Abstract: An electronic view finder includes a display element that displays an image, and an eyepiece lens that is disposed on an eyepoint side of the display element and that is used for observing the image. The eyepiece lens consists of a first lens, a second lens having refractive power of a different sign from the first lens, and a third lens having positive refractive power in order from a display element side. Diopter is adjustable by moving at least one lens of the eyepiece lens. A television distortion of the image displayed by the display element varies depending on the diopter.

Abstract: An eyepiece lens consists of a first lens group including a cemented lens, a second lens group consisting of one negative lens, and a third lens group consisting of a plurality of positive lenses in order from an object side to an eye side. The eyepiece lens satisfies Conditional Expression: ?1.2<f/f2<?0.8 related to a focal length f of an entire system and a focal length f2 of the second lens group.

Abstract: An imaging lens set includes a plastic lens element. The plastic lens element having a central axis includes an object-side surface and an image-side surface, wherein the image-side surface is located opposite to the object-side surface. Each of the object-side surface and the image-side surface includes an effective optical section and a lens peripheral section in order from the central axis to an edge of the plastic lens element. The effective optical section is for being passed through by an imaging light and aspheric. The lens peripheral section surrounds the effective optical section. At least one of the lens peripheral section of the object-side surface and the lens peripheral section of the image-side surface includes at least one annular groove structure, wherein the annular groove structure includes a plurality of stepped surfaces and is not in contact with the optical elements.

Abstract: A lens shift mechanism of one embodiment of the present disclosure includes: a projection lens; a cylindrical housing that holds the projection lens; and an operating unit that moves the cylindrical housing in one axial direction perpendicular to an optical axis of the projection lens. The operating unit includes a pair of a main shaft and a countershaft extending in the one axial direction and disposed to be opposed to each other across the cylindrical housing, and a pair of elastic bodies provided respectively for the main shaft and the countershaft. The pair of elastic bodies are parallel to the one axial direction, and have biasing directions opposite to each other.

Abstract: This disclosure describes optical assemblies that generate output with substantial stability over a wide variation in temperature. The optical assemblies can be integrated, for example, as part of array generators arranged to project an array or other pattern of dots onto an object or projection plane.

Abstract: An objective optical system for endoscope includes a first group having a negative refractive power, an aperture stop, and a second group having a positive refractive power. The first group includes a negative meniscus lens having a convex surface directed toward the object side, and a positive lens having a convex surface directed toward the object side. The second group includes a predetermined lens, a positive cemented lens, and a positive single lens, or includes the predetermined lens, the positive single lens, and a positive cemented lens. The predetermined lens is a meniscus lens having a convex surface directed toward an image side. and an image-side lens, and the following conditional expressions (1?), (2), and (4?) are satisfied: 0.7<|R1/R2|<1.1??(1?), 0.6<|R1/FL|<3??(2), and 5?|Fc/FL|?7??(4?).

Abstract: A display apparatus includes a frame and an image display apparatus for a left eye 3 and an image display apparatus for a right eye which are attached to the frame. Each image display apparatus 30 includes an image forming apparatus 40 and an optical system 50 configured to guide an image from the image forming apparatus 40 to a pupil of an observer 10. The optical system 50 includes a reflecting mirror 51 and a lens group 52. The image forming apparatus 40 is curved. A normal NLL of the reflecting mirror 51 included in the optical system of the image display apparatus for a left eye and a normal NLR of the reflecting mirror 51 included in the optical system of the image display apparatus for a right eye intersect with each other in a space on an opposite side of the observer 10 with respect to the reflecting mirror 51.

Abstract: Provided is an eyepiece optical system including at least three lenses disposed in order from an observation object (Ob) along an optical axis. A final lens disposed closest to an eye point (EP) (corresponds to the third lens (L3) in FIG. 1) is fixed when adjusting the diopter, and the following conditional expressions (1) and (2) are satisfied: 2.2<|fe/fa<6.0??(1) 0.5<|Re2/fa|<5.0??(2) where fe denotes a focal length of the final lens, fa denotes a focal length of the total eyepiece optical system (EL), and Re2 denotes a radius of curvature of the eye point (EP) side lens surface of the final lens. When an optical surface is aspherical, a paraxial radius of curvature is used for calculation.

