CN117555113A - Optical system, projection lens and projection equipment - Google Patents

Abstract

The embodiment of the invention provides an optical system, a projection lens and projection equipment, wherein the optical system consists of a first lens, a second lens, a diaphragm, a third lens and a fourth lens; the distance between the first lens and the second lens is L1, the distance between the second lens and the diaphragm is L2, the distance between the third lens and the diaphragm is L3, and the distance between the third lens and the fourth lens is L4; L2-L3 is more than or equal to 0 and less than or equal to 1.5mm; L1-L4 is more than or equal to 0 and less than or equal to 0.6mm; the refractive index of the first lens is n1, and the Abbe number is v1; the second lens is an aspheric lens with negative focal power, the refractive index of the second lens is n2, and the Abbe number is v2; the third lens is an aspheric lens with negative focal power, the refractive index of the third lens is n3, and the Abbe number is v3; the fourth lens is an aspheric lens with positive focal power, the refractive index of the fourth lens is n4, and the Abbe number is v4; wherein n1 is more than n2, n1 is more than n3, n1 is more than n4, and n2-n3 is more than or equal to 0 and less than or equal to 0.2; v1 is more than v2, v1 is more than v3, v4 is more than v2, v4 is more than v3, and 0 is less than or equal to |v2-v3 is less than or equal to 3.

Description

Optical system, projection lens and projection equipment

Technical Field

The present disclosure relates to the field of projection technologies, and in particular, to an optical system, a projection lens, and a projection apparatus.

Background

With the increase of market demand, the field is focused on improving the optical performance of projection equipment, at present, the edge of a projection picture and the edge of a curtain can be guaranteed to coincide only when the height and the horizontal position between a projection screen and the projector need to guarantee a specified distance, and particularly in the field of ultra-short focal projection, the specified distance is difficult to guarantee when the height between the projector and the curtain is high, the offset of the projection picture can be achieved by adjusting the projector, and the bigger the offset is, the worse the definition of the projection picture is.

Disclosure of Invention

An objective of the present invention is to provide an optical system, a projection lens and a projection device, which are used for solving the problem of poor definition of a projection image. The specific technical scheme is as follows:

an embodiment of a first aspect of the present invention provides an optical system applied to a projection lens, the optical system including a first lens, a second lens, a diaphragm, a third lens, and a fourth lens sequentially disposed from an object side to an image side along a direction of an optical axis of the projection lens; the distance between the first lens and the second lens is L1, the distance between the second lens and the diaphragm is L2, the distance between the third lens and the diaphragm is L3, and the distance between the third lens and the fourth lens is L4; L2-L3 is more than or equal to 0 and less than or equal to 1.5mm; L1-L4 is more than or equal to 0 and less than or equal to 0.6mm; the first lens is a spherical lens or an aspherical lens with positive focal power, the refractive index of the first lens is n1, and the Abbe number is v1; the second lens is an aspheric lens with negative focal power, the refractive index of the second lens is n2, and the Abbe number is v2; the third lens is an aspheric lens with negative focal power, the refractive index of the third lens is n3, and the Abbe number is v3; the fourth lens is an aspheric lens with positive focal power, the refractive index of the fourth lens is n4, and the Abbe number is v4; wherein n1 is more than n2, n1 is more than n3, n1 is more than n4, and n2-n3 is more than or equal to 0 and less than or equal to 0.2; v1 is more than v2, v1 is more than v3, v4 is more than v2, v4 is more than v3, and 0 is less than or equal to |v2-v3 is less than or equal to 3.

In addition, the optical system according to the embodiment of the first aspect of the present application may further have the following technical features:

in some embodiments, the refractive index n1 of the first lens satisfies: n1 > 1.7, the abbe number v1 of the first lens satisfying: v1 is more than 40 and less than 50.

In some embodiments, the refractive index n4 of the fourth lens and the refractive index n1 of the first lens satisfy: n1-n4 > 0.2; the abbe number v4 of the fourth lens and the abbe number v3 of the third lens satisfy: v4-v3 > 15.

In some embodiments, the object side of the first lens is convex and the image side of the first lens is concave; the object side surface of the second lens is a convex surface, and the image side surface of the second lens is a concave surface; the object side surface of the third lens is a concave surface, and the image side surface of the third lens is a convex surface; the object side surface of the fourth lens is a concave surface or a convex surface, and the image side surface of the fourth lens is a convex surface.

In some embodiments, the radius of curvature of the object-side surface of the first lens element at the optical axis is R1, and the radius of curvature of the image-side surface of the first lens element at the optical axis is R2; wherein, the R1 and the R2 satisfy: r1 is more than or equal to 1mm and less than or equal to 50mm; r2 is more than or equal to 100mm and less than or equal to 300mm; the curvature radius of the object side surface of the second lens is R3 at the optical axis, and the curvature radius of the image side surface of the second lens at the optical axis is R4; wherein, the R3 and the R4 satisfy: r3 is more than or equal to 10mm and less than or equal to 100mm; r4 is more than or equal to 1mm and less than or equal to 30mm; the curvature radius of the object side surface of the third lens is R5 at the optical axis, and the curvature radius of the image side surface of the third lens at the optical axis is R6; wherein, the R5 and the R6 satisfy: r5 is less than or equal to 50mm and less than or equal to 10mm; -70mm < R6 < 30mm; the radius of curvature of the object side surface of the fourth lens element at the optical axis is R7, and the radius of curvature of the image side surface of the fourth lens element at the optical axis is R8, wherein R7 and R8 satisfy: r7 is 1000mm or more and 4000mm or less; r8 is less than or equal to-10 mm and less than or equal to-100 mm.

