Abstract: A telescope or binoculars includes an erecting system having a plurality of reflecting surfaces. First and second reflecting surfaces and third and fourth reflecting surfaces respectively face each other at right angles. An intersection line between extended surfaces of the first and second reflecting surfaces is perpendicular to the intersection line between extended surfaces of the third and fourth reflecting surfaces. An objective lens is located between the second and third reflecting surfaces and converges object light that is reflected by the first and second reflecting surfaces for forming an image. An eyepiece is located between the fourth reflecting surface and an eye point to magnify the image formed by the objective lens.

Abstract: In an image stabilizing apparatus in which an actuator for a pivoting gimbal suspension is controlled by a feedback loop, the gain of feedback loop based on the angular position is enhanced when the angular velocity is at a first set value or higher until the angular velocity becomes a second set value or lower, whereby a panning mode is automatically attained when a pan/tilt operation is carried out. Also the gain of feedback loop based on the angular position is enhanced when the angular velocity is enhanced until a lapse of a predetermined time after starting the pivoting control of the gimbal suspension, whereby the behavior of gimbal suspension is stabilized.

Abstract: A telescope is provided with a rearview mirror having a mirror surface opposite to the observer. The rearview mirror is located on both sides of the eyepiece, the objective lens, or the telescope body and can be rotatably attached, insertably attached, clipped, or fastened. The rearview mirror is parallel to or tilting to the lens of the eyepiece. The objective lens can be circular, square, or any other shape.

Abstract: An image stabilizing optical system having both a simple configuration and high optical performance can be used as an optical system for observation such as a telescope or a binocular. The image stabilizing optical system consists of a first lens group having positive refractive power, a second lens group having negative refractive power and disposed movably in a direction substantially perpendicular to the optical axis, and an erecting prism system, all of which are arranged in order from an object. The optical system includes an objective lens system for forming an erected image at a position on the eye-side of the erecting prism system and an eyepiece lens system having positive refractive power as a whole and magnifying the erected image so as to allow the magnified erected image to be observed. The first lens group includes at least one positive lens and one negative lens.

Abstract: In an image stabilizing apparatus in which inner and outer gimbals are pivoted about two pivotal axes so as to fix an erect prism with respect to an inertial system, a torsion coil spring 240 is disposed to provide one-side stressing between the inner and outer gimbals 7, 107, so as to pivotally stress the inner gimbal 7 with respect to the outer gimbal 107 in one direction. When image stabilizing control is started, the elastic force of the torsion coil spring 240 instantly changes the angular position of the inner gimbal 7, so that a capacitor is charged earlier, thereby enhancing the response in PWM control.

Abstract: A device having night vision capability, in particular a laser distance-measuring device, has at least two optical channels (A-C), of which a first (A) focuses the low-level light emitted by an object by a mirror (2) and of an optical system (3) onto the entry window (4) of a low-light-level amplifier (5). The image of the object, which is available at the exit window (6) of the low-light-level amplifier (5), is displayed in a predetermined wavelength range and is electronically amplified, and is projected by a further mirror (8) to a receptor (13′) on the second optical channel. The first optical channel (A) responsible for night observation has at least one of the mirrors (2; 8) in the form of a first splitter mirror (2; 8) which can be switched on or off and reflects the light in the predetermined wavelength range but is essentially completely transparent for the laser wavelength.

Abstract: A binocular assembly that includes a hands free support mechanism for supporting the binoculars in front of the user's eyes without using any of the user's hands. The hands free support mechanism includes an adjustable head securing strap and a pair of positioning arms. Each of the pair of positioning arms rigidly extends from one of the binocular elements of a user adjustable binocular assembly at an angle “A” of between twenty-five and forty-five degrees.

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 portable imaging system for viewing distant objects is disclosed comprising an optical lensing system for magnifying a viewed distant object; a sensing system for simultaneously sensing said viewed distant object; a processor means interconnected to said sensing system for processing said sensed image and forwarding it to a printer mechanism; and a printer mechanism connected to said processor means for printing out on print media said sensed image on demand by said portable imaging system. Preferably the system further comprises a detachable print media supply means provided in a detachable module for interconnection with said printer mechanism for the supply of a roll of print media and ink to said printer mechanism. The printer mechanism can comprise an ink jet printing mechanism providing a full color printer for the output of sensed images. The preferred embodiment is implemented as a system of binoculars with a beam splitting device which projects said distant object onto said sensing system.

