Telephoto lens and imaging system

Abstract

The application discloses a telephoto lens and an imaging system, and relates to the technical field of photography. The telephoto lens comprises a shell, a first lens group and a second lens group. The first lens group and the second lens group are located in the shell, and the first lens group and the second lens group are arranged in sequence along an optical axis from an object plane to an image plane. The first lens group has positive focal power, and the second lens group has negative focal power. The total focal length of the telephoto lens is the difference between the absolute value of the positive focal power of the first lens group and the absolute value of the negative focal power of the second lens group. The first lens group can reciprocally move along the optical axis relative to the second lens group to realize focusing. The telephoto lens and the imaging system can reduce the optical total length of the lens and improve the imaging image quality.

Description

Technical Field

[0001] This invention relates to the field of photography technology, and in particular to a teleconverter lens and imaging system. Background Technology

[0002] External lenses for mobile phones, especially teleconverters, are mainly used to extend the focal length of mobile phone photography, enabling users to clearly capture details in distant shooting scenarios such as concerts. Their working principle is similar to that of a telescope, improving the shooting effect of distant scenes through magnification.

[0003] Currently, mobile phone external lenses on the market are mainly divided into two categories: Universal mobile phone external lenses have the advantage of being compatible with lenses from different brands and models of mobile phones. However, due to a lack of specific design, these lenses often have a negative impact on the relative illumination, chromatic aberration, resolution, and distortion control of the image during imaging.

[0004] Professional-grade external lenses for mobile phones are typically designed to match specific mobile phone lenses, thus offering superior optical quality and maintaining original image quality without sacrificing relative illumination, chromatic aberration, resolution, or distortion control. However, their drawback is that they are usually larger and less portable. Summary of the Invention

[0005] The main objective of this invention is to propose a teleconverter lens that aims to improve image quality while reducing the overall optical length of the lens.

[0006] To achieve the above objectives, the present invention proposes a teleconverter lens, comprising a housing, a first lens group, and a second lens group. The first lens group and the second lens group are located within the housing and are arranged sequentially from the object plane to the image plane along the optical axis. The first lens group has positive optical power, and the second lens group has negative optical power. The design length of the teleconverter lens is equal to the length of the first lens group plus the distance between the image-side focal plane of the first lens group and the final surface of the first lens group, minus the distance between the object-side focal plane of the second lens group and the starting surface of the second lens group plus the length of the second lens group. The first lens group can reciprocate relative to the second lens group along the optical axis to achieve focusing. The first lens group includes a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, a seventh lens, and an eighth lens; the first lens, the second lens, the third lens, the fifth lens, and the eighth lens are positive power lenses; the fourth lens, the sixth lens, and the seventh lens are negative power lenses; the third lens and the fourth lens are bonded together to form a first cemented lens with negative power; the fifth lens and the sixth lens are bonded together to form a second cemented lens with positive power; the seventh lens and the eighth lens are bonded together to form a third cemented lens with positive power. The second lens group includes a ninth lens, a tenth lens, an eleventh lens, and a twelfth lens; the tenth lens and the twelfth lens are positive power lenses; the ninth lens and the eleventh lens are negative power lenses; the tenth lens and the eleventh lens are bonded together to form a fourth cemented lens with negative power.

[0007] In one embodiment, the optical power of the first lens group is ΦⅠ, and the optical power of the second lens group is ΦⅡ, satisfying the following relationship: -0.4 < ΦⅠ / ΦⅡ < -0.3.

[0008] In one embodiment, the Abbe number of the fifth lens is Vd5, and the Abbe number of the sixth lens is Vd6, satisfying the following relationship: 50 <Vd5-Vd6<60。

[0009] In one embodiment, the refractive index of the seventh lens is Nd7, and the refractive index of the eighth lens is Nd8, satisfying the following relationship: 0.1 <Nd7-Nd8<0.25。

[0010] In one embodiment, the optical power of the fourth cemented lens is Φj4, and the optical power of the second lens group is ΦⅡ, satisfying the following relationship: 0.8 < Φj4 / ΦⅡ < 1.2.

