A transparent optical component consisting of one or more pieces of optical glass with surfaces so curved (usually spherical) that they serve to converge or diverge the transmitted rays from an object, thus forming a real or virtual image of that object.  

FEGFE supplies lenses with following materials: BK7, Fused Silica, ZnSe, Ge, Silicon, ZnS, Sapphire, CaF₂ and MgF₂.