Abstract: The present disclosure relates to a technical field of optical lenses, and discloses a zoom lens. The zoom lens, being sequentially from an object side to an image side, includes a first lens having a negative refractive power, a second lens group having a positive refractive power, a fifth lens having a positive refractive power, and a sixth lens having a negative refractive power, when zooming, among the first lens, the second lens group, the fifth lens, and the sixth lens, a spacing in an optical axis direction of adjacent lenses or lens groups changes, the second lens group includes a second lens having a positive refractive power, a third lens having a negative refractive power, and a fourth lens having a negative positive power. During photographing, when an F number (FNO) of a wide-angle end is less than or equal to 2.0, the zoom lens becomes bright.

Abstract: A lens unit which is capable of efficiently combining a plurality of plastic lenses, which are small, easy to assemble, and inexpensive, and holding them with high accuracy without increasing the outer diameter of the lens unit. A first lens and a second lens are made of plastic, and the second lens is fitted and held on a rear side of the first lens in a direction of an optical axis. A gate for use in molding the second lens is disposed on a cut surface formed by cutting out a part of an outer periphery of the second lens, and a convex portion corresponding in shape to a remaining part of the gate after molding of the second lens is disposed in a space between an inner peripheral surface of a portion of the first lens in which the second lens is fitted and held and the cut surface.

Abstract: An imaging optical system comprises a first lens group composed of a negative single lens, a second lens group composed of a positive lens element and a negative lens element attached together, an aperture stop, a third lens group composed of a positive lens element and a negative lens element attached together, and a fourth lens group composed of a negative single lens, in this order from an object side. Expressions 0.37<hF/IH<0.5 and 0.37<hR/IH<0.5 are satisfied where “IH” denotes a maximum image height on an image plane, “hF” denotes an incident height of a principal ray, directed to a position of the maximum image height on the image plane, at its entrance into the first lens group, and “hR” denotes an exit height of the principal ray at its exit from the fourth lens group.

Abstract: An imaging lens substantially consists of a negative first lens group and a positive second lens group in this order from the object side. The first lens group substantially consists of only a first lens, which is one biconcave lens. The second lens group substantially consists of, in the following order from the object side: a cemented lens, which is formed by bonding a positive lens and a negative lens, in this order from the object side, and which has a positive refractive power as a whole; an aperture stop; a positive lens; and a negative lens. The imaging lens is configured to satisfy the conditional expressions (1a): 0<f23/f<2.5 and (2a): 0<f45/f<6 at the same time.

Abstract: An imaging lens provided with a negative first lens group and a positive second lens group arranged in order from the object side. The first lens group is composed of a first group first lens which is a negative single lens, and the second lens group is composed of a positive second group first lens, a positive second group second lens, and a negative second group third lens arranged in order from the object side. The second group first lens is a biconvex lens, the second group second lens is a biconvex lens, the second group third lens is a meniscus lens, an aperture stop is disposed between the second group first and second lenses, and the second group second and third lenses form a cemented lens. The imaging lens satisfies conditional expressions (1): ?0.89?f1/f<0 and (4): 0.3<dt1/f<0.8.

Abstract: A tube lens includes a singlet and a doublet with a long front tube length between a lens stop and the tube lens. The front tube length is 1.0 to 1.5 times an effective focal length of the tube lens. The front tube length provides sufficient space for an optical platform, a folding mirror, and a telescope. The telescope rotates between a 2× mode with front and back doublets and a 1× mode with a clear aperture. The field angle of the tube lens is 4.0 degrees. Specific glass types correct the lateral color in a system for digital pathology with a white LED and a color CCD sensor. The system for digital pathology further includes an objective lens with a numerical aperture at 0.50-0.55, and a Kohler illumination system with a numerical aperture of critical illumination at 0.75-0.85 times the numerical aperture of the objective lens.

Abstract: An imaging lens provided with a negative first lens group and a positive second lens group arranged in order from the object side. The first lens group is composed of a first group first lens which is a biconcave negative single lens, and the second lens group is composed of a positive second group first lens, an aperture stop, a positive second group second lens, and a negative second group third lens arranged in order from the object side, in which the second group second lens and the second group third lens are cemented together to form a cemented lens. When f1 and f2 are taken as the focal lengths of the first group first lens and the second group first lens respectively, the imaging lens satisfies a conditional expression (4a?): 0.62<|f1/f2|<0.82.

