In 1927, Adams began working with Albert M. Bender, a San Francisco insurance magnate and arts patron. Bender helped Adams produce his first portfolio in his new style, "Parmelian Prints of the High Sierras", which included his famous image "Monolith, the Face of Half Dome", which was taken with his Korona view camera, using glass plates and a dark red filter (to heighten the tonal contrasts). On that excursion, he had only one plate left, and he "visualized" the effect of the blackened sky before risking the last image. He later said, "I had been able to realize a desired image: not the way the subject appeared in reality but how it "felt" to me and how it must appear in the finished print." One biographer calls "Monolith" Adams's most significant photograph because the "extreme manipulation of tonal values" was a departure from all previous photography. Adams's concept of visualization, which he first defined in print in 1934, became a core principle in his photography.