An athermalized ultra-short back focal length projection lens

Abstract

The application discloses athermalized ultra-short back focal length projection lens and relates to the technical field of lens design.The athermalized ultra-short back focal length projection lens comprises a lens system, and the lens system comprises, in sequence from the object side to the image side along the optical axis, a first lens, a second lens, a third lens, a fourth lens, an aperture diaphragm and a fifth lens.The third lens and the fourth lens are glued together.The first lens is an aspherical lens with negative focal power, the object side is a convex surface, and the image side is a concave surface.The second lens is an aspherical lens with positive focal power, and the image side is a convex surface.The third lens is a spherical lens with negative focal power, and the image side is a concave surface.The fourth lens is a spherical lens with positive focal power, the object side is a convex surface, and the image side is a convex surface.The fifth lens is a spherical lens with positive focal power, the object side is a convex surface, and the image side is a plane.The application weakens the thermal defocus phenomenon of the projection lens and reduces the cost.

Description

Technical Field

[0001] This invention relates to the field of lens design technology, and in particular to a non-thermalized ultra-short back focal length projection lens. Background Technology

[0002] With the development of technology, micro-projection technology, with its miniaturization and lightweight design, has gradually entered people's lives. In today's rapidly developing information age, it is increasingly favored and has become an important trend in projection display development. Combined with new LED light sources, miniaturized micro-projectors can be realized and applied to various occasions, meeting people's needs for projection displays and improving their quality of life.

[0003] Currently, projection lenses are widely used in various industries. However, the overall size of projection lenses on the market is relatively large, with a large number of lenses. Most of them adopt a prism structure, which leads to relatively high costs and is not conducive to the application of miniaturized projection. In addition, when existing projection lenses work in a wide temperature range of -40℃ to +85℃, changes in ambient temperature can easily cause defocusing, resulting in a significant decrease in system image quality. Summary of the Invention

[0004] The purpose of this invention is to provide a heat-free ultra-short back focal length projection lens, which reduces the thermal defocusing phenomenon of the projection lens and lowers the cost.

[0005] To achieve the above objectives, the present invention provides the following solution:

[0006] A non-thermalized ultra-short back focal length projection lens includes: a lens system;

[0007] The lens system comprises, along the optical axis from the object side to the image side, the following components in sequence: a first lens, a second lens, a third lens, a fourth lens, an aperture stop, and a fifth lens; the third lens and the fourth lens are cemented together.

[0008] The first lens is an aspherical lens with negative optical power, the object side is convex, and the image side is concave.

[0009] The second lens is an aspherical lens with positive optical power, and the image-side surface is convex.

[0010] The third lens is a spherical lens with negative optical power and a concave image side.

[0011] The fourth lens is a spherical lens with positive optical power, the object side is convex, and the image side is convex.

[0012] The fifth lens is a spherical lens with positive optical power, with a convex object side and a flat image side.

[0013] Optionally, the first lens and the second lens are both plastic aspherical lenses, and the third lens, the fourth lens and the fifth lens are all glass spherical lenses.

[0014] Optionally, the ratio range of the focal length of each lens to the total focal length of the lens system is as follows:

[0015] -1.7≤f1 / f≤-1.6;2.1≤f2 / f≤2.3;-1.7≤f3 / f≤-1.5;1.2≤f4 / f≤1.4;2.8≤f5 / f≤3.0;

[0016] Wherein, f1 is the focal length of the first lens, f is the total focal length of the lens system, f2 is the focal length of the second lens, f3 is the focal length of the third lens, f4 is the focal length of the fourth lens, and f5 is the focal length of the fifth lens.

[0017] Optionally, the total length of the optical system of the projection lens and the total focal length of the lens system satisfy: TTL / f≤7.23;

[0018] Where TTL is the total length of the optical system and f is the total focal length of the lens system.

[0019] Optionally, the athermalized ultra-short back focal length projection lens also includes: a light valve protective glass and a light valve;

[0020] The protective glass for the light valve and the light valve are sequentially arranged along the optical axis on the image side of the fifth lens.

