Exclude category with add_filter(‘pre_get_posts’

function exclude_category($query) {
if ($query->is_home) {
$query->set('cat', '-7,-67,-6');
}
return $query;
}
add_filter('pre_get_posts', 'exclude_category');

Hi I found this to exclude categories on my index page (home). it works a little bit to good…
It affects also my 2 sidebars.
I make the calls in the sidebars with

query_posts('showposts=30&cat=7,-6');

How can i make this affectr only my main ?