A glimpse at Sotheby’s single-lot sale of more than 500 photographs by the 20th-century visionary Shells, 1927 Charis, Santa Monica, 1936 Pepper No. 30, 1930 Sand Dunes, Oceano, 1934 Legs in Hammock, Laguna (Detail), 1937 Grasses Against Sea, Big Sur, 1937