Patent ID: 12235517

Reference numerals:10refers to first lens,11refers to first surface,12refers to second surface,20refers to second lens,21refers to third surface,22refers to fourth surface,30refers to third lens,31refers to fifth surface,32refers to sixth surface,40refers to fourth lens,41refers to seventh surface,42refers to eighth surface,50refers to image plane,60refers to aperture diaphragm, and70refers to vignetting diaphragm.

DETAILED DESCRIPTION

In order to further understand the features, the technical means, and the achieved specific objectives and functions of the present invention, the present invention is further described in detail hereinafter with reference to the accompanying drawings and the specific embodiments.

With reference toFIG.1toFIG.9,

a basic embodiment of the present invention discloses a large-aperture four-piece optical lens, which comprises a first lens10with positive focal power, a second lens20with negative focal power, a third lens30with positive focal power and a fourth lens40with positive focal power which are sequentially arranged along a light incident direction (e.g., rightward direction of each ofFIGS.2and6) from an object side (e.g., left side of each ofFIGS.2and6) to an image side (e.g., right side of each ofFIGS.2and6). Two surfaces of the first lens10are an S1 surface i.e., a first surface)11facing toward the object side and an S2 surface (i.e., a second surface)12facing toward the image side, two surfaces of the second lens20are an S3 surface i.e., a third surface)21facing toward the object side and an S4 surface (i.e., a fourth surface)22facing toward the image side, two surfaces of the third lens30are an S5 surface (i.e., a fifth surface)31facing toward the object side and an S6 surface (i.e., a sixth surface)32facing toward the image side, and two surfaces of the fourth lens40are an S7surface (i.e., a seventh surface)41facing toward the object side and an S8 surface (i.e., an eighth surface)42facing toward the image side. The S1 surface11, the S2 surface12, the S3 surface21, the S4 surface22, the S5 surface31, the S6 surface32, the S7 surface41and the S8 surface42are sequentially arranged along a light incident direction from the object side to the image side. An image plane50is provided on the image side of the whole optical lens to face the S8 surface42, and the image plane50is a plane on which the image is formed, which means that the image plane50is located at an image focal point of a whole optical lens. An aperture diaphragm60is arranged on the object side of the S1surface11or arranged between the S2 surface12and the S3 surface21. Ideally, the aperture diaphragm60is located on the object side of the S1 surface11. When applied to a vehicle headlight lens, considering a modeling design requirement, the aperture diaphragm60may be arranged between the S2 surface12and the S3 surface21, so that a structural body of the aperture diaphragm60can be hidden inside the lens, and the structural body of the aperture diaphragm60cannot be observed outside the vehicle headlight lens. A vignetting diaphragm70is arranged on the S7 surface41, and the vignetting diaphragm70is generally a lens mount. The S1 surface11, the S2 surface12, the S5 surface31, the S6 surface32and the S7 surface41are all convex surfaces, and the S4 surface22is a concave surface.

A distance between the aperture diaphragm60and an object focal point of the whole optical lens is |ST-Fobj|, ST represents a distance between the aperture diaphragm60and a center of the whole optical lens, and Fobjrepresents a distance between the object focal point of the whole optical lens and the center of the whole optical lens. A focal length of the whole optical lens is f0, and in practical application, the object focal point of the whole optical lens may be inside the first lens10, so that the aperture diaphragm60is arranged near the object focal point of the whole optical lens, which means that the following formula: |ST-Fobj|<0.7f0is satisfied.

An effective diameter of light passing through the S1 surface11is d1, an effective diameter of light passing through the S2 surface12is d2, an effective diameter of light passing through the S3 surface21is d3, an effective diameter of light passing through the S4 surface22is d4, an effective diameter of light passing through the S5 surface31is d5, an effective diameter of light passing through the S6 surface32is d6, an effective diameter of light passing through the S7 surface41is d7, and an effective diameter of light passing through the S8 surface42is d8. The effective diameters d1˜d8of the light passing through the S1 surface11to the S8 surface42satisfy the following relationship: di>0.9dj, i<j, i is an integer ranging from 1 to 7, j is an integer ranging from 2 to 8, and d is an effective diameter of the light passing through a corresponding optical surface. Along a light incident direction, the effective diameters of the light passing through the S1 surface11to the S8 surface42are changed basically conforming to a trend of gradual decrease.

