Hydrogen-Alpha filter

For those interested in imaging and image processing with DSLR, CCD, webcam or film.
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bchamberlain
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Hydrogen-Alpha filter

#1 Post by bchamberlain » Sun Dec 07, 2014 4:56 pm

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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DRatledge
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Re: Hydrogen-Alpha filter

#2 Post by DRatledge » Mon Dec 08, 2014 8:41 am

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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bchamberlain
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Re: Hydrogen-Alpha filter

#3 Post by bchamberlain » Mon Dec 08, 2014 11:17 am

Thanks David. A comprehensive answer from you as usual

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