"It might be said that the subject of Callahan"s photographs is photography, and that his world exists essentially as aformal problem." John Szarkowski Harry Callahan was one of the most respected and influential American photographers of the modern era. He was a master of traditional genres such as portraiture, landscape, architecture and nature studies, but also experimented with new ways of using the medium. One of Callahan"s favorite themes was the repeating pattern, whether in multiple reeds reflected on a lake"s surface or the rows of windows on a building"s facade. While lesser known than some of his other work, Callahan"s collages demonstrate an intense interest in and profound understanding of the process of photographic seeing. Callahan knew that every photograph is to some extent a fragment taken from a larger reality. His collages are rigorous yet playful exploration of the relation of a part to its whole. The images have a unique dynamism, like that of mosaics, because they continuously shift the viewer"s attention back and forth between the individual fragments and the overall pattern. The images exemplify Callahan"s unassuming virtuosity. Harry Callahan (1912-1999), born in Detroit, began his career as an amateur photographer. In 1938 he joined Chrysler"s Camera Club and two years later became a member of Detroit"s Photo Guild. After attending a lecture and workshop by Ansel Adams in 1941, and a meeting with Alfred Stieglitz in 1942, Callahan decided to devote his energies to photography. In 1946 he followed an invitation by László Moholy-Nagy to teach at Chicago"s Institute of Design. He left in 1961 to chair the photography department at the Rhode Island School of Design. Callahan held that position until 1973 and retired from teaching altogether four years later. Harry Callahan was the recipient of numerous distinctions, and he was chosen to represent the United States at the 1978 Venice Biennial, the first photographer to be so honoured. Since his first one-person show in 1947, Callahan"s work has been the subject of over 60 solo and group exhibitions.