA[A4]]> <![CDATA[A6]]> <![CDATA[A8]]> <![CDATA[A 10 ]]> S1 0.00 -5.61E-07 -1.73E-10 5.56E-14 -8.95E-18 S2 -1.00 -1.52E-08 -5.29E-11 2.52E-16 -1.26E-18 S7 -1.00 5.24E-07 -6.47E-10 -5.71E-14 -1.29E-19 S11 -1.00 7.12E-07 5.76E-10 3.31E-13 0.00E+00 S12 1.30 3.00E-06 2.04E-08 5.38E-12 0.00E+00 S13 1.00 -5.18E-06 -3.51E-08 6.87E-12 0.00E+00 S16 1.00 7.21E-06 4.50E-09 -4.71E-11 0.00E+00 S17 0.02 1.80E-06 5.49E-09 2.81E-12 -3.24E-16 S21 1.00 -2.58E-06 2.51E-09 -1.26E-11 5.04E-15 S22 0.00 9.51E-05 -1.67E-09 2.29E-11 0.00E+00 S23 0.61 -1.88E-05 1.93E-09 -1.90E-11 1.49E-15

[0037] Table 2 lists the aspherical parameters of each aspherical lens in the dual-focal-length lens of this embodiment, including: the quadratic surface constant K, the fourth-order aspherical coefficient A4, the sixth-order aspherical coefficient A6, the eighth-order aspherical coefficient A8, and the tenth-order aspherical coefficient A1. 10 .

[0038] Table 3 Zoom data for wide-angle and telephoto ends

[0039] Wide-angle end telephoto end T1 98.90 6.00 T2 6.80 27.50 T3 1.40 12.80 T4 2.75 63.70

[0040] Combination Figure 1 As shown in Table 1 above, the dual-focal-length lens of this embodiment uses 13 lenses and forms a four-group architecture with optical power in the order of "negative-positive-positive-negative". It achieves an aperture of 4.8 and has high imaging quality in different temperatures within the range of -20 to 60°C. The field of view at the wide-angle end is greater than 74°, and it takes into account both small distortion and high magnification optical zoom performance.

[0041] The optical system satisfies the following relationship:

[0042] The first fixed lens group G1 has a negative focal length and consists of three monolithic lenses. It satisfies the following relationship:

[0043] -2.0≤FG1 / Fw≤-1.8;

[0044] -0.5≤FG1 / Ft≤-0.4;

[0045] FG1, Fw, and Ft are the focal lengths of the first lens group G1, the wide-angle end, and the telephoto end, respectively.

[0046] In this design, the first lens group is a negative lens, which can quickly converge a large field of view beam to meet the requirements of a large field of view and a small aperture at a short focal length. It also helps to increase the light transmission aperture while meeting the aperture limit, improve the image resolution, and reduce distortion at dual focal lengths, ensuring minimal distortion in the captured image.

[0047] The wide-angle optical system of this scheme has a field of view of 74° and an infinity working distance. Its image-side MTF is as follows: Figure 2 As shown, the MTF curves of each field of view are close to each other, indicating that the aberration correction of each field of view is relatively consistent; their field curvature and distortion are as follows: Figure 3 As shown, its value is within an acceptable range for medium format wide-angle optical lenses.

[0048] The telephoto optical system of this scheme has a field of view of 20° and an infinity working distance. Under these conditions, its image-side MTF is as follows: Figure 4 As shown, the MTF curves of each field of view are relatively close to each other, indicating that the aberration correction of each field of view is consistent and good; their field curvature and distortion are as follows. Figure 5 As shown, its value is within a good range for microscopic images.

[0049] In summary, the medium format dual focal length lens optical system of the present invention is designed to meet the needs of urban drones for optical imaging cameras in terms of larger field of view, higher resolution, and less distortion, thereby solving the bottleneck problem of independent control of this core component in drone imaging.

[0050] The embodiments described above are merely for illustrating the technical ideas and features of the present invention. Their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be used to limit the patent scope of the present invention. That is, all equivalent changes or modifications made in accordance with the spirit disclosed in the present invention should still be covered within the patent scope of the present invention.