Abstract: In an observation device including a display device, paired ocular optical systems each include a resin lens having a shape defined by an arch and a chord, and provided with a molding gate in an outer peripheral portion of the arc shape, and is appropriately set in: a difference RC between the radius of the resin lens and the length of a line connecting the midpoint of the chord and the point on the optical axis; the diameter D of the resin lens; an angle ? between a direction connecting a midpoint of a long side of the display surface and the point on the optical axis and a direction connecting the molding gate and the point on the optical axis; and an acute angle ? between directions connecting the point on the optical axis and the respective molding gates of the resin lenses in the paired ocular optical systems.

Abstract: An ocular optical system includes a first lens element, a second lens element and a third lens element from an eye-side to a display-side in order along an optical axis. The first lens element, the second lens element and the third lens element each include an eye-side surface and a display-side surface. The eye-side surface of the first lens element has a concave portion in a vicinity of the optical axis. The display-side surface of the third lens element has a concave portion in a vicinity of a periphery of the third lens element. The ocular optical system satisfies 1?TTL/ER?10, wherein TTL is a distance from the eye-side surface of the first lens element to the display screen along the optical axis, and ER is a distance from a pupil of the observer to the eye-side surface of the first lens element along the optical axis.

Abstract: An ocular optical system adapted for an imaging ray of a display image being entered an observer's eye through the ocular optical system to form an image is provided. The ocular optical system includes a first lens and a second lens arranged in order from an eye-side to a display-side along an optical axis. Each of the first lens and the second lens has an eye-side surface and a display-side surface. A maximum distance between the display-side surface of the first lens and the eye-side surface of the second lens parallel to a direction of the optical axis is less than 5 millimeters, and the ocular optical system satisfies: 6?DLD/EPD?20. DLD is a diagonal length of the displayed image corresponding to a single pupil of the observer, and EPD represents an exit pupil diameter of the ocular optical system.

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.

Abstract: An optical imaging system for pickup, sequentially arranged from an object side to an image side, comprising: the first lens element with positive refractive power having a convex object-side surface, the second lens element with refractive power, the third lens element with refractive power, the fourth lens element with refractive power, the fifth lens element with refractive power; the sixth lens element made of plastic, the sixth lens with refractive power having a concave image-side surface with both being aspheric, and the image-side surface having at least one inflection point.

Abstract: A low-profile hybrid lens system, for imaging a scene onto an image plane, includes (a) a wafer-level lens with (i) a planar substrate having opposing first and second surfaces, (ii) a first lens element of a first material and disposed on the first surface, and (iii) a second lens element of a second material and disposed on the second surface; (b) a first cast lens; and (c) a second cast lens; wherein the wafer-level lens, the first cast lens, and the second cast lens are optically coupled in series. A method for manufacturing a low-profile hybrid lens system includes mounting a wafer-level lens, a first cast lens, and a second cast lens in a fixture to optically couple, in series, the wafer-level lens and the first and second cast lenses.

Abstract: An ocular optical system EL for observing an image displayed on an image display element Ob has, in order from the image display element Ob: a first lens L1 which is a positive lens; a second lens L2 which is a negative lens having a strong concave surface facing the image display element Ob; and a third lens L3 which is a positive lens having a strong convex surface facing the eye point EP in order to implement both high magnification and size reduction, wherein the first lens L1 is cemented and integrated with the image display element Ob, in order to reduce the size of the ocular optical system EL while ensuring tele-centricity and sufficiently wide luminous flux.

Abstract: An optical imaging system for pickup, sequentially arranged from an object side to an image side, comprising: the first lens element with positive refractive power having a convex object-side surface, the second lens element with refractive power, the third lens element with refractive power, the fourth lens element with refractive power, the fifth lens element with refractive power; the sixth lens element made of plastic, the sixth lens with refractive power having a concave image-side surface with both being aspheric, and the image-side surface having at least one inflection point.

