Abstract: A telescope-type stereomicroscope which is outfitted with an objective and two magnification changers arranged downstream of the objective. In this telescope-type stereomicroscope, the light from an object that is being examined enters the objective. Two light bundles of the light re-exiting from the objective, which are oriented parallel to one another, enter the magnification changers. The optical axes of the magnification changers are arranged at a fixed distance from one another. Each magnification changer has an entrance pupil for the light bundle associated with it. The entrance pupil has a diameter DEP that depends on the respective selected magnification, where the condition DEP>B/1.06 is met at the maximum selected magnification. Optionally, the stereomicroscope meets the condition tan(?)?0.16 with respect to the angle ? at which the light coming from an extra-axial point P at the object enters the magnification changers at the lowest possible magnification setting.

Abstract: A description is given of a telescopic sight with variable magnification, comprising a fixed objective and first image plane assigned thereto, a variable system with second image plane assigned thereto, and a fixed eyepiece for viewing the second image plane and that has a stop in the vicinity of the first image plane whose aperture diameter can be varied as a function of the magnification of the variable system in order to suppress scattered and/or false light.

Abstract: Various embodiments described herein include a scope for a firearm having a large range of zoom. The scope comprising a movable zoom selector for adjusting magnification of an image viewed through the scope. The scope further includes an objective, an ocular, and an erector assembly positioned between the objective and ocular. The erector assembly includes at least three optical elements movable relative to one another in response to operation of the zoom selector.

Abstract: Various embodiments described herein comprise a scope for a firearm having a large range of zoom. The scope comprising a movable zoom selector for adjusting magnification of an image viewed through the scope. The scope further comprises an objective, an ocular, and an erector assembly positioned between the objective and ocular. The erector assembly comprises at least three optical elements movable relative to one another in response to operation of the zoom selector.

Abstract: A description is given of a telescopic sight with variable magnification, comprising a fixed objective and first image plane assigned thereto, a variable system with second image plane assigned thereto, and a fixed eyepiece for viewing the second image plane and that has a stop in the vicinity of the first image plane whose aperture diameter can be varied as a function of the magnification of the variable system in order to suppress scattered and/or false light.

Abstract: The invention in microgravity uses the natural effect of capillary action and surface tension of a liquid substance inside a cylindrical chamber to form a curved meniscus suitable to use in a space telescope. The geometry of the meniscus can be controlled by using a boundary line that fixes the contact point of the meniscus and then controlling the volume of the liquid. The meniscus geometry can then be controlled to form a reflective liquid mirror dish that is suitable to use in a space telescope.

Abstract: A dual field of view sighting system uses liquid crystals, flip-polarizers and/or flip-mirrors to select between at least two fields of view.

Abstract: A telescopic sight includes a zoom mechanism with which an angle of adjustment of sighting can be enlarged, such that sighting precision of the telescopic sight can be stably maintained, and with which zooming can be performed with a light touch. The telescopic sight includes a zoom ring, an annular gear, a circumferential gear, an intermediate gear and a transmission mechanism. The zoom ring is turnably provided at an outer periphery of a lens barrel of a telescopic sight. The annular gear is provided at an inner periphery face of the zoom ring. The circumferential gear is rotatably provided, concentrically with the annular gear, at an inner periphery of the lens barrel. The intermediate gear is interposed between the annular gear and the circumferential gear and transmit rotation of the annular gear to the circumferential gear.

Abstract: Apparatus and method for viewing a target. A primary lens produces an image plane of the target, and an optical magnifier in an optical path of the primary lens magnifies a region of the image plane, providing a magnified image. A detector receives the magnified image.

Abstract: A vision aid in the form of telescopic spectacles has two lens systems, which each comprise at least one objective lens (70) and one eyepiece (71). An autofocussing element which changes the focal length of the lens systems for sharp focussing thereof according to the distance of the telescopic spectacle from the object is assigned to the lens systems. Furthermore, an element for changing the magnification factor by changing the focal length of the lens systems (“zoom”) and finally an element for matching the parallax between the lens systems of the vision aid to the focal length which has been set according to the distance of the telescopic spectacles from the object are assigned to the lens systems. The parallax is adapted using adjustable optical elements (11) which are located in the beam path of the lens systems, with which elements the angle (13) between the beam paths (14) running from the lens systems (1) to the object can be changed.

