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Canon 6D and IDAS NB1 - How to enhance OIII

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#1 Marco1968

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Posted 23 October 2021 - 10:39 AM

Greetings,

 

sorry if this question has been asked before - since sveral months I am doing OSC narrowband astroimaging of emission nebulae with a modified Canon 6D DSLR and IDAS NB1 filter.

 

I think the NB1 filter is able to retain an acceptable color balance, in fact I can process the images in PixInsight using the same workflow I apply for broadband and do not have difficulty in preventing the stars to have a wrong color cast.

 

Still, the nebulae in the final images show a predominant red color while green/blue is typically very weak.

 

Extracting the 3 R, G, B channels indeed there is good amount of green and blue signal in the image (I noted the signal in G and B images seems to be the exactly the same).

 

I would appreciate to have some guidance or to be directed to a tutorial that I can follow to achieve a better color richness in my images (please note that I have PixInsight but unfortunately cannot use StarNet due to old CPU).

 

An additional question: is there a duo- or tri- narrowband filter that would work better with the 6D?

 

I read a lot of messages about the Triad, STC, Optolong etc but seem that these will make the color balace more difficult to obtain.

 

Thank you in advance and Clear Skies!

 

Marco


Edited by Marco1968, 23 October 2021 - 10:42 AM.


#2 bobzeq25

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Posted 23 October 2021 - 11:00 AM

Color "balance" with these filters is a slippery concept.   If you simply reproduce what the camera is seeing, many diffuse nebula would come out simply red, Ha is overpoweringly strong, compared to other emissions.  People often like to create more interesting images by deliberately misbalancing color.  An excellent example is the iconic Pillars of Creation image.  A balanced image of that is just red.

 

The NB1 is a fine duo band filter, pretty much as good as any.  Since it only sees two small bands of color, color is inherently unbalanced to some degree.

 

If you want to boost the O(III) on a particular image.  Shoot a longer total imaging time to make the weak O(III) signal less noisy.  Just crank up the blue and green channels.

 

You're correct that, if you want to misbalance color on the nebula while balancing it on the stars you need to separate out the nebula and the stars.  If you don't use Starnet, you can do a good job with just a StarMask.


Edited by bobzeq25, 23 October 2021 - 11:03 AM.

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#3 charles.tremblay.darveau

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Posted 23 October 2021 - 11:36 AM

I have used the ZWO duo-band and more recently the IDAS NBZ. Looking at NB1 spec, seems the bandpass is closer to the duo-band (or l-enhance). The bandwidth on the OIII is a bit on the large side which may leave a bit of light pollution, but it should still be a fine filter to start out as bobzeq25 said. If you eventually decide to upgrade your gear, look for a 7-10nm bandwidth which will help contrast.

 

Let me split your question in 2 parts, first the DSO colour balance and then the star balance. For the DSO part:

  • the one thing that I found that help the most was to un-link the Pixinsight autostretch.  By default, it links channels which means it applies same stretch function to all channel. Because HA is dominant, the linked stretch gives mostly a red image.
  • I normally combine B/G in a O layer with pixmath, and R-> Ha, for a HOO combination
  • I then play with histogram tools until I'm happy with colour balance.
  • At the end, I apply some colour saturation. Color mask (e.g. mask applied to a single color) can help as well.

 

For the star part, most narrowband will naturally reduce star colour. I usually apply a starmask (or starnet) then play with colour balance until chroma is balanced. A lot of people acquire a separate RGB (no filter) dataset to add back star colour. I don't because I'm lazy XD


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#4 Marco1968

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Posted 24 October 2021 - 04:26 AM

Thank you both very much for the clarifications and good advice,

 

I will definitely experiment more with PixInsight pixelmath (function that I have not tried yet) to enhance OIII and star mask / color mask to keep the stars from having odd colors

 

Clear Skies!

 

Marco


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