Abstract: A line generator according to the present invention includes a light source, a first lens group, and a second lens group. An optical axis is set to a position of a light beam which travels orthogonal to incidence surfaces of both the first and second lens groups and the first lens group is configured such that light beams from the light source are not collimated in a first direction in a plane orthogonal to the optical axis and are collimated or focused only in a second direction orthogonal to the first direction in the plane orthogonal to the optical axis and the second lens group is configured such that the light beams which have passed through the first group form a line.

Abstract: A zoom lens has a negative object side lens unit (or first lens unit G1), a positive image side lens unit (or third lens unit G3), a positive intermediate lens unit (or second lens unit G2), and an aperture stop. The distance between the object side lens unit and the intermediate lens unit is smaller at the telephoto end than at the wide angle end, the distance between the intermediate lens unit and the image side lens unit is larger at the telephoto end than at the wide angle end, the intermediate lens unit moves in such a way that it is located closer to the object side at the telephoto end than at the wide angle end, the image side lens unit moves in such a way that it is located closer to the image side at the telephoto end than at the wide angle end, the aperture stop moves integrally with the intermediate lens unit. The image side lens unit is composed of two lens component including a front lens component and a positive rear lens component arranged in the mentioned order from the object side.

Abstract: An image pickup lens includes a first lens having a positive meniscus shape convex toward an object side, a second lens disposed on an image side of the first lens and has a meniscus shape convex toward the image side, and an aperture stop disposed on the object side of the image side surface of the first lens, and satisfies conditional expressions given below, in which f is a focal length of the entire system, f1 is a focal length of the first lens, f2 is a focal length of the second lens, R5 is a paraxial radius of curvature of the object side surface of the second lens, and R6 is a paraxial radius of curvature of the image side surface of the second lens. 1.00<f1/f<1.50 1.1<f2/f1<3.9 2.0<(R5+R6)/(R5?R6)<5.

Abstract: It is to provide an imaging lens that can improve optical performance while reducing size and weight. An imaging lens includes, in order from an object side to an image surface side, a diaphragm, a first lens that is a biconvex lens, and a second lens that is a lens having a negative power whose concave surface faces the object side, wherein conditions expressed by the following expressions are to be satisfied: ?0.3?r1/r2<?0.1 and 0.8?f1/FL?0.98 (where, r1: center radius curvature of the object side face of the first lens, r2: center radius curvature of the image surface side face of the first lens, f1: focal distance of the first lens, and FL: focal distance of the entire lens system).

Abstract: Provided is a lens unit (3) wherein a plurality of wafer lenses (10, 20) are layered and covered by cover package (30). In each of wafer lenses (10, 20), resin molded sections (14, 16, 24, 26) are formed on a glass substrate (12, 22), and a lens section (14a, 16a, 24a, 26a) is formed on a part of the resin molded section (14, 16, 24, 26). A sloped section (14e) formed around the lens section (14a) arranged closest to the object side in the lens unit (3) and an end section (32a) forming an opening section of the cover package (30) are fitted with each other.

Abstract: An imaging lens system with two lenses is provided. The imaging lens system with two lenses, along an optical axis from an object side to an image side, includes an aperture stop; a first lens having positive refractive power and being a plano-convex lens with a convex surface on the image side; and a second lens having negative refractive power and being a meniscus lens with a concave surface on the object side and a convex surface on the image side.

Abstract: An imaging lens (LN) includes one or two lens blocks (BK), and an aperture stop (ape). The lens block (BK) includes a plane-parallel lens substrate (LS) and a lens (L) formed of different materials. In the imaging lens (LN), a first lens block (BK1) disposed at the most object-side exerts a positive optical power, and a conditional formula defined by the absolute difference between the index of refraction of a first lens substrate (LS1) and the index of refraction of a lens (L[LS1o]) contiguous with an object-side substrate surface of the first lens substrate (LS) is fulfilled.

Abstract: An optical system includes, in order from an enlargement conjugate side to a reduction conjugate side, a first lens unit having a negative refractive power and a second lens unit having a positive refractive power. In the optical system, an aperture stop is located closer to the reduction conjugate side than the first lens unit, one or more positive lenses are located closer to the reduction conjugate side than the aperture stop, and the one or more positive lenses include a P-th positive lens located closest to the reduction conjugate side. Various optical qualities may be appropriately set to effectively control chromatic aberration for the entire image plane, provide high optical performance, and achieve a wide angle of view.

