Catherine Naglestad - Alcina

Actually there are many more nude Sopranos to find (mostly as Salome), I posted the list below on SexyandFunny Forums a few years back;
Carol Neblett in Thais, New orleans, 1973 (full nudity)
Carolyn Sampson in Semele, New York, 2004 (full nudity)
Hildegard Behrens in Salomè, Madrid, 1985 (full nudity) finally bought DVD and posted clip to SexyandFunnyforums in 2009
Karen Huffstodt in Salomè, Lyon, 1990 (full nudity)
Josephine Barstow in Salomè, Amsterdam, 1994 (full nudity)
Helen Field in Salomè, Los Angeles, 1998 (full nudity)
Tina Kyberg in Salomè, Aarhus, 1999 (topless)
Cynthia Makris in Salomè, Tokyo, 2000 (topless)
(Full nudity) in Milwaukee and other cities in 2007
Catherine Naglestad in Salomè, Paris, 2006 (full nudity)
Erika Sunnegårdh in Salomè, Malmo, 2007 and Milwaukee 2008 and Bologna 2008 (full nudity) - brief clips have been posted in several forums but the full performance would be a find!
Gabriella Ravazzi in The Golden Cockerel, Trieste, 1974 (topless)
Francesca Patanè in Macbeth, Modena, 2001 (full nudity) and in Salome 2008
Angela Denoke in Makropoulos Case, Paris 2007 (topless)
Angela Denoke in Parsifal, Wien, 2006 (topless)
Agnes-Adele Habereder,Diana Montague and Birgitta Svenden (as the Rhinemaidens) In Das Rheingold, Bayreuth Festival, 1983 (full nudity)
Salomè – Top less performances by Sopranos
Marquita Lister
Inga Nielsen