Abstract: Electronic binoculars comprise a body containing an electronic camera having an electromechanical zoom, a single display, a power source, and electronics for modifying the output of the camera, including a variable electronic zoom. A lens is positioned between the user's eyes and the display to further magnify the image. External controls toggle power and select modifications to the image to be performed by the electronics.

Abstract: A night vision monocular having an optical axis is provided which includes a housing having a distal end and a proximal end; an objective lens assembly having at least one objective lens, the objective lens assembly being engaged within the housing at the distal end; an eyepiece lens assembly having at least one eyepiece lens, the eyepiece lens assembly being engaged within the housing at the proximal end; and an image intensifying tube being engaged within the housing between the objective lens assembly and the eyepiece lens assembly and optically communicating with the objective lens assembly and the eyepiece lens assembly, such that light entering the night vision monocular via the objective lens assembly is intensified via the image intensifying tube and further such that the intensified light is focused via the eyepiece lens assembly onto an eye of a viewer.

Abstract: An adjusting apparatus of a binocular telescope with a binocular body including a pair of juxtaposed telephoto optical systems is provided. The apparatus includes a diopter adjusting shaft for adjusting a difference in diopter between the pair of juxtaposed telephoto optical systems. The diopter is adjusted by rotating the diopter adjusting shaft to move an objective lens in one of the pair of juxtaposed telephoto optical systems. A focus adjusting shaft for adjusting a focus of the optical systems is also provided. The focus is adjusted by moving the focus adjusting shaft in a direction parallel to an optical axis. The focus adjusting shaft rotates the diopter adjusting shaft to move the objective lenses of the pair of optical systems in an integral manner in an optical axis direction. An operation member for rotating the diopter adjusting shaft and a connecting member for connecting the diopter adjusting shaft and the operating member are provided.

Abstract: An optical system for a binocular is provided with an objective optical system, an erecting system and an eyepiece. The objective optical system includes a front lens group having positive refractive power, and a rear lens group having negative refractive power. The rear lens group is capable of moving in a direction orthogonal to an optical axis to stabilize an image when the binocular is moved due to hand-held shaking of a user.

Abstract: An improved ocular mounting assembly having a pair of ocular support arms which can be extended by sliding out of a box-section assembly housing for supporting a pair of ocular devices attached to the ends of the support arms. The improvement is a pair of stabilizers disposed inside the assembly housing and providing stability against rotational motion when the arms are extended. In one embodiment, the stabilizers are interference-fitted balls, retained in position by retainer holes in the assembly housing, and receding into recess cut-outs at the end of the support arms when the arms are fully retracted. In an alternate embodiment, the stabilizers are L-shaped, and can be either an integral part of the housing or bonded to it with adhesive.

Abstract: An zooming adjustment mechanism for an optical system is provided for reducing the length of the optical system along its optical axis, and enable the size down of the optical system. A cam ring is provided for adjusting distances between a first lens and a second lens that are constituting a telescope optical system in a binocular. Each of a first cam groove and a second cam groove includes two grooves. Two first cam grooves and two second cam grooves are formed on an outer circumferential surface at a distance along the circumferential direction. The two first cam grooves and the two second cam grooves are formed on the same area of the circumferential direction about the axis of the cam ring, i.e., the axis of a main shaft direction.

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: An optical device includes: an optical system of which a magnification ratio can be altered; a focusing ring which is actuated in order to set the optical system to a focus position; and a zoom actuation member which is actuated in order to change the magnification ratio of the optical system. And the zoom actuation member is rotated about a support point by actuation force which is applied at an actuation point, and the actuation point is at a position farther removed from the focusing ring, than is the support point.

