\begin{table}%t1
\caption{\label{instruments}Optical instruments employed in our survey.}
\small
%\centerline
{      
\begin{tabular}{lccccccccc}      
\hline    
\hline    
\multicolumn{6}{c}{} &
\multicolumn{2}{c}{Sloan $i'$ filter} &
\multicolumn{2}{c}{Sloan $z'$ filter} \\
Telescope  & Observatory& Camera             & Detectors                   & Pixel size   & Area        & $\lambda$$_{\rm c}$ & $\Delta \lambda$ & $\lambda$$_{\rm c}$ & $\Delta \lambda$ \\
	   &            &                    &                             &(\arcsec/pix) &(arcmin$^2$) & (nm)                & (nm)             & (nm)                & (nm)             \\ 
\hline      
5-m Hale   & Palomar    & LFC$^{{a}}$ & $6\times (1024 \times2048)$ & 0.360        & 450         & 768                 & 154              & 900                 & 180              \\
3.5-m CAHA & Calar Alto & LAICA              & $4\times (4096 \times4096)$ & 0.225        & 940         & 770                 & 150              & 920                 & 160              \\
\hline
\end{tabular}}
\smallskip
 $^{{a}}$ The original size of each CCD detector is $2048\times4096$, and the pixel size is~0\farcs18. We applied a $2\times2$ binning to all LFC CCDs.
 \end{table}