Abstract: A motorized telescopic adjustment device 10 is disclosed which is connected to an adjustment ring 6 of a telescopic sight 4 for firearms 2 or the like including: a battery 12, a motor 14 with a switch 16 electronically interconnected to power the motor 14, a drive 30 interconnected to the motor 14 and the adjustment ring 6 to adjust the telescopic sight adjustment ring 6, a support bracket assembly 40 adapted to adjustably mount the device 10 on the telescopic sight 4 and a motor connection 60 for securably mounting the motor 14 on the support bracket assembly 40. The support bracket assembly 40 includes a front and a rear mounting bracket subassemblies 42, 44 which are adjustable along a rod 50 which extends between the front and rear mounting bracket subassemblies 42, 44, the front mounting bracket subassembly 42 including a protruding boss 49 for receiving the rod 50.

Abstract: A real image type zoom finder that, albeit being reduced in size and thickness, can gain high enough zoom ratios and an imaging system equipped with such a real image type zoom finder. The real image type zoom finder comprises an objective optical system, an image-erection optical system and an eyepiece optical system. The objective optical system comprises a negative first lens group, a positive second lens group, a negative third lens group and a positive fourth lens group. Upon zooming, the first lens group and the fourth lens group remain fixed, the second lens group moves toward the object side at the telephoto, not the wide-angle end, and the third lens group moves toward the image side at the telephoto, not the wide-angle end. The first lens group consists of one single lens of double-concave shape, and that single lens satisfies condition regarding a shape factor.

Abstract: A real image type variable magnification finder comprises, an object optical system having positive refracting power which forms an objective image as a middle image, a view frame arranged near a position of the middle image, and an eyepiece optical system having positive refracting power which forms a pupil for observing the middle image, wherein an erect image optical surface for making the erect image by bending optical path is formed on the way of these optical paths. The object optical system comprises, in order from an object side, a negative lens element which is a single lens, a positive lens element which is a single lens, wherein both lens elements are moved by changing a distance between the negative lens element and the positive lens element when magnification is varied.

Abstract: The polar-axis telescope has an objective lens, a focal plate, an eyepiece, a zoom optical system, and a zoom optical system driver. The objective lens forms an object image, and the focal plate is arranged on a focal plane of the objective lens. The eyepiece is arranged backward of the focal plate and forms an observed image. The zoom optical system is arranged between the objective lens and the eyepiece. The zoom optical system makes the observed image appear gradually bigger while maintaining an in-focus situation. The zoom optical system driver shifts the zoom optical system along a polar-axis, corresponding to an optical axis of the polar-axis telescope, so as to change a magnification.

Abstract: A sighting telescope has an inner tube that moves transversely of the telescope axis relative to an outer tube, and operating elements arranged mutually at an angle for transversely displacing the inner tube. In an embodiment of the invention, the outer tube has an enlarged internal diameter in the region of the operating elements. In a second embodiment of the invention, a leaf spring is arranged for producing a restoring force on the inner tube, extends in a substantially radial direction, and has radially offset support places, both on the outer tube and on the inner tube. The leaf spring is preferably arranged in the neighborhood of the enlarged internal diameter.

Abstract: A vari-focal polar alignment scope includes an objective optical system, a relay optical system, and an eyepiece optical system, in that order from the object side. The relay optical system includes an erecting vari-focal viewing optical system, including a positive condenser lens element, and positive second and third relay lens groups which relatively move in the optical axis direction so as to vary the magnification of the polar alignment scope, wherein the following conditions (1), (2) and (3) are satisfied: 6.0<fo/fe<10.0??(1); ?4.0<M2L<?1.0??(2); and 0.2<M3L<0.6??(3); wherein fo designates the focal length of the objective optical system; fe designates the focal length of the eyepiece optical system; M2L designates the lateral magnification of the second lens group of the relay optical system at a low magnification; and M3L designates the lateral magnification of the third lens group of the relay optical system at a low magnification.

Abstract: A real-image finder optical system includes a positive objective optical system, an erecting optical system, and a positive eyepiece optical system, thereby an object image, which is formed by the objective optical system, and is upside down and reversed from left to right, is reinverted by the erecting optical system to the proper orientation. The erecting optical system includes a plurality of reflection surfaces, at least one of which is provided along an optical path on the object side with respect to the position where the object image is formed, and at least another of which is provided along an optical path on the eyepiece side with respect to the position where the object image is formed. The eyepiece optical system includes a positive lens element having a transverse magnification of more than 1.0 provided between the object image (finder image) and the reflection surface provided on the eyepiece side with respect to the position where the object image is formed.