Abstract: In order from the object side, a first lens having positive power with a convex observation-side surface, a second lens having negative power and a meniscus shape with a concave object-side surface, and a third lens having positive power with an observation-side surface having a smaller radius of curvature than that of an object-side surface are provided. The first, second and third lenses are single lenses. The conditional expressions (1): 0.9<f1/f3<5.0, (2): 10.0<TL<17.0 and (3): 15.0<f<25.0 are satisfied at the same time, where f1 is a focal length of the first lens, f3 is a focal length of the third lens, f is a focal length of the entire system, and TL is a distance along an optical axis from an object-side lens surface of the first lens to the observation-side lens surface of the third lens.

Abstract: There is provided an eyepiece lens which has a long length from an image display surface to a first lens, a high observation magnification, and a large apparent field of view. An eyepiece lens used to observe an image displayed on the image display surface includes a first lens with a positive refractive power, a second lens with a negative refractive power, and a third lens with a positive refractive power sequentially from the image display surface side to the observation side. The lens surface of the first lens on the image display surface side has a convex shape on the image display surface side. The lens surface of the second lens on the observation side has a concave shape on the observation side. The focal length of the eyepiece lens, the focal length of the lens surface, and the focal length of the lens surface are set appropriately.

Abstract: Provided are an ocular zoom optical system which has a wide apparent field of view even on a low power side and in which aberrations are favorably corrected while a sufficient eye relief is secured over the entire zoom range, and an optical instrument including the ocular zoom optical system. The ocular zoom optical system 3 includes, in order from the object side: a first lens group G1 having a negative refractive power; a second lens group G2 having a positive refractive power; and a third lens group G3 having a positive refractive power and at least one aspheric surface. An intermediate image I? is formed between the first lens group G1 and the second lens group G2. During zooming, the third lens group G3 is fixed on the optical axis, and the first lens group G1 and the second lens group G2 are moved in directions opposite to each other with the intermediate image I? interposed therebetween.

Abstract: An ocular optical system used to view an image displayed on an image display surface, which includes a first lens having positive refractive power, a second lens of meniscus shape having negative refractive power with its concave surface facing the image display surface side, and a third lens having positive refractive power arranged in this order from the image display surface side to a viewer side. A focal length of the first lens, a focal length of the second lens and a focal length of the entire system need to be determined suitably.

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.

Abstract: In order from the object side, a first lens having positive power with a convex observation-side surface, a second lens having negative power and a meniscus shape with a concave object-side surface, and a third lens having positive power with an observation-side surface having a smaller radius of curvature than that of an object-side surface are provided. The first, second and third lenses are single lenses. The conditional expressions (1): 0.9<f1/f3<5.0, (2): 10.0<TL<17.0 and (3): 15.0<f<25.0 are satisfied at the same time, where f1 is a focal length of the first lens, f3 is a focal length of the third lens, f is a focal length of the entire system, and TL is a distance along an optical axis from an object-side lens surface of the first lens to the observation-side lens surface of the third lens.

Abstract: A lens module comprises a barrel, a first lens, a first spacer ring, a second lens having an effective aperture A, a second spacer ring having an inner diameter B, and a third lens having an effective aperture C. The first lens, the first spacer ring, the second lens, the second spacer ring, the third lens and the infrared cut-off filter are coaxially assembled within the barrel, along an axial direction of the barrel in that order. The first spacer ring is sandwiched between the first lens and the second lens, the second spacer ring is sandwiched and located between the second lens and the third lens. The inner diameter B of the second spacer ring is smaller than the effective aperture C of the third lens and larger than the effective aperture A of the second lens, so as to satisfy the condition of C>B>A.

