Abstract: From an object, a first lens that is a meniscus lens having a convex surface that faces an object, a second lens that faces a concave surface of the first lens, a third lens having a concave surface that faces the second lens, and a fourth lens that is a positive lens having a convex back surface, (1) ?3<?4, (2) 0.5<Ymax/f<0.8, and (3) ?d<1.5 f are satisfied, where ?3 is an Abbe number of the third lens, ?4 is an Abbe number of the fourth lens, Ymax is a maximum height of an image, f is a composite focal length, ?d is a distance between a first surface of the first lens and a second surface of the fourth lens, the first surface facing the object and the second surface facing an imaging plane, any one surface of the first lens and the fourth lens having a non-spherical surface.

Abstract: From an object, a first lens that is a meniscus lens having a convex surface that faces an object, a second lens that faces a concave surface of the first lens, a third lens having a concave surface that faces the second lens, and a fourth lens that is a positive lens having a convex back surface, (1) ?3<?4, (2) 0.5<Ymax/f<0.8, and (3) ?d<1.5f are satisfied, where ?3 is an Abbe number of the third lens, ?4 is an Abbe number of the fourth lens, Ymax is a maximum height of an image, f is a composite focal length, ?d is a distance between a first surface of the first lens and a second surface of the fourth lens, the first surface facing the object and the second surface facing an imaging plane, any one surface of the first lens and the fourth lens having a non-spherical surface.

Abstract: The hydraulic substance according to the present invention comprises a certain amount of solid particles A (such as portland cement and mixed cement comprising portland cement), an average diameter thereof is 5 to 50 .mu.m, and solid particles B (such as silica fume comprising amorphous silica), an average diameter thereof is less than 1/5 of the particles A, and the particles B have such characteristic that they cohere to the surfaces of the particles A in water, and the quantity of the particles B is arranged such that they cover at least to make a single layer over the whole or part of surfaces of the particles A to cover whole or part of surfaces of particles A with particles B at least with a single layer, and the quantity of the water is arranged such that it is less than 60% of the total amount of the particles A and particles B.