Multi passband light pollution suppression filter designed to give minimal colour shift in imaging. Information here:
http://www.sciencecenter.net/hutech/idas/lps.htm
and here:
http://www.optcorp.com/product.aspx?pid=4172
48mm mounted filter screws into 2" internal thread of imaging train. As new condition - completely unmarked.
New cost US$189 plus shipping. Selling for $120 which includes postage Australia wide.