Abstract: An eyepiece for a night vision goggle (NVG) system includes a first lens element axially aligned with second and third lens elements. The first, second and third lens elements are sequentially positioned between a viewer and an object formed on a screen surface. The first lens element is formed as a doublet having two cemented elements. The second lens element includes a convex surface facing the doublet and a concave surface facing toward the third lens element. The third lens element includes a first convex surface facing the second lens element and a second convex surface facing the object. The second lens element is formed with two even aspheric surfaces comprised of only even coefficients and is substantially uniform in thickness.

Abstract: The eyepiece optical system of the invention is characterized by comprising, in order from the display plane side on which images being viewed are formed toward the exit side, a first lens component of positive refracting power, a reflecting member having only one reflective surface, a second lens component of negative refracting power and a third lens component of positive refracting power. The lens component here means a lens block that, in an optical path involved, contacts air at only two surfaces: the display-plane-side refractive surface and the exit-side refractive surface.

Abstract: An ocular lens used in an optical apparatus, such as a telescope optical system, includes the following lens groups sequentially arranged from the object side: a first lens group G1 having negative refracting power; a second lens group G2 including a lens component having a convex surface facing the viewer's eye side; and a third lens group G3 having positive refracting power. An object-side focal plane of the third lens group G3 is located between the second lens group G2 and the third lens group G3. The first lens group G1 includes the following lens components sequentially arranged from the object side: a first lens component G1A having a convex surface facing the object side, having negative refracting power, and having a meniscus shape; and a second lens component G1B having negative refracting power.

Abstract: An innovative anamorphic eyepiece is described, which uses a microlens array with complex surface features used in conjunction with a modified microdisplay to provide a high resolution image with a panoramic field of view. An optical system can be based on such an eyepiece with a microlens array and modified microdisplay that can provide a large, panoramic field of view to the user. The microdisplay is modified to increase the resolution in the horizontal axis.

Abstract: The invention provides a viewing optical system positioned between a viewing plane as a virtual plane and an eye point. The viewing optical system comprises, in order from the viewing plane side, a first lens group including a positive lens or a negative lens, a second lens group including a cemented lens in which at least one negative lens and at least one positive lens are cemented together, and a third lens group including a positive lens. Of lenses forming the first, second, and third lens groups, at least one lens surface is an aspheric surface.

Abstract: The eyepiece optical system of the invention is characterized by comprising, in order from the display plane side on which images being viewed are formed toward the exit side, a first lens component of positive refracting power, a reflecting member having only one reflective surface, a second lens component of negative refracting power and a third lens component of positive refracting power. The lens component here means a lens block that, in an optical path involved, contacts air at only two surfaces: the display-plane-side refractive surface and the exit-side refractive surface.

Abstract: A light source contains at least one light-emitting diode installed in the casing or on the base, and a lens system located along the light flux. The lens system comprises a plane-convex lens, a first plane-concave lens, and a composite lens 4 that are located along the light flux. The composite lens 4 is made up of a second and third plane-concave lenses. Flat surfaces of all of the lenses 4 are outflow faces for the light flux. Axes of symmetry of the second and third plane-concave lenses are normal to each other, whereas axes of symmetry of the first and second plane-concave lenses are parallel to each other. The first plane-concave lens is made movable along the light flux, and has a relocation drive therefor. A solenoid or an electric motor with a gear can be used as the drive. The technical result of the invention is believed to be the improvement of performance indicators, and the structure simplification.

Abstract: A fixed-focus lens disposed between a magnified side and a minified side. The fixed-focus lens has an optical axis and includes a reflective system and a refractive system. The reflective system includes a reflection mirror with a negative refractive power. The refractive system is disposed between the reflection mirror and the minified side and includes a first lens group and a second lens group. The first lens group has a positive refractive power. The second lens group is disposed between the first lens group and the minified side, and has a positive refractive power. The fixed-focus lens satisfies F/H>0.23, where F is an effective focal length and H is an image height.

