Celestial hemisphere:  Northern  ·  Constellation: Taurus (Tau)  ·  Contains:  16 Tau  ·  17 Tau  ·  18 Tau  ·  19 q Tau  ·  20 Tau  ·  21 Tau  ·  22 Tau  ·  23 Tau  ·  24 Tau  ·  25 eta Tau  ·  26 Tau  ·  27 Tau  ·  28 Tau  ·  Alcyone  ·  Asterope  ·  Atlas  ·  Barnard's Merope Nebula  ·  Celaeno  ·  Electra  ·  IC 349  ·  LBN 770  ·  LBN 771  ·  LBN 772  ·  M 45  ·  Maia  ·  Maia Nebula  ·  Merope  ·  Merope Nebula  ·  NGC 1432  ·  NGC 1435  ·  And 13 more.
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The Pleiades - M45, Niall MacNeill
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The Pleiades - M45

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The Pleiades - M45, Niall MacNeill
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The Pleiades - M45

Equipment

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Description

Here is a 4 panel image of the Pleiades, taken on my C14 with the Hyperstar and ZWO ASI 1600MC.

The Pleiades or Messier 45 is a very bright star cluster, visible to the naked eye. At a distance of 444 light years it is the closest Messier object tp the Earth. The cluster is made up of hot blue stars that formed within only the last 100 million years. They are moving together and ploughing through a dust cloud. The clouds reflect the blue light from the stars and and generates the reflection nebula. However, you can see areas of the dust that are not blue and are not being directly illuminated by the blue stars, but by white stars further afield.

I had no end of trouble with reflections in the raw data and it took a lot of work to remove them….or at least to reduce them to an acceptable level. This is actually an issue with the camera, the ZWO ASI 1600MC, where the glass protection window in front of the sensor has no anti-reflection (AR) coating. This means light from a  bright star comes down from the primary mirror and whilst most of it goes through to the sensor, some reflects back from the protection window, back to the mirror to return and land in a different spot on the sensor. When using my Canon EOS 5D mk II with the Hyperstar I don't get such reflections. Version B, shows one of the panels which exhibited the worst of the reflections.

I did manage to remove them with great difficulty. The technique to do so is ingenious and Rodney Watters put me on to it. It was developed by Adam Block, and is available on his website. My thanks to him for developing this amazing technique. Basically, he notes that reflections are often present in one or two colour channels but may be absent in another, or even the Luminance channel. Here they were strongly present in Blue, less so in Green and largely absent in Red. To remove them a Preview is created around the offending reflection. This is saved for each of the colour channels. The Linear Fit process is then used to match the brightness of the Red Preview area to that of the Target image, say the Blue. There is then a technique to paste the adjusted Red Preview area into the Blue image. A feathered mask over the area is used to ensure no boundaries can be seen and the reflection disappears. Magic!

Revision C shows the same panel before and after the removal of the reflections. Not absolutely perfect, but a massive improvement and frankly, rescued the image from my perspective in that it allowed me to produce an image of a quality worthy of posting on AstroBin. However, I had to deal with 19 refections across 4 panels, a very arduous process. 

So imaging at f/1.9, which gives me a wonderfully large FOV and is very fast, is great, but with this camera I cannot have a bright star in the FOV without having to deal with these reflections. That is very annoying and basically means I need to look at a new camera option if I want to do more of this sort of imaging.

Comments

Revisions

  • Final
    The Pleiades - M45, Niall MacNeill
    Original
  • The Pleiades - M45, Niall MacNeill
    B
  • The Pleiades - M45, Niall MacNeill
    C

B

Title: The Pleiades - M45

Description: Panel 3 showing a number of reflection artefacts

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C

Title: The Pleiades - M45

Description: Panel 3 before and after reflection artefact removal

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The Pleiades - M45, Niall MacNeill