\begin{table}%t2
\caption{\label{image_info}Flux calibration, quality and source extraction information\protect\\ of the
         images.}
%\centering
\par
\begin{tabular}{cccccc}
\hline\hline
  & Zero-point &  Seeing  &   Number   & 50\% eff. & 4.5$\sigma$ \\
  &  (AB mag)  & (arcsec) & of sources & (AB mag)  &   (AB mag)    \\
\hline
$U$ &   32.911   &   1.06   &   51500    &   26.7    &     28.9      \\
$B$ &   33.830   &   0.94   &   76071    &   26.3    &     29.1      \\
$V$ &   34.110   &   1.03   &   68278    &   26.3    &     28.6      \\
\hline
\end{tabular}
\end{table}