Abstract: A housing for a magnification loupe is provided having a body portion for an eyepiece lens and a nose portion for an objective lens. The body portion for the eyepiece lens includes outer circumferential threads over which the objective nose portion fits. The objective nose portion includes a pin slot defining an arc across the body of the nose. The arc is configured such that a pin may be secured through the holes in the nose piece to co-act with the threads of the eyepiece body such that radial movement is prohibited.

Abstract: A viewing apparatus in which an object image formed by an objective lens system is viewed through an eyepiece system includes a beam splitter which is located closer to an object than a focal plane of the objective lens system in a light path of the objective lens system, a negative lens provided in an optical path of light split by the beam splitter, and a photographing optical system attachment/detachment portion provided on a light emission side of the negative lens.

Abstract: An optical system capable of focal length adjustment and so forth with a simple arrangement in which a desired portion of an optical element is selectively utilized by moving an aperture in a direction approximately perpendicular to the optical axis. The optical system has at least two optical elements and includes a first unit positioned at the object side to form a first image and a second unit for projecting the first image onto an image plane. A deflecting mirror for selecting an optical path is positioned in the vicinity of the first image. The first or second unit is formed from a variable focal length optical element having at least two continuous rotationally asymmetric surfaces.

Abstract: A telescopic zoom lens system has a minimum magnification thereof is more than 2, and includes a positive objective lens group, and a positive eyepiece lens group, in this order from the object. Further, a zooming lens group which is made moveable along the optical axis upon zooming is positioned on the side of the object with respect to the primary image forming plane of the objective optical system.

Abstract: A binocular, including a right and left lens barrels respectively having a right and left telescope optical systems, is provided with a space occupied by a movement member that moves lenses to vary at least magnification so as to reduce the size of the binocular. First and second lens sliders, connected to a first and second lens, are moved along an optical axis direction of the telescope optical system so that the first and second lens, are moved along the optical axis direction. The first and second lens sliders move inside the space defined by the right and left telescope optical systems and a flat supporting plate.

Abstract: A motorized, finger operated mechanism for focusing or otherwise adjusting a telescopic sight. The power focusing device generally includes a battery powered motorized focus mechanism operably attachable to the focusing ring of a telescopic sight, a wireless receiver and a wireless controller. The operator controls the focusing mechanism by manipulation of the controller. The focus mechanism includes a motor, a reduction drive, a power source and a device to engage the focusing ring. The focus mechanism may be secured to an existing telescopic sight or integrated into the telescopic sight design.

Abstract: First lens frame has first front and rear shaft bearings that engage with the first guiding shaft along the optical axis, and a second shaft bearing that engages with a second guiding shaft along the optical axis. The first front and rear shaft bearings are spaced apart from each other along the first guiding shaft. Second lens frame has third front and rear shaft bearings that engage with the second guiding shaft, spaced apart form each other, and fourth shaft bearing that engages with the first guiding shaft. The third front and rear shaft bearings are arranged with the second shaft bearing between them, and fourth shaft bearing is disposed between the first front and second shaft bearings.

Abstract: A reflector telescope (10) includes at least one moveable secondary mirror assembly, thereby allowing control over the distance between the primary and secondary mirrors. A preferred telescope tube assembly includes a plurality of frame elements, between which is defined an optical path. An inner end of the telescope tube assembly supports a primary mirror assembly (200). In a preferred version of the reflector telescope, an inner secondary mirror assembly (300) and an outer secondary mirror assembly (400) are carried by the telescope tube assembly. Each secondary mirror assembly includes a secondary mirror and optical equipment such as an eyepiece. The secondary mirror assemblies can be slid along the frame elements of the telescope tube assembly, allowing the distance between the primary and secondary mirrors to be controlled.

Abstract: A simplified hand held stereoscopic imaging system in which stereoscopic recording and three-dimensional playback of objects viewed with the device is provided with a single recording element and a single playback element.