Abstract: An erecting prism of a binocular includes a first and a second prism, which are held by a holder, and the holder being supported vertically movable and laterally immobile with respect to a thin plate. The thin plate is supported laterally movable and vertically immobile with respect to a right moving body. A shaft reception means is provided, for rotatably supporting a jig, at the right eyepiece cylinder that is attached to the rear wall 303B of the right moving body. The position of erecting prism is adjusted by using a jig to move the holder vertically with respect to the thin plate, and to move the thin plate laterally with respect to the right moving body. The jig may be supported by the shaft reception means and rotated.

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 binocular telescope with an imaging function, comprises binocular optical systems including a couple of observation optical systems having objective lenses and eyepieces, and an imaging device including an imaging optical system, for actualizing a visual field of a field angle that is substantially equal to a real field of an image observed through the binocular optical systems, and a photoelectric converting unit for converting an image obtained by the imaging optical system into an electric signal. The observation optical system and the imaging optical system have their optical axes different from each other.

Abstract: A binocular includes a right and left lens barrels respectively having a right and left telescope optical systems. The right and left telescope optical systems include focus arrangement structures in which both eyepiece lenses are simultaneously moved the same distance with respect to each objective lenses. There are provided two diopter correction structures independently and separately in the right and left telescope optical systems. In one diopter correction structure, a left objective lens is adjusted with respect to a right objective lens to correct a diopter difference between the two telescope optical systems on a manufacture process. In the other diopter correction structure, the location of the right objective lens is adjusted along the optical axis direction on an usual operation by an observer.

Abstract: A viewing optical instrument includes an objective optical system and an eyepiece optical system such that an object image formed through the objective optical system is magnified and observed through the eyepiece optical system. The viewing optical instrument includes an eyepiece adjusting device which allows the eyepiece optical system to rotate relative to the objective optical system about a rotational axis at which an optical axis of the objective optical system intersects a focal plane formed by the objective optical system. A detector detects an inclination of a surface of a sighting object relative to a plane which is normal to the optical axis of the objective optical system, and a controller control the eyepiece optical system to rotate about the rotational axis in accordance with the inclination detected by the detector.

Abstract: A close-up attachment lens for a binocular includes a close-up lens group located on the object side of a pair of objective lenses of the binocular and is detachably attached to the binocular on the object side of the objective lenses. The close-up lens group is provided with a single optical system of positive power which covers the pair of objective lenses and has an optical axis parallel with and spaced from optical axes of the objective lenses at an equal distance. A pair of aperture stops are provided in front of the corresponding objective lenses of the binocular when the close-up attachment lens is attached to the binocular.

Abstract: A lengthwise-direction driving frame is supported in an opening of a flange by holding members, being slidable in a lengthwise direction. The opening of the flange includes inner walls parallel to the lengthwise direction. A lateral-direction driving frame, which holds correction lenses, is supported in an opening of the lengthwise-direction driving frame, being slidable in a lateral direction. The opening of the lengthwise-direction driving frame includes inner walls parallel to the lateral direction. A tip of a shaft of a lengthwise-direction actuator abuts at all times against a pressed member which is fixed on the lengthwise-direction driving frame. A tip of a shaft of a lateral-direction actuator abuts at all times against a pressed member which is fixed on the lateral-direction driving frame. The lengthwise-direction and lateral-direction actuators are respectively fixed on the flange.

Abstract: A pair of binoculars includes a compact focusing mechanism providing an open reach-through space between the body tubes of the binoculars with an enhanced area for the user to grasp and hold each body tube. The focusing mechanism further provides for adjustment of the body tube spacing without affecting focusing. The focusing mechanism includes a compact focusing knob structure situated on an outside of an articulated bridge connecting the body tubes and used for adjusting and maintaining a desired distance between the tubes. The focusing mechanism includes respective arms extending from the focusing knob to each of the body tubes, the ends of the levers riding on the inside of a conically shaped plunger coaxial with a pivot point of the bridge so that adjusting a spacing between the body tubes does not affect focusing. When positioned inwardly, the focusing knob produces a longitudinal movement of the plunger to effect focusing of both focusing elements simultaneously.

