A large-aperture four-element lens

Abstract

The present invention discloses a four-piece lens with a large aperture, which includes, along the optical axis from the object side to the image side, at least one aspherical first lens with positive optical power, a biconcave second lens with negative optical power, a biconvex third lens with positive optical power, and a biconvex fourth lens with positive optical power arranged in sequence; the second lens and the third lens are glued together; |f1| / EFL > 3.5, where f1 is the focal length of the first lens (10) and EFL is the effective focal length of the lens system; BFL / EFL > 0.8, where BFL is the back focal length; BFL / OAL > 0.4, where OAL is the overall length of the lens system; OAL / EFL < 2.2; BFL * 0.9 mm < f4 < BFL * 2.0 mm, where f4 is the focal length of the fourth lens (13); NA > 0.35, where NA is the numerical aperture of the system; the larger the value of NA, the higher the light energy utilization rate; min(Di) / max(Di) > 0.8, where Di is the effective aperture of the i-th surface. It has the characteristic of a long back focal length and can provide sufficient rear mechanical space for the illumination optical module of DLP.

Description

Technical Field

[0001] The invention relates to an optical lens, and in particular discloses a large-aperture four-piece lens. Background Art

[0002] The optical part of the low beam of a conventional existing headlight system using the projection principle is composed of a combination of a light source, a light energy collecting element, a light and dark cut-off line structure, and a convex lens.

[0003] The newly developed pixel headlights, also known as matrix headlights, use digital light projection technology, so that the headlights not only have lighting functions, but can also project patterns on the ground, such as weather conditions, road navigation, or other symbols for pedestrians or vehicles outside the car to identify, and use as a kind of light language.

[0004] Micro LEDs are used as the light source in headlights with tens of thousands of pixels. However, digital micromirror technology (DMD or DLP) is required for headlights with millions of pixels. Since DMDs don't emit light themselves, projection lenses require a long back focus to allow the illumination optical module to have space for light energy to illuminate the DMD, reflect from the DMD, and then couple into the projection lens. Some projection lenses use the optical lenses of traditional DLP projectors, typically with up to 10 lenses.

[0005] In addition, due to the complex driving environment of automobiles, the application environment of headlights may also be relatively harsh. They need to meet the requirements of normal operation in ambient temperatures ranging from -45℃ to 85℃ without major performance changes. Therefore, the projection lens of high-pixel headlights must have stable back focus within a large temperature range of -45℃ to 85℃.

[0006] Cost is also a significant factor in projection lenses. Spherical glass lenses are cheaper than aspherical glass lenses, while injection-molded plastic lenses are cheaper than spherical lenses of the same aperture and can utilize free-form or aspherical surfaces. However, injection-molded plastic lenses have a significant disadvantage: poor thermal stability, primarily manifested in large temperature variations in the refractive index and thermal expansion coefficient. Improper design can lead to a dramatic deterioration in the optical performance of the lens in high and low temperature environments. However, the advantage of plastic lenses is that they offer greater design freedom in terms of surface shape, are lightweight, and are less expensive. Therefore, it is necessary to provide a method that, in response to the long back focus characteristics of DLP and the wide range of high and low temperature applications required for automotive headlights, can fully utilize the advantages of both plastic and glass lenses while avoiding the shortcomings of both.

[0007] The Chinese patent application publication number is CN114280758 A, and the application publication date is April 5, 2022. It discloses an optical lens and an electronic device including the optical lens. The optical lens sequentially includes, along the optical axis, from the first side to the second side: a first lens with a positive optical power, whose first side is convex and the second side is concave; a second lens with a negative optical power, whose first side is concave; a third lens with a positive optical power, whose second side is convex; and a fourth lens with a positive optical power, whose first side is convex and the second side is concave. The defect of this prior art is that, aiming at the long back focal length characteristic of DLP, there is still room for improvement in providing space for the long back focal length while ensuring the imaging quality. In view of this situation, it is urgent to solve. Summary of the Invention

[0008] Based on this, in view of the problems of the prior art, it is necessary to provide a four-piece lens with a large aperture, which has the characteristic of a long back focal length and can provide sufficient rear mechanical space for the illumination optical module of DLP.

