This filter was only used a few times.
Its in perfect condition.
New sells for $89.00
Its yours for $40.00 shipping included CONUS.
Here is what Park has to say about the filter.
Anti Light Pollution Filters
These ALP (Anti Light Pollution ) filters utilize state-of-the-art multi-layer coating technology to selectively filter out the mercury vapor and sodium light pollution. These filters are of tremendous value in the city since they block man-made light, and in dark sky locations they block neutral oxygen transmission (natrual sky glow). ALP filters are not used for Lunar, planetary or terrestrial photography. Threaded to fit eyepieces and camera adapters.