KR101754604B1 - Projection lens unit of projector - Google Patents

Abstract

A projection lens unit of a projector is disclosed. A projection lens unit according to an aspect of the present invention includes a first lens to a seventh lens sequentially disposed in a direction of an image element in a screen on which an image is projected. Wherein the first lens is a lens having negative power and at least one surface is an aspherical surface, the second lens is a lens having a positive power and at least one surface is an aspherical surface, And the fourth and fifth lenses are glass lenses having negative power and the sixth lens is a glass lens having positive power and at least one surface is an aspherical surface, , And the seventh lens is a glass lens having a positive power.

Description

[PROJECTION LENS UNIT OF PROJECTOR]

The present invention relates to a projection lens unit of a projector capable of minimizing problems caused by changes in performance of a lens due to heat.

A projector is a device for realizing a small image by using an optical means in a large screen. An apparatus for projecting an image in a projector is an optical engine, and a projection lens unit is coupled to an optical engine to enlarge and project an image at a certain ratio. Projectors can be divided into CRT (Cathode Ray Tube) projection, LCD (Liquid Crystal Display) projection, and DLP (Digital Light Processing) projection method depending on the type of device that implements the image.

The projector includes a light source such as an LED (Laser Emission Diode), a lens and a prism for refracting and reflecting the light emitted from the light source, and the like. In addition, the projector has a structure shielded from the outside to prevent dust or the like from entering. Therefore, the heat generated inside the projector can not be easily emitted to the outside, which causes a problem that the optical system such as the projection lens unit including the lens can not exert its original function. Particularly, when a large amount of heat is generated inside the projector, a thermal drift phenomenon occurs in which the focus of the plastic lens is affected by heat. And because of the thermal drift, the projector can not project the image as designed, and the image finally formed on the screen is distorted.

On the other hand, the projector uses a plastic lens instead of an expensive glass lens to lower the manufacturing cost. Plastic lenses have the advantage that they are relatively inexpensive and light in weight compared to glass lenses, but have a problem of being affected by heat (change in focal length) more than glass lenses.

Korean Patent Publication No. 10-0859608

SUMMARY OF THE INVENTION Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and it is an object of the present invention to provide a projection lens unit of a projector which can minimize a thermal effect while using a plastic lens.

Other objects of the present invention will become more apparent through the embodiments described below.

A projection lens unit according to an aspect of the present invention includes a first lens to a seventh lens sequentially disposed in a direction of an image element in a screen on which an image is projected. Wherein the first lens is a lens having negative power and at least one surface is an aspherical surface, the second lens is a lens having a positive power and at least one surface is an aspherical surface, And the fourth and fifth lenses are glass lenses having negative power and the sixth lens is a lens having positive power and at least one surface is an aspherical surface, , And the seventh lens is a glass lens having a positive power.

The projection lens unit according to the present invention may include one or more of the following embodiments. For example, the first lens has a meniscus shape in which the incident surface is convex in the screen direction, the second lens has a meniscus shape concave in the screen direction, the third lens has a convex shape in the screen direction, The fourth and fifth lenses have a shape in which a double-sided concave lens and a double-sided convex lens are joined together. The sixth lens has a convex shape in the direction of the image element, and the seventh lens has a convex shape on both sides .

A diaphragm may be provided between the third lens and the fourth lens.

The second lens and the sixth lens may have a longer focal length than the third lens and the seventh lens having positive power.

The first lens, the second lens, and the sixth lens may all have the same material, refractive index, and dispersion factor.

The present invention can provide a projection lens unit of a projector which can minimize the influence of heat while lowering the manufacturing cost by using a plastic lens.

1 is a diagram illustrating a projection lens unit according to a first embodiment of the present invention.
FIG. 2 is a graph showing MTF performance at a high temperature (50 ° C) condition of a projection lens unit to which the performance change designing technique according to the present invention is not applied.
FIG. 3 is a graph showing MTF performance at a high temperature (50 ° C) condition of the projection lens unit according to the first embodiment to which the performance change designing technique according to the present invention is applied.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention is capable of various modifications and various embodiments, and specific embodiments are illustrated in the drawings and will be described in detail in the detailed description. It is to be understood, however, that the invention is not to be limited to the specific embodiments, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

The terminology used in this application is used only to describe a specific embodiment and is not intended to limit the invention. The singular expressions include plural expressions unless the context clearly dictates otherwise. In the present application, the terms "comprises" or "having" and the like are used to specify that there is a feature, a number, a step, an operation, an element, a component or a combination thereof described in the specification, But do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or combinations thereof.

