Abstract: Provided are an optical lens assembly and an electronic apparatus. The optical lens assembly includes a first lens having a positive refractive power, a second lens having a negative refractive power, a third lens having a positive refractive power, a fourth lens having a refractive power, and a moving lens group movable to be inserted in or removed from between the third lens and the fourth lens, wherein the first, second, third, and fourth lenses and the moving lens group are sequentially arranged from an object side to an image side. The moving lens group is moved between the third lens and the fourth lens for infrared (IR) photography.

Abstract: The present disclosure relates to the field of optical lenses and provides a camera optical lens. The camera optical lens includes, from an object side to an image side: a first lens; a second lens having a negative refractive power; a third lens having a positive refractive power; a fourth lens; a fifth lens; and a sixth lens. The camera optical lens satisfies following conditions: 1.50?f1/f?10.00; and ?20.00?R3/d3??5.00. The camera optical lens can achieve a high imaging performance while satisfying a design requirement for ultra-thin, wide-angle camera lenses with large apertures.

Abstract: An extender lens is removably inserted into a master lens, performs an increase in a focal length without changing an imaging position due to insertion, and consists of a positive first lens group and a negative second lens group in order from the object side. The first lens group consists of one or more positive lenses in order from the object side, and a three-lens cemented lens having three lenses of a positive lens, a negative lens, and a positive lens having cemented together in order from the object side. The following Conditional Expression (1) relating to an Abbe number ?1n of the negative lens of the three-lens cemented lens is satisfied: 26<?1n<40.

Abstract: A lens assembly includes sequentially from an object side to an image side along an optical axis a first lens, a second lens, a third lens, a fourth lens, a stop, a fifth lens, a sixth lens, a seventh lens and an eighth lens. The first lens is a meniscus lens with refractive power. The second lens is a meniscus lens with refractive power. The third lens is a biconcave lens with negative refractive power. The fourth lens is a biconvex lens with positive refractive power. The fifth lens is a biconvex lens with positive refractive power. The sixth lens is with positive refractive power. The seventh lens is with negative refractive power. The eighth lens is with positive refractive power. The sixth lens and the seventh lens are cemented together.

Abstract: An imaging lens, substantially consisting of six lenses, composed of a first lens having a positive refractive power and a meniscus shape with a convex surface on the object side, a second lens having a negative refractive power, a third lens having a positive refractive power, a fourth lens having a positive refractive power, a fifth lens having a negative refractive power and a biconcave shape, and a sixth lens having a negative refractive power, disposed in order from the object side.

Abstract: Provided is a zoom lens including a focus lens portion, a zoom portion, an aperture stop, and a relay portion that does not move for zooming but comprises a negative fourth-first unit, a fourth-second unit interchangeable for an optical path, a positive fourth-third unit, and a fourth-fourth unit insertable for the optical path for shifting a focal length range of an entire system to a long focal length side after removing the fourth-second unit from the optical path, and a distance on an optical axis between the aperture stop and a last lens surface of the fourth-fourth unit in a state of inserting the fourth-fourth unit in the optical path, a distance on the optical axis between a first lens surface and the last lens surface of the fourth-fourth unit, and an aperture diameter in an opened state of the aperture stop satisfy a predetermined conditions.

Abstract: A variable magnification optical system includes a relay lens group (a fifth lens group) substantially consisting of a relay front group and a relay rear group with a predetermined air space therebetween, and which is fixed during magnification change and has image formation action, and an extender lens group insertably and detachably arranged between the relay front group and the relay rear group, and which extends a focal length toward a telephoto side without changing an image formation position. The extender lens group substantially consists of a first lens group having positive refractive power and a second lens group having negative refractive power in this order from an object side. The second lens group is a cemented lens substantially consisting of a convex meniscus lens, a biconcave lens and a convex meniscus lens in this order from the object side.