Abstract: Optical qualities of a production lot of base material used in the fabrication of semi-finished lenses may be accurately determined by employing chipper plate samples produced from the base material in accordance with aspects of the present invention. In various implementations of the present invention, the chipper plates samples may be fabricated by subjecting base material to an extended cycle time and temperature profile using a mold having cavities of different thicknesses. The resulting chipper plates provide an improved indication of the color of semi-finished lenses molded from the production lot as well as an improved indication of resin stabilizer defects that may be utilized during a pelletizing process to control and enhance the quality of a production lot. Furthermore, the chipper plates may be provided by suppliers as samples of a production lot to enable customers to base purchasing decisions on a reliable and accurate measure of optical properties.

Abstract: Providing a sighting device having a simple structure, being easy to manufacture and free from parallax. A sighting device comprises, in order from a target object side, a positive meniscus lens having a convex surface facing the target object and a negative meniscus lens having a convex surface facing the target object, wherein the surface of said positive meniscus lens that faces away from said target object or the surface of said negative meniscus lens that faces toward said target object is adapted to constitute a semi-transparent reflection surface or a wavelength selective reflection surface, and a point source is provided at a focal point of a catadioptric optical system constituted by said semi-transparent reflection surface or said wavelength selective reflection surface and a refracting surface of the negative meniscus lens having with the convex surface facing said target object, the refracting surface facing away from said target object side.

Abstract: An eyepiece lens includes, in order from an image display surface side to an observer side, a positive first lens, a negative second lens, and a positive third lens. A surface on the image display surface side of the positive first lens has a refractive power stronger than a refractive power of an opposite surface thereof. The negative second lens has a meniscus shape, and a surface on the image display surface side of the negative second lens has a convex shape. Both surfaces of the positive third lens have a convex shape. In the eyepiece lens, during diopter adjustment, the first through the third lenses move along an optical axis. A focal length (f) of the entire eyepiece lens and a diagonal length (H) of the image display surface satisfy the following conditions: 0.45<H/f<0.70, and 21.0 (mm)<f<29.0 (mm).

Abstract: A finder optical system includes an image taking lens configured to form a photogenic subject image, an erecting image forming member configured to convert the photogenic subject image an erecting image, and an ocular lens configured to enable observation the erecting image of the photogenic subject image therethrough, wherein the ocular lens includes, in an order from the erecting image forming member to the observation side, a first lens group of negative refracting power, a second lens group of positive refracting power and configured to move in an optical axis direction to perform diopter adjustment, and a third lens group having at least one positive lens and at least one negative lens and having a positive or negative overall refracting power, and wherein, when a focal length of the whole system as the ocular lens is at ?1 diopter is denoted by f, a composite focal length of the negative lens or lenses of the third lens group is denoted by f3n, a conditional expression ?0.55<f3n/f<?0.

Abstract: The present invention provides a photographing optical lens assembly comprising, in order from an object side to an image side: a first lens element with positive refractive power having a convex object-side surface and a concave image-side surface; a second lens element with negative refractive power having a concave object-side surface and a convex image-side surface, the object-side and image-side surfaces thereof being aspheric; and a third lens element with negative refractive power having a convex object-side surface and a concave image-side surface, the object-side and image-side surfaces thereof being aspheric and at least one inflection point being formed on the image-side surface, wherein the lens assembly is further provided with a stop disposed between an object and the first lens element.

Abstract: An optical system for a digital light projection system is provided. The optical system comprises a plurality of LED arrays, wherein each LED array comprises a plurality of LEDs. The optical system also comprises an optical concentrator element positioned substantially adjacent to each of the LED arrays, wherein each concentrator element totally internally reflects light emitted from the plurality of LEDs within the corresponding LED array so as to provide substantially uniform light at an output surface of each concentrator element, and wherein the concentrator element has a complex conic shape.

Abstract: The invention relates to an eyepiece optical system that, albeit being of small size, works in favor of gaining an angle of field and optical performance, and an electronic view finder incorporating such an eyepiece optical system. Specifically, the invention is characterized by comprising, in order from an object side to an exit side thereof, a first lens group that is a single lens that has positive refracting power and is in a meniscus configuration concave on its object side, a second lens group that is a single lens that has negative refracting power and is in a meniscus configuration concave on its object side, and a third lens group that is a single lens that has positive refracting power, wherein an object-side concave lens surface in the first lens group is an aspheric surface, an object-side concave lens surface in the second lens group is an aspheric surface, and an exit-side lens surface in the third lens group is an aspheric surface.