[0011] In one embodiment, the full aperture of the first lens is DM1, and the distance from the object-side surface of the first lens to the object-side surface of the second lens is TH1, satisfying the following relationship: 3 <DM1 / TH1<4。

[0012] In one embodiment, the total optical length of the teleconverter is less than 60 mm.

[0013] In one embodiment, the full aperture of the first lens is DM1, and the full aperture of the twelfth lens is DM12, satisfying the following relationship: 5 <DM1 / DM12<5.6。

[0014] In one embodiment, the full aperture of the first lens is DM1, which is less than 44 mm.

[0015] The present invention also proposes an imaging system including the above-mentioned teleconverter lens, the imaging system further including an imaging lens, the teleconverter lens and the imaging lens being arranged sequentially from the object plane to the image plane along the optical axis.

[0016] The technical solution of this invention utilizes a Galilean structure, whose length is approximately the difference in focal lengths of two lenses, under the same exit pupil diameter and magnification. This structure is more compact and portable than a Keplerian structure, whose length is approximately the sum of the focal lengths of two lenses. It achieves high-magnification imaging while shortening the overall optical length, contributing to lens miniaturization. The first lens group is a movable group, and the second lens group is a fixed group. Focusing is achieved by axially moving the first lens group.

[0017] The technical solution of the present invention utilizes the second cemented lens of the first lens group to eliminate axial chromatic aberration and transverse chromatic aberration, avoiding purple fringing in the image; the third cemented lens corrects field curvature and astigmatism, reducing tolerance sensitivity; the fourth cemented lens of the second lens group corrects distortion and expands the light beam into parallel light, so that the edge illumination is not affected, so that the teleconverter lens of the present invention meets the requirements of lightweight and miniaturization while ensuring that the image quality is not affected. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the structure of an embodiment of the teleconverter lens provided by the present invention; Figure 2 A transverse chromatic aberration curve of a teleconverter lens provided in an embodiment of the present invention; Figure 3 The graph shows the longitudinal spherical aberration, field curvature, and distortion of a teleconverter lens provided in an embodiment of the present invention. Figure 4 The MTF curve of a teleconverter lens provided in an embodiment of the present invention.

[0020] Explanation of icon numbers: L1, First lens; L2, Second lens; L3, Third lens; L4, Fourth lens; L5, Fifth lens; L6, Sixth lens; L7, Seventh lens; L8, Eighth lens; L9, Ninth lens; L10, Tenth lens; L11, Eleventh lens; L12, Twelfth lens; G, Flat glass; STO, Aperture stop.

[0021] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0023] It should be noted that if the embodiments of the present invention involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a specific posture. If the specific posture changes, the directional indicators will also change accordingly.

[0024] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the use of "and / or" or "and / or" throughout the text includes three parallel solutions. For example, "A and / or B" includes solution A, solution B, or a solution where both A and B are satisfied. Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0025] In existing teleconverters, a Keplerian structure is typically used to achieve high magnification. The basic Keplerian structure consists of two positive power lenses. While this structure can achieve high magnification, it has the following drawbacks: the Keplerian structure's length is approximately the sum of the focal lengths of the two lenses, resulting in a relatively long overall optical length, making it difficult to compress the overall size and hindering lightweight and miniaturized designs. Furthermore, the Keplerian structure produces an inverted real image, requiring image flipping correction via software algorithms. This not only increases the computational burden of image processing but may also introduce interpolation errors and detail loss, affecting the final image quality.

[0026] Reference Figure 1This invention proposes a teleconverter lens, comprising a housing, a first lens group, and a second lens group. The first and second lens groups are located within the housing and arranged sequentially along the optical axis from the object plane to the image plane. The first lens group has positive optical power, and the second lens group has negative optical power. The design length of the teleconverter lens = the length of the first lens group + the distance between the image-side focal plane of the first lens group and the final surface of the first lens group - the distance between the object-side focal plane of the second lens group and the starting surface of the second lens group + the length of the second lens group. The first lens group can reciprocate relative to the second lens group along the optical axis to achieve focusing.

