\begin{table}%t2
%\centering
\par
\caption{Observing log.}\label{t2}
\begin{tabular}{lrrcl}
\noalign{\smallskip}
\hline
\hline
\noalign{\smallskip}
NGC & Date & Airmass & Exp. (s) & Comments \\
\noalign{\smallskip}
\hline
\noalign{\smallskip}
1651 & 96 Dec 20 & 1.295 & 2 & \\
1711 & 20 & 1.410 & 2 & \\
1783 & 20 & 1.246 & 2 & \\
1786 & 21 & 1.327 & 0.5 & \\
1806 & 20 & 1.544 & 2 & \\
  %      \\
1818 & 20 & 1.225 & 2 & \\
1831 & 20 & 1.210 & 2 & b, d \\
1847 & 21 & 1.308 & 2 & \\
1850 & 20 & 1.324 & 2 & \\
1856 & 21 & 1.410 & 2 & \\
   %     \\
1866 & 20 & 1.231 & 2 & \\
1868 & 21 & 1.188 & 2 & \\
1967 & 21 & 1.369 & 2,0.5,0.3 & \\
1978 & 21 & 1.235 & 2 & \\
1983 & 20 & 1.311 & 2 & \\
    %    \\
1987 & 22 & 1.341 & 2 & b \\
2004 & 21 & 1.378 & 1 & b \\
2031 & 20 & 1.449 & 2 & c \\
2074 & 21 & 1.335 & 2 & a \\
2100 & 21 & 1.434 & 1 & c \\
    %    \\
2107 & 21 & 1.294 & 2 & eN \\
2134 & 20 & 1.379 & 2 & b \\
2136 & 22 & 1.291 & 2 & d \\
2154 & 22 & 1.364 & 2 & \\
2155 & 22 & 1.260 & 2 & \\
    %   \\
2157 & 21 & 1.445 & 2 & \\
2164 & 22 & 1.512 & 2 & \\
2214 & 22 & 1.475 & 2 & \\
\hline
\end{tabular}
\begin{tabular}{ll}
a  \ Centering difficult due to sparse field. \\
b  \ Centering might be influenced by a bright star. \\
c  \ Centering might be influenced by numerous bright stars. \\
d  \ Cloudy and/or bad seeing. \\
eN \ Changing sky location toward North. 
\end{tabular}
\end{table}