Abstract: A lens assembly includes a first lens, a second lens, a third lens, and a fourth lens. The first lens is with positive refractive power and includes a concave surface facing an object side and a convex surface facing an image side. The second lens is with negative refractive power and includes a concave surface facing the object side. The third lens is with positive refractive power. The fourth lens is with refractive power and includes a concave surface facing the image side. The first lens, the second lens, the third lens, and the fourth lens are arranged in order from the object side to the image side along an optical axis. The lens assembly satisfies: TTL/f>1.2; wherein TTL is a total length of optical system of the lens assembly and f is an effective focal length of the lens assembly.

Abstract: A wide-angle lens assembly includes a first lens, a second lens, a third lens, a fourth lens, and a fifth lens, wherein the first lens, the second lens, the third lens, the fourth lens, and the fifth lens are arranged in order from an object side to an image side along an optical axis. The first lens is a meniscus lens with negative refractive power. The second lens is with positive refractive power and includes a convex surface facing the object side. The third lens is with positive refractive power and includes a convex surface facing the image side. The fourth lens is with positive refractive power and includes a convex surface facing the object side. The fifth lens is with negative refractive power and includes a concave surface facing the object side and a convex surface facing the image side.

Abstract: The present invention has, in order from an object: a first lens (L1) having negative refractive power; a second lens (L2), which is a positive meniscus lens having a convex surface facing the object; an aperture stop (S); and a third lens (L3) having a convex surface facing the object, and satisfies the following conditional expression (1): 6.6<|f12/f|??(1) where f12 denotes a composite focal length of the first lens (L1) and the second lens (L2), and f denotes a focal length of the optical system (WL).

Abstract: An imaging lens substantially consists of a first lens-group, a stop and a second lens-group in this order from an object-side. The first lens-group substantially consists of three or less lenses including at least one negative lens and a positive lens. The second lens-group substantially consists of a 21st lens-group and a 22nd lens-group in this order from the object-side. The 21st lens-group substantially consists of three or less lenses and has positive refractive-power. The 22nd lens-group substantially consists of two lenses of a negative lens and a positive lens in this order from the object-side. Predetermined conditional formulas about distance on an optical-axis from a most-object-side lens surface in an entire system to an image-plane, maximum image height, distance on the optical-axis from a most-object-side lens surface in the first lens-group to a most-image-side lens surface in the second lens-group, and focal-length of the entire system are satisfied.

Abstract: An imaging lens includes a first lens having negative refractive power; a second lens having positive refractive power; a third lens having positive refractive power; a stop; and a fourth lens having positive refractive power arranged in the order from an object side to an image plane side. The first lens has an image plane-side surface having a positive curvature radius. The second lens has an image plane-side surface having negative curvature radius. The third lens has an image plane-side surface having a negative curvature radius. The fourth lens has an object-side surface having a positive curvature radius and an image plane-side surface having a negative curvature radius. The first lens has a specific focal length and a specific Abbe's number to satisfy specific conditional expressions.

Abstract: A projector for projecting light onto a projection surface includes a first group (1) with a negative meniscus, a second group (2) with positive refractive power, a third group (3) with a single lens, a fourth group (4) with a lens with positive refractive power, and a field lens (5) with positive refractive power, such that the light passes through the projection objective from the fourth to the first group. In order to be provide a high image quality with a small number of optical components and the smallest dimensions, the projector is configured so the common focal width of the fourth group (4) and the field lens (5) is smaller than twice the image circle diameter (9) of the projection objective and the maximum free diameter (8) is smaller than the overall focal width, and in particular smaller than 0.8 times the overall focal width of the projection objective.

Abstract: Provided is an endoscope objective optical system 1 including, in order from an object side, a first lens 2 composed of a negative single lens, a second lens 3 composed of a positive single lens, an aperture stop 4, a third lens 5 composed of a positive single lens, and a fourth lens 6 composed of a positive combined lens, wherein the third lens 5 has a meniscus shape having a convex surface facing the image side. The endoscope objective optical system (1) satisfies the following conditions: 0.3<Df/f<1.15,??(1) n1<1.79,??(2) n2>n1,??(3) 0.6<IH/f<0.83,??(4) and |r1|?|r2|+d1>1.

