Migrant Daughter, 1936

Oh, how I love Shorpy, “The 100-Year-Old Photo Blog.” The photo above was taken by Dorothy Lange for the Farm Security Administration in November 1936. The caption reads: “Daughter of migrant Tennessee coal miner. Living in American River camp near Sacramento, California.” I need to learn more about Lange. How did photos like this happen? How much posing and staging was involved? What kind of camera and film did she use?