CN105090886B

CN105090886B - Lens and lens system and application thereof

Info

Publication number: CN105090886B
Application number: CN201410152967.1A
Authority: CN
Inventors: 余闻天
Original assignee: Hangzhou Great Star Industrial Co Ltd
Current assignee: Hangzhou Great Star Industrial Co Ltd
Priority date: 2014-04-16
Filing date: 2014-04-16
Publication date: 2022-09-02
Anticipated expiration: 2034-04-16
Also published as: CN105090886A

Abstract

A lens and lens system and use thereof, the lens comprising a front surface, a rear surface, and side surfaces extending between the front and rear surfaces; the rear surface defines a rearward facing cavity; the front surface includes a central surface, and an edge surface circumferentially connecting the central surface, the edge surface extending between the central surface and the side surface; the lens is a rotationally symmetric body defining a central axis; the lens is placed on the central axis in a matching way, and an LED light source which can move in the cavity or a light source similar to the LED light source form a lens system, so that high utilization rate of emergent light of the light source is realized, and functions of collimation and focusing of incident light are realized. The lens system can be used for a flashlight with an adjustable focusing function.

Description

Lens and lens system and application thereof

Technical Field

The present invention relates to an optical device, and more particularly, to a lens and a lens system and use thereof.

Background

With the continuous development of semiconductor materials and processes, Light Emitting Diodes (LEDs) are gradually replacing conventional light sources. The special light-emitting principle of the light-emitting diode is that the energy consumed by the light-emitting diode under the condition of achieving the same brightness is far lower than that of a common incandescent lamp, and the light-emitting diode has the advantages of long service life, no pollution and the like, and has wide prospects in the fields of illumination and backlight.

In an LED lighting product, in order to obtain proper light distribution and illumination intensity, a lens is often installed in front of an LED lamp bead to converge light, for example, a fresnel lens is used to convert light emitted from a focus of the fresnel lens into parallel light.

In addition, in order to further make full use of LED light, the current mainstream method is to arrange a cavity on the lens, and arrange the LED light source in the cavity. Because the light emitted by the LED as a point light source is distributed in a 180-degree space, all the light emitted by the LED can be incident into the lens theoretically by using the method, and the emergent direction of the incident light is adjusted according to the structure of the lens so as to achieve the effects of convergence, light uniformization and the like.

In some cases there is also a requirement for the spot of the emerging light, which can generally be achieved by adjusting the relative position of the LED light source and the lens.

To achieve all the requirements as described above, the shape of the lens needs to be obtained by accurate simulation calculations. Currently, such lenses generally have a front surface, a side surface, and a rear surface, and the rear surface defines a cavity as a placement area for an LED light source, so that all light emitted from the LED can be confined in the cavity. In this case, it is necessary to calculate and derive the arc shapes of the front surface, the rear surface and the side surfaces according to the designed light path, which also involves the matching of the surfaces with each other, which is particularly important for realizing the light path control of the light.

This is easier to achieve without regard to the cost of the lens material. With further considerations regarding lens cost, various more material-saving product designs continue to be created, which achieve material savings primarily by reducing the distance between the front and back surfaces, i.e., making the lens thinner. The requirements for the accuracy of the shape of the arc surfaces of the front, rear and side surfaces and their mutual cooperation are even higher, resulting in greater design difficulty and longer design cycle.

Also for lens processing, the more processing surfaces that need to be precisely controlled or have a high processing difficulty, the more difficult it is for lens preparation, thereby directly affecting product yield.

Accordingly, those skilled in the art have made an effort to develop a lens that can achieve a high utilization rate of light for an LED light source (or a light source similar to an LED), has a condensing and focusing function, and is material-saving, simple in structure, and capable of reducing a high-precision optical surface required as much as possible.

Disclosure of Invention

In order to achieve the above object, the present invention provides a lens, a lens system of the lens cooperating with a light source and a use thereof.

The lens comprises a front surface, a rear surface, and side surfaces extending between the front surface and the rear surface, the front surface being located in front of the lens, the rear surface being located in rear of the lens; the rear surface defining a rearward facing cavity; the front surface includes a central surface, and an edge surface circumferentially connecting the central surface, the edge surface extending between the central surface and the side surface; the lens defines a central axis; the cavity includes a sidewall and a bottom defining a cavity space, the central axis passing through the central surface and the bottom; the corresponding line segment of the edge surface on the central cross section, namely the edge line segment, is formed by alternately connecting a line segment parallel to the central axis and a line segment vertical to the central axis and is similar to a right-angled step shape.

