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h-alpha filters for imaging


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hi all

i'm slowly getting to grips with ccd imaging and have been thinking about getting a h-alpha filter as i believe (and please correct me if i am wrong) that i will be able to get some better deep sky images even with a moon about. my question is tho i have been looking at filters and seen that there is lots of types, 7nm, 35nm, what is the difference between them and what would be best for me?

thanks glen

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Hydrogen alpha is light emitted by nebulae at 656 nm wavelenth. The light colour/wavelength is very specific, so ideally you want to isolate it as much as possible. A 7nm wavelength transmits a 7nm range of wavelengths centred on 656nm.

So basically, narrower wavelengths are more effective as they cut out more ambient light (starlight, moonlight, light pollution), but they are usually more expensive.



Edited by Andrew*
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As Andrew said, the narrower the better and also the more expensive. I use an Astronomik 12nm Ha filter though I got it in a set with the L,R,G & B together. I have been perfectly happy with the 12nm and considering it is 3/4 the price of the 6nm I will probably stay with it.

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