A fixed focus lens and optical projection system

Abstract

Embodiments of the present application disclose a kind of fixed focus lens and optical projection system.The fixed focus lens includes sequentially arranged first lens, second lens, third lens, fourth lens, fifth lens, sixth lens, seventh lens, eighth lens, ninth lens and tenth lens along the optical axis from object side to image side;The first lens, the second lens, the sixth lens, the seventh lens and the ninth lens have negative focal power, and the third lens, the fourth lens, the fifth lens, the eighth lens and the tenth lens have positive focal power.Embodiments of the present application can realize a kind of TR≤0.5, diagonal field of view angle reaches 120°, distortion≤1.5%Small projection ratio low distortion wide-angle lens, while various aberrations such as chromatic aberration, spherical aberration and field curvature can be corrected and balanced, high pixel is realized, and imaging quality is guaranteed.

Description

Technical Field

[0001] The present invention relates to the field of optical system technology, and in particular to a fixed-focus lens and an optical projection system. Background Technology

[0002] With the development of technology, the application range of projection products is becoming wider and wider, and as a result, people's demands for the performance of projection lenses are becoming more and more diverse.

[0003] In the industry, the projection distance divided by the screen width is called the throw ratio, abbreviated as TR. Generally speaking, existing projection lenses typically have a large TR value, often requiring a greater distance to project a suitable screen size, thus failing to adequately meet the needs of indoor projection. Furthermore, existing projection lenses have a relatively small field of view, which cannot effectively meet the demands of large screens. Summary of the Invention

[0004] This invention provides a fixed-focus lens and an optical projection system to achieve a wide-angle lens with a small projection ratio and low distortion, thus solving the problem that projection lenses cannot meet the needs of indoor projection and large-screen projection.

[0005] In a first aspect, embodiments of the present invention provide a fixed-focus lens, comprising a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, a seventh lens, an eighth lens, a ninth lens, and a tenth lens arranged sequentially along the optical axis from the object side to the image side; The first lens, the second lens, the sixth lens, the seventh lens, and the ninth lens have negative optical power, while the third lens, the fourth lens, the fifth lens, the eighth lens, and the tenth lens have positive optical power.

[0006] Optionally, the first lens is a plastic aspherical lens, the seventh lens is a glass aspherical lens, and the second, third, fourth, fifth, sixth, eighth, ninth, and tenth lenses are all glass spherical lenses.

[0007] Optionally, the first lens is a convex-concave lens, the second lens is a concave-concave lens, the third lens is a convex-concave lens, the fourth lens is a convex-concave lens, the fifth lens is a convex-convex lens, the sixth lens is a concave-convex or concave-concave lens, the seventh lens is a concave-convex or concave-concave lens, the eighth lens is a convex-convex lens, the ninth lens is a convex-concave lens, and the tenth lens is a convex-convex lens.

[0008] Optionally, the opposing surfaces of the ninth lens and the tenth lens are glued together to form a cemented lens assembly.

[0009] Optionally, each lens in the fixed-focus lens satisfies the following condition: 0.535 <F1 / F2<0.950; -17.053 <F2 / F3<-4.300; 0.247 <F3 / F4<1.401; 0.097 <F4 / F5<0.866; -3.950 <F5 / F6<-0.879; 0.287 <F6 / F7<2.850; -1.189 <F7 / F8<-0.270; -0.301 <F9 / F8<-0.020; 0.190 <FA / F8<0.410; Wherein, F1, F2, F3, F4, F5, F6, F7, F8, F9, and FA are the optical powers of the first lens, the second lens, the third lens, the fourth lens, the fifth lens, the sixth lens, the seventh lens, the eighth lens, the ninth lens, and the tenth lens, respectively.

