\begin{table}%t2
%\begin{center}
\par
\caption{Filter systems used for the $\Delta a$ measurements, the units are \AA.}
\label{filters}
\begin{tabular}{ccccccc}
\hline
\hline
System & \multicolumn{2}{c}{$g_1$} & \multicolumn{2}{c}{$g_2$} & \multicolumn{2}{c}{$y$} \\
     & $\lambda_c$ & $\lambda_{1/2}$ & $\lambda_c$ & $\lambda_{1/2}$ & $\lambda_c$ 
	 & $\lambda_{1/2}$ \\
\hline
1    & 5020 & 130 & 5240 & 130 & 5485 & 230 \\
2    & 5010 & 130 & 5215 & 130 & 5485 & 230 \\
3    & 5020 & 130 & 5240 & 130 & 5505 & 230 \\
4    & 5026 & 111 & 5238 & 138 & 5466 & 230 \\
5    & 5017 & 120 & 5212 & 120 & 5494 & 228 \\
6    & 5027 & 222 & 5205 & 107 & 5509 & 120 \\
7    & 5017 & 110 & 5212 & 120 & 5473 & 188 \\
\hline
\end{tabular}
%\end{center}
\par
\end{table}