PURPOSE: To provide an inexpensive triplet lens using a plastic lens having an excellently compensated off-axis chromatic aberration by composing the lens of three lenses of a glass lens and plastic lenses and a diaphragm and satisfying a specified condition.

CONSTITUTION: This lens is composed, in order from the object side, of a glass lens L1, plastic lenses L2, L3 and a diaphragm S and satisfys the conditions (0.57<f1/f<0.72, 0.5<d2/d4<0.8, 0.25<Σd/f<0.3, 0.13<n1-n3<0.26, and 6<ν1-ν3<18, where f, f1 are the focal distances of the whole system and the glass lens L1, respectively, d2, d4 are the distances between optical axes from the surfaces of the lenses L1, L2 on the image sides to the surfaces of the lenses L2, L3 on the object sides, respectively, Σd is the distances between optical axes from the surface of the lens L1 on the object side to the surface of the lens L3 on the image side, n1, n3 are the refractive indices of the lenses L1, L3 for d line and ν1, ν3 are the Abbe numbers of lenses L1, L3, respectively).