Narrowband imaging questions

[blinky]

Im new to narrowband imaging and have a few questions around the way the narrowband images are converted to colour - I know there are no rules and ultimately it is down to the individual how they combine and present but I just wondered about some general 'rules of thumb' to guide me in this new aspect of imaging!

So....

Do you always try and get all three narrowband images, so Ha, O3, SII and then resort to creating a false channel when you dont have time etc or are there reasons/targets that Ha only or Ha & O3 work best?  I suppose I mean are there targets that gathering one of the channels is not worth it as there is no data?

If you are generating a missing channel, is it a mix of the other 2 or can/do you use one of the channels twice?

What colour do you assign to each channel and again, in general, do you always go with the same combination, or again does this depend on target?

Do you go for the same exposures?  I found the other night that I had to double my O3 when on the Heart Nebula (which has been my only target so far), and again what about number of subs, do you try and get the same for each channel?

Are there any gotchas to watch out for when imaging and combining narrowband into RGB?  My last camera was a OSC QHY8 so this is all new, but so far Im enjoying the new challenge ? 

 

 

[RichLD]

Hiya, I'm at work at the mo so can't go into any real detail, however in my limited experience I've stuck with the HST pallette (Ha=G, Sii=R, Oiii=G).

I try to get equal signal on all channels but most of the time the Ha dominates by a country mile. It's best to check other images out online and look at which lines were used  before you dedicate hours of precious imaging time to non existent Sii, for example. Oiii, even with a very narrow bandpass, is the most affected by the moon imho.

Here is a great tutorial for processing NB from JP Metsivainio https://astroanarchy.blogspot.com/2009/11/power-of-tone-mapping.html?m=1

FWIW I tend to stick to deep, mono Ha only images these days.

HTH

Rich

[don4l]

I use different methods.

 

If I am imaging a largish nebula that has plenty of Ha, but little OIII, then I will typically get an hour of Ha, and 30 mins each of Green and Blue.

I will then scale each image so that the stars are about equal brightness.  I then do a colour combine mapping the Ha into the red channel, and the green and blue as normal.  This produces an acceptable image in my opinion.  This is of course very subjective.

 

Sometimes I add the Ha in as a luminance layer.

 

Sometimes I also take SII and OIII data.  This can be used "as is" or combined with the Green and Blue channels as you see fit.  Personally, I usually add the SII to the green and the OIII to the Blue.

 

 

[blinky]

How does this look for my first narrowband

[blinky]

I had a problem with the O3 when i took it - was out of focus so its not going to win any awards!

[blinky]

Here is just the Ha uncropped (had rotated the camera for the O3 so its cropped)

[Hallingskies]

On 04/10/2018 at 13:11, blinky said:

Do you always try and get all three narrowband images, so Ha, O3, SII and then resort to creating a false channel when you dont have time etc or are there reasons/targets that Ha only or Ha & O3 work best?  I suppose I mean are there targets that gathering one of the channels is not worth it as there is no data?

 

I’ve used HaRGB for years but now I’m just getting to grips with multi-narrowband imaging as well.  There doesn’t seem to be any hard and fast rules for what filters and exposure ratios are best for any particular object, although I usually take a look on this forum to see what others have done before going after a target.  Olll seems particularly sensitive to conditions and I find I lose a lot of contrast if I try and image in Olll when there’s a lot of moonlight about.  I also find I need about twice the Olll exposure relative to Ha when looking at emission nebulae (though I guess planetaries are stronger in Olll), if it is there at all.

There is the added complication of differing filter bandwidths as well.  Some folk are going for the super narrow (and super expensive!) Ha and Olll filters and it is interesting to see the forum feedback on these.

It would be good if there were a table which listed objects against suggested exposure ratios in Ha/Sll/Olll/Hb (assuming that you aren’t imaging at very short f ratios, which can affect the interference filter function, so I believe) but then I suppose everyone would have their own opinion about what works best!

[iansmith]

I image planetary nebula using Ha and O3 narrowband filters. I tend to do equal amounts of time in each filter, typically 4 to 6 hours total per filter.  On my Atik 414 sub lengths were 15 to 20 minutes for best results. I now have a QSI6120 and 10 minute subs seem to work with this camera. Channel assignment depends on what I find pretty to look at! I normally start with 100% Ha for red, a 50/50 mixture of Ha and O3 for  green and 100% O3 for blue. I'll adjust as desired after that.

Cheers, Ian

 

[blinky]

Thanks Ian, good to hear what others do. Not had a clear night ina couple of weeks to try it out again though!

[carastro]

You can use just Ha and Oiii in some targets.   In particular the veil looks good in that.  I added Sii to it once and decided I preferred it without.  You can use the Oiii as both green and blue, it's called bicolour. 

Carole 

[blinky]

Ah OK, see what you mean