In some embodiments, the second lens and the third lens are the same shape.

In some embodiments, the L1, the L2, the L3, the L4 each satisfy: l1 is more than or equal to 0.6mm and less than or equal to 0.7mm; l2 is more than or equal to 11mm and less than or equal to 12mm; l3 is more than or equal to 12mm and less than 13mm; l4 is more than or equal to 0.1mm and less than or equal to 0.15mm.

In some embodiments, the material of the first lens is glass, and the material of the second lens, the material of the third lens and the material of the fourth lens are all optical plastics.

In some embodiments, the glass is a billow glass.

Embodiments of the second aspect of the present application provide a projection lens including the optical system described above.

Embodiments of a third aspect of the present application provide a projection apparatus comprising a projection lens as described above.

In this embodiment of the present application, the diaphragm is disposed between the second lens and the third lens, and the diaphragm has a light-transmitting area, where the center of the light-transmitting area coincides with the optical axis, so as to limit the light beam passing through on the optical axis. The distance between the second lens and the diaphragm is equal to or less than 0 and equal to or less than 1.5mm, namely, the distance between the third lens and the diaphragm is close to the distance between the second lens and the diaphragm; the distance between the first lens and the second lens is more than or equal to 0 and less than or equal to 0.6mm, namely, the distance between the first lens and the second lens is close to the distance between the third lens and the fourth lens, so that the first lens to the fourth lens are sequentially arranged from the object side to the image side along the optical axis, the distance between the first lens and the diaphragm is close to the distance between the fourth lens and the diaphragm, and through the arrangement, the vertical axis aberration such as the fringe visual field coma aberration, the distortion, the multiplying power chromatic aberration and the like can be effectively reduced. In addition, the refractive index and Abbe number of the second lens and the third lens which are close to the diaphragm are close to each other, wherein the n2-n3 is more than or equal to 0 and less than or equal to 0.2, and v2-v3 is more than or equal to 0 and less than or equal to 5, so that the high-order vertical axis chromatic aberration can be further reduced. n1 is larger than n2, n1 is larger than n3, n1 is larger than n4, the first lens is a lens with positive focal power, large-angle light rays can enter the optical system easily, and meanwhile, the refractive index of the first lens is larger, so that the light rays can be folded as much as possible, the view field of the projection lens is increased, barrel distortion of the edge view field is reduced, and the contrast of the edge view field is improved. The abbe numbers of the first lens and the fourth lens are larger than those of the second lens and the third lens, so that the chromatic aberration of light rays entering the optical system and the emergent optical system is smaller, and the definition of a projection picture is improved. In addition, the second lens and the third lens which are closer to the diaphragm are lenses with negative focal power, and the first lens and the fourth lens which are farther from the diaphragm are lenses with positive focal power, so that the field curvature of a projection picture can be reduced.

Of course, it is not necessary for any one product or method of practicing the invention to achieve all of the advantages set forth above at the same time.

Drawings

In order to more clearly illustrate the embodiments of the invention or the technical solutions in the prior art, the drawings used in the embodiments or the description of the prior art will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the invention, and other embodiments may be obtained according to these drawings to those skilled in the art.

Fig. 1 is a schematic structural diagram of an optical system according to an embodiment of the present application;

FIG. 2 is a dot column diagram corresponding to a 40 inch frame projected by an optical system according to an embodiment of the present disclosure;

fig. 3 is an MTF chart (Modulation Transfer Function ) corresponding to an optical system projecting a 40 inch frame according to an embodiment of the present application;

FIG. 4 is a dot column diagram corresponding to an optical system projecting an 80 inch frame according to an embodiment of the present disclosure;

fig. 5 is an MTF diagram corresponding to an optical system projecting an 80 inch frame according to an embodiment of the present application;

FIG. 6 is a dot column diagram corresponding to a 120 inch frame projected by an optical system according to an embodiment of the present disclosure;

fig. 7 is an MTF diagram corresponding to a 120-inch image projected by an optical system according to an embodiment of the present application.

Reference numerals:

an optical axis 1; a first lens 10; the object side 11 of the first lens; the image side 12 of the first lens; a second lens 20; the object side 21 of the second lens; the image side 22 of the second lens; a third lens 30; the object side 31 of the third lens; the image side 32 of the third lens; a fourth lens 40; the object side 41 of the fourth lens; an image side 42 of the fourth lens; a diaphragm 50.

Detailed Description

The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. Based on the embodiments of the present invention, those of ordinary skill in the art will be able to devise all other embodiments that are obtained based on this application and are within the scope of the present invention.

