Isolating the subject by use of the widest-possible aperture is an ever-present temptation when tackling portraits. But is it always a good idea? Accurate focus becomes critical and, with very fast full-frame lenses such as the f/0.95 Noctilux, or, even, the workaday f/1.4 Summilux, unwanted aberrations can intrude on the perfect picture. Eyes in focus, noses or ears fuzzy, we’ve all done shots that have had to be discarded once viewed on a 27in screen. Trouble is, with f/1 or f/1.4 on tap there’s always an itch to turn the focus ring to the widest stop. The dangers are less acute with crop sensors, admittedly, but it is nevertheless something to guard against.
Chris Gampat of Thephotoblogger.com has some good advice for tackling portraits:
Lots of folks will tell you that you should always focus on the eyes when shooting a portrait. Why? Because eyes are the metaphorical windows to the soul. It’s very easy for those photographers to also get caught up in shooting portraits with their lenses wide open all the time. Don’t do that–especially when working with portraits.