CN111123488A

CN111123488A - Projection lens

Info

Publication number: CN111123488A
Application number: CN201811292745.4A
Authority: CN
Inventors: 欧阳巨星; 周巍衡
Original assignee: Beijing Ledu Exhibition Technology Development Co ltd
Current assignee: Beijing Ledu Exhibition Technology Development Co ltd
Priority date: 2018-11-01
Filing date: 2018-11-01
Publication date: 2020-05-08

Abstract

The invention relates to a projection lens, which comprises the following components in sequence from an object end to an imaging surface along the optical axis direction: the lens comprises a first lens group, a second lens group, a third lens group and a prism; the first lens group has negative focal power; the second lens group has positive focal power; the third lens group has positive optical power. The invention adopts a reverse telephoto structure, so that the lens has a larger field of view and a longer back focus. The first lens group adopts negative focal power to effectively balance off-axis aberration, and the diaphragm ST is arranged between the second lens group G2 and the third lens group G3, so that the whole lens structure is symmetrical relative to the diaphragm ST, and coma, astigmatism, vertical axis chromatic aberration, distortion and the like can be corrected well. The second lens adopts the aspheric surface design, can improve the flat field nature of camera lens greatly, effectively promotes camera lens analytic power, simultaneously, only adopts 1 aspheric surface, avoids increasing the degree of difficulty for the installation and debugging. The prism has the function of turning light, and is convenient for the layout of an optical machine system.

Description

Projection lens

Technical Field

The invention relates to the technical field of projection, in particular to a projection lens.

Background

In recent years, Cathode Ray Tube (CRT) projection apparatuses have been replaced by light, thin and small projection apparatuses such as Liquid Crystal Display (LCD) projection apparatuses and Digital Light Processing (DLP) projection apparatuses. Since the era of CRT projectors, bulb light sources were the dominant light source of projectors, and although projection technologies have been changing and CRTs have been gradually upgraded to LCD and DLP projection technologies, the changes in light sources have not been so rapid. Until recently, new light sources such as laser light sources have become the main angle.

However, the current projector lens is greatly influenced by visible light changes, the problem of long-distance imaging weakening of the long-focus lens is not well solved all the time, and the short-focus lens has poor high-definition image imaging effect.

Disclosure of Invention

In view of the above, there is a need to improve the projection lens in the prior art, and provide a projection lens with high resolution, large displacement, small distortion and no chromatic aberration.

The invention adopts the following technical scheme to realize the aim:

a projection lens sequentially comprises from an object end to an imaging surface along the optical axis direction: the lens comprises a first lens group, a second lens group, a third lens group and a prism;

the first lens group has negative focal power;

the second lens group of the first lens group sequentially comprises a first lens and a second lens from an object end to an imaging surface along the optical axis direction of the second lens group, the first lens is a spherical lens, and the second lens is an aspheric lens;

the first lens comprises a first lens front surface facing the object end and a first lens rear surface facing the imaging plane; the second lens comprises a second lens front surface facing the object end and a second lens rear surface facing the imaging plane; the front surface of the first lens and the front surface of the second lens are convex surfaces, and the rear surface of the first lens and the rear surface of the second lens are concave surfaces.

The second lens group has positive focal power;

the second lens group sequentially comprises a third lens and a fourth lens from an object end to an imaging surface along the optical axis direction of the second lens group; the third lens is a cemented lens, and the fourth lens is a single lens;

the third lens includes: the front surface of the third lens faces the object end, the first gluing surface is positioned in the middle, and the back surface of the third lens faces the imaging surface; the fourth lens includes: the front surface of the fourth lens faces the object end, and the rear surface of the fourth lens faces the imaging surface; the front surface of the third lens, the front surface of the fourth lens and the rear surface of the fourth lens are convex surfaces, and the rear surface of the third lens is a concave surface. The third lens front surface, the first gluing surface, the third lens rear surface, the fourth lens front surface and the fourth lens rear surface are spherical surfaces.

