Optical system including molded optical element and method of manufacturing the optical system @PPR$4
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Abstract HQ^9[HN.
An optical system that includes a molded optical element having a non-uniform refractive index distribution due to molding and a method of manufacturing the optical system is disclosed. Data of the non-uniformity of the refractive index distribution associated with molding of the molded optical element is acquired and used in order to determine the form of an aspheric surface of the molded optical element for correcting aberrations caused by the non-uniformity of the refractive index distribution. This data may be acquired by measuring the refractive index distribution of an optical element molded based on initial design values that are based on assuming uniformity in the refractive index distribution of the molded optical element or it may be computed based on the form of the molded optical element. The optical element may include a concave optical surface and may be a lens element that includes an aspheric surface. (px*R~}
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Inventors: Tanaka, Takashi; (Kawagoe City, JP) ; Fujita, Hiroaki; (Kawaguchi City, JP) r]k*7PK
Correspondence Name and Address: ARNOLD INTERNATIONAL _m9~*
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Assignee Name and Adress: FUJINON CORPORATION `OKo=e~,
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Serial No.: 058367 d?:`n9`
Series Code: 11 p`>AnfG
Filed: February 16, 2005 YXF#c)#
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U.S. Current Class: 65/29.11; 65/DIG.13 \#PP8
U.S. Class at Publication: 065/029.11; 065/DIG.013 wL'oImE
Intern'l Class: C03B 011/16 W1xf2=z`)T
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Foreign Application Data \Y*!f|=of
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Date Code Application Number U?8i'5)
Mar 29, 2004 JP 2004-095269 \).Nag +
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Claims c#=&!FRe
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What is claimed is: T3=(`
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1. An optical system including a molded optical element having a non-uniform refractive index distribution due to molding, wherein: data of the non-uniformity of the refractive index distribution associated with molding of the molded optical element has been acquired and has been used in order to determine the form of an aspheric surface of the molded optical element for correcting aberrations caused by the non-uniformity of the refractive index distribution. Jf2e<?`
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2. The optical system including a molded optical element according to claim 1, wherein: data of the non-uniformity of the refractive index distribution associated with molding of the molded optical element has been acquired by measuring the refractive index distribution of an optical element molded based on initial design values that are based on assuming uniformity in the refractive index distribution of the molded optical element; and said data has been used to compute a corrected form of said aspheric surface by correcting said initial design values. y'^F,WTM
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3. The optical system including a molded optical element according to claim 1, wherein: the optical system is provided with a plurality of molded optical elements; one or more of the plurality of molded optical elements has a form that is likely to acquire much more non-uniformity of the refractive index distribution due to molding than one or more others of the plurality of molded optical elements; and data of the non-uniformity of the refractive index distribution associated with molding of a molded optical element has been acquired only for an optical element that has a form that is likely to acquire much more non-uniformity of the refractive index distribution due to molding, and said data has been used in order to determine the form of an aspheric surface of the molded optical element for correcting aberrations caused by the non-uniformity of the refractive index distribution. W+KF2(lB
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4. The optical system including a molded optical element according to claim 2, wherein: the optical system is provided with a plurality of molded optical elements; one or more of the plurality of molded optical elements has a form that is likely to acquire much more non-uniformity of the refractive index distribution due to molding than one or more others of the plurality of molded optical elements; and data of the non-uniformity of the refractive index distribution associated with molding of a molded optical element has been acquired only for an optical element that has a form that is likely to acquire much more non-uniformity of the refractive index distribution due to molding, and said data has been used in order to determine the form of an aspheric surface of the molded optical element for correcting aberrations caused by the non-uniformity of the refractive index distribution. V]Sgx00;
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5. The optical system including a molded optical element according to claim 1, wherein the molded optical element includes a concave optical surface. + a-D#^2;
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6. The optical system including a molded optical element according to claim 2, wherein the molded optical element includes a concave optical surface. q$F) !&
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7. The optical system including a molded optical element according to claim 3, wherein the molded optical element includes a concave optical surface. bV_j`:MD
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8. The optical system including a molded optical element according to claim 4, wherein the molded optical element includes a concave optical surface. F"I*-!o
