Abstract: An optical scanning device (1) for scanning an information layer (2) includes a radiation source (6) for supplying a radiation beam (14), a lens system (7) having an optical axis (OO?), and a detection system 8) including: (i) an astigmatism generating element (9) for generating a first amount of astigmatism (W1) represented by a vector (Wo,1, ?1), so as to transform the radiation beam to a first astigmatic radiation beam (29); (ii) an astigmatism correcting element (27) for generating a second amount of astigmatism (W2) represented by a vector (Wo,2, ?2), so as to transform the first astigmatic radiation beam to a second astigmatic radiation beam (30) having a third amount of astigmatism (W3) represented by a vector (Wo,3, ?3), and (iii) a detector (28) for transforming the second astigmatic radiation beam to an electrical signal. According to the invention, W3 is adapted to the detector and that Wo,2 and ?2 comply substantially with the following equation: (Wo,1, 2?1)+(Wo,2, 2?2)=(Wo,3, 2?3).

Abstract: An objective lens for converging a monochromatic light flux having a specific wavelength in a range of 350 to 450 nm on an optical information recording medium while the objective lens is placed facing the optical information recording medium, the objective lens comprising: a lens body containing a polymer resin having an alicyclic structure; a first film having a refractive index of less than 1.7 for light having a wavelength of 405 nm; a second film having a refractive index of 1.7 or more for the light having the wavelength of 405 nm; and a third film having a refractive index of 1.55 or less for the light having the wavelength of 405 nm, wherein: the first film, the second film and the third film are provided on the lens body; the first film is provided between the lens body and the second film; the second film is provided between the first film and the third film; and a thickness of the first film is in a range of 50 to 15000 nm.

Abstract: An optical scanning device (1) for scanning an information layer (4) of an optical record carrier (2), the information layer (4) being covered by a transparent layer (3) of thickness td and refractive index nd. The device comprises a radiation source (11) for generating a radiation beam (12, 15, 20) and an objective system (18) for converging the radiation beam on the information layer. The objective system is characterised in comprising a lens comprising a synthetic resin on a substrate, the total thickness t of the lens satisfying the condition: Formula (I), where FWD+td/nd<0.51, and FWD is the free working distance between the lens (18) and carrier (2) and ? is the entrance pupil diameter of the lens (18), where t, td, ? and FWD are expressed in millimeters.

Abstract: A lens assembly for an image sensor comprises an aperture, a first lens, a second lens and a third lens, which are arranged sequentially from the object side. The first lens is a planoconvex lens or a positive meniscus lens whose convex surface faces the object side; the second lens is a negative meniscus lens with a convex surface facing the image side and at least has an aspherical surface; and the third lens is a positive meniscus lens with a convex surface facing the object side and, at least, has an aspherical surface. The sensitivity of decentration and the aberration-correction effect of the whole lens assembly in accordance with the present invention can be effectively improved.

Abstract: The present invention provides an optical lens having a high refractive index and a low light absorption characteristic in an ultraviolet-wavelength region; a condenser lens composed of the optical lens, fit for the near-field optical recording/reproducing system; an optical pickup that includes the condenser lens and can reduce the condensed light spot irradiating a recording medium and also manage to make the recording medium higher in recording density and greater in capacity; and an optical recording/reproducing apparatus comprising the optical pickup to enable optical recording and reproduction in high recording density to be performed.

Abstract: A lens is provided for converting a laser beam into laser lines of uniform brightness. The lens has an emission plane through which the laser beam passes, the emission plane having a continuous incline. There is also provided a method for designing the lens.

Abstract: The invention relates to an optical scanning device (1) for scanning an information layer (2) by means of a radiation beam (4). The device includes: a radiation source (6) for providing said radiation beam, a lens system (7) for transforming said radiation beam to a converging beam (16), and a wavefront modifier including a first element (301) and a second element (302) having each an aspheric surface and being mutually movable in a plane perpendicular to an optical axis (12) of said lens system for introducing a wavefront modification (W1) in said converging beam. According to the invention, the aspheric surfaces of said first and second elements are shaped so that a mutual rotational displacement of the elements about an axis of rotation (ZA) which is parallel to said optical axis (12) generates said wavefront modification (W1).