The third lens group has positive focal power;

the third lens group sequentially comprises an aperture, a fifth lens, a sixth lens, a seventh lens and an eighth lens from an object end to an imaging surface along the optical axis direction of the third lens group; the fifth lens and the sixth lens are cemented lenses, and the seventh lens and the eighth lens are single lenses;

the fifth lens comprises a fifth lens front surface facing the object end, a second gluing surface positioned in the middle and a fifth lens rear surface facing the imaging surface; the sixth lens comprises a sixth lens front surface facing the object end, a third gluing surface positioned in the middle and a sixth lens rear surface facing the imaging surface; the seventh lens comprises a seventh lens front surface facing the object end and a seventh lens rear surface facing the imaging plane; the eighth lens includes an eighth lens front surface facing the object end and an eighth lens rear surface facing the image plane. The front surface of the fifth lens, the rear surface of the sixth lens, the front surface of the seventh lens, the rear surface of the seventh lens, the front surface of the eighth lens and the rear surface of the eighth lens are convex surfaces; the front surface of the sixth lens is a concave surface; the fifth lens front surface, the second adhesive surface, the fifth lens rear surface, the sixth lens front surface, the third adhesive surface, the sixth lens rear surface, the seventh lens front surface, the seventh lens rear surface, the eighth lens front surface and the eighth lens rear surface are spherical surfaces.

The projection lens meets the following conditional expression:

(1)16<TT/f<24，

(2)2<BFL/f，

and TT is the total length of the projection lens, f is the focal length of the projection lens, and BFL is the back focal length of the projection lens, namely the distance from the last lens of the third lens group to an imaging surface.

The projection lens meeting the conditions has the characteristics of high resolution, large displacement, small distortion, no chromatic aberration and the like.

Further, the projection lens further satisfies the following conditional expression:

(3)-0.5<f1/f3<-0.8

wherein f1 is a focal length of the first lens group, and f3 is a focal length of the third lens group.

The conditional expression (3) can simultaneously ensure that the telecentric system is controlled and the requirement of wide viewing angle is met.

(4)1.5<f2/f3<2.5

wherein f2 is the focal length of the second lens group.

Conditional expression (4) ensures that the projection lens maintains a negative positive power distribution and that the second lens group G2 and

the aberrations generated by the third lens group G3 can be balanced.

The projection lens has the following beneficial technical effects:

(1) the invention adopts a reverse telephoto structure, so that the lens has a larger field of view and a longer back focus. The first lens group adopts negative focal power to effectively balance off-axis aberration, and the diaphragm ST is arranged between the second lens group G2 and the third lens group G3, so that the whole lens structure is symmetrical relative to the diaphragm ST, and coma, astigmatism, vertical axis chromatic aberration, distortion and the like can be corrected well.

(2) The second lens adopts the aspheric surface design, can improve the flat field nature of camera lens greatly, effectively promotes camera lens analytic power, simultaneously, only adopts 1 aspheric surface, avoids increasing the degree of difficulty for the installation and debugging. The prism has the function of turning light rays, and facilitates layout of an optical-mechanical system.

The noun explains:

the focal power (focal power), which is equal to the difference between the image and object beam convergence, characterizes the ability of the optical system to deflect light rays, and is commonly referred to by the letters

And (4) showing. The optical power characterizes the refractive power of the optical system for an incident parallel light beam.

The larger the value of (A), the more the parallel beam is folded;

when bent, it is cohesive;

when this occurs, the flexion is divergent.

When it is, it corresponds to, i.e., plane refraction.

A cemented lens (double-cemented lens) is a lens obtained by cementing lenses together. This combined lens formed with two lenses is an effective method for achieving a short focal length, a large magnification and a good image quality. Cemented lenses are used to minimize or eliminate chromatic aberration. Compared to a monolithic lens, an achromatic lens can form a smaller spot.

The single lens refers to a lens consisting of only one piece of optical glass, and includes a plano-convex lens, a plano-concave lens, a biconvex lens, a biconcave lens, a crescent lens, and the like.

A prism is a transparent object surrounded by two intersecting planes that are not parallel to each other for splitting or dispersing light beams. The prism is a polyhedron made of transparent materials (such as glass, crystal and the like).

A spherical lens means a lens having a constant curvature from the center to the edge of the lens.

The aspherical lens has a curvature that continuously changes from the center to the edge. The curvature radius of the aspheric lens is changed along with the central axis, so that the aspheric lens is used for improving the optical quality, reducing optical elements and reducing the design cost.

Drawings

Fig. 1 is a schematic structural diagram of a projection lens according to a preferred embodiment of the invention.

