Hydrogen Alpha narrowband for clusters?

[BrendanC]

Hi all,

I recently got me one of these: https://www.svbony.com/h-alpha-filter-7nm/#F9169A

It's to use with my EOS1000D with the IR filter removed, so that I can get a nice luminance layer for my DSOs, emission nebulae in particular.

However, the UK weather being what it is, I haven't had the chance to use it yet - but this coming Thursday, there's a chance I can do some work, HOWEVER, as is so often the case, the Moon will be bright and high.

So, I'll be shooting to the conditions, and capturing a cluster or two instead. Which leads to my question: will I get any benefit from using the filter when shooting clusters? Part of me thinks yes, because it might cut through the moonlight, but I'm not sure.

I know the real answer is 'try it and see' but given the scarcity of good nights recently, if anyone could just tell me and avoid me losing a night, that would be great.

Thanks, Brendan

 

[vlaiv]

Answer is no.

Actually - answer is no, unless there is associated nebulosity and nebulosity is Ha in nature - like stellar nursery type of object - large Ha cloud with hot young stars - but then it would only improve SNR on nebulosity and not stars.

Both stars and moonlight are broad band targets - which is sort of intuitive if you think about it - moonlight is actually sunlight reflected of a moon - which in turn is starlight as sun is a star.

By using NB filter you will both cut down moonlight but also starlight coming from stars - effect will be same as using ND filter or aperture mask - reduction of received light. Only effect - worse SNR.

NB filters work not because they block moon light - but because they block the moon light and pass target wavelength largely unaffected (second part being very important). If second part is missing - well then it ain't gonna work

[tooth_dr]

Also to add, dont think that using Ha as luminance is that good an idea.

[BrendanC]

@vlaiv Thanks!

@tooth_dr Hmmm, according to Mr Astrobackyard it can be either as luminance or added to the red channel? See https://astrobackyard.com/dslr-ha-filter/ and https://www.youtube.com/watch?v=6F5KY9skll8&t=250s. This really is my very first tentative toe in the narrowband waters so I'm back to being a noobtard I'm afraid.

 

Edited October 19, 2021 by BrendanC

[tooth_dr]

2 hours ago, BrendanC said:

Mr Astrobackyard

I'm not familiar with Mr Astrobackyard, but I dont really watch many astro tutorials on YT.   I have found that using Ha as a luminance layer leaves everything overwhelmingly salmon pink colour, but I'm not that experienced, so YMMV, so look forward to seeing your results.  I tend to add Ha into the red channel and recombine into the RGB image.