Abstract: There is provided a zoom lens including, in order from an object side to an image side, a first lens group having negative refractive power, a second lens group having positive refractive power, a third lens group having positive refractive power, and a fourth lens group having positive refractive power. In zooming from a wide-angle end to a telescopic end, the first lens group moves to the object side in a manner that a distance toward the second lens group shortens, and a distance between the third lens group and the fourth lens group lengthens. The third lens group includes a single lens or a single cemented lens.

Abstract: Provided is an endoscope objective optical system 1 including, in order from an object side, a first lens 2 composed of a negative single lens, a second lens 3 composed of a positive single lens, an aperture stop 4, a third lens 5 composed of a positive single lens, and a fourth lens 6 composed of a positive combined lens, wherein the third lens 5 has a meniscus shape having a convex surface facing the image side. The endoscope objective optical system (1) satisfies the following conditions: (1) 0.3<Df/f<1.15, (2) n1<1.79, (3) n2>n1, (4) 0.6<IH/f<0.83, and (5) |r1|?|r2|+d1>1.

Abstract: An endoscope optical system, including a front group and a rear group arranged in this order from an object side such that an aperture stop is arranged between the front and rear groups, wherein the front group includes a negative lens and a positive lens arranged in this order from the object side, the rear group includes a positive lens and a cemented lens arranged in this order from the object side, and when f (unit: mm) denotes a focal length of an entire endoscope optical system, EX (unit: mm) denotes a distance (which takes a minus sign on the object side with respect to an image plane) from the image plane to an exit pupil, and f2 (unit: mm) denotes a focal length of the rear group, the endoscope optical system satisfies conditions: ?10<EX/f<?6??(1), and 1.15<f2/f<1.35??(2).

Abstract: An imaging lens includes a first lens having negative refractive power; a second lens having positive refractive power; a third lens having positive refractive power; a stop; and a fourth lens having positive refractive power arranged in the order from an object side to an image plane side. The first lens has an image plane-side surface having a positive curvature radius. The second lens has an image plane-side surface having negative curvature radius. The third lens has an image plane-side surface having a negative curvature radius. The fourth lens has an object-side surface having a positive curvature radius and an image plane-side surface having a negative curvature radius. The first lens has a specific focal length and a specific Abbe's number to satisfy specific conditional expressions.

Abstract: A projection lens consists of first and second les groups and a stop. The first lens group is formed of a negative lens. The second lens group is formed of three positive lenses and a negative lens. The stop is disposed between the first and second lens groups or in the second lens group. The first and second lens groups are arranged in order from a magnification side. The projection lens is telecentric on a reduction side. The projection lens is configured to satisfy the following conditional expressions (1) and (2): 1.0?f2h/f?5.0??(1) ?2.5?f1/f??0.8??(2) where f2h is a focal length of an aspheric lens of at least one of the first and second positive lenses of the second lens group, f is a focal length of the whole system, and f1 is a focal length of the first lens group.

Abstract: An image forming optical system of the present invention is characterized by comprising three groups having, in order from an object side to an image side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a positive refractive power, or four groups with one more lens group added to the image side, the first lens group comprises one lens component facing its concave surface toward the object side, the second lens group comprises a single lens having a positive refractive power and a cemented lens having a negative refractive power as a whole, and the third lens group comprises a lens component having a positive refractive power, wherein upon zooming from the wide-angle end toward the telephoto side, the amount of movement of the first lens group in the optical axis direction in an area, where the focal length of the entire image pickup optical system is 3.

Abstract: An objective optical system including an objective optical system having a field angle of 140° or larger and including a front group, an aperture stop, and a positive rear group arranged in that order from an object side. The front group has at least one aspherical surface and includes a negative first lens disposed closest to the object side and satisfying the following conditional expression: 0?r2/r1<0.24, 0.1<|g2/g1|<2.2 and ?1.8<f1/fl<?0.8, where r1 denotes the radius of curvature of the object side of the first lens, r2 denotes the radius of curvature of an image side of the first lens, g1 denotes the focal length of the front group, g2 denotes the focal length of the rear group, f1 denotes a focal length of the first lens, and fl denotes the focal length of the entire system.

Abstract: An imaging lens includes a first lens group having a first lens that directs a concave surface to an image plane side and is negative; a second lens group having a second lens that directs a concave surface to an object side and is positive; an aperture; a third lens group having a third lens that is positive; and a fourth lens group having a joined lens that is composed of a fourth lens that is positive and a fifth lens that is negative. In the configuration, when the whole lens system has a focal length f and a composite focal length of the first lens group to the third lens group is Fa, the imaging lens satisfies the following relation: 0.3<f/Fa<1.0.

