Siskind was part of the ab ex New York gang in the late 40s and 50s. He was good friends with Franz Kline and Motherwell and hung out at the Cedar Tavern from time to time. After Kline's death from heart disease, Siskind did a series of images (wall abstracts) as an homage to his friend. As pointed out in the previos post, Siskind was considered an equal to the painters and shared gallery space on the same walls. (although I doubt his prints shared the same amounts on the price tags)
Harry Calahan did a lot of experimenting with camera movement, multiple exposures both b&w and color. I don't know how much he was influenced by the ab exr's, but it was a time of stretching the boundries of all art, sort of an anti F64 in photography.