Canon DSLR cameras are worldwide in use for astronomical imaging. Canon recommends Astronomik filters in order to suppress most sources of artifical light pollution.

Read this helpfull article in Canons ''Knowlegde-Base'' with an introduction to astronomical imaging. Canons's suggestion: Astronomik CLS Clip filters to achieve the very best results! The Astronomik CLS filter offers outstanding results in reducing the effect of most artifical light sources and a simultaneous retention of balanced and natural colours.

Read the full article here: http://www.learn.usa.canon.com/resources/articles/2012/astrophotography_techniques.shtml?WT.mc_id=EM1209EO08001&RID=1-7OQORM&CON=1-L9M-2318&PRO=&CID=1-7MO7ZS