Abstract: An observation optical system includes, in order from an object side, an objective lens having a first lens unit of positive refractive power, a second lens unit of negative refractive power and a third lens unit of positive refractive power, an erect optical system, and an eyepiece lens of positive refractive power for observing an object image formed through the objective lens, wherein an air separation between the first lens unit and the second lens unit and an air separation between the second lens unit and the third lens unit are made variable to effect variation of magnification.

Abstract: A convergence tube for stereomicroscopes in which both observation beam paths are inclined relative to one another at an angle of convergence &agr; and image inversion elements are provided in both observation beam paths. Four planar reflectors R1 to R4 are provided in each of the two beam paths and are arranged relative to one another in such a way that the axis beams incident on and emergent from the reflectors R1, R2 lie in a common plane E1,2, the axis beams incident on and emergent from the reflector R3 describe a plane E3 that forms an angle &bgr;=90°+&agr;/4 with the plane E1,2, and the axis beams incident on and emergent from the reflector R4 describe a plane E4 that forms an angle &bgr;2=&agr;/2 with plane E3.

Abstract: In binoculars, a lens supporting frame which supports correction lenses, comprises a lengthwise-direction and a lateral-direction driving frames. A bar is formed on a frame mounted on an inner wall of the binoculars, being positioned approximately close to a center of the lens supporting frame. Guide holes are formed in the bar. Each guide hole is respectively positioned at a portion corresponding to an upper and a lower edge portions of the lengthwise-direction driving frame. Guide pins are respectively mounted on a center portion of the upper and the lower edge portions so as to pierce the guide holes, projecting to a side of objective lenses. When the lens supporting frame is driven in the lengthwise direction, a lengthwise-direction driving actuator pushes one of the guide pins, the lengthwise-direction driving frame being led by the guide pins in the lengthwise direction.

Abstract: An image-blur correcting optical system includes a positive blur-correcting lens group constituted by the rear lens group which is arranged to move in a direction perpendicular to the optical axis, in accordance with the magnitude of a shake imposed on the optical system. The image-blur correcting optical system satisfies the following conditions: 0.04<A/fO<0.2  (1) 0.35<B/fO<0.5  (2) TL/fO>1.1  (3) A: the distance between the blur-correcting lens group and an optical element on the object-side of the blur-correcting lens group; B: the distance between the blur-correcting lens group and an optical element on the operator's eye-side of the blur-correcting lens group; FO: the focal length of the objective optical system; and TL: the distance between the object-side surface of the most object-side lens element in the objective optical system and the image plane thereof.

Abstract: This invention relates to an optical apparatus for observation which is provided with drive control means for driving a variable angle prism on the basis of an output signal from vibration detecting means and in which the variable angle prism is installed between an objective lens and an erect prism.

Abstract: A protective assembly structured to protect an optical device, such as a pair of binoculars that include a pair of lenses, a pair of eye pieces, and a main body having at least a pair of interconnecting shafts extending from the lenses. The protective assembly itself includes a resilient material housing having a first and a second housing segments structured to receive a corresponding interconnecting shaft of the optical device snugly and protectedly therein.

Abstract: A binocular includes a hood, an eyepiece lens panel, and an objective lens panel. The hood has top, left side, and right side portions that are integrally formed. The left and right side portions have free edges that extend downwardly from the top to form an open bottom. The open bottom of the hood allows the hood to flex when an outwardly directed force is applied so that the left and right sides can be further separated from one another. This separation allows the eyepiece lens panel and the objective lens panel to be inserted within the hood during assembly of the binoculars to be held by the hood. The eyepiece lens panel has a flat plate frame and two lenses that are integrally formed as a one piece construction. The objective lens panel also has a flat plate frame and two lenses that are also integrally formed as one piece. The hood may further include alignment members to secure and align the eyepiece lens panel.

Abstract: An optical system for a binocular is provided with an objective optical system, an erecting system and an eyepiece. The objective optical system includes a first lens group having positive refractive power, a second lens group having negative refractive power and a third lens group having positive refractive power. The second lens group and/or the third lens group is capable of moving in a direction perpendicular to an optical axis to stabilize an image. The objective optical system satisfies the following conditions: (1) 0.1<d12/f0 (2) 0.7<f0/f1<3.0 where, d12 is a distance between the first lens group and the second lens group, f0 is the focal length of the objective optical system, and f1 is the focal length of the first lens group.

