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The UHCs are useful for nebulae, but the DGM NBP will probably do at least as well as these, and cost significantly less. The broadband ones are supposed to be less effective in general, but I never tried one. There is a review of a whole bunch of different specialised (i.e., not simple coloured) filters in the August 2005 issue of Astronomy. (Libraries in the larger universities, e.g. Melbourne, Monash, will have a subscription.)
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