WO2008091073A1

WO2008091073A1 - The rectifying filter of image formation surface's brightness in lens using equipment

Info

Publication number: WO2008091073A1
Application number: PCT/KR2008/000263
Authority: WO
Inventors: Seung-Tae Jeong
Original assignee: Seung-Tae Jeong
Priority date: 2007-01-23
Filing date: 2008-01-16
Publication date: 2008-07-31
Also published as: KR20080069406A; KR100862013B1

Abstract

The present invention relates to a filter for rectifying the brightness of an image formation surface of an optical device using a lens and a method for rectifying the brightness of the image formation surface using the filter. The rectifying filter includes a concave lens which is made of a transparent material and has a concave front surface and a flat rear surface, and a convex lens which has the same refractive index as that of the concave lens, is semi-transparent in order to absorb light, has a flat front surface and a convex rear surface corresponding to the front surface of the concave lens, and is bonded to the concave lens in such a manner that the convex rear surface of the convex lens comes into contact with the concave front surface of the concave lens. The rectifying filter includes the concave lens and the convex lens which have the same refractive index, and the convex lens absorbs light and the thickness of the convex lens gradually decreases as it goes from the center thereof to the edge thereof. The rectifying filter is located in front of the image formation surface so as to prevent generation of a brightness variation on the image formation surface.

Description

THE RECTIFYING FILTER OF IMAGE FORMATION SURFACE S BRIGHTNESS IN LENS USING EQUIPMENT

Technical Field

[1] The present invention relates to a filter for rectifying the brightness of an image formation surface of an optical device using a lens and a method of rectifying the brightness of the image formation surface using the same, and more particularly, to a method of rectifying the brightness of an image formation surface corresponding to a component of an optical device having a lens using a rectifying filter that prevents generation of a variation in the brightness of the image formation surface. Background Art

[2] A conventional optical device having a lens, such as a portable digital camera or a fixed monitoring camera, is arranged in such a manner that an image of an object 1 passes through the lens 2 and is formed on an image formation surface 3a of an image- forming part 3, as shown in FIG. 1.

[3] The brightness of the edge of the image formation surface is lower than the brightness of the center of the image formation surface, which is referred to as vignette effect.

[4] That is, there occurs a variation in brightness such that the brightness becomes gradually increased as it goes toward the center of the image formation surface, and the brightness becomes gradually decreased as it goes toward the edge of the image formation surface.

[5] This brightness variation brings about various problems because it exists even when a picture of an object is captured.

[6] For example, a digital camera included in a book scanner or a business card scanner is configured to capture a picture of a book or a business card, and a character recognition unit is configured to automatically recognize characters included in the captured image.

[7] However, it is difficult to correctly recognize the characters included in the captured image when such a brightness variation occurs on an image formation surface of the digital camera.

[8] In order to solve this problem, Korean Patent Application No. 10-2005-0111961

(Laid-Open publication No. 10-2005-0118139) entitled "Optical system for monitoring camera using aspherical surface" and Korean Patent Application No. 10-2002-0019982 (Laid-Open publication No. 10-2003-0081649) entitled "CCD camera having image correcting function" have been proposed. [9] However, the optical system and the CCD camera are expensive, have a complicated structure and do not produce satisfactory effect. Disclosure of Invention

Technical Problem

[10] Accordingly, the present invention has been made to solve the above-mentioned problems occurring in the conventional art, and a primary object of the present invention is to provide an image formation surface brightness rectifying filter which is inexpensive, has a simple structure and prevents generation of a brightness variation on an image formation surface of an optical device using a lens and an image formation surface brightness rectifying method using the same. Technical Solution

[11] To accomplish the object of the present invention, there is provided a filter for rectifying the brightness of an image formation surface of an optical device using a lens, which includes a concave lens which is made of a transparent material and has a concave front surface and a flat rear surface.

[12] In addition, the rectifying filter includes a convex lens which has the same refractive index as that of the concave lens, is semi-transparent in order to absorb light, has a flat front surface and a convex rear surface corresponding to the front surface of the concave lens, and is bonded to the concave lens in such a manner that the convex rear surface of the convex lens comes into contact with the concave front surface of the concave lens.

