“Simple Secrets,” a somewhat unconventional survey of Walker Evans’ career, was selected from the Atlanta-based Hill family’s extensive collection of his photographs. Evans’ most famous body of work, the Depression-era scenes from tenant farms and small towns, was largely unrepresented (though his celebrated ability to accord the human subject a straightforward dignity in harsh circumstances was demonstrated in a group of earlier pictures shot in Cuba). Thirteen previously unpublished photographs were particularly welcome, drawing attention to lesser-known aspects of the photographer’s work,