\begin{table}%t1
 %\centering
\par
\caption{\label{tab:filters}Exposure times, limiting magnitudes for point-like sources and zero points~(AB) for the observations in each band.}
\begin{tabular}{cccccc}
\hline\hline\noalign{\smallskip}
Filter 	& $N_{\exp}$ & Exptime &     Mag      &    Mag       & Zero point \\
        &           &   (s)   & (5$\sigma$)  & (20$\sigma$) &  \\
\hline  
$g$  & 12 & 3600 & 28.0 & 26.0 & 28.4 \\
$r$  &  3  &  900 & 26.0 & 24.2 & 27.7  \\ 
$u$  &  4  &  1200 & 27.2 & 25.0 & 27.1  \\
\hline
\end{tabular}
\end{table}