Quote:
Originally Posted by MortonH
CLS or 'deep sky' filters are for use in light-polluted areas. At a dark-sky site, you won't get much benefit from them, so you're better off using a UHC filter instead.
I have a Lumicon deep sky filter and it does make a difference in light-polluted areas. However, it's no substitute for a really dark sky.
Morton
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While not an expert on this topic, I basically agree with Morton's comments. The CLS (or any "light pollution filter") will not make a poor observing site into a good one...
All filters block some light spectrum (some more, some less, some specific, some not so specific)...there are comparisons on websites like Cloudy Nights to give you some more detailed information (from some folks that know a lot more than me).
The CLS is a "compromise" (my words)...it is an attempt to gain some nebulosity without darkening the night sky so much that you can't see the stars...the CLS is/was "optimized" to take out more light from street lights...
The CLS will help bring out some more nebulosity in some objects at a "not dark" site (I've used mine from my backyard on a number of occassions)...it will do the same at a dark sky site...but, it is not a "magic" solution that makes viewing suddenly fabulous.
Other filters UHC, NPB OIII etc. (this varies from different manufacturers) are more restrictive in the light they let through than the CLS and you can then get even more contrast than either no filter or a less restrictive one.
