Beamer: Hide Backup Slides from Navigation Panel

Question

I have some slides, which are not part of the main presentation, but can be shown if the audience asks some questions and I have put theses slides at the end of my presentation. I am using the Frankfurt theme, which adds navigation circles for each slide under the section titles. The problem is, that the backup slides also show up as navigation circles. How can I get rid of the bullets for these slides only?

Normally I could only get the navigation circles to be shown, if I added a subsection before the slide which I wanted a circle for, but lately the circles are added for every slide regardless of the definition of a subsection.

Answer 1

Make an appendix. Example (also handles putting appendix frames under a different counter):

\documentclass{beamer}
% http://www-ljk.imag.fr/membres/Jerome.Lelong/latex/appendixnumberbeamer.sty
% Reference: http://tex.stackexchange.com/questions/2541/beamer-frame-numbering-in-appendix
\usepackage{appendixnumberbeamer}
% Add total frame count to slides, optional. From Stefan,
% http://www.latex-community.org/forum/viewtopic.php?f=4&t=2173
\expandafter\def\expandafter\insertshorttitle\expandafter{%
  \insertshorttitle\hfill\insertframenumber\,/\,\inserttotalframenumber}

\newcommand{\makesection}{%
  \begin{frame}This is a slide.\end{frame}
  \subsection{First Subsection}
  \begin{frame}This is a slide.\end{frame}
  \subsection{Second Subsection}
  \begin{frame}This is a slide.\end{frame}
}
\usetheme{Berlin}
\author{The Author}
\title{The Title}
\date{2011/06/21}
\begin{document}

\begin{frame}
\titlepage
\end{frame}

\section{First Section} \makesection

\section{Second Section} \makesection

\section{Third Section} \makesection

\appendix
\section{Additional Material} \makesection

\end{document}