http://saturn.jpl.nasa.gov/cgibin/gs2.cgi?path=../multimedia/images/saturn/images/PIA05391.jpg&type=image
That's big! Taken from 24 million miles away. I got to thinking, if Mercury orbits the Sun at about 36 million miles, how big does the Sun look like from the surface of Mercury then !
The cameras on Cassini are fairly powerful telescopes, given the weight available. Apparently, the wide-angle camera is a 57mm f3.5 refractor with 3.5 degree field of view, and the narrow-angle camera is a 190mm f10.5 reflector with a 0.35 degree field of view.