Abstract: A zoom lens system includes a negative first lens group, a positive second lens group, and a positive third lens group, in that order from the object side, wherein upon zooming from the short focal length extremity to the long focal length extremity, the distance between the first lens group and the second lens group decreases, and the distance between the second lens group and the third lens group increases. The second lens group includes a positive first sub-lens group and a negative second sub-lens group, in that order from the object side. The second sub-lens group is a focusing lens group which is moved along the optical axis direction during a focusing operation. The following condition (1) is satisfied: ?1.5<F2/F2B<?0.7??(1), wherein F2 designates the focal length of the second lens group, and F2B designates the focal length of the second sub-lens group.

Abstract: An imaging lens provided with a negative first lens group and a positive second lens group disposed in order from the object side. The first lens group is composed of a first group first lens which is a negative biconcave single lens, and the second lens group is composed of a positive second group first lens, an aperture stop, a positive second group second lens, and a negative second group third lens disposed in order from the object side. The second group second lens and second group third lens are cemented together to form a cemented lens. The imaging lens is configured to satisfy a conditional expression (3) 0.9<dt3/f<1.3, and further configured to satisfy conditional expression (1) 31<?d2<55 or (1?): 35<?d2 and a conditional expression (2): ?10<?d1??d2<25.

Abstract: A wide-angle photographic lens system enabling correction of distortion composed of four lenses, in which a first lens, an iris, a second lens, a third lens and a fourth lens sequentially arranged along an optical axis from an object, wherein the first lens has weak refractivity, the second lens has positive refractivity, the third lens has strong positive refractivity, and the fourth lens has negative refractivity, wherein the lens system satisfies relations, |f1/f|>4, f3/f<1.5, and te/tc<0.5, wherein f1 is a focal length of the first lens, f is a total focal length of all the lenses, f3 is a focal length of the third lens, to is a lens thickness on an effective diameter of a rear surface of the third lens, and tc is a center thickness of the third lens.

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: A wide-angle image capturing lens assembly includes four lens elements with refractive power, in order from an object side to an image side, a first lens element, a second lens element, a third lens element and a fourth lens element and each of the first through fourth lens elements is single and non-cemented. The first lens element with negative refractive power has a concave image-side surface. The second lens element with refractive power has a concave object-side surface and a convex image-side surface. The third lens element with positive refractive power has a convex image-side surface. The fourth to lens element with negative refractive power has a concave object-side surface and a convex image-side surface, wherein both of the object-side surface and the image-side surface of the fourth lens element are aspheric.

Abstract: An imaging lens includes: a first lens group; an aperture stop; and a second lens group having a positive power, in this order from an object side. The first lens group includes a first lens having a negative power and a second lens having a positive power. The imaging lens satisfies Conditional Formulae (1), (2), and (3): ?0.50<f/f1<0.20??(1) 0.08<d12/f<0.35??(2) 2.5<TL/Y<4.0??(3) wherein f is the focal length of the entire system, f1 is the focal length of the first lens group, d12 is a distance along an optical axis from the image side lens surface of the first lens to the object side lens surface of the second lens, TL is the distance along the optical axis from the most object side lens surface within the first lens group to an imaging surface Sim, and Y is a maximum image height, when focused on an object at infinity.

Abstract: An endoscope objective lens substantially consists of four lens groups consisting of, in order from the object side, a negative first lens group, a positive second lens group, a negative third lens group and a positive fourth lens group. During focusing from the farthest object to the nearest object, the first lens group is fixed, and the second lens group and the third lens group are moved along the optical axis. The third lens group includes a cemented lens that is formed by a positive lens and a negative lens cemented together in this order from the object side, and the cemented surface of the cemented lens is oriented such that the concave surface faces the object side.