Abstract: An object is to provide an endoscope objective lens in which the aberrations are less susceptible to manufacturing errors and in which the variation in field curvature caused by focusing is small. There is provided an endoscope objective lens including: in sequence from an object side, a front group having negative refractive power, an aperture stop, and a rear group having positive refractive power; and a focusing lens that has a negative refractive power and that can be inserted into an optical path between the front group and the rear group. The focusing lens is inserted into the optical path in a normal observation state and is retracted from the optical path in a short-distance observation state, in which the working distance is smaller than that in the normal observation state.

Abstract: Provided is a camera apparatus including a lens apparatus which is attachable thereto and detachable therefrom, the camera apparatus including: an optical system; and an optical element which is insertable to and removable from an optical path of the optical system, in which: the optical element includes a surface having positive refractive power; and the optical system includes a surface having negative refractive power.

Abstract: Provided is a zoom lens including a focus lens portion, a zoom portion, an aperture stop, and a relay portion that does not move for zooming but comprises a negative fourth-first unit, a fourth-second unit interchangeable for an optical path, a positive fourth-third unit, and a fourth-fourth unit inserteable for the optical path for shifting a focal length range of an entire system to a long focal length side after removing the fourth-second unit from the optical path, and a distance on an optical axis between the aperture stop and a last lens surface of the fourth-fourth unit in a state of inserting the fourth-fourth unit in the optical path, a distance on the optical axis between a first lens surface and the last lens surface of the fourth-fourth unit, and an aperture diameter in an opened state of the aperture stop satisfy a predetermined conditions.

Abstract: A lens barrel includes an image-pickup optical system that includes a main optical system and an extender optical system, an extender barrel configured to hold the extender optical system, a housing configured to house the extender barrel, a rotator configured to hold the extender barrel to rotatably support the extender barrel in the housing, to insert the extender optical system into the main optical system, and to retreats the extender optical system from the main optical system, and a retreat restraint. When the retreat restraint is in the first state, the extender optical system is retreated to a position which is not associated with formation of the optical image, but the extender optical system is undetachable from the rotator, and when the retreat restraint is in the second state, the extender optical system is detachable from the rotator.

Abstract: Provided is an endoscope objective optical system that allows close-up observation while ensuring sufficient image brightness. Provided is an endoscope objective optical system consisting of a front group, an aperture stop, and a back group disposed in order from an object side; and a meniscus lens that can be inserted in and removed from an optical path between the aperture stop and the front group or the back group, with a convex surface thereof facing the aperture stop side.

Abstract: An optical system (OL) includes a magnification conversion optical unit (EXT) configured to be insertable and removable at a position between an aperture stop (SP) and an image plane (IP) of the optical system in order to change a focal length of the optical system, a total lens length of the optical system is constant before and after insertion of the magnification conversion optical unit, and a length Lp on an optical axis from the aperture stop to the image plane of the optical system, and a length Le on the optical axis from a lens surface closest to an object side of the magnification conversion optical unit to the image plane when the magnification conversion optical unit is inserted are appropriately set.

Abstract: A lens barrel includes a fixed cylinder configured to hold a plurality of lens units that constitute a main optical system, an extender configured to be rotatably held by the fixed cylinder and disposed between the plurality of lens units, a first shaft configured to rotate the extender around a first axis that is parallel to an optical axis of the main optical system so that the extender is inserted into or retracted from an optical path of the main optical system, a second shaft configured to rotate around a second axis that is parallel to the optical axis so as to transmit a rotation to the first shaft, and an exterior member attached to the fixed cylinder, the second shaft is attached to the exterior member, the exterior member is attached to the fixed cylinder, and the rotation of the second shaft is transmitted to the first shaft.

Abstract: Provided is an endoscope objective optical system that allows close-up observation while ensuring sufficient image brightness. Provided is an endoscope objective optical system consisting of a front group, an aperture stop, and a back group disposed in order from an object side; and a meniscus lens that can be inserted in and removed from an optical path between the aperture stop and the front group or the back group, with a convex surface thereof facing the aperture stop side.