[13] The rear surface of the concave lens is located in front of the image formation surface of the optical device using a lens so as to prevent generation of a brightness variation on the image formation surface.

Advantageous Effects

[14] The image formation surface brightness rectifying filter according to the present invention includes the concave lens and the convex lens which have the same refractive index. The convex lens absorbs light.

[15] The center of the convex lens is thickest and the thickness of the convex lens decreases toward the edge thereof in a curved- surface form, and thus generation of a brightness variation on the image formation surface can be prevented when the convex lens is located in front of an image formation surface of an image-forming part. Brief Description of the Drawings

[16] Further objects and advantages of the invention can be more fully understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

[17] FIG. 1 illustrates an image-forming structure of a conventional optical device using a lens; [18] FIG. 2(A) is a function graph of a brightness variation generating state for explaining the present invention; [19] FIG. 2(B) is a function graph of a state in which a brightness variation is not generated for explaining the present invention; [20] FIG. 3 illustrates setting of a filter for rectifying the brightness of an image formation surface of an optical device using a lens according to the present invention; [21] FIG. 4(A) is a cross-sectional view of a convex lens included in the filter for rectifying the brightness of an image formation surface of an optical device using a lens according to the present invention; [22] FIG. 4(B) is a cross-sectional view of a concave lens included in the filter for rectifying the brightness of an image formation surface of an optical device using a lens according to the present invention; [23] FIG. 4(C) is a cross-sectional view of a combined structure of the convex lens and the concave lens included in the filter for rectifying the brightness of an image formation surface of an optical device using a lens according to the present invention; [24] FIG. 5 illustrates a process of producing the filter for rectifying the brightness of an image formation surface of an optical device using a lens according to the present invention using an ultraviolet (UV) curable resin; and [25] FIG. 6 illustrates setting of the filter for rectifying the brightness of an image formation surface of an optical device using a lens according to the present invention in a semiconductor exposure system.

[26] <Explanation on reference numerals of main elements of the drawings>

[27] 1: Object 2: Lens

[28] 3: Image-forming part 3a: Image formation surface

[29] 4: Release agent 5: Ultraviolet lamp

[30] 6: Exposure lamp 7: Wafer

[31] 10: Concave lens 20: Convex lens

[32] 30: UV curable resin

[33] 100: Filter

Best Mode for Carrying Out the Invention

[34] The present invention will be explained with reference to the attached drawings.

[35] However, the attached drawings are merely exemplarily provided in order to explain the technical spirit of the present invention in more detail, and hence the technical spirit of the present invention is not limited to embodiments illustrated in the attached drawings. [36] As illustrated in FIG. 2(A), when the brightness of the center of an image formation surface according to vignette effect is " 1 " and a distance from the center is "r" if the brightness is decreased to "I(r)" a brightness variation is not generated only when the brightness is corrected as illustrated in FIG. 2(B). [37] Thus, when the transmissivity of a filter is T(r), "T(r) x I(r) = I(R )" that is, "T(r) =