Abstract: According to the present invention, there is provided an objective lens for an optical head device which condenses two or more laser beams having wavelengths corresponding to two or more optical recording mediums having different thicknesses of transparent substrates on recording surfaces of the optical recording mediums via one optical condensing system to record information on the recording surfaces and/or reproduce the information on the recording surfaces, the objective lens comprising: a refractive surface including: a middle region which is formed in a middle portion of the refractive surface centering on an optical axis of the objective lens and which is used with respect to all of the optical recording mediums; one or more peripheral regions which are concentrically formed outside the middle region; and an aperture limiting ring band which is concentrically formed between the middle region and the peripheral region or between the peripheral regions.

Abstract: An objective lens capable of recording or reproducing informations of HD, DVD and CD is provided. A reference lens 2a and a close-contact lens 2b are closely in contact and bonded, the material of the close-contact lens 2b is different from the material of the reference lens 2a, a lens surface of the reference lens and a lens surface of the close-contact lens have aspherical shapes, the reference lens has a light-converging function, and the close-contact lens has a region providing a positive refractive power and a region providing a negative refractive power to construct an objective lens for optical information recording media.

Abstract: An optical apparatus provided in an optical pickup includes first and second light sources, a light splitting element, a condensing lens, a mounting base, a light receiving element, and a protruding piece formed on the condensing lens. The condensing lens guides transmission light from the first light source or reflection light from the second light source that are split by the light splitting element to the light receiving element. By grasping the protruding piece to protrude in a direction perpendicular to a lens axis of the condensing lens, and adjusting a mounting position of the condensing lens on the mounting base, a sufficient amount of light for stable control of a light output is applied to the light receiving element for light output monitor.

Abstract: In a beam shaping device for converting the laser light emitted from a semiconductor laser light source from an elliptic beam to a circular beam, the light-entrance-side and light-exit-side surfaces of the beam shaping device both have a curvature only in the major-axis direction of the cross section of the elliptic beam. Of the light-entrance-side and light-exit-side surfaces, one is a circular-arc cylindrical surface and the other is a non-circular-arc cylindrical surface.

Abstract: An optical system includes an objective lens; and a plastic coupling lens to change a divergent angle of a light flux emitted from a light source and is structured such that the light flux emitted from the light source passes through both of the coupling lens and the objective lens when the light flux is converged onto an optical information recording medium and the reflected light flux reflected from the optical information recording medium passes through the objective lens without passing through the coupling lens when the reflected light flux is detected by a photo-detector. A ring-shaped diffractive structure is formed on at least one surface of the coupling lens and the diffractive structure generates an under-spherical aberration when a light flux having a longer wavelength comes in, and the coupling lens has a positive refractive power as a whole.

Abstract: An aspheric lens focuses light emitting from a light-emitting diode (LED) of a light-generating dental device for curing light-curable compounds during dental procedures. The LED is preferably affixed to the end of an extension arm extending away from a light-generating dental device. A transparent shield, which is removably attachable to the extension arm, protects the aspheric lens from physical contact during use. The aspheric lens, which has a flat end and an aspheric end, is held in place by the extension arm and/or the transparent shield with the flat end of the aspheric lens being held in close proximity to the LED. Light emitted from the LED enters the flat end of the lens and exists the aspheric end of the lens, which focuses the light for curing light-curable compounds during dental procedures.

Abstract: There is provided an objective lens for an optical pick-up used for different types of optical discs. The objective lens has at least one surface on which a plurality of annular zones are formed. The at least one surface is divided into an inner area having a low NA and an outer area having high NA outside the inner area. Further, with regard to a light beam used for a second optical disc (e.g., a DVD), an optical path difference generated between at least one of steps formed between adjacent annular zones of the plurality of annular zones within the outer area is lower by a predetermined amount than an integral multiple of a wavelength of the light beam used for the second optical disc.

Abstract: An optical pickup apparatus for recording or reproducing data on a signal recording surface of a high-density optical medium that has the signal recording surface and at least one substrate includes an optical module for generating and emitting beams and receiving reflected beams from an optical medium and a solid immersion lens (SIL) arranged on an optical path between the optical module and the optical medium, having a first surface being planar and facing the substrate of the optical medium, and a second surface being aspherical and facing the optical module, so that the SIL may be nearly in contact with the substrate of the optical medium.

Abstract: The present invention is intended, as an object thereof, to improve stability against both temperature changes and light source output changes, and includes an achromatic lens having a composite structure of glass or a plastic lens having a diffraction grating counteracting a focal length change due to a wavelength change of light, where a lens holder is adhered to an opposite side to a light source of an overhang of the achromatic lens made of glass while the lens holder is adhered to a light source side of the overhang of the plastic lens with the diffraction grating.