Abstract: A zoom lens includes, in order from an object side to an image side, a first lens unit having a positive refractive power, which does not move for zooming, a second lens unit having a negative refractive power, which moves during zooming, a third lens unit having a negative refractive power, which moves during zooming, an aperture stop, and a fourth lens unit having a positive refractive power, which does not move for zooming. The fourth lens unit includes a first lens sub-unit, a focal length conversion optical system configured to be inserted into or removed from an optical path, and a second lens sub-unit. A focal length of the second lens sub-unit, a distance from the aperture stop to a lens surface at the most object side of the second lens sub-unit, and an F-number of the entire zoom lens at a wide-angle end are appropriately set.

Abstract: A teleconverter lens system is attachable to or detachable from an object side of a main lens system and facilitates performing telephotographing. A photographing apparatus includes the teleconverter lens system. The teleconverter lens system includes: a first lens having a negative refractive power; a second lens having a positive refractive power; a third lens having a negative refractive power; and a fourth lens having a positive refractive power, wherein the first, second, third, and fourth lenses are sequentially arranged from an object side to an image side of the teleconverter lens system. The first and second lenses are cemented together, and the second lens has a meniscus shape in which a convex surface is formed on the object side of the second lens.

Abstract: A lens system and an image capturing device having the same include a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, a fourth lens group having a positive refractive power, and a fifth lens group being exchangeable with the third lens group.

Abstract: A zoom lens includes, in order from an object side to an image side, a first lens unit having a positive refractive power, which does not move for zooming, a second lens unit having a negative refractive power, which moves during zooming, a third lens unit having a negative refractive power, which moves during zooming, an aperture stop, and a fourth lens unit having a positive refractive power, which does not move for zooming. The fourth lens unit includes a first lens sub-unit, a focal length conversion optical system configured to be inserted into or removed from an optical path, and a second lens sub-unit. A focal length of the second lens sub-unit, a distance from the aperture stop to a lens surface at the most object side of the second lens sub-unit, and an F-number of the entire zoom lens at a wide-angle end are appropriately set.

Abstract: A zoom lens system including at least one lens group that is positioned to be movable along an optical axis of image light for photographing; and a movable frame including a plurality of selection lens groups, the movable frame being movable between a photographing position and a storage position, wherein the photographing position is a position in which one of the selection lens groups is selectively positioned on the optical axis, and the storage position is a position in which all of the selection lens groups are outside the optical axis, and the movable frame including a storage portion that houses at least a portion of the at least one lens group when the movable frame is moved to the storage position.

Abstract: A lens system and an image capturing device having the same include a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, a fourth lens group having a positive refractive power, and a fifth lens group being exchangeable with the third lens group.

Abstract: A zoom lens system having a high zoom ratio and excellently correcting various aberrations over an entire zoom range between a wide angle end and a telephoto end to obtain high optical performance in the entire zoom range, includes, in order from an object side to an image side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit, and a fourth lens unit. The fourth lens unit includes a front subunit and a rear subunit, the rear subunit being constituted by two negative lenses and at least three positive lenses. The rear subunit includes a first rear-subunit and a second rear-subunit. Each of the first rear-subunit and the second rear-subunit includes a negative lens and at least one positive lens. Lens materials are suitably set for the first rear-subunit and the rear second-subunit.

Abstract: The invention relates to an optical system for the projection of digital image data comprising a fixed focal length lens and a pivotable focal length extender. The principal field of application of the invention is digital cinema projection, usually employing the wide-screen format 1.9:1 or the Cinemascope format 2.37:1 (width:height). For format changeover during projection, two different fixed focal lengths are realized by the insertion or removal of the focal length extender (1755) into the lens. The projection lens according to the invention has more favorable optical properties than the conventional zoom lenses, such as a minimal chromatic transverse aberration, high telecentricity, very small distortions and a small volume and weight.

