Abstract: An objective lens consists of a single lens element, and has a light source side surface formed into a convex surface having a large curvature and an optical recording medium side surface has a small curvature. The both surfaces are aspheric surfaces. Also, the objective lens satisfies the following expressions (1) to (3): 0.7<NA<0.98??(1) 0.70<d/f<1.40??(2) 0.48<X<0.55??(3). where NA denotes a numerical aperture of the objective lens on an optical recording medium side, d denotes a thickness of the objective lens on an optical axis in mm, and f denotes a focal length of the objective lens in mm. X is equal to (X1?X2)·(n?1)/(NA·f), where X1 and X2 denote values relating to sag amounts in the respective surfaces, and n denotes a refractive index.

Abstract: An objective lens consists of a single lens element. A light source side surface is formed into a convex surface having a large curvature, and an optical recording medium side surface has a small curvature. The both surfaces are formed into aspheric surfaces. Also, the objective lens satisfies the following expressions (1) to (3): 0.70<NA<0.98??(1) 0.70<d/f<3.00??(2) 0.50<g/d<0.80??(3) where NA denotes a numerical aperture of the objective lens on an optical recording medium side, d denotes a thickness, in mm, of the objective lens on an optical axis, and g is a distance, in mm, from a tangential plane that is perpendicular to the optical axis and is tangent to a vertex of the light source side surface of the objective lens, to a center of gravity of the objective lens.

Abstract: A zoom lens is provided and includes: a first lens group having a positive power, a second lens group having a negative power, a stop, a third lens group having a positive power, and a fourth lens group having a positive power in order. Zooming is performed by moving at least the first lens group, the second lens group, the stop, and the third lens group along the optical axis. During zooming, the stop is moved so as to be closer to an image plane at a wide-angle end than at a telephoto end and to be closer to the second lens group at the telephoto end than at the wide-angle end. The following conditional expressions (1) and (2) are satisfied. For the conditional expressions (1) and (2), fw is a focal length at the wide-angle end of the entire system, ft is a focal length at the telephoto end of the entire system, f1 is a composite focal length of the first lens group, and X1 is a displacement of the first lens group during zooming from the wide-angle end to the telephoto end. 4.0<f1/fw<7.0??(1) 0.

Abstract: An objective lens for converging light emitted from a light source on an optical recording medium to record and reproduce information consists of a single lens having at least one aspheric surface. The following conditional expressions (1) to (3) are satisfied: N?1.75??(1) 0.5<f/f1<0.6??(2) 0.8<d/(NA·De)<1.0??(3) where N denotes a refractive index, f denotes a focal length (mm), f1 denotes a focal length (mm) of a light source side surface, d denotes a thickness (mm) on an optical axis, NA denotes a numerical aperture on an optical recording medium side, and De denotes an effective aperture (mm) of the light source side surface.

Abstract: A laser beam output from a semiconductor laser light source 1 is transmitted through a cover glass 2 in the optical axis Z direction, is incident on a molded lens 4 in a state of divergent rays, is converted into convergent rays by the molded lens 4, and is applied onto a recording face 5 of the optical recording medium. A diaphragm 3 is arranged. An area of each lens surface onto which a luminous flux of the laser beam restricted by the diaphragm 3 is applied corresponds to an effective area. The following expression (1) is satisfied: d1?d0?0.04 mm??(1) where d0 denotes an effective aperture of one of the lens surfaces, and d1 denotes an outer diameter of the one of the lens surfaces.

Abstract: Disclosed are a zoom lens and an imaging apparatus having a high zoom ratio, a small total length, and a small overall size. A zoom lens includes a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, a fourth lens group having a negative refractive power, and a fifth lens group having a positive refractive power which are arranged in this order from an object side. A gap between the lens groups is changed to change power. The zoom lens satisfies the following Condition expression 1: 0.05<|f4|/ft<0.25 ??[Condition expression 1] (where ft indicates the focal length of the entire system at a telephoto end and f4 indicates the focal length of the fourth lens group).

Abstract: A zoom lens is provided and includes: in order from an object side thereof, a first lens group having a negative refractive power, a stop; a second lens group having a positive refractive power; and a third lens group having a positive refractive power. The magnification of the zoom lens is varied from a wide angle end to a telephoto end by changing a space between the first lens group and the second lens group and a space between the second lens group and the third lens group. The first lens group includes: in order from an object side thereof, a negative lens having at least one aspherical surface and having a concave surface on an image side thereof; and a positive meniscus lens having a convex surface on the object side thereof. The zoom lens satisfies conditional expressions specified in the specification.