Abstract: An image forming optical system has a positive lens group disposed closer to its object side than an aperture stop, and the values of ?gF1 and other constants of at least one lens LA included in the positive lens group fall within three ranges including a range bounded by the straight lines given by the equation ?gF1=?1×?d1+?gF1 (where ?1=?0.00566) into which the lowest and highest values in the range given by a first conditional expression are substituted respectively, a range bounded by the straight lines given by the equation nd1=a1×?d1+b1 (where a1=?0.0267) into which the lowest and highest values in the range given by a second conditional expression are substituted respectively, and a range defined by a third conditional expression.

Abstract: A first part has first, second and third inwardly-facing surface portions angularly spaced about an axis, and a second part has outwardly-facing fourth, fifth and sixth surface portions spaced angularly about the axis, a radial distance from the axis to each surface portion decreasing progressively in a given direction along the axis. Each of the fourth, fifth and sixth surface portions faces, is closely adjacent to, and is substantially congruent in shape with a respective one of the first, second and third surface portions. At least one of the first and second parts is an optical component.

Abstract: A compact wide-angle zoom lens and an image pickup device having the same. The zoom lens includes a first lens group having a negative refractive power and a second lens group having a positive refractive power in an order from an object side to an image side, performs zooming by varying a distance between the first and second lens groups, and performs focusing by using a first lens closest to the object side in the second lens group.

Abstract: An imaging lens (LN) includes one or two lens blocks (BK), and an aperture stop (ape). The lens block (BK) includes a plane-parallel lens substrate (LS) and a lens (L) formed of different materials. In the imaging lens (LN), a first lens block (BK1) disposed at the most object-side exerts a positive optical power, and a conditional formula defined by the absolute difference between the index of refraction of a first lens substrate (LS1) and the index of refraction of a lens (L[LS1o]) contiguous with an object-side substrate surface of the first lens substrate (LS) is fulfilled.

Abstract: An imaging optical system has, in order from the object side to the image side thereof, a front lens group, an aperture stop, and a rear lens group. A lens located closest to object side in said front lens group always remains fixed in position, with satisfaction of the following conditions (1) and (2): 1.15?fb/IH??1.7 ??(1) ?4.0?fn/f??1.3 ??(2) where f is a focal length of the whole imaging optical system, fn is a focal length of a first negative lens in said front lens group, fb is a back focus of the imaging optical system upon focusing on an object point at infinity, and IH? is a distance from an optical axis of a position where a chief ray from a maximum incident half angle of view (?) upon focusing on an object point at infinity is imaged at the imaging plane.

Abstract: An imaging lens includes a first lens group having a positive refractive power, an aperture stop, and a second lens group having a positive refractive power, which are disposed in order from an object. The first lens group has a first lens component having a negative refractive power and a second lens component having a positive refractive power, which are disposed in order from the object, and conditions expressed by the expressions 0.12<f/f1<0.47 and 0.016<D12/f<0.079 are satisfied, when f1 is a focal length of the first lens group, f is a focal length of the imaging lens, and D12 is an air distance between the first lens component and the second lens component of the first lens group.

Abstract: The present invention is an imaging lens of which optical performance does not deteriorate even in a high temperature environment, various aberrations are well corrected, optical length is short, and back focus is sufficiently secured, the imaging lens comprising a first diaphragm S1, a first junction type compound lens, a second diaphragm S2, and a second junction type compound lens, characterized in that the first diaphragm, the first junction type compound lens, the second diaphragm and the second junction type compound lens are arranged in this sequence from an object side to an image side. The first junction type compound lens comprises a first lens L1, a second lens L2 and a third lens L3, arranged in the sequence from the object side to the image side, and the second junction type compound lens comprises a fourth lens L4, a fifth lens L5 and a sixth lens L6, arranged in this sequence from the object side to the image side.

Abstract: A projection lens and a projection device using the same are provided. The projection device includes a projection lens and an optical element. The projection lens includes a first lens group and a second lens group from an image side sequentially. The first lens group has a negative refracting power, and the first lens group includes an aspherical lens surface. The second lens group has a positive refracting power. The first lens group has a first focal length f1, and the second lens group has a second focal length f2. The first focal length f1 and the second focal length f2 satisfy the following two conditions: 0.5<|f1/f2|<1.5, and ?35 mm<f1<?15 mm.

