Abstract: An imaging lens includes, in order from an object side to an image side, a first lens having two surfaces both being convex aspheric surfaces; a second lens being aspherical and having a negative refractive power; a third lens being aspherical and having a positive refractive power; a fourth lens being aspherical and having a negative refractive power; and a fifth lens being aspherical, the fifth lens having a concave rear surface facing the image side on the optical axis, the rear surface having an inflection point at a position near its circumference, the fifth lens having a front surface facing the object side, the front surface having a smaller curvature than any other lens surface, and the fifth lens serves also as an infrared cut filter; wherein the imaging lens satisfies the following conditions: (1) TTL/2ih<0.85; and (2) 0.7<ih/f<1.1.

Abstract: An imaging optical system, including: a first lens being a meniscus lens with a positive refractive power, the first lens having a convex surface facing the object side; a second lens being a biconvex lens; a third lens being a meniscus lens with a negative refractive power, the third lens having a convex surface facing the object side; a fourth lens being a meniscus lens, the fourth lens having a convex surface or a concave surface facing the object side; a fifth lens having a concave surface facing the object side; and a sixth lens having a convex surface facing the image side; at least one surface of two surfaces of the lenses L1 to L6 has an aspherical shape. The imaging optical system satisfies the following conditions (1) and (2): 0.23<Y/f<0.29??(1) 0.9<TTL/f<1.0??(2).

Abstract: An imaging lens includes, in order from an object side to an image side, a first lens having two surfaces both being convex aspheric surfaces; a second lens being aspherical and having a negative refractive power; a third lens being aspherical and having a positive refractive power; a fourth lens being aspherical and having a negative refractive power; and a fifth lens being aspherical, the fifth lens having a concave rear surface facing the image side on the optical axis, the rear surface having an inflection point at a position near its circumference, the fifth lens having a front surface facing the object side, the front surface having a smaller curvature than any other lens surface, and the fifth lens serves also as an infrared cut filter; wherein the imaging lens satisfies the following conditions: (1) TTL/2ih<0.85; and (2) 0.7<ih/f<1.1.

Abstract: An imaging optical system, including: a first lens being a meniscus lens with a positive refractive power, the first lens having a convex surface facing the object side; a second lens being a biconvex lens; a third lens being a meniscus lens with a negative refractive power, the third lens having a convex surface facing the object side; a fourth lens being a meniscus lens, the fourth lens having a convex surface or a concave surface facing the object side; a fifth lens having a concave surface facing the object side; and a sixth lens having a convex surface facing the image side; at least one surface of two surfaces of the lenses L1 to L6 has an aspherical shape. The imaging optical system satisfies the following conditions (1) and (2): 0.23<Y/f<0.29??(1) 0.9<TTL/f<1.

Abstract: An ISDN tie line connecting system connects an ISDN tie line between two private branch exchanges via an ISDN office line using an ISDN primary rate interface. The ISDN tie line connecting system includes a tie line interface, a provisional interface for connecting an office line interface, and an interface loop-back part which is coupled to each private branch exchange. The interface loop-back part carries out a conversion between the tie line interface and the provisional interface with respect to the ISDN primary rate interface.