Further, any cross section of the lens passing through the central axis, i.e. the central cross section, is the same in figure, i.e. it is defined that the lens is a symmetrical body, and the central axis is the central axis

Further, a corresponding line segment of the central surface on the central cross section, i.e., a central line segment, is an arc. Alternatively, the central surface is a curved surface.

Further, the arc of the central line segment is convex in a direction away from the bottom, i.e. the central surface is convex towards the front of the lens.

Further, the extending direction of the edge line segment parallel to the central axis is the same as the arc-shaped convex direction of the central line segment, and the edge line segment extends away from the central line segment in the direction perpendicular to the central axis. I.e. the rim surface and the central surface substantially form a bowl shape with the opening of the bowl being located in front of the lens, opposite the opening of the cavity.

Further, the corresponding line segment of the sidewall on the central cross section, namely the sidewall line segment, is a straight line or an arc line.

Further, the sidewall line segments are parallel to the central axis, i.e. the sidewall is cylindrical.

Further, the bottom is an arc surface or a plane, and when the bottom is an arc surface, the protruding direction of the arc surface is not limited, and may be the same as or opposite to the protruding direction of the central surface. The principle is that the bottom part cooperates with the central surface to form a convex lens or to achieve the effect of a convex lens.

Further, the side wall cooperates with the side surface to satisfy: the incident light emitted by the point light source positioned on the central axis is emitted into the lens by the side wall, and then the reflected light reflected by the side surface is parallel to the central axis. Under the condition that the refractive index of the lens and the position of the light source are determined, the corresponding curve of the side surface on the central cross section is deduced by a mathematical method aiming at the refraction and reflection light paths of the light, a curve equation is obtained, and therefore the curved surface appearance of the side surface is determined.

Further, the dimensions of the edge surface satisfy: the reflected light reflected by the side surfaces is emitted directly from the edge surface. The reflected light combined with the side surface is parallel to the central axis, and the emergent light of the edge surface is a collimated light beam.

Further, the shape of the side surface satisfies: the side surface totally reflects incident light entering from the side wall.

Further, the central surface cooperates with the bottom to satisfy: incident light emitted by the point light source positioned on the central axis is emitted into the lens from the bottom, and corresponding emergent light is emitted from the central surface only. This allows the size combination of the central surface and the bottom to be derived simply by the refractive index equation, with the lens refractive index determined.

Further, the shape of the edge surface satisfies: outgoing light emerging from the central surface is not blocked by the edge surface. I.e. the step height of the edge surface does not block the outgoing light from the central surface.

Further, the side surface is plated with a total reflection film.

Further, the total reflection film is silver.

Further, the material of the lens is polymethyl methacrylate (PMMA).

The lens system adopting the lens comprises the lens and a light source, wherein the light source provides incident light of the lens.

Further, the light source is on a central axis of the lens.

Further, the light source is movable along the central axis.

Further, the range of movement of the light source is inside the cavity of the lens, including a position at a distance of 0 from the cavity.

Further, the range of movement of the light source is from 0mm from the cavity to 10mm deep into the cavity.

Further, when the light source moves in the process of being 0mm far from the cavity to being 10mm deep into the cavity, the maximum included angle of emergent light emitted from the central surface of the lens is 8-90 degrees.

Further, the light source is an LED light source or a light source similar to an LED, that is, a light source having characteristics of good monochromaticity of the LED light source, and the emitted light is distributed in a 180-degree space.

The lens system can be used for a flashlight with an adjustable focusing function.

The lens and lens system of the present invention have the following advantages:

1. the LED light source (or the light source similar to the LED) can be fully utilized to emit light, so that high utilization rate of light energy is realized;

2. the emergent light is divided into collimated emergent light and adjustable emergent light, and the proportion of the emergent light of the two parts can be conveniently adjusted in design so as to adapt to different use requirements;

3. the adjustable light spot range is large, and various use requirements can be met;

4. the optical surface with high processing precision or difficulty only has a side surface, so that the manufacturing difficulty is reduced.