FIG. 2 is a field curvature diagram of a projection lens according to an embodiment of the present invention.

Fig. 3 is a distortion diagram of a projection lens according to an embodiment of the invention.

FIG. 4 is a color difference diagram of a projection lens according to an embodiment of the present invention.

Description of the main elements

First lens group	G1
		First lens	L1
Second lens	L2
		Front surface of the first lens	L1S1
Rear surface of the first lens	L1S2
		Front surface of the second lens	L2S1
Rear surface of the second lens	L2S2
		Second lens group	G2
Third lens	L3
		Fourth lens	L4
Front surface of the third lens	L3S1
		The first adhesive surface	L3S2
Rear surface of the third lens	L3S3
		Front surface of the fourth lens	L4S1
Rear surface of the fourth lens	L4S2
		Third lens group	G3
Aperture	ST
		Fifth lens element	L5
Sixth lens element	L6
		Seventh lens element	L7
Eighth lens element	L8
		Front surface of fifth lens	L5S1
Second adhesive surface	L5S2
		Rear surface of fifth lens	L5S3
Front surface of sixth lens	L6S1
		Third cemented surface	L6S2
Rear surface of sixth lens	L6S3
		Front surface of seventh lens	L7S1
Rear surface of seventh lens	L7S2
		Front surface of eighth lens	L7S1
Rear surface of eighth lens	L8S2
		Prism	G4
Image plane	G5

The following detailed description will further illustrate the invention in conjunction with the above-described figures.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the following description of the present invention will be made in detail by way of embodiments with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

It will be understood that when an element is referred to as being "secured to" another element, it can be directly on the other element or intervening elements may also be present. When an element is referred to as being "connected" to another element, it can be directly connected to the other element or intervening elements may also be present. In contrast, when an element is referred to as being "directly on" another element, there are no intervening elements present. The terms "vertical," "horizontal," "left," "right," and the like as used herein are for illustrative purposes only.

The present invention will be described in further detail below with reference to the accompanying drawings.

Referring to fig. 1, a projection lens according to an embodiment of the present invention sequentially includes, from an object end to an image plane G5 along an optical axis direction: a first lens group G1 with negative focal power, a second lens group G2 with positive focal power, a third lens group G3 with positive focal power and a prism G4.

In the present embodiment, the first lens group G1 includes, in order from the object end to the image plane in its optical axis direction, a first lens L1 and a second lens L2. The first lens L1 includes a first lens front surface L1S1 and a first lens rear surface L1S 2. The second lens L2 includes a second lens front surface L2S1 and a second lens rear surface L2S 2. The first lens front surface L1S1 and the second lens front surface L1S2 are convex surfaces, and the first lens rear surface L1S2 and the second lens rear surface L2S2 are concave surfaces. The first lens front surface L1S1 and the first lens rear surface L1S2 are spherical surfaces. The second lens front surface L1S2 and the second lens rear surface L2S2 are aspherical surfaces.

In the present embodiment, the second lens group G2 includes, in order from the object end to the image plane in the optical axis direction thereof, a third lens L3 and a fourth lens L4. The third lens L3 is a cemented lens including a third lens front surface L3S1, a first cemented surface L3S2 and a third lens rear surface L3S 3. The fourth lens L4 includes a fourth lens front surface L4S1 and a fourth lens rear surface L4S 2. Wherein the third lens front surface L3S1, the fourth lens front surface L4S1, and the fourth lens rear surface L4S2 are convex surfaces, and the third lens rear surface L3S2 is concave surface. The third lens front surface L3S1, the first cemented surface L3S2, the third lens rear surface L3S3, the fourth lens front surface L4S1, and the fourth lens rear surface L4S2 are all spherical surfaces.

