SagaTwenty years ago, at the Basel Art Fair, Astrid Ullens bought a photograph by Brancusi, more or less on the spur of the moment. This proved to be the first step in the formation of an impressive collection that today comprises more than 5,000 photographs, some by such renowned figures as Lewis Baltz, Lee Friedlander, Helen Levitt and Walker Evans, others by young photographers like Francesco Neri, Georges Senga, Massao Mascaro and Tarrah Krajnak.