Abstract: An optical pickup lens having a lens and a lens holder, each of which has at least one mark in a direction of rotation based on an optical axis of the lens as a center of rotation. The mark(s) of the lens holder is provided so as to oppose the mark(s) of the lens. Preferably, the marks of the lens and the marks of the lens holder are provided at regular intervals. Since both the lens and the lens holder have the marks thereon, the lens can be mounted on the lens holder at a predetermined angle in the direction of rotation of the lens based on the center of rotation of the lens.

Abstract: An optical module has a first light source which emits a first light beam from a first light emission point in a predetermined direction, a second light source which emits a second light beam from a second light emission point in the predetermined direction, and an optical element. The optical element includes a plurality of reflection surfaces for reflecting the first and second light beams, and finally outputting the first and second light beams in the predetermined direction with a separation between the first and second light beams smaller than a distance between the first and second light emission points.

Abstract: An aspherical lens (10, 10?) has an aspherical surface (101, 101?) and an opposite flat surface (102, 102?). A multiple-step grating is defined in the flat surface by a photolithographic method. The aspherical lens has a reduced chromatic aberration effect, and can thus provide a clear image. Furthermore, an effect of the aspherical lens having the grating is equivalent to that of a conventional aspherical lens unit. Thus, when the aspherical lens is used in an optical system, it can reduce a bulk and a weight of the optical system.

Abstract: An objective lens for use in an optical pickup apparatus has two positive lenses of a first lens arranged at a light source side and a second lens arranged at an information recording medium side and the objective lens comprises a first surface being a light source side optical surface of the first lens and a third surface being a light source side optical surface of the second lens, and at least two optical surfaces including the first surface and the third surface are made to be an aspherical surface respectively, and the objective lens satisfies the following formulas: NA?0.8 1.2 mm>f>0.3 mm ?0.06>?SAG>?0.24 ?SAG=(X1??X3?)/(NA4·f·(1+|m|)) X1?=X1·(N1?3)3/f1 X3?=X3·(N2?1)3/f2.

Abstract: An optical element having an optical axis, comprises an element body having the maximum first length of 4 mm or less in the optical axis direction and the second maximum length of 6 mm or less in the direction perpendicular to the optical axis direction; wherein the element body is made of a resin containing a polymer having an alicyclic structure and is treated by one of heat treatment and wet-heat treatment for 16 hours or longer at a temperature lower by 35° C. to 45° C. than the glass transition temperature of the resin after the element body has been formed by injecting the resin in a mold, where the glass transition temperature of the resin is measured by differential-scanning-calorimetry method at heating rate 10° C./min on the basis of JIS K7121.

Abstract: An optical pickup lens device includes, in the order from the light source side, collimating means for converting a bundle of rays into parallel rays or predetermined convergent or divergent rays, the collimating means being movably held along a direction of an optical axis of a bundle of rays emitted from a light source; an aberration correcting element for allowing a bundle of rays emitted from the collimating means to be transmitted therethrough; and an objective lens element having a numerical aperture of 0.8 or more, and converging a bundle of rays coming from the aberration correcting element onto the information recording medium to form a spot. The aberration correcting element and the objective lens element are integrally held together in a direction orthogonal to the optical axis so as to perform tracking on the information recording medium, and satisfy predetermined conditions.

Abstract: An optical lens whose focal length is different on first and second planes perpendicular to each other is provided. The optical lens is configured such that a convex element, which is formed integrally with a substrate having a flat face, has a convex curved face that functions as an optical lens and is shaped such that the curvature on a first cross section and the curvature on a second cross section perpendicular to and intersecting with the first cross section are different from each other, whereby the focal lengths on the first and second cross sections are different from each other. A groove of a substantially elliptical shape or a substantially rectangular shape is formed along the boundary between the substrate and the convex element. The optical lens is used to produce a focus error signal or is incorporated into an optical pickup apparatus.

Abstract: An objective lens is configured of a first crown-glass lens and a second flint-glass lens, whereby it can exhibit substantially identical optical properties at a plurality of recording/reproducing light source wavelengths, particularly, in both 650 nm and 405 nm wavelength bands. Also, by maximizing the difference in glass transition point between the first and second lenses, one of the first and second lenses having a higher glass transition point is molded first, to allow that first molded lens to serve as a mold tool for molding the other lens. This dispenses with the steps of aligning and adhesive bonding the two lenses, whereby this objective lens can be used at a plurality of wavelengths as a single objective lens, and thus an information recording/reproducing apparatus can be of a simple configuration.

