View Full Version : Sodium Filters for light pollution

2012-Nov-06, 05:43 PM
i've heard people mention sodium filters for reducing light polution, but when ever i try to google them later, i get water filters.

does anyone here use them?
what is a good source?
what fine print should i be looking for?


2012-Nov-06, 06:51 PM
Glassbiowers use a dysprosium/neodymium ("dydymium") filter to cut the glare of sodium in their torches. I think that's the same sodium line seen in many streetlights. This would make a big enough difference in light pollution to make up for the overall light loss only under conditions when sodium lamps are a big problem and nothing else is comparably bright. (San Jose's carpet of low-pressure sodium yellow comes to mind). My initial though would be to find a glassblower and try one out, even in a naked-eye view - the broad-band attenuation might be so large that it results in a net loss even with the darker sky.

ETA: Google shows that there are more tailored astronomical filters based on neodymium, so take all the above with a large sodium-inclusive grain.

2012-Nov-06, 11:05 PM
all feedback is welcomed and appreciated.

especially if it gets me something other than water filters.

2012-Nov-07, 03:15 AM
Standard LP filters like those from IDS and and others all block the sodium line as well as other light pollution lines.

They'd be far better than filters that just block Na.

From this and other posts of yours I gather you are just starting in astrophotography or you'd know about these filters and some of the other things you've asked about. I suggest you get a good basic book on the subject such as Covington's Astrophotography for the amateur or others of that type.

A CD book on basic imaging with a DSLR is Lodriguss' beginner's guide


2012-Nov-08, 01:22 AM
Thanks for the links.

yeah, guilty

I'm just getting back into Astronomy after taking 20 years off to raise kids.
the prices on a lot of hardware have come down to the point where i can start try learning things i couldn't even consider before.
I started at the book store(i'm a bookworm anyway), but most of what they had was worthless.

thanks again for the feedback.