Abstract: A multi-magnification viewing and aiming scope includes a first imaging group including an objective lens lying on the optical path and an eyepiece lens lying on the optical path. The first imaging group forms a first image having a first magnification on the optical path at an image location. A second imaging lens group may be controllably inserted into the optical path between at least some elements of the objective lens and the eyepiece lens. Upon insertion of the second imaging lens group into the optical path an optical combination of the first imaging group and the second imaging lens group forms a second image having a second magnification on the optical path at substantially the image location. The insertion may be accomplished by a tumbler mechanism upon which the second imaging lens group is mounted. The tumbler mechanism controllably pivots the second imaging lens group about a tumbler axis perpendicular to the optical path, between inserted and non-inserted positions.

Abstract: A lens module (800) includes a lens barrel (20), a base (10), and a temperature compensation module (30). A first lens (201) is disposed in the lens barrel. The lens barrel is disposed in the base. The temperature compensation module is detachably installed in the base, and the temperature compensation module includes a temperature compensation lens (302). The temperature compensation lens is configured for compensating for deformation of the first lens caused by temperature changes.

Abstract: An optical system includes a primary lens group having a central beam path therethrough and including a front lens group and a rear lens group. An anamorphic lens group lies on the central beam path and is positioned between the front lens group and the rear lens group. The anamorphic lens group includes at least one optically powered anamorphic lens that has different enlargements of a light beam along different axes perpendicular to the central beam path. The anamorphic lens group may be mounted on structure that allows it to be removed from the central beam path. An image transceiver is either an image source that directs a light beam through the primary lens group and the anamorphic lens group, or is an image receiver that receives a light beam through the primary lens group and the anamorphic lens group.

Abstract: An optical accessory having a high optical performance arranged to change an optical characteristic of a shooting lens and to be attached on the object side of a shooting lens is provided. The optical accessory FE is to be detachably attached to the object side of a master lens M and has at least one lens FE having a negative refractive power. The image-side surface r2 of the lens FE is designed to have an aspherical shape having a negative refractive power that decreases toward its periphery.

Abstract: A zoom lens in which a precise focus detection signal can be detected while a user can observe an image to be shoot without being affected by insertion/removal of an extender lens into an optical axis. A relay lens unit stationary during zooming includes lens unit L21 including a branch element, lens unit L22 interchangeable with extender lens unit insertable into/removable from optical path to change focal length range of the entire system and positive lens unit L23 in order from object side to image side, and the zoom lens satisfies specific conditions among distance from an aperture stop to front principal point of L21, distance from rear principal point of L21 to front principal point of L22, distance from rear principal point of L22 to front principal point of L23, refractive power of L21, and refractive power of the entire system of the zoom lens at wide-angle end.

Abstract: An imaging device includes a refractive imager lying in an optical path, and optionally a telescope that directs the optical path to the refractive imager. The refractive imager includes a first lens group that forms an intermediate image of a scene on the optical path, wherein the first lens group includes a first-lens-group positive-power lens, and a first-lens-group negative-power lens. A second lens group relays the intermediate image to a final image surface on the optical path, wherein the second lens group includes a second-lens-group positive-power lens, and a second-lens-group negative-power lens. A third lens group may be selectively inserted into the optical path between the first lens group and the second lens group and selectively removed from the optical path. The third lens group includes a third-lens-group positive-power lens, and a third-lens-group negative-power lens.

Abstract: A converter lens includes a front unit and a rear unit disposed on an image side with respect to the front unit. The front unit has positive optical power and includes two positive lens elements. The two positive lens elements are spaced apart. The rear unit has negative optical power and includes a positive lens element and a negative lens element.

