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 Post subject: Hydrogen-Alpha filter
PostPosted: Sun Dec 07, 2014 4:56 pm 
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Location: Atherton
David mentioned this type of filter as being very dear. I just wondered whether the one in the add on this web link is good enough as it's less than £50


http://www.ebay.co.uk/itm/like/13116916 ... 0&ff14=108


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 Post subject: Re: Hydrogen-Alpha filter
PostPosted: Mon Dec 08, 2014 8:41 am 
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Bill,
Hydrogen alpha filters are fabulous filters for red nebula. They are excellent light pollution filters and permit imaging at full Moon when it is always clear - or so it seems.
Prices are directly proportional to how narrowband they are. Generally, but not always, narrower provides more contrast. A 6 or 7 nm bandpass is good compromise - narrower gets very expensive. The sky watcher is 12 nm which is OK but it is only 1.25 inch which is too small for DSLRs.
With DSLRs when using h-alpha filters only 1 in 4 pixels - the red ones - are recording a signal. So for colour images you also need to shoot the object with a normal filter and combine the results. It starts to get very complicated but for faint nebulae it will/should produce the best results.


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 Post subject: Re: Hydrogen-Alpha filter
PostPosted: Mon Dec 08, 2014 11:17 am 
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Thanks David. A comprehensive answer from you as usual


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