[0010] Optionally, each lens in the fixed-focus lens satisfies the following condition: 1.45 <ND3<1.86; 1.50 <ND5<1.73; 1.73 <ND6<2.12; 1.67 <ND7<2.10; 1.49 <ND8<1.61; 1.79 <ND9<1.89; 1.51 <NDA<1.65; Wherein, ND3, ND5, ND6, ND7, ND8, ND9, and NDA are the refractive indices of the third lens, the fifth lens, the sixth lens, the seventh lens, the eighth lens, the ninth lens, and the tenth lens, respectively.

[0011] Optionally, each lens in the fixed-focus lens satisfies the following condition: 1.97 <VD8 / VD9<2.66; 1.79 <VDA / VD9<2.66; Wherein, VD8, VD9, and VDA are the Abbe numbers of the eighth lens, the ninth lens, and the tenth lens, respectively.

[0012] Optionally, the fixed-focus lens satisfies the following condition: 1.450 <BFL / ImgH<1.758; Wherein, BFL is the back focal length of the fixed-focus lens, and ImgH is the diagonal length of the effective imaging area on the imaging surface of the fixed-focus lens.

[0013] Optionally, the fixed-focus lens further includes an aperture stop located between the fifth lens and the sixth lens.

[0014] In a second aspect, embodiments of the present invention also provide an optical projection system, including an image source and a protective glass, a prism, and a fixed-focus lens as described in any one of the first aspects, which are sequentially located on the light-emitting side of the image source.

[0015] The fixed-focus lens and optical projection system provided in this invention, by setting a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, a seventh lens, an eighth lens, a ninth lens, and a tenth lens arranged sequentially along the optical axis from the object side to the image side; wherein the first lens, the second lens, the sixth lens, the seventh lens, and the ninth lens have negative optical power, and the third lens, the fourth lens, the fifth lens, the eighth lens, and the tenth lens have positive optical power, can realize a small projection ratio, low distortion wide-angle lens with a TR≤0.5, a diagonal field of view of 120°, and distortion≤1.5%, and can correct and balance various aberrations such as chromatic aberration, spherical aberration, and field curvature, achieving high pixel count and ensuring image quality. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the structure of an optical projection system provided in Embodiment 1 of the present invention; Figure 2 yes Figure 1 The spherical aberration curve of the fixed-focus lens is shown. Figure 3 yes Figure 1 The field curvature distortion diagram of the fixed-focus lens shown; Figure 4 This is a schematic diagram of the structure of an optical projection system provided in Embodiment 2 of the present invention; Figure 5 yes Figure 4 The spherical aberration curve of the fixed-focus lens is shown. Figure 6 yes Figure 4 The field curvature distortion diagram of the fixed-focus lens is shown. Detailed Implementation

[0017] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, the accompanying drawings show only the parts relevant to the present invention, and not all of the structures.

[0018] The terminology used in the embodiments of this invention is for the purpose of describing specific embodiments only and is not intended to limit the invention. It should be noted that directional terms such as "upper," "lower," "left," and "right" described in the embodiments of this invention are used to describe the angles shown in the accompanying drawings and should not be construed as limiting the embodiments of this invention. Furthermore, in the context, it should be understood that when referring to an element being formed "on" or "below" another element, it can be formed not only directly on or below the other element, but also indirectly on or below it through intermediate elements. The terms "first," "second," etc., are used for descriptive purposes only and do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0019] Figure 1 This is a schematic diagram of an optical projection system provided in Embodiment 1 of the present invention, for reference. Figure 1 The optical projection system includes a fixed-focus lens 100, which includes a first lens 11, a second lens 12, a third lens 13, a fourth lens 14, a fifth lens 15, a sixth lens 16, a seventh lens 17, an eighth lens 18, a ninth lens 19, and a tenth lens 20 arranged sequentially along the optical axis from the object side to the image side; the first lens 11, the second lens 12, the sixth lens 16, the seventh lens 17, and the ninth lens 19 have negative optical power, and the third lens 13, the fourth lens 14, the fifth lens 15, the eighth lens 18, and the tenth lens 20 have positive optical power.