Abstract: A gear is formed on the outer circumference of the disk unit 20a of the zoom operating member 20 and on the outer circumference of the right zoom drive member 18, and an intermediate gear 19 that engages and connects with each of these gears is located between them. In other words, the zoom operating member 20 and the right zoom drive member 18 are connected to each other in a non-integrated fashion. When the zoom operating member 20 is manually rotated around the eye distance adjustment axis 22, the right zoom drive member 18 rotates via the intermediate gear 19 and the left zoom drive member 21 simultaneously rotates via the connecting member 11.

Abstract: A real image mode variable magnification finder has an objective optical system with positive refracting power, an image erecting optical system, and an ocular optical system with positive refracting power. The objective optical system has a first lens unit with negative refracting power, a second lens unit with negative refracting power, a third lens unit with positive refracting power, and a fourth lens unit with negative refracting power. When the magnification of the finder is changed, at least one lens unit, namely the third lens unit is moved. In this way, the total length of the objective optical system can be reduced, and thus a compact finder is obtained.

Abstract: A zoom lens comprises a plurality of optical elements each of which includes a transparent body having two refracting surfaces and a plurality of reflecting surfaces and is arranged so that a light beam enters the transparent body from one of the two refracting surfaces, repeatedly undergoes reflection, and exits from the other of the two refracting surfaces, and/or a plurality of optical elements on each of which a plurality of reflecting surfaces made from front surface mirrors are integrally formed, and each of which is arranged so that an entering light beam repeatedly undergoes reflection by the plurality of reflecting surfaces and exits from the optical element.

Abstract: A real-image zoom finder optical system in which the objective lens system, the condenser lens system, the erecting optical system and the eyepiece lens system are arranged in this order from the object. The objective lens system includes a negative lens group (O1) and a positive lens group (O2), in this order from the object, and these lens groups are moveable along the optical axis upon zooming. Further, the negative lens group (O1) includes a negative meniscus single lens element (O11) having a convex surface facing towards the object, and a meniscus single lens element (O12) having a convex surface facing towards the image, in this order from the object.

Abstract: A motor-driven focusing apparatus of a telescope, includes a telescopic optical system which includes a focusing lens group guided along an optical axis; a motor-driven lens moving device which drives the focusing lens group along the optical axis; a manual operating switch for actuating the motor-driven lens moving device; and a lens-control device for controlling the motor-driven lens moving device when the manual operating switch is turned ON, so that the moving amount per unit time of a focal point of the telescopic optical system, that is caused by a movement of the focusing lens group, is kept substantially at a constant speed regardless of the position of the focusing lens group on the optical axis, the constant speed being selected from one or more constant speeds.

Abstract: The invention relates to an optical imaging system for imaging an object with progressively adjustable magnification. The inventive system comprises an imaging plane for projecting an image field originating from the object and an imaging optical system situated on the object side in front of the imaging plane, preferably with a fixed focal length for producing the image field on the imaging plane. Said imaging optical system and/or said imaging plane are arranged so that they can move in the direction of the optical axis in order to adjust the magnification and/or focus the image appearing on the imaging plane.

Abstract: A real image mode variable magnification finder has an objective optical system with positive refracting power, an image erecting optical system, and an ocular optical system with positive refracting power. The objective optical system has a first lens unit with negative refracting power, a second lens unit with negative refracting power, a third lens unit with positive refracting power, and a fourth lens unit with negative refracting power. When the magnification of the finder is changed, at least one lens unit, namely the third lens unit is moved. In this way, the total length of the objective optical system can be reduced, and thus a compact finder is obtained.

Abstract: To provide a front tele-converter that may cause less aberrations and has a superior imaging quality though it has a high magnification, disclosed is a front tele-converter TC having an afocal magnification higher than 1.9, which is detachably mountable to a photo-taking lens L on its object side. The front tele-converter has, in order from the object side, a positive lens group GF having a positive refractive power and a negative lens group GR having a negative refractive power. The positive lens group GF has a positive cemented lens, the negative lens group GR has a positive lens with its convex surface facing the image side, and the lens groups fulfill a specific condition.

Abstract: The invention is directed to an infrared Kepler telescope which includes an objective defining an optical axis and including a positive front group and a negative rear group all arranged on the optical axis. The objective further includes an interchangeable optic interposed between the positive front group and the negative rear group with the interchangeable optic being configured to operate as a magnification changer. An ocular is mounted on the optical axis rearward of the negative rear group and the rear group and the ocular are fixedly pregiven. The positive front group is a first positive front group and is exchangeable with at least a second positive front group. The interchangeable optic is a first interchangeable optic and is exchangeable with at least a second interchangeable optic.

