\begin{table}%t2
\caption{APLC optimization for an obscuration of 30\%.}
\label{tab2}
%\centering
\small
\begin{tabular}{lcc}
\hline \hline
Parameters & Value range  & Optimal APLC configuration (FPM range in $\lambda/D$) \\
\hline
Obscuration & 30\% & 4.7  \\
Spider (arm) & 3--7 & 4.6--4.8  \\
Spider (size) & 15--90 cm & 4.6--4.8  \\
Shear pupil &  0.5--2\% & 4.7--4.9 \\
Segment reflectivity  & 0.25--5\% & 4.5--4.7 \\
Low-order aberrations & 1--100 nm rms & 3.5--6.0 \\
Chromatism ($\Delta \lambda \slash \lambda$) & 1.4--5\%  &  4.7--4.8 \\
Chromatism ($\Delta \lambda  \slash \lambda $)  & 5--20\%  &  4.8--5.3 \\
\hline
\end{tabular}
\end{table}