[0020] The optical power of a lens is equal to the difference between the convergence of the image-side beam and the convergence of the object-side beam, characterizing the optical system's ability to deflect light. A larger absolute value of the optical power indicates a stronger ability to bend light, while a smaller absolute value indicates a weaker ability. When the optical power is positive, the refraction of light is converging; when the optical power is negative, the refraction of light is diverging. In this embodiment, all lenses can be housed in a single lens barrel (…). Figure 1 (Not shown in the image) Within the lens, the first lens 11, second lens 12, sixth lens 16, seventh lens 17, and ninth lens 19 are configured with negative optical power, while the third lens 13, fourth lens 14, fifth lens 15, eighth lens 18, and tenth lens 20 are configured with positive optical power. This essentially defines the specific role each lens plays in the overall optical system, allowing for the convergence or divergence of light rays. In other words, by appropriately setting the positive and negative values ​​of the optical power of each lens, the relative beam convergence or divergence effects of each lens within the entire lens are effectively limited. This facilitates achieving wide-angle, low-projection-ratio, and low-distortion performance, while also helping to correct and balance various aberrations such as chromatic aberration, spherical aberration, and field curvature, achieving high pixel count and ensuring image quality.

[0021] The above technical solution, by setting up a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, a seventh lens, an eighth lens, a ninth lens, and a tenth lens arranged sequentially along the optical axis from the object side to the image side; wherein the first lens, the second lens, the sixth lens, the seventh lens, the eighth lens, and the tenth lens have negative optical power, and the third lens, the fourth lens, the fifth lens, the eighth lens, and the tenth lens have positive optical power, can realize a wide-angle lens with a small projection ratio and low distortion, a TR≤0.5, a diagonal field of view of 120°, and distortion≤1.5%, and can correct and balance various aberrations such as chromatic aberration, spherical aberration, and field curvature, achieving high pixel count and ensuring image quality.

[0022] In one specific embodiment, the first lens 11 may be a plastic aspherical lens, the seventh lens 17 may be a glass aspherical lens, and the second lens 12, the third lens 13, the fourth lens 14, the fifth lens 15, the sixth lens 16, the eighth lens 18, the ninth lens 19 and the tenth lens 20 may all be glass spherical lenses.

[0023] Furthermore, the first lens 11 can be a convex-concave lens, the second lens 12 can be a concave-concave lens, the third lens 13 can be a convex-concave lens, the fourth lens 14 can be a convex-concave lens, the fifth lens 15 can be a convex-convex lens, the sixth lens 16 can be a concave-convex or concave-concave lens, the seventh lens 17 can be a concave-convex or concave-concave lens, the eighth lens 18 can be a convex-convex lens, the ninth lens 19 can be a convex-concave lens, and the tenth lens 20 can be a convex-convex lens.

[0024] The first lens 11 and the seventh lens 17 are set aspherical lenses, mainly to use the aspherical structure to correct the aberrations of the first lens 11 and the seventh lens 17, which are prone to obvious aberrations. The first lens 11 is made of plastic, mainly because plastic aspherical lenses are easier to manufacture and can save manufacturing costs to a certain extent.

[0025] In addition, all lenses except the first lens 11 are made of glass. The main purpose of this is to reduce the sensitivity of the lenses to temperature by using glass, to ensure the image quality of the lenses at different temperatures, to meet the usage requirements under temperature conditions of -40℃ to 95℃, and to be more suitable for the use needs of different projection scenarios in indoor and outdoor lighting.

[0026] By setting each lens to have a different concave or convex shape, the essence is to adjust the curvature direction of the lens surface to achieve the optical power of the lens, so as to achieve the matching of optical power between the lenses and meet the performance requirements of small projection ratio.

[0027] Continue to refer to Figure 1In a specific embodiment of the present invention, the opposing surfaces of the ninth lens 19 and the tenth lens 20 may be glued together to form a cemented lens assembly.

