Equivalents is a series of photographs of clouds taken by Alfred Stieglitz from 1925 to 1934. They are generally recognized as the first photographs intended to free the subject matter from literal interpretation, and, as such, are some of the first completely abstract photographic works of art.
Stieglitz took at least 220 photographs that he called Equivalent or Equivalents; all feature clouds in the sky. The majority of them show only the sky without any horizon, buildings or other objects in the frame, but a small number do include hills or trees. One series from 1927 prominently features poplar trees in the foreground.
Almost all of the photographs are printed very darkly so the sky often appears black or nearly black. The contrast between the sky and the much lighter clouds is striking in all but a few of the prints. Some images include the sun either as a distinct element in the photograph or as an illuminating force behind the clouds.
The multiple series Stieglitz called Equivalents combined two very important aspects of his photography: the technical and the aesthetic. He was a master at both, but with Equivalents he succeeded in bringing his skills to a new level. On the technical side, Stieglitz had been fascinated by the special problems of photographing clouds ever since the summer of 1887, when he took his first pictures of clouds over Lake Como in Italy. Until the 1920s most photographic emulsions were orthochromatic, which meant they were primarily sensitive to light on the blue end of the spectrum. This made photographing clouds particularly difficult because unless special filters were used the sky would appear very light and the clouds would be lost against it. Over the years Stieglitz repeatedly took photographs of clouds using orthochromatic emulsions, but he reported "Every time I developed [a cloud negative] I was so wrought up, always believing I had nearly gotten what I was after – but had failed."
In 1922 Stieglitz read a commentary about his photography by Waldo Frank that suggested the strength of his imagery was in the power of the individuals he photographed. Stieglitz was outraged, believing Frank had at best ignored his many photographs of buildings and street scenes, and at worst had accused him of being a simple recorder of what appeared in front of him. He resolved immediately to begin a new series of cloud studies "to show that (the success of) my photographs (was) not due to subject matter – not to special trees or faces, or interiors, to special privileges – clouds were there for everyone…" He said "I wanted to photograph clouds to find out what I had learned in forty years about photography. Through clouds to put down my philosophy of life –…My aim is increasingly to make my photographs look so much like photographs that unless one has eyes and sees, they won't be seen – and still everyone will never forget them having once looked at them."