Abstract: An image forming lens includes: a first optical system positioned in an object side, a second optical system positioned in an image side, and an aperture stop interposed between the first optical system and the second optical system, wherein the first lens system includes a first F lens group which is positioned in the object side and has at least two negative lenses, and a first R lens group which is positioned in the aperture stop side and has at least one lens, wherein a distance between the first F lens group and the first R lens group is set to be largest, and wherein the second optical system includes a second F lens group in which, in the order from the aperture stop side, a first positive lens, a first negative lens, a second negative lens, and a second positive lens are arranged, and a second R lens group positioned in the aperture stop side and having at least one positive lens.

Abstract: An imaging optics capable of compensating for chromatic aberration is provided with a light shielding means in a surface peripheral area of a certain lens element in a lens system so as to block a light flux of a specified wavelength range, thereby eliminating chromatic aberration in halo of the light flux of the specified wavelength range when it passes the periphery of the lens system. Thus, the invention provides the imaging optics that, without an increase in the number of pieces of lens elements and without a use of an expensive specified low-dispersion glass material, in contrast with the prior art imaging optics of the same optical performances, well compensates for chromatic aberration, especially, in halo.

Abstract: An apochromatic lens with an aperture and exclusively refractive optical elements, comprising a plurality of lenses arranged in lens groups along an optical axis, wherein lenses of different materials are provided and wherein the lenses respectively comprise one of the following listed materials: calcium fluoride (CaF2), synthetic quartz (SiO2) or another radiation-resistant optical material.

Abstract: In an imaging lens, one compound lens and two single lenses are arranged in a lens barrel. On the light output side of the lens barrel, a filter is arranged with a distance from lens barrel. With a further distance from the filter, an imaging element is arranged. In the compound lens, a resin lens is bonded to a base member lens, having an output surface center of the resin lens displaced by a prescribed amount relative to an output surface center of the base member lens, so that a transmission decentration amount attributed to the base member lens, not including the resin lens, and the single lenses is cancelled by a transmission decentration amount by the resin lens when taken as a whole lens system. Thus, the imaging lens capable of suppressing reduction in resolving power due to transmission decentration of the lenses is obtained.

Abstract: An image pickup lens includes: a first lens block with a positive power and a second lens block. The first lens block includes a first lens substrate, a lens portion 1a with a positive power, formed on an object-side surface of the first lens substrate, and a lens portion 1b with a negative power, formed on an image-side surface of the first lens substrate. The object-side surface of the lens portion 1a is a convex surface, and an image-side surface of the lens portion 1b is a concave surface. The second lens block includes a second lens substrate, and a lens portion 2a with a negative power, formed on an object-side surface of the second lens substrate. The object-side surface of the lens portion 2a is a concave surface. The image pickup lens satisfies the predetermined conditional expressions.

Abstract: Disclosed are a projection lens that has a simple inner focus structure, an appropriate back focal length, telecentricity, a high optical performance, and a small size and can effectively correct, particularly, lateral chromatic aberration, and a projection display device. A projection lens includes a first lens group having a negative refractive power and a second lens group having a positive refractive power arranged in this order from a magnification side. A fifth lens arranged closest to a reduction side in the first lens group is moved along an optical axis to adjust focus, and at least two lenses are made of a material with anomalous dispersion capable of reducing chromatic aberration in a wide visible range.

Abstract: An image system adapted to a projection display apparatus includes a first lens group having a negative refractive power, a second lens group having a positive refractive power, an aspheric reflector, and a curved reflector. The second lens group includes an aspheric lens which is the nearest to the light valve in the second lens group. A material of the aspheric lens includes glass, the thermal-optical coefficient of the glass is between 1.0×10?6/K and 12.5×10?6/K, and the refractive index of the glass is between 1.482 and 1.847. The aspheric reflector is disposed front of the first lens group for reflecting the image beam passing through the first lens group and second lens group. The curved reflector is disposed above the first lens group for reflecting the image beam reflected by the aspheric reflector onto the screen. The image system has a good imaging quality.

Abstract: An objective optical system includes, in order from the object side, a first unit having two lenses with negative refracting power and positive refracting power, a stop, and a second unit with positive refracting power to satisfy the following condition: 3.0<fb/fL where fb is the back focus of the objective optical system in air and fL is the focal length of the entire objective optical system.