[0028] Those skilled in the art will understand that the ninth lens 19 and the tenth lens 20 are respectively convex-concave and biconvex lenses. Based on this, by reasonably modifying the surface shape of the ninth lens 19 and the tenth lens 20, such as the radius of curvature, the curvature of their adjacent surfaces can be made consistent and then cemented together. At the same time, it ensures that the ninth lens 19 and the tenth lens 20 can achieve a match between positive and negative optical powers, which is beneficial for correcting aberrations such as chromatic aberration.

[0029] In one specific embodiment, each lens in the fixed-focus lens 100 satisfies the following condition: 0.535 <F1 / F2<0.950; -17.053 <F2 / F3<-4.300; 0.247 <F3 / F4<1.401; 0.097 <F4 / F5<0.866; -3.950 <F5 / F6<-0.879; 0.287 <F6 / F7<2.850; -1.189 <F7 / F8<-0.270; -0.301 <F9 / F8<-0.020; 0.190 <FA / F8<0.410; Among them, F1, F2, F3, F4, F5, F6, F7, F8, F9, and FA are the optical powers of the first lens 11, the second lens 12, the third lens 13, the fourth lens 14, the fifth lens 15, the sixth lens 16, the seventh lens 17, the eighth lens 18, the ninth lens 19, and the tenth lens 20, respectively.

[0030] As in the above embodiments, by reasonably setting the optical power of each lens to meet a certain proportional relationship with the optical power of other lenses, the specific role of each lens in the entire optical system of the lens is further defined. Taking the first lens as an example, in this embodiment, the ratio of its optical power to that of the second lens is limited to between 0.535 and 0.950. This essentially limits the light divergence capability of the first lens, that is, its ability to increase the exit field of view in the entire lens. This allows the first lens to simultaneously increase the field of view and the final projected image, ensuring a large field of view range while avoiding excessive aberrations introduced by an excessively large field of view, which would affect the image quality. Taking the fifth lens 15 and the sixth lens 16 as another example, limiting their optical power ratio range to -3.950 to -0.879 is more about limiting the ability of the fifth lens 15 and the sixth lens 16, which are waist lenses of the entire optical system, to converge the light beam within a suitable range, thereby avoiding the lens introducing excessive aberrations while converging the light beam.

[0031] In summary, this embodiment sets the optical power of each lens to meet the aforementioned proportional relationship with other lenses. On the one hand, this limits the role of each lens in the entire lens, ensuring the cooperation of each lens to achieve clear imaging. On the other hand, it also provides a basis for using glass or plastic materials for manufacturing while ensuring that some lenses have the limited optical power, and for adjusting the imaging by using aspherical or spherical surface shapes. This helps to reduce the manufacturing difficulty and cost of optical lenses.

[0032] In one specific embodiment, each lens in the fixed-focus lens 100 satisfies the following condition: 1.45 <ND3<1.86; 1.50 <ND5<1.73; 1.73 <ND6<2.12; 1.67 <ND7<2.10; 1.49 <ND8<1.61; 1.79 <ND9<1.89; 1.51 <NDA<1.65; Wherein, ND3, ND5, ND6, ND7, ND8, ND9, and NDA are the refractive indices of the third lens 13, the fifth lens 15, the sixth lens 16, the seventh lens 17, the eighth lens 18, the ninth lens 19, and the tenth lens 20, respectively. In the above embodiment, limiting the refractive indices of some lenses to a certain range ensures the lens's refractive effect on light, which is more conducive to reducing the angle of incidence and lowering the lens sensitivity.

[0033] In one specific embodiment, each lens in the fixed-focus lens 100 satisfies the following condition: 1.97<VD8 / VD9<2.66; 1.79<VDA / VD9<2.66; wherein VD8, VD9 and VDA are Abbe numbers of the eighth lens (18), the ninth lens (19) and the tenth lens (20) respectively. The Abbe number is an index representing the dispersion ability of a medium. In this specific embodiment, the above-mentioned combination is adopted, which is beneficial for correcting axial chromatic aberration and lateral chromatic aberration, and enables clearer imaging.

