  We report on time-resolved optical imaging of the X-ray binary SAX
J1808.4-3658 during its quiescent state and 2008 outburst. The binary,
containing an accretion-powered millisecond pulsar, has a large sinusoidal-like
modulation in its quiescent optical emission. We employ a Markov chain Monte
Carlo technique to fit our multi-band light curve data in quiescence with an
irradiated star model, and derive a tight constraint of $50^{+6}_{-5}$ deg on
the inclination angle $i$ of the binary system. The pulsar and its companion
are constrained to have masses of $0.97^{+0.31}_{-0.22} M_{\sun}$ and
$0.04^{+0.02}_{-0.01} M_{\sun}$ (both 1$\sigma$ ranges), respectively. The
dependence of these results on the measurements of the companion's projected
radial velocity is discussed. We also find that the accretion disk had nearly
constant optical fluxes over a $\sim$500 day period in the quiescent state our
data covered, but started brightening 1.5 months before the 2008 outburst.
Variations in modulation during the outburst were detected in our four
observations made 7-12 days after the start of the outburst, and a
sinusoidal-like modulation with 0.2 mag amplitude changed to have a smaller
amplitude of 0.1 mag. The modulation variations are discussed. We estimate the
albedo of the companion during its quiescence and the outburst, which was
approximately 0 and 0.8 (for isotropic emission), respectively. This large
difference probably provides additional evidence that the neutron star in the
binary turns on as a radio pulsar in quiescence.