Abstract: Provided is a zoom lens, including in order from a magnification conjugate side to a reduction conjugate side: a first lens unit having a negative refractive power; a second lens unit having a positive refractive power; a third lens unit having a positive refractive power; a fourth lens unit having a negative refractive power; a fifth lens unit having a negative refractive power; and a sixth lens unit having a positive refractive power. The first and sixth lens units do not move for zooming, while the second to fifth lens units move to the magnification conjugate side during zooming from a wide-angle end to a telephoto end. Each of the second and third lens units is composed of a single positive lens. Movement amounts of the second, third and fourth lens units during zooming from the wide-angle end to the telephoto end satisfy appropriate relationships.

Abstract: There is provided a lens system (10) that projects projected light onto a screen (6) and includes, in order from the screen (6) side thereof, a first lens (L11) that is a meniscus-type lens with negative refractive power and is convex on the screen (6) side; a second lens (L12), a third lens (L13) and a fourth lens (L14) that are meniscus-type lenses with positive refractive power and are concave on the screen (6) side. In addition, the effective diameter of a concave surface (S6) of the third lens (L13) is larger than the effective diameter of the concave surface (S3) of the second lens (L12), the effective diameter of the concave surface (S8) of the fourth lens (L14) is larger than the effective diameter of the concave surface (S6) of the third lens (L13), and part of the convex surface (S7) of the third lens (L13) and part of the concave surface (S8) of the fourth lens (L14) are located in a shared space along the optical axis.

Abstract: A single focus wide-angle lens module includes a fixed aperture diaphragm, a first, a second, a third and a forth lens arranged from an object side to an image side in the following sequence: the first lens, the fixed aperture diaphragm, the second lens, the third lens and the forth lens. The first lens has a negative refractive power, a concave surface toward the image side, and at least one aspheric surface. The second lens has a positive refractive power and a concave surface toward the object side, and said second lens is made of glass. Further, the third lens has a meniscus shape, a positive refractive power, a concave surface toward the object side, and at least one aspheric surface. The fourth lens has a positive refractive power, a convex surface toward the object side, and at least one aspheric surface.

Abstract: A zoom lens includes three groups that are a negative first group, a positive second group, and a positive third group in order from an object side. The first group includes a negative cemented lens formed by joining together, from the object side, a first lens formed by a negative single lens and a second lens formed by a positive single lens. The second group includes, from the object side, a third lens formed by a positive single lens and a cemented lens formed by joining together a fourth lens formed by a positive single lens and a fifth lens formed by a negative single lens. The third group includes a sixth lens formed by a positive single lens.

Abstract: An objective lens for an endoscope, including a negative front lens group and a positive rear lens group arranged such that an aperture stop is positioned therebetween, wherein the front lens group has at least a front-side negative lens and a front-side positive lens arranged in this order from an object side, and the rear lens group has at least a rear-side positive lens and a cemented lens arranged in this order from the object side, the cemented lens being configured by cementing together negative and positive lenses. The objective lens satisfies following conditions: ?4.5?fF/f??2.0 and 1.5?fRP/f?2.5, where fF (unit: mm) represent of the front lens group, f (unit: mm) represents a total focal length of the front lens group and the rear lens group, and fRP (unit: mm) represents a focal length of the rear-side positive lens.

Abstract: A zoom lens includes a first lens unit with a negative refractive power, a second lens unit with a positive refractive power, and a third lens unit with a positive refractive power in order from the object side to the image side. The first lens unit includes a negative lens and a positive lens. When the curvature radius of the object side surface and that of the image side surface of the negative lens are respectively defined as R11 and R12 and the curvature radius of the object side surface and that of the image side surface of the positive lens are respectively defined as R21 and R22, the following conditional expression is satisfied: ?5.6<(R12+R21)/(R12?R21)<?4.7 and 1.5<(R11+R22)/(R11?R22)<2.3.

Abstract: A display device comprises a light source consisting of three emission elements, each of which emits light of different wavelength regions corresponding to the respective colors of red, green and blue, and a display module consisting of a display part wherein each pixel has two types of color filters that transmit red and green light and green and blue light, respectively. One frame of video signals is split during display to become two subframes and it is possible to alternately emit for each subframe green light, which is transmitted through both color filters, and red and blue light, each of which is transmitted through only one filter.