[0034] In addition, the fixed-focus lens (100) can be selected to satisfy the following condition: 1.450<BFL / ImgH<1.758; wherein BFL is the back focal length of the fixed-focus lens (100), and ImgH is the diagonal length of the effective imaging area on the imaging surface of the fixed-focus lens (100). Designing the fixed-focus lens (100) to satisfy the above proportional relationship between back focal length and diagonal length can limit the overall size of the fixed-focus lens, which is beneficial for saving enough installation space for the prism and the flat plate filter when applied to a projection system, facilitates assembly, is beneficial for reducing the volume and realizing miniaturization.

[0035] Further, the fixed-focus lens (100) further comprises a stop (21), and the stop (21) is located between the fifth lens (15) and the sixth lens (16).

[0036] The stop (21) is used in an optical system to limit the beam size, and determines the amount of light that enters the photosensitive element through the lens, that is, it is used to control the light flux of the lens, which means that the stop (21) directly determines the aperture size of the optical lens. In the fixed-focus lens (100) provided in this embodiment, the stop (21) is arranged between the fifth lens (15) and the sixth lens (16). The waist position of the entire optical system is used to control the light flux, which can ensure the amount of light transmitted through the stop on the basis of effectively limiting the aperture size of the optical system, and ensure the imaging brightness; in addition, the stop can block off-axis light, effectively reduce off-axis aberrations and ensure the imaging clarity.

[0037] Based on the same inventive concept, an embodiment of the present invention further provides an optical projection system, with continued reference to Figure 1 , the optical projection system comprises an image source (200), and a protective glass (300), a prism (400) and any one of the fixed-focus lenses (100) provided by the above embodiments that are sequentially located at the light exit side of the image source (200). Moreover, since the optical projection system comprises the fixed-focus lens (100) of the above embodiment, it has the same or similar beneficial effects as the fixed-focus lens (100), which will not be repeated herein.

[0038] Based on the above same inventive concept, the present invention provides three different specific embodiments. Table 1 shows design values of focal length relationships, refractive indexes, Abbe number ratios and back focal length / diagonal length for the optical lens in the three embodiments provided by the embodiments of the present invention.

[0039] First, Figure 1 The relevant design values, such as the optical power ratio, of the fixed-focus lens in Embodiment 1 are shown in Table 1: Table 1 The parameter design values ​​of each lens in the fixed-focus lens in this embodiment are shown in Table 2: Table 2 shows a design value for each lens in the fixed-focus lens in Example 1. The surface numbers in Table 2 are assigned according to the surface sequence of each lens. "S1" represents the front surface of the first lens, "S2" represents the rear surface of the first lens, and so on. The radius of curvature represents the curvature of the lens surface; a positive value indicates the surface curves towards the image plane, and a negative value indicates the surface curves towards the object plane. "PL" indicates the surface is planar with an infinite radius of curvature. "Standard surface" indicates the surface is a standard sphere. Thickness represents the central axial distance between the current surface and the next surface. Refractive index represents the ability of the material between the current and next surfaces to deflect light; a blank space indicates the current location is air with a refractive index of 1. The Abbe number represents the dispersion characteristics of the material between the current and next surfaces; a blank space indicates the current location is air. The K value represents the magnitude of the best-fit conic coefficient for the aspherical surface.

[0040] The aspherical conic coefficients can be defined using the following aspherical formulas, but are not limited to the following representations: Where z is the sag of the aspherical surface. Let be the fundamental curvature at the vertex. For conic section constants, The radial coordinate is perpendicular to the optical axis. For higher-order terms, For aspherical surfaces, the term is of higher order.