An embodiment of the first aspect of the present application provides an optical system applied to a projection lens, as shown in fig. 1, the optical system is composed of a first lens 10, a second lens 20, a diaphragm 50, a third lens 30, and a fourth lens 40 sequentially disposed from an object side to an image side along a direction of an optical axis 1 of the projection lens; the distance between the first lens 10 and the second lens 20 is L1, the distance between the second lens 20 and the diaphragm 50 is L2, the distance between the third lens 30 and the diaphragm 50 is L3, and the distance between the third lens 30 and the fourth lens 40 is L4; L2-L3 is more than or equal to 0 and less than or equal to 1.5mm; L1-L4 is more than or equal to 0 and less than or equal to 0.6mm; the first lens 10 is a spherical or aspherical lens having positive optical power, the refractive index of the first lens 10 is n1, and the abbe number is v1; the second lens 20 is an aspherical lens having negative optical power, the refractive index of the second lens 20 is n2, and the abbe number is v2; the third lens 30 is an aspherical lens having negative optical power, the refractive index of the third lens 30 is n3, and the abbe number is v3; the fourth lens 40 is an aspherical lens having positive optical power, the refractive index of the fourth lens 40 is n4, and the abbe number is v4; wherein n1 is more than n2, n1 is more than n3, n1 is more than n4, and n2-n3 is more than or equal to 0 and less than or equal to 0.2; v1 is more than v2, v1 is more than v3, v4 is more than v2, v4 is more than v3, and 0 is less than or equal to |v2-v3 is less than or equal to 3.

In this embodiment, the diaphragm 50 is disposed between the second lens 20 and the third lens 30, and the diaphragm 50 has a light-transmitting area, and the center of the light-transmitting area coincides with the optical axis 1 to limit the light beam passing through the optical axis 1. 0.ltoreq.L2-L3.ltoreq.1.5 mm, i.e. the distance between the second lens 20 and the diaphragm 50 is close to the distance between the third lens 30 and the diaphragm 50; 0.ltoreq.L1-L4.ltoreq.0.6 mm, i.e. the distance between the first lens 10 and the second lens 20 is close to the distance between the third lens 30 and the fourth lens 40, and the first lens 10 to the fourth lens 40 are sequentially arranged from the object side to the image side along the optical axis 1, and therefore, the distance between the first lens 10 and the diaphragm 50 is close to the distance between the fourth lens 40 and the diaphragm 50, by which arrangement the fringe field coma, distortion, chromatic aberration of magnification and the like can be effectively reduced. The aberration (aberration) refers to a deviation from an ideal state of gaussian optics (first order approximation theory or paraxial rays) in an optical system, in which a result obtained by non-paraxial ray tracing is inconsistent with a result obtained by paraxial ray tracing. Aberrations fall into two main categories: chromatic aberration (chromatic aberration) and monochromatic aberration (monochromatic aberration). The chromatic aberration is an aberration generated by different refractive indexes when light with different wavelengths passes through the lens because the refractive index of the lens material is a function of the wavelength, and the chromatic aberration can be divided into position chromatic aberration and multiplying power chromatic aberration. In addition, the refractive index and Abbe number of the second lens 20 and the third lens 30 which are closer to the diaphragm 50 are close to each other, which is 0.ltoreq.n2-n3.ltoreq.0.2, 0.ltoreq.v2-v3.ltoreq.5, can be further reduced. Chromatic aberration is a dispersion phenomenon, which is a phenomenon in which the speed of light or refractive index in a medium changes with the wavelength of an optical wave, and dispersion in which the refractive index of light decreases with an increase in wavelength may become normal dispersion, while dispersion in which the refractive index increases with an increase in wavelength may become negative dispersion (or negative anomalous dispersion). Thereby improving the definition of the projection picture. n1 is larger than n2, n1 is larger than n3, n1 is larger than n4, the first lens 10 is a lens with positive focal power, so that large-angle light rays can enter the optical system, meanwhile, the refractive index of the first lens 10 is larger, and the light rays can be folded as much as possible, so that the field of view of the projection lens is increased, barrel distortion of the edge field of view is reduced, and the contrast of the edge field of view is improved. v1 > v2, v1 > v3, v4 > v2, and v4 > v3, i.e., the abbe numbers of the first lens 10 and the fourth lens 40 are greater than the abbe numbers of the second lens 20 and the third lens 30, so that the chromatic aberration of light entering the optical system and the outgoing optical system is smaller. In addition, the second lens and the third lens closer to the diaphragm 50 are lenses having negative power, and the first lens 10 and the fourth lens 40 farther from the diaphragm 50 are lenses having positive power, which can reduce curvature of field of the projection screen. The monochromatic aberration is an aberration that occurs even when highly monochromatic light is used, and the monochromatic aberration is classified into two types, i.e., "blurring imaging" and "deforming imaging" according to the effect to be produced; the former category includes spherical aberration (spherical aberration), astigmatism (astigmatism), and the latter category includes field curvature (field curvature), distortion (aberration), and the like.

The first lens 10 may be a spherical lens or an aspherical lens, which has low cost and good optical performance. The second lens 20, the third lens 30 and the fourth lens 40 are non-curved lenses, so that the overall optical system has more flexible design space, and is favorable for solving the adverse phenomena of unclear imaging, distortion of vision, narrow field of view and the like under the condition of smaller and thinner lenses, and therefore, the optical system can have good imaging quality without arranging too many lenses, and the overall length of the optical system is more favorable for shortening.

