M64 Black Eyed Galaxy with 16” Dobson Sony A7s and 10000 images

Hello,

With almost the same processing as my previous M63 image, please find my image of the M64 galaxy aka Black Eyed Galaxy: using a 16" dobson telescope at 1800mm FL, Sony A7s DSLR and Siril with a stack of 10000 images.


LInk to full version

Optics and sensor:

  • Telescope: Dobson Orionx XX16g 16" with 1800mm focal length and coma corrector
  • Capture: 16000 full frame RAW of 1 second duration with Sony A7s at 6400 ISO

Siril processing:

  • FITS compression: Used 32Bits float Rice FITS compression with a quantification factor of 32
  • Preprocessing: 1000* darks 1s 6400 ISO with dark optimisation, offset and flats
  • Alignment: Global star alignment to handle field rotation of Dobson mount
  • Stacking: Linear fit using 10000 images from a total of 1
  • Crop of the stacked image (field rotation)
  • Image was finalized with PixInsight

Fabrice

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Grate work! It looks amaizing. I’ve one question: after using global star alignment you are still seeing field rotation in your images. Why?

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Thanks for your message @rbarbera. Sorry for my late reply :slight_smile:
Ok sorry it was not clear in my original message: there is no remaining field rotation in the stacked image (global star alignment take care of it), but because of rotation, during stacking some portions of the image are not present in all the rotated images especially in the corners: for example depending on the reference image, the corners may have only 50% of the 10000 images with pixels to stack in the final image. This require to crop the final image because of this field rotation consequence.

Now all it’s clear :). Yes, with the field rotation you loose field… from each frame, but the common/aligned portion must looks fine. I’ve misunderstood you. Thanks for your explanation.

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