A radius of curvature of the S3 surface21is r3, a radius of curvature of the S4surface22is r4, |r4|<|r3|, and a radius of curvature of the S7 surface41is r7, a radius of curvature of the S8 surface42is r8, |r7|<|r8|. An equivalent focal length of the fourth lens40is greater than that of the third lens30, that is, f4>f3, and the equivalent focal length of the fourth lens40is greater than that of the first lens10, that is, f4>f1.

A distance between centers of the S6 surface32and the S7 surface41is G67, and a distance between centers of the S2 surface12and the S3 surface21is G23, G67<G23.

In operation, a ray sequentially reaches the S1 surface11, the S2 surface12, the S3 surface21, the S4 surface22, the S5 surface31, the S6 surface32, the S7 surface41, the S8 surface42and the image plane50. The optical lens of the present invention can significantly improve a chromatic dispersion performance of a vehicle headlight, and reduce a sensitivity of the lens to axial tolerance in assembly, with a high assembly tolerance rate and a low assembly difficulty.

For a Tessar lens based on a classic Cook's three-piece variant, as shown inFIG.1, the aperture diaphragm is generally arranged at a middle lens, which can reduce or correct common aberration, such as field curvature, astigmatism and chromatic aberration, through structural symmetry. However, this structure, on one hand, may lead to a small numerical aperture for describing an overall light energy utilization rate; and on the other hand, may also lead to a very large chief ray angle CRA of a chief ray of a large field of view on an image surface. An illumination intensity of a general light source satisfies a Lambert's cosine law, and the illumination intensity is maximum at a 0-degree position, decays to 0.5 at a 60-degree position, and is 0 at a 90-degree position. Due to a large chief ray angle CRA, it is indicated that energy obtained by the lens system is lower for a solid angle of the same size.

According to the present invention, the aperture diaphragm60is arranged at the object focal point of the optical lens, thus forming an image space telecentric lens, so that the chief rays of the fields of view are parallel, that is, the chief ray angles CRA of the chief rays of the fields of view on the image plane50are all 0 degree, which means that the energy utilization rate of the present invention is higher for the solid angle of the same size. In practical application, the aperture diaphragm60is arranged near the object focal point of the optical lens, and the chief ray angles of the chief rays of the fields of view on the image plane50are all less than 20 degrees, with a high energy utilization rate.

In the embodiment, a back focal length of the whole optical lens is greater than 2 mm, which means that a distance between the S8 surface42and the image50is greater than 2 mm. Since the light source may generate a certain amount of heat in use, the four-piece optical lens provided with sufficient rear intercept can effectively avoid deformation of parts caused by heating.

In the embodiment, the S8 surface42is a flat surface or a concave surface.

In the embodiment, the S1 surface11, the S2 surface12, the S3 surface21, the S4 surface22, the S5 surface31, the S6 surface32, the S7 surface41and the S8 surface42are spherical surfaces or aspherical surfaces, which means that the S1 surface11to the S8 surface42may all be spherical surfaces, or the S1 surface11to the S8 surface42may all be aspherical surfaces, or the S1 surface11to the S8 surface42comprise spherical surfaces and aspherical surfaces. The aspherical surface is a rationally designed surface type.

In the embodiment, the first lens10, the second lens20, the third lens30and the fourth lens40are single lenses or cemented lenses, which means that the first lens10, the second lens20, the third lens30and the fourth lens40may all be single lenses, or the first lens10, the second lens20, the third lens30and the fourth lens40may all be cemented lenses, or the first lens10, the second lens20, the third lens30and the fourth lens40comprise single lenses and cemented lenses. The cemented lens, also known as an achromatic lens, is formed by cementing two single lenses, and a multi-color imaging performance of the cemented lens is much better than that of the single lens.

In the embodiment, the first lens10, the second lens20, the third lens30and the fourth lens40are glass lenses or plastic lenses, which means that the first lens10, the second lens20, the third lens30and the fourth lens40may all be glass lenses, or the first lens10, the second lens20, the third lens30and the fourth lens40may all be plastic lenses, or the first lens10, the second lens20, the third lens30and the fourth lens40comprise glass lenses and plastic lenses.

