\begin{table}%t2
\caption{Optical broad-band imaging photometric calibration \mbox{parameters}.}             
\label{fotometria}      
%\centering
\small
\begin{tabular}{c c c c}
\hline\hline       
Band & Zero point  &  Colour coeff. & Extinction coeff.\\ 
     & (for 1 ADU s\me)&                &\\ 
\hline                    
   $B$ & 25.94 $\pm$ 0.01   &  0.029 $\pm$ 0.006 &  --0.20 $\pm$ 0.01\\  
   $V$ & 25.84 $\pm$ 0.01   & --0.062 $\pm$ 0.003 & --0.112 $\pm$ 0.007\\
   $R$ & 25.67 $\pm$ 0.01   &  --0.10 $\pm$ 0.01  & --0.076 $\pm$ 0.007\\
 \hline                  
\end{tabular}
\end{table}