CN105759405A

CN105759405A - Optical system with increased field angle, and projection lens

Info

Publication number: CN105759405A
Application number: CN201410790187.XA
Authority: CN
Inventors: 刘美鸿; 母林; 纪超超
Original assignee: Shenzhen Estar Displaytech Co
Current assignee: Shenzhen Quechao Parking Technology Co ltd
Priority date: 2014-12-17
Filing date: 2014-12-17
Publication date: 2016-07-13
Anticipated expiration: 2034-12-17
Also published as: CN105759405B

Abstract

The invention discloses an optical system with an increased field angle, and a projection lens. The optical system is used for amplifying a first image subjected to the optical system into a second image. The optical system comprises a lens assembly and a concave mirror. The lens assembly includes a plurality of lenses arranged front and back along an optical path and sharing the same main optical axis. The first image sequentially forms a first intermediate image and a second intermediate image in the lens assembly. The concave mirror is arranged at the back of the lens assembly and is used for reflecting the second intermediate image to form an amplified second image. The transmittance of the optical system is 0.2 to 0.25. The focal length of the optical system is -2.9 mm to -3.2 mm. The offset of the first image relative to the main optical axis is larger than 120%. According to the technical scheme of the invention, the field angle is increased and the imaging effect is improved. Meanwhile, the short-distance projection of a large image is realized.

Description

Optical system capable of increasing field angle and projection lens

Technical Field

The present invention relates to the field of optical systems, and more particularly, to an optical system and a projection lens capable of increasing the angle of view.

Background

The ultra-short-focus projection lens can effectively shorten the projection distance of the projector, and is an important solution for projecting large-size pictures at short distance in the market at present.

There are three ways in the design of shortening the focal length of the projection lens: refractive, reflective, and hybrid. The lens with the refraction design is composed of lenses, including spherical lenses or aspheric lenses, and the lens lenses of the lens with the refraction design are large in number and various in variety, so that the structure is often complex and is not beneficial to manufacturing. The lens of reflective design all comprises the speculum, including spherical or aspherical mirror, and the speculum can be convex surface, concave surface or plane mirror, but the processing of aspherical mirror and the degree of difficulty that detects are great, and the cost and the manufacturing degree of difficulty of camera lens have undoubtedly been increased to the speculum of multichip. The hybrid lens integrates the technical characteristics of refraction and reflection, adopts a design mode of combining a lens and a reflector, and is the mainstream scheme of the ultra-short-focus projection lens in the market at present.

There are also many structures proposed that are based on the hybrid design principle of refraction followed by reflection. With the difference of specific structural design, the lens or system based on the hybrid design principle of refraction and reflection has certain difference in image quality such as distortion, spherical aberration or chromatic aberration. Since the projected image is reflected to reach the screen, the image is easily distorted on the projection screen due to a slight error of the reflector. The ultra-short focus projection lens is required to project a large-size picture in a short distance, i.e. a large field angle is required, and simultaneously, the image deformation is required to be reduced. In the prior art, a projection lens which has a large field angle and can project a high-quality image with little deformation is difficult to realize.

Disclosure of Invention

The invention mainly solves the technical problem of providing an optical system and a projection lens capable of increasing the angle of view, reducing image deformation, improving imaging quality, increasing the angle of view and projecting a large image at a short distance.

In order to solve the technical problems, the invention adopts a technical scheme that: an optical system capable of increasing an angle of view is provided for imaging a first image entering the optical system as an enlarged second image. The optical system includes a lens group and a concave mirror. The lens group comprises a plurality of lenses which are arranged in front and at the back along a light path and have the same main optical axis, and the first image forms a first intermediate image and a second intermediate image in the lens group in sequence. The concave reflector is positioned behind the lens group and used for reflecting the second intermediate image to form an amplified second image. The transmittance of the optical system is 0.2-0.25, the focal length is-2.9 mm-3.2 mm, and the offset of the first image relative to the main optical axis is more than 120%.

The concave surface of the concave reflector is a free-form surface.

Wherein the lens group includes a first lens group and a second lens group. The first lens group includes five lenses for imaging the first image as a first intermediate image. The second lens group includes eight lenses for imaging the first intermediate image into a second intermediate image.

The first lens group comprises a first lens, a second lens, a third lens, a fourth lens and a fifth lens which are sequentially arranged along an optical path; the first lens is a biconvex lens, the second lens is a biconvex lens, the third lens is a convex-concave lens, the fourth lens is a biconcave lens, and the fifth lens is a convex-concave lens.

Wherein the fourth lens and the fifth lens are glued into a whole.

Wherein the fourth lens has a higher refractive index than the fifth lens; the dispersion of the fourth lens is larger than that of the fifth lens; the abbe number of the fourth lens is lower than that of the fifth lens.

