Is it possible to show only node contents in shadowbox pages? I'm looking for a method to display content (nodes) in a shadowbox overlay without any blocks or menus around it. even if the user is logged in. 

Has someone an Idea how to do this are there even better parameters for rel shadowbox than the height and width parameter to reduce  the window size?
For Drupal7:

Add to your theme template.php (or add inner of function code to existing function prepropress_page closer to the end) next function:

/**
 * Override or insert variables into the page templates.
 */
function YOURTHEME_preprocess_page(&amp;$vars, $hook) {
  if (isset($_GET['shadow']) &amp;&amp; $_GET['shadow']) {
    $vars['theme_hook_suggestions'][] = 'page__empty';
  }
}


Add page--empty.tpl.php to your theme folder - take original copy from page.tpl.php, but remove printing all header, sidebars, footer regions. E.g.:

&lt;?php
/**
 * @file
 * Returns the HTML for Drupal page only with content region = empty page.
 */
?&gt;
&lt;?php if ($title): ?&gt;
  &lt;h1 class="page__title title" id="page-title"&gt;&lt;?php print $title; ?&gt;&lt;/h1&gt;
&lt;?php endif; ?&gt;
&lt;?php print render($page['content']); ?&gt;


Make shadowbox scripts added to any page (shadowbox ui settings), and you can do next anywhere:

&lt;a href="/node/1?shadow=1" rel="shadowbox" title="About"&gt;About&lt;/a&gt;


So, any link with url?shadow=1 and rel="shadowbox" will shown on shadowbox popup window only content without sidebars. Control size of window on rel="shadowbox" as documented.

For shadowbox links that generated automatically (views, fields) you should override it via settings or template.