Sara Wager Astrophotography
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The difference in data in narrowband imaging

Narrowband imaging is classed as using filters that only allow a very narrow band width of light through them. Traditionally the filters used are
  • Ha (Hydrogen Alpha)
  • OIII (Oxygen III)
  • SII (Sulphur II)

The light wavelengths that these filters allow to pass are as follows
  • OIII 501nm
  • Ha 656nm
  • SII 672nm

This can be demonstrated by the following diagram of part of the light spectrum - This shows the Ha, OIII and SII bandwidths.
Picture
This can be compared to the normal RGB filters (diagram below) where the bandwidths are very different. From this image you can see the bandwidths of light filtered by the more usual Red, Green and Blue filters.
  • Blue 400-500nm
  • Green 500-600nm
  • Red 600-700nm
Picture
RGB filters are often called broadband filters, due to the large amount of light they pick up, whereas the narrowband filters will allow a much smaller range of light through them.
Narrowband filter data is generally combined in processing to the following colours 

  • Ha - Green
  • OIII - Blue
  • SII - Red

This will produce the more traditional HST (Hubble Space Telescope) palette, such as the images below. Each of these contain Ha, OIII and SII data.
Picture
Picture
Picture
Picture
What I think is interesting to be able to show, is the difference in data collected by the different filters. My camera is mono and so colour is added in the processing stage, when I assign the specific filters to the RGB channels as listed above.

It is due to the different data that is captured through each filter that you get details in different colours. 

Here is the narrowband data for NGC1491. This is Ha, OIII and SII data taken through 3nm Astrodon filters. Here you can see that you really do get different structure and detail coming through in each filter.
Picture
Here you can see the difference between the different filters. Ha tends to pick up the general emission nebula, whereas OIII and certainly SII are more specific in the data that they actually capture. With SII here it's possible to see that it picks up only certain parts and doesn't tend to add to the emission nebula clouds and nebulosity.
© Sara Wager 2020
All images on this website are not to be reproduced or used without permission.

  • Recent images
  • Images Gallery
    • Interesting images
  • About me
    • Star People article
  • Buy My Prints
  • My Blog
  • Latest Dual rig adventure
  • Astro Pixel Processor tutorials
  • Asteroids and me.....
    • How to find asteroids
    • How to create an asteroid time lapse
  • My observatory
    • The observatory rebuild
    • Equipment
    • Light pollution and astro darkness
  • My guide to image capture
    • Dual imaging set up
    • Real world comparison - Kodak / Sony chip
    • Creating an inset in Photoshop
    • Artistic one channel processing
    • Rubbish in, Rubbish out - you decide
    • Image process tutorials
    • Start / finish - Processing is THE key
    • Building a mosaic >
      • SGPro - Creating a mosaic in software
    • The difference in RGB and Ha light
    • The benefits of extra subs in graphics
    • Narrowband information
    • To bin or not to bin...
  • Equipment reviews
    • PrimaLuceLab Eagle S
    • All things ODK 10
    • PrimaLuceLab PLUS mounting system
    • Avalon linear guide settings
    • Starting out with the Avalon StarGO - Fitting and connecting to a PC
    • Avalon StarGO - Setting a custom park
    • Mallincam All Sky
    • Aviosys IP Power 9258 4 port
    • Avalon M-Tre mount
  • My published images
  • Links
    • Other Astrophotographers
  • Useful books
  • Write in my Guestbook
    • Contact me