The object side may be understood as a side close to a position where a projection screen (e.g. a projection curtain, a projection wall) is located; the image side is understood to be the side that is closest to the location of the display assembly, such as an LCD. In addition, the optical system formed by the first lens element 10, the second lens element 20, the third lens element 30 and the fourth lens element 40 in the projection lens further has a virtual image plane, and the image plane is located at the image side of the fourth lens element 40. It should be noted that the specific shape of the aspherical mirror in the embodiments is not limited to the shape of the aspherical mirror shown in the drawings, which are mainly for example reference and are not drawn to scale.

In some embodiments of the present application, the refractive index n1 of the first lens 10 satisfies: n1 > 1.7, the Abbe number v1 of the first lens 10 satisfies: v1 is more than 40 and less than 50.

In the embodiment of the application, n1 is greater than 1.7, so that the first lens 10 can convert light as much as possible and simultaneously reduce the thickness of the lens, thereby reducing the weight and the length of the optical system. The refractive index n1 of the first lens 10 satisfies: while n1 > 1.7, the abbe number v1 of the first lens 10 satisfies: the v1 is more than 40 and less than 50, and the arrangement can effectively compensate the spherical aberration and the axial chromatic aberration of the optical system.

In some embodiments of the present application, the refractive index n4 of the fourth lens 40 and the refractive index n1 of the first lens 10 satisfy: n1-n4 > 0.2; the abbe number v4 of the fourth lens 40 and the abbe number v3 of the third lens 30 satisfy: v4-v3 > 15.

In the embodiment of the present application, the refractive index difference between the refractive index of the first lens 10 and the refractive index of the fourth lens 40 is greater than 0.2, the abbe number difference between the fourth lens 40 and the third lens 30 is greater than 15, and the arrangement can reduce the chromatic aberration while correcting the spherical aberration of the optical system.

In some embodiments of the present application, as shown in fig. 1, the object side 11 of the first lens is convex, and the image side 12 of the first lens is concave; the object side surface 21 of the second lens is a convex surface, and the image side surface 22 of the second lens is a concave surface; the object side surface 31 of the third lens is concave, and the image side surface 32 of the third lens is convex; the object side 41 of the fourth lens element is concave or convex, and the image side 42 of the fourth lens element is convex.

In this embodiment, the first lens element 10 is a lens element with positive focal power, the object side surface 11 of the first lens element is convex, and the image side surface 12 of the first lens element is concave, so that the energy of the ghost image generated by reflection in the central area of the object side surface 11 of the first lens element projected on the image surface can be reduced, and the imaging quality of the optical system can be improved. The second lens 20 is an aspheric lens with negative focal power, the object side surface 21 of the second lens is a convex surface, and the image side surface 22 of the second lens is a concave surface, which is beneficial to improving the collection capability of the marginal field light and reducing the working caliber of the first lens 10. The third lens element 30 has an aspherical surface with negative optical power, the object-side surface 31 of the third lens element is concave, and the image-side surface 32 of the third lens element is convex, so that the residual Gao Jieqiu difference and astigmatism of the optical system can be corrected when the third lens element is used in combination with the surface of the second lens element 20. The fourth lens element 40 has an aspheric surface with positive optical power, and the object-side surface 41 of the fourth lens element is concave or convex, and the image-side surface 42 of the fourth lens element is convex, so that the light can be smoothly transited and the deflection angle of the light can be reduced.

In some embodiments of the present application, the radius of curvature of the object side surface 11 of the first lens element at the optical axis 1 is R1, and the radius of curvature of the image side surface 12 of the first lens element at the optical axis 1 is R2; wherein, R1 and R2 satisfy: r1 is more than or equal to 1mm and less than or equal to 50mm; r2 is more than or equal to 100mm and less than or equal to 300mm; the radius of curvature of the object side surface 21 of the second lens element at the optical axis 1 is R3, and the radius of curvature of the image side surface 22 of the second lens element at the optical axis 1 is R4; wherein, R3 and R4 satisfy: r3 is more than or equal to 10mm and less than or equal to 100mm; r4 is more than or equal to 1mm and less than or equal to 30mm; the radius of curvature of the object side surface 31 of the third lens element at the optical axis 1 is R5, and the radius of curvature of the image side surface 32 of the third lens element at the optical axis 1 is R6; wherein, R5 and R6 satisfy: r5 is less than or equal to 50mm and less than or equal to 10mm; -70mm < R6 < 30mm; the radius of curvature of the object side surface 41 of the fourth lens element at the optical axis 1 is R7, and the radius of curvature of the image side surface 32 of the fourth lens element at the optical axis 1 is R8, wherein R7 and R8 satisfy: r7 is 1000mm or more and 4000mm or less; r8 is less than or equal to-10 mm and less than or equal to-100 mm.

The radius of curvature is a physical quantity describing the magnitude of curvature of a curve, and is used to describe the amount of curvature of a curve at a certain point. In this embodiment of the present application, the positive radius of curvature indicates the degree to which the curve of the lens protrudes toward the object side, that is, the stronger the degree to which the curve protrudes toward the object side, the smaller and positive the value of the radius of curvature. Conversely, a negative radius of curvature indicates the degree to which the curve of the lens is convex toward the image side, i.e., the greater the degree to which the curve is convex toward the image side, the smaller and negative the absolute value of the radius of curvature value.