[0027] The first lens group includes a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, a fifth lens L5, a sixth lens L6, a seventh lens L7, and an eighth lens L8; the first lens L1, the second lens L2, the third lens L3, the fifth lens L5, and the eighth lens L8 are positive power lenses; the fourth lens L4, the sixth lens L6, and the seventh lens L7 are negative power lenses; the third lens L3 and the fourth lens L4 are bonded together to form a first cemented lens with negative power; the fifth lens L5 and the sixth lens L6 are bonded together to form a second cemented lens with positive power; and the seventh lens L7 and the eighth lens L8 are bonded together to form a third cemented lens with positive power.

[0028] The second lens group includes the ninth lens L9, the tenth lens L10, the eleventh lens L11, and the twelfth lens L12; the tenth lens L10 and the twelfth lens L12 are positive power lenses; the ninth lens L9 and the eleventh lens L11 are negative power lenses; the tenth lens L10 and the eleventh lens L11 are bonded together to form a fourth cemented lens with negative power.

[0029] The basic Galilean structure includes a lens with positive optical power and a lens with negative positive optical power. The technical solution of the present invention adopts a Galilean structure, that is, the teleconverter of the present invention consists of a first lens group with positive optical power and a second lens group with negative optical power from the object side to the image plane. This allows light to exit as parallel light after passing through the second lens group and directly generate an upright image, avoiding the image inversion correction process, reducing the computational burden and the loss of image details.

[0030] The technical solution of this invention utilizes a Galilean structure, whose length is approximately the difference in focal length between two lenses, under the same exit pupil diameter and magnification. This structure is more compact and portable than a Keplerian structure, whose length is approximately the sum of the focal lengths of two lenses. It achieves high-magnification imaging while shortening the overall optical length of the teleconverter, contributing to lens miniaturization. The first lens group is a moving group, and the second lens group is a fixed group. Focusing is achieved by reciprocating axially with the first lens group.

[0031] The technical solution of the present invention uses the second cemented lens of the first lens group to eliminate axial chromatic aberration and lateral chromatic aberration, avoiding purple fringing in imaging; the third cemented lens corrects field curvature and astigmatism, reducing the tolerance sensitivity; the fourth cemented lens of the second lens group corrects distortion and expands the light beam into parallel light, so that the marginal illumination is not affected, enabling the teleconverter lens of the present invention to meet the requirements of lightweight and miniaturization while ensuring that the imaging quality is not affected.

[0032] In an embodiment of the present invention, the optical power of the first lens group is ΦⅠ, and the optical power of the second lens group is ΦⅡ, satisfying the following relationship: -0.4 < ΦⅠ / ΦⅡ < -0.3, so as to achieve a 3-fold magnification of the teleconverter lens, meeting the needs of users for distant view and portrait photography.

[0033] In an embodiment of the present invention, the Abbe number is an important parameter to measure the dispersion characteristics of materials. The larger the value, the smaller the dispersion and the clearer the imaging. The Abbe number of the fifth lens L5 is Vd5, and the Abbe number of the sixth lens L6 is Vd6, satisfying the following relationship: 50 < Vd5 - Vd6 < 60, thereby correcting chromatic aberration and avoiding purple fringing in imaging. Refer to Figure 2 , the lateral chromatic aberration of the teleconverter lens is effectively controlled, and obvious purple fringing will not occur, ensuring the authenticity of imaging colors.

[0034] In an embodiment of the present invention, the refractive index of the seventh lens L7 is Nd7, and the refractive index of the eighth lens L8 is Nd8, satisfying the following relationship: 0.1 < Nd7 - Nd8 < 0.25, thereby correcting field curvature and astigmatism, reducing the tolerance sensitivity.

