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Experience reducing light polution with filters?

Filters EAA
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#1 jhwilmes

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Posted 26 February 2024 - 04:32 PM

Hi all,

 

I have a couple scenarios to ask about, for higher light polution areas (say, bortle 5-9), the main objective being to improve object visibility (SNR).

 

Here are the scenarios I have in mind -

1 - color camera.  Would a dual-band filter be a good choice?  What about a tri-band or quad-band filter?  What targets would I make more visible/invisible if I (or anyone else) took this approach?  What filters are recommended/not recommended for EAA?

 

2 - mono camera.  Would a daul-band filter (similar to above) be a good choice?  What about a tri-band or quad-band filter?  For EAA, I might appreciate the extra light compared to a mono-band filter.  Or would a mono-band filter (assuming it isn't an extremely narrow bandpass) provide sufficient light, and the other filter types do not improve anything?

 

What real-world experience do you have with these scenarios?

 

Most of the time, I use a monochrome camera with a quad-band filter - although in my case, this is done to improve resolution when using a refractor, with only a slight reduction in light polution.



#2 BrentKnight

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Posted 26 February 2024 - 05:16 PM

Filters will work on emission nebulae and planetary nebulae.  A simple H-alpha for mono, or a dual-band with H-alpha and OIII for either mono or OSC.  No filters will help with galaxies (to any real extent) or reflection nebulae.  For smaller galaxies that don't see any improvement with filters, I find a good mono camera to be the best for getting the most in the shortest time.  It's probably best to stick with filters in the 7nm range, but I can get good results with the 3nm L-Ultimate if I use longer subs and generally longer total exposures.  

 

Luckily, I live and capture on the better end of your range (average SQM-L reads 19.5) and I have the best luck sticking with targets that are near the meridian and above any horizon about 25°.  Better sky conditions mean better SNR in less time, but I can get pretty great EAA captures of galaxies, clusters and nebulae in under 60 minutes.  Light shields setup on the ground around your rig that can block nearby lights from directly impacting your captures can help too.

 

EAA itself is a great tool against LP if the goal is to see more than visual.


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#3 dob45

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Posted 27 February 2024 - 06:28 AM

Filters will work on emission nebulae and planetary nebulae.  A simple H-alpha for mono, or a dual-band with H-alpha and OIII for either mono or OSC.  No filters will help with galaxies (to any real extent) or reflection nebulae.  For smaller galaxies that don't see any improvement with filters, I find a good mono camera to be the best for getting the most in the shortest time.  It's probably best to stick with filters in the 7nm range, but I can get good results with the 3nm L-Ultimate if I use longer subs and generally longer total exposures.  

 

Luckily, I live and capture on the better end of your range (average SQM-L reads 19.5) and I have the best luck sticking with targets that are near the meridian and above any horizon about 25°.  Better sky conditions mean better SNR in less time, but I can get pretty great EAA captures of galaxies, clusters and nebulae in under 60 minutes.  Light shields setup on the ground around your rig that can block nearby lights from directly impacting your captures can help too.

 

EAA itself is a great tool against LP if the goal is to see more than visual.

Can the L-enhance filter also be used with mono cameras? (I haven't tried yet!)
 



#4 BrentKnight

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Posted 27 February 2024 - 08:52 AM

Can the L-enhance filter also be used with mono cameras? (I haven't tried yet!)
 

I used my L-eNhance with the 294MM-Pro and it works just fine.  Like I've mentioned in other posts, that filter is generally easier to use because the bandpass windows are so wide but it does not give really great OIII performance (compared to the L-Ultimate at least).  Very similar results with just say a 7nm H-alpha filter. 

 

I've no interest in adding a filter wheel (I like to pretend I'm keeping things simple), but I believe you get better OIII performance using separate filters because the OIII will generally need longer exposures than the H-alpha.  Folks who use Jocular could speak more about this though... 

 

Since I got the L-Ultimate, I haven't used my H-alpha again.  I'm not sure I'll use the L-eNhance anymore either, but it might work better on the fast, little FMA180 paired with the 294MM-Pro - I'll have to test.


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#5 alphatripleplus

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Posted 27 February 2024 - 09:19 AM

I stick to using separate OIII and H-alpha filters with my mono cameras, and use a dual band only with my colour camera. As Brent mentions, you'll get better OIII performance the narrower the OIII band (I use 7nm), because the OIII signal is typically weaker than H-alpha and is more easily swamped by LP (or moonlight) if you have a wider OIII band.


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