The first lens element 10 has a positive refractive power, and the object side surface 11 of the first lens element has a smaller radius of curvature, i.e. the object side surface 11 of the first lens element has a larger degree of curvature at the optical axis 1, so that more light can enter the first lens element 10, and the image side surface 12 of the first lens element has a larger radius of curvature, i.e. the image side surface 12 of the first lens element has a smaller curvature at the optical axis 1, so that the light can smoothly transition into the second lens element 20, and the first lens element 10 can perform a better converging effect on the light entering the optical system. The radius of curvature of the object side surface 21 of the second lens is larger, and the radius of curvature of the image side surface 22 of the second lens is smaller, that is, the degree of curvature of the object side surface 21 of the second lens at the optical axis 1 is smaller than the degree of curvature of the image side surface 22 of the second lens, so that light can be emitted at a large angle. The radius of curvature of the object side 31 of the third lens is smaller, and the radius of curvature of the image side 32 of the third lens is larger, that is, the degree of curvature of the object side 31 of the third lens toward the image side on the optical axis 1 is greater than the degree of curvature of the image side 32 of the third lens, so that the light rays scattered by the second lens 20 are further scattered; the object side 41 of the fourth lens has a larger radius of curvature, enabling smooth transition of light rays for final imaging. Through setting up the radius of curvature of different lenses, the optical power and the face type of different lenses of reasonable collocation can be effective control first lens 10, second lens 20, third lens 30 and fourth lens 40 thickness moderate, do benefit to balanced aberration, improve optical system's resolution, realization long focal length design that can be better can keep great angle of view simultaneously. The resolution is an important index for evaluating the image quantity, and the resolution is higher as the resolution is higher.

More specifically, the calculation of the surface shape of the aspherical mirror can be referred to as the following equation 1:

wherein Z is the distance between the corresponding point on the aspheric surface and the plane tangent to the vertex of the aspheric surface, r is the distance between the corresponding point on the aspheric surface and the optical axis 1, c is the curvature of the vertex of the aspheric surface, k is the conic coefficient, A _i Is the coefficient corresponding to the i-th higher term in the aspheric surface type formula.

In this embodiment, after light passes through the first lens 10, the second lens 20, the diaphragm 50, the third lens 30 and the fourth lens 40 in sequence, an image plane circle with a diameter of 140mm can be formed on an image plane, 4 inches and 4.5 inches of LCD screens can be correspondingly matched, the projection screen can be more than 70% offset by matching 4.5 inches of LCD screens, the projection screen can be more than 100% offset by matching 4 inches of LCD screens, and the screen with a size of 40 inches to 120 inches of screen can be clearly projected on the projection screen.

For example, taking a projection lens to achieve clear projection of a 40-120 inch frame on a projection screen as an example, the relevant parameters in the optical system provided in the embodiments of the present application may be designed as shown in table 1 and table 2. In table 1, focal length, radius of curvature, and thickness, and spacing between adjacent surfaces are all in millimeters. Table 2 is the aspherical parameters of the corresponding surfaces in table 1, where k is the conic coefficient and a_i is the coefficient corresponding to the i-th higher term in equation 1 above. The elements from the object side to the image side according to fig. 1 are arranged in the order of the elements from top to bottom in table 1, for example, the surface numbers 1 and 2 correspond to the object side 11 of the first lens and the image side 12 of the first lens, respectively, i.e. in the same element, the surface with the smaller surface number is the object side and the surface with the larger surface number is the image side. The optical axes 1 of the lenses in the embodiments of the present application are on the same straight line, that is, the optical axis 1 of the optical system in the embodiments of the present application.

Table 1:

table 2:

through experiments, the imaging effects of projecting pictures of different sizes according to the optical system designed by substituting the parameters in the above tables 1 and 2 into the data obtained in the formula 1 in the embodiment of the present application are shown in fig. 2 to 7. Fig. 2 and 3 are respectively a dot column diagram and an MTF (Modulation transfer Function) diagram corresponding to the area of the projection screen of the optical system being 40 inches; fig. 4 and 5 are respectively a dot column diagram and an MTF diagram corresponding to the case where the area of the projection screen of the optical system is 80 inches; fig. 6 and 7 are a dot line graph and an MTF graph, respectively, corresponding to the case where the area of the projection screen of the optical system is 120 inches.

The abscissa of the MTF graph represents the radial dimension position from the center of the image plane to the edge of the image plane from left to right. The leftmost is zero, the center field of view, the rightmost is the edge field of view, in millimeters. The ordinate of the MTF plot, from bottom to top, from 0 to 1, has no units representing the percentage of imaging diathesis approaching physical conditions. 1 is 100%,1 is an ideal value, and cannot be achieved in reality, and the curve can only be infinitely close to 1, but cannot be equal to 1.

In fig. 2, 4 and 6, the point diagram obtained by taking the image plane of the optical system as the test plane is shown as 400 in fig. 2, 200 in fig. 4 and 400 in fig. 6, and the reference point is the centroid of the optical system.

