“In March of 1985, the photographer Robert Frank arrived with a paper sack at the School of the Museum of Fine Arts in Boston to use Polaroid’s 20-by-24-inch camera. It was a hulking beast of an apparatus, worlds away from the diminutive 35-millimeter Leica that had freed him to roam the country while shooting “The Americans,” the 1959 book of photos that crowned him a king of counterculture and the most imitated photographer alive today.”