# US 9,753,271 B2 · Eyepiece lens, viewfinder optical system and optical apparatus equipped with the same, and method for manufacturing eyepiece lens > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 9,753,271 B2 - Document ID: US9753271B2 - Status: Granted - Kind: B2 - Application number: 15/062,078 - Filed: 2016-03-05 - Published: 2016-06-30 - Granted: 2017-09-05 - Earliest claimed: 2011-12-28 - Assignees: Nikon Corporation - Applicants: Nikon Corporation - Inventors: Issei Tanaka; Hiroki Harada; Taku Matsuo - Web page: https://patentgrep.com/patent/US9753271B2 ## CPC - G02B 25/001: {Eyepieces} - G02B 1/11: Anti-reflection coatings - G02B 1/115: Multilayers - G02B 9/12: having three components only - G02B 13/18: with lenses having one or more non-spherical faces, e.g. for reducing geometrical aberration {(G02B13/002 takes precedence)} - G02B 23/14: Viewfinders (for photographic apparatus G03B13/02) - G02B 27/0018: {with means for preventing ghost images (anti-reflection coatings G02B1/11)} - G03B 13/06: with lenses with or without reflectors - G03B 13/08: with reflected image of frame - G02B 9/56: all components being simple lenses - G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS - G03B: APPARATUS OR ARRANGEMENTS FOR TAKING PHOTOGRAPHS OR FOR PROJECTING OR VIEWING THEM; APPARATUS OR ARRANGEMENTS EMPLOYING ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ACCESSORIES THEREFOR (optical parts of such apparatus G02B; photosensitive materials or processes for photographic purposes G03C; apparatus for processing exposed photographic materials G03D) ## Abstract An eyepiece lens (EL) used for a viewfinder optical system (VF) for viewing, using the eyepiece lens (EL), an image formed by an objective lens (OL), an image displayed by a display member, or an object, wherein an antireflection coating (101) is disposed on at least one surface among the optical surfaces constituting the eyepiece lens (EL), and the antireflection coating (101) includes at least one layer (101g) formed by a wet process. ## Claims ### Claim 1 An eyepiece lens comprising, in order from an object along an optical axis, a first lens group having negative refractive power, a second lens group having positive refractive power, and a third lens group having negative refractive power, wherein an antireflection coating is disposed on at least one optical surface of the eyepiece lens, and wherein the following conditional expression is satisfied: Nn(ABE)>1.870 where Nn (ABE) denotes an average value of refractive indexes, with respect to d-line, of all lenses having negative refractive power in the first and third lens groups. ### Claim 2 (depends on 1) The eyepiece lens according to claim 1, wherein at least one of the first lens group, the second lens group and the third lens group is movable along an optical axis to perform diopter adjustment. ### Claim 3 (depends on 1) The eyepiece lens according to claim 1, wherein the second lens group includes a biconvex lens component. ### Claim 4 (depends on 1) The eyepiece lens according to claim 1, wherein the third lens group includes a meniscus lens component having a convex surface facing the object. ### Claim 5 (depends on 1) The eyepiece lens according to claim 1, wherein the following conditional expression is satisfied: 30.0>ν(ABE) where ν (ABE) denotes an average value of Abbe numbers, with respect to d-line, of all lenses having negative refractive power in the first and third lens groups. ### Claim 6 (depends on 5) The eyepiece lens according to claim 5, wherein the following conditional expression is satisfied: ν2>40 where ν2 denotes an average value of Abbe numbers, with respect to d-line, of all lenses in the second lens group. ### Claim 7 (depends on 1) The eyepiece lens according to claim 1, wherein at least one optical surface of the second lens group is aspherical. ### Claim 8 (depends on 1) The eyepiece lens according to claim 1, wherein the following conditional expression is satisfied: S3>2.4 where S3 denotes a shape factor of a lens component located closest to an eye point in the third lens group, which is a value defined by (Ro3+Re3)/(Ro3−Re3), where Ro3 denotes a radius of curvature of an object side surface of the lens component, and Re3 denotes a radius of curvature of the eye point side surface of the lens component. ### Claim 9 (depends on 1) The eyepiece lens according to claim 1, wherein the second lens group is movable along an optical axis to perform diopter adjustment. ### Claim 10 (depends on 1) The eyepiece lens according to claim 1, wherein the antireflection coating is a multilayer film, and at least one of the layers satisfies the following conditional expression: nd≦1.30 where nd denotes a refractive index with respect to d-line. ### Claim 11 (depends on 10) The eyepiece lens according to claim 10, wherein an outermost surface layer constituting the multilayer film satisfies the conditional expression: nd≦1.30. ### Claim 12 (depends on 10) The eyepiece lens according to claim 10, wherein said one optical surface on which the antireflection coating is formed is a lens surface which is concave as viewed from an eye point. ### Claim 13 (depends on 12) The eyepiece lens according to claim 12, wherein the lens surface which is concave viewed from the eye point is a lens surface closest to the object among the optical surfaces of the first, second, and third lens groups. ### Claim 14 (depends on 12) The eyepiece lens according to claim 12, wherein the lens surface which is concave viewed from the eye point is a lens surface closest to an image plane among the optical surfaces of the first, second, and third lens groups. ### Claim 15 (depends on 10) The eyepiece lens according to claim 10, wherein said one optical surface on which the antireflection coating is formed is a lens surface which is concave as viewed from an object. ### Claim 16 (depends on 15) The eyepiece lens according to claim 15, wherein the concave lens surface on which the antireflection coating is formed is a lens surface closest to an image plane among the optical surfaces of the second lens group. ### Claim 17 (depends on 10) The eyepiece lens according to claim 10, wherein said one optical surface on which the antireflection coating is formed is an optical surface other than an optical surface closest to an eye point. ### Claim 18 (depends on 1) A viewfinder optical system for viewing an image formed by an objective lens, comprising the eyepiece lens according to claim 1. ### Claim 19 (depends on 18) An optical apparatus, comprising the viewfinder optical system according to claim 18. ### Claim 20 A method for manufacturing an eyepiece lens comprising: constructing the eyepiece lens to include, in order from an object along an optical axis, a first lens group having negative refractive power, a second lens group having positive refractive power, and a third lens group having negative refractive power; disposing an antireflection coating, which includes at least one layer formed by a wet process, on at least one optical surface of the eyepiece lens; and disposing a lens having said one optical surface on which the antireflection coating is formed, in a lens barrel, and wherein the eyepiece lens is constructed such that the following conditional expression is satisfied: Nn(ABE)>1.870 where Nn (ABE) denotes an average value of refractive indexes, with respect to d-line, of all lenses having negative refractive power in the first and third lens groups. ### Claim 21 (depends on 20) The method for manufacturing an eyepiece lens according to claim 20, wherein the following conditional expression is satisfied: nd≦1.30 where nd denotes a refractive index, with respect to d-line, of said one layer formed by the wet process. ### Claim 22 (depends on 20) The method for manufacturing an eyepiece lens according to claim 20, wherein said one optical surface on which the antireflection coating is formed is a lens surface which is concave as viewed from an eye point.