Abstract: The invention relates to an eyepiece optical system that, albeit being of small size, works in favor of gaining an angle of field and optical performance, and an electronic view finder incorporating such an eyepiece optical system. Specifically, the invention is characterized by comprising, in order from an object side to an exit side thereof, a first lens group that is a single lens that has positive refracting power and is in a meniscus configuration concave on its object side, a second lens group that is a single lens that has negative refracting power and is in a meniscus configuration concave on its object side, and a third lens group that is a single lens that has positive refracting power, wherein an object-side concave lens surface in the first lens group is an aspheric surface, an object-side concave lens surface in the second lens group is an aspheric surface, and an exit-side lens surface in the third lens group is an aspheric surface.

Abstract: A diopter-adjustable eyepiece lens EL, comprising first through third lenses L1 through L3, satisfies the condition ?0.9<S1<?0.3, wherein first lens L1 shape factor S1 denotes a shape factor of the first lens L1, Re1 denotes the radius of curvature of a concave surface of the first lens L1 on an eyepoint EP side and Rs1 denotes the radius of curvature of a concave surface of the first lens L1 on the object side. The diopter adjustment satisfies also the condition 0.4<d2/?d<0.6 wherein d2 denotes an air gap along the optical axis between the first lens L1 and the second lens L2 when diopter adjustment is carried out so that diopter becomes maximum on the negative side, and Ed denotes an air gap along the optical axis between a concave surface of the first lens L1 on the eyepoint side and a concave surface of the third lens L3 on the object side when diopter adjustment is carried out so that diopter becomes maximum on the negative side.

Abstract: A zoom eyepiece lens system EL includes, in order from an eyepoint EP side: a first lens group G1 having positive refractive power; a second lens group G2 having positive refractive power; and a third lens group G3 having negative refractive power. Upon zooming from a low magnification end state to a high magnification end state, the second lens group G2 and the third lens group G3 move along an optical axis in opposite directions with each other. The second lens group G2 includes, in order from the eyepoint EP side, a first lens L3 having negative refractive power, a second lens L4 having positive refractive power, and a third lens L5 having positive refractive power. At least one aspherical surface is formed on the third lens L5.

Abstract: The invention provides a viewing optical system comprising: a screen on which an object image by a taking lens is formed, an image erection optical system for erecting the object image formed on the screen, and an eyepiece lens system of positive refracting power for guiding a light beam leaving the image erection optical system to the eyeball of a viewer, wherein: the image erection optical system comprises a plurality of reflecting surfaces, the eyepiece optical system comprises, in order from a screen side to an exit pupil side, a first lens element of negative refracting power, a second lens element convex on both the screen side and the exit pupil side, and a third lens element that is of negative refracting power and has a meniscus shape concave on the exit pupil side, and the third lens element satisfies the following condition (1): 0.13<DL3/fe<0.

Abstract: The invention relates to an eyepiece optical system that, albeit being of small size, works in favor of gaining an angle of field and optical performance, and an electronic view finder incorporating such an eyepiece optical system. Specifically, the invention is characterized by comprising, in order from an object side to an exit side thereof, a first lens group that is a single lens that has positive refracting power and is in a meniscus configuration concave on its object side, a second lens group that is a single lens that has negative refracting power and is in a meniscus configuration concave on its object side, and a third lens group that is a single lens that has positive refracting power, wherein an object-side concave lens surface in the first lens group is an aspheric surface, an object-side concave lens surface in the second lens group is an aspheric surface, and an exit-side lens surface in the third lens group is an aspheric surface.

