Excerpt Versions

I am creating a new theme where I need Excerpt in different lengths
i.e. For Slide Show the length of 30, for Blog page 50, for one sidebar widget 20.

I defined Excerpt length in function.php

function new_excerpt_length($length) {
	return 50;
}
add_filter('excerpt_length', 'new_excerpt_length');

Can someone help me built more then one level or version of Excerpt that can be used in various locations.