The second lens group comprises a sixth lens, a seventh lens, an eighth lens, a ninth lens, a tenth lens, an eleventh lens, a twelfth lens and a thirteenth lens which are sequentially arranged along an optical path; wherein, at least one aspheric lens is included; the sixth lens element is a biconvex lens, the seventh lens element is a biconvex lens, the eighth lens element is a convex-concave lens, the ninth lens element is a concave-convex lens, the tenth lens element is a biconcave lens, the eleventh lens element is an aspheric lens, the twelfth lens element is a concave-convex lens, and the thirteenth lens element is a concave-convex lens.

Wherein the optical system further comprises an aperture stop; the aperture diaphragm and the first lens group have the same main optical axis, and the aperture diaphragm is arranged between the first lens group and the second lens group.

Wherein the aperture stop is provided at a position of the first intermediate image.

In order to solve the technical problem, the invention adopts another technical scheme that: a projection lens is provided, which comprises the optical system capable of increasing the angle of field.

The invention has the beneficial effects that: different from the prior art, the concave reflector is used for reflecting the second intermediate image formed by the first image through the lens group, so that the deformation of the second image obtained by reflection can be reduced, the imaging quality is improved, the field angle is increased, and meanwhile, the optical path of the concave reflector is increased, and short-distance projection is realized. The first image forms a first intermediate image with small distortion through the lens group, the lens group corrects the first intermediate image to form a second intermediate image, and finally the image beam of the second intermediate image is projected to the screen through the concave reflector to form an almost distortion-free image.

Drawings

FIG. 1 is a schematic structural diagram of a first embodiment of an optical system capable of increasing an angle of view according to the present invention;

FIG. 2 is a schematic structural diagram of a second embodiment of the optical system capable of increasing the field angle according to the present invention;

FIG. 3 is a schematic structural diagram of a third embodiment of an optical system capable of increasing an angle of field according to the present invention;

FIG. 4 is a schematic diagram illustrating the imaging principle of an embodiment of the projection lens of the present invention;

fig. 5 is an overall schematic diagram of imaging by the projection lens according to the embodiment of the invention.

Wherein,

first image 100, 200, 400

Lens group 101

First intermediate image 103, 403

Second intermediate image 104, 404

Concave reflector 105, 405

First lens group 201, 301, 401

Second lens group 202, 302, 402

First lens 2011

Second lens 2012

Third lens 2013

Fourth lens 2014

Fifth lens 2015

Sixth lens 2021

Seventh lens 2022

Eighth lens 2023

Ninth lens 2024

Tenth lens 2025

Eleventh lens 2026

Twelfth lens 2027

Thirteenth lens 2028

Aperture stops 306, 406

Projection lens 407

Display device 408

Prism 409

Screen 410

Detailed Description

The projection optical system and the projection lens according to the present invention will be described in detail with reference to the accompanying drawings and embodiments.

Please refer to fig. 1, which is a schematic structural diagram of an optical system capable of increasing an angle of view according to a first embodiment of the present invention.

An optical system capable of increasing an angle of field for imaging a first image 100 entering the optical system as an enlarged second image includes a lens group 101 and a concave mirror 105.

The lens group 101 includes a plurality of lenses arranged in front and behind along a light path and having the same main optical axis, and the first image 100 sequentially forms a first intermediate image 103 and a second intermediate image 104 in the lens group 101. The concave mirror 105 is located behind the lens group 101, and reflects the second intermediate image 104 to form an enlarged second image. In this embodiment, the concave mirror 105 and the lens assembly 101 have the same main optical axis, and the concave surface of the concave mirror 105 is a free-form surface. The transmittance of the optical system is 0.2-0.25, the focal length is-2.9 mm-3.2 mm, and the offset of the first image 100 relative to the main optical axis is more than 120%.

Different from the prior art, the invention can reduce the deformation of the second image obtained by reflection by using the concave reflector 105 to reflect the second intermediate image 104 formed by the first image 100 through the lens group 101, improve the imaging quality and increase the angle of view, and meanwhile, the concave reflector 105 increases the optical path to realize short-distance projection. The first image 100 forms a first intermediate image 103 with small distortion through the lens assembly 101, the lens assembly 101 corrects the first intermediate image 103 to form a second intermediate image 104, and finally the image beam of the second intermediate image 104 is projected to the screen through the concave reflector 105 to form an almost distortion-free image, so that the image distortion is reduced, the aberration is improved, the angle of view is increased by using the concave reflector 105 to reflect and form the intermediate image twice through the lens assembly 101, and the optical system of the structure has lower transmittance, thereby realizing the short-distance projection of the large image.