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; and a fourth lens having negative refractive power, arranged from an object side to an image plane side. In the first lens, a curvature radius of an image-side surface is positive. In the second lens, curvature radii of the object-side surface and the image-side surface are both negative. In the third lens, a curvature radius of the object-side surface is positive and a curvature radius of the image-side surface is negative. When a whole lens system has a focal length f and the first lens has a focal length f1, the imaging lens satisfies the following conditional expression: ?3.0<f1/f<?1.

Abstract: The disclosed internal focusing large-aperture medium telephoto lens has as lens groups a positive first lens group, a positive second lens group, and a third lens group, in that order from the object side. When focusing on nearby objects, the first lens group and the third lens group have a fixed position relative to the image surface, and the second lens group displaces toward the object side. The second lens group has only one negative lens, and, in order from the object side, has at least a positive lens, a negative lens, and a positive lens. The following expression is fulfilled: ?0.5<(R1+R2)(R1?R2)<?0.1 (wherein, R1: radius of curvature of the object side surface of the negative lens in the second lens group; R2: radius of curvature of the image side surface of the negative lens in the second lens group).

Abstract: An imaging optical system comprises a first lens group composed of a negative single lens, a second lens group composed of a positive lens element and a negative lens element attached together, an aperture stop, a third lens group composed of a positive lens element and a negative lens element attached together, and a fourth lens group composed of a negative single lens, in this order from an object side. Expressions 0.37<hF/IH<0.5 and 0.37<hR/IH<0.5 are satisfied where “IH” denotes a maximum image height on an image plane, “hF” denotes an incident height of a principal ray, directed to a position of the maximum image height on the image plane, at its entrance into the first lens group, and “hR” denotes an exit height of the principal ray at its exit from the fourth lens group.

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: A zoom lens comprises, in order from an object side, a first lens group with a negative refracting power; a second lens group with a positive refracting power; a third lens group with a positive refracting power; and a fourth lens group with a refracting curved surface. Upon zooming from a wide-angle end to telephoto end, at least the first lens group, second lens group, and third lens group move, and a spacing between the respective lens groups are changed. The first lens group comprises; in order from the object side to an image side, a negative lens component with a negative refracting power and a positive lens component with a positive refracting power which are arranged on an optical axis with a predetermined spacing therebetween. The total number of the lens components in the first lens group is two.

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: 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 optical lens system comprises, in order from an object side to an image side: the first lens element with negative refractive power having a convex object-side surface and a concave image-side surface; the second lens element with positive refractive power; the third lens element with positive refractive power having the object-side surface and the image-side surface being aspheric; the fourth lens element with negative refractive power having a concave image-side surface and at least one aspheric surface. There are four lens elements with refractive power. Such arrangements can enable a larger field of view, reduce the volume of the system, and further obtain higher resolution for the optical lens system of the present invention.

Abstract: An image reading lens is provided and includes: in order from an object side of the image reading lens, a first lens of a negative lens having a meniscus shape directing a concave surface toward the object side thereof; a second lens having a biconvex shape; a stop; a third lens of a positive lens having a meniscus shape directing a convex surface toward an image side thereof; and a fourth lens of a negative lens having a meniscus shape directing a concave surface toward the object side thereof. The image reading lens satisfies the following conditional expressions: 2.4<f3/f<3.5 0.007<D2/f<0.028 where f represents a focal length of the image reading lens, f3 represent a focal length of the third lens, and D2 represents a spacing between an image-side surface of the first lens and an object-side surface of the second lens.

Abstract: A wide-angle lens system includes a negative first meniscus lens element, a positive second lens element, a positive third biconvex lens element, and a negative fourth meniscus lens element, in this order from the object; wherein said wide-angle lens system satisfies the following condition: 0.25<H/(p3+p4)<0.60 wherein H designates the distance between the second principal point of the positive third biconvex lens element and the first principal point of the negative fourth meniscus lens element, when the focal length of the entire wide-angle lens system is normalized to 1.0; p3 designates the refractive power of the positive third biconvex lens element when the focal length of the entire wide-angle lens system is normalized to 1.0; f3 designates the focal length of the positive third biconvex lens element when the focal length of the entire wide-angle lens system is normalized to 1.0, i.e.

