Optical lens and imaging device

Abstract

The present application relates to an optical lens, comprising eight lenses arranged in sequence along the optical axis from the object side to the image side. The first lens, the third lens, the sixth lens and the seventh lens are positive lenses, and the second lens, the fourth lens and the eighth lens are negative lenses. The object side surface of the first lens, the second lens, the fourth lens, the fifth lens and the sixth lens is convex near the optical axis, and the image side surface is concave near the optical axis. The object side surface and the image side surface of the eighth lens are concave near the optical axis. The object side surface of the third lens and the seventh lens is convex near the optical axis. The optical lens satisfies TTL / ImgH<1.25. The imaging device of the present application comprises the optical lens and an imaging element for converting the optical image formed by the optical lens into an electrical signal. The imaging device has a large image surface and thin characteristics, so as to meet the high pixel requirement, and has the advantages of better light convergence and thin size.

Description

TECHNICAL FIELD

[0001] The present application relates to optical lenses and imaging devices, and in particular, to an optical lens comprising eight lenses and an imaging device. BACKGROUND

[0002] In recent years, with the rise of smart phones, the demand for small imaging devices is increasing. At the same time, with the advancement of semiconductor manufacturing process technology, the pixel size of photosensitive devices is shrinking, and the pixel of imaging devices is getting higher and higher, and accordingly, the requirements for the optical characteristics of optical lenses are also getting higher and higher. Therefore, there is an urgent need for optical lenses with excellent optical characteristics and small size. SUMMARY

[0003] The purpose of the present application is to provide an optical lens and an imaging device with a large image surface, a small size, and good light convergence capability.

[0004] An optical lens comprising eight lenses, namely 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, wherein the first lens to the eighth lens are sequentially arranged along an optical axis from an object side to an image side. The first lens has positive refractive power, and the object side surface thereof is convex near the optical axis, and the image side surface thereof is concave near the optical axis. The second lens has negative refractive power, and 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 positive refractive power, and the object side surface thereof is convex near the optical axis. The fourth lens has negative refractive power, and the object side surface thereof is convex near the optical axis, and the image side surface thereof is concave near the optical axis. The fifth lens has refractive power, and the object side surface thereof is convex near the optical axis, and the image side surface thereof is concave near the optical axis. The sixth lens has positive refractive power, and the object side surface thereof is convex near the optical axis, and the image side surface thereof is concave near the optical axis. The seventh lens has positive refractive power, and the object side surface thereof is convex near the optical axis. The eighth lens has negative refractive power, and the object side surface thereof is concave near the optical axis, and the image side surface thereof is concave near the optical axis. The optical lens satisfies TTL / ImgH<1.25, wherein TTL is the distance from the object side surface of the first lens near the optical axis to the image surface of the optical lens, and ImgH is half of the effective imaging height of the optical lens.

[0005] As an embodiment, the optical lens satisfies 3.11<f6 / f<3.99, wherein f6 is the focal length of the sixth lens, and f is the total effective focal length of the optical lens.

[0006] As an embodiment, the optical lens satisfies 7.22<f3 / f<15.5, and -40.91<f4 / f<-26.14, wherein f3 is the focal length of the third lens, and f4 is the focal length of the fourth lens.

[0007] As an embodiment, the optical lens satisfies 0.81 < CT2 / T23 < 0.92, wherein CT2 is the thickness of the second lens on the optical axis, and T23 is the interval of the second lens and the third lens on the optical axis.

[0008] As an embodiment, the optical lens satisfies 3.75 ≤ CT3 / T34 ≤ 5.93, wherein CT3 is the thickness of the third lens on the optical axis, and T34 is the interval of the third lens and the fourth lens on the optical axis.

