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I just read an answer to a question regarding astrophotography and I wonder what filters (and other stuff that helps) I can use for astrophotography for reducing the "effect" of light pollution.

I would like to shoot objects at night near somewhat light-polluted areas, but with stars as visible as possible.

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Getting rid of the light is the main fix. A slingshot may work in isolated cases :-). In areas of moderate light pollution where a significant proportion of the effect is caused by light incident on the camera or area immediate to the camera, local shields MAY help. This could start at a matte black painted box or similar around the camera. For the serious, light shielding of a site may be possible (tress or whatever) or good siting. BUT once the light is "in the air" at altitude so that you get a uniform downward "glow", going somewhere better is about the only cure. – Russell McMahon Aug 13 '12 at 12:44
My first idea was cutting the energy lines... but a slingshot might work too ;) – Ria Aug 13 '12 at 13:55
up vote 5 down vote accepted

Depending on the target you are interested in imaging and the sensor you are using, you may be able to use a variety of filters.

If you are interested in emission nebula, then usually a contrast-enhancing filter helps. These come in two strengths usually, a lower strength that lets more of the continuous light through (which helps keep star colors intact) and a high strength version which helps eliminate more of the background skyglow and reject more of the sodium and mercury vapor city lights.

If you are looking at a nebula that features light primarily in Hydrogen Alpha or Beta or Oxygen 3, then you can use a notch filter just for that specific wavelength. These are the best option for eliminating nearly all the skyglow and light pollution in an area. The narrower the bandwidth is better for these cases. Popular bandwidths are 7nm to 5nm.

There is a third option which is a very gentle filter based on didymium doped glass which can help reject some yellowish skyglow. It's a commonly used filter to enhance the red colors of fall foliage.

Choosing the right filter depends on your imaging sensor, too. If you are using a one-shot color sensor (DSLR and film are examples of this) then the former contrast enhancing filter would be more appropriate than a notch filter.

Note that if you are going after bright targets like the moon and planets, filters are usually not a big issue except to minimize telescope artifacts like CA and purple fringes. Then you would be considering IR and UV blocking filters and maybe minus violet filters.

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CLS light pollution filter is also quite good. It blocks the light from mercury and sodium-vapor lamps and lets the most of the visible light and H-alpha emissions pass. (…) – OH6KVU Aug 14 '12 at 12:26
The CLS is an example of the lower-strength contrast filter which is good for moderate light pollution and skyglow applications. Other makers are Baader, Hutech, Lumicon, and a host of parts from Orion, Celestron, Meade, etc. – smigol Aug 14 '12 at 15:41

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