In this embodiment, the concave mirror 105 having a concave surface of a free-form curved surface is used, which has more degrees of freedom, and has a smooth and textured surface, and can reduce optical loss and image distortion, so that the reflected image has high brightness and is not deformed, thereby greatly improving the image quality of the optical system.

Please refer to fig. 2, which is a schematic structural diagram of an optical system capable of increasing an angle of view according to a second embodiment of the present invention. In the present embodiment, the lens group includes a first lens group 201 and a second lens group 202. The first lens group 201 includes five lenses for imaging the first image as a first intermediate image. The second lens group 202 includes eight lenses for imaging the first intermediate image into a second intermediate image.

The five lenses of the first lens group 201 are respectively a first lens 2011, a second lens 2012, a third lens 2013, a fourth lens 2014 and a fifth lens 2015 which are arranged in front and behind each other along the optical path. The first lens 2011 is a biconvex lens, the second lens 2012 is a biconvex lens, the third lens 2013 is a convex-concave lens, the fourth lens 2014 is a biconcave lens, and the fifth lens 2015 is a convex-concave lens. The five lenses image the first image entering the optical system as a first intermediate image with a small amount of distortion.

After passing through the optical system, the light beams emitted from the object points on the axis form different angles with the optical axis and intersect the optical axis at different positions, so that a circular diffuse spot is formed on the image plane, and the diffuse spot is called spherical aberration. In addition, the light with different wavelengths has different colors, and the refractive indexes of the light passing through the lens are different, so that a color spot can be formed on the image side by one point of the object side, or the image is provided with a halo, and the image is blurred. Therefore, spherical aberration and chromatic aberration need to be eliminated to improve the imaging quality. In the present embodiment, the fourth lens 2014 and the fifth lens 2015 are cemented into a single body in order to eliminate spherical aberration and chromatic aberration. The single convex lens has negative spherical aberration and the single concave lens has positive spherical aberration, so that the spherical aberration can be effectively eliminated by gluing the single convex lens and the single concave lens. The refractive index of the fourth lens 2014 is higher than that of the fifth lens 2015. The dispersion of the fourth lens 2014 is greater than the dispersion of the fifth lens 2015. The abbe number of the fourth lens 2014 is lower than that of the fifth lens 2015. The cemented fourth lens 2014 and fifth lens 2015 are effective in eliminating chromatic aberration because the larger the abbe number of the lenses, the smaller the chromatic aberration at a given optical angle, and in general, the negative chromatic aberration occurs in the convex lens and the positive chromatic aberration occurs in the concave lens. Therefore, the biconcave fourth lens 2014 and the biconcave fifth lens 2015 are cemented into a single body so that their chromatic aberrations compensate each other. Further, the difference between the refractive index and the abbe number of the fourth lens 2014 and the fifth lens 2015 is large, so that the positive and negative spherical aberrations can be minimized while eliminating the chromatic aberration, and the residual spherical aberration is generated to balance the spherical aberrations of the other lenses.

The eight lenses of the second lens group 202 at least include an aspheric lens for correcting spherical aberration caused by the spherical lens in the collimating and focusing system, and by adjusting the surface constant and aspheric coefficients, the aspheric lens can eliminate the spherical aberration to the maximum extent, so that the imaging is clear, thereby improving the imaging quality. The eight lenses are a sixth lens 2021, a seventh lens 2022, an eighth lens 2023, a ninth lens 2024, a tenth lens 2025, an eleventh lens 2026, a twelfth lens 2027, and a thirteenth lens 2028, respectively, which are arranged in tandem along the optical path. The sixth lens element 2021 is a biconvex lens element, the seventh lens element 2022 is a biconvex lens element, the eighth lens element 2023 is a convex-concave lens element, the ninth lens element 2024 is a concave-convex lens element, the tenth lens element 2025 is a biconcave lens element, the eleventh lens element 2026 is an aspheric lens element, the twelfth lens element 2027 is a concave-convex lens element, and the thirteenth lens element 2028 is a concave-convex lens element. The aspheric lens simplifies elements related to improving optical quality, improves system stability and reduces the comprehensive cost of the system.

Please refer to fig. 3, which is a schematic structural diagram of an optical system capable of increasing an angle of view according to a third embodiment of the present invention.

The present embodiment is different from the second embodiment in that an aperture stop 306 is further disposed between the first lens group 301 and the second lens group 302 in the present embodiment, and the aperture stop 306 and the first lens group 301 have the same main optical axis. The aperture stop 306 can improve the definition of an image, control the depth of field, improve the imaging quality, and also control the range of an imaging object space and control the brightness of an image plane. The aperture stop 306 is arranged at the position of the first intermediate image, so that the imaging quality of an off-axis point can be improved, reflected light spot components are eliminated, and the effect of improving the image contrast can be achieved. An image formed by the aperture stop 306 passing through the first lens group 301 matches the exit pupil of the optical system.