Abstract: An observation optical system includes, in order from an object side, an objective lens having a first lens unit of positive refractive power, a second lens unit of negative refractive power and a third lens unit of positive refractive power, an erect optical system, and an eyepiece lens of positive refractive power for observing an object image formed through the objective lens, wherein an air separation between the first lens unit and the second lens unit and an air separation between the second lens unit and the third lens unit are made variable to effect variation of magnification.

Abstract: A stereoscopic objective lens system for video endoscopes and borescopes includes two full-diameter doublets and two lens pairs forming a stereo lens set. A rotatable dual telescope is disposed between the two doublets and the stereo lens pairs, establishing a Galilean telescope associated with each stereo channel. The Galilean telescopes are each rotatable, preferably in convert, to be in or out of alignment with the system optical axis. When out of alignment, the Galilean telescopes have no effect along the optical path. When in alignment, the Galilean telescopes provide an increase or decrease in magnification, depending on orientation of the telescopes. The full-diameter doublets present equal-angle pairs from symmetrically disposed object points to the lenses of the stereo lens pair. This equal-angle property enables accurate object/image mapping onto the final stereo image pair, such that all parts of each left/right image can be mapped to within a fraction of a video pixel to each other.

Abstract: Correction lenses are driven by a lengthwise-direction actuator in order to correct a tremble of a focused image in the lengthwise direction. A rotational motion of the lengthwise-direction actuator is transmitted to the correction lenses through a lengthwise-direction direct drive mechanism. A previous rotational direction of a motor of the lengthwise-direction actuator is memorized. It is judged that a rotational direction of the motor for correcting the tremble is the same as or the reverse of the previous rotational direction. If the rotational directions are the reverse, a driving pulse amount of the motor is adjusted such that a pulse count for canceling a play of engaging portions of the lengthwise-direction direct drive mechanism is included. With respect to correcting the tremble in the lateral direction, the same operation as described above is performed.

Abstract: Binocular telescopic magnifying spectacles, both telescopes of which are pivotally mounted on a common plane, wherein each imaginary pivoting axis (8) of the telescopes 91) lies outside the telescopes (1) and on the side opposite the telescopes (1) of the ocular exit pupil (9) at a distance (d) from the ocular exit pupil (9), which is smaller than the diameter of the eye (D). The adjustment device for convergence and the adjustment device for the distance are mechanically coupled.

Abstract: A binocular-like vision system (50) for enabling an observer to view an object. The system includes an input end (72,90) that receives light from the object and an optical transfer system (62,64,86,88) that receives the light received from the input end and transfers the received light to an image intensifier (68) which intensifies the received light, wherein the intensified received light is transferred to and transmitted out of an output end (80,92) of the system, wherein the light transmitted out of the output end forms a field of view of the object that is greater than a 60 degree horizontal field of view.

Abstract: An optical system for a binocular is provided with an objective optical system, an erecting system and an observing optical system. The objective optical system includes a first lens having positive refractive power, a second lens and a third lens arranged in the order from an object side. At least one lens surface of the first lens is an aspherical surface. One of the second and third lenses has positive refractive power, the other has negative refractive power. The first lens is capable of moving in a direction orthogonal to an optical axis to stabilize an image.

Abstract: A binocular includes a pair of objective lenses, a pair of eyepieces for observing images formed by the pair of objective lenses, and a connection member arranged to integrally interconnect at least respective parts of the pair of objective lenses, wherein optical images being observed are stabilized by driving and decentering the connection member with respect to optical axes of the pair of objective lenses.

Abstract: A lightweight and small-sized high-power monocular, or binoculars, including a wide-view telescopic optical system to have a wide view and a bright field of view is provided. The wide-view telescopic optical system includes a reverse reflection optical system interposed between an objective lens system and an eye lens system. The reverse reflection optical system includes a first reflector arranged at an angle of 45 degrees to an incident optical axis. The reverse reflection optical system also includes a right-angled isosceles triangle prism having roof surfaces whose ridge line is laid on an axis parallel with the incident optical axis so as to receive a reflected light from the first reflector at a part of an oblique side surface of the prism. The reverse reflection optical system further includes a second reflector arranged to oppose another part of the oblique side surface of the right-angled isosceles triangle prism from which light reflected by the prism is emitted.