Abstract: An optical unit includes a first lens, a second lens, a diaphragm, a third lens, a fourth lens, and a fifth lens, which are arranged in the stated order from an object side to an image plane side. The second lens has a convex shape. The third lens has a meniscus shape. The fourth lens has a convex shape. The fifth lens has a negative power.

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: An optical lens system for taking image comprises, in order from an object side to an image side: a first lens element with positive refractive power having an aspheric convex object-side surface and an aspheric concave image-side surface; a second lens element with positive refractive power having an aspheric convex object-side surface and an aspheric concave image-side surface. Radii of curvature of the object-side surface of the first lens element, the object-side and image-side surfaces of the second lens element are R1, R3 and R4 respectively, focal lengths of the optical lens system for taking image, the first and second lens elements are f, f1, f2 respectively, an on-axis distance between the first and second lens elements is T12, a center thickness of the second lens element is CT2, they satisfy the relations: 0.76 mm?1<1/R1<2.0 mm?1; 0.4<R3/R4<1.15; 0.35<(f/f1)?(f/f2)<0.72; T12/CT2>1.0.

Abstract: It is to provide an imaging lens that can improve optical performance while reducing size and weight. An imaging lens includes, in order from an object side to an image surface side: a diaphragm 2, a first lens 3 having a positive power whose convex surface faces the object side, and a second lens 4 that is a meniscus lens having a negative power whose convex surface faces the object side, wherein a condition expressed by the following expression is to be satisfied: 0.4?r1/FL?0.55 (where, r1: center radius curvature of the object side face 3a of the first lens, and FL: focal distance of the entire lens system).

Abstract: Providing an optical system having excellent optical performance with sufficiently correcting spherical aberration and curvature of field, an imaging apparatus, and a method for forming an image by the optical system. The optical system includes a plurality of lens groups, at least one of the plurality of lens groups having an A lens that satisfies at least one of given conditional expressions.

Abstract: An imaging lens includes a first lens group having a positive refractive power, an aperture stop, and a second lens group having a positive refractive power, which are disposed in order from an object. The first lens group has a first lens component having a negative refractive power and a second lens component having a positive refractive power, which are disposed in order from the object, and conditions expressed by the expressions 0.12<f/f1<0.47 and 0.016<D12/f<0.079 are satisfied, when f1 is a focal length of the first lens group, f is a focal length of the imaging lens, and D12 is an air distance between the first lens component and the second lens component of the first lens group.

Abstract: A lens component of the present invention is made by cementing a lens LA and a lens LB having a refracting power smaller than a refracting power of the lens LA, and satisfies predetermined conditional expressions. Moreover, in an image forming optical system of the present invention which includes a lens group B having a negative refracting power, a lens group C having a positive refracting power and which moves only toward an object side at the time of zooming from a wide angle end to a telephoto end, and one or two more lens groups additionally, one of the lens components of the present invention is used in the lens group B.

Abstract: The present invention provides a wide-angle optical system constituted of, in order from the object side to the image side, front group 11, stop 12, and rear group 13. The front group 11 is constituted, in order from the object side to the image side, of first lens 111 having negative optical power, second lens 112 having negative optical power, and third lens 113 having positive optical power. The rear group 13 is constituted, in order from the object side to the image side, of fourth lens 131 having positive optical power, and fifth lens 132 having negative optical power. The opposite surface from the stop of each of the paired lenses 113 and 131 arranged at the both sides of the stop 12 is a convex surface.

Abstract: An image forming optical system according to the present invention is characterized in that, in an image forming optical system having a positive lens group, a negative lens group, and an aperture stop, the positive lens group is disposed at an object side of the aperture stop, the positive lens group has a cemented lens which is formed by cementing a plurality of lenses, in a rectangular coordinate system in which a horizontal axis is let to be Nd and a vertical axis is let to be ?d, when a straight line indicated by Nd=?×?d+? (where, ?=?0.017) is set, Nd and ?d of at least one lens forming the cemented lens is included in both of areas namely, an area which is determined by a line when a lower limit value is in a range of a following conditional expression (1a), and a line when an upper limit value is in a range of the following conditional expression (1a), and of an area determined by following conditional expressions (2a) and (3a). 1.45<?<2.15??(1a) 1.30<Nd<2.

Abstract: A five-lens image lens system is revealed. The five-lens image lens system includes a first lens group with a negative power and a second lens group with a positive power. Along an optical axis in order from an object plane to an image plane, the first lens group includes a negative first lens and a negative second lens while at least one of optical surfaces of the first lens and the second lens is an aspherical optical surface. The second lens group includes a positive third lens, a positive fourth lens, and a negative fifth lens from the object plane to the image plane while an image-side lens surface of the positive fourth lens is glued with an object-side lens surface of the negative fifth lens.