Abstract: A sighting device includes a fixed-position objective lens group lying on an optical axis, an eyepiece lens group lying on the optical axis, and a variable-position objective lens group lying on the optical axis and positioned between the fixed-position objective lens group and the eyepiece lens group. A variable-lens position of the variable-position objective lens group relative to the fixed-position objective lens group or the eyepiece lens group may be controllably varied. A mechanical aperture stop lies on the optical axis between the fixed-position objective lens group and the eyepiece lens group. A stop axial position and/or a stop size of the mechanical aperture stop may be varied according to the position of the variable-position objective lens group.

Abstract: A zoom lens includes first to fourth lens units arranged in order from an object, respectively. The first lens unit is fixed during power-varying and has positive optical power. The second lens unit is movable during power-varying. The third lens unit is movable so as to compensate image-plane fluctuation in accordance with the power-varying. The fourth lens unit is fixed during the power-varying and has positive optical power. The first lens unit includes a first lens subunit having positive optical power, and a second lens subunit having negative optical power, arranged in order from the object, respectively. One of the first and second lens subunits moves upon focus adjustment. Further, the following conditions are satisfied: ?2.5<f1b/f1a<?0.6 and 0.2<f1/fT<0.8. Wherein f1, f1a, f1b, and fT respectively represent the focal lengths of the first lens unit, the first lens subunit, the second lens subunit, and the overall system of the zoom lens at its telephoto end.

Abstract: A zoom lens includes, in order from an object side to an image side, a first lens unit of positive refractive power, a second lens unit of negative refractive power arranged to move during variation of magnification, a third lens unit arranged to compensate for shift of an image plane due to the variation of magnification, and a fourth lens unit of positive refractive power, wherein the fourth lens unit has a first lens subunit of negative refractive power, and an image is displaced by moving the first lens subunit in such a way as to have a component perpendicular to an optical axis of the zoom lens.

Abstract: A switchable dual field of view objective system 20 comprises a front lens A and a rear lens C with an intermediate lens B switchable between in-use and out-of-use positions. Lens A is positively powered and lens C is negatively or positively powered but has little power in comparison to lens A. Lens C has two lens components 24, 25 of which component 24 is negatively powered and is located proximal to intermediate lens B. Lens B and component 24 are carried in common by a carrier 28 which is movable along the axis to provide distance focussing in both fields of view.

Abstract: An attachment lens satisfactorily corrects aberrations by using a diffraction surface. The attachment lens is installed on an image surface side of a master lens unit (M) serving as a photographic optical system, and it extends a focal length of the master lens unit (M) toward a longer focal length side. The attachment lens has a diffraction surface (D) which is composed of a diffraction grating shaped rotationally symmetrical with respect to an optical axis and which has a negative refractive power with respect to a diffracted light ray of a design order of diffraction. The attachment lens is adapted to satisfy a conditional expression given below when a height of an axial paraxial ray incident upon the diffraction surface, which has the negative refractive power, from an optical axis is denoted as h.sub.D, and a height of a pupil paraxial ray incident upon the diffraction surface, which has the negative refractive power, from the optical axis is denoted as H.sub.D :.vertline.h.sub.D H.sub.D .vertline.>h.

Abstract: An extender lens group removably incorporated in a zoom lens equipped with a temperature compensating feature for increasing the prim-lens focal length to achieve increased magnification is comprised of a front extender lens sub-group including four lens elements and a rear extender lens sub-group including two lens elements, the front extender lens sub-group including two positive bi-convex lens elements each of which has a strong curvature at the subject side surface followed by an overall positive doublet comprising a positive bi-convex lens element with a strong curvature at the subject side surface and a negative bi-concave lens element with a strong curvature at the image side surface and the rear extender lens sub-group including an overall positive doublet comprising a bi-concave lens element with a strong curvature at the image side surface and a positive meniscus lens element with a concave surface on the subject side.