Abstract: A zoom lens having an optical element for deflecting an optical path includes, in order from an object: a first lens group having positive refractive power; a second lens group having negative refractive power; a third lens group having positive refractive power; a fourth lens group having positive refractive power; and a fifth lens group having negative refractive power. The third lens group has a plurality of lenses, and the following conditional expressions 1.00<PL/fW<1.75 and 0.30<PL/fT<0.45 are satisfied, where PL denotes an optical path length of the optical element for deflecting the optical path, fW denotes a focal length of the zoom lens in a wide angle end state, and fT denotes a focal length of the zoom lens in a telephoto end state.

Abstract: An imaging lens comprises, in order from an object side: a first lens that has a negative refractive power and is convex toward the object side; a second lens that has a positive refractive power and is a meniscus lens convex toward the object side; a stop; a third lens that has a positive refractive power and is convex toward an image side; and a cemented lens that has a positive refractive power as a whole and is formed by cementing a fourth lens and a fifth lens, wherein assuming that an Abbe number of the second lens with respect to d-line is ?2, a distance on an optical axis from a vertex of a surface of the first lens facing toward the object side to an image plane of the imaging lens is L, a focal length of the imaging lens is f, and a back focus of the imaging lens is Bf, the following conditional expressions (1) to (3) are satisfied: ?2>30??(1), 2.5<L/f<4.0??(2), and 0.5<Bf/f<1.3??(3).

Abstract: An imaging lens comprises, in order from an object side: a first lens having a negative refractive power with a concave surface directed to an image side thereof; a second lens having a positive refractive power with a convex surface directed to an image side thereof and having an absolute value of a radius of curvature on the image side is equal to or smaller than that on an object side thereof; an aperture stop; a third lens which is a planoconvex lens having a plane on an object side thereof or a double-convex lens having on an object side thereof a surface of which an absolute value of a radius of curvature is larger than that on an image side thereof; and a compound lens of a fourth lens and a fifth lens, the compound lens having a positive composite power.

Abstract: A wide-angle lens includes, in order from the object side to the image side, a first lens element of negative refractive power, a second lens element of positive refractive power, a third lens element of positive refractive power and a cemented doublet element of positive refractive power consisting of a fourth lens element and a fifth lens element cemented together. The combined focal length of the second, third, fourth and fifth lens elements satisfies one specified condition, which allows the wide-angle lens to be effectively shortened and makes the construction thereof compact.

Abstract: An imaging lens comprises, in order from an object side: a first lens that has a negative refractive power and is convex toward the object side; a second lens that has a positive refractive power and is a meniscus lens convex toward the object side; a stop; a third lens that has a positive refractive power and is convex toward an image side; and a cemented lens that has a positive refractive power as a whole and is formed by cementing a fourth lens and a fifth lens, wherein assuming that an Abbe number of the second lens with respect to d-line is ?2, a distance on an optical axis from a vertex of a surface of the first lens facing toward the object side to an image plane of the imaging lens is L, a focal length of the imaging lens is f, and a back focus of the imaging lens is Bf, the following conditional expressions (1) to (3) are satisfied: ?2>30 ??(1), 2.5<L/f<4.0 ??(2), and 0.5<Bf/f<1.3 ??(3).

Abstract: To provide a high-brightness, small, low-cost optical apparatus which covers a wide-angle to super-wide-angle region and which reliably corrects various aberrations with a small number of lenses. At least one negative lens unit 1, a meniscus lens 2 that is convex on an object side, an aperture stop S, and a double-convex positive lens 3 are arranged in order from the object side. At least one of the lenses positioned on the object side of the aperture stop S and the positive lens 3 include respective aspherical surfaces.

Abstract: A zoom lens system includes a negative first lens group, a positive second lens group, a positive third lens group and positive fourth lens group, in this order from the object. The negative first lens group includes a reflection member, and the first lens group remains stationary when zooming is being performed from the short focal length extremity to the long focal length extremity. The zoom lens system satisfies the following conditions: 1.0<f2 /(fw×ft)1/2<1.5 ??(1) 1.2<|f1a|/fw<1.8 (f1a<0 ) ??(2) 2.0<f1b/ft<4.0 ??(3) wherein f2: the focal length of the positive second lens group; fw: the focal length of the entire zoom lens system at the short focal length extremity; ft: the focal length of the entire zoom lens system at the long focal length extremity; f1a: the combined focal length of an object-side lens element with respect to the reflection member; and f1b: the combined focal length of image-side lens elements with respect to the reflection member.