[0009] As an embodiment, the optical lens satisfies 0.71 ≤ CTmax-CTmin < 0.79, and 0.22 < CT1 / ∑CT < 0.24, wherein CTmax is the thickness of the lens with the largest thickness on the optical axis among the first to eighth lenses on the optical axis, CTmin is the thickness of the lens with the smallest thickness on the optical axis among the eight lenses on the optical axis, CT1 is the thickness of the first lens on the optical axis, and ∑CT is the sum of the thicknesses of all the lenses on the optical axis.

[0010] As an embodiment, the optical lens satisfies 0.2 < R11 / R12 < 0.35, wherein R11 is the radius of curvature of the object side surface of the first lens, and R12 is the radius of curvature of the image side surface of the first lens.

[0011] As an embodiment, the object side surface and the image side surface of each of the first to eighth lenses are aspheric surfaces.

[0012] As an embodiment, the optical lens satisfies 0.9 < Vd1 / Vd5 < 3, wherein Vd1 is the Abbe number of the first lens, and Vd5 is the Abbe number of the fifth lens.

[0013] An imaging device includes the optical lens described above and an imaging element for converting an optical image formed by the optical lens into an electric signal.

[0014] The imaging device of the present application includes the optical lens described above and an imaging element for converting an optical image formed by the optical lens into an electric signal. The imaging device has a large image surface and a thin profile, thereby satisfying a high pixel requirement, while having a better light converging ability and a thin size advantage. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 FIG. 1 is a structural schematic diagram of an optical lens according to an embodiment of the present application.

[0016] Figure 2 FIG. 4 is an astigmatism and distortion curve diagram of the optical lens according to the embodiment of the present application.

[0017] Figure 3 FIG. 5 is a spherical aberration curve diagram of the optical lens according to the embodiment of the present application.

[0018] Figure 4 The chromatic aberration curve of the optical lens of the embodiment one of the present application.

[0019] Figure 5 The structural schematic diagram of the optical lens of the embodiment two of the present application.

[0020] Figure 6 The astigmatism and distortion curve of the optical lens of the embodiment two of the present application.

[0021] Figure 7 The spherical aberration curve of the optical lens of the embodiment two of the present application.

[0022] Figure 8 The chromatic aberration curve of the optical lens of the embodiment two of the present application.

[0023] Figure 9 The structural schematic diagram of the optical lens of the embodiment three of the present application.

[0024] Figure 10 The astigmatism and distortion curve of the optical lens of the embodiment three of the present application.

[0025] Figure 11 The spherical aberration curve of the optical lens of the embodiment three of the present application.

[0026] Figure 12 The chromatic aberration curve of the optical lens of the embodiment three of the present application.

[0027] Figure 13 The structural schematic diagram of the optical lens of the embodiment four of the present application.

[0028] Figure 14 The astigmatism and distortion curve of the optical lens of the embodiment four of the present application.

[0029] Figure 15 The spherical aberration curve of the optical lens of the embodiment four of the present application.

[0030] Figure 16 The chromatic aberration curve of the optical lens of the embodiment four of the present application.

[0031] Figure 17 The structural schematic diagram of the optical lens of the embodiment five of the present application.

[0032] Figure 18 The astigmatism and distortion curve of the optical lens of the embodiment five of the present application.

[0033] Figure 19 The spherical aberration curve of the optical lens of the embodiment five of the present application.

[0034] Figure 20 The chromatic aberration curve of the optical lens of the embodiment five of the present application. Detailed Implementation

[0035] In the description of this invention, the object side of a lens refers to the side of the lens facing the object, and the image side refers to the side of the lens facing the imaging plane. When a cross-section is made at any point on the object side surface of the lens, if the object side surface is always located on the image side of the cross-section and its radius of curvature is positive, then the object side surface of the lens is convex; otherwise, the object side surface of the lens is concave. When a cross-section is made at any point on the image side surface of the lens, if the image side surface is always on the object side of the cross-section and its radius of curvature is negative, then the image side surface of the lens is convex; otherwise, the image side surface of the lens is concave. If a cross-section is made at any point on either the object side surface or the cross-section of the image side surface of the lens, and the object side surface or the image side surface is partially on the image side of the cross-section and partially on the object side of the cross-section, then the surface has a point of inflection. The determination of the concavity or convexity of the object side and image side surfaces near the optical axis still applies to the above method.

