The CLS filters are designed to cut out much of the wavelengths of light associated with artificial light pollution. The EOS clip version clips into a Canon DSLR with an APS-C sized sensor and can be used with any lens that would normally work with the camera (as far as I know). It can also be used with a camera attached to a telescope through a T-ring adapter.
I have the 2" version of this filter and it works well
EDIT: forgot to add that this one is not really suitable for a modded camera, for that you would want this version:
http://www.bintel.com.au/Astrophotog...oductview.aspx