Book excerpt: Image sharpness is one of photography's yin/yang propositions. Soft focus can impair a photograph, and just as readily enhance it-in some cases, greatly enhance it. What we perceive as blur, as soft zones in a picture, function in very much the same manner as deep shadows or overexposed highlights. By minimizing or concealing certain details in the image by selectively throwing areas out of focus at will, the photographer can direct a viewer's attention through the image as he or she intends. Like the rest stops in a piece of music, creatively manipulated zones of softness can totally govern.