[0036] Furthermore, the equations for the aspherical curves of each aspherical lens are expressed as follows:

[0037]

[0038] Where Z is the distance vector from the origin of the aspherical surface at a height of r along the optical axis; c is the paraxial curvature of the aspherical surface (radius of curvature R = 1 / c, which is the reciprocal of the curvature); k is the conic coefficient; Ai is the i-th order coefficient of the aspherical surface, and the higher order coefficients used in this invention are A4, A6, A8, and A... 10 A 12 A 14 A 16 .

[0039] The imaging device of the present invention mainly includes a housing with a through hole, an optical lens assembled within the housing, and an imaging element for converting the optical image formed by the optical lens into an electrical signal. The imaging element is disposed on the imaging surface of the optical lens. The optical lens includes eight lenses of optical power fixed sequentially along the optical axis from the object side to the image side, namely, 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.

[0040] The first lens has positive refractive power, with its object-side surface being convex near the optical axis and its image-side surface being concave near the optical axis. The configuration of the first lens allows it to effectively balance low-order aberrations.

[0041] The second lens has negative refractive power, with its object-side surface being convex near the optical axis and its image-side surface being concave near the optical axis. The configuration of the second lens helps to eliminate the aberrations produced by the first lens.

[0042] The third lens with positive refractive power, the fourth lens with negative refractive power, the fifth lens, the sixth lens with positive refractive power and the seventh lens with positive refractive power cooperate to effectively correct the on-axis spherical aberration and reduce the peripheral astigmatism field curvature, so that the optical lens has better light converging capability. The fifth lens can have positive refractive power or negative refractive power. The image side surface of the third lens and the seventh lens can be concave or convex at the near optical axis.

[0043] The eighth lens has negative refractive power, and the object side surface thereof is concave at the near optical axis, and the image side surface thereof is concave at the near optical axis, which helps to make the principal point of the optical imaging system away from the image side end, thereby effectively shortening the overall length of the optical imaging system, which is beneficial to the miniaturization of the system, and at the same time can correct off-axis aberration to improve the peripheral imaging quality.

[0044] Meanwhile, the optical lens satisfies TTL / ImgH<1.25, where TTL is the distance from the object side surface of the first lens at the near optical axis to the image surface of the optical lens, and ImgH is half of the effective imaging height of the optical lens, which ensures that the optical lens has a large image surface and thin characteristics.

[0045] The optical lens also optionally satisfies 3.11<f6 / f<3.99, where f6 is the focal length of the sixth lens, and f is the total effective focal length of the optical lens. A reasonable focal length of the sixth lens helps to balance the off-axis astigmatism and improve the imaging quality of the edge field of view.

[0046] The optical lens also optionally satisfies 7.22<f3 / f<15.5 and -40.91<f4 / f<-26.14, where f3 is the focal length of the third lens, and f4 is the focal length of the fourth lens. A reasonable focal length range of the third lens can better balance the on-axis aberration and reduce the sensitivity of the optical system. A reasonable focal length range of the fourth lens helps to balance the high-order aberration and improve the imaging quality of the lens.

[0047] The optical lens also optionally satisfies 0.81<CT2 / T23<0.92, where CT2 is the thickness of the second lens on the optical axis, and T23 is the distance between the second lens and the third lens on the optical axis. Such a configuration makes the structure of the optical lens more compact and more reasonable.

[0048] The optical lens also optionally satisfies 3.75≤CT3 / T34≤5.93, where CT3 is the thickness of the third lens on the optical axis, and T34 is the distance between the third lens and the fourth lens on the optical axis. Such a configuration makes the structure of the optical lens more compact and more reasonable.

