\begin{table}%t3
%\centering
\caption{The median, first and last decile of background and seeing for the
  WFILAS narrowband imaging for all three fields combined. One
  pixel corresponds to 0\farcs238.}
\label{tab:imgquality}
\begin{tabular}{lcrrrrrr}
  \hline\hline\noalign{\smallskip}
  Filter  & No. of & \multicolumn{3}{c}{Background ($\mu$Jy/$\Box$\arcsec)} & \multicolumn{3}{c}{Seeing (\arcsec)}\\
  & frames & 10\%  &  50\% &  90\%          &  10\% & 50\% & 90\%\\
  \hline 
  \na\    &  92    & 17    & 27    & 36             & 0.65  & 0.79 & 1.12\\
  \nb\    &  75    & 19    & 30    & 41             & 0.64  & 0.84 & 1.16\\
  \nc\    &  77    & 17    & 27    & 36             & 0.63  & 0.80 & 1.10\\
  \med\   &  80    & 17    & 22    & 33             & 0.65  & 0.83 & 1.09\\
  \hline 
\end{tabular}
\par
\end{table}