[0021] Optionally, the distance between each lens satisfies: 9.0 < L4 / L3 < 10.0, 9.0 < L4 / L5 < 18.0;

[0022] Wherein, L3 is the distance between the first intersection point and the aperture stop, L4 is the distance between the aperture stop and the second intersection point, and L5 is the distance between the third intersection point and the fourth intersection point;

[0023] The first intersection point is the intersection of the image-side surface of the fourth lens and the optical axis; the second intersection point is the intersection of the object-side surface of the fifth lens and the optical axis; the third intersection point is the intersection of the image-side surface of the fifth lens and the optical axis; and the fourth intersection point is the intersection of the surface of the light valve protective glass near the fifth lens and the optical axis.

[0024] Optionally, the distance between the third intersection point and the light valve is ≤3mm.

[0025] Optionally, the Abbe number of the third lens is less than the Abbe number of the fourth lens.

[0026] Alternatively, 1.84 ≤ (R11 + R12) / (R11 - R12) ≤ 2.16;

[0027] Wherein, R11 is the radius of curvature of the object side of the first lens, and R12 is the radius of curvature of the image side of the first lens.

[0028] According to the specific embodiments provided in this invention, the present invention discloses the following technical effects:

[0029] This invention discloses a thermal-free ultra-short back focal length projection lens, comprising: a lens system; the lens system, along the optical axis from the object side to the image side, sequentially comprising: a first lens, a second lens, a third lens, a fourth lens, an aperture stop, and a fifth lens; the third and fourth lenses are cemented together. This invention employs a 5-lens design, and through the combination of different lens shapes, curvatures, spacing, and materials, the selection of the aperture stop position, and the combination of cemented lenses, various aberrations in the projection lens imaging system are corrected to achieve clear imaging; furthermore, the thermal defocusing phenomenon of the projection lens is not significant within a temperature range of -40℃ to +85℃, reducing the thermal defocusing phenomenon and lowering costs. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments 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 these drawings without creative effort.

[0031] Figure 1 This is a schematic diagram of the structure of the athermalized ultra-short back-cut projection lens provided in an embodiment of the present invention;

[0032] Figure 2 A schematic diagram of the optical path of an athermalized ultra-short back-cutoff projection lens provided in an embodiment of the present invention;

[0033] Figure 3 The modulation transfer function diagram of the athermalized ultra-short back-cut projection lens provided in the embodiment of the present invention;

[0034] Figure 4 Defocus curve of the anechoic ultra-short back focal length projection lens provided in this embodiment of the invention at room temperature +20℃;

[0035] Figure 5 The defocus curve of the anechoic ultra-short back focal length projection lens provided in this embodiment of the invention at a low temperature of -40℃;

[0036] Figure 6The defocus curve of the anechoic ultra-short back focal length projection lens provided in this embodiment of the invention at a high temperature of +85°C;

[0037] Figure 7 A dot plot of a non-thermalized ultra-short back-cut projection lens provided in an embodiment of the present invention;

[0038] Figure 8 The relative illumination diagram of the athermalized ultra-short back-cut projection lens provided in this embodiment of the invention.

[0039] Symbol explanation:

[0040] First lens—1, Second lens—2, Third lens—3, Fourth lens—4, Aperture stop—5, Fifth lens—6, Light valve protective glass—7, Light valve—8. Detailed Implementation

[0041] 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 some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0042] The purpose of this invention is to provide a non-thermalized ultra-short back focal length projection lens, which aims to reduce thermal defocusing of the projection lens and lower costs.

[0043] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0044] Example

[0045] Figure 1 This is a schematic diagram of the athermalized ultra-short back focal length projection lens structure provided in Embodiment 1 of the present invention. Figure 1 As shown, the athermalized ultra-short back focal length projection lens in this embodiment includes: a lens system.

[0046] The lens system, along the optical axis from the object side to the image side, includes, in sequence: a first lens 1, a second lens 2, a third lens 3, a fourth lens 4, an aperture stop 5, and a fifth lens 6; the third lens 3 and the fourth lens 4 are cemented together.

[0047] The first lens 1 is an aspherical lens with negative optical power, the object side is convex and the image side is concave.

[0048] The second lens 2 is an aspherical lens with positive optical power and a convex image side.

[0049] The third lens 3 is a spherical lens with negative optical power, and its image-side surface is concave.

[0050] The fourth lens 4 is a spherical lens with positive optical power, with a convex object side and a convex image side.

