\begin{table}%t6
\caption{Range of  the expected $f_{\rm X}/f_{{\rm opt}}$  flux ratios (min/max value in
logarithmic units)  for the different object classes and \textit{EPIC} fields.  The  X-ray fluxes
refer to  the full {\it   XMM}-Newton energy range (0.3$-$10~keV), while
the optical fluxes  refer to the Johnson's $B$  ({\it top}) and $V$ ({\it middle})
bands and to the $B_j$ band ({\it bottom}). For each source class the slight differences in the $f_{\rm X}/f_{{\rm opt}}$ values are due to the different $N_{\rm H}$ of the various \textit{EPIC} fields, which affects the count-rate-to-flux conversion factor.}\label{Fx_opt}
\small%\centering
\par
\begin{tabular}{c|cccccc}
 \hline\hline
Field ID	& Stars		& WDs		& CVs		& Galaxies	& Clusters	& AGN	\\
	& min/max & min/max & min/max & min/max & min/max & min/max \\ \hline
1	& --3.90/+0.50	& +1.00/+2.70	& --1.02/+1.42	& --0.54/+1.83	& +0.38/+2.11	& +0.25/+1.72	\\
2	& --3.91/+0.49	& +0.99/+2.69	& --1.02/+1.41	& --0.54/+1.83	& +0.37/+2.10	& +0.26/+1.73	\\
3	& --3.93/+0.47	& +0.95/+2.65	& --1.04/+1.39	& --0.55/+1.82	& +0.38/+2.11	& +0.23/+1.70	\\
4	& --3.94/+0.45	& +0.89/+2.60	& --1.06/+1.38	& --0.56/+1.81	& +0.38/+2.11	& +0.22/+1.69	\\
5	& --3.80/+0.60	& +1.11/+2.81	& --0.91/+1.52	& --0.44/+1.94	& +0.48/+2.21	& +0.35/+1.82	\\
6	& --3.81/+0.59	& +1.10/+2.80	& --0.92/+1.51	& --0.45/+1.92	& +0.46/+2.19	& +0.34/+1.81	\\
7	& --3.84/+0.56	& +1.04/+2.74	& --0.96/+1.48	& --0.47/+1.91	& +0.46/+2.20	& +0.32/+1.78	\\
8	& --3.78/+0.62	& +1.12/+2.82	& --0.90/+1.54	& --0.42/+1.95	& +0.49/+2.22	& +0.37/+1.84	\\
 \hline
\end{tabular}
\par
\begin{tabular}{c|cccccc}
 \hline
Field ID	& Stars		& WDs		& CVs		& Galaxies	& Clusters	& AGN	\\
	& min/max & min/max & min/max & min/max & min/max & min/max \\
	 \hline
1	& --4.33/+0.87	& +0.65/+3.11	& --1.54/+1.63	& --0.89/+2.04	& +0.07/+2.00	& --0.10/+2.25	\\
2	& --4.33/+0.86	& +0.64/+3.10	& --1.55/+1.62	& --0.89/+2.04	& +0.06/+2.00	& --0.09/+2.26	\\
3	& --4.35/+0.84	& +0.60/+3.06	& --1.57/+1.60	& --0.90/+2.03	& +0.07/+2.00	& --0.12/+2.23	\\
4	& --4.37/+0.83	& +0.55/+3.01	& --1.58/+1.59	& --0.90/+2.02	& +0.07/+2.00	& --0.13/+2.22	\\
5	& --4.22/+0.97	& +0.76/+3.22	& --1.44/+1.73	& --0.78/+2.15	& +0.17/+2.10	& +0.01/+2.36	\\
6	& --4.24/+0.96	& +0.76/+3.22	& --1.45/+1.72	& --0.80/+2.13	& +0.15/+2.08	& --0.01/+2.34	\\
7	& --4.27/+0.93	& +0.69/+3.15	& --1.48/+1.69	& --0.81/+2.12	& +0.16/+2.09	& --0.03/+2.32	\\
8	& --4.21/+0.99	& +0.78/+3.23	& --1.42/+1.75	& --0.77/+2.16	& +0.18/+2.11	& +0.02/+2.37	\\ 
\hline
\end{tabular}
\par
\begin{tabular}{c|cccccc} \hline
Field ID	& Stars		& WDs		& CVs		& Galaxies	& Clusters	& AGN	\\
	& min/max & min/max & min/max & min/max & min/max & min/max \\ \hline
1	& --4.19/+0.43	& +0.74/+2.65	& --1.33/+1.31	& --0.81/+1.72	& +0.13/+1.91	& --0.02/+1.70	\\
2	& --4.19/+0.43	& +0.73/+2.64	& --1.33/+1.30	& --0.81/+1.72	& +0.12/+1.91	& +0.00/+1.71	\\
3	& --4.21/+0.41	& +0.69/+2.59	& --1.35/+1.28	& --0.82/+1.71	& +0.13/+1.91	& --0.04/+1.68	\\
4	& --4.23/+0.39	& +0.64/+2.55	& --1.37/+1.27	& --0.82/+1.71	& +0.13/+1.91	& --0.05/+1.67	\\
5	& --4.08/+0.54	& +0.85/+2.76	& --1.22/+1.41	& --0.70/+1.83	& +0.23/+2.01	& +0.09/+1.81	\\
6	& --4.09/+0.53	& +0.85/+2.75	& --1.24/+1.40	& --0.72/+1.81	& +0.21/+2.00	& +0.07/+1.79	\\
7	& --4.13/+0.49	& +0.78/+2.68	& --1.27/+1.37	& --0.73/+1.80	& +0.21/+2.00	& +0.05/+1.77	\\
8	& --4.07/+0.55	& +0.87/+2.77	& --1.21/+1.43	& --0.69/+1.84	& +0.24/+2.03	& +0.10/+1.82	\\ \hline
\end{tabular}
\end{table}