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Cat's Eye Nebula (NGC 6543)


alan4908

I found the object very difficult to process due to the extremely bright core.

The problem is that with 600s sec exposures, it was not possible to see anything but white in the core region. On inspecting the corresponding FITS images I discovered that whilst the ADU values of my CCD where not at their maximum level they where in the non-linear region of the my camera, which starts at around 47000 ADU's.  

After trying various techniques, I eventually watched an Adam Block tutorial video on how to create a high dynamic range image using CCDstack. Here, the approach is to take much shorter exposures (I choose 60s) and then combine them with the 600s exposures.  The combination is done on a per pixel level by instructing CCDstack to reject any pixel from the 600s image that is 40000 ADU's or above and to replace it with the corresponding pixel from the 60s image. The result is a high dynamic range image for the LRGB channels which I then processed via my conventionally PS and Pixinsight workflow. 

The image represents just over 8 hours integration. 

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