[0049] The optical lens also optionally satisfies 0.71≤CTmax-CTmin<0.79, 0.22<CT1 / ∑CT<0.24, wherein CTmax is the thickness of the lens with the largest thickness on the optical axis among the first to eighth lenses on the optical axis, CTmin is the thickness of the lens with the smallest thickness on the optical axis among the eight lenses on the optical axis, controlling the difference between the two is conducive to adjusting the lens uniformity and better forming. CT1 is the thickness of the first lens on the optical axis, and ∑CT is the sum of the thicknesses of all lenses on the optical axis, controlling the ratio is conducive to adjusting the thickness of the first lens, so that the lens volume is smaller.

[0050] The optical lens also optionally satisfies 0.2<R11 / R12<0.35, wherein R11 is the curvature radius of the object side surface of the first lens, and R12 is the curvature radius of the image side surface of the first lens. Controlling the ratio of R11 and R12 in a reasonable range helps to reduce the sensitivity of the optical system.

[0051] The optical lens also optionally satisfies 0.9<Vd1 / Vd5<3, wherein Vd1 is the dispersion coefficient of the first lens, and Vd5 is the dispersion coefficient of the fifth lens. Controlling the ratio of the two in a reasonable range helps to control the overall optical system chromatic aberration.

[0052] Preferably, the eight lenses do not contact each other or only contact at the edges, are not movable relative to each other, and the object side surface and the image side surface of each lens are aspherical surfaces, which can effectively reduce the thickness of the lens.

[0053] The specific embodiments of the imaging device applicable to the above embodiments are further described below with reference to the accompanying drawings.

[0054] Embodiment one:

[0055] The imaging device of embodiment one mainly includes a shell with a through hole, an optical lens assembled in the shell, and an imaging element for converting the optical image formed by the optical lens into an electrical signal. As shown in Figure 1 The optical lens 10 mainly includes eight lenses arranged at intervals, specifically, in order from the object side to the image side: an aperture 101, a first lens 102, a second lens 103, a third lens 104, a fourth lens 105, a fifth lens 106, a sixth lens 107, a seventh lens 108, an eighth lens 109, and a filter 110. The aperture 101 is arranged at the object side surface close to the first lens 102. Figure 1 Reference numeral 111 indicates the imaging surface of the optical lens 10, and the surface of the imaging element of the imaging device should be located on the imaging surface.

[0056] The structure of the optical lens 10 of embodiment one is arranged to satisfy the parameters listed in Table 1-1, Table 1-2, and Table 1-3.

[0057] Table 1-1 is the basic parameters of the optical lens of Example One, including the total effective focal length f of the optical lens, the relative aperture FNO of the optical lens, the maximum field of view FOV of the optical lens, the radius of curvature (unit: mm), the thickness (unit: mm), the refractive index and the dispersion coefficient of the lens material, and the focal length (unit: mm) of the lens. The surface serial number is coded from the object side to the image side.

[0058] Table 1-2 is the aspheric coefficients of each lens in Example One, which satisfy the above aspheric formula (1).

[0059] Table 1-3 is the values of the conditions satisfied by the optical lens of Example One.

[0060] Figure 1-1 shows the optical lens of Example One. Figure 2 Figure 1-2 shows the astigmatism and distortion curve of the optical lens of Example One. Figure 3 Figure 1-3 shows the spherical aberration curve of the optical lens of Example One. Figure 4 Figure 1-4 shows the chromatic aberration curve of the optical lens of Example One.

[0061]

[0062]

[0063]

[0064]

[0065] Example Two:

[0066] The imaging device of Example Two mainly includes a housing with a through hole, an optical lens assembled in the housing, and an imaging element for converting the optical image formed by the optical lens into an electrical signal. As shown in Figure 5 The optical lens 20 mainly includes eight lenses arranged at intervals, specifically, in order from the object side to the image side: a diaphragm 201, a first lens 202, a second lens 203, a third lens 204, a fourth lens 205, a fifth lens 206, a sixth lens 207, a seventh lens 208, an eighth lens 209, and a filter 210. The diaphragm 201 is arranged at the object side surface close to the first lens 202. Figure 5 Reference numeral 211 indicates the imaging surface of the optical lens 20, and the surface of the imaging element of the imaging device should be located on the imaging surface.