The terms first, second, etc. may be used to describe various components, but the components should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from another.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout the specification and claims. The description will be omitted.

1 is a diagram illustrating a projection lens unit 100 according to a first embodiment of the present invention. 2 is a graph showing MTF performance of the projection lens unit 100 according to the first embodiment of the present invention.

Referring to FIG. 1, a projection lens unit 100 according to an exemplary embodiment of the present invention is used in an optical projector (not shown). The projection lens unit 100 is sequentially arranged in the direction from the screen 110, The first lens L1 to the seventh lens L7 are arranged in the order from the object side to the image side. A diaphragm S is positioned between the third lens L3 and the fourth lens L4.

The first lens L1 is a meniscus lens having negative power and at least one aspheric surface and the incident surface S2 being convex toward the screen 110. [

The second lens L2 corresponds to a lens having positive power and at least one aspheric surface and a concave meniscus lens in the direction of the screen 110.

The third lens L3 is a lens having a positive power and corresponds to a convex lens in the direction of the screen 110. [

The fourth lens L4 and the fifth lens L5 have a shape in which the fourth lens L4 having a concave shape on both sides and the fifth lens L5 having a convex shape on both sides are bonded to each other and the negative power . The fourth lens L4 and the fifth lens L5 are all glass lenses. The chromatic aberration can be reduced by bonding the fourth lens L4 and the fifth lens L5 to each other.

The sixth lens L6 is a lens having positive power and at least one aspheric surface, and the exit surface S11 has a convex shape in the direction of the image element 140. [

The seventh lens L7 is a glass lens having positive power and has a convex shape on both sides.

As described above, the projection lens unit 100 according to the present embodiment can reduce the size of the projector by using the glass lenses L3, L4, L5, and L7 and the plastic lenses L1, L2, and L6 at the same time, can do. Further, the projection lens unit according to the present embodiment is characterized in that variations in lens performance due to heat generated by using the plastic lenses (L1, L2, L6) can be minimized.

Table 1 below illustrates power (focal distance), refractive index (Nd), dispersion coefficient (Vd), and materials of the first lens to the seventh lens of the projection lens unit according to this embodiment.

Lens number Face number Focal length Refractive index (Nd) The dispersion coefficient (Vd) material L1 S1 to S2 -15.962 1.53 56.0 E48R L2 S3 to S4 115.046 1.53 56.0 E48R L3 S5 to S6 19.326 1.74 44.7 LAF2 L4 S8 to S10 -17.874 1.76 27.5 EFD4 L5 1.49 70.4 FC5 L6 S11 to S12 44.977 1.53 56.0 E48R L7 S13 to S14 17.201 1.62 58.1 BACD15

As can be seen from Table 1, the second lens L2 and the sixth lens L6 having positive power have a positive power and a positive power, respectively, and the third lens L3 and the seventh lens L7 And the focal length is formed to be longer. This is because, in the case of a lens having a short focal length, a change in the overall performance of the projection system due to a change in properties of the lens becomes large. Therefore, in the case of the projection lens unit according to the present embodiment, when the focal length of the front lens group L1 to L3 and the rear lens group L4 to L7 are in the normal temperature (20 DEG C) condition and the high temperature (50 DEG C) condition, To L3) and the rear lens units (L4 to L7) can be minimized to minimize the change in performance due to heat.

As can be seen from Table 1, the first lens L1, the second lens L2, and the sixth lens L6 corresponding to the plastic lenses are all formed of the same material E48R, and the refractive index and the dispersion coefficient Can be the same.

Table 2 below is a table illustrating the specifications of the first lens L1 to the seventh lens L7 of the projection lens unit 100 according to the present embodiment.