In the embodiment, an Abbe number of the first lens10is Vd1, an Abbe number of the second lens20is Vd2, an Abbe number of the third lens30is Vd3, and an Abbe number of the fourth lens40is Vd4, Vd1−Vd2>25, and Vd3−Vd2>25.

In Embodiment 1, a structure of an optical lens is shown inFIG.2, and the optical lens is arranged according to Table 1, Table 2, Table 3 and Table 4 below.

TABLE 1Parameters of surfaces in Embodiment 1EffectiveSerial No.Type ofRadius of curvatureThicknessRefractiveAbbe numberdiameterof surfacesurfacer (mm)(mm)index nVddObjectSphericalInfinity25,000surfacesurfaceApertureSphericalInfinity0.0041.88diaphragmsurfaceS1Aspherical46.8315.421.49257.9841.89surfaceS2Aspherical−10.404.5041.08surfaceS3Aspherical20.422.431.58427.8630.35surfaceS4Aspherical4.626.5625.75surfaceS5Spherical20.9913.801.48770.4226.50surfaceS6Spherical−30.170.0925.59surfaceS7Spherical17.9611.241.75552.3020.65surfaceS8Spherical54.094.3114.42surfaceImageSphericalInfinity0.0010.00planesurface

An expression of the aspherical surface is as follows:

z=c⁢r21+1-(1+k)⁢c2⁢r2+A⁢r4+B⁢r6+C⁢r8+D⁢r1⁢0+E⁢r1⁢2+F⁢r1⁢4+G⁢r1⁢6+H⁢r1⁢8+Jr2⁢0

wherein z is a vector height of an r position on the aspherical surface, c is a paraxial curvature of the aspherical surface, c=1/r, r is a radius of curvature, k is a conic coefficient, and A to J are higher-order coefficients.

TABLE 2Parameters of aspherical surfaces in Embodiment 1S1S2S3S4Conic coefficient k0−4.932−8.84E−01−1.77E+00A−1.90E−051.10E−05−1.07E−045.28E−06B9.32E−08−4.95E−083.52E−071.25E−07C−3.69E−106.47E−11−6.71E−10−6.40E−10D6.38E−134.00E−163.73E−138.26E−13E−3.68E−16000Other higher-order coefficients are all 0

TABLE 3Design parameters of optical lenses in Embodiment 1Backfocalf11f12f13f14focalNumerical1/2 FOVParameterlength f0(mm)(mm)(mm)(mm)(mm)lengthf/EPDaperture NA(°)Value28.319.00−10.8127.8531.414.300.670.7410.0

TABLE 4Constrained relationships in Embodiment 1Constrained relationshipResult|ST − Fobj| < 0.7f0|ST − Fobj| = 12.81 mm, so that the condition is satisfiedEffective diameterIt can be seen from Table 1 that the condition is satisfieddi> 0.9djThe S7 surface is providedA vignetting coefficient of ½ FOV is 0.45with the vignetting diaphragm|r4| < |r3|It can be seen from Table 1 that the condition is satisfiedr4< 0It can be seen from Table 1 that the condition is satisfiedf4> f3It can be seen from Table 3 that the condition is satisfiedf4> f1It can be seen from Table 3 that the condition is satisfied|r7| < |r8|It can be seen from Table 1 that the condition is satisfiedG67< G23It can be seen from Table 1 that the condition is satisfiedThe back focal length is greaterIt can be seen from Table 3 that the rear intercept is 4.3than 2 mmmm, and the condition is satisfied

To sum up, it can be seen that the numerical aperture in Embodiment 1 reaches 0.74, which is much greater than 0.125 of the Tessar lens, so that the energy utilization rate is significantly improved. An astigmatism and field curvature curve and a distortion curve in Embodiment 1 are shown inFIG.3, an on-axis chromatic aberration curve is shown inFIG.4, and a MTF (Modulation Transfer Function) curve is shown inFIG.5. It can be seen that the optical lens has a good imaging quality when applied to a projection imaging system.