[0041] The coefficients of even-order terms for each aspherical surface in the above embodiment 1 are shown in Table 3: Table 3 Parameters of each aspherical surface Table 4 shows the technical specifications of the fixed-focus lens in this embodiment: Figure 2 yes Figure 1 The spherical aberration curve of the fixed-focus lens is shown below. Figure 3 yes Figure 1 The field curvature distortion diagram of the fixed-focus lens shown is for reference. Figure 2In the figure, the vertical axis is a dimensionless quantity representing the normalized entrance pupil radius, and the horizontal axis represents the distance from the image sensor surface to the focal point on each wavelength axis. The horizontal axis values ​​for different wavelengths of light (0.459μm, 0.535μm, and 0.618μm) are all within ±0.1mm, meaning that the axial chromatic aberration of each wavelength in this fixed-focus lens is no greater than 0.1mm. Therefore, it can be seen that the fixed-focus lens provided in this embodiment can effectively correct axial chromatic aberration, ensuring minimal difference in chromatic aberration between different wavelengths of light. (Reference) Figure 3 In the coordinate system on the left side of the figure, the horizontal coordinate represents the magnitude of the field curvature, in mm; the vertical coordinate represents the normalized image height, which has no unit; where T represents the meridion and S represents the arc loss; from Figure 3 It can be seen that the fixed-focus lens in this embodiment effectively controls field curvature, meaning that during imaging, the difference in image quality between the center and the periphery is small; in the coordinate system on the right, the horizontal axis represents the magnitude of distortion, expressed as a percentage; the vertical axis represents the normalized image height, which has no unit; from Figure 3 It can be seen that the distortion of the fixed-focus lens in this embodiment is ≤1.5%.

[0042] Figure 4 This is a schematic diagram of an optical projection system provided in Embodiment 2 of the present invention, for reference. Figure 4 The optical projection system includes a fixed-focus lens 100, which comprises a first lens 11, a second lens 12, a third lens 13, a fourth lens 14, a fifth lens 15, a sixth lens 16, a seventh lens 17, an eighth lens 18, a ninth lens 19, and a tenth lens 20 arranged sequentially along the optical axis from the object side to the image side. The first lens 11, second lens 12, sixth lens 16, seventh lens 17, and ninth lens 19 have negative optical power, while the third lens 13, fourth lens 14, fifth lens 15, eighth lens 18, and tenth lens 20 have positive optical power. The opposing surfaces of the ninth lens 19 and the tenth lens 20 are cemented together to form a cemented lens assembly.

[0043] Figure 4 The relevant design values, such as the optical power ratio, of the fixed-focus lens in Embodiment 2 are shown in Table 1, and the parameter design values ​​of each lens in this Embodiment 2 are shown in Table 5. Table 5 shows a design value for each lens in the fixed-focus lens in Example 2. The even-order coefficients of each aspherical surface in the above embodiment 2 are shown in Table 6: Table 6 Parameters of Aspherical Surfaces Table 7 shows the technical specifications of the fixed-focus lens in this embodiment two: Figure 5 yes Figure 4 The spherical aberration curve of the fixed-focus lens is shown below. Figure 6 yes Figure 4 The field curvature distortion diagram of the fixed-focus lens shown is for reference. Figure 5 The abscissa values ​​of different wavelengths of light (0.459μm, 0.535μm, and 0.618μm) are all within the range of ±0.1mm. That is, the axial chromatic aberration of each wavelength in this fixed-focus lens is no greater than 0.1mm. Therefore, it can be seen that the fixed-focus lens provided in this embodiment can effectively correct axial chromatic aberration, ensuring that there are minimal differences in the chromatic aberration of images from different wavelengths of light. (Reference) Figure 6 As can be seen from the left coordinate system, the fixed-focus lens of this embodiment 2 is effectively controlled in terms of field curvature, that is, during imaging, the difference between the image quality in the center and the image quality in the periphery is small; in the right coordinate system, the distortion of the fixed-focus lens of this embodiment 2 is ≤1.5%.

[0044] Note that the above description is merely a preferred embodiment of the present invention and the technical principles employed. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and various obvious changes, readjustments, combinations, and substitutions can be made without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments, and may include many other equivalent embodiments without departing from the concept of the present invention, the scope of which is determined by the scope of the appended claims.