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9. A method of manufacturing an optical system including a molded optical element comprising the following steps: acquiring data of the non-uniformity of the refractive index distribution due to molding of the molded optical element; computing aberrations due to the non-uniformity of the refractive index distribution based on the acquired data of the non-uniformity of the refractive index distribution; computing a corrected form of a molded optical surface of the molded optical element that corrects said aberrations due to the non-uniformity of the refractive index distribution; and molding the molded optical element with a mold having duplicating surfaces corresponding to the corrected form. J<rlz5':
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10. The method of manufacturing an optical system including a molded optical element according to claim 9, wherein the step of acquiring data of the non-uniformity of the refractive index distribution includes the following steps: making a first mold based on initial design values that assumes uniformity in the refractive index distribution of a molded optical element; molding a first molded optical element in the first mold; measuring the refractive index distribution of said first molded optical element; computing data of the non-uniformity of the refractive index distribution of said first molded optical element; and in said step of computing a corrected form of a molded optical surface, the corrected form is computed by correcting initial design values based on the computed data of the non-uniformity of the refractive index distribution of said first molded optical element. a~,Kz\Tt
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11. The method of manufacturing an optical system including a molded optical element according to claim 9, said optical system including a plurality of molded optical elements, said plurality of molded optical elements including at least one molded optical element having a form that is not likely to acquire non-uniformity of the refractive index distribution and at least one molded optical element having a form that is likely to acquire non-uniformity of the refractive index distribution, wherein said steps are performed only on an optical element having a form that is likely to acquire non-uniformity of the refractive index distribution. B;V5x/
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12. The method of manufacturing an optical system including a molded optical element according to claim 10, said optical system including a plurality of molded optical elements, said plurality of molded optical elements including at least one molded optical element having a form that is not likely to acquire non-uniformity of the refractive index distribution and at least one molded optical element having a form that is likely to acquire non-uniformity of the refractive index distribution, wherein said steps are performed only on an optical element having a form that is likely to acquire non-uniformity of the refractive index distribution. }B`Ku5 M
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13. The method of manufacturing an optical system including a molded optical element according to claim 9, wherein the molded optical element is a lens having a concave optical surface. $%Z3;:<Uf-
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14. The method of manufacturing an optical system including a molded optical element according to claim 10, wherein said first molded optical element is a lens having a concave optical surface. Y~}5axSPH
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15. The method of manufacturing an optical system including a molded optical element according to claim 11, wherein the molded optical element is a lens having a concave optical surface. ?IILt=)<
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16. The method of manufacturing an optical system including a molded optical element according to claim 12, wherein the molded optical element is a lens having a concave optical surface. T<P0T<
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17. The method of manufacturing an optical system including a molded optical element according to claim 9, wherein: the molded optical element is a lens element having at least one aspheric surface; and in the step of computing a corrected form of a molded optical surface, the corrected form includes the shape of said aspheric surface. LX\)8~dp
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18. The method of manufacturing an optical system including a molded optical element according to claim 10, wherein: said first molded optical element is a lens element having at least one aspheric surface; and in the step of computing a corrected form of a molded optical surface, the corrected form includes the shape of said aspheric surface. Fwb5u!_,
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19. The method of manufacturing an optical system including a molded optical element according to claim 11, wherein: said molded optical element is a lens element having at least one aspheric surface; and in the step of computing a corrected form of a molded optical surface, the corrected form includes the shape of said aspheric surface. `^x9(i/NE
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20. The method of manufacturing an optical system including a molded optical element according to claim 12, wherein: said molded optical element is a lens element having at least one aspheric surface; and in the step of computing a corrected form of a molded optical surface, the corrected form includes the shape of said aspheric surface. +pz}4M`
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Description P3!Atnv2
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FIELD OF THE INVENTION f0DK>L
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[0001] The present invention relates to an optical system including a molded optical element having a non-uniform refractive index distribution due to molding, and to a method of manufacturing the optical system. P#MK
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BACKGROUND OF THE INVENTION q_sEw~~@!