[0067] The structure of the optical lens 20 of Example Two is arranged so as to satisfy the parameters listed in Table 2-1, Table 2-2, and Table 2-3.

[0068] Table 2-1 is the basic parameters of the optical lens of Example Two, including the total effective focal length f of the optical lens, the relative aperture FNO of the optical lens, the maximum field of view FOV of the optical lens, the radius of curvature (unit: mm), the thickness (unit: mm), the refractive index and the dispersion coefficient of the lens material, and the focal length (unit: mm) of the lens. The surface serial number is from the object side to the image side.

[0069] Table 2-2 is the aspheric coefficients of each lens in Example Two, which satisfy the above aspheric formula (1).

[0070] Table 2-3 is the values of the conditions satisfied by the optical lens of Example Two.

[0071] Figure 2-1 shows the astigmatism curve of the optical lens of Example Two. Figure 6 Figure 2-2 shows the distortion curve of the optical lens of Example Two. Figure 7 Figure 2-3 shows the chromatic aberration curve of the optical lens of Example Two. Figure 8

[0072]

[0073]

[0074]

[0075]

[0076]

[0077] Example Three:

[0078] The imaging device of Example Three mainly includes a housing with a through hole, an optical lens assembled in the housing, and an imaging element for converting the optical image formed by the optical lens into an electrical signal. As shown in Figure 9 the optical lens 30 mainly includes eight lenses arranged at intervals, specifically, in order from the object side to the image side: a diaphragm 301, a first lens 302, a second lens 303, a third lens 304, a fourth lens 305, a fifth lens 306, a sixth lens 307, a seventh lens 308, an eighth lens 309, and a filter 310. The diaphragm 301 is arranged at the object side surface close to the first lens 302. Figure 9 Reference sign 311 indicates the imaging surface of the optical lens 30, and the surface of the imaging element of the imaging device should be located on the imaging surface.

[0079] The structure of the optical lens 30 of Example Three is arranged so as to satisfy the parameters listed in Table 3-1, Table 3-2, and Table 3-3.

[0080] ​Table 3-1 is the basic parameters of the optical lens of Example Three, including the total effective focal length f of the optical lens, the relative aperture FNO of the optical lens, the maximum field of view FOV of the optical lens, the radius of curvature (unit: mm), the thickness (unit: mm), the refractive index and the dispersion coefficient of the lens material, and the focal length (unit: mm) of the lens. The surface serial number is coded from the object side to the image side.

[0081] Table 3-2 is the aspheric coefficients of each lens in Example Three, which satisfy the above aspheric formula (1).

[0082] Table 3-3 is the values of the conditions satisfied by the optical lens of Example Three.

[0083] Figure 1 shows the astigmatism and distortion curve of the optical lens of Example Three. Figure 10 Figure 2 shows the spherical aberration curve of the optical lens of Example Three. Figure 11 Figure 3 shows the chromatic aberration curve of the optical lens of Example Three. Figure 12

[0084]

[0085]

[0086]

[0087]

[0088]

[0089] Example Four:

[0090] The imaging device of Example Four mainly includes a housing with a through hole, an optical lens assembled in the housing, and an imaging element for converting the optical image formed by the optical lens into an electrical signal. As shown in Figure 13 the optical lens 40 mainly includes eight lenses arranged at intervals, specifically, in order from the object side to the image side: a diaphragm 401, a first lens 402, a second lens 403, a third lens 404, a fourth lens 405, a fifth lens 406, a sixth lens 407, a seventh lens 408, an eighth lens 409, and a filter 410. The diaphragm 401 is arranged at the object side surface close to the first lens 402. Figure 13 Reference sign 311 indicates the imaging surface of the optical lens 40, and the surface of the imaging element of the imaging device should be located on the imaging surface.

