Reduces benzil stereospecifically to (S)-benzoin. Can also reduce 1-phenyl-1,2-propanedione, 1,4-naphthoquinone, 1-(4-methyl-phenyl)-2-phenyl-ethane-1,2-dione, 1-(4-fluoro-phenyl)-2-phenyl-ethane-1,2-dione, methyl benzoylformate, p-nitrobenzaldehyde in decreasing order. (S)-benzoin + NADP(+) = benzil + H(+) + NADPH Inhibited by Cibacron blue 3 GA. Optimum pH is 6.0-8.0. Optimum temperature is 50 degrees Celsius (at pH 6.5). Belongs to the short-chain dehydrogenases/reductases (SDR) family.