Abstract: Glass compositions for a core/cladding type distributed-index optical element produced by a thermal-interdiffusion process using a double crucible is provided. The glass compositions comprises a glass composition for core containing 18 mol %<Li.sub.2 O.ltoreq.30 mol %, 0 mol %.ltoreq.Na.sub.2 O.ltoreq.12 mol %, 0 mol %.ltoreq.PbO.ltoreq.5 mol %, 8 mol %.ltoreq.MgO.ltoreq.18 mol %, 0.5 mol %.ltoreq.BaO.ltoreq.5 mol %, 1 mol %.ltoreq.TiO.sub.2 .ltoreq.10 mol %, and 40 mol %.ltoreq.SiO.sub.2 .ltoreq.65 mol % as major components, where 18 mol %<(Li.sub.2 O+Na.sub.2 O).ltoreq.30 mol %, 50 mol %.ltoreq.(SiO.sub.2 +TiO.sub.2).ltoreq.66 mol %, and 8 mol %.ltoreq.(MgO+PbO).ltoreq.22 mol %; and comprises a glass composition for cladding containing 18 mol %<R.sub.2 O.ltoreq.30 mol %(R.sub.2 O.dbd.Na.sub.2 O+K.sub.2 O), 0 mol %.ltoreq.PbO.ltoreq.5 mol %, 8 mol % .ltoreq.MgO.ltoreq.18 mol %, 0.5 mol %.ltoreq.BaO.ltoreq.5 mol %, 1 mol %.ltoreq.TiO.sub.2 .ltoreq.10 mol %, and 40 mol %.ltoreq.SiO.sub.2 .ltoreq.

Abstract: In a rod lens array in which a plurality of rod lenses each having a refractive-index distribution in the radial direction are arranged in one row such that the optical axes are parallel to each other, and in a life-size imaging optical apparatus using the rod lens array, the outside diameter of each rod lens is such that 0.05 mm.ltoreq.R.ltoreq.0.25 mm and 0.5R.ltoreq.r.sub.0 .ltoreq.1.0R (2R: the distance between the optical axes of adjacent rod lenses and r.sub.0 : the radius of the effective area of each rod lens that provides a lens action) and the degree of overlap m defined by m=x.sub.0 /2R is such that 1.61.ltoreq.m.ltoreq.1.80 or 2.06.ltoreq.m.ltoreq.2.50 where X.sub.0 is the view radius of a single rod lens which is given by X.sub.0 =-r.sub.0 /cos(Z.sub.0 .pi./P).

Abstract: In a rod lens array in which a plurality of rod lenses each having a refractive-index distribution in the radial direction are arranged in two rows such that the optical axis for one row is parallel to that for the other row, and in a life-size imaging optical apparatus using the rod lens array, the outside diameter of each rod lens is such that 0.05 mm.ltoreq.R.ltoreq.0.25 mm and 0.5R.ltoreq.r.sub.0 .ltoreq.1.0R (2R: the distance between the optical axes of adjacent rod lenses and r.sub.0 : the radius of the effective area of each rod lens that provides a lens action) and the degree of overlap m defined by m=X.sub.0 /2R is such that 1.46.ltoreq.m.ltoreq.1.64 (where X.sub.0 is the view radius of a single rod lens which is given by X.sub.0 =-r.sub.0 /cos(Z.sub.0 .pi./P).