Abstract: An exemplary wide-angle lens includes, in this order from the object side to the image side thereof, a first lens having negative refraction of power, a second lens having positive refraction of power, a third lens 30 having positive refraction of power, and a fourth lens having negative refraction of power, wherein the wide-angle lens satisfies the formulas: R1>R2>0, R1/R2>4.5, R8<R7<0, and 2<|R8/R7|<2.25, where R1 is the radius of curvature of the object-side surface of the first lens, R2 is the radius of curvature of the image-side surface of the first lens, R7 is the radius of curvature of the object-side surface of the fourth lens, and R8 is the radius of curvature of the image-side surface of the fourth lens.

Abstract: An image reading lens is provided and includes: in order from an object side of the image reading lens, a first negative lens having a meniscus shape; a second lens having a double-convex shape; an aperture stop; a third positive lens having a meniscus shape with a convex surface on an image side of the image reading lens; and a fourth negative lens having a meniscus shape with a concave surface on the object side.

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 large aperture wide-angle lens includes, arranged in order from the object side, a first lens group having negative refractive power, a second lens group having positive refractive power, a stop, a third lens group having positive refractive power, and a fourth lens group having negative refractive power. The first lens group is formed of one lens element, and the second lens group is formed of one or two lens elements. Each of the third and fourth lens groups includes at least one aspheric surface and each may be formed of two lens components that are lens elements. The wide-angle lens preferably satisfies specified conditions related to f-number, focal length and back focal length of the wide-angle lens, focal lengths of the first and fourth lens groups, maximum image height at the image surface, and indexes of refraction and Abbe numbers of particular lens elements.

Abstract: Optical assemblies for use in medical or other devices so as to image an object under examination onto an image sensor include a plurality of lens elements that can be retained in lens barrel. The lens elements and the lens barrel can be sealed with a compressible gasket. In one example, at least one lens element is made of an injection-moldable plastic and at least one lens element is made of a relatively dispersive optical glass. A lens barrel diameter or lens diameter can be selected to permit access to the object under examination with surgical or other tools. Aperture plates can be situated so as to reduce flare in the object image.

Abstract: An image scanning lens includes, arranged in order from the object side, a first lens element having negative refractive power and a meniscus shape with its convex surface on the object side, a biconvex second lens element and a biconcave third lens element that are cemented together, a stop, a biconcave fourth lens element and a biconvex fifth lens element that are cemented together, and a sixth lens element having negative refractive power and a meniscus shape with its convex surface on the image side. The image scanning lens may include only these six lens elements. The image scanning lens satisfies certain conditions related to the focal lengths of the first lens element, the second and third lens elements together, the entire image scanning lens, radii of curvature of various surfaces, and anomalous dispersion of various lens elements. An image reader with an image pickup device, such as a CCD, uses the image scanning lens.

Abstract: A taking lens system includes, in order from an object side thereof, a first lens group (negative refracting), a second lens group (positive refracting), an aperture stop and a third lens group (positive refracting). Focusing from an infinite distance to a finite distance is performed by setting the second lens group and the third lens group such that the position of the second lens group upon focusing on a finite distance is located on an image side of the taking lens system with respect to the position of the second lens group upon focusing on an infinite distance and the position of the third lens group upon focusing on a finite distance is located on an object side of the taking lens system with respect to the position of the third lens group upon focusing on an infinite distance, while the first lens group remains fixed.

Abstract: An image pickup unit which consists of an objective optical system and a solid-state image pickup device: the objective optical system being composed of a first negative lens unit comprising a first meniscus lens element having a convex surface on the object side and negative power, a second positive lens unit comprising a convex lens element and an aperture stop disposed between the first lens unit and the second lens unit and this image pickup unit having a small outside diameter, allowing a field angle to be changed little due to variations of parts and an assembling variation, and having a maximum field angle of 150° or larger.

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: An endoscope objective optical system includes a negative first lens group, a positive second lens group, a positive third lens group, and a negative fourth lens group, in this order from the object. The positive second lens group and the positive third lens group are arranged to move while the object distance is varied without changing the overall length from the first lens group to an imaging plane. Due to this arrangement, the focal length of the endoscope objective optical system is varied while maintaining an in-focus state.

