Abstract: A zoom lens comprising, in the order of an increasing distance from an object; a fixed first lens group (1) having a positive refractive power; a second lens group (2) containing an aspherical surface, having a negative refractive power and being in charge of a variable power action by being moved; a fixed third lens group (3) containing an aspherical surface and having a positive refractive power; and a fourth lens group (4) containing an aspherical surface, having a positive refractive power and moving while following up a moving object point; wherein the surface on the image plane side of a lens positioned closest to the image plane in the third lens group (3) has a concave plane having a strong refractive power with respect to the image plane and a relation, 2.0<L/CL1<2.

Abstract: A porous metal material (22) is manufactured by a method comprising a step of utilizing a magnetic field to orient numerous metal staple fibers (3), and holding these metal staple fibers (3) on the metal substrate sheet (9) in a state of being more or less perpendicular thereto by means of an adhesive (19) supplied to the metal substrate sheet (9), and a step of removing the adhesive (19) by pyrolysis, and integrally joining the metal staple fibers (3) and metal substrate sheet (9) by sintering.

Abstract: A method of producing a coated magnetic recording medium includes a step of coating a nonmagnetic substrate with a magnetic paste layer mainly composed of acicular or granular magnetic particles and a resin binder, a spontaneous drying step for a specific period for inducing leveling of the coated surface and spontaneous volatilization of solvent without applying a magnetic field from outside after coating the magnetic paint, a first orientation step for dissipating the aggregated particles by a sudden change in magnetic field while inducing magnetic moment in magnetic particles by a strong DC magnetic field inside the coated surface and in a longitudinal direction of the medium for arraying the magnetic particles in the coated surface in the longitudinal direction, and a succeeding second orientation step for suppressing the magnetic repulsive force among the particles while arraying the magnetic particles by a DC magnetic field in the coated surface in the longitudinal direction.