[0009] To solve the problems of the prior art, the present invention discloses a four-piece lens with a large aperture, which includes, along the optical axis, from the object side to the image side, at least one aspherical first lens with a positive optical power, a biconcave second lens with a negative optical power, a biconvex third lens with a positive optical power, and a biconvex fourth lens with a positive optical power arranged in sequence; the second lens and the third lens are glued together;

[0010] It satisfies the following conditional formulas:

[0011] |f1| / EFL > 3.5, where f1 is the focal length of the first lens and EFL is the effective focal length of the lens system;

[0012] BFL / EFL > 0.8, where BFL is the back focal length;

[0013] BFL / OAL > 0.4, where OAL is the total length of the lens system;

[0014] OAL / EFL < 2.2;

[0015] BFL * 0.9mm < f4 < BFL * 2.0mm, where f4 is the focal length of the fourth lens;

[0016] NA > 0.35, where NA is the numerical aperture of the system; NA is the numerical aperture of the system, and the larger the value, the higher the light energy utilization rate;

[0017] min(Di) / max(Di) > 0.8, where Di is the effective aperture of the i-th surface.

[0018] Preferably, the first lens is set as an injection-molded aspherical surface.

[0019] Preferably, the second lens, the third lens, and the fourth lens are all spherical glass lenses.

[0020] Preferably, the Abbe number of the optical material of the second lens is less than 30.

[0021] Preferably, the curvature radii of both surfaces of the fourth lens are set to be the same.

[0022] A four-piece lens with a large aperture, which includes, along the optical axis from the object side to the image side, at least one aspherical first lens with positive optical power, a biconcave second lens with negative optical power, a biconvex third lens with positive optical power, and a biconvex fourth lens with positive optical power arranged in sequence; the second lens and the third lens are separated into two independent lenses;

[0023] It satisfies the following conditional expressions:

[0024] |f1| / EFL > 3.5, where f1 is the focal length of the first lens and EFL is the effective focal length of the lens system;

[0025] BFL / EFL > 0.8, where BFL is the back focal length;

[0026] BFL / OAL > 0.4, where OAL is the overall length of the lens system;

[0027] OAL / EFL < 2.2;

[0028] BFL * 0.9mm < f4 < BFL * 2.0mm, where f4 is the focal length of the fourth lens;

[0029] NA > 0.35, where NA is the numerical aperture of the system;

[0030] min(Di) / max(Di) > 0.8, where Di is the effective aperture of the i-th surface.

[0031] The beneficial effects of the present invention are as follows:

[0032] 1. The lens of the present invention has the characteristic of a long back focal length, and can provide sufficient rear mechanical space for the illumination optical module of DLP;

[0033] 2. The present invention has excellent thermal stability. The first lens is mainly used to correct the high-order aberrations of the system, and has a small optical power, so that it is minimally affected by temperature. The other three lenses use glass lenses, and the relative temperature optical performance of glass lenses changes little. Therefore, through combined application, the lens can be adapted to fields with a wide temperature application range;

[0034] 3. The present invention is a hybrid glass-plastic design, which can improve the performance while reducing the cost. Description of the Drawings

[0035] Figure 1 This is a structural diagram of embodiment 1 of the present invention.

[0036] Figure 2 This is an MTF curve diagram of Example 1 of the present invention.

[0037] Figure 3 Graphs showing the astigmatism curve and the distortion curve of the first embodiment of the present invention.

[0038] Figure 4 This is a structural diagram of embodiment 1 of the present invention.

[0039] Figure 5 This is an MTF curve diagram of Example 1 of the present invention.

[0040] Figure 6 Graphs showing the astigmatism curve and distortion curve of the first embodiment of the present invention.

[0041] Figure 7 This is a structural diagram of embodiment 1 of the present invention.

[0042] Figure 8 This is an MTF curve diagram of Example 1 of the present invention.

