http://www.ci.tucson.az.us/arthazards/photo2.html (http://www.ci.tucson.az.us/arthazards/photo2.html)
http://user.icx.net/~jfairstein/celestial.html (http://user.icx.net/~jfairstein/celestial.html)
http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=002bHB (http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=002bHB)
http://www-ehs.ucsd.edu/lab/2007.htm (http://www-ehs.ucsd.edu/lab/2007.htm)
http://bjornburton.org/ilford.html (http://bjornburton.org/ilford.html)