Abstract: The invention concerns photochromic compounds with the following Formula: ##STR1## in which: R.sup.1 is a asymmetric aliphatic monocyclic group with the Formula, ##STR2## where l=1-12, and R.sup.9 is H or an alkyl, alkoxy, dialkylamino, alkyl ester or CN group with the condition that at least one of the R.sup.9 groups is not H,R.sup.2 -R.sup.7 can have a variety of meanings, A represents a (hetero)aromatic ring which can be substituted and n is a whole number.Application to the production of photochromic articles made of organic polymer, notably lenses.

Abstract: A stereoscopic-vision endoscope of the present invention comprises a tubular elongated insertional part, an objective optical system situated in the insertional part, a relay optical system situated in the insertional part for transmitting an object image formed by the objective optical system, a pupil dividing stop for dividing a light beam emanating from an object image formed by the relay optical system into a plurality of portions, an image formation optical system for receiving light beams from the pupil dividing stop so as to form a plurality of object images having parallax, and imaging devices for picking up the object images formed by the image formation optical system. The relay optical system satisfies the condition .phi..sup.2 /L>0.43 (where .phi. denotes an outer diameter of a system of relay lenses, and L denotes a relay length of the relay optical system).

Abstract: Described are novel photochromic spiro(indoline) fluoranthenoxazine compounds having certain substituents on the 1 and 3 positions of the indoline portion of the compounds and which may be represented by the following graphic formula: ##STR1## Also described are polymeric organic host materials that contain or that are coated with such compounds.

Abstract: An optical device including a lens located between a first port and a second port, and a photodetector having a photodetecting surface located in the vicinity of the second port. The first port and the second port have a first aperture and a second aperture, respectively. The lens has a converging portion for converting a light beam so as to couple the first aperture and the second aperture, and a deflecting portion for deflecting a part of a light beam from the first port to make the part incident on the photodetecting surface. The converging portion and the deflecting portion are integral with each other, for example. By using this optical device, light power can be monitored stably with no polarization dependence.

Abstract: A zoom lens system includes first to fifth lens groups arranged in this order from the object side. The first, third and fifth lens groups are fixed. The second lens group is moved in the direction of the optical axis of the zoom lens system when zooming the zoom lens system and the fourth lens group is moved in the direction of the optical axis to correct change in the image position due to the zooming and to correct change in the image position due to change in the object distance. The first lens group has a positive refracting power, the second lens group has a negative refracting power, the third lens group has a negative refracting power, the fourth lens group has a positive refracting power and the fifth lens group has a positive refracting power.

Abstract: The present invention provides an zoom lens with an anamorphic converter that is small, light weight, has high precision, and also high performance. The zoom lens includes, in order from the object side, a first lens group with positive refractive power, a second lens group with negative refractive power, a third lens group with positive and negative refractive power, a fourth lens group with positive refractive power, and a fifth lens group with positive refractive power. The second lens group moves along the optical axis and first lens group is fixed along the optical axis when zooming from the maximum wide-angle state to the maximum telephoto state.

Abstract: A telescope includes a master telescope whose aberration has been independently corrected and which has an objective lens and an ocular lens. A rear conversion lens is provided on the image side of the objective lens of the master telescope and is made of a single lens having a concave surface that faces an object side. The rear conversion lens meets the requirements defined by the following relationships: f.sub.o '/f.sub.o >1 and 0.5<(dx.sub.2 /dh.sub.2)/(dx.sub.1 /dh.sub.1)<1.3, wherein "f.sub.o " represents the focal length of the objective lens of the master telescope; "f.sub.o '" represents the resultant focal length of the objective lens of the master telescope and the rear conversion lens; "dx.sub.1 /dh.sub.1 " represents an inclination of an incident surface of the rear conversion lens at an incident point thereof, upon which light is incident at a height h.sub.1 ; "dx.sub.2 /dh.sub.

