Official websites use .gov
A
.gov website belongs to an official
government organization in the United States.
Secure .gov websites use HTTPS
A lock (
) or https:// means you've safely
connected to the .gov website. Share sensitive
information only on official, secure websites.
Curves showing the properties of three films, two 400 speed index screen / film combinations with differing contrasts and film latitudes and one 200 speed index; a) characteristic curve showing the variation in optical density with air kerma incident on the cassette, and b) variation in contrast with incident air kerma.
