ابن سهل
Ibn Sahl, a mathematician active in Baghdad during the 980s, is the first Islamic scholar known to have compiled a commentary on Ptolemy's "Optics". His treatise "Fī al-'āla al-muḥriqa" "On the burning instruments" was reconstructed from fragmentary manuscripts by Rashed (1993). The work is concerned with how curved mirrors and lenses bend and focus light. Ibn Sahl also describes a law of refraction mathematically equivalent to Snell's law. He used his law of refraction to compute the shapes of lenses and mirrors that focus light at a single point on the axis.