\begin{table}%t2
%%\centering
\par
\caption{Theoretical performance in the optical system nominal thermal
  range. We list the MTF at Nyquist frequency and the diameter the 
encircling~70\% of the energy.\label{tab2}}
\begin{tabular}{lcccccc} 
\hline \hline
  & {\bf MTF at} & {\bf70\% Encircled} & {\bf MTF at} & {\bf 70\%  Encircled} &{\bf MTF at} &{\bf 70\% Encircled}\\
{\bf FOV}  &{\bf Nyquist} & {\bf energy (\boldmath$\mu$m)}&{\bf Nyquist} & {\bf energy (\boldmath$\mu$m)}&{\bf Nyquist} & {\bf energy (\boldmath$\mu$m)}\\
  &\multicolumn{2}{c}{$T=-20$ C}& \multicolumn{2}{c}{$T=0$ C (nominal) } &\multicolumn{2}{c}{$T=+20$ C}\\
\hline
0$\degr$ &72&10.1&80&6.7&58&13.1\\
1$\degr$&71&10.3&80&6.7&59&13.0\\
2$\degr$&69&10.7&81&6.4&60&12.6\\
$2\fdg62$&67&11.0&80&6.3&61&12.2\\
\hline
\end{tabular}
\end{table}