Abstract: A lens system comprising, in order from an object side: a first lens group G1; and a second lens group G2 having positive refractive power; the first lens group G1 including a sub-lens group GS11 having positive refractive power, and a sub-lens group GS12 having negative refractive power, the sub-lens group GS12 having negative refractive power including a meniscus lens having a convex surface facing the object side, given conditions being satisfied, thereby providing a lens system having high optical performance with excellently correcting various aberrations, and an optical apparatus equipped therewith.

Abstract: A lens assembly comprises a first lens and a second lens. The first lens includes a first central round portion and a first peripheral stepped portion surrounding the first central round portion. The first peripheral stepped portion comprises a downward-facing surface, a first supporting surface, and a first inclined surface interconnected. The second lens includes a second central round portion and a second peripheral stepped portion surrounding the second central round portion. The second peripheral stepped portion includes an upward-facing surface, a second inclined surface, a third surface, and a second supporting surface. The second lens is engaged on the first lens in a manner that the first supporting surface contacts the second supporting surface, the downward-facing surface is facing toward the upward-facing surface, the first inclined surface contacts the second inclined surface but a gap is defined between the first inclined surface and the third surface.

Abstract: Image capture lens modules and image capture systems are presented. An image capture lens module includes a first compound lens with a first lens element, a second lens element, and a third lens element arranged in sequence from an object side to an image side. A second compound lens includes a fourth lens element, a fourth lens element, and a fifth lens element arranged in sequence from an object side to an image side. A curvature radius of the first lens element is positive, a curvature radius of the third lens element is negative, a curvature radius of the fourth lens element is negative, and a curvature radius of the sixth lens element is negative. An abbe number of the first lens element exceeds 55 and an abbe number of the third lens element is less than 30.

Abstract: An imaging optical system, including a first lens group; an aperture stop; a second lens group having a positive power, the first lens group, the aperture stop and the second lens group being arranged from a side of an object sequentially, wherein the second lens group includes a second front lens group having a positive power and a second rear lens group having a positive power, the second front lens group and the second rear lens group being arranged sequentially from the object side, wherein, when focusing from an infinity-distance object to a short-distance object, the first lens group and the aperture stop are fixed, and the second front lens group and the second rear lens group are moved with a mutually different movement amount.

Abstract: A fixed-focus lens module includes an outer lens barrel, an inner lens, a first lens, and a second lens group. The outer lens barrel includes a first open end, a first cavity, and a second open end arranged in the order from the object side to the image side of the outer lens barrel. The inner lens barrel is received in the outer lens barrel adjacent to the first open end. The first lens is received in the inner lens barrel. The second lens group is received in the outer lens barrel adjacent to the second open end. An gap is defined between an outer wall of the inner lens barrel and an inner wall of the outer lens barrel at the first open end, and the center axis of the inner lens barrel is adjustable relative to the outer lens barrel for adjusting the alignment between the first lens and the second lens group.

Abstract: Providing a compact rear-focus optical system having excellent optical performance, an imaging apparatus, and a method for focusing the rear-focus optical system. The system includes, in order from an object, a first lens group G1 having positive refractive power, an aperture stop S, and a second lens group G2. At least a portion of the second lens group G2 is movable along an optical axis of the rear-focus optical system upon focusing. Given conditional expressions are satisfied.

Abstract: A wide-angle lens optical system, including, in a sequence from an object side, a first lens group having a positive or negative refractive power, a stop, and a second lens group having positive refractive power, wherein the first lens group comprises, in a sequence from the object side, a front group having negative refractive power and a rear group having positive refractive power, and the wide-angle lens optical system satisfies the following Inequalities: 1.0 < f II f < 1.45 0.6 ? ? f Ia f Ib ? < 1.5 where f denotes the overall focal distance of the lens optical system, fII denotes the focal distance of the second lens group, fIa denotes the focal distance of the front group of the first lens group, and fIb denotes the focal distance of the rear group of the first lens group.

Abstract: An optical system comprising two lens cells, each lens cell comprising multiple lens elements, to provide imaging over a very wide image distance and within a wide range of magnification by changing the distance between the two lens cells. An embodiment also provides scannable laser spectroscopic measurements within the field-of-view of the instrument.