Face number Surface type Radius of curvature Thickness (mm) S1 Asphere 17.6866 1.6000 S2 Asphere 5.5772 10.341 S3 Asphere -14.5847 5.300 S4 Asphere -13.2841 3.622 S5 Sphere 14.5087 3.642 S6 Sphere Infinity 1.933 Stop Sphere Infinity 7.368 S8 Sphere -12.0868 0.800 S9 Sphere 11.3325 3.935 S10 Sphere -19.0394 0.300 S11 Asphere -377.3861 1.815 S12 Asphere -22.6578 0.300 S13 Sphere 27.6793 3.904 S14 Sphere -16.7230 3.500

The coefficients of the aspherical surface in the projection lens unit according to the first embodiment of the present invention are shown in Tables 3 to 5 below.

S1 face S2 side K 0.0000 K -0.7836 A -2.59120E-04 A -1.58429E-04 B 2.42590E-06 B -2.57383E-07 C -2.70573E-08 C 5.19311E-08 D 1.43592E-10 D -1.72740E-09 E -2.62314E-13 E 1.17164E-11

S3 side S4 face K -0.6557 K -0.5379 A 7.42307E-06 A -9.44427E-06 B -4.00107E-07 B -3.17547E-07 C 8.86051E-09 C 2.72901E-09 D -1.35504E-10 D -3.01733E-11

S11 side S12 side K 0.0000 K 6.7862 A -2.39975E-05 A 1.73193E-04 B 2.81353E-06 B 2.91789E-06 C -1.46640E-07 C -7.64952E-08 D 2.63827E-09 D 1.05281E-09 E -2.07024E-11 E -2.79143E-12

Referring to Tables 1 to 5, the first lens L1 includes an incident surface S1 directed toward the screen 110 and an incident surface S2 ) Corresponds to a plastic aspheric lens having a convex surface in the screen direction. The first lens L1 has a first surface S1 having a curvature radius of 17.6866 and a second surface S2 having a curvature radius of 5.5772 so that the first surface S1 has a larger radius of curvature As shown in FIG. The thickness of the first lens L1 (the distance between the first surface S1 and the second surface S2) is 1.6 mm, the refractive index is 1.53 and the dispersion coefficient is 56.0.

The third surface S3 and the fourth surface S4 of the second lens L2 all have a concave shape in the direction of the screen 110. [ The second lens L2 corresponds to an aspherical lens made of plastic and has a refractive index of 1.53, a dispersion coefficient of 56.0 and a thickness of 5.300 mm (a distance between the third surface S3 and the fourth surface S4) . The distance between the second surface S2 and the third surface S3 corresponding to the distance between the first lens L1 and the second lens L2 is 10.341 mm.

The third lens L3 corresponds to a glass lens having a convex shape toward the screen 110, and its incident surface S6 can be formed flat. The third lens L3 has a refractive index of 1.74 and a dispersion coefficient of 44.7. And the third lens L3 has a thickness of 3.642 mm (a distance between the fifth surface S5 and the sixth surface S6). The distance between the fourth surface S4 and the fifth surface S5 corresponding to the distance between the second lens L2 and the third lens L3 is 3.622 mm.

The diaphragm S is located between the third lens L3 and the fourth lens L4. The distance between the diaphragm S and the sixth surface S6 of the third lens L3 is 1.933 mm and the distance between the eighth surface S8 of the fourth lens L4 corresponds to 7.368 mm

The fourth lens L4 is a glass lens having a concave shape on both sides and the fifth lens L5 is a glass lens having a convex shape on both sides and both are in contact with each other. The overall focal length of the fourth lens L4 and the fifth lens L5 corresponds to -17.874. The fourth lens L4 has a refractive index of 1.76 and a dispersion coefficient of 27.5, and the fifth lens L5 has a refractive index of 1.49 and a dispersion coefficient of 70.4. The fourth lens L4 has a thickness of 0.8 mm (a distance between the eighth surface S8 and the ninth surface S9), and the fifth lens L5 has a thickness of 3.935 mm (the ninth surface S9 ) And the tenth surface S10). The distance between the tenth surface S10 and the eleventh surface S11 corresponding to the distance between the fifth lens L5 and the sixth lens L6 is 0.3 mm.