Abstract: A lens system includes a master lens system and a conversion lens system. The master lens system has a first lens, a second lens, a third lens, and a fourth lens, which are sequentially arranged from an object side of the lens system to an image side thereof, and has a first diaphragm which is arranged between the third lens and the fourth lens. The first lens is a positive meniscus lens having a convex surface toward the object side. The second lens is a negative lens. The third lens is a positive lens. The fourth lens is a negative meniscus lens having a concave surface toward the object side. The conversion lens system is arranged in such a manner that the conversion lens system can be freely inserted and removed between the third lens and the fourth lens of the master lens system.

Abstract: A vari-focal viewfinder optical system which comprises an objective lens system for forming an image of an object to be photographed, reflecting members for erecting the image formed by the objective lens system, an eyepiece lens component for allowing observation of the image formed by the objective lens system, and a lens component which has a positive refractive power and is disposed so as to be settable and removable into and out of an optical path between the reflecting members and the eyepiece lens component, and is configured so as to change observing visual fields by varying a focal length of the eyepiece lens component by using the lens component which has the positive refractive power and is settable and removable into and out of the optical path. This vari-focal viewfinder optical system permits observing images with no strange impression and makes it possible to configure cameras compact.

Abstract: A zoom lens having a super wide angle has a first lens group having positive refracting power and arranged on an object side of the zoom lens; a second lens group having negative refracting power and arranged on an image side of the zoom lens; and a converter lens having positive refracting power and detachably attached between the first and second lens groups. A focal length of the zoom lens is changed by changing a distance between the first and second lens groups. The distance between the first and second lens groups is set to be wide on a wide angle side in a zooming region and narrow on a telescopic side in the zooming region. The focal length of the zoom lens at the super wide angle is set to be shorter than that at a wide angle end in the zooming region by mounting the converter lens on the wide angle side.

Abstract: An afocal optical module simulator (aoms) for use in conjunction with one or two other optical modules to simulate an afocal variator optical system. The aoms is comprised of an optical module having a front and a rear end, and includes a movable negative lens. The front end of the aoms includes a mechanism for securing a front optical module which may include as its rear most element a positive lens system which will be located juxtaposed to, but spaced from, the movable negative lens within the aoms. Similarly, the rear end of the aoms includes a mechanism for securing a rear optical module, which includes as its front most element a positive lens system which will be located juxtaposed to, but spaced from, the movable negative lens within the aoms.

Abstract: A varifocal lens system is constructed by two or more lens groups and has a function for changing a focal length of the lens system by changing a distance between the lens groups while the position of an image face is constantly held. An auxiliary lens constructed by two lens groups having negative and positive refracting powers is inserted into an increased clearance between lens groups in a shortest focal length state such that a lens group having the negative refracting power is located on an object side. The focal length of the lens system is transited to the side of a focal length shorter than the shortest focal length without changing the position of the image face by the insertion of the auxiliary lens. The auxiliary lens can be constructed by a single lens group having negative refracting power. In accordance with the above structure, focal lengths of the varifocal lens system can be transited to each other without increasing an entire length of the varifocal lens system.

Abstract: A focal length changeable lens system for use with an on-chip micro-lens equipped solid-state imaging device, whose exit pupil is located at a long distance and whose focal length is changeable between a long focal length and a short focal length. The lens system includes a first positive power lens group, a second positive power lens group and a third positive power lens group arranged in order from the object end. The lens system further includes an aperture stop fixedly disposed between the first and second lens groups where the subject focal point of the third lens group is positioned. When the second lens group is out of the optical axis, the lens system provides a long focal length, and when the first lens group is out of the optical axis, the lens system provides a short focal length.

Abstract: An infrared refractive reimaging afocal telescope (10) has an objective lens group (12), an eyepiece lens group (14), and a switching lens group (16). The system (10) provides a plurality of magnification modes in a compact arrangement. The system (10) utilizes lenses (40, 42, 44, 46) with diffractive surfaces to provide for magnification changes and chromatic aberration correction. The system provides for excellent image quality in all modes using a minimum number of lens elements.