[0051] The fifth lens 6 is a spherical lens with positive optical power, with a convex object side and a flat image side.

[0052] As an optional implementation, the first lens 1 and the second lens 2 are both plastic aspherical lenses, and the third lens 3, the fourth lens 4 and the fifth lens 6 are all glass spherical lenses.

[0053] As an optional implementation, the ratio range of the focal length of each lens to the total focal length of the lens system is as follows:

[0054] -1.7≤f1 / f≤-1.6;2.1≤f2 / f≤2.3;-1.7≤f3 / f≤-1.5;1.2≤f4 / f≤1.4;2.8≤f5 / f≤3.0。

[0055] Where f1 is the focal length of the first lens 1, f is the total focal length of the lens system, f2 is the focal length of the second lens 2, f3 is the focal length of the third lens 3, f4 is the focal length of the fourth lens 4, and f5 is the focal length of the fifth lens 6.

[0056] As an optional implementation, the total length of the optical system of the projection lens and the total focal length of the lens system satisfy: TTL / f≤7.23.

[0057] Where TTL is the total length of the optical system and f is the total focal length of the lens system.

[0058] As an optional implementation, the athermalized ultra-short back focal length projection lens also includes: a light valve protective glass 7 and a light valve 8.

[0059] The light valve protective glass 7 and the light valve 8 are arranged sequentially along the optical axis on the image side of the fifth lens 6.

[0060] As an optional implementation, the distance between each lens satisfies: 9.0 < L4 / L3 < 10.0, 9.0 < L4 / L5 < 18.0.

[0061] Where L3 is the distance between the first intersection point and the aperture stop 5, L4 is the distance between the aperture stop 5 and the second intersection point, and L5 is the distance between the third intersection point and the fourth intersection point.

[0062] The first intersection point is the intersection of the image side surface of the fourth lens 4 with the optical axis; the second intersection point is the intersection of the object side surface of the fifth lens 6 with the optical axis; the third intersection point is the intersection of the image side surface of the fifth lens 6 with the optical axis; and the fourth intersection point is the intersection of the surface of the light valve protective glass 7 near the fifth lens with the optical axis.

[0063] Specifically, the distance L4 between the aperture stop 5 and the fifth lens 6 is limited to a certain distance, so that the light emitted by the illumination system can enter the light valve 8. The prism is removed by the illumination system and the imaging system sharing the fifth lens 6, which greatly reduces the cost.

[0064] As an optional implementation, the distance between the third intersection point and the light valve 8 is ≤3mm.

[0065] As an optional implementation, the Abbe number of the third lens 3 is less than the Abbe number of the fourth lens 4.

[0066] Specifically, the cemented doublet lens obtained by cementing the third lens 3 and the fourth lens 4 is used to correct chromatic aberration, and the image side of the third lens 3 is set as a concave surface to correct other aberrations.

[0067] As an optional implementation, 1.84≤(R11+R12) / (R11-R12)≤2.16.

[0068] Wherein, R11 is the radius of curvature of the object side of the first lens 1, and R12 is the radius of curvature of the image side of the first lens 1.

[0069] Specifically, the direction of light can be effectively controlled by properly configuring the radius of curvature of the image side of the first lens 1, allowing the light to be transmitted smoothly, such as... Figure 2 The light path shown represents the light beam emitted by the lighting system (i.e., Figure 2 The dashed line (in the diagram) indicates the beam entering the fifth lens, passing through the protective glass of the light valve, and then reaching the light valve. The reflected beam is then reflected by the light valve, and sequentially passes through the protective glass of the light valve, the fifth lens, the aperture stop, the fourth lens, the third lens, the second lens, and the first lens, thus forming an image. This effectively corrects spherical aberration and coma in optical lenses, greatly improving their imaging performance.

[0070] Specifically, the radius of curvature (in mm), center thickness d (in mm), refractive index (Nd), and Abbe constant (Vd) of the first lens 1, the second lens 2, the third lens 3, the fourth lens 4, and the fifth lens 6 are shown in Table 1.