5. The lens is similar to a bowl shape, so that the manufacturing material is saved.

Drawings

FIG. 1 is a front view of a preferred embodiment of a lens of the present invention;

FIG. 2 is a cross-sectional view taken along line A-A of FIG. 1;

FIG. 3 is a schematic illustration of the entry and exit of partially collimated light rays from the lens of FIG. 2, only showing light rays to the right of the central axis;

FIG. 4 is a schematic diagram of the total collimated light incident and emergent of the lens shown in FIG. 2;

FIG. 5 is a schematic illustration of the entry and exit of partially focused light rays from the lens of FIG. 2, with the light source located outside the lens cavity, showing only light rays to the right of the central axis;

FIG. 6 is a schematic diagram of the entrance and exit of the totally focused light rays of the lens of FIG. 2, with the light source located outside the lens cavity;

FIG. 7 is a schematic illustration of the entry and exit of a partially focused light beam from the lens of FIG. 2, with the light source located within the lens cavity, showing only the light beam to the right of the central axis;

FIG. 8 is a schematic diagram of the entrance and exit of the total focused light rays of the lens of FIG. 2, with the light source located within the lens cavity;

FIG. 9 is a schematic diagram of the light incident and exiting of the lens of FIG. 2 with the light source located in the lens cavity;

FIG. 10 is a calculated graph of the curve corresponding to the side surface of the lens shown in FIG. 2 in a central cross-section;

FIG. 11 is a schematic diagram of the critical point of the curve corresponding to the side surface of the lens of FIG. 2 in a central cross-section;

FIG. 12 is a schematic view of another preferred embodiment of the lens of the invention with the convex direction of the bottom curve away from the central surface;

FIG. 13 is a schematic view of another preferred embodiment of the lens of the present invention, with the bottom being planar;

FIG. 14 is a schematic view of a preferred embodiment of a flashlight employing the lens system of the present invention with the LED light source at the mouth of the lens;

FIG. 15 is a schematic view of the LED light source of the flashlight of FIG. 14 within the cavity of the lens.

Detailed Description

The conception, the specific structure and the technical effects of the present invention will be further described with reference to the accompanying drawings to fully understand the objects, the features and the effects of the present invention.

The lens 1 as shown in fig. 1 and 2, comprises a front surface 2, a rear surface 3, and a side surface 4 extending between the front surface 2 and the rear surface 3; the rear surface defines a rearward facing cavity 5; the front surface 2 comprises a central surface 201, and an edge surface 202 circumferentially connecting the central surface 201, the edge surface 202 extending between the central surface 201 and the side surface 4; the lens 1 defines a central axis 6, and any cross section of the lens 1 passing through the central axis 6, namely a central cross section, is the same in figure, namely the lens 1 is defined as a symmetrical body, and the central axis is the central axis 6; the cavity 5 comprises a sidewall 501 and a bottom 502, the sidewall 501 and the bottom 502 defining a cavity space, the central axis 6 passing through the central surface 201 and the bottom 502; the corresponding line segment of the edge surface 202 in the central cross-section, i.e. the edge line segment 204, is composed of line segments parallel to the central axis 6 and line segments perpendicular to said central axis 6, which are alternately connected. Similar to a right-angled step shape, i.e. the corresponding line segment of the edge surface 202 in the central cross-section is a stepped line segment, which is composed of a plurality of line segments connected parallel or perpendicular to the central axis 6.

The corresponding line segment of the central surface 201 in the central cross-section, i.e. the central line segment 203, is curved, i.e. it defines that the central surface 201 is a symmetrical arc along the central axis 6, which in this embodiment is a spherical surface, which is convex in the opposite direction to the opening of the cavity 5 and in the same direction as the extension of the edge surface 202 along the central axis 6. At the same time, the extension of the edge surface 202 in a direction perpendicular to the central axis 6 is away from the central surface 201. The side wall 501 of the cavity 5 is parallel to the central axis 6, i.e. the side wall 501 is cylindrical.

The lens 1 needs to be used with a light source located on the central axis 6, and the characteristics of the lens 1 will be further described below by taking a point light source as an example, as shown in fig. 3 and 4, the point light source 7 located on the central axis 6 provides incident light, the incident light entering the lens 1 from the side wall 501 is reflected by the side surface 4 to be parallel to the central axis 6, and finally the reflected light is emitted from the edge surface 202. Since the edge surface 202 comprises only a torus perpendicular and parallel to the central axis 6, the outgoing light from the edge surface 202 is also parallel to the central axis 6, achieving collimated outgoing light to the incoming light. Using the above-mentioned profile of the sidewall 501 and the edge surface 202, and under the premise of the determination of the lens material (refractive index), the collimation function can be realized by only precisely calculating the arc shape of the side surface 4 in design, and the total reflection is realized on the side surface 4 (the calculation method derived from the side surface 4 is described in detail below). In terms of processing difficulty, the side wall 501 and the edge surface 202 of the lens 1 only include the surfaces perpendicular or parallel to the central axis 6, and processing is relatively simple to implement, only the side surface 4 needs to be strictly controlled in precision, and factors influencing optical surfaces with each other are greatly reduced.

