\begin{table}%T3
\caption{\label{tab:slope_fixed}Slope $\alpha$ of the luminosity
  functions for the different wavebands as determined from an
  error-weighted fit to the data in Table~\ref{tab:slope_single} under
  the assumption that $\alpha(z)={\rm const.}$ (upper part). In the
  lower part of the table we show the best values of $\alpha$ after
  combining the UV~bands and the blue optical bands.}
%\centering
\par
\begin{tabular}{l|c}
\hline\hline
Filter  & $\alpha(z)={\rm const.}$\\
\hline
{1500~\AA\ } & $-1.01 \pm 0.08$\\
{2800~\AA\ } & $-1.06 \pm 0.07$\\
{$u'$ }        & $-1.10 \pm 0.08$\\
{$g'$ }        & $-1.26 \pm 0.04$\\
{$B$  }        & $-1.24 \pm 0.04$\\
\hline
{1500~\AA\ and 2800~\AA\ and $u'$} & $-1.07 \pm 0.04$\\
{$g'$ and $B$ }	                & $-1.25 \pm 0.03$\\
\hline
\end{tabular}
\end{table}