Abstract: A high performance fixed focal length optical imaging system for example for a cine camera is operable to receive radiation from an object space and deliver the received radiation through the optical system so as to form an image at an image surface in an image space. The imaging system has the advantage of providing high relative illumination and high contrast at elevated spatial frequencies even when using a fast aperture.

Abstract: An illumination optics illuminates an object field of a projection exposure apparatus for microlithography. The illumination optics include a condenser group of optical components which guide a bundle of useful light. An objective group of bundle-guiding components is arranged downstream of the condenser group. At least one component of the condenser group and at least one component of the objective group are displaceable for compensation of deviations of the object field, which is in an actual illumination state, from a desired illumination state.

Abstract: An achromatic refractive beam shaping optical system that transforms the intensity distribution of a light beam, preferably provides transformation of a beam which intensity distribution described by Gaussian function to a beam of uniform intensity. The system consists of at least two lens groups, one of lens groups is made from at least two lenses having different characteristics, of spectral dispersion, thus achromatic for a certain spectral range optical design providing zero or negligible for practical applications wave aberration is realized. By choosing parameters of lens groups the system can be realized as a telescope of Galilean or Keplerian type, or as a collimator, or as an objective lens. To provide adjustment features one lens group of the system is movable along the optical axis.

Abstract: An image pickup lens includes: a first lens block with a positive power and a second lens block. The first lens block includes a first lens substrate, a lens portion 1a with a positive power, formed on an object-side surface of the first lens substrate, and a lens portion 1b with a negative power, formed on an image-side surface of the first lens substrate. The object-side surface of the lens portion 1a is a convex surface, and an image-side surface of the lens portion 1b is a concave surface. The second lens block includes a second lens substrate, and a lens portion 2a with a negative power, formed on an object-side surface of the second lens substrate. The object-side surface of the lens portion 2a is a concave surface. The image pickup lens satisfies the predetermined conditional expressions.

Abstract: An imaging optical system consists of, in order from its object side, a front lens group of negative refracting power, and a rear lens group of positive refracting power. A lens component is defined by a lens body having only two surfaces: an object side surface and an image side surface in contact with air on an optical axis. The front lens group comprises, in order from its object side, a first lens component concave on its image side and having negative refracting power, and a second lens component concave on its image side and having negative refracting power. The rear lens group comprises, in order from its object side, a third lens component convex on its object side and having positive refracting power, and a fourth lens component having positive refracting power. The sum of the total number of lens components in the front lens group and the total number of lens components in the rear lens group is 4.

Abstract: A zoom lens includes, in order from an object side to an image side, a first lens unit having a negative refractive power and a second lens unit having a positive refractive power. In the zoom lens, an interval between the first and second lens units becomes smaller at a telephoto end than at a wide-angle end during zooming. The first lens unit includes, in order from the object side to the image side, a first lens having a negative refractive power, a second lens having a negative refractive power, which is made of a plastic and has an aspheric lens surface, and a third lens unit having a positive refractive power. In the zoom lens, a refractive index and an Abbe number of the plastic (Nd, ?d), a focal length of the second lens (fn), and a focal length of the first lens unit (f1) are appropriately set.

Abstract: An imaging optical system, including a first lens group; an aperture stop; a second lens group having a positive power, the first lens group, the aperture stop and the second lens group being arranged from a side of an object sequentially, wherein the second lens group includes a second front lens group having a positive power and a second rear lens group having a positive power, the second front lens group and the second rear lens group being arranged sequentially from the object side, wherein, when focusing from an infinity-distance object to a short-distance object, the first lens group and the aperture stop are fixed, and the second front lens group and the second rear lens group are moved with a mutually different movement amount.

Abstract: An optical system includes a first optical element and a second optical element on at least one of an enlargement side and a reduction side relative to a point P at which a light axis and a paraxial chief ray intersect. Each of the first optical element and second optical element is composed of a solid material having a refractive light incident surface and a refractive light emergent surface. The optical system satisfies the following conditional expressions: ??gF1>0.0272, ??gF2<?0.0278, and f1×f2<0 where ??gF1 and ??gF2 denote anomalous partial dispersion values of the first and second optical elements for the g-line and F-line, respectively, and f1 and f2 denote focal lengths of the first and second optical elements, respectively, when the light incident surfaces and the light emergent surfaces of the first and second optical elements are in contact with air.