I(R )/I(r)" must be satisfied. [38] For this reason, in the present invention, an image formation surface brightness rectifying filter 100 is located in front of an image formation surface of an optical device having a lens, as illustrated in FIG. 3, so as to prevent generation of a brightness variation on the image formation surface. [39] The image formation surface brightness rectifying filter 100 according to the present invention includes a concave lens 10 made of a transparent material and having a concave front surface and a flat rear surface as shown in FIG. 4. [40] In addition, the image formation surface brightness rectifying filter 100 includes a convex lens 20 which has the same refractive index as that of the concave lens 10 and is made of a semi-transparent material in order to absorb light. [41] The convex lens has a flat front surface and a convex rear surface corresponding to the concave front surface of the concave lens 10. [42] The concave lens 10 and the convex lens 20 are bonded to each other in such a manner that the convex rear surface of the convex lens 20 comes into contact with the concave front surface of the concave lens 10. [43] It is preferable that the degree of semi-transparency of the convex lens 20 corresponds to an optical density of 1 to 2. [44] The concave lens 10 and the convex lens 20 must have the same refractive index because a clear image is not formed if the concave lens 10 and the convex lens 20 have different refractive indexes. [45] For example, when the concave lens 10 uses a glass having a refractive index of 1.5 and the convex lens 20 uses a synthetic resin having a refractive index of 1.4, the concave lens 10 and the convex lens 20 obstruct formation of an image, and thus a clear image cannot be obtained. [46] In the above-described structure of the image formation surface brightness rectifying filter 100, the convex lens 20 is semi-transparent so as to absorb light. The convex lens 20 is thickest at the center thereof and the thickness of the convex lens 20 decreases gradually in a curved shape as it goes toward the edge thereof, and thus generation of a brightness variation on the image formation surface 3a of the optical device can be prevented. [47] If the light absorption coefficient of the convex lens 20 is "α" transmissivity at "r" corresponds to T( r ) e

[48] That is, the following equations will be satisfied:

[49]

„ -uJι(r) J( Ru )

U r ) = C =

HR )

[50] and

- \n (J(Ro) I( R) hi r) u

[51] The image formation surface brightness rectifying filter 100 according to the present invention can be fabricated using a known conventional lens manufacturing method, an injection molding method and a method using a UV curable resin. [52] A method of fabricating the image formation surface brightness rectifying filter 100 using the conventional lens manufacturing method will be described. [53] (1) Concave lens fabricating step

[54] The concave lens 10 is fabricated such that it is made of a transparent material and has a concave front surface and a flat rear surface. [55] (2) Convex lens fabricating step

[56] The convex lens 20 is fabricated such that it has the same refractive index as that of the concave lens 10, is made of a semi-transparent material in order to absorb light, and has a flat front surface and a convex rear surface corresponding to the concave front surface of the concave lens 10. [57] (3) Bonding step

[58] The concave lens 10 and the convex lens 20 are bonded to each other using a transparent optical adhesive in such a manner that the convex rear surface of the convex lens 20 comes into contact with the concave front surface of the concave lens

10.

[59] (4) Grinding step

[60] The bonded structure of the concave lens 10 and the concave lens 20 is grinded using a grinding process of the conventional lens manufacturing method. [61] (5) Polishing step

[62] The ground structure of the concave lens 10 and the convex lens 20 is polished through a polishing process of the conventional lens manufacturing method. [63] When the injection molding method is used, the concave lens 10 and the convex lens 20 are respectively formed separately through an injection molder, and then the concave lens 10 and the convex lens 20 are bonded to each other using a transparent optical adhesive.

[64] Even when the concave lens 10 and the convex lens 20 are fabricated by means of the injection molding method, the grinding process and the polishing process can also be carried out as in the conventional lens fabrication method.

[65] Referring to FIG. 5, the method using a UV curable resin locates a translucent UV curable resin 30 including uniformly mixed light-absorbing dyes on a flat plate on which a release agent 4 is coated, puts the concave lens 10 (fabricated through the injection molding method or the conventional lens manufacturing method) on the UV curable resin 30, and presses the concave lens 10 such that the UV curable resin 30 is filled in the concave portion of the concave lens 10.

[66] Then, the UV curable resin 30 is cured through a UV lamp 5, and then the cured

UV curable resin and the concave lens 10 are separated from the flat plate.

[67] In an optical device having a lens, CCD and CMOS type cameras have an image sensor as an image-forming part.

[68] In this case, the image formation surface brightness rectifying filter 100 is constructed in such a manner that the flat rear surface of the concave lens 10 is attached onto the image formation surface of the image sensor using a transparent optical adhesive.

[69] The image formation surface brightness rectifying filter 100 according to the present invention can be used in a semiconductor exposure system so as to simplify the structure of the semiconductor exposure system and remarkably reduce the manufacturing cost of the semiconductor exposure system.