[0043] Figure 9 Graphs showing the astigmatism curve and distortion curve of the first embodiment of the present invention.

[0044] Reference numerals are: a first lens 10 , a second lens 11 , a third lens 12 , and a fourth lens 13 . DETAILED DESCRIPTION

[0045] In order to further understand the features, technical means, specific objectives and functions achieved by the present invention, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0046] refer to Figures 1 to 9 .

[0047] The basic embodiment of the present invention discloses a large-aperture four-element lens, which includes, arranged in sequence from the object side to the image side along the optical axis, at least one aspherical first lens 10 with positive optical power, a second biconcave lens 11 with negative optical power, a third biconvex lens 12 with positive optical power, and a fourth biconvex lens 13 with positive optical power; the second lens and the third lens are cemented together into one body;

[0048] The first lens 10 is configured as an injection-molded aspheric surface. The first lens is implemented by injection molding, thereby reducing costs. Using an aspheric surface increases the degree of freedom in design and corrects the aberration of the rear part of the system.

[0049] The second lens 11, the third lens 12, and the fourth lens 13 are all spherical glass lenses.

[0050] The Abbe number of the optical material of the second lens 11 is less than 30.

[0051] The curvature radii of both surfaces of the fourth lens 13 are set to be the same.

[0052] It satisfies the following conditional expressions:

[0053] |f1| / EFL > 3.5, where f1 is the focal length of the first lens 10 and EFL is the effective focal length of the lens system; this limits the contribution of the optical power of the first lens to the optical power of the system. Since the first lens is realized by injection molding and the optical properties of plastic lenses change greatly in high and low temperature environments, by reducing its optical power contribution in the system, the influence of its optical performance on the system in high and low temperature environments can be limited.

[0054] BFL / EFL > 0.8, where BFL is the back focal length, BFL / OAL > 0.4, where OAL is the total length of the lens system, where BFL is the back focal length and OAL is the total length of the lens system; this limits the ratio of the back focal length to the total length of the system, making the back focal length long enough. Since the imaging surface is for DMD application, a long back focal length is required to provide enough space for the illumination optical path to couple light energy.

[0055] OAL / EFL < 2.2; this limits the ratio of the total length of the system to the effective focal length of the lens system, making the design of the lens compact enough and reducing the space of the lens.

[0056] BFL * 0.9mm < f4 < BFL * 2.0mm, where f4 is the focal length of the fourth lens 13; this limits the optical power of the fourth lens to be in a relatively reasonable range, so as to provide better imaging quality and reduce aberration.

[0057] NA > 0.35, where NA is the numerical aperture of the system; NA is the numerical aperture of the system, and the larger the value, the higher the light energy utilization rate; this limits the system to have a high light energy utilization rate.

[0058] min(Di) / max(Di) > 0.8, where Di is the effective aperture of the i-th surface. This constraint limits the ratio of the minimum aperture size to the maximum aperture size to be not less than 0.8, meaning that the aperture sizes of each lens of the lens are close, so that the volume space utilization rate of the lens is relatively high, which is also beneficial to the design of the lens barrel and reduces the weight.

[0059] Example 1, the first surface of the first lens 10 in this example is a concave surface, as Figure 1 ; The MTF curve graph is as Figure 2 , and its relative astigmatism curve and distortion curve are as Figure 3 .

[0060] Table 1, Parameters of each surface of Example 1

[0061]

[0062] Table 2, Parameters of each surface of Example 1

[0063] Surface serial number k A B C D E F S1 0 -1.82E-05 0.00E+00 0.00E+00 0.00E+00 0.00E+00 0.00E+00 S2 0 -5.44E-07 2.26E-08 -6.32E-11 5.83E-14 1.05E-15 -2.38E-18

[0064] The expression for aspheric surface is as follows:

[0065]

[0066] Where z is the aspheric surface at position r; c is the paraxial curvature of the aspheric surface, c = 1 / R, (i.e., the paraxial curvature c is the inverse of the surface curvature radius R); k is the cone coefficient; A~J are high-order coefficients.

