  Image photometry reveals that the F ring is approximately twice as bright
during the Cassini tour as it was during the Voyager flybys of 1980 and 1981.
It is also three times as wide and has a higher integrated optical depth. We
have performed photometric measurements of more than 4,800 images of Saturn's F
ring taken over a five-year period with Cassini's Narrow Angle Camera. We show
that the ring is not optically thin in many observing geometries and apply a
photometric model based on single-scattering in the presence of shadowing and
obscuration, deriving a mean effective optical depth tau = 0.033. Stellar
occultation data from Voyager PPS and Cassini VIMS validate both the optical
depth and the width measurements. In contrast to this decades-scale change, the
baseline properties of the F ring have not changed significantly from 2004 to
2009. However, we have investigated one major, bright feature that appeared in
the ring in late 2006. This transient feature increased the ring's overall mean
brightness by 84% and decayed with a half-life of 91 days.
