Martin Brown wrote:
Filters do what they say on the can. Remove light at specific
wavelengths and make everything a bit dimmer. If conditions are right
then it removes the unwanted light pollution faster than it dims the
object you are trying to see. But there is no free lunch - beware of any
advertising copy claiming "inky pitch black skies".

You mean I should not try to market my spare eyepiece caps as
IPB (Inky Pitch Black) filters?

Brian Tung
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.txt