[0091] The structure of the optical lens 40 of Example Four is arranged so as to satisfy the parameters listed in Table 4-1, Table 4-2, and Table 4-3.

[0092] ​Table 4-1 lists the basic parameters of the optical lens in Example 4, including the total effective focal length f, the relative aperture FNO, the maximum field of view FOV, the radius of curvature (in mm), the thickness (in mm), the refractive index and dispersion coefficient of the lens material, and the focal length (in mm). The surface numbers are numbered from the object side to the image side.

[0093] Table 4-2 shows the aspherical coefficients of each lens in Example 4. These coefficients all satisfy the above aspherical formula (1).

[0094] Table 4-3 shows the values ​​of the conditions satisfied by the optical lens in Example 4.

[0095] Appendix Figure 14 The diagram shows the astigmatism and distortion curves of the optical lens in Embodiment 4. Figure 15 A spherical aberration curve of the optical lens of Embodiment 4 is shown. Figure 16 The chromatic aberration curve of the optical lens in Embodiment 4 is shown.

[0096]

[0097]

[0098]

[0099]

[0100] Example 5:

[0101] The imaging device in Embodiment 5 mainly includes a housing with a through hole, an optical lens assembled within the housing, and an imaging element for converting the optical image formed by the optical lens into an electrical signal. Among them, such as... Figure 17 As shown, the optical lens 50 mainly includes eight lenses spaced apart from each other. Specifically, from the object side to the image side, it includes: an aperture stop 501, a first lens 502, a second lens 503, a third lens 504, a fourth lens 505, a fifth lens 506, a sixth lens 507, a seventh lens 508, an eighth lens 509, and a filter 510. The aperture stop 501 is located near the object-side surface of the first lens 502. Figure 17 The reference numeral 511 indicates the imaging surface of the optical lens 50, and the surface of the imaging element of the imaging device should be located on the imaging surface.

[0102] The optical lens 50 of Embodiment 5 is configured to meet the parameters listed in Tables 5-1, 5-2 and 5-3.

[0103] Table 5-1 is the basic parameters of the optical lens of Example Five, including the total effective focal length f of the optical lens, the relative aperture FNO of the optical lens, the maximum field of view FOV of the optical lens, the radius of curvature (unit: mm), the thickness (unit: mm), the refractive index and the dispersion coefficient of the lens material, and the focal length (unit: mm) of the lens. The surface serial number is coded from the object side to the image side.

[0104] Table 5-2 is the aspheric coefficients of each lens in Example Five, which satisfy the above aspheric formula (1).

[0105] Table 5-3 is the values of the conditions satisfied by the optical lens of Example Five.

[0106] Figure 1 shows the astigmatism curve of the optical lens of Example Five. Figure 18 Figure 2 shows the distortion curve of the optical lens of Example Five. Figure 19 Figure 3 shows the chromatic aberration curve of the optical lens of Example Five. Figure 20

[0107]

[0108]

[0109]

[0110]

[0111] In summary, Examples One to Five respectively satisfy the relationships shown in Table 6 below.

[0112] Table 6 Comparison of parameters of optical lenses of imaging devices of five examples

[0113]

[0114]

[0115] In summary, the above optical lens adopts an eight-piece lens structure, and by reasonably selecting the material and the refractive power, when certain conditions are met, the entire optical lens has good light converging ability, has the advantages of good optical performance, large image surface, and thin size. The imaging device configured with the above optical lens has the advantages of good optical performance, large image surface, and thin size while meeting the high pixel requirement.

[0116] In addition, the terms "first", "second", and the like are only used to distinguish one feature from another, and do not represent any limitation on the features.

