Abstract: An optical filter includes a substrate and a first filter layer stacked on a first surface of the substrate. The first filter layer includes a plurality of lower refractive index layers having a refractive index of less than 3; a plurality of higher refractive index layers having a refractive index of greater than 3; and a plurality of medium refractive index layers having a refractive index of 3 or more and smaller than that of the higher refractive index layers, and one higher refractive index layer and one medium refractive index layer are interposed in at least one of regions between two lower refractive index layers.

Abstract: An optical filter includes a substrate and a first filter layer stacked on a first surface of the substrate. The first filter layer includes a plurality of lower refractive index layers having a refractive index of less than 3; a plurality of higher refractive index layers having a refractive index of greater than 3; and a plurality of medium refractive index layers having a refractive index of 3 or more and smaller than that of the higher refractive index layers, and one higher refractive index layer and one medium refractive index layer are interposed in at least one of regions between two lower refractive index layers.

Abstract: The disclosed head cover for golf clubs is designed to be conveniently and rapidly placed upon or removed from a head of a golf club. The head cover may include a head receiving part and a shaft receiving part that extends longitudinally from the head receiving part. The shaft receiving part can have the shape of a bird bill and may comprise facing upper and lower mandibles. The mandibles may be the same length and be formed by two slots which extend in parallel from opposite sides of an end opening to the head receiving part. A fastening member can be provided on each of the upper and lower mandibles and may detachably fasten the mandibles to each other by a magnetic force. The fastening member may include magnets and a metal plate.