[0067] Table 3, Design parameters of the optical lens of Example 1

[0068]

[0069] Table 4, Constraints of Example 1

[0070] Constraints Design Results |f1 / EFL|>3.5 |f1 / f|=5.40, knowing satisfaction BFL / EFL>0.8 BFL / EFL>0.91, knowing satisfaction BFL / OAL>0.4 BFL / OAL=0.48, contentment OAL / EFL<2.2 OAL / EFL=1.91, contentment BFL*0.9mm <f4<2.0mm*BFL From the design parameters, we know that min(Di) / max(Di)>0.8 From the design parameters, we know that NA>0.35 From the design parameters, we know that

[0071] In the second embodiment, the first surface of the first lens 10 of this embodiment is a plane. Figure 4 ;MTF curve diagram as follows Figure 5 , its relative astigmatism curve and distortion curve are as follows Figure 6 .

[0072] Table 5, Parameters of each surface of Example 2

[0073]

[0074] Table 6, Parameters of each surface of Example 2

[0075] Surface serial number k A B C D E F S2 0 1.71E-05 -2.98E-08 4.89E-10 -2.63E-12 7.11E-15 -7.15E-18

[0076] The expression for aspheric surface is as follows:

[0077]

[0078] Where z is the aspheric surface at position r, c is the paraxial curvature of the aspheric surface, c = 1 / R (i.e., the paraxial curvature c is the inverse of the surface curvature radius R); k is the cone coefficient; A~J are high-order coefficients.

[0079] Table 7, Design parameters of the optical lens of Example 2

[0080]

[0081] Table 8, Constraints of Example 2

[0082] Constraints Design Results |f1 / EFL|>3.5 |f1 / f|=5, knowing satisfaction BFL / EFL>0.8 BFL / EFL=0.882, knowing satisfaction BFL / OAL>0.4 BFL / OAL=0.46, contentment OAL / EFL<2.2 OAL / EFL=1.91, contentment BFL*0.9mm <f4<2.0mm*BFL From the design parameters, we know that min(Di) / max(Di)>0.8 From the design parameters, we know that NA>0.35 From the design parameters, we know that

[0083] In the third embodiment, the first surface of the first lens 10 of this embodiment is convex, and the curvature radius of both surfaces of the fourth lens 13 is the same, which is convenient for processing and assembly. There is no problem of installing the front and back surfaces in reverse. The front and back surfaces are the same. Figure 7 ;MTF curve diagram as follows Figure 8 , its relative astigmatism curve and distortion curve are as follows Figure 9 .

[0084] Table 9, parameters of each surface of Example 3

[0085]

[0086] Table 10, Parameters of each surface of Example 3

[0087] Surface serial number k A B C D E F S1 0 -1.82E-05 0.00E+00 0.00E+00 0.00E+00 0.00E+00 0.00E+00 S2 0 1.71E-05 -2.98E-08 4.89E-10 -2.63E-12 7.11E-15 -7.15E-18

[0088] The expression for aspheric surface is as follows:

[0089]

[0090] Where z is the aspheric surface at position r, c is the paraxial curvature of the aspheric surface, c = 1 / R (i.e., the paraxial curvature c is the inverse of the surface curvature radius R); k is the cone coefficient; A~J are high-order coefficients.

[0091] Table 11, design parameters of the optical lens of Example 3

[0092]

[0093] Table 12, Constraints of Example 3

[0094] Constraints Design Results |f1 / EFL|>3.5 |f1 / f|=5, knowing satisfaction BFL / EFL>0.8 BFL / EFL=0.882, knowing satisfaction BFL / OAL>0.4 BFL / OAL=0.44, contentment OAL / EFL<2.2 OAL / EFL=1.91, contentment BFL*0.9mm <f4<2.0mm*BFL From the design parameters, we know that min(Di) / max(Di)>0.8 From the design parameters, we know that NA>0.35 From the design parameters, we know that

[0095] The lens of the present invention has the characteristics of long back focus, which can provide sufficient rear mechanical space for the DLP lighting optical module; it has excellent thermal stability, the first lens is mainly used to correct the high-order aberrations of the system, and the optical focal length is small, which can minimize the impact of temperature, and the other three lenses use glass lenses, and the optical performance of glass lenses changes little with relative temperature, so their combined application can make the lens adapt to fields with a wide range of temperature applications; the present invention is a glass-plastic hybrid design, which can improve performance while reducing costs.