Abstract: An optical scanning device for scanning an information layer (104) of an optical record carrier (102) includes a radiation source (110) for generating a radiation beam (108) and a high-NA objective system (118) for converging the radiation beam on the information layer. The objective system includes a first lens (116) and a second lens (117). The first lens includes a glass body and the second lens is made of plastic. The signs of the temperature-dependences of the spherical aberration of the first and second lens are different, thereby reducing the temperature-dependence of the spherical aberration of the objective system as a whole.

Abstract: An objective lens that satisfies conditions: ?0.02<f1×M1<0.02??(1) ?0.02<f2×M2<0.02??(2) ?0.29<f3×M3<?0.19.??(3) At least one of lens surfaces of the objective lens includes a diffracting structure having a first region for converging the third light beam on a data recording layer of the third optical disc. The diffracting structure within the first region is configured such that a diffraction order at which diffraction efficiency of the first light beam is maximized is a sixth order, a diffraction order at which the diffraction efficiency of the second light beam is maximized is a fourth order, and a diffraction order at which the diffraction efficiency of the third light beam is maximized is a third order.

Abstract: An optical pickup actuator includes a base having a holder installed at one side thereof, a moving portion in which an objective lens is installed at the periphery thereof and a guide hole is formed, a bobbin coupled to the guide hole, a magnetic driving portion provided at the base and symmetrically arranged to make the moving portion perform focusing and tracking, and suspensions having one end supported at the holder and the other end fixed to the moving portion to be connected to the bobbin. Thus, since the magnetic driving portion is symmetrically arranged, a pitching mode and a rolling mode generated due to an asymmetrical structure are prevented. Also, the AC sensitivity and DC sensitivity can be improved.

Abstract: A low-cost bright image-pick up lens of a small size is provided which is short in total length, wherein the angle of field is beyond 30°; the angle of incidence onto the image pickup device is narrowed; and various aberrations are appropriately corrected. The image-pick up lens comprises, from the side of an object, an aperture stop, a biconvex positive lens, and a meniscus lens having a concave surface on the object side, and each of the lenses includes at least one aspheric surface.

Abstract: An optical scanning device (1) for scanning an information layer (4) of an optical record carrier (2), the device including a radiation source (11) for generating a radiation beam (12) and an objective system (18) for converging the radiation beam (12) on the information layer, the objective system (18) being characterized in that the ratio of the root mean square of the optical path difference's (OPD's) generated by the objective system at oblique beam entrance to the system satisfies the condition of formula (I) within the field of the objective system, where OPD(A31) is the contribution of the third order Zernike coma to the root mean square wavefront aberration and OPD(A51) is the contribution of the fifth order Zernike coma to the root mean square wavefront aberration.

Abstract: An optical system for use in an optical pickup apparatus has a chromatic aberration correcting element having plural ring-shaped zones divided with a stepped section in such a way that one of the neighboring ring-shaped zones located apart from the optical axis has a longer optical path than the other one located closer to the optical axis, and an objective lens having plural ring-shaped zones divided with a stepped section shaped in the optical axis direction in such a way that the stepped section causes a optical path difference between light fluxes having passed through the neighboring ring-shaped zones. The ring-shaped zonal structure of the chromatic aberration correcting element corrects a deviation of a focal point caused by the objective lens due to a wavelength fluctuation of an incident light flux coming into the optical system.

Abstract: The invention relates to an optical device for focusing a laser beam, comprising a source of emission of a laser beam, for example a substantially elliptic and astigmatic laser beam, a focusing lens of the laser beam and first aperture adapted to select a central portion of the laser beam. The first aperture is directly applied on the focusing lens, and comprises a coating made of a substantially opaque material which are applied (for example, by spraying, sputtering, evaporation, printing, painting) on a peripheral portion of a front surface of the focusing lens so as to allow the propagation of the central portion of the laser beam and obstruct the propagation of a surrounding portion of beam. The device of the invention is extremely simple from the constructive point of view, and is inexpensive and small-sized.