Abstract: There is provided a wide angle lens system configured to obtain excellent image forming performance even in a half field angle region of 40 degrees to 50 degrees. A wide angle lens system is constituted of a first lens having a negative refractive power, a light path bending member having no refractive power, a second lens having a positive refractive power, an aperture which adjusts a light amount, a first cemented lens formed by cementing a third lens having a positive refractive power and a fourth lens having a negative refractive power, a fifth lens having a positive refractive power, and an optically equivalent member which functions as a faceplate of an optical low-pass filter and a solid state imaging element.

Abstract: At least one exemplary embodiment is directed to a zoom lens includes first, second, and third lens units having negative, positive, and positive refractive powers, respectively, in order from an object side to an image side and performs zooming by moving each lens unit. The first lens unit includes a negative lens whose surface on the image side has a concave shape and a positive lens whose surface on the object side has a convex shape in order from the object side to the image side. At least one surface of the negative lens has an aspheric shape.

Abstract: A compact zoom lens system includes, from the object side to the image side, a negative first lens group (1), a positive second lens group (2), a positive third lens group (3) and a positive fourth lens group (4). The first lens group is stationary, and both the second and third lens groups are movable for effecting focal length change. The fourth lens group is also movable to compensate for image plane shift due to focal length change and thereby maintain the position of the image plane. The compact zoom lens system has a significantly reduced lens count and thus has an overall length of only 20 mm while achieving an approximately 3× zoom ratio. Sufficient back focal length is ensured even for such a short overall length. By employing aspheric lenses (10, 20, 301, 31, 41) for aberration correction, a high level of optical performance can be ensured.

Abstract: A four-group endoscope objective lens includes, in order from the object side, a first lens group of negative refractive power, a second lens group of positive refractive power, a diaphragm, and third and fourth lens groups of positive refractive power. The second and fourth lens groups each include a lens component that includes two lens elements. Some lens elements of the first, third, and fourth lens groups have particular shapes or refractive powers. The endoscope objective lens may include only six lens elements and satisfy certain specified conditions.

Abstract: An imaging lens includes, in order from the object side: a first lens component of negative refractive power with two aspheric surfaces including a concave surface near the optical axis on the image-side; a second lens component of positive refractive power with a convex surface on the object side; a third lens component having positive refractive power and including lens elements having positive and negative refractive powers; and a fourth lens component having an aspheric surface on the image side that is convex near the optical axis and is concave at the periphery. The imaging lens satisfies a specified condition to assure a sufficient back focus for insertion of additional optical elements, a sufficiently small imaging lens diameter, and favorable correction of aberrations. The imaging lens has a wide picture angle, consists of only 5 lens elements in the disclosed embodiments, and is particularly suited for a text imaging camera.

Abstract: A zoom lens system has four lens units, i.e., in order from an object side to an image side, a first lens unit of negative optical power, a second lens unit of positive optical power, a third lens unit of positive optical power, and a fourth lens unit of positive optical power. During zooming from a wide-angle end to a telephoto end, a space between the first lens unit and the second lens unit decreases, a space between the second lens unit and the third lens unit varies, and a space between the third lens unit and the fourth lens unit increases. Two negative lens elements constituting the first lens unit are made from high refractive index materials. Accordingly, a small-sized zoom lens system capable of obtaining a desired wide angle of field at the wide-angle end, a desired zoom ratio and high optical performance with a minimum number of lens elements can be provided.

Abstract: An image-taking apparatus has an image sensor for converting an optical image into an electrical signal, and a taking lens system for forming the optical image on the light-receiving surface of the image sensor. The most object-side surface of the taking lens system is an aspherical surface that has a positive optical power in a central portion thereof and a negative optical power in a peripheral portion thereof, and the following condition is fulfilled: ?90<Da<?20, where Da represents the distortion (%) observed at the maximum half view angle in the diagonal direction of the image sensor.

