Lens having a high refractive index with a low dispersion

A lens having a low dispersion and a high refractive index, comprising a copolymer of at least one polyfunctional allyl monomer selected from the group consisting of diallylorthophthalate, diallylisophthalate, diallylterephthalate, diallylchlorendate, triallylcyanurate and triallylisocyanurate with at least one monomer of the formula ##STR3## in which X is H, CH.sub.3 or Cl,

• Y is H, CH.sub.3, C.sub.2 H.sub.5, n-C.sub.3 H.sub.7, iso-C.sub.3 H.sub.7, OCH.sub.3, C.sub.6 H.sub.11, Cl, Br, CH.sub.2 Cl, CH.sub.2 Br, C.sub.6 H.sub.5, CH.sub.2 C.sub.6 H.sub.5 or SCH.sub.3,
• m is 0, 1 or 2, and
• n is 0, 2, 3, 4 or 5,
• the polyfunctional allyl monomer comprising about 70 to 90% of the copolymer by weight, at most about 10% by weight of the polyfunctional allyl monomer comprising a trifunctional allyl monomer.