Light Pollution

[Hemsy]

Hi Gazers,

I've stumbled across various threads on this forum that mention light pollution filters. Could someone tell me exactly what these are and how they work? Like the majority of us, I am effected by the glow of city lighting, and I don't always have the opportunity to visit a dark location. LP is pretty frustrating, especially when you have seen the beauty of the night sky from a dark site.

Actually, where we live, they plan to turn off all street lighting at 7.00am - even during the winter, so that may help a little in the future.

Rgds,

Ed

[Grunthos]

Actually, where we live, they plan to turn off all street lighting at 7.00am - even during the winter, so that may help a little in the future.

7pm would be better though

One of the better articles i have seen on filter description and comparison can be found at Prairie Astronomy.

(Credit card on standby...)

[Neil McRae]

The Broadband or light pollution reduction (LPR) filters are nebulae filters that block the light pollution in the sky and transmit the H-alpha, H-beta, and O-III spectral lines and makes observing nebulae from the city and light polluted skies possible. These filters block Sodium and Mercury Vapour street lights. These filters help in revealing the details of nebulae in light polluted skies.

Neil

[LukeSkywatcher]

Light pollution filters work by cutting out certain wave lengths. Different filters cut out different light. The Skywatcher filter available from Flo (above) works very well at cutting out the oragne glow from the average suburban street light.

Well worth the money.

[paul schofield]

I bought a Skywatcher Narrowband UHC filter hoping this would help with light pollution, I dont know if its me, but it does not seem to help at all with light pollution. It just makes everything I look at turquoise from stars to nebulas. Dont know if I am doing something wrong though.

[LukeSkywatcher]

I bought one of these:

First Light Optics - Skywatcher Light Pollution Filter

I can aim my scope between two street lights and it is if they are not there.

[umadog]

Paul, UHC filters do help with light pollution but they work better on some objects than others. Check out this resource: Filter Performance Comparisons - Article

Many of the nebulae is Cygnus can go from invisible to visible with an OIII (and also a UHC). When Cygnus reappears, be sure to check out the Veil, N. America, and Crescent nebulae. I've also noticed big contrast boosts with M8 and M17. Filters help to bring out the darker regions of the Orion Nebula, but they serve mostly to dim the brighter regions.

The important thing to keep in mind is that filters cut out light and so your maximum useful magnification decreases. You should probably be shooting for somewhere between 5x and 10x per inch if you're using a UHC. Also, given the decrease in brightness, you need to be well dark adapted. Using a hood over the eyepiece may also be necessary if you notice back-reflections coming off the filter.

You're right that stars change colour and become dimmer. This is a consequence of how the filters work and means that the views become less aesthetically pleasing in many situations.