[0035] In an embodiment of the present invention, the optical power of the fourth cemented lens is Φj4, and the optical power of the second lens group is ΦⅡ, satisfying the following relationship: 0.8 < Φj4 / ΦⅡ < 1.2, thereby uniformly expanding the light beam entering the second lens group and making the marginal illumination not affected.

[0036] In an embodiment of the present invention, the full aperture of the first lens L1 is DM1, and the distance from the object side of the first lens L1 to the object side of the second lens L2 is TH1, satisfying the following relationship: 3 < DM1 / TH1 < 4. By controlling the ratio of the full aperture to the thickness of the first lens L1, while ensuring sufficient light transmission, it avoids the increase in the volume and weight of the teleconverter lens caused by the excessive thickness of the first lens L1.

[0037] In an embodiment of the present invention, the overall optical length of the teleconverter lens is less than 60 mm, achieving a compact structural design, which is convenient for carrying and using.

[0038] In an embodiment of the present invention, the full aperture of the first lens L1 is DM1, and the full aperture of the twelfth lens L12 is DM12, satisfying the following relationship: 5 < DM1 / DM12 < 5.6, so that the teleconverter lens has a reasonable full aperture gradient, controls the optical distortion within 1%, and expands the light beam into parallel light.

[0039] Referring to Figure 3 , the optical distortion of the teleconverter lens is less than 1%, and the field curvature is effectively corrected, ensuring the authenticity of the geometric shape of the image. At the same time, it can also improve the passing rate of the marginal light entering the teleconverter lens, and thus there is no loss of marginal illuminance and no effect of blocking the captured image, ensuring the uniformity of the image brightness. Among them, in Figure 3 , S represents the sagittal direction, and T represents the tangential direction, which respectively reflect the imaging performance of the optical system in different directions. S1, S2, S3, S4, S5, S6 respectively represent the sagittal field curvatures at wavelengths of 650 nm, 610 nm, 555 nm, 510 nm, 470 nm, and 435 nm, and are represented by solid lines. T1, T2, T3, T4, T5, T6 respectively represent the tangential field curvatures at wavelengths of 650 nm, 610 nm, 555 nm, 510 nm, 470 nm, and 435 nm, and are represented by dashed lines.

[0040] The modulation transfer function (Modulation Transfer Function, abbreviated as MTF) is used to quantitatively describe the resolution of the lens. Referring to Figure 4 's MTF curve graph, the central resolution of the teleconverter lens fully reaches the diffraction limit, and the marginal resolution of the teleconverter lens basically reaches the diffraction limit.

[0041] In an embodiment of the present invention, the full aperture DM1 of the first lens L1 is less than 44 mm, avoiding the increase in the volume and weight of the teleconverter lens caused by the overly large full aperture of the first lens L1.

[0042] Embodiment 1 Referring to Figure 1 , the teleconverter lens includes a first lens group, a second lens group, a flat glass G, and an aperture STO in sequence from the object side to the image plane. The light passes through the aperture STO and enters an ideal lens (not shown) of the simulated mobile phone lens and reaches the image plane. After connecting the ideal lens, the focal length f of the teleconverter lens is 44.64 mm, the aperture value F is 2.53, the image plane diameter is 6.7 mm, and the diagonal field angle is 8.5°.

[0043] Specifically, in this embodiment, the surface types, curvature radii, thicknesses, refractive indices, and Abbe numbers of the multiple lenses of the teleconverter lens are as shown in Table 1 below.

[0044] Table 1 Design value table of the optical physical parameters of the teleconverter lens in Embodiment 1

[0045] In Table 1 above, the surface numbers are assigned according to the surface sequence of each lens; the radius of curvature represents the degree of curvature of the lens surface, with a positive value indicating that the surface bends towards the image plane and a negative value indicating that the surface bends towards the object plane; the thickness represents the central axial distance between the current surface and the next surface; the refractive index represents the ability of the material between the current surface and the next surface to deflect light; a blank space indicates that the current position is air with a refractive index of 1; the Abbe number represents the dispersion characteristics of the material between the current surface and the next surface. The refractive index of FCD1 optical glass is 1.49700, and the Abbe number is 81.5.