In the present embodiment, the third lens group G3 includes, in order from the object end to the image plane in the optical axis direction thereof, a stop ST, a fifth lens L5, a sixth lens L6, a seventh lens L7, and an eighth lens L8. The fifth lens L5 is a cemented lens including a fifth lens front surface L5S1, a second cemented surface L5S2, and a fifth lens rear surface L5S 3. The sixth lens L6 is a cemented lens including a sixth lens front surface L6S1, a third cemented surface L6S2, and a sixth lens rear surface L6S 3. The seventh lens L7 includes a seventh lens front surface L7S1 and a seventh lens rear surface L7S 2. The eighth lens L8 includes an eighth lens front surface L8S1 and an eighth lens rear surface L8S 2. Wherein the fifth lens front surface L5S1, the fifth lens rear surface L5S3, the sixth lens rear surface L6S3, the seventh lens front surface L7S1, the seventh lens rear surface L7S2, the eighth lens front surface L7S1, and the eighth lens rear surface L8S2 are convex. The sixth lens front surface L6S1 is concave. The fifth lens front surface L5S1, the second cemented surface L6S2, the fifth lens rear surface L5S3, the sixth lens front surface L6S1, the third cemented surface L6S2, the sixth lens rear surface L6S3, the seventh lens front surface L7S1, the seventh lens rear surface L7S2, the eighth lens front surface L7S1, and the eighth lens rear surface L8S2 are all spherical surfaces.

The prism G4 is used for turning light and facilitating the layout of the optical machine system.

The invention adopts a reverse telephoto structure, so that the lens has a larger field of view and a longer back focus. The first lens group adopts negative focal power to effectively balance off-axis aberration, and the diaphragm ST is arranged between the second lens group G2 and the third lens group G3, so that the whole lens structure is symmetrical relative to the diaphragm 23, and coma, astigmatism, vertical axis chromatic aberration, distortion and the like can be corrected well. In addition, the second lens L2 adopts the aspheric surface design, can improve the flat field nature of camera lens greatly, effectively promotes the camera lens analytic power, simultaneously, only adopts 1 aspheric surface, avoids increasing the degree of difficulty for the installation and debugging.

The projection lens satisfies the following conditional expressions:

(1)16<TT/f<24

(2)2<BFL/f

The condition formula (1) limits the whole length of the projection lens, and ensures the balance between the total length of the lens and aberration under the matching of negative and positive focal power;

conditional expression (2) ensures that the optical-mechanical system has enough space to be placed between the third lens group G3 and the image plane G5.

(3)-0.5<f1/f3<-0.8

wherein f1 is the focal length of the first lens group, and f3 is the focal length of the third lens group.

The conditional expression (3) can ensure the control of the telecentric system and the satisfaction of the wide viewing angle.

(4)1.5<f2/f3<2.5

wherein f2 is the focal length of the second lens group.

Conditional expression (4) ensures that the projection lens maintains negative, positive, and positive power distribution, and enables the aberrations generated by the second lens group G2 and the third lens group G3 to be balanced with each other.

Each optical component of the projection lens provided by an embodiment of the present invention satisfies the conditions in tables 1 and 2. Wherein R is the curvature radius of the optical surface of each lens, D is the on-axis distance from the corresponding optical surface to the next optical surface, Nd is the refractive index of the corresponding lens to D light (the wavelength is 587nm), and Vd is the Abbe number of the D light in the corresponding lens; k represents aspheric conic coefficients, a2 represents second-order aspheric coefficients, a4 represents fourth-order aspheric coefficients, a6 represents sixth-order aspheric coefficients, and A8 represents eighth-order aspheric coefficients.

TABLE 1

Surface of	Surface type	R	D	Nd	Vd
						L1S1	Spherical surface	5.08	0.53	1.80	46.57
L1S2	Spherical surface	2.22	0.86
						L2S1	Aspherical surface	3.04	0.35	1.59	29.91
L2S2	Aspherical surface	1.12	2.96
						L3S1	Spherical surface	19.08	0.74	1.60	38.01
L3S2	Spherical surface	-3.35	0.36	1.49	70.42
						L3S3	Spherical surface	3.35	0.51
L4S1	Spherical surface	4.75	0.70	1.74	49.24
						L4S2	Spherical surface	-7.27	3.04
Stop	Plane surface	-	0.72
						L5S1	Spherical surface	15.21	0.23	1.90	31.32
L5S2	Spherical surface	2.04	0.56	1.49	70.42
						L5S3	Spherical surface	-2.92	0.02
L6S1	Spherical surface	-75.37	0.75	1.50	81.59
						L6S2	Spherical surface	-1.40	0.28	1.91	35.26
L6S3	Spherical surface	-14.09	0.03
						L7S1	Spherical surface	42.34	0.87	1.50	81.59
L7S2	Spherical surface	-2.09	0.02
						L8S1	Spherical surface	13.63	0.51	1.78	47.52
L8S2	Spherical surface	-5.64

TABLE 2

Surface of	K	A2	A4	A6	A8
						L2S1	-1.1	0	-9.14E-03	2.72E-05	1.30E-05
L2S2	-0.88	0	2.34E-02	-8.54E-03	1.58E-04

The field curvature, distortion, and spherical aberration of the projection lens of the present embodiment are shown in fig. 2 to 4, respectively.