Abstract: A zoom lens is provided and includes: a first lens group having a positive power, a second lens group having a negative power, a stop, a third lens group having a positive power, and a fourth lens group having a positive power in order. Zooming is performed by moving at least the first lens group, the second lens group, the stop, and the third lens group along the optical axis. During zooming, the stop is moved so as to be closer to an image plane at a wide-angle end than at a telephoto end and to be closer to the second lens group at the telephoto end than at the wide-angle end. The following conditional expressions (1) and (2) are satisfied. For the conditional expressions (1) and (2), fw is a focal length at the wide-angle end of the entire system, ft is a focal length at the telephoto end of the entire system, f1 is a composite focal length of the first lens group, and X1 is a displacement of the first lens group during zooming from the wide-angle end to the telephoto end. 4.0<f1/fw<7.0??(1) 0.

Abstract: An objective optical system is formed of a diffractive optical element with a diffractive surface formed on a virtual plane and an objective lens for focusing three collimated light beams of three different wavelengths at three different numerical apertures onto desired positions of three different recording media with substrates that include different thicknesses, such as an AOD, a DVD, and a CD, that introduce different amounts of spherical aberration in the focused beams. The objective optical system provides compensating spherical aberration to the three light beams by varying the distance between the diffractive optical element and the objective lens with the recording medium being used. The objective optical system focuses second-order diffracted light of one wavelength and first-order diffracted light of the other two wavelengths. An optical pickup device includes the objective optical system, the recording media, and a light source that provides the three light beams.

Abstract: A positive first lens group G1, a negative second lens group G2, an aperture diaphragm St, a positive third lens group G3, and a positive fourth lens group G4 are sequentially arranged, and a movement of the lens groups and the aperture diaphragm St during zooming is optimized in combination with an appropriate conditional expression. During zooming, a position of the aperture diaphragm St on an optical axis at a wide-angle end is closer to an image plane than that at a telephoto end, and a space on the optical axis at the wide-angle end between the aperture diaphragm St and the third lens group G3 is larger than that at the telephoto end, thereby suppressing the length of the whole lens. Also, heights of rays passing through the first lens group G1 are lowered, thereby suppressing the lens diameter of the first lens group G1.

Abstract: A variable-power optical system includes, in order from an object side, first to fifth lens groups. The first and third lens groups are fixed at a time of varying magnification and at a time of focusing. The second, fourth and fifth lens groups are movable at the time of varying magnification. The first, third and fourth lens groups have positive refractive powers. The second and fifth lens groups have negative refractive powers. The fourth lens group has a focusing function. The following conditional expressions are satisfied. 0.4<fw/f1<0.8 0.5<|f2/fw|<0.8 where fw denotes a focal length of the whole system at an wide end, f1 denotes a focal length of the first lens group, and f2 denotes a focal length of the second lens group.

Abstract: A laser beam output from a semiconductor laser light source 1 is transmitted through a cover glass 2 in the optical axis Z direction, is incident on a molded lens 4 in a state of divergent rays, is converted into convergent rays by the molded lens 4, and is applied onto a recording face 5 of the optical recording medium. A diaphragm 3 is arranged. An area of each lens surface onto which a luminous flux of the laser beam restricted by the diaphragm 3 is applied corresponds to an effective area. The following expression (1) is satisfied: d1?d0?0.04 mm??(1) where d0 denotes an effective aperture of one of the lens surfaces, and d1 denotes an outer diameter of the one of the lens surfaces.

Abstract: An objective lens for converging light emitted from a light source on an optical recording medium to record and reproduce information consists of a single lens having at least one aspheric surface. The following conditional expressions (1) to (3) are satisfied: N?1.75??(1) 0.5<f/f1<0.6??(2) 0.8<d/(NA·De)<1.0??(3) where N denotes a refractive index, f denotes a focal length (mm), f1 denotes a focal length (mm) of a light source side surface, d denotes a thickness (mm) on an optical axis, NA denotes a numerical aperture on an optical recording medium side, and De denotes an effective aperture (mm) of the light source side surface.