[0096] As the fourth embodiment of the present invention, a four-piece lens with a large aperture includes, along the optical axis from the object side to the image side, at least one aspherical first lens 10 with positive optical power, a biconcave second lens 11 with negative optical power, a biconvex third lens 12 with positive optical power, and a biconvex fourth lens 13 with positive optical power; the second lens 11 and the third lens 12 are separated into two independent lenses;

[0097] It satisfies the following conditional expressions:

[0098] |f1| / EFL>3.5, where f1 is the focal length of the first lens 10 and EFL is the effective focal length of the lens system;

[0099] BFL / EFL>0.8, where BFL is the back focal length;

[0100] BFL / OAL>0.4, where OAL is the overall length of the lens system;

[0101] OAL / EFL<2.2;

[0102] BFL*0.9mm<f4<BFL*2.0mm, f4 is the focal length of the fourth lens 13;

[0103] NA>0.35, NA is the numerical aperture of the system;

[0104] min(Di) / max(Di)>0.8, Di is the effective aperture of the i-th surface.

[0105] The above-described embodiments only represent four embodiments of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the patent of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the appended claims.

Claims

1. A large-aperture four-element lens, characterized in that: From the object side to the image side along the optical axis, there are successively arranged at least one aspherical first lens (10) with positive optical power, a biconcave second lens (11) with negative optical power, a biconvex third lens (12) with positive optical power, and a biconvex fourth lens (13) with positive optical power; the second lens and the third lens are cemented together as one body; It satisfies the following conditional expressions: |f1| / EFL > 3.5, where f1 is the focal length of the first lens (10) and EFL is the effective focal length of the lens system; BFL / EFL > 0.8, where BFL is the back focal length; BFL / OAL > 0.4, where OAL is the overall length of the lens system; OAL / EFL < 2.2; BFL * 0.9mm < f4 < BFL * 2.0mm, where f4 is the focal length of the fourth lens (13); NA > 0.35, where NA is the numerical aperture of the system; min(Di) / max(Di) > 0.8, where Di is the effective aperture of the i-th surface.

2. The large-aperture four-piece lens according to claim 1, characterized in that: The first lens (10) is set as an injection-molded aspherical lens.

3. The large-aperture four-piece lens according to claim 1, characterized in that: The second lens (11), the third lens (12), and the fourth lens (13) are all set as spherical glass lenses.

4. The large-aperture four-piece lens according to claim 1, wherein: The Abbe number of the optical material of the second lens (11) is less than 30.

5. The large-aperture four-piece lens according to claim 1, characterized in that: The curvature radii of both surfaces of the fourth lens (13) are set to be the same.

6. A large-aperture four-element lens, characterized in that: From the object side to the image side along the optical axis, there are successively arranged at least one aspherical first lens (10) with positive optical power, a biconcave second lens (11) with negative optical power, a biconvex third lens (12) with positive optical power, and a biconvex fourth lens (13) with positive optical power; the second lens (11) and the third lens (12) are separated into two independent lenses; It satisfies the following conditional expressions: |f1| / EFL > 3.5, where f1 is the focal length of the first lens (10) and EFL is the effective focal length of the lens system; BFL / EFL > 0.8, where BFL is the back focal length; BFL / OAL > 0.4, where OAL is the overall length of the lens system; OAL / EFL < 2.2; BFL * 0.9mm < f4 < BFL * 2.0mm, where f4 is the focal length of the fourth lens (13); NA > 0.35, where NA is the numerical aperture of the system; min(Di) / max(Di) > 0.8, where Di is the effective aperture of the i-th surface.

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