As shown in FIG. 2, the Airy spot radius is 2.098 μm; the first field of view is the central field of view of the image plane circle, the RMS (Root mean square) radius of the spot is 34.821 μm, the GEO (geometric) radius of the circle centered on the reference point and containing all the light rays is 107.925 μm; the distance between the second view field and the center view field of the image plane circle is 25.017mm, the RMS radius of the light spot is 35.174 μm, and the GEO radius of the circle which takes the reference point as the center and contains all light rays is 121.545 μm; the distance between the third view field and the center view field of the image plane circle is 35.015mm, the RMS radius of the light spot is 31.347 μm, and the GEO radius of the circle which takes the reference point as the center and contains all light rays is 74.865 μm; the distance between the fourth field of view and the central field of view of the image plane circle is 49.020mm, the RMS radius of the light spot is 35.452 μm, and the GEO radius of the circle which takes the reference point as the center and contains all light rays is 73.861 μm; the distance between the fifth view field and the center view field of the image plane circle is 65.022mm, the RMS radius of the light spot is 31.852 μm, and the GEO radius of the circle which takes the reference point as the center and contains all light rays is 106.074 μm; the distance between the sixth field of view and the central field of view of the image plane circle was 70.126mm, the RMS radius of the spot was 36.225 μm, and the GEO radius of a circle centered on the reference point and containing all the light rays was 100.054 μm.

As shown in FIG. 4, the Airy spot radius is 2.013 μm; the first field of view is the central field of view of the image plane circle, the RMS radius of the spot is 26.535 μm, and the GEO radius of the circle centered on the reference point and containing all the light rays is 82.815 μm; the distance between the second view field and the center view field of the image plane circle is 25mm, the RMS radius of the light spot is 26.505 mu m, and the GEO radius of the circle which takes the reference point as the center and contains all light rays is 89.479 mu m; the distance between the third view field and the center view field of the image plane circle is 34.993mm, the RMS radius of the light spot is 26.423 μm, and the GEO radius of the circle which takes the reference point as the center and contains all light rays is 67.594 μm; the distance between the fourth field of view and the central field of view of the image plane circle is 48.995mm, the RMS radius of the light spot is 31.899 μm, the GEO radius of a circle centered on the reference point and containing all light rays is 68.220 μm, the distance between the fifth field of view and the central field of view of the image plane circle is 64.994mm, the RMS radius of the light spot is 25.211 μm, and the GEO radius of a circle centered on the reference point and containing all light rays is 66.705 μm; the distance between the sixth field of view and the central field of view of the image plane circle was 70.099mm, the RMS radius of the spot was 28.191 μm, and the GEO radius of a circle centered on the reference point and containing all the light rays was 90.366 μm.

As shown in FIG. 6, the Airy spot radius is 1.973 μm; the first field of view is the central field of view of the image plane circle, the RMS radius of the spot is 24.970 μm, and the GEO radius of the circle centered on the reference point and containing all the light rays is 71.369 μm; the distance between the second view field and the center view field of the image plane circle is 24.991mm, the RMS radius of the light spot is 25.964 μm, and the GEO radius of the circle which takes the reference point as the center and contains all light rays is 74.032 μm; the distance between the third view field and the center view field of the image plane circle is 34.983mm, the RMS radius of the light spot is 28.993 μm, and the GEO radius of the circle which takes the reference point as the center and contains all light rays is 73.284 μm; the distance between the fourth field of view and the central field of view of the image plane circle is 48.984mm, the RMS radius of the light spot is 34.866 μm, and the GEO radius of the circle which takes the reference point as the center and contains all light rays is 82.338 μm; the distance between the fifth view field and the center view field of the image plane circle is 64.982mm, the RMS radius of the light spot is 29.771 μm, and the GEO radius of the circle which takes the reference point as the center and contains all light rays is 89.325 μm; the distance between the sixth field of view and the central field of view of the image plane circle was 70.087mm, the RMS radius of the spot was 31.899 μm, and the GEO radius of a circle centered on the reference point and containing all the light rays was 103.749 μm.

As can be seen from the dot patterns of the images projected by the optical system shown in fig. 2, 4 and 6, the RMS radius of the light spot is smaller than 40 μm in the whole field, the GEO radius of the circle centered on the reference point and containing all the light rays is smaller than 122 μm, and the optical system is applicable to the projection screen with single pixel size larger than 40 μm; as can be seen from the MTF diagrams of three different-sized projection pictures projected by the optical system shown in fig. 3, 5 and 7, the MTF values of the three-sized projection pictures are all higher than 0.3, so that, in summary, the optical system can be applied to a projection lens applicable to a projection screen with a single pixel size of more than 40 μm, and can realize clear projection in the range of 40 inches to 120 inches of the projection picture.

In some embodiments of the present application, the second lens 20 and the third lens 30 are the same shape.

In this embodiment, the second lens 20 and the third lens 30 are identical in shape and are both aspheric lenses with negative optical power, so that light can be diverged, and when the second lens 20 and the third lens 30 are manufactured, the same manufacturing process and manufacturing parameters can be used, so that the manufacturing efficiency of the second lens 20 and the third lens 30 can be improved.

As shown in fig. 1, the shapes of the second lens 20 and the third lens 30 may not be exactly the same, and the surface shapes of the second lens 20 and the third lens 30 may be approximately the same.

In some embodiments of the present application, L1, L2, L3, L4 satisfy respectively: l1 is more than or equal to 0.6mm and less than or equal to 0.7mm; l2 is more than or equal to 11mm and less than or equal to 12mm; l3 is more than or equal to 12mm and less than 13mm; l4 is more than or equal to 0.1mm and less than or equal to 0.15mm. In this embodiment of the present application, by limiting L1, L2, L3, and L4, it is possible to realize that lens combination is more compact on the premise that the optical system realizes a longer working distance.