On the premise that the lens material (refractive index) is determined, in order to realize the total reflection of the side surface 4, there is a certain limit to the shape of the side surface 4, so that the total reflection on the side surface 4 may not be satisfied in design according to certain specific size requirements, and then a total reflection film, such as silver, may be plated on the side surface 4.

As shown in fig. 5-8, the point light source 7 is located on the central axis 6, and the point light source 7 can be moved along the central axis 6 to the inside of the cavity 5. The incident light entering the lens 1 from the bottom 502 can obtain various size combinations of the central surface 201 and the bottom 502 from the refraction equation under the premise that the lens material (refractive index) is determined, so as to realize that the corresponding emergent light exits from the central surface 201. In this embodiment, the central surface 201 and the bottom 502 are respectively a spherical surface and an elliptical spherical surface, and the convex directions are the same, and they together form a convex lens to converge the incident light, so that the emergent light forms a uniform light spot within a certain range. In this case, the shape of the edge surface 202 (or the step height of the step structure) is sufficient to block the outgoing light from the central surface 201. When the point light source 7 gradually enters the cavity 5, the maximum included angle of emergent light is increased, and the adjustment of the size of the light spot is realized.

Fig. 9 shows a complete ray diagram of the emitted light of the light source 7 focused and collimated by the lens 1.

Fig. 10 is a graph of a curve equation corresponding to a side surface in a central cross section, wherein the Y axis is the central axis, and further includes a light path 9, a curve 10 corresponding to a side surface in a central cross section, a sidewall line segment 11 parallel to the Y axis, and included angles a, b, c, d, and the calculation method of the curve equation is explained in detail as follows:

setting lens parameters: r is the radius of the opening of the cavity at the bottom of the lens, R is the radius of the bottom of the lens, and n is the refractive index of the lens.

The target is as follows: under the above parameter conditions, the curve equation y = f (x) of total reflection collimated light is formed

1. Solving the tangent equation of the Pn point:

∵f′(x)=tand

∵(90°-c)+2d=180°

∴

then the slope of the line equation through this point:

substituting the Pn (Xn, Yn) coordinates, the tangent through Pn satisfies the equation:

the neighboring point Pn +1 of Pn can be approximately considered to be also on the tangent line.

2. Pn +1 point in the ray equation:

∵y=tanc?(x-r)+rcota

∵

∴

3. constraint conditions are as follows:

by total reflectionCritical angle determines the ultimate slope

Thus, there are:

since direct solution is not easy, the limit case is not assumed: when a → 90 °, the value is obtained

Can be totally reflected, which can be realized by common PMMA and PC materials; a → 0 °, substitution gives: when n is>1, the curved surface can be totally reflected, which is obviously true; order to

The function monotonically decreases at 0< a <90 °. Therefore, if the curved surface can totally reflect light rays having an initial incident angle of a = θ at the same refractive index n, the light rays having a' = θ - Δ θ (both θ and Δ θ are greater than 0) can also be totally reflected without fail.

Judging from the previous special value that the known a → 90 deg. only requires the refractive index to be greater than 1.414 for total reflection to occur,

therefore, the total reflection is also performed for angles below 90 °, and the result of a → 0 ° verifies the correctness of this reasoning.

Therefore, the curve can be totally reflected for any initial incident angle a of light, and the design only needs to consider the requirement on the height of the lens structure.

4. Solving a discrete solution of a curve equation:

solving the system of equations (1) and (2) with the P0 coordinate as Pn and a =1 ° substitution gives the system of equations for X and Y.

Solving the system of equations (3) and (4) yields P1(X1, Y1)

Taking the coordinate of P1(X1, Y1) as P0 again, and substituting a =2 ° into (1) and (2) can obtain a new equation system

Similarly, solving the system of equations (5) and (6) yields P2(X2, Y2)

By analogy, a series of P point coordinates can be obtained.

Fitting the discrete points P0- > Pn to a curve equation by statistical software, such as Excel, MATLAB, polynomial: y = f (x).

