You don't say what format you are using. 85 mm is a bit long on DX and traditionally considered the shortest for FX format. You also don't need lenses with the widest aperture possible. At typical portrait distances apertures (check your spelling for this word) of f/2.8 and f/4 will yield shallow enough DOF to isolate your subject from the background. Remember, it's nice to have most, if not all, of the subjects face in focus.