The sixth lens L6 corresponds to a plastic lens in which the exit surface S11 has a convex shape in the direction of the image element 140. [ The sixth lens L6 has a refractive index of 1.53 and a dispersion coefficient of 56.0. The sixth lens L6 has a thickness of 1.815 mm (a distance between the eleventh surface S11 and the twelfth surface S12). The distance between the twelfth surface S12 and the thirteenth surface S13 corresponding to the distance between the sixth lens L6 and the seventh lens L7 is 0.3 mm.

The seventh lens L7 is a glass lens in which both surfaces S13 and S14 are convex. The seventh lens L7 has a refractive index of 1.62 and a dispersion coefficient of 58.1. The seventh lens L7 has a thickness of 3.904 mm (a distance between the thirteenth surface S13 and the fourteenth surface S14). The distance between the fourteenth surface S14 corresponding to the incident surface of the seventh lens L7 and the total internal reflection prism 120 is 3.500 mm.

The total internal reflection prism 120 is disposed behind the projection lens unit 100 or after the fourteenth surface S14 of the seventh lens L7 to direct the image light from the image element 140 toward the seventh lens L7 . A cover glass 130 is disposed between the image element 140 and the internal total reflection prism 120.

Table 6 below shows the focal lengths of the respective lenses (L1 to L7) at 20 占 폚 and 50 占 폚.

Lens number (face number) Focal Length (20 ° C) Focal Length (50 ° C) Variation L1 (S1 to S2) -15.962 -16.076 -0.114 L2 (S3 to S4) 115.046 116.140 1.094 L3 ((S5 to S6) 19.326 19.327 0.001 L4, L5 ((S8 to S10) -17.874 -17.872 0.002 L6 ((S11 to S12) 44.977 45.309 0.332 L7 (S13 to S14) 17.201 17.200 -0.001

Table 7 below shows the change of the focal length of the front lens group (L1 to L3) and rear lens group (L4 to L7) according to the temperature change.

Lens group Focal Length (20 ° C) Focal Length (50 ° C) Variation All groups (L1 to L3) 13.697 13.732 0.035 The posterior (L4 to L7) 18.127 18.185 0.058

As can be seen from Table 7, the focal distance variation amounts of the all-lens groups L1 to L3 and the total variation amounts of the focal length variation amounts of the rear lens groups L4 to L7 at room temperature (20 DEG C) and high temperature (50 DEG C) Is -0.023, which is relatively small. As can be seen from FIG. 2 and FIG. 3 MTF graph, the image is not largely distorted when the performance change design technique is applied.

As described above, the projection lens unit 100 according to the first embodiment of the present invention includes a total of seven lenses L1 to L7, and the plastic lenses L1, L2, L6 and the glass lenses L3, L4, L5, L7), it is possible to reduce the manufacturing cost and realize the light weight of the apparatus. In addition, by forming the first lens L1 to the seventh lens L7 with the focal length, shape and material as shown in Tables 1 and 2, it is possible to minimize problems caused by lens performance changes .

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. It will be understood that the invention may be varied and varied without departing from the scope of the invention.

100: projection lens unit
110: Screen
120: total internal reflection prism
130: cover glass
140: Image element

Claims (5)

A first lens to a seventh lens sequentially disposed in the direction of an image element in a screen on which an image is projected,
Wherein the first lens is a lens having negative power and at least one aspherical surface,
The second lens has a positive power and at least one surface is an aspherical surface,
The third lens is a glass lens having a positive power,
The fourth and fifth lenses are glass lenses having negative power and are mutually bonded,
The sixth lens is a lens having positive power and at least one aspherical surface,
And the seventh lens is a glass lens having a positive power. The method according to claim 1,
Wherein the first lens has a meniscus shape whose incident surface is convex in the screen direction,
The second lens has a concave meniscus shape in the screen direction,
The third lens has a convex shape in the screen direction,
Wherein the fourth and fifth lenses have a shape in which a lens having a concave shape on both sides and a lens having a convex shape on both sides are joined together,
The sixth lens has a shape in which the exit surface convex in the image element direction,
And the seventh lens has a convex shape on both sides thereof. The method according to claim 1,
And a diaphragm is provided between the third lens and the fourth lens. The method according to claim 1,
Wherein the second lens and the sixth lens have a focal length longer than that of the third lens and the seventh lens having a positive power. The method according to claim 1,
Wherein the first lens, the second lens, and the sixth lens are all of the same material, refractive index, and dispersion factor.

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