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Old 19-09-2018, 10:28 PM
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astronobob (Bob)
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Which Ha Filter to add with RGB

Howdy IISpacers

I am currently deciding on which Ha nb filter to add to RGB
Have (attached) options from the BinTel range and I am not sure if there are other Ha filters of different abilities or range, for lack of better words,,, ?

I see the main two options are 6nm & 12nm but also a 7nm which seems odd in regards ?

Apon delving into some thinking, I have assumed/concluded that the 12nm has a twice as wide bandpass than the 6nm - which would catch more Ha, yes ?
Question: Have I got that right ?

Sounds to me that the 12nm would suit me best, , a little more signal to combat noise with uncooled cmos chips perhaps - particularly in regards to the info on the said page
which quotes :

"6nm filters are the perfect choice for capturing delicate detail in heavily light polluted skies. They are also
appropriate with sensitive, low noise cameras under dark skies and for imaging faint detail in objects surrounded
by rich star fields – and hence prone to overly saturated stars in the image. Best with f/3.75 to f/15 telescopes.

12nm filters are for photographers using typical DSLR cameras, inexpensive One Shot Colour CCD cameras or “noise limited” devices.
The wider 12nm bandpass filters are also preferred generally when using cameras with an integrated guiding chip (behind the filters).
Far fewer guide stars will be available at 6nm compared to 12nm. Best with f/2.8 telescopes and up.


My image scope will be the 10" SW Newt F4.7 with the small field zwo asi 290 non cooled, hence more noise,

Thanx in advance for any insight, further advice and/or reassurance
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  #2  
Old 19-09-2018, 11:06 PM
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billdan (Bill)
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I have assumed/concluded that the 12nm has a twice as wide bandpass than the 6nm - which would catch more Ha, yes ?

No it doesn't work like that, Ha is at precisely 656.3nm wavelength, there is no Ha outside that frequency. However NII is a doublet at 654.8nm and 658.4nm.

So the wider bandwidth Ha filters will allow the NII to pass through as well. You would need a 3nm Astrodon filter to pass Ha only and reject NII.

Cheers
Bill
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Old 20-09-2018, 08:04 AM
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RickS (Rick)
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Hi Bob,

As Bill mentioned, the Ha line is very narrow, so a wider filter won't give you more Ha. It will let in more light pollution and non-Ha red light. So, generally the narrower the better, especially if you have bad light pollution, but it will cost you more.

Cheers,
Rick.
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Old 20-09-2018, 05:52 PM
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astronobob (Bob)
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Can't thank you enough Bill & Ric ,,,,
----
----
Ha is at precisely 656.3nm wavelength, there is no Ha outside that frequency

Cheers : Bill, Precise info very much appreciated and valued from you
= Awesome
'
---------------------------------------------
,
,
,
RickS
Appreaciate your "on-the-spot" expertise aswell champ
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