In Embodiment 2, a structure of an optical lens is shown inFIG.6, and the optical lens is arranged according to Table 5, Table 6, Table 7 and Table 8 below.

TABLE 5Parameters of surfaces in Embodiment 2Serial No. ofType ofRadius ofThicknessRefractiveAbbeEffectivesurfacesurfacecurvature r (mm)(mm)index nnumber Vddiameter dObjectSphericalInfinity25000surfacesurfaceS1Aspherical42.6228.5101.49257.9828.93surfaceS2Aspherical−12.8707.44128.16(aperturesurfacediaphragm)S3Aspherical−115.8602.3901.58427.8620.16surfaceS4Aspherical4.6412.62618.30surfaceS5Aspherical7.1859.3541.58660.6019.07surfaceS6Aspherical−22.5941.78917.65surfaceS7Spherical11.8905.6131.75552.3012.47surfaceS8Spherical20.2943.1159.74surfaceImageSphericalInfinity0.007.99planesurface

An expression of the aspherical surface is as follows:

z=c⁢r21+1-(1+k)⁢c2⁢r2+A⁢r4+B⁢r6+C⁢r8+D⁢r1⁢0+E⁢r1⁢2+F⁢r1⁢4+G⁢r1⁢6+H⁢r1⁢8+Jr2⁢0

wherein z is a vector height of an r position on the aspherical surface, c is a paraxial curvature of the aspherical surface, c=1/r, r is a radius of curvature, k is a conic coefficient, and A to J are higher-order coefficients.

TABLE 6Parameters of aspherical surfaces in Embodiment 2S1S2S3S4S5S6Conic−7.17110872−5.5889.36E+00−2.54E+00−2.88−25.40coefficient kA3.56E−062.36E−067.44E−058.32E−056.35E−05−2.22E−04B−8.65E−08−2.25E−08−1.42E−065.47E−071.04E−063.70E−06C2.83E−10−8.74E−111.14E−08−4.13E−08−8.28E−09−1.79E−08D−6.66E−132.12E−13−1.02E−102.43E−100E+000.00E+00E0.00E+000E+004.73E−130E+000E+000E+00Other higher-order coefficients are all 0

TABLE 7Design parameters of optical lenses in Embodiment 2Backfocalf11f12f13f14focalNumerical1/2 FOVParameterlength f0(mm)(mm)(mm)(mm)(mm)lengthf/EPDaperture NA(°)Value18.8921.10−7.5110.4929.413.120.670.7512.0

TABLE 8Constrained relationships in Embodiment 2Constrained relationshipResult|ST − Fobj| < 0.7f0|ST − Fobj| = 6.62 mm, so that the condition is satisfiedEffective diameterIt can be seen from Table 5 that the condition isdi> 0.9djsatisfiedThe S7 surface isA vignetting coefficient of ½ FOV is 0.72provided with the vignetting diaphragm|r4| < |r3|It can be seen from Table 5 that the condition is satisfiedr4< 0It can be seen from Table 5 that the condition is satisfiedf4> f3It can be seen from Table 7 that the condition is satisfiedf4> f1It can be seen from Table 7 that the condition is satisfied|r7| < |r8|It can be seen from Table 5 that the condition is satisfiedG67< G23It can be seen from Table 5 that the condition is satisfiedThe back focal length isIt can be seen from Table 7 that the rear intercept is 3.12greater than 2 mmmm, and the condition is satisfied

To sum up, it can be seen that the numerical aperture in Embodiment 2 reaches 0.75, which is much greater than 0.125 of the Tessar lens, so that the energy utilization rate is significantly improved. An astigmatism and field curvature curve and a distortion curve in Embodiment 2 are shown inFIG.7, an on-axis chromatic aberration curve is shown inFIG.8, and a MTF (Modulation Transfer Function) curve is shown inFIG.9. It can be seen that the optical lens has a good imaging quality when applied to a projection imaging system.

The above embodiments only express some implementation modes of the present invention, and the descriptions thereof are specific and detailed, but cannot be understood as limiting the scope of the patent of the present invention. It shall be pointed out that those of ordinary skills in the art may further make several modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent of the present invention shall be subject to the appended claims.