Abstract: At least two Fresnel lenses are formed on a transparent substrate, and a set of parallel plates are established in an acute included angle (from 19° to 90°) with the transparent substrate by an inclined exposure process employing a thick film photoresist. The parallel plates are separately placed over the Fresnel lenses. Metal layers are separately deposited on the outside surfaces of the parallel plates far from the acute included angle. A transparent polymeric material is overlaid on the surface of the transparent substrate till the parallel plates are immersed. An objective lens, placed over a photo detector, is formed on the surface of the transparent polymeric material. A laser diode is placed at a location on the surface of the substrate opposite to one of the Fresnel lenses, and the photo detector is placed at a location on the surface of that opposite to another of the Fresnel lenses.

Abstract: A lens includes a plane surface whose normal direction virtually conforms to an optical axis direction, and a reflecting part is provided on the plane surface to reflect only light within a predetermined waveband. Consequently, inclination of the lens can be detected with high accuracy.

Abstract: An objective lens for scanning DVD and HD-DVD optical disks, comprising a first part and a second part, wherein said first part is shaped to comprise a first surface and an opposing second surface, said second part is shaped to comprise a third surface and an opposing fourth surface, said first surface is of a convex shape providing a main part of the lens power, said third surface is shaped to fit said first surface, and wherein said fourth surface is a generally aspherical surface, said second part being formed of synthetic resin material and said first part being formed of a material having a refractive index n1 having a value between 1.65 and 2, wherein the Abbe number V1 of the first part and the Abbe number V0 of the second part comply with the following relation (Formula I).

Abstract: A hybrid lens and a projection optical system having the hybrid lens are provided. The projection optical system includes a hybrid lens that is positioned along an optical path between a fluorescent surface and a screen onto which light emitted from the fluorescent surface is projected to form an image. The hybrid lens includes a spherical lens and an aspherical lens formed of plastic on at least one surface of the spherical lens. Accordingly, aberration can be corrected to improve image quality.

Abstract: Disclosed is an objective lens for a DVD/CD compatible optical pickup, which improves optical efficiency while minimizing aberration occurring due to different disc thicknesses of different optical storage media. The objective lens has first and second aspherical lens surfaces.

Abstract: A long-throw, tight focussing optical coupler has a first passive optical element capable of coupling light between an optical source and an optical destination and a second passive optical element, capable of coupling light between the optical source and the optical destination, located between the first passive optical element and one of the optical source or the optical destination such that, a light beam from the optical source will be transferred to the optical destination when the optical source and optical destination are spaced apart by a distance.

Abstract: There is provided an objective lens used for at least three types of optical discs when thicknesses are respectively represented by t1, t2 and t3, t1 as 0.6 mm, t2 is 0.6 mm and t3 is 1.2 mm. When numerical apertures for the first, second and third optical discs are respectively represented by NA1, NA2 and NA3, a relationship NA1>NA2>NA3 is satisfied. When the first and second optical discs are used, collimated light beams are incident on the objective lens. When the third optical disc is used, a diverging beam is incident on the objective lens. The following conditions are satisfied: ?0.02<f1×M1<0.02 * * * (1), ?0.02<f2×M2<0.02 * * * (2), and ?0.29<f3×M3<?0.19 * * * (3).

Abstract: An optical lens whose focal length is different on first and second planes perpendicular to each other is provided. The optical lens is configured such that a convex element, which is formed integrally with a substrate having a flat face, has a convex curved face that functions as an optical lens and is shaped such that the curvature on a first cross section and the curvature on a second cross section perpendicular to and intersecting with the first cross section are different from each other, whereby the focal lengths on the first and second cross sections are different from each other. A groove of a substantially elliptical shape or a substantially rectangular shape is formed along the boundary between the substrate and the convex element. The optical lens is used to produce a focus error signal or is incorporated into an optical pickup apparatus.

Abstract: When a ratio R between a total angle ? of a widening angle in a median intensity of light of a light source (a GaN based semiconductor laser) and a total angle 2/? of a widening angle of light defining a numerical aperture NA of a collimator optical system (collimator lens) is defined as R=(sin?1NA)×2/?, the numerical aperture of the collimator optical system (collimator lens) is set so that 2.0?R?0.58. Thus, an image exposure device is provided that can suppress stray light of a light source that emits a large amount of stray light.

Abstract: A lens is provided for converting a laser beam into laser lines of uniform brightness. The lens has an emission plane through which the laser beam passes, the emission plane having a continuous incline. There is also provided a method for designing the lens.