It can also be solved programmatically, an example of the program is as follows:

clear all;clc

% The Frist Step defines The adjustable variable

r = 6%

R = 8.5%,% defines the radius of the bottom of the curved surface

n = 1.49% defines the refractive index of the material

angles = (90: -0.5:40);% defines the calculation angle range

% The Second Step defines intermediate variables

num=length(angles);

Y0=R;Z0=0;

for i=1:num

a(i)=(angles(i)*pi/180);

c(i)=asin(cos(a(i))/n);

k1(i)=tan((pi/2+c(i))/2);

k2(i)=tan(c(i));

end

Cyclic solution of% The Third Step equation

for i=1:num

syms y;

f1=k1(i)*(y-Y0)+Z0;

f2=k2(i)*(y-r)+r*cot(a(i));

f=f1-f2;

yy=solve(f);

y=double(yy);

z=k1(i)*(y-Y0)+Z0;

Y0=y;

Z0=z;

Py(i)=Y0;

Pz(i)=Z0;

end

% The Forth Step polynomial fitting aspheric coefficients

cftool

% note that x = Py y = Pz is set at the time of fitting.

As shown in fig. 11, the critical point 14 of the extension length of the curve 10 is determined by the light path 12 and the curve 10, and the light path 12 is the light path generated by the light incident from the bottom of the sidewall, and satisfies the refraction relation:

sin θ 1= n × sin θ 2, n is a refractive index of the lens, and θ 1, θ 2 are an incident angle and a refraction angle of the light ray, respectively. In order to satisfy that the light incident from the side wall can reach the side surface, the end point of the upward extension of the curve 10 should not be lower than the critical point 14. The critical point 14 also defines the size of the edge surface.

In the same way, the fit of the central surface and the bottom can also be analyzed. At this time, the light path of the light incident from the bottom and the most edge far from the central axis needs to be analyzed, so that the extending width of the central surface is enough to cover the refracted light in the light path, that is, the incident light emitted by the point light source positioned on the central axis is incident into the lens from the bottom, and the corresponding emergent light is only emitted from the central surface.

The lens shape according to the present invention is not limited to the structure shown in the above-described embodiment. Another lens shape that may be used is shown in fig. 12, where the curvature of the base 502 is convex away from the central surface 201. Another lens shape that may be used is shown in fig. 13, where the base 502 is planar.

It should also be noted that the shape of the sidewall 501 may be changed arbitrarily, and the curve equation of the sidewall line segment is considered in the calculation, and the curved surface of the side surface matching with the sidewall line segment can be calculated by the above calculation method.

The various lenses are particularly suitable for being matched with an LED light source (or a light source similar to an LED) to form a lens system, and the technical effects of zooming, collimation and the like can be realized, and meanwhile, higher light intensity utilization rate can be obtained. When the LED light source is disposed on the central axis 6 and the movable range is within the cavity 5 (including the distance from the cavity 5 being 0), the light emitted from the LED light source can be completely received by the sidewall 501 and the bottom 502. Meanwhile, the size of the emergent light spot can be adjusted by adjusting the position of the LED light source in the cavity 5.

In a more specific embodiment, the lens is made of polymethyl methacrylate with a refractive index of 1.49, and is designed to achieve a variation of the maximum included angle of the outgoing light from the central surface 201 of the lens 1 in the range of 8-90 degrees when the light source is moved 0-10mm deep into the cavity 5.

The lens system can be used for a flashlight with a focusing function, and can be used as a light source and an optical element of the flashlight. Referring to fig. 14 and 15, a flashlight employing the lens system of the present invention is shown, wherein the flashlight 15 includes a handle 17 and a barrel 18, both of which are telescopically configured to extend and retract between limits. The lens 1 and the LED light source 16 are fixed to a lens barrel 18 and a handle 17, respectively, and move relative to each other by extending and contracting the lens barrel 18 and the handle 17, thereby realizing a focusing function. Fig. 14 and 15 show the LED light sources 16 in the mouth and cavity of the lens 1, respectively. The relative movement of the handle 17 and the barrel 18 is not limited to the above-described manner, and both may be extended and retracted by a screw structure. Any connection that allows relative movement between the lens 1 and the LED light source 16 can be used to achieve the focusing function of the flashlight.

The lens system can also be applied to other occasions needing to adjust the spot size (or focus and astigmatism interactive change), such as a flash system of a camera, a stage lighting system and the like.

In addition, under the influence of lens processing, flashlight assembly precision and size of the LED light source, in practical use, part of light rays in collimated light cannot be collimated and emitted, so that when the LED light source moves, a bright ring with the size changed along with the light rays appears in light spots, and the method completely depends on the actual processing and assembly precision and the size of the LED light source.