Claims

1. A fixed-focus lens, characterized in that, The fixed-focus lens comprises a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, a seventh lens, an eighth lens, a ninth lens, and a tenth lens arranged sequentially from the object side to the image side along the optical axis; the fixed-focus lens has ten lenses with optical power. The first lens, the second lens, the sixth lens, the seventh lens, and the ninth lens have negative optical power, while the third lens, the fourth lens, the fifth lens, the eighth lens, and the tenth lens have positive optical power. The opposing surfaces of the ninth lens and the tenth lens are cemented together to form a cemented lens assembly; the fixed-focus lens has one cemented lens assembly. Each lens in the fixed-focus lens satisfies the following condition: 0.535 <F1 / F2<0.950; -7.507 <F2 / F3<-4.300; 0.247 <F3 / F4<1.401; 0.097 <F4 / F5<0.866; -2.866 <F5 / F6<-0.879; 0.287 <F6 / F7<2.850; -1.189 <F7 / F8<-0.270; -0.301 <F9 / F8<-0.020; 0.190 <FA / F8<0.410; Wherein, F1 is the optical power of the first lens, F2 is the optical power of the second lens, F3 is the optical power of the third lens, F4 is the optical power of the fourth lens, F5 is the optical power of the fifth lens, F6 is the optical power of the sixth lens, F7 is the optical power of the seventh lens, F8 is the optical power of the eighth lens, F9 is the optical power of the ninth lens, and FA is the optical power of the tenth lens.

2. The fixed-focus lens according to claim 1, characterized in that, The first lens is a plastic aspherical lens, the seventh lens is a glass aspherical lens, and the second, third, fourth, fifth, sixth, eighth, ninth, and tenth lenses are all glass spherical lenses.

3. The fixed-focus lens according to claim 2, characterized in that, The first lens is a convex-concave lens, the second lens is a concave-concave lens, the third lens is a convex-concave lens, the fourth lens is a convex-concave lens, the fifth lens is a convex-convex lens, the sixth lens is a concave-convex or concave-concave lens, the seventh lens is a concave-convex lens, the eighth lens is a convex-convex lens, the ninth lens is a convex-concave lens, and the tenth lens is a convex-convex lens.

4. The fixed-focus lens according to claim 1, characterized in that, The third lens, the fifth lens, the sixth lens, the seventh lens, the eighth lens, the ninth lens, and the tenth lens satisfy the following conditions: 1.45 <ND3<1.86; 1.50 <ND5<1.73; 1.73 <ND6<2.12; 1.67 <ND7<2.10; 1.49 <ND8<1.61; 1.79 <ND9<1.89; 1.51 <NDA<1.65; Wherein, ND3 is the refractive index of the third lens, ND5 is the refractive index of the fifth lens, ND6 is the refractive index of the sixth lens, ND7 is the refractive index of the seventh lens, ND8 is the refractive index of the eighth lens, ND9 is the refractive index of the ninth lens, and NDA is the refractive index of the tenth lens.

5. The fixed-focus lens according to claim 1, characterized in that, The eighth lens, the ninth lens, and the tenth lens satisfy the following conditions: 1.97 <VD8 / VD9<2.66; 1.79 <VDA / VD9<2.66; Wherein, VD8 is the Abbe number of the eighth lens, VD9 is the Abbe number of the ninth lens, and VDA is the Abbe number of the tenth lens.

6. The fixed-focus lens according to claim 1, characterized in that, The fixed-focus lens meets the following condition: 1.450 <BFL / ImgH<1.758; Wherein, BFL is the back focal length of the fixed-focus lens, and ImgH is the diagonal length of the effective imaging area on the imaging surface of the fixed-focus lens.

7. The fixed-focus lens according to claim 1, characterized in that, The fixed-focus lens also includes an aperture stop, which is located between the fifth lens and the sixth lens.

8. An optical projection system, characterized in that, It includes an image source and a protective glass, a prism, and a fixed-focus lens as described in any one of claims 1-7, which are located sequentially on the light-emitting side of the image source.

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