Abstract: An optical device having a dioptric correction device comprises a reference image display unit which is placed in the optical path extending from an object image to the optical system. The reference image is used for dioptric correction. The left and right reference images are different and are displayed on the left and right reference image display units when dioptric correction is performed. The reference image display unit is placed at a predetermined position between the optical system and an image display unit. Since the reference image is positioned at the predetermined position, both of the image of the image display unit and the reference image may be seen clearly.

Abstract: A telescopic sight with variable magnification includes an adjusting ring for varying the magnification. The telescopic sight housing and an eyepiece stub are arranged together in a single part. The adjusting ring is arranged between the eyepiece and an object in a groove formed between the telescopic sight housing and the eyepiece stub.

Abstract: A real image mode variable magnification finder optical system is provided with an objective system having a positive refracting power, a correctly erect image forming system having a plurality of reflecting members for converting an intermediate image formed by the objective system into a correctly erect image, and an eyepiece system having a positive refracting power. The objective system includes a first lens unit having a negative refracting power, a second lens unit having a positive refracting power, and a third lens unit having a negative refracting power. At least one of the light reflecting members is arranged between the third lens unit and a position of said intermediate image, and the first, second and third lens units are adapted to be moved along the optical axis when magnification of the optical system is to be changed. Thus, the finder optical system enables one to change magnification thereof with high ratios and to form a good image of visual field with decreased flare.

Abstract: A finder optical system has an objective optical system for forming an intermediate image of an object and an eyepiece optical system, and is disposed independent of a photographing optical system. The objective optical system includes a reflecting member. A lens unit situated on the object side of the intermediate image is used as a correcting lens and moved along the optical axis. The finder optical system is thus corrected for diopter and satisfies a condition:0.1<.vertline.1000.times..alpha..sub.F /f.sub.R.sup.2 .vertline.<7.0where .alpha.F is the maximum longitudinal magnification of the correcting lens and f.sub.R is the focal length of the eye-piece optical system.

Abstract: A real image mode zoom finder includes, in order from the object side, an objective optical system with positive refracting power having a first lens unit with negative refracting power, a second lens unit with positive refracting power, a third lens unit with positive refracting power, and a fourth lens unit with negative refracting power; an image erecting system for erecting an intermediate image formed by the objective optical system; and an ocular optical system with positive refracting power. In this case, each of lens units constituting the objective optical system is constructed with a single lens, and the object-side surface of the first lens unit is configured to be concave. Moreover, the objective optical system satisfies the following condition:2.5<.alpha..sub.T(R2) <5.7where .alpha..sub.T(R2) is a combined longitudinal magnification ranging from the second lens unit of the objective optical system to the intermediate image at the telephoto position of the finder.

Abstract: A binocular includes first and second swingable bodies respectively accommodating telescope systems. The binocular further includes two drive rings respectively provided to the swingable bodies and an operation knob. A transmission unit is provided to transmit the rotation of the operation knob to the drive rings. The transmission unit includes two pairs of a first gear and a second gear. The first gear and the second gear engage with each other so that a contact point of pitch circles thereof is located on each of the swing axis.

Abstract: The invention is directed to an infrared Kepler telescope which includes an objective defining an optical axis and including a positive front group and a negative rear group all arranged on the optical axis. The objective further includes an interchangeable optic interposed between the positive front group and the negative rear group with the interchangeable optic being configured to operate as a magnification changer. An ocular is mounted on the optical axis rearward of the negative rear group and the rear group and the ocular are fixedly pregiven. The positive front group is a first positive front group and is exchangeable with at least a second positive front group. The interchangeable optic is a first interchangeable optic and is exchangeable with at least a second interchangeable optic.