Abstract: An adaptor lens is provided for attachment between a lens of a camera and a camera body, in order to provide the camera with adaptor lens attached, a smaller effective screen size than the camera without the adaptor lens attached. The adaptor lens is formed of, in order from the object side, a front lens group and a rear lens group. The front lens group is formed of, in sequential order from the object side, a negative lens element and at least one meniscus lens element with its concave surface on the object side. The rear lens group is formed of, in sequential order from the object side, a positive lens element with a convex surface on the object side, and a negative lens element. Various conditions are, preferably, satisfied in order to maintain favorable correction of axial chromatic aberration and lateral color.

Abstract: A zoom lens disclosed herein, having excellent optical performance within a full zoom range, is appropriate for use as a photographing lens for a lens-shutter camera, a video camera, and a digital still camera. The zoom lens includes at least four lens units from the object side, i.e., a first lens unit of negative refractive power, a second lens unit of positive refractive power, a third lens unit of positive refractive power, and a fourth lens unit of negative refractive power. A zooming operation is performed by axially moving the lens units so that the spacing between the first lens unit and the second lens unit becomes wider at the telephoto end than at the wide-angle end, the spacing between the second lens unit and the third lens unit becomes wider at the telephoto end than at the wide-angle end, and the spacing between the third lens unit and the fourth lens unit becomes narrower at the telephoto end than at the wide-angle end.

Abstract: Projection lens systems (13) for use in CRT projection televisions (10) are provided. From the screen side, the systems have three lens units (U1, U2, U3), the first two units (U1, U2) forming a retrofocus lens and the third unit (U3) being associated with the CRT during use and serving to correct field curvature. At its screen end, the first lens unit (U1) has a negative element (E1) which has a screen surface (S1) which is concave to the screen. The second lens unit (U2) has two positive subunits (US1, US2), the first subunit (US1) being a color correcting doublet composed of glass and the second subunit having a positive lens element (E2) at its screen end. The projection lens systems are fully color corrected, have f/#'s of 1.0 for an infinite conjugate, have half fields of view of at least 25°, and are economical to manufacture.

Abstract: A zoom lens system including a positive first lens group and a negative second lens group, in this order from the object, wherein zooming is performed by varying the distance between the first lens group and the second lens group. The positive first lens group includes a negative first sub-lens-group, a positive second sub-lens-group, and a positive third sub-lens-group, in this order from the object, wherein the zoom lens system satisfies the following condition: 0.7<fT/f1-2<1.5  (1) wherein fT designates the focal length of the entire zoom lens system at the long focal length extremity; and f1-2 designates the focal length of the positive second sub-lens-group in the first lens group.

Abstract: An objective lens including first, second, third, and fourth lens units in order from the object side. The first lens unit consists of a first lens of negative refractive power in the shape of a meniscus with a concave surface toward the image field side. The second lens unit consists of a second lens of positive refractive power. The third lens unit consists of a composite lens having joined together a third lens of negative refractive power with a concave surface toward the object side and a fourth lens of positive refractive power with a convex surface toward the image field side, the third lens unit having as a whole negative refractive power. The fourth lens unit consists of a fifth lens of positive refractive power. The objective lens has a predetermined condition for focal length.

Abstract: An image-forming lens having four lens elements of refractive power, in order from the object side, of: negative, positive, positive, and negative. By making the distance from image-side surface of the first element to the image-side surface of the second lens element to be greater than or equal to 0.3 f and less than or equal to 1.5 f, where f is the focal length of the image-forming lens, an image-forming lens having an F# of approximately 2.8 and a picture angle of about 60 degrees is obtained. A diaphragm may be positioned such that the distance along the optical axis from the diaphragm to the object side of the fourth lens is less than or equal to the focal length of the image-forming lens.

Abstract: A high-resolution objective for large-format photography has a pair of positive meniscuses flanking a stop area forming a lens aperture; and a respective negative cemented doublet on a side of each meniscus turned away from the stop area, the positive meniscuses being composed of glass having anomalous partial dispersion, a refractive index n.sub.e <1.63 and a dispersion or Abbe number .nu..sub.e >63, the cemented doublets each having a negative lens element and a positive lens element, the negative lens element being composed of a lead-free, arsenic-free and antimony-free glass with an anomalous dispersion, a refractive index n.sub.e >1.63 and an Abbe number .nu..sub.e <50.