Abstract: An image-taking apparatus has an image sensor for converting an optical image into an electrical signal, and a taking lens system for forming the optical image on the light-receiving surface of the image sensor. The most object-side surface of the taking lens system is an aspherical surface that has a positive optical power in a central portion thereof and a negative optical power in a peripheral portion thereof, and the following condition is fulfilled: −90<Da<−20, where Da represents the distortion (%) observed at the maximum half view angle in the diagonal direction of the image sensor.

Abstract: A fixed focal length, wide-angle lens includes, in order from the object side, a negative first lens group that includes a plastic negative lens element, a positive second lens group that includes a plastic positive lens element, a positive third lens group that includes a positive lens element joined on its image side to another lens element, and a positive fourth lens group. In the preferred embodiments, all lens groups except the third lens group are single lens elements that each include an aspheric lens surface. Also, the wide-angle lens preferably satisfies specified conditions that, together with the use of plastic lenses, joined lens elements, and aspheric surfaces, enables a high performance, compact, wide-angle lens of relatively simple construction to be produced.

Abstract: A four-group endoscope objective lens includes, in order from the object side, a first lens group of negative refractive power, a second lens group of positive refractive power, a diaphragm, and third and fourth lens groups of positive refractive power. The second and fourth lens groups each include a lens component that includes two lens elements. Some lens elements of the first, third, and fourth lens groups have particular shapes or refractive powers. The endoscope objective lens may include only six lens elements and satisfy certain specified conditions.

Abstract: A taking lens system has, from the object side, a front lens unit including a first lens element and a second lens element, an aperture stop, and a rear lens unit including a third positive lens element, a fourth negative lens element, and a fifth positive lens element. In the taking lens system, the following condition is fulfilled: 0.3<F/F345<0.9 where F represents the focal length of the entire taking lens system; and F345 represents the composite focal length of the third to fifth lens elements.

Abstract: A wide-angle lens of fixed focal length formed of four lens groups of negative, positive, positive and positive refractive power, respectively, in order from the enlarging side is disclosed. The fourth lens group as well as one of the lens groups of among the first lens group, the second lens group and the third lens group are fixed in position. The other two lens groups of among the first lens group, the second lens group and the third lens group are moved during focusing, and specified conditions are satisfied in order to: (1) insure that the wide-angle lens is nearly telecentric on its reducing side, (2) maintain favorable correction of aberrations, (3) maintain a sufficiently large back focus for insertion of necessary components, and (4) enable the wide-angle lens to be compact. Preferably, the movement amount during a given focus adjustment of one of the two moveable lens groups is directly proportional to the movement amount of the other moveable lens group.

Abstract: A wide-angle lens of fixed focal length formed of four lens groups of negative, positive, positive and positive refractive power, respectively, in order from the enlarging side is disclosed. The fourth lens group as well as one of the lens groups of among the first lens group, the second lens group and the third lens group are fixed in position. The other two lens groups of among the first lens group, the second lens group and the third lens group are moved during focusing, and specified conditions are satisfied in order to: (1) insure that the wide-angle lens is nearly telecentric on its reducing side, (2) maintain favorable correction of aberrations, (3) maintain a sufficiently large back focus for insertion of necessary components, and (4) enable the wide-angle lens to be compact. Preferably, the movement amount during a given focus adjustment of one of the two moveable lens groups is directly proportional to the movement amount of the other moveable lens group.

Abstract: A taking lens system has, from the object side, a front lens unit, an aperture stop, and a rear lens unit. The front lens unit is composed of two lens elements that are, from the object side, a positive glass element and a negative plastic lens element. The rear lens unit has a positive plastic lens element disposed at the image-side end thereof. On the object side of this positive plastic lens element is disposed solely a lens element made of glass.

Abstract: A wide-angle zoom lens is disclosed having four lens groups of negative, positive, positive, and positive refractive power, in order from the object side. By satisfying prescribed conditions, the overall length as well as the outer diameter of the wide-angle zoom lens can be kept small, the number of lens elements required can be minimized so as to keep manufacturing costs low, yet a high-quality image is provided over the entire range of zoom. During zooming, the first and fourth lens groups remain in a fixed position while the second and third lens groups are moved along the optical axis. The first lens group G.sub.1 includes at least one negative lens element with a concave surface of strong curvature on the image side. The second lens group G.sub.2 has at least one biconvex lens. The third lens group G.sub.3 may consist of a single positive lens. The following conditions are satisfied:-2.5<f.sub.1 /f.sub.w <-1.52.0<f.sub.2 /f.sub.w <4.0wheref.sub.