Abstract: An objective lens for converging light emitted from a light source onto an optical recording medium to record and reproduce information consists of a single lens that has at least one aspheric surface. The following conditional expressions (1) and (2) are satisfied: ?0.90<R1/R2<?0.45??(1) 0.70<d/f<1.40??(2) where R1 denotes a radius of curvature (mm) of a light source side surface near an optical axis, R2 denotes a radius of curvature (mm) of an optical recording medium side surface near the optical axis, d denotes a thickness (mm) on an optical axis, and f denotes a focal length (mm).

Abstract: A positive first lens group G1, a negative second lens group G2, an aperture diaphragm St, a positive third lens group G3, and a positive fourth lens group G4 are sequentially arranged, and a movement of the lens groups and the aperture diaphragm St during zooming is optimized in combination with an appropriate conditional expression. During zooming, a position of the aperture diaphragm St on an optical axis at a wide-angle end is closer to an image plane than that at a telephoto end, and a space on the optical axis at the wide-angle end between the aperture diaphragm St and the third lens group G3 is larger than that at the telephoto end, thereby suppressing the length of the whole lens. Also, heights of rays passing through the first lens group G1 are lowered, thereby suppressing the lens diameter of the first lens group G1.

Abstract: An objective optical system focuses light from a light source onto at least two different types of optical recording media having different substrate thicknesses in order to record or reproduce information on the optical recording media by using a variable refractive power element and an objective lens. The variable refractive power element may be a liquid crystal element with concentric zones that serves as a transparent plate having no convergence effect when no voltage is applied when selecting an AOD, DVD, or CD and as a converging lens when a voltage is applied when selecting a BD. Alternately, the variable refractive power element may electrically vary the refractive index of a nanoparticle dispersion or at least one liquid of a two-liquid lens element. A diffractive optical element may be used to assist in focusing light to four recording media. An optical pickup device includes the objective optical system.

Abstract: A laser beam output from a semiconductor laser light source 1 is transmitted through a cover glass 2 in the optical axis Z direction, is incident on a molded lens 4 in a state of divergent rays, is converted into convergent rays by the molded lens 4, and is applied onto a recording face 5 of the optical recording medium. A diaphragm 3 is arranged. An area of each lens surface onto which a luminous flux of the laser beam restricted by the diaphragm 3 is applied corresponds to an effective area. The following expression (1) is satisfied: d1?d0?0.04 mm??(1) where d0 denotes an effective aperture of one of the lens surfaces, and d1 denotes an outer diameter of the one of the lens surfaces.

Abstract: A variable power optical system is provided and includes a positive first lens group, a negative second lens group, a positive fifth lens group, a positive third lens group, and a negative fourth lens group containing first to third sub lens groups, in order from the side of an object. The second lens group is moved, thereby performing variable power and the third lens group is moved, thereby correcting image surface variation caused by the variable power and performing focusing. The fourth lens group is fixed at the variable power time and the focusing time. To correct image blurring, only the second sub lens group is moved in a direction perpendicular to an optical axis. Accordingly, a sufficiently good image blurring correction function can be exerted and a simple and compact configuration as a whole can be implemented.

Abstract: An objective lens consists of a single lens element, and has a light source side surface formed into a convex surface having a large curvature and an optical recording medium side surface has a small curvature. The both surfaces are aspheric surfaces. Also, the objective lens satisfies the following expressions (1) to (3): 0.7<NA<0.98 ??(1) 0.70<d/f<1.40 ??(2) 0.48<X<0.55 ??(3). where NA denotes a numerical aperture of the objective lens on an optical recording medium side, d denotes a thickness of the objective lens on an optical axis in mm, and f denotes a focal length of the objective lens in mm. X is equal to (X1?X2)·(n?1)/(NA·f), where X1 and X2 denote values relating to sag amounts in the respective surfaces, and n denotes a refractive index.

Abstract: An objective lens consists of a single lens element. A light source side surface is formed into a convex surface having a large curvature, and an optical recording medium side surface has a small curvature. The both surfaces are formed into aspheric surfaces. Also, the objective lens satisfies the following expressions (1) to (3): 0.70<NA<0.98 ??(1) 0.70<d/f<3.00 ??(2) 0.50<g/d<0.80 ??(3) where NA denotes a numerical aperture of the objective lens on an optical recording medium side, d denotes a thickness, in mm, of the objective lens on an optical axis, and g is a distance, in mm, from a tangential plane that is perpendicular to the optical axis and is tangent to a vertex of the light source side surface of the objective lens, to a center of gravity of the objective lens.