In some embodiments of the present application, the material of the first lens 10 is glass, and the material of the second lens 20, the material of the third lens 30 and the material of the fourth lens 40 are all optical plastics.

In the embodiment of the present application, the refractive index and abbe number of the glass are higher, the optical performance is better, and the chromatic aberration of the second lens 20, the third lens 30 and the fourth lens 40 made of optical plastics can be compensated. The plastic has lower cost and is convenient to process, so that the first lens 10 is manufactured by glass in the optical system, the second lens 20, the third lens 30 and the fourth lens 40 are manufactured by optical plastic, the manufacturing cost can be reduced on the premise of improving the optical performance, and the processing adjustment of each lens can be conveniently implemented according to the actual application requirement.

In some embodiments of the present application, the glass is a billow glass. In the embodiment of the present application, the optical performance of the glass is good and the refractive index is large, so that a thinner lens can be manufactured, and the weight of the whole optical system can be reduced.

Embodiments of a second aspect of the present application provide a projection lens including the above optical system.

In the projection lens provided in the embodiment of the second aspect of the present application, as shown in fig. 1, in an optical system included in the projection lens, a diaphragm 50 is disposed between the second lens 20 and the third lens 30, and the diaphragm 50 has a light-transmitting area, where a center of the light-transmitting area coincides with the optical axis 1 to limit a light beam passing through the optical axis 1. 0.ltoreq.L2-L3.ltoreq.1.5 mm, i.e. the distance between the second lens 20 and the diaphragm 50 is close to the distance between the third lens 30 and the diaphragm 50; 0.ltoreq.L1-L4.ltoreq.0.6 mm, i.e. the distance between the first lens 10 and the second lens 20 is close to the distance between the third lens 30 and the fourth lens 40, and the first lens 10 to the fourth lens 40 are sequentially arranged from the object side to the image side along the optical axis 1, and therefore, the distance between the first lens 10 and the diaphragm 50 is close to the distance between the fourth lens 40 and the diaphragm 50, by which arrangement the fringe field coma, distortion, chromatic aberration of magnification and the like can be effectively reduced. In addition, the refractive index and Abbe number of the second lens 20 and the third lens 30 which are closer to the diaphragm 50 are close to each other, which is 0.ltoreq.n2-n3.ltoreq.0.2, 0.ltoreq.v2-v3.ltoreq.5, can be further reduced. Thereby improving the definition of the projection picture. n1 is larger than n2, n1 is larger than n3, n1 is larger than n4, the first lens 10 is a lens with positive focal power, so that large-angle light rays can enter the optical system, meanwhile, the refractive index of the first lens 10 is larger, and the light rays can be folded as much as possible, so that the field of view of the projection lens is increased, barrel distortion of the edge field of view is reduced, and the contrast of the edge field of view is improved. v1 > v2, v1 > v3, v4 > v2, and v4 > v3, i.e., the abbe numbers of the first lens 10 and the fourth lens 40 are greater than the abbe numbers of the second lens 20 and the third lens 30, so that the chromatic aberration of light entering the optical system and the outgoing optical system is smaller. In addition, the second lens and the third lens closer to the diaphragm 50 are lenses having negative power, and the first lens 10 and the fourth lens 40 farther from the diaphragm 50 are lenses having positive power, which can reduce curvature of field of the projection screen.

Embodiments of the third aspect of the present application provide a projection apparatus including the above projection lens.

In the projection apparatus provided in the embodiment of the third aspect of the present application, in an optical system included in a projection lens, as shown in fig. 1, a diaphragm 50 is disposed between the second lens 20 and the third lens 30, and the diaphragm 50 has a light-transmitting area, and a center of the light-transmitting area coincides with the optical axis 1 to limit a light beam passing through on the optical axis 1. 0.ltoreq.L2-L3.ltoreq.1.5 mm, i.e. the distance between the second lens 20 and the diaphragm 50 is close to the distance between the third lens 30 and the diaphragm 50; 0.ltoreq.L1-L4.ltoreq.0.6 mm, i.e. the distance between the first lens 10 and the second lens 20 is close to the distance between the third lens 30 and the fourth lens 40, and the first lens 10 to the fourth lens 40 are sequentially arranged from the object side to the image side along the optical axis 1, and therefore, the distance between the first lens 10 and the diaphragm 50 is close to the distance between the fourth lens 40 and the diaphragm 50, by which arrangement the fringe field coma, distortion, chromatic aberration of magnification and the like can be effectively reduced. In addition, the refractive index and Abbe number of the second lens 20 and the third lens 30 which are closer to the diaphragm 50 are close to each other, which is 0.ltoreq.n2-n3.ltoreq.0.2, 0.ltoreq.v2-v3.ltoreq.5, can be further reduced. Thereby improving the definition of the projection picture. n1 is larger than n2, n1 is larger than n3, n1 is larger than n4, the first lens 10 is a lens with positive focal power, so that large-angle light rays can enter the optical system, meanwhile, the refractive index of the first lens 10 is larger, and the light rays can be folded as much as possible, so that the field of view of the projection lens is increased, barrel distortion of the edge field of view is reduced, and the contrast of the edge field of view is improved. v1 > v2, v1 > v3, v4 > v2, and v4 > v3, i.e., the abbe numbers of the first lens 10 and the fourth lens 40 are greater than the abbe numbers of the second lens 20 and the third lens 30, so that the chromatic aberration of light entering the optical system and the outgoing optical system is smaller. In addition, the second lens and the third lens closer to the diaphragm 50 are lenses having negative power, and the first lens 10 and the fourth lens 40 farther from the diaphragm 50 are lenses having positive power, which can reduce curvature of field of the projection screen.