Abstract: When the DVD provided with the DVD substrate 2 having thickness t2 of 0.6 mm is installed in the optical disc apparatus, the light beam 4 having wavelength ?1=655 nm is used as luminous flux of numerical aperture NA=0.63 to be condensed on the information surface 2a on the DVD substrate 2. When the CD provided with the CD substrate 3 having thickness t2 of 1.2 mm is installed in the optical disc apparatus, the light beam 5 having wavelength ?2=790 nm is effectively used as luminous flux of approximate numerical aperture NA=0.45 to be condensed on the information surface 3a on the DVD substrate 3. The wavefront aberration caused by a thickness difference between the DVD substrate 2 and CD substrate 3 is canceled out by the chromatic aberration caused by a wavelength difference between the light beams 4 and 5. Therefore, in spite of the difference in the transparent substrates, the light beams are suitably condensed respectively on the information surface 2a and 3a.

Abstract: An optical pickup apparatus for reproducing information from an optical information recording medium or for recording information onto an optical information recording medium, is provided with a first light source for emitting first light flux having a first wavelength; a second light source for emitting second light flux having a second wavelength, the first wavelength being different from the second wavelength; a converging optical system having an optical axis and a diffractive portion, and a photo detector; wherein in case that the first light flux passes through the diffractive portion to generate at least one diffracted ray, an amount of n-th ordered diffracted ray of the first light flux is greater than that of any other ordered diffracted ray of the first light flux, and in case that the second light flux passes through the diffractive portion to generate at least one diffracted ray, an amount of n-th ordered diffracted ray of the second light flux is greater than that of any other ordered diffracted

Abstract: An integrated type optical pickup module apparently approximates a plurality of light-emitting points of semiconductor lasers. An optical element is interposed between first and second semiconductor lasers. The optical element has first and second reflecting surfaces perpendicular to each other. The first and second reflecting surfaces reflect laser beams projected from the first and second semiconductor lasers, respectively. The optical element further has a mounting surface perpendicular to both the first and second reflecting surfaces. The optical element is mounted, via the mounting surface of the optical element, to a submount having a top surface on which the first and second semiconductor lasers are mounted. Heterojunction surfaces of the first and second semiconductor lasers may be substantially perpendicular to the first and second reflecting surfaces, respectively.

Abstract: A recess 14 is provided in a lens accommodating portion 13 of a laser holder 10 for holding a collimator lens C, whereby positional accuracy and adhesion strength of the lens and a light source are improved.

Abstract: An objective lens for recording and/or reproducing information of an optical information recording medium, comprises a first lens group having a positive refractive power and a second lens group having a positive refractive power. The first lens group and the second lens group are arranged in this order from a light source side. The objective lens is a finite conjugate type to converge a divergent light flux from a light source onto an information recording plane of the optical information recording medium and satisfies the following formula: NA?0.65 where NA is an image-side numerical aperture necessary for conducting recording and/or reproducing information of the optical information recording medium.

Abstract: An objective lens system for optical pickups reading and/or writing information by condensing a luminous flux from a light source onto an optical information recording medium, consists of, a single lens having, from a light source side, a first surface convex to the light source side and a second surface convex to an image side. A medium of the single lens is a homogeneous medium. At least one of the two surfaces is aspherical. The system satisfies the predetermined conditions.

Abstract: An objective lens for use in an optical pickup apparatus, comprises a first lens molded with a plastic and having an optically functional section, flange section provided around the periphery of the optically functional section, and a first contacting section provided on the flange section; and a second lens molded with a plastic, located opposite to the first lens and having an optically functional section, a flange section provided around the periphery of the optically functional section, and a second contacting section provided on the flange section. The first lens and the second lens are joined in such a way that the first contacting section and the second contacting section are brought in contact with each other.

Abstract: An optical recording/reproducing apparatus is arranged so that, upon recording or reproducing a recording medium having a plurality of recording layers, the gap of the lens groups at the time of forming a converged light spot on this first recording layer is DIS(1), the gap of the lens groups at the time of forming the converged light spot on the N-th layer (the farthest layer from the surface of the recording medium) is DIS(N) and the neutral point of the spherical-aberration correcting mechanism is set at a position satisfying the following expression: lens group gap dst(3)=((DIS (1)+DIS(N))/2.

Abstract: A lens device which can be used as an objective lens in an optical pickup apparatus includes an objective lens provided along a light path facing a disc and having a predetermined effective diameter, and light controlling means provided along the light path for controlling the light in an intermediate region between near and far axes of an incident light beam, thus providing a simplified and inexpensive device for using discs of differing thickness in a single disc drive, by reducing the spherical aberration effect.