[0071] Table 1 Lens Parameter Table

[0072] S11 aspherical 10.25 2.59 1.54 55.71 S12 aspherical 3.55 11.23 1.54 / S21 aspherical 23.09 3.48 1.64 23.97 S22 aspherical -13.43 4.97 / / S31 spherical 162.42 1.01 1.95 17.94 S32 spherical 7.96 3.11 1.71 53.86 S41 spherical -13.09 1.02 / / STO spherical infinity 8.86 / / S51 spherical 13.31 2.91 1.83 37.22 S52 spherical infinity 0.51 / / S61 spherical infinity 1.1 1.51 62.91 S62 spherical infinity 0.36 / / IMA spherical infinity 0 / /

[0073] In Table 1, the radius of curvature represents the degree of curvature of the lens surface. A positive radius of curvature indicates that the surface bends towards the image plane, a negative radius of curvature indicates that the surface bends towards the object plane, and infinity indicates that the surface is flat. Thickness / gap represents the central axial distance from the current surface to the next surface. Refractive index represents the ability of the current lens material to deflect light. Abbe number represents the dispersion characteristics of the current lens material.

[0074] S11 is the object-side surface of the first lens 1, S12 is the image-side surface of the first lens 1, S21 is the object-side surface of the second lens 2, S22 is the image-side surface of the second lens 2, S31 is the object-side surface of the third lens 3, S32 is the image-side surface of the third lens 3 and the object-side surface of the fourth lens 4, S41 is the image-side surface of the fourth lens 4, STO is the aperture stop 5, S51 is the object-side surface of the fifth lens 6, S52 is the image-side surface of the fifth lens 6, S61 is the object-side surface of the light valve protective glass 7, S62 is the image-side surface of the light valve protective glass 7, and IMA is the light valve surface.

[0075] The coefficients of the aspherical lenses 1 and 2 are shown in Table 2.

[0076] Table 2. Coefficients of Aspherical Lenses (First Lens 1 and Second Lens 2)

[0077] S11 -4.86 -8.40E-05 -1.20E-06 -2.10E-08 -7.70E-11 4.17E-12 -4.01E-13 S12 -0.79 2.02E-05 -3.69E-06 -2.47E-07 -1.39E-08 -8.38E-10 -4.90E-11 S21 2.29 -5.50E-05 1.16E-08 1.62E-08 5.70E-10 2.98E-12 -2.01E-14 S22 -2.34 -1.97E-05 1.89E-07 3.84E-09 1.58E-10 2.41E-12 1.24E-13

[0078] The aspherical lens coefficients in Table 2 are the coefficients of each term in the aspherical function (aspherical polynomial), which is: .

[0079] Where Z is the sag of the lens along the optical axis, k is the conic coefficient of the surface, r is the half-aperture of the lens perpendicular to the optical axis, c is the curvature of the lens, A is the coefficient of the 4th order term of the aspherical polynomial, B is the coefficient of the 6th order term of the aspherical polynomial, C is the coefficient of the 8th order term of the aspherical polynomial, D is the coefficient of the 10th order term of the aspherical polynomial, E is the coefficient of the 12th order term of the aspherical polynomial, and F is the coefficient of the 14th order term of the aspherical polynomial.

[0080] Figure 3 The modulation transfer function (MTF) diagram of the athermalized ultra-short back-cutoff projection lens provided in this embodiment of the invention is used to represent the relationship between modulation density and the number of line pairs per millimeter in the image, and is used to evaluate the ability to reproduce details of the imaged object surface; by Figure 3 As can be seen, all field-of-view curves are above 0.45, indicating excellent resolution.

[0081] Figure 4 , Figure 5 , Figure 6The graphs show the defocus curves of the anechoic ultra-short back focal length projection lens provided in the embodiments of the present invention at 20℃, -40℃, and 85℃. It can be seen that the defocus amount of the anechoic ultra-short back focal length projection lens provided in the embodiments of the present invention is less than 10μm at both low temperature (-40℃) and high temperature (+85℃). Such a small defocus amount ensures that the lens can project clear images at both low temperature (-40℃) and high temperature (+85℃).

[0082] Figure 7 The dot plot of the anechoic ultra-short back-clip projection lens provided in this embodiment of the invention shows that all root mean square radius values ​​are less than 5 μm, which is smaller than the size of a single pixel of the light valve, thus enabling clear imaging.

