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Starting out with narrowband, which filters to get?

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#1 Jeff2011

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Posted 06 August 2014 - 01:27 PM

Terry brought up a subject that I am very interested in, but did not want to hijack his thread so I will start my own.

 

I want to start doing narrowband and my plan was to get the Astrodon 5nm Ha, OIII and SII filters.  I will be imaging at f6.3 with an aperture of 4 inches.  Will the 5nm give me good results with my setup?  Will I regret not going with the 3nm for some or all?

 



#2 Madratter

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Posted 06 August 2014 - 01:52 PM

My own feeling is that you will regret not having the OIII in 3nm at least. The moon scatters a lot of light right around that wavelength (it peaks near there). But as I said in Terry's thread, this is all theoretical for me. I have NO, ZERO, ZILCH, experience with OIII or SII at this point. Then again, you could just do your OIII when the Moon is less of a factor. And it is not like it is going to be horrible. Terry has gotten some very nice images using the Baader filters where the OIII is 8.5nm.



#3 Goofi

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Posted 06 August 2014 - 02:03 PM

Jeff, I have the Baader 8nm Ha and OIII filters; I don't regret getting them - they were all I could afford.

If cost is no issue, there's a strong case to be made for the 3nm filters ... but if cost is an issue I think 5 or 8nm are good enough.

 

If you were only getting one filter - get Ha. I'm amazed what's out there that Ha filters bring out.

The 8nm OIII filter gets rough about 4 days either side of a full moon for me; the closer to the moon I image the harder it is.

What I do is just image with the OIII when the moon isn't an issue.

 

I did not purchase a SII filter and  don't regret it or miss it. That might just be me and my tastes...

There's tons you can do with Ha and OIII ... 



#4 josh smith

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Posted 06 August 2014 - 02:27 PM

I did not get the contrast I was looking for with my 8.5 nm OIII filter.  The data was mismatched somewhat with the Ha.  My recommendation would be to hold off and get the 3nm if you are planning on imaging in any light pollution or during the time when the moon is up more.  If you only plan plan on imaging from dark sites with no moon in the sky, I believe that the wider 5 or 8.5 nm may be enough.  My own opinion and advice, but others will surely have had a different experience.



#5 terry59

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Posted 06 August 2014 - 02:49 PM

Do you want to shoot Ha and NII separately?



#6 rflinn68

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Posted 06 August 2014 - 02:56 PM

I have the 5nm H-alpha and like it very much. I will most likely get the 5nm SII as well but I'm leaning towards the 3nm OIII.



#7 anismo

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Posted 06 August 2014 - 03:48 PM

Don't you need more integration time going to 3mm vs 7mm?  I shoot 15 minute subs at 7mm Ha/OIII . I wonder if it is going to require 30min subs at 3mm ?  Are there good comparisons between the 7mm , 5mm and 3mm version with integration time that anyone can share?



#8 rflinn68

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Posted 06 August 2014 - 04:15 PM

Anis, What is the peak transmission of your 7nm filter? In the narrowband FAQ section on the Astrodon website one question is "Do I need a longer exposure with 3nm filters". He says: No, because the peak transmission is still above 90% for both 3 and 5nm filters. In fact, it will take you longer to reach the sky noise limit with the narrower filter due to the lower background.

 

But then he goes on to state that he takes 30 min subs with both the 3 and 5 nm filters. I'm not sure how it would translate with your 7nm filter. But for Jeff here asking about the 5nm and 3nm it would seem that its not an issue. I have done a lot of images with the 5nm H-alpha filter and only used 5 min subs and got a good signal. (Enough for me anyway)  :shrug:  Soon I hope to be able to do at least 20 min subs.  :D



#9 Jeff2011

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Posted 06 August 2014 - 04:39 PM

Thanks for all the responses.  I think the best thing for me to do is get the Ha filter for now and see how others fare with the OIII and SII.   Terry, I don't know enough about narrowband imaging to answer your question.  I don't think I will be acquiring NII separately.



#10 rflinn68

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Posted 06 August 2014 - 04:47 PM

I don't think I will be acquiring NII separately.

 

Then you'll probably want the 5nm H-alpha but some people shoot all three at 3nm and dont use NII. I wanted to include the nitrogen with one filter so opted for the 5nm since I just have a 7 position wheel. Well, that and I just didnt want to have to shoot NII once I had all my NB filters! :p



#11 gdd

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Posted 06 August 2014 - 04:58 PM

I have not done narrowband yet but would like to after I get my camera modded. It seems to me that 3nm filters will pass almost as much of the desired emission signal as the wider filters but with less noise. It would not be that 3nm filter requires more integration time as that it allows more integration time. Am I correct?

 

The 3nm filters would also dim the stars in the image which may be good or bad depending on what you are trying to achieve. If you want to see more  and brighter background stars without needing a separate set of exposures without the filter maybe a wider filter, even a 12nm, might be better. 

 

Gale



#12 hytham

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Posted 06 August 2014 - 06:17 PM

Something that needs to be taken into consideration when you get into the world of narrowband is the focal length you plan on imaging with them.  If you image with a system that has a focal length less than F5, the transimission rate of that given spectral line decreases.  This will require longer and more sub-exposures.  Again,  if you're imaging with a 3nm filter at a focal length less than 5, your transmittance decreases.  The peak trasmiittance with Astrodon filters are guaranteed >90% at F9.  This is important to remember.  I currently image with 3nm and 5nm filters at F5 without any problems.

The other point to take into consideration is whether you will be automating your focusing routine.  Astrodon guarantees parfocal up until F4, but anything beyond that will require refocusing.

 

My current and future set up:

 

Current Narrowband:

Ha 5nm (I wanted to keep the NII line because I plan on imaging planetary nebulae in the future and didn't need the increased contrast)

OIII 3nm (light scatters far too easily due to shorter wavelength ~500nm)

SII 5nm (isn't susceptible to LP and less susceptilbe to moon ... no need for 3nm for my needs)

 

Future Narrowband:

HII 3nm (increased contrast.  My plan is for mono imaging)

NIR >700nm (Image through dusty regions to highlight background galaxies and clusters encompassed in dust)

 

 

 


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