RGB Composition of Dual Narrowband Images

-


Using the L-eXtreme dual narrowband filter allows taking quite impressive pictures of various nebulae. However, it will create quite unnaturally looking star colors and will filter out features of the object that are not particularly emitting the spectral lines of Ha or OIII.  Some objects, due to their physical structure, look quite different in the narrowband than in images taken over the full RGB continuum. The crab nebula M1 is a good example for this.


M1 the crab nebula in HaOIII, 40x90sec
C9.25 on EQ6-R Pro, ASI294MC PRO, L-eXtreme


M1 the crab nebula unfiltered RGB image,
40x60sec, C9.25 on EQ6-R Pro, ASI 294MC Pro


It is interesting to look at and compare these pictures individually.  However, I wanted to try combining them in a meaningful way. Basically I had five different "channels" - red, green, blue, Ha and OIII and was looking for good ways to compose an image from that. There are several ways for doing that, some more flexible than others. I ended up using Astro Pixel Processor (APP) using the following steps:

  • register all raw images to align them
  • stack and color correct the RGB images as usual 
  • stack the filtered images and create an Ha and an OIII image using corresponding function un APP
  • use the APP function to remove stars on the Ha and OIII images
  • adjust the histogram on the Ha and OIII images to make the background black
  • use the RGB composition tool in APP to create various flavors of combined images


The RGB composition tool in APP
the individual channels can be flexibly mapped to 
RGB and Luminance


Composite RGBHOO image


The same exercise carried out with pictures of "Thor’s Helmet":


NGC2350 "Thor’s Helmet", 25x120sec
C9.25 on EQ6-R Pro, Reducer 1/6.3,ASI294MCPro, L-eXtreme 

NGC2350 "Thor’s Helmet", 25x90sec
C9.25 on EQ6-R Pro, Reducer 1/6.3,ASI294MCPro


Composite RGBHOO image of pictures above


















Popular posts from this blog

Controlling the Telescope with a Berry

-
Image
One of the things that made me reluctant to seriously start with astrophotography was the prospect of spending long nights outside in front of a laptop that is tied to the telescope with a long USB cable. Nights that would typically end in disappointment and anger after I inadvertently tripped over that cable - at least that had been my experience in some early attempts.   This time I wanted to take a different approach. The entire setup should be controlled by a little computer that is directly attached to the equipment, while the control would happen remotely over the network.  I guess there are three main technical approaches that you can take to achieve this: mini-pc being controlled over remote desktop; basically using ascom and a similar imaging software as you would use in the "long USB" scenario.  "out of the box" solution from an astronomy equipment vendor like the ASIair Linux based solution using Kstars/Ekos/Indi running e.g. on a Rasperry Pi I am not sur
Read more

December Nebulae - fighting star halos

-
Image
The Horsehead Nebula is almost a mandatory mandatory object to capture with every new optics. I was eager to see how the Hyperstar world do with it. Unfortunately weather and moon were not quite supportive of this plan. As even thin clouds lead to huge halos around the bright star(s) I had to discard quite a number of frames. Luckily over Christmas it was possible to collect a decent amount of data in reasonable quality. IC434 the Horsehead Nebula 152x60sec, C9 Hyperstar, ASI294Pro IC443 the Jellyfish Nebula is quite a beautiful object. However, the original frame I chose contained two relatively bright stars and the Optolong filter is creating a gigantic halo around them - one was even able to the cabling of the Hyperstar within the halo. My PixInsight craftsmanship proved insufficient to fully fix that, so I tried to tame one of the halos and cropped the image to remove the 2nd one. IC443 Jellyfish Nebula 117x120sec, C9 Hyperstar, Optolog L-eXtreme, ASI294Pro Shot at the same nights
Read more

Galaxies at a larger scale

-
Image
The primary focus of the C9.25 at 2350mm in combination with the sensor size of my ASI 294 is giving a field of view that turned out to be a nice fit for imaging most of the spring galaxies.   However, there are a number of objects that do not quite fit. So I spent a few nights end of April to image a with the 1/6.3 reducer. This is giving a slightly larger field of view. More suitable for some of the larger objects. In addition to the larger galaxies I tried some groups of galaxies. Here it was a bit harder to get a good fit. HCG 44 may actually be better without the reducer. The famous Leo triplet is too big to fit within the FOV - so I captured only two of them. I think they are beautiful - even as a pair.  For the really huge galaxies - like e.g. the Andromeda galaxy - as well as the large scale galaxy groups even shorter focal lengths would be required. I still need to find a good solution for that. In the meantime I enjoy how these medium sized objects turned out.
Read more