Problems trying to do an LDAP search filter

Question

I am trying to get a list of users in our LDAP server by way of an LDAP filter.

We have a custom object class called, say customuser, which we use instead of the user object class.

Our base dn is like the following: dc=somedomain,dc=edu

So the dn for the group I am trying to list users of is: cn=staff,ou=group,dc=somedomain,dc=edu

So I was thinking the filter would be like the following: (&(objectCategory=customuser) (memberOf=cn=staff,ou=group,dc=somedomain,dc=edu))

However this filter does not work, it returns 0 entries.