[70] Specifically, the rear surface of the concave lens 10 of the image formation surface brightness rectifying filter 100 is located in front of a wafer 7 in the semiconductor exposure system having an exposure lens 6, as illustrated in FIG. 6, to thereby prevent generation of a brightness variation on the wafer 7 corresponding to an image formation surface. Industrial Applicability

[71] The filter for rectifying the brightness of an image formation surface of an optical device using a lens according to the present invention has a simple structure and is inexpensive, and thus the filter can be used for any optical device having a lens, such as a portable digital camera or a fixed monitoring camera.

[72] Furthermore, when the image formation surface brightness rectifying filter according to the present invention is applied to a digital camera which is included in a book scanner or a business card scanner and has a character recognition unit for automatically recognizing characters of a captured image, generation of a brightness variation is prevented so that the characters can be correctly recognized from the captured image.

Claims

[1] A filter for rectifying the brightness of an image formation surface of an optical device using a lens, comprising: a concave lens which is made of a transparent material and has a concave front surface and a flat rear surface; and a convex lens which has the same refractive index as that of the concave lens, is semi-transparent in order to absorb light, has a flat front surface and a convex rear surface corresponding to the front surface of the concave lens, and is bonded to the concave lens in such a manner that the convex rear surface of the convex lens comes into contact with the concave front surface of the concave lens, wherein the rear surface of the concave lens is located in front of the image formation surface of the optical device using a lens so as to prevent generation of a brightness variation on the image formation surface.

[2] A filter for rectifying the brightness of an image formation surface of an optical device using a lens, comprising: a concave lens which is made of a transparent material and has a concave front surface and a flat rear surface; and a convex lens which has the same refractive index as that of the concave lens, is semi-transparent in order to absorb light, has a flat front surface and a convex rear surface corresponding to the front surface of the concave lens, and is bonded to the concave lens in such a manner that the convex rear surface of the convex lens comes into contact with the concave front surface of the concave lens, wherein the rear surface of the concave lens is located in front of the a wafer of a semiconductor exposure system having an exposure lens so as to prevent generation of a brightness variation on the wafer corresponding to an image formation surface.

[3] The rectifying filter according to claim 1, wherein the front surface of the concave lens and the rear surface of the convex lens are bonded to each other using a transparent optical adhesive.

[4] The rectifying filter according to claim 1 or 3, wherein the rear surface of the concave lens is attached to an image formation surface of an image sensor using a transparent optical adhesive.

[5] A method for rectifying the brightness of an image formation surface of an optical device using a lens, wherein the rear surface of a concave lens included in a rectifying filter is located in front of the image formation surface of the optical device using a lens to rectify a brightness variation on the image formation surface, the rectifying filter comprising the concave lens which is made of a transparent material and has a concave front surface and a flat rear surface, and a convex lens which has the same refractive index as that of the concave lens, is semi-transparent in order to absorb light, has a flat front surface and a convex rear surface corresponding to the front surface of the concave lens, and is bonded to the concave lens in such a manner that the convex rear surface of the convex lens comes into contact with the concave front surface of the concave lens.

[6] The method according to claim 5, wherein the rectifying filter is manufactured through a concave lens fabrication step of fabricating the concave lens using a conventional lens manufacturing method, a convex lens fabrication step of fabricating the convex lens using the conventional lens manufacturing method, and a bonding step of bonding the rear surface of the convex lens to the front surface of the concave lens using a transparent optical adhesive.

[7] The method according to claim 5, wherein the rectifying filter is manufactured through a concave lens fabrication step of fabricating the concave lens using a conventional injection molding method, a convex lens fabrication step of fabricating the convex lens using the injection molding method, and a bonding step of bonding the rear surface of the convex lens to the front surface of the concave lens using a transparent optical adhesive.

[8] The method according to claim 5, wherein the rectifying filter is manufactured in such a manner that a semi-transparent UV curable resin including uniformly mixed light-absorbing dyes is placed on a flat plate on which a release agent is coated, the concave lens is put on the UV curable resin and pressed such that the UV curable resin is filled in the concave portion of the concave lens, the UV curable resin is cured through a UV lamp, and the concave lens and the cured UV curable resin are separated from the flat plate.