On an April morning in 1927, Adams undertook a difficult four-thousand-foot climb through heavy snow to the granite outcropping known as the Diving Board, where he set up his 6 1/2 x 8 1/2-inch view camera, inserted a glass plate, and waited for the light to fall directly on the sheer granite cliff. He made one exposure with a yellow filter. Then it occurred to him that if he used a dark red filter, both sky and cliff would register darker in the finished print than in the actual scene. He changed to the red filter, with this dramatic result.

Driving back to Santa Fe, New Mexico on October 31, 1941, after what had been a disappointing day for picture-taking, photographer Ansel Adams (1902-84) brought his car to an abrupt stop, yelling to his companions to bring him his tripod, exposure…

"Only when I had completed the prints [of this image] months later did I realize why the subject had a familiar aspect: I had seen the remarkable photographer made by Timothy O'Sullivan in 1873, in an album of his original prints that I once…