Abstract: An image taking lens LA comprises an aperture S1, a first lens L1 and a second lens L2 which are arranged in this order from an object side to an image side. The first lens L1 has a positive power and a meniscus shape with a convex surface facing an object; and the second lens L2 has a positive power with a convex surface facing an image. The first lens L1 and the second lens L2 satisfy the following formulae (1) and (2): 0.30<R1/R2<0.65??(1) 0.30<d3/F<0.50??(2) This image taking lens formed of the two lenses is small in size and has a high optical performance, in which the entire image taking lens has a short focal length.

Abstract: An image taking lens 1 comprises a stop 2, a first lens 3 having a positive power and biconvex configuration, a second lens 4 having a negative power and having a meniscus configuration in which a concave surface is disposed to face an object, a third lens 5 having a positive power and a meniscus configuration in which a convex surface is disposed to face an image, and a fourth lens 6 having a negative power and a meniscus configuration in which a convex surface is disposed to face the object, which are arranged in this order from the object. The lenses 3 to 6 satisfy the following formulae (1) to (4), 3.00<F1/d1<10.00??(1) ?20.0<F2/d3<?10.0??(2) 50.0<?1<60.0??(3) 20.0<?2<30.0??(4) hereupon, F1: focal length of the first lens; F2: focal length of the second lens; d1: a center thickness of the first lens; d3: a center thickness of the second lens; ?1: an Abbe's number of the first lens; and ?2: an Abbe's number of the second lens.

Abstract: An image taking lens LA comprises an aperture S1, a first lens L1 and a second lens L2 which are arranged in this order from an object side to an image side. The firs lens L1 has a positive power and a meniscus shape with a convex surface facing an object; and the second lens L2 has a positive power with a convex surface facing an image. The first lens L1 and the second lens L2 satisfy the following formulae (1) and (2): 0.30<R1/R2<0.65 ??(1) 0.30<d3/F<0.50 ??(2) This image taking lens formed of the two lenses is small in size and has a high optical performance, in which the entire image taking lens has a short focal length.

Abstract: An image taking lens 1 comprises a stop 2, a first lens 3 having a positive power and biconvex configuration, a second lens 4 having a negative power and having a meniscus configuration in which a concave surface is disposed to face an object, a third lens 5 having a positive power and a meniscus configuration in which a convex surface is disposed to face an image, and a fourth lens 6 having a negative power and a meniscus configuration in which a convex surface is disposed to face the object, which are arranged in this order from the object. The lenses 3 to 6 satisfy the following formulae (1) to (4), 3.00<F1/d1<10.00??(1) ?20.0<F2/d3<?10.0??(2) 50.0<?1<60.0??(3) 20.0<?2<30.0??(4) hereupon, F1: focal length of the first lens; F2: focal length of the second lens; d1: a center thickness of the first lens; d3: a center thickness of the second lens; ?1: an Abbe's number of the first lens; and ?2: an Abbe's number of the second lens.

Abstract: A process for producing a lactam copolymer, which comprises copolymerizing an omega-lactam and a diene polymer having an amino or imino group at molecular ends by the action of an alkaline catalyst and a polyfunctional co-catalyst, the proportions of the components satisfying the following equations (I) and (II)a/c>1/4 (I)b/c>1 (II)wherein a, b and c represent the equivalent weights of the alkaline catalyst, the polyfunctional co-catalyst and the diene polymer, respectively, per equivalent of omega-lactam.

Abstract: A molded article is formed by a reaction injection molding method wherein a starting material, e.g., an .omega.-lactam, is injected into a mold, the inner pressure of which is maintained at 0.5 to 20 kg/cm.sup.2 .multidot.G with an inert gas; and the inner pressure of the mold is maintained at a level higher than the pressure increased by injection of the starting material until the polymerization molding of the starting material is completed.

Abstract: A process for preparing polyamides having improved impact strength and elongation comprising polymerizing an -lactam in the presence of (1) an alkali catalyst and (2) the reaction product of (a) a polyfunctional co-catalyst such as a polyisocyanate and (b) a polyoxyalkalene amine. The polyamides of the present invention are particularly useful for making strong tough molded or cast articles.