Abstract: A wide-field eyepiece, formed of at least four lens groups and five lens elements, is disclosed which satisfies predetermined conditional expressions, so as to provide an eyepiece having an angle of view of at least 65 degrees with less than 6% distortion. The wide-field eyepiece is formed of, in order from the side of an image position 1 formed by an objective lens (not illustrated): a first lens group G.sub.1 of negative refractive power that includes a first lens element L.sub.1 having a concave surface on both sides, a second lens group G.sub.2 of positive refractive power that includes a second lens element L.sub.2 having a convex surface on the side of an observer's eye position, a third lens group G.sub.3 of positive refractive power wherein a lens element surface thereof has a convex surface on both sides and is cemented to a negative lens element having a concave surface on the side nearest the image 1 formed by the objective lens; and a fourth lens group G.sub.

Abstract: A photographic lens system composed of a negative first lens group, a diaphragm, and a positive second lens group, in this order from the object side. The second lens group has a positive meniscus lens element having a convex surface facing the image side, a cemented sub-lens group having a positive lens element and a negative lens element, and a positive single lens element, in this order from the object side, wherein the photographic lens system satisfies the following conditions:1.5<.vertline.f.sub.1 .vertline./f<5.0 (1)1.1<f.sub.2 /f<2.0 (2)0.6<D.sub.AS /f.sub.2 <1.2 (3)whereinf designates the focal length of the entire optical system;f.sub.1 designates the focal length of the first lens group;f.sub.2 designates the focal length of the second lens group;D.sub.AS designates the distance from the diaphragm to the first principal point of the second lens group.

Abstract: An objective lens system for an endoscope having an image transfer optical fiber bundle comprises from the object end a first lens of negative power having a concave image side surface, a second lens of positive power having a radius of curvature greater on an image side than on an object side, a third lens of positive power having a radius of curvature greater on the object side than on the image side, a doublet lens of positive power which comprises a forth lens element and a fifth lens element, and an aperture diaphragm interposed between the second and third lenses and satisfies the following relations:.vertline.d.multidot.f/f.sub.R.sup.2 .vertline.<0.11v2<45.0where f is the equivalent focal length of the entire objective lens system, f.sub.

Abstract: An objective lens for an endoscope includes a first lens group having one negative lens, a second lens group having at least one positive lens, and a third lens group including a positive lens. The objective lens satisfies the following relationship:.theta..sub.g,d <-2.223.times.10.sup.-3 .cndot..nu..sub.d +1.365wherein .theta..sub.g,d =(n.sub.g -n.sub.d)/(n.sub.F -n.sub.C), n.sub.g represents the refractive index of the glass material of the first lens group at the g-line, n.sub.d represents the refractive index of the glass material of the first lens group at the d-line, n.sub.F represents the refractive index of the glass material of the first lens group at the F-line, n.sub.C represents the refractive index of the glass material of the first lens group at the C-line, and .nu..sub.d represents the Abbe number of the glass material of the first lens group.

Abstract: An objective lens system for an endoscope comprises from the subject end to the image end a meniscus lens element of negative optical power having a concave image side surface, a plano-convex lens element of positive optical power having a convex subject side surface, an aperture element, a plano-convex lens element of positive optical power having a convex image side surface and a biconvex lens element of positive optical power.

Abstract: A wide field eyepiece with inside focus includes first and second lens groups G.sub.1 and G.sub.2. The first lens group G.sub.1 includes a negative cemented lens component and the second lens group G.sub.2 includes a positive lens component whose face of greater curvature is faced toward the eye point, a positive cemented lens component and a positive lens component whose face of greater curvature is faced toward the object. The first and second lens groups G.sub.1 and G.sub.2 are arranged in this order from the object side. The following formulae (1), (2) and (3) are satisfied,-4<f.sub.1 /f<-1.5 (1)1.3<f.sub.2 /f<2 (2)1<d.sub.12 /f<3.5 (3)wherein f represents the focal length of the overall lens system, f.sub.1 represents the focal length of the first lens group G.sub.1, f.sub.2 represents the focal length of the second lens group G.sub.2 and d.sub.12 represents the axial air separation between the first lens group G.sub.1 and the second lens group G.sub.2.