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[0002] Although it is common to manufacture optical elements made of plastic using a molding process, recently molding processes particularly known as glass molding methods have been used for molding lenses made of glass. For example, in imaging optical systems used for digital still cameras and video cameras, because aspheric lenses have recently come to be widely used, such molding processes designed for mass production have been widely used for producing aspheric lenses. Bd&`Xfebj
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[0003] Molding processes for forming glass lenses include a heating process to soften the glass used as the raw material, a pressing process to press mold the softened glass raw material within a mold, a cooling process to cool the molded glass after this press molding, and a removal process to remove the cooled molded product from the mold. As a result, the refractive index distribution inside the molded product, which should ideally be uniform, may become non-uniform. If an optical system is manufactured using this molded optical element of which the refractive index distribution has become non-uniform, aberrations occur due to the non-uniformity of the refractive index distribution, degrading the optical performance. R&*@@F-dx
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[0004] Japanese Laid-Open Patent Application 2000-249917 describes a method of correction which uses aspheric surfaces in order to correct aberrations caused by the non-uniformity of the refractive index distribution (non-uniformity of the refractive index distribution in the radial direction centered on the optical axis) inside a lens of a projection optical system or an illumination optical system used in an exposure device. However, Japanese Laid-Open Patent Application 2000-249917 states that polishing is used as part of the lens processing, and there is no description regarding the non-uniformity of the refractive index distribution due to molding. L5f$TLw
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[0005] Recently, image pickup elements such as CCDs (Charge Coupled Device) used in digital still cameras, including image pickup elements that include more than five million pixels have been developed, and the number of pixels will continue to increase. Therefore, higher and higher resolutions are demanded of imaging lenses used in digital still cameras and similar imaging devices. Consequently, non-uniformity of the refractive index distribution inside the lens due to molding is a problem that can no longer be ignored in determining optical performance. :^#vxdIC?
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[0006] There is no description in Japanese Laid-Open Patent Application 2000-249917 of the non-uniformity of the refractive index distribution due to molding, and it is believed that the non-uniformity of the refractive index distribution that is described therein does not consider the non-uniformity generated by the processing, but relates to the non-uniformity of the refractive index distribution of the lens material itself that is placed in the mold. Also, while an aspheric surface is used for correcting aberrations caused by the non-uniformity of the refractive index distribution, processing of the aspheric surface is performed by the further processing of a molded lens element. It is believed that this is performed, for example, by further polishing of the lens element. Because it is difficult to remold a molded lens element after molding, the method described in Japanese Laid-Open Patent Application 2000-249917 cannot be immediately adopted to an optical system having a molded optical element. Although it is believed that individually reprocessing each lens element which has been manufactured is effective for optical systems of exposure devices that are to be produced in small quantity and for which expensive production is acceptable, it is not suitable for optical systems for products that are to be mass produced, such as digital still cameras, because it is too labor intensive and too costly. D:9
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[0007] On the other hand, much more non-uniformity of the refractive index distribution due to molding is likely to occur for certain forms of molded lens elements, for example, especially in cases where the lens element has a concave optical surface where the difference in thickness between the center and the periphery is large. This is believed to be a result of the cooling process after press molding, wherein the speed of cooling and contraction is different in different parts of the lens element, and this difference generates internal distortions. Therefore, there are many cases where the non-uniformity of the refractive index distribution is similarly distributed for molded optical elements of the same form. Additionally, in manufacturing an optical system having a molded optical element, properties attributable to molding need to be considered. Note that methods of manufacturing optical elements that use a long time in the cooling process or in relieving non-uniformity of the refractive index distribution by an annealing process after molding are not preferred because they tend to increase production costs. nxfoWy
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BRIEF SUMMARY OF THE INVENTION <