Abstract: A real image type zoom finder includes: an objective lens having a plurality of lenses, having a positive refracting power; a field diaphragm provided in the vicinity of a focal point of the objective lens, for defining a viewing field; a structure for erecting an image formed by the objective lens; and an eyepiece having a positive refracting power for enlarging an image formed by the objective lens and the field diaphragm. The objective lens includes at least a first lens group provided closest to an object side, having a negative refracting power, and satisfies the following conditions:1.9<f.sub.B /f.sub.W and1.0<.vertline.f.sub.1 .vertline./f.sub.W <2.0where f.sub.B represents a minimum value of a distance between a surface of the object lens closest to a pupil side and the field diaphragm, which is equivalent to a corresponding air gap, f.sub.1 represents a focal length of the first lens group, and f.sub.W represents a focal length at a wide angle end of the objective lens.

Abstract: A binocular includes two telescope systems with parallel axes, eyepiece frames having a concave surface facing a user, adjustable eye cups with a secure locking mechanism, operation controls placed between the telescope systems, a focus adjustment mechanism, a diopter correction mechanism, and a magnifying-power-varying mechanism. The magnifying-power-varying mechanism includes rotatable cam rings and guide rings connected by a single connecting belt that moves perpendicular to the optical axes to rotate the cam rings. The connecting belt is supported and held in position so that it does not bind. The position of magnifying-power-varying lenses can be adjusted. The positions of the guide rings with respect to the telescope systems can also be adjusted.

Abstract: A binocular includes two parallel telescope systems two swingable bodies respectively accommodating the telescope systems, a supporting body which swingably supports the swingable bodies so that the swingable bodies are respectively swingable about two parallel swing axes, two drive rings rotatably provided to the swingable bodies, an operation knob provided to the supporting body which, and two rotating bodies respectively linked to the drive rings. Each of the rotating bodies located across a border of the swingable body and the supporting body.

Abstract: A viewfinding system for use with an optical system that creates a first object image includes an objective block which is sealed as a unit. The objective block includes a focusing screen for forming the first object image and relay optics for transmitting the first object image. A zoom block includes a zoom optical system for providing a modification of the magnification of the first object image to provide a second object image. An eyepiece block receives the second object image and includes a reflecting member and an eyepiece through which the second object image is observed. The eyepiece block is sealed and the second object image is realized within the sealed eyepiece block.

Abstract: A binocular includes two telescope systems with parallel axes, eyepiece frames, adjustable eye cups, operation controls positioned between the telescope systems, a focus adjustment mechanism, a diopter correction mechanism, and a magnifying-power-varying mechanism. The focus adjustment mechanism and diopter correction mechanism are arranged coaxially. The magnifying-power-varying mechanism includes rotatable cam rings and guide rings connected by a single connecting belt that moves perpendicular to the optical axes to rotate the cam rings. The connecting belt is supported and held in position so that it does not bind. The position of magnifying-power-varying lenses can be adjusted. During assembly, the magnifying-power-varying lenses can be mounted in the guide rings in a number of positions by rotating the lens frames holding the lenses about the optical axis and inserting sliders in linear guide grooves.

Abstract: A viewfinder optical system has a relay optical system and an eyepiece optical system. The relay optical system has a first, a second, and a third relay lens. The eyepiece optical system has a first and a second eyepiece lens. The first eyepiece lens, which is disposed closest to a secondary-image plane formed by the relay optical system has an aspherical surface on its secondary-image plane side.

Abstract: A binocular including two telescope systems with parallel axes, eyepiece frames having a concave surface facing a user, adjustable eye cups with a secure locking mechanism, operation controls placed between the telescope systems, a focus adjustment mechanism, a diopter correction mechanism, and a magnifying-power-varying mechanism. The focus adjustment mechanism and diopter correction mechanism are arranged coaxially. The magnifying-power-varying mechanism includes rotatable cam rings and guide rings connected by a single connecting belt that moves perpendicular to the optical axes to rotate the cam rings. The connecting belt is supported and held in position so that it does not bind. The position of magnifying-power-varying lenses can be adjusted. During assembly, the magnifying-power-varying lenses can be mounted in the guide rings in a number of positions by rotating the lens frames holding the lenses about the optical axis and inserting sliders in linear guide grooves.

Abstract: A penta mirror diagonal and zoom lens assembly for refracting or catadioptric astronomical telescopes includes a specially adapted zoom lens with a key extending outward from an objective lens and an adaptor designed for insertion and retention in a viewing end of an astronomical or catadioptric telescope. The adaptor includes a keyway which mates with the key on the zoom lens, thus allowing the zoom lens to be used only with the adaptor. The zoom lens itself is specially designed for use with astronomical or catadioptric telescopes.