[0117] ​While the application has been described in connection with specific embodiments thereof, it will be understood that it is capable of further modifications and this application is intended to cover any variations, uses, or adaptations of the application following, in general, the principles of the application and including such departures from the present disclosure as come within known or customary practice within the art to which the application pertains.

Claims

1.An optical lens comprising eight lenses, which are 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, respectively, the first lens to the eighth lens are sequentially arranged along an optical axis from an object side to an image side; characterized in that: the first lens has positive refractive power, an object side surface thereof is convex at a near optical axis, and an image side surface thereof is concave at the near optical axis; the second lens has negative refractive power, an object side surface thereof is convex at the near optical axis, and an image side surface thereof is concave at the near optical axis; the third lens has positive refractive power, an object side surface thereof is convex at the near optical axis; the fourth lens has negative refractive power, an object side surface thereof is convex at the near optical axis, and an image side surface thereof is concave at the near optical axis; the fifth lens has refractive power, an object side surface thereof is convex at the near optical axis, and an image side surface thereof is concave at the near optical axis; the sixth lens has positive refractive power, an object side surface thereof is convex at the near optical axis, and an image side surface thereof is concave at the near optical axis; the seventh lens has positive refractive power, an object side surface thereof is convex at the near optical axis; the eighth lens has negative refractive power, an object side surface thereof is concave at the near optical axis, and an image side surface thereof is concave at the near optical axis; the optical lens satisfies TTL / ImgH < 1.25, wherein TTL is a distance from the object side surface of the first lens at the near optical axis to an image plane of the optical lens, and ImgH is half of an effective imaging height of the optical lens; the optical lens satisfies 3.11 < f6 / f < 3.99, wherein f6 is a focal length of the sixth lens, and f is a total effective focal length of the optical lens; the optical lens satisfies 7.22 < f3 / f < 15.5 and -40.91 < f4 / f < -26.14, wherein f3 is a focal length of the third lens, and f4 is a focal length of the fourth lens; the optical lens satisfies 0.81 < CT2 / T23 < 0.92, wherein CT2 is a thickness of the second lens on the optical axis, and T23 is a distance between the second lens and the third lens on the optical axis; the optical lens satisfies 3.75 ≤ CT3 / T34 ≤ 5.93, wherein CT3 is a thickness of the third lens on the optical axis, and T34 is a distance between the third lens and the fourth lens on the optical axis; the optical lens satisfies 0.71 ≤ CTmax-CTmin < 0.79 and 0.22 < CT1 / ΣCT < 0.24, wherein CTmax is a thickness of a lens with a maximum thickness on the optical axis among the first to eighth lenses on the optical axis, CTmin is a thickness of a lens with a minimum thickness on the optical axis among the eight lenses on the optical axis, CT1 is a thickness of the first lens on the optical axis, and ΣCT is a sum of the thicknesses of all the lenses on the optical axis; the optical lens satisfies 0.2 < R11 / R12 < 0.35, wherein R11 is a curvature radius of the object side surface of the first lens, and R12 is a curvature radius of the image side surface of the first lens; each of the object side surface and the image side surface of each of the first to eighth lenses is aspherical; and the optical lens satisfies 0.9 < Vd1 / Vd5 < 3, wherein Vd1 is a dispersion coefficient of the first lens, and Vd5 is a dispersion coefficient of the fifth lens. ​ ​ ​ ​ ​ ​ ​ ​ ​ 2. The optical lens of claim 1, wherein, ​ 3. The optical lens of claim 1, wherein, ​ 4. The optical lens of claim 1, wherein, ​ 5. The optical lens of claim 1, wherein, ​ 6. The optical lens of claim 1, wherein, ​ 7. The optical lens of claim 1, wherein, ​ 8. The optical lens of claim 1, wherein, ​ 9. An image forming apparatus characterized by comprising: An optical lens as claimed in any one of claims 1 to 8 and an imaging element for converting an optical image formed by the optical lens into an electrical signal.

Images