The Prints and Photographs Divison of the Library of Congress is one of the nation's greatest resources for the study of photography.  Among the 13 million photographs and negatives housed in the Division are numerous original masterworks and notable documentary photographs.   Photography curators will discuss how this treasure trove was brought together and treat you to a sampling of these visual gems.  Included will be the first known photographic portrait of President Lincoln, Walker Evans's first draft of the classic  Let Us Now Praise Famous Men, W. Eugene Smith's gritty unpublished survey of Pittsburgh, early art photography from the Coville Collection of the Clarence White School of Photography and contemporary American landscape photographs by John Pfahl.