[0046] The present invention also proposes an imaging system including the above-mentioned teleconverter lens, the imaging system further including an imaging lens, the teleconverter lens and the imaging lens being arranged sequentially from the object plane to the image plane along the optical axis.

[0047] The above description is merely an exemplary embodiment of the present invention and does not limit the scope of patent protection of the present invention. Any equivalent structural transformations made using the contents of the present invention's specification and drawings under the technical concept of the present invention, or direct / indirect applications in other related technical fields, are included within the scope of patent protection of the present invention.

Claims

1. A teleconverter lens, characterized in that, The teleconverter includes a housing, a first lens group, and a second lens group. The first and second lens groups are located inside the housing and are arranged sequentially from the object plane to the image plane along the optical axis. The first lens group has positive optical power, and the second lens group has negative optical power. The design length of the teleconverter is equal to the length of the first lens group plus the distance between the image-side focal plane of the first lens group and the final surface of the first lens group, minus the distance between the object-side focal plane of the second lens group and the starting surface of the second lens group plus the length of the second lens group. The first lens group can reciprocate relative to the second lens group along the optical axis to achieve focusing. Of these, 12 lenses have diopter properties; The first lens group includes a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, a seventh lens, and an eighth lens; the first lens, the second lens, the third lens, the fifth lens, and the eighth lens are positive power lenses; the fourth lens, the sixth lens, and the seventh lens are negative power lenses; the third lens and the fourth lens are bonded together to form a first cemented lens with negative power; the fifth lens and the sixth lens are bonded together to form a second cemented lens with positive power; the seventh lens and the eighth lens are bonded together to form a third cemented lens with positive power. The second lens group includes a ninth lens, a tenth lens, an eleventh lens, and a twelfth lens; the tenth lens and the twelfth lens are positive power lenses; the ninth lens and the eleventh lens are negative power lenses; the tenth lens and the eleventh lens are bonded together to form a fourth cemented lens with negative power. The optical power of the first lens group is ΦⅠ, and the optical power of the second lens group is ΦⅡ, satisfying the following relationship: -0.4 < ΦⅠ / ΦⅡ < -0.3; The full aperture of the first lens is DM1, and the distance from the object-side surface of the first lens to the object-side surface of the second lens is TH1, satisfying the following relationship: 3 <DM1 / TH1<4; The total optical length of the teleconverter is less than 60mm.

2. The teleconverter lens as described in claim 1, characterized in that, The Abbe number of the fifth lens is Vd5, and the Abbe number of the sixth lens is Vd6, satisfying the following relationship: 50 <Vd5-Vd6<60。 3. The teleconverter lens as described in claim 1, characterized in that, The seventh lens has a refractive index of Nd7, and the eighth lens has a refractive index of Nd8, satisfying the following relationship: 0.1 <Nd7-Nd8<0.25。 4. The teleconverter lens as described in claim 1, characterized in that, The optical power of the fourth cemented lens is Φj4, and the optical power of the second lens group is ΦⅡ, satisfying the following relationship: 0.8 < Φj4 / ΦⅡ < 1.

2.

5. The teleconverter lens as described in claim 1, characterized in that, The first lens has a full aperture of DM1, and the twelfth lens has a full aperture of DM12, satisfying the following relationship: 5 <DM1 / DM12<5.6。 6. The teleconverter lens as described in claim 5, characterized in that, The full aperture of the first lens is DM1, which is less than 44mm.

7. An imaging system, characterized in that, The imaging system includes a teleconverter lens as described in any one of claims 1-6, and further includes an imaging lens, wherein the teleconverter lens and the imaging lens are arranged sequentially along the optical axis from the object plane to the image plane.

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