Referring to fig. 4 and 5, fig. 4 is a schematic diagram illustrating an imaging principle of a projection lens according to an embodiment of the present invention; fig. 5 is an overall schematic diagram of imaging by the projection lens according to the embodiment of the invention. The invention also provides a projection lens 407, and the projection lens 407 further comprises the optical system capable of increasing the field angle. The projection lens 407 further includes a display device 408 and a prism 409 arranged in sequence along the optical path. The optical system is located behind the prism 409. The display device 408 is used to display a first image 400, the first image 400 passes through the prism 409 and then enters the optical system to be refracted twice to form an intermediate image, i.e. a first intermediate image 403 and a second intermediate image 404, and the concave mirror 405 is located behind the second intermediate image 404, reflects the second intermediate image 404, and finally forms an enlarged second image on the screen 410. For example, in the present embodiment, the first image 400 displayed by the display device 408 is refracted and imaged as the first intermediate image 403 through the prism 409 and the first lens group 401. The first intermediate image 403 passes through the aperture stop 406 and is refracted by the second lens group 402 to be imaged as a second intermediate image 404. A mirror 405 is positioned behind second intermediate image 404 and reflects second intermediate image 404 to ultimately form an enlarged second image on screen 410. The optical system capable of increasing the angle of view may be any of the optical systems of the first, second, and third embodiments described above.

The invention reduces the deformation of the image, increases the optical path, realizes short-focus projection, increases the angle of view and has lower transmittance at the same time by using the concave reflector to reflect the intermediate image. And the intermediate image is formed twice by combining the lens group, so that the aberration is further improved, and a high-quality image is obtained.

The above description is only an embodiment of the present invention, and not intended to limit the scope of the present invention, and all modifications of equivalent structures and equivalent processes performed by the present specification and drawings, or directly or indirectly applied to other related technical fields, are included in the scope of the present invention.

Claims

1. An optical system capable of increasing an angle of view for imaging a first image entering the optical system as a magnified second image, comprising:

the lens group comprises a plurality of lenses which are arranged in front and at the back along a light path and have the same main optical axis, and the first image forms a first intermediate image and a second intermediate image in the lens group in sequence;

the concave reflector is positioned behind the lens group and used for reflecting the second intermediate image to form an amplified second image;

the transmittance of the optical system is 0.2-0.25, the focal length is-2.9 mm-3.2 mm, and the offset of the first image relative to the main optical axis is more than 120%.

2. The optical system of claim 1, wherein the concave surface of the concave mirror is a free-form surface.

3. The optical system of claim 2, wherein the lens group comprises:

a first lens group including five lenses for imaging the first image as a first intermediate image;

and the second lens group comprises eight lenses and is used for imaging the first intermediate image into a second intermediate image.

4. The optical system according to claim 3, wherein the first lens group includes a first lens, a second lens, a third lens, a fourth lens, and a fifth lens arranged in this order along the optical path; the first lens is a biconvex lens, the second lens is a biconvex lens, the third lens is a convex-concave lens, the fourth lens is a biconcave lens, and the fifth lens is a convex-concave lens.

5. The optical system of claim 4, wherein the fourth lens and the fifth lens are cemented together as a single piece.

6. The optical system according to claim 5, wherein the fourth lens has a higher refractive index than the fifth lens; the dispersion of the fourth lens is larger than that of the fifth lens; the abbe number of the fourth lens is lower than that of the fifth lens.

7. The optical system according to claim 6, wherein the second lens group includes a sixth lens, a seventh lens, an eighth lens, a ninth lens, a tenth lens, an eleventh lens, a twelfth lens, and a thirteenth lens arranged in this order along the optical path; wherein, at least one aspheric lens is included; the sixth lens element is a biconvex lens, the seventh lens element is a biconvex lens, the eighth lens element is a convex-concave lens, the ninth lens element is a concave-convex lens, the tenth lens element is a biconcave lens, the eleventh lens element is an aspheric lens, the twelfth lens element is a concave-convex lens, and the thirteenth lens element is a concave-convex lens.

8. The optical system of claim 7, further comprising an aperture stop; the aperture diaphragm and the first lens group have the same main optical axis, and the aperture diaphragm is arranged between the first lens group and the second lens group.

9. An optical system according to claim 8, characterised in that the aperture stop is provided at the position of the first intermediate image.

10. A projection lens comprising the optical system according to any one of claims 1 to 9 capable of increasing an angle of field.