Claims

1. A medium format dual focal length lens optical system, comprising, along the optical axis from the object side to the image side, a first fixed group (G1), a zoom group (G2), a compensation group (G3), and a focusing group (G4), and further comprising an aperture stop (STO), characterized in that, The first fixed group (G1) and the focusing group (G4) have negative optical power, and the zoom group (G2) and the compensation group (G3) have positive optical power; The zoom group (G2), the compensation group (G3), and the focus group (G4) are movable along the optical axis; The aperture stop (STO) is fixed in the middle of the two lenses in the compensation group; The focal length Fw at the wide-angle end of the dual-focal-length lens, the focal length Ft at the telephoto end of the dual-focal-length lens, and the distance TTL from the first surface of the first fixed group (G1) to the imaging surface satisfy the following relationship: 55≤TTL / (Ft / Fw)≤65. Along the optical axis from the object side to the image side, the first fixed group (G1) sequentially includes: a first lens (L1) with negative optical power, a second lens (L2) with positive optical power, and a third lens (L3) with negative optical power. The object-side surface (S1) and image-side surface (S2) of the first lens (L1) are convex and concave, respectively; The object-side surface (S3) and image-side surface (S4) of the second lens (L2) are convex and concave, respectively; The object-side surface (S5) and image-side surface (S6) of the third lens (L3) are both concave; The object-side surface (S1) and image-side surface (S2) of the first lens (L1) are both aspherical.

2. The medium format dual focal length lens optical system according to claim 1, characterized in that, Along the optical axis from the object side to the image side, the zoom group (G2) sequentially includes: a fourth lens (L4) with positive optical power, a fifth lens (L5) with positive optical power, a sixth lens (L6) with negative optical power, and a seventh lens (L7) with negative optical power. The object-side surface (S7) and image-side surface (S8) of the fourth lens (L4) are both convex; The object-side surface (S9) and image-side surface (S10) of the fifth lens (L5) are both convex; The object-side surface (S10) and image-side surface (S11) of the sixth lens (L6) are both concave; The object-side surface (S11) and image-side surface (S12) of the seventh lens (L7) are convex and concave, respectively. The object-side surface (S7) of the fourth lens (L4) is aspherical; The image-side surface (S11) of the sixth lens (L6) is aspherical; The object-side surface (S11) and image-side surface (S12) of the seventh lens (L7) are both aspherical. The fifth lens (L5), the sixth lens (L6), and the seventh lens (L7) are cemented together to form a cemented triplet lens.

3. The medium format dual focal length lens optical system according to claim 1, characterized in that, Along the optical axis from the object side to the image side, the compensation group (G3) sequentially includes: an eighth lens (L8) with positive optical power and a ninth lens (L9) with positive optical power. The object-side surface (S13) and image-side surface (S14) of the eighth lens (L8) are both convex; The object-side surface (S16) and image-side surface (S17) of the ninth lens (L9) are concave and convex, respectively. The object-side surface (S13) of the eighth lens (L8) is aspherical; The object-side surface (S16) and image-side surface (S17) of the ninth lens (L9) are both aspherical.

4. The medium format dual focal length lens optical system according to claim 1, characterized in that, Along the optical axis from the object side to the image side, the focusing group (G4) sequentially includes: a tenth lens (L10) with negative optical power, an eleventh lens (L11) with positive optical power, a twelfth lens (L12) with positive optical power, and a thirteenth lens (L13) with negative optical power. The object-side surface (S18) and image-side surface (S19) of the tenth lens (L10) are both concave; The object-side surface (S19) and image-side surface (S20) of the eleventh lens (L11) are both convex; The object side (S21) and image side (S22) of the twelfth lens (L12) are convex and concave, respectively. The object side (S22) and image side (S23) of the thirteenth lens (L13) are both convex and concave; The object-side surface (S21) and image-side surface (S22) of the twelfth lens (L12) are both aspherical. The object-side surface (S22) and image-side surface (S23) of the thirteenth lens (L13) are both aspherical. The tenth lens (L10) and the eleventh lens (L11) are cemented together to form a cemented doublet lens; The twelfth lens (L12) and the thirteenth lens (L13) are cemented together to form a cemented doublet lens.

5. The medium format dual focal length lens optical system according to claim 1, characterized in that, The focal length of the first fixed group (G1) is negative, and it satisfies the following relationship: -2.0≤FG1 / Fw≤-1.8; -0.5≤FG1 / Ft≤-0.4; FG1, Fw, and Ft are the focal lengths of the first fixed group (G1), the wide-angle end, and the telephoto end, respectively.

6. The medium format dual focal length lens optical system according to claim 1, characterized in that, The focal length FG1 of the first fixed group and the focal length Fw of the dual focal length lens at the wide-angle end satisfy the condition: -2.0≤FG1 / Fw≤-1.8; the focal length FG2 of the zoom group and the focal length Fw of the dual focal length lens at the wide-angle end satisfy the condition: 1.8≤FG2 / Fw≤2.0; the focal length FG2 of the compensation group and the focal length Fw of the dual focal length lens at the wide-angle end satisfy the condition: 1.1≤FG3 / Fw≤1.3; and the focal length FG4 of the focusing group and the focal length Fw of the dual focal length lens at the wide-angle end satisfy the condition: -1.2≤FG4 / Fw≤-1.0.

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