The Jackson Fine Art Gallery in Atlanta is presenting a selection of photographs by Frederick Sommer, taken from the collection of a passionate admirer who built up his collection from 1973 to 1994 during many visits to Prescott, Arizona, where he watched the master at work. To introduce Sommer, let us start with what his friend Emmet Gowin told me for an interview published last month in Camera: “Just before I graduated I discovered the work of Frederick Sommer and asked Harry Callahan who he was.