The foregoing detailed description of the preferred embodiments of the invention has been presented. It should be understood that numerous modifications and variations could be devised by those skilled in the art in light of the present teachings without departing from the inventive concepts. Therefore, the technical solutions available to those skilled in the art through logic analysis, reasoning and limited experiments based on the prior art according to the concept of the present invention should be within the scope of protection defined by the claims.

Claims

1. A lens comprising a front surface, a back surface, and side surfaces extending between the front surface and the back surface; the rear surface defining a rearward facing cavity; the front surface includes a central surface, and an edge surface circumferentially connecting the central surface, the edge surface extending between the central surface and the side surface; the lens defines a central axis; the cavity includes a sidewall and a bottom defining a cavity space, the central axis passing through the central surface and the bottom; the corresponding line segments of the edge surface on the central cross section, namely edge line segments, are formed by alternately connecting line segments parallel to the central axis and line segments vertical to the central axis;

any cross section of the lens passing through the central axis, namely a central cross section, is the same in pattern; the corresponding line segment of the central surface on the central cross section, namely a central line segment, is an arc line; the arc-shaped convex direction of the central line segment is far away from the bottom; the extending direction of the edge line segment parallel to the central axis is the same as the arc-shaped convex direction of the central line segment, and the edge line segment extends away from the central line segment in the direction perpendicular to the central axis; the corresponding line segment of the side wall on the central cross section, namely the side wall line segment, is a straight line or an arc line; the side wall of the cavity is parallel to the central axis; the dimensions of the edge surface satisfy: the reflected light reflected by the side surfaces all exit directly from the edge surface; the shape of the side surface satisfies: the side surface totally reflects incident light entering from the side wall; the central surface cooperates with the bottom to satisfy: incident light emitted by a point light source positioned on the central axis is emitted into the lens from the bottom, and corresponding emergent light is emitted from the central surface only; the shape of the edge surface satisfies: outgoing light emitted from the central surface is not blocked by the edge surface; wherein the shape of the side surface is determined by:

i) the tangent of the point Pn of the corresponding curve of the side surface on the central cross section satisfies the equation:

equation 1:

ii) taking the adjacent point Pn +1 of the point Pn on the tangent line to obtain the ray equation of the point Pn + 1:

equation 2:

iii) setting the constraint:

iv) substituting the point P0, a ═ 1 ° into said formula 1 and said formula 2, yields:

equation 3:

equation 4:

v) solving the system of equations of said formula 3 and said formula 4 to obtain a point P1(X1, Y1);

vi) substituting the point P1(X1, Y1), a ═ 2 ° into the equations 1 and 2 again, resulting in a new system of equations, i.e., equations 5 and 6:

equation 5:

equation 6:

vii) solving the system of equations of said equation 5 and said equation 6 to obtain a point P2(X2, Y2);

viii) by analogy, obtaining a series of coordinates of the point Pn;

ix) fitting a series of discrete points P0-Pn of the points Pn into a curve equation;

wherein (Xn, Yn) represents the coordinates of the point Pn in a coordinate system having the horizontal axis as the central axis and the vertical axis perpendicular to the central axis; r represents the aperture radius of the cavity at the bottom, R represents the radius of the bottom, n represents the refractive index of the lens, and a represents the angle of incident light with the central axis.

2. The lens of claim 1, wherein the base is a curved surface or a flat surface.

3. The lens of claim 1, wherein the side surfaces are plated with a total reflection film.

4. The lens of claim 3, wherein the total reflection film is silver.

5. The lens of claim 1 wherein the material of the lens is polymethylmethacrylate.

6. A lens system using the lens according to any one of claims 1 to 5, comprising the lens, a light source providing incident light to the lens.

7. The lens system of claim 6 wherein the light source is on a central axis of the lens.

8. The lens system of claim 7 wherein the light source is movable along the central axis.

9. The lens system of claim 8 wherein the range of motion of the light source is inside a cavity of the lens.

10. The lens system of claim 9 wherein the light source is moved a distance of 0mm from the cavity to 10mm deep into the cavity.

11. The lens system of claim 10 wherein the maximum included angle of exit light from the central surface of the lens is 8-90 degrees when the light source is moved from 0mm deep into the cavity to 10mm deep into the cavity.

12. The lens system of any of claims 6-11, wherein the light source is an LED light source.

13. Use of a lens system according to claim 12 for a flashlight with adjustable focus.