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bb4
member
Reged: 04/16/07
Posts: 65
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I have been able to find little information on when to use an h alpha filter and with what other filters. I currently have a used 7nm baader unmounted filter and would like to know when to use it and when not to use it. One reason why I am so interested here is I have 1 5 slot internal filter wheel and already have LRGB mounted. I am in a city and need a light pollution filter as well. I am trying to decide if i really need to use the h alpha on a regular basis. if the answer is no then it would simplify my filter wheel operation since i would have the 5 filters that I need in there already. Thanks everyone.
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Tiny
super member
Reged: 05/02/08
Posts: 197
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Theres a few different types. Lumicon makes one that would be classified as a Cut-off filter. It passes everything above the H-Alpha wave length. Atranomik makes one that is far narrower so it only captures H-Alpha and neighboring wavelengths. The Baader you currently own would most closely resemble this. Then there are solar versions which you wont be interested in if you arent imaging the sun.
They can be useful for photographing emission nebulae and super nova remnants. Whether or not you should use one is up to you and what your targets will be.
Its probably also worth mentioning that a number of LP filters suitable for astro-imaging also pass the H-Alpha wave lengths, for example the Lumicon Deep Sky, so if you were to use a filter like this you may find that an H-Alpha only filter is completely redundant.
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bb4
member
Reged: 04/16/07
Posts: 65
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Thanks much Tiny. that was very helpful.
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Keith
Vendor
Reged: 05/14/05
Posts: 234
Loc: Costa Mesa, CA USA
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a modern narrowband HA filter is the BEST filter to use (especially if you have a proper monochrome CCD camera) to shoot nebulae. You can take an astro field trip to central park in New York City on full moon and get excellent HA data.
HA and LP filters are 2 totally different filters, HA ONLY works for nebs, but it works ALOT BETTER than LP, which only minimizes skyglow from sodium and mercury lights, but does NOT block okygen skyglow, incandescent or flourescent lighting. HA ONLY lets the HA through, so you get a nice black background with the nebula standing out nicely.
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Tiny
super member
Reged: 05/02/08
Posts: 197
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true, if your LP is really that bad. Its a matter of tastes, try both and see what you like, and of course the H-Alpha limits you to those specific objects [nebula/nova remnants] which it really does well where as the Deep Sky filter is really ment for general AP. Either are a good choice to have none the less.
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