[0083] Through simulation verification, the field curvature, distortion and lateral chromatic aberration of the athermalized ultra-short back-cutoff projection lens were obtained. It was found that the field curvature was within ±0.1mm, the distortion varied within less than 2%, the field curvature and distortion were small, the dispersion was small, and it was close to the diffraction limit.

[0084] Figure 8 This is a relative illumination diagram of the athermalized ultra-short back-cut projection lens provided in an embodiment of the present invention, from... Figure 8 As can be seen, the relative illumination of the lens at the maximum field of view is greater than 90%, and the amount of light entering is sufficient, ensuring that there will be no dark corners in the projected image after the projection lens and the lighting system are matched.

[0085] The beneficial effects of this invention are:

[0086] (1) It operates within a wide temperature range of -40℃ to +85℃ and will not defocus due to changes in ambient temperature, thus preventing a significant decrease in the system's imaging quality.

[0087] (2) The projection lens is small in size and has little distortion.

[0088] (3) The system's optical architecture is simple and easy to assemble.

[0089] (4) The design uses a combination of glass and plastic and is prism-free, which greatly reduces costs.

[0090] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0091] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the system and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. An athermalized ultra-short back focal length projection lens characterized by, include: Lens system; The lens system has a total of 5 lenses; The lens system comprises, along the optical axis from the object side to the image side, the following components in sequence: a first lens, a second lens, a third lens, a fourth lens, an aperture stop, and a fifth lens; the third lens and the fourth lens are cemented together. The first lens is an aspherical lens with negative optical power, the object side is convex, and the image side is concave. The second lens is an aspherical lens with positive optical power, and the image-side surface is convex. The third lens is a spherical lens with negative optical power and a concave image side. The fourth lens is a spherical lens with positive optical power, the object side is convex, and the image side is convex. The fifth lens is a spherical lens with positive optical power, the object side is convex, and the image side is flat. The ratios of the focal length of each lens to the total focal length of the lens system range as follows: -1.7≤f1 / f≤-1.6;2.1≤f2 / f≤2.3;-1.7≤f3 / f≤-1.5;1.2≤f4 / f≤1.4;2.8≤f5 / f≤3.0; Wherein, f1 is the focal length of the first lens, f is the total focal length of the lens system, f2 is the focal length of the second lens, f3 is the focal length of the third lens, f4 is the focal length of the fourth lens, and f5 is the focal length of the fifth lens. The total length of the optical system of the projection lens and the total focal length of the lens system satisfy: TTL / f≤7.23; Where TTL is the total length of the optical system and f is the total focal length of the lens system.

2. The athermalized ultrashort back focal length projection lens of claim 1, wherein, The first lens and the second lens are both plastic aspherical lenses, while the third lens, the fourth lens and the fifth lens are all glass spherical lenses.

3. The athermalized ultrashort back focal length projection lens of claim 1, wherein, The athermalized ultra-short back focal length projection lens also includes: a light valve protective glass and a light valve; The protective glass for the light valve and the light valve are sequentially arranged along the optical axis on the image side of the fifth lens.

4. The athermalized ultrashort back aperture projection lens of claim 3, wherein, The distances between the lenses satisfy the following conditions: 9.0 < L4 / L3 < 10.0, 9.0 < L4 / L5 < 18.0; Wherein, L3 is the distance between the first intersection point and the aperture stop, L4 is the distance between the aperture stop and the second intersection point, and L5 is the distance between the third intersection point and the fourth intersection point; The first intersection point is the intersection of the image-side surface of the fourth lens and the optical axis; the second intersection point is the intersection of the object-side surface of the fifth lens and the optical axis; the third intersection point is the intersection of the image-side surface of the fifth lens and the optical axis; and the fourth intersection point is the intersection of the surface of the light valve protective glass near the fifth lens and the optical axis.

5. The athermalized ultrashort back aperture projection lens of claim 4, wherein, The distance between the third intersection point and the light valve is ≤3mm.

6. The athermalized ultrashort back aperture projection lens of claim 1, wherein, The Abbe number of the third lens is less than that of the fourth lens.

7. The athermalized ultrashort back aperture projection lens of claim 1, wherein, 1.84≤(R11+R12) / (R11-R12)≤2.16; Wherein, R11 is the radius of curvature of the object side of the first lens, and R12 is the radius of curvature of the image side of the first lens.

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