Abstract: In a diffraction type optical pickup lens, at least one surface of a convergent lens is formed with such an aspheric surface that a luminous flux having a wavelength ?1 is converged at a first predetermined position. At least one surface of the convergent lens is formed with a zone plate having such a wavelength selectivity that a luminous flux having a wavelength ?2 is converged at a second predetermined position whereas the luminous flux having a wavelength ?1 is transmitted therethrough as it is. The convergent lens is transparent to the luminous fluxes having the wavelengths ?1 and ?2.

Abstract: In a diffraction type optical pickup lens, at least one surface of a convergent lens is formed with such an aspheric surface that a luminous flux having a wavelength &lgr;1 is converged at a first predetermined position. At least one surface of the convergent lens is formed with a zone plate having such a wavelength selectivity that a luminous flux having a wavelength &lgr;2 is converged at a second predetermined position whereas the luminous flux having a wavelength &lgr;1 is transmitted therethrough as it is. The convergent lens is transparent to the luminous fluxes having the wavelengths &lgr;1 and &lgr;2.

Abstract: A luminous flux diameter variable type objective lens having a wavelength selectivity is disposed within a luminous flux. Arranged on a surface of the lens are a first region 11 with no diffraction gratings, and a second region 12 with diffraction gratings. The diffraction gratings each having a rectangular cross section are linearly arranged in the second region 12. The thickness (height) h of the diffraction grating 12A is set to such a value that the ratio of ± first-order diffracted light becomes much greater for the light having a wavelength of 780 nm used for CD-R, whereas the ratio of zero-order diffracted light becomes substantially 100% for the light having a wavelength of 635 nm used for DVD.

Abstract: A diffractive optical element includes an optically functioning part including a diffraction grating and a flange part disposed around the optically functioning part. On an outer circumferential face of the flange part, there are at least three protrusions at respective different locations. The protrusions project outward from the outer circumferential face.

Abstract: A plastic lens which is easy to mold and has favorable optical precision. This plastic lens has a flange at the outer periphery of an optically functioning portion, a part of the peripheral surface of the flange being provided with a gate-positioning projection, and a side face of the gate-positioned projection including a cut-off portion.

Abstract: Provided is a storage case for a diffraction grating, which accommodates the diffraction grating in a constant orientation, so as to improve efficiency in the operation for assembling the diffraction grating. The storage sections each accommodate a diffraction grating Each storage section forms a storage space for accommodating a diffraction grating. The storage space is equipped with a rib for engaging the outer peripheral portion of the diffraction grating.

Abstract: Provided is an optical lens which can reduce and easily adjust astigmatism. The optical lens has a flange at an outer periphery of an optically functioning portion. The flange has smaller-diameter sections recessed inward from its outer peripheral portion. The smaller-diameter sections are located at positions symmetrical to each other about an optical axis of the optically functioning portion.

Abstract: A multifocal lens having a plurality of focal points with focal positions different from each other includes a central optical portion, centered at an optical axis, having a predetermined refractive index. The lens further includes at least one outer optical portion which is an optical member disposed like a ring around an outer periphery of the central optical portion so as to be centered at the optical axis, each having a different refractive index different from the predetermined refractive index and having an optical surface continuous with an optical surface of another optical portion disposed on the center side.

Abstract: An optical lens made of plastic includes an optically functioning part, a flange part and disposed around the optically functioning part. The flange part has an outer circumferential face having a cylindrical surface about a lens optical axis. A gate-removed part is located at the outer circumferential face as an outward-projecting quadratic surface. The gate-removed part is located between a virtual outer circumferential face and a plane passing through a tolerance limit on the lens optical axis side. The virtual outer circumferential face is defined when a residual gate part is cut along a cylindrical surface coaxial with the lens optical axis and having a radius identical to that of the outer circumferential face. The plane is set on the lens optical axis side when the residual gate part is removed by cutting the flange part.

Abstract: A lens includes a center-of-gravity adjusting section in order to prevent the center of gravity of the lens from shifting due to removal of a gate portion formed during molding, thereby providing an optical lens which is easily handled and a method of making the optical lens. An optical lens having a flange at the outer periphery of an optically functioning portion includes a gate-cut section formed by cutting off a part of the flange together with a gate portion, continuously with the flange, and a center-of-axis adjusting section, formed by removing a part of the flange, for positioning the center of gravity in alignment with the optical axis of the optically functioning portion.

Abstract: A plastic lens has a flange provided with a reflecting plane, so that its inclination upon assembling can be detected and adjusted efficiently and accurately. This plastic lens has the flange at an outer periphery of an optically functioning portion. A surface of the flange surrounding the optically functioning portion is a reflecting plane perpendicular to an optical axis of the optically functioning portion.

Abstract: A plastic lens includes an optically functioning section, a flange section disposed at an outer periphery thereof, a reference surface formed at an outer peripheral portion of the flange section and adapted to become a reference for attachment, and a tapered surface formed on at least a part of the outer peripheral portion of the flange section which is located closer to the optically functioning section side than is the reference surface so as to taper down its diameter along the optical axis of the optically functioning section. The tapered surface forms a surface at which a gate for resin injection is located upon manufacture.

Abstract: A lens case containing lenses includes a tubular case body and lenses contained in the case body. The case body includes first and second opposed walls having respective inner surfaces, and two protrusions projecting from each of the inner surfaces. The protrusions on the inner surface of the first wall are directly opposite corresponding protrusions on the inner surface of the second wall. Each of the lenses has a central optically functioning part and circumferential peripheral flanges, and the flanges of the lenses abut the protrusions.

Abstract: An objective lens for a pickup optical system for optically reading out information recorded in a recording medium , includes a first lens body and a second lens body integrally attached to a surface of the first lens body and having a micro Fresnel portion for focusing light to a predetermined position of the recording medium. When the objective lens is used for a pickup optical system, the micro Fresnel portion faces away from an accommodation region for accommodating the recording medium to prevent dust from attaching to the micro Fresnel portion.

Abstract: An optical lens made of plastic comprises an optically functioning part, a flange part disposed around the optically functioning part, and a gate-removed part located at an outer circumferential face of the flange part. The gate-removed part is defined by removing a residual gate part projecting from the outer circumferential face. The surface of the gate-removed part is covered with a hygroscopicity adjusting part. The hygroscopicity adjusting part is made of a material less hygroscopic than the plastic of which the optical lens is made.