  The Chinese Small Telescope ARray (CSTAR) carried out high-cadence
time-series observations of 27 square degrees centered on the South Celestial
Pole during the Antarctic winter seasons of 2008, 2009 and 2010. Aperture
photometry of the 2008 and 2010 i-band images resulted in the discovery of over
200 variable stars. Yearly servicing left the array defocused for the 2009
winter season, during which the system also suffered from intermittent frosting
and power failures. Despite these technical issues, nearly 800,000 useful
images were obtained using g, r & clear filters. We developed a combination of
difference imaging and aperture photometry to compensate for the highly
crowded, blended and defocused frames. We present details of this approach,
which may be useful for the analysis of time-series data from other
small-aperture telescopes regardless of their image quality. Using this
approach, we were able to recover 68 previously-known variables and detected
variability in 37 additional objects. We also have determined the observing
statistics for Dome A during the 2009 winter season; we find the extinction due
to clouds to be less than 0.1 and 0.4 mag for 40% and 63% of the dark time,
respectively.