Abstract: A zoom eyepiece lens system EL includes, in order from an eyepoint EP side: a first lens group G1 having positive refractive power; a second lens group G2 having positive refractive power; and a third lens group G3 having negative refractive power. Upon zooming from a low magnification end state to a high magnification end state, the second lens group G2 and the third lens group G3 move along an optical axis in opposite directions with each other. The second lens group G2 includes, in order from the eyepoint EP side, a first lens L3 having negative refractive power, a second lens L4 having positive refractive power, and a third lens L5 having positive refractive power. At least one aspherical surface is formed on the third lens L5.

Abstract: An eyepiece lens system for an electronic viewfinder, usable to be disposed on an optical axis between a reflective LCD of the viewfinder and a last optical surface of the viewfinder, the eyepiece lens system comprising: a first lens having a positive refractive index; a second lens having a negative refractive index; and a third lens having a positive refractive index, wherein the first lens, the second lens, and the third lens are disposed in this order from a side of the LCD to a side of the last optical surface, satisfying the conditions: 18 mm<f1<20 mm, ?18 mm<f2<?16 mm, 18 mm<f3<20 mm, 19 mm<f<21 mm, and 0?HH?/f<+0.13 where f1 is a focal length of the first lens, f2 is a focal length of the second lens, f3 is a focal length of the third lens, f is a combined focal length of the first to the third lenses, and HH? is distance in an optical axis direction between a rear principal point H and a front principal point H?.

Abstract: The invention provides a viewing optical system positioned between a viewing plane as a virtual plane and an eye point. The viewing optical system comprises, in order from the viewing plane side, a cemented lens in which at least one negative lens and at least one positive lens are cemented together and one positive lens, and satisfies the following condition (1). ?8<r3/f<?0.2??(1) Here r3 is the radius of curvature of the lens surface positioned in the cemented lens and nearest to the viewing plane side, and f is the focal length of the whole viewing optical system.

Abstract: The invention provides a viewing optical system positioned between a viewing plane as a virtual plane and an eye point. The viewing optical system comprises, in order from the viewing plane side, a first lens group including a positive lens or a negative lens, a second lens group including a cemented lens in which at least one negative lens and at least one positive lens are cemented together, and a third lens group including a positive lens. Of lenses forming the first, second, and third lens groups, at least one lens surface is an aspheric surface.

Abstract: A finder optical system includes an image taking lens configured to form a photogenic subject image, an erecting image forming member configured to convert the photogenic subject image an erecting image, and an ocular lens configured to enable observation the erecting image of the photogenic subject image therethrough, wherein the ocular lens includes, in an order from the erecting image forming member to the observation side, a first lens group of negative refracting power, a second lens group of positive refracting power and configured to move in an optical axis direction to perform diopter adjustment, and a third lens group having at least one positive lens and at least one negative lens and having a positive or negative overall refracting power, and wherein, when a focal length of the whole system as the ocular lens is at ?1 diopter is denoted by f, a composite focal length of the negative lens or lenses of the third lens group is denoted by f3n, a conditional expression ?0.55<f3n/f<?0.

Abstract: The invention provides a viewing optical system comprising: a screen on which an object image by a taking lens is formed, an image erection optical system for erecting the object image formed on the screen, and an eyepiece lens system of positive refracting power for guiding a light beam leaving the image erection optical system to the eyeball of a viewer, wherein: the image erection optical system comprises a plurality of reflecting surfaces, the eyepiece optical system comprises, in order from a screen side to an exit pupil side, a first lens element of negative refracting power, a second lens element convex on both the screen side and the exit pupil side, and a third lens element that is of negative refracting power and has a meniscus shape concave on the exit pupil side, and the third lens element satisfies the following condition (1): 0.13<DL3/fe<0.

Abstract: Provided is a dot sighting device with large caliber for binocular vision in which sighting can be performed rapidly and accurately by minimizing parallax. The dot sighting device is attached to and detached from a mount for a heavy machine gun. In addition, by using the dot sighting device with large caliber, a user can rapidly and accurately sight and fire a target by taking into consideration types and characteristics of the target and a distance to the target.