Abstract: A relay optical system is disclosed that comprises, in axial order from the object side, first, second, third, and fourth lens groups having a negative, a positive, a positive, and a negative refractive power, respectively. An aperture stop is between the second and third lens groups. Relative to the aperture stop, the first lens group is symmetrical with the fourth lens group and the second lens group is substantially symmetrical with the third lens group. The relay optical system fulfills at least the conditions:-0.3<f/f1<-0.10.5<f/f2<1.1wherein f1 and f2 are the focal lengths of the first and second lens groups, respectively, and f is the overall focal length of the relay optical system.

Abstract: A variable focal length optical system includes, in succession from an object side, a first lens component, a second lens component, a third lens component, and a fourth lens component, wherein at least two air gaps of a first air gap between the first lens component and the second lens component, a second air gap between the second lens component and the third lens component, and a third air gap between the third lens component and the fourth lens component change when the focal length of the zoom lens is changed.

Abstract: An objective lens for an endoscope including a first lens group including one negative lens, a second lens group having a positive power, a third lens group having a negative power, and an aperture stop provided between the first lens group and the second lens group. The objective lens satisfies the relationships:-1.4<f.sub.1 /f<-0.5,0.55<f.sub.2 /f<0.85;andf.sub.3 /f<-2.0,Where f designates a focal length of the entire objective lens; f.sub.1 designates a focal length of the first lens group; f.sub.2 designates a focal length of the second lens group; and f.sub.3 designates a focal length of the third lens group.

Abstract: A wide-angle lens system includes a first, second, third and fourth lens components which are arranged in this order in a direction from an object side to an image surface side along an optical axis. A stop is provided between the second lens component and the third lens component. The first lens component comprises a double-concave lens, the first lens component having a first refracting power .phi.1 which is negative. The second lens component comprises a positive lens and a negative lens which are arranged in this order in the direction, the second lens component having a second refracting power .phi.2 which is positive. The third lens component comprises a negative lens, a positive lens and a negative lens which are arranged in this order in the direction, the third lens component having a third refracting power .phi.3 which is positive. The fourth lens component comprises a negative lens, the fourth lens component having a fourth refracting power .phi.4 which is negative.

Abstract: A scanning lens converges light deflected by a deflector onto a surface to be scanned, comprises a first lens having a negative power in both a main scanning direction and in an auxiliary scanning direction, a second lens having a positive power in both the main scanning direction and in the auxiliary scanning direction, a third lens having a positive power in both the main scanning direction and in the auxiliary scanning direction, and a fourth lens provided with a cylindrical surface having a negative power in the auxiliary scanning direction. The first, second, third and fourth lenses are arranged in this order from the deflector. The first, second and third lenses are formed so that curvature of field in the auxiliary scanning direction is reduced. A bow of an abaxial scanning line, which cannot be corrected by the first, second and third lenses, can be corrected by the cylindrical surface of the fourth lens.

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 f.theta. scanning lens arrangement, arranged from a polygonal mirror side to an imaging surface side, including a first, second, third, and fourth lens with having negative, positive, positive, and negative power, respectively, in the main scanning and subscanning directions is provided. The ratio of the focal length in the main scanning direction of the fourth lens versus the focal length in the main scanning direction of the entire f.theta. lens is selected to simultaneously minimize astigmatism, field curvature, and linearity error. Further, the ratio of the focal length in a subscanning direction of the first lens versus the focal length in the subscanning direction of the second lens is selected to minimize curving of scanning lines displaced from the optical axis.

Abstract: A single focal length lens system has a first negative lens element and a last negative lens element. The first negative lens element is disposed at an object side end of the lens system and the object side surface thereof is concave. The last negative lens element is disposed at an image side end of the lens system. The lens system fulfills the following condition: ##EQU1## wherein .phi.f represents the refractive power of the first negative lens element; and .phi.1 represents the refractive power of the last negative lens element.