zend模块自动加载

I have developed a small application and now I want to create and administrator module. In the future I would like to add different modules but for now i would like to treat this admin as a module and to access it like http://host/module/controller

I have read about zend_autoloader and wrote this in my Bootstrap.php

protected function _initAutoload() {
        $autoloader = new Zend_Application_Module_Autoloader(array(
            'namespace' => 'Admin',
            'basePath' => '/modules/admin'
        ));

I have created a default IndexController with the default index view file. When I try to access http://host/admin or http://host/admin/index i get an application error and of course the view is not loaded.

What am i doing wrong?