Abstract: An eyepiece cover for binoculars has two cover parts (1, 2) connected by a joint (3). By rotation around the joint (3) the cover parts (1, 2) are adjusted to the distance between the eyepieces. The adjusted distance is fixed by the friction in the joint, whereby said friction can also be formed by a catch.

Abstract: An optical architecture for an infrared vision system for binoculars or a camera. This system includes a front afocal, a scanner, an optical device forming an image of the scene and a cooled detector with cold stop. This architecture has an aperture stop which is seperate from the cold stop thereby causing varaitons in the structure flux over the extent of the detector. These varations are corrected by a suitable shape of the cold stop which smooths out the photometric inefficiency over the extent of the detector and decreases the photometric inefficiency.

Abstract: A lens system comprising a plurality of lenses have a peripheral region and a central region. The central region includes a first lens of nonunity power. The central region has a different field of view from the peripheral region.

Abstract: The invention aims to provide binoculars suitable to be used in a theater or a sports stadium, which can provide a wide and bright field of view on one hand, and which are compact and lightweight with improved portability and maneuverability on the other hand. Inverse reflection of an image is achieved by providing optical systems of inverse reflection, each comprising a pair of specular reflectors opposed to each other on an object side and an eyepiece side, respectively, so that an optical axis of light exiting the optical system of inverse reflection on the eyepiece side extends in parallel with an optical axis of light entering the optical system of inverse reflection on the object side, and one or more object lens(es) is or are placed on one or more path(s) selected from optical paths of reflection from respective specular reflectors forming the optical systems of inverse reflection.

Abstract: A telescopic lens tube protector to be fitted on telescopically connected lens tubes of a monocular or binocular telescope for protecting same from shocks of collisional impacts or the like. The lens tube protector is arranged to enshroud the entire outer peripheries of the telescopic lens tubes and constituted by a cover case which partially contains a cushioning bag structure or structures or which as a whole is in the form of a cushioning bag structure containing a cushioning material in a sealed state.

Abstract: There is provided an improved night vision goggle having a housing containing an objective lens assembly, an image intensifier tube, a collimator assembly, a splitter member, and a pair of afocal telescopes. The optical axis of the afocal telescopes are offset from the optical axis of the collimator and objective lens assemblies. A pair of achromatic doublet lens assemblies are mounted side-by-side on the exit side of the collimator and near the entrance pupils of the telescopes. The optical axes of the doublet lens assemblies are coaxial with the optical axes of the telescopes. The achromatic doublet lens assemblies thus collect light from a sub-diameter, decentered aperture of the collimator assembly, and correct axial chromatic aberration in the telescopes.

Abstract: A binocular has a focusing mechanism and a convergence angle correction mechanism. Focusing is achieved by moving an objective optical system or eyepiece optical system along an optical axis. The convergence angle correction mechanism, which is interlocked with the focusing mechanism, decenters an element of the objective optical system translationally with respect to the optical axis. The translational decentering is achieved by moving the objective optical element in a direction at an angle to the optical axis.

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: An optical system for a binocular is provided with an objective optical system, an erecting system and an eyepiece. The objective optical system includes a first lens having positive refractive power, a second lens having negative refractive power and a third lens having positive refractive power. The third lens is movable in a direction orthogonal to an optical axis to stabilize an image. The objective optical system satisfies the following relationships:0.05<d.sub.12 /f.sub.0 <0.20; and0.5<.vertline.tan 1.degree./(.phi..sub.13 -.phi..sub.12)<5.0 (unit: mm)where d.sub.12 is a distance between the first lens and the second lens, f.sub.0 is the focal length of the objective optical system, .phi..sub.12 is a composite power of the first and second lenses, and .phi..sub.13 is a composite power of the first, second and third lenses.