In fig. 2, curves T and S are a meridional field curvature characteristic curve and a sagittal field curvature characteristic curve, respectively.

In fig. 3, the curve is a distortion characteristic curve.

In fig. 4, the aberration curves of the projection lens are observed for the F-line (486 nm wavelength), the d-line (587 nm wavelength), and the C-line (656 nm wavelength), respectively.

According to the projection lens, the projection lens has the characteristics of high resolution, short focal length and the like through the limitation of the four formulas, so that the imaging quality of the projection lens is improved.

The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.

The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.

Claims

1. A projection lens, characterized in that: include in proper order from the object end to the imaging surface along its optical axis direction: the lens comprises a first lens group, a second lens group, a third lens group and a prism;

the first lens group has negative focal power; the second lens group has positive focal power; the third lens group has positive optical power.

2. The projection lens of claim 1 wherein: the first lens group and the second lens group sequentially comprise a first lens and a second lens from an object end to an imaging surface along the optical axis direction of the first lens group, the first lens is a spherical lens, and the second lens is an aspheric lens.

3. The projection lens of claim 2 wherein:

the first lens comprises a first lens front surface facing the object end and a first lens rear surface facing the imaging plane;

the second lens comprises a second lens front surface facing the object end and a second lens rear surface facing the imaging plane;

the first lens front surface and the second lens front surface are convex surfaces, and the first lens rear surface and the second lens rear surface are concave surfaces.

4. The projection lens of claim 1 wherein:

the second lens group comprises a third lens and a fourth lens in sequence from an object end to an imaging surface along the optical axis direction of the second lens group; the third lens is a cemented lens, and the fourth lens is a single lens.

5. The projection lens of claim 4, wherein:

the third lens includes: the front surface of the third lens faces the object end, the first gluing surface is positioned in the middle, and the rear surface of the third lens faces the imaging surface;

the fourth lens includes: a fourth lens front surface facing the object end, a fourth lens rear surface facing the imaging plane;

the front surface of the third lens, the front surface of the fourth lens and the rear surface of the fourth lens are convex surfaces, and the rear surface of the third lens is a concave surface; the third lens front surface, the first gluing surface, the third lens rear surface, the fourth lens front surface and the fourth lens rear surface are spherical surfaces.

6. The projection lens of claim 1 wherein:

7. the projection lens of claim 6 wherein:

the fifth lens comprises a fifth lens front surface facing the object end, a second gluing surface positioned in the middle and a fifth lens rear surface facing the imaging surface;

the sixth lens comprises a sixth lens front surface facing the object end, a third gluing surface positioned in the middle and a sixth lens rear surface facing the imaging surface;

the seventh lens comprises a seventh lens front surface facing the object end and a seventh lens rear surface facing the imaging plane;

the eighth lens comprises an eighth lens front surface facing the object end and an eighth lens rear surface facing the imaging plane;

wherein the fifth lens front surface, the fifth lens rear surface, the sixth lens rear surface, the seventh lens front surface, the seventh lens rear surface, the eighth lens front surface and the eighth lens rear surface are convex surfaces; the front surface of the sixth lens is a concave surface; the fifth lens front surface, the second cemented surface, the fifth lens rear surface, the sixth lens front surface, the third cemented surface, the sixth lens rear surface, the seventh lens front surface, the seventh lens rear surface, the eighth lens front surface, and the eighth lens rear surface are all spherical surfaces.

8. The projection lens of any of claims 1-7, wherein: the projection lens meets the following conditional expression:

(1)16<TT/f<24，

(2)2<BFL/f；

9. The projection lens of any of claims 1-7, wherein:

the projection lens further satisfies the following conditional expressions: (3) -0.5< f1/f3< -0.8;

10. The projection lens of any of claims 1-7, wherein:

the projection lens further satisfies the following conditional expressions: (4)1.5< f2/f3< 2.5;

wherein f2 is the focal length of the second lens group.