It is noted that relational terms such as first and second, and the like are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Moreover, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one … …" does not exclude the presence of other like elements in a process, method, article, or apparatus that comprises an element.

In this specification, each embodiment is described in a related manner, and identical and similar parts of each embodiment are all referred to each other, and each embodiment mainly describes differences from other embodiments. In particular, for system embodiments, since they are substantially similar to method embodiments, the description is relatively simple, as relevant to see a section of the description of method embodiments.

The foregoing is merely a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention are included in the protection scope of the present invention.

Claims (11)

1. An optical system, characterized in that it is applied to a projection lens, and the optical system is composed of a first lens (10), a second lens (20), a diaphragm (50), a third lens (30) and a fourth lens (40) which are sequentially arranged from an object side to an image side along the direction of an optical axis (1) of the projection lens; the distance between the first lens (10) and the second lens (20) is L1, the distance between the second lens (20) and the diaphragm (50) is L2, the distance between the third lens (30) and the diaphragm (50) is L3, and the distance between the third lens (30) and the fourth lens (40) is L4;

0≤|L2-L3|≤1.5mm；

0≤|L1-L4|≤0.6mm；

the first lens (10) is a spherical mirror or an aspherical mirror with positive focal power, the refractive index of the first lens (10) is n1, and the Abbe number is v1;

the second lens (20) is an aspherical mirror with negative focal power, the refractive index of the second lens (20) is n2, and the Abbe number is v2;

the third lens (30) is an aspherical mirror with negative focal power, the refractive index of the third lens (30) is n3, and the Abbe number is v3;

the fourth lens (40) is an aspherical lens with positive focal power, the refractive index of the fourth lens (40) is n4, and the Abbe number is v4;

wherein n1 is more than n2, n1 is more than n3, n1 is more than n4, and n2-n3 is more than or equal to 0 and less than or equal to 0.2;

v1＞v2，v1＞v3，v4＞v2，v4＞v3，0≤|v2-v3|≤3。

2. the optical system of claim 1, wherein the optical system is configured to,

the refractive index n1 of the first lens (10) satisfies: n1 is more than 1.7,

the Abbe number v1 of the first lens (10) satisfies: v1 is more than 40 and less than 50.

3. An optical system according to claim 2, wherein,

the refractive index n4 of the fourth lens (40) and the refractive index n1 of the first lens (10) satisfy: n1-n4 > 0.2

The Abbe number v4 of the fourth lens (40) and the Abbe number v3 of the third lens (30) satisfy: v4-v3 > 15.

4. The optical system of claim 1, wherein the optical system is configured to,

the object side surface (11) of the first lens is a convex surface, and the image side surface (12) of the first lens is a concave surface;

the object side surface (21) of the second lens is a convex surface, and the image side surface (22) of the second lens is a concave surface;

the object side surface (31) of the third lens is a concave surface, and the image side surface (32) of the third lens is a convex surface;

the object side surface (41) of the fourth lens is concave or convex, and the image side surface (42) of the fourth lens is convex.

5. The optical system of claim 4, wherein the optical system is configured to,

the curvature radius of the object side surface (11) of the first lens at the optical axis (1) is R1, and the curvature radius of the image side surface (12) of the first lens at the optical axis (1) is R2; wherein, the R1 and the R2 satisfy:

1mm≤R1≤50mm；

100mm≤R2≤300mm；

the curvature radius of the object side surface (21) of the second lens at the optical axis (1) is R3, and the curvature radius of the image side surface (22) of the second lens at the optical axis (1) is R4; wherein, the R3 and the R4 satisfy:

10mm≤R3≤100mm；

1mm≤R4≤30mm；

the curvature radius of the object side surface (31) of the third lens at the optical axis (1) is R5, and the curvature radius of the image side surface (32) of the third lens at the optical axis (1) is R6; wherein, the R5 and the R6 satisfy:

-50mm≤R5≤-10mm；

-70mm≤R6≤-30mm；

the radius of curvature of the object side surface (41) of the fourth lens element at the optical axis (1) is R7, and the radius of curvature of the image side surface (42) of the fourth lens element at the optical axis (1) is R8, wherein the R7 and the R8 satisfy:

1000mm≤R7≤4000mm；

-10mm≤R8≤-100mm。

6. the optical system according to claim 1, wherein the second lens (20) and the third lens (30) are identical in shape.

7. An optical system according to any one of claims 1-6, characterized in that,

the L1, L2, L3 and L4 respectively satisfy the following conditions:

0.6mm≤L1≤0.7mm；11mm≤L2≤12mm；12mm≤L3＜13mm；0.1mm≤L4≤0.15mm。

8. the optical system according to any one of claims 1 to 6, wherein the material of the first lens (10) is glass, and the material of the second lens (20), the third lens (30) and the fourth lens (40) is an optical plastic.

9. The optical system according to claim 8, wherein the glass is a billow glass.

10. A projection lens characterized by comprising the optical system according to any one of claims 1 to 9.

11. A projection device comprising a projection lens according to claim 10.