Abstract: A zoom lens comprises a first lens group having negative refractive power; a second lens group having positive refractive power; a third lens group having negative refractive power and a fourth lens group having positive refractive power. Upon varying magnification, distances between the first lens group and the second lens group, between the second lens group and the third lens group and between the third lens group and the fourth lens group vary. The second lens group includes a front lens group, an aperture stop, and a rear lens group. Each of the front lens group and the rear lens group includes at least one negative lens. At least a part of the lenses in the second lens group is moved as a group to have a component in a direction perpendicular to an optical axis.

Abstract: A zoom lens comprises, in order from an object side: a first lens group G1 having negative refractive power; a second lens group G2 having positive refractive power; a third lens group G3 having negative refractive power and a fourth lens group G4 having positive refractive power. Upon varying magnification, a distance between the first lens group G1 and the second lens group G2, a distance between the second lens group G2 and the third lens group G3 and a distance between the third lens group G3 and the fourth lens group G4 are varied. The second lens group G2 includes, in order from the object side, a front lens group G2F, an aperture stop S, and a rear lens group G2R. Each of the front lens group G2F and the rear lens group G2R includes at least one negative lens. At least a part of the lenses in the second lens group G2 is moved as a movable group to have a component in a direction perpendicular to the optical axis. Thus, the zoom lens can have high optical performances.

Abstract: A manufacturing method includes, cutting out a plurality of rings, polishing the rings, adjusting the plurality of rings so that they exhibit circumferential lengths respectively predetermined for them, nitriding the plurality of rings, and assembling in order to layer the plurality of rings into a multi-layered ring; wherein after the rings are cut out from the pipe, each of them is polished one by one so that their order is not changed; in nitriding, they are subjected to a nitriding process in a state where they are set in a jig in order to keep their order; and in assembling, the rings are assembled so that rings that were parts originally adjacent to each other in a state of the pipe become layers that are adjacent to each other in the multi-layered ring.

Abstract: A hearing aid (100) comprises a body case (2) that is worn behind an ear (1), a sound conductor (3) that is linked at one end to the body case (2) and is linked at the other end to an earpiece (6), and an engaging component (8) for holding the earpiece linked to the other end of the sound conductor in the external auditory canal (7) of the ear (1). The engaging component (8) is made up of a first arc part (8a) disposed on the earpiece (6) side, a second arc part (8b) that is larger than the first arc part (8a) and is disposed opposite the first arc part (8a), a first linking part (8c) that links one end of the first arc part (8a) and one end of the second arc part (8b), and a second linking part (8d) that links the other end of the first arc part (8a) and the other end of the second arc part (8b). The second linking part (8d) has a shape such that its center part protrudes toward the first linking part (8c). This constitution allows the hearing aid (100) to be put on more easily.

Abstract: A hearing aid (100) comprises a body case (2) that is worn behind an ear (1), a sound conductor (3) that is linked at one end to the body case (2) and is linked at the other end to an earpiece (6), and an engaging component (8) for holding the earpiece linked to the other end of the sound conductor in the external auditory canal (7) of the ear (1). The engaging component (8) is made up of a first arc part (8a) disposed on the earpiece (6) side, a second arc part (8b) that is larger than the first arc part (8a) and is disposed opposite the first arc part (8a), a first linking part (8c) that links one end of the first arc part (8a) and one end of the second arc part (8b), and a second linking part (8d) that links the other end of the first arc part (8a) and the other end of the second arc part (8b). The second linking part (8d) has a shape such that its center part protrudes toward the first linking part (8c). This constitution allows the hearing aid (100) to be put on more easily.

Abstract: The forming recesses of a lower die and an upper die are formed to have a semi-oval profile so as to provide a forming space almost oval in section with the dies closed. The parting line between the lower die and the upper die is deviated as much as h from the major axis of the forming space toward the upper die side, and the opening width of the forming recess of the lower die is set to be slightly larger than the opening width of the forming recess of the upper die. A metal bent tube is plastic-deformed into an almost oval shape in section by closing the dies while being compressed in a peripheral direction by the lower and upper dies to eliminate spring-back caused by bending, whereby the buckling and pinching toward the outer side of the tube wall is prevented by the expanded portion of the lower die and buckling toward the inner side of the tube wall is prevented by a step difference formed by the difference in opening width between the lower die and the upper die.

Abstract: The forming recesses of a lower die and an upper die are formed to have a semi-oval profile so as to provide a forming space almost oval in section with the dies closed. The parting line between the lower die and the upper die is deviated as much as h from the major axis of the forming space toward the upper die side, and the opening width of the forming recess of the lower die is set to be slightly larger than the opening width of the forming recess of the upper die. A metal bent tube is plastic-deformed into an almost oval shape in section by closing the dies while being compressed in a peripheral direction by the lower and upper dies to eliminate spring-back caused by bending, whereby the buckling and pinching toward the outer side of the tube wall is prevented by the expanded portion of the lower die and buckling toward the inner side of the tube wall is prevented by a step difference formed by the difference in opening width between the lower die and the upper die.