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Old 24-10-2020, 03:04 PM
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MLParkinson (Murray)
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Location: Heathcote, Sydney
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Repeat of Eta Carina Nebula with a Borg 55 mm f/3.6 Astrograph

Last year I posted a similar Eta Carina image using the same equipment used to create this new rendition. Forum members questioned the absence of detail in the image. Also, the dominate colour hues were not complementary. I know I don’t respond quickly, but I do listen to your constructive suggestions and take them on board to improve my work flow.

For this new image using new raw data, I have replaced the star colours with broadband filter RGB star colours. I have also improved the colour palette of the processed image; according to the Photoshop colour picker tool, the two hues representing the nebulosity are about 170 degrees apart on the colour wheel, which by my reckoning is sufficiently close to complementary.

Importantly, I have also improved the configuration of the Borg optical elements, enabling me to achieve focus closer to the “sweet spot” of back focus distance. Homing in on the correct back focus distance is crucial to getting the most from ultra-fast optics. Certainly it was easier to adjust the focus ring by hand to obtain round stars in all four corners.

Imaging a wide field using a 200 mm focal length lens with 5.4 micrometre x 5.4 micrometre pixels cannot compete with the resolution of a Takahashi refractor with large format camera. Even so, my new image is sharp and focussed close to perfect across the entire KAF-8300 sensor. The attached 200 kB thumbnail under-samples the full resolution image. The version uploaded to my Flickr account captures most of the detail in the original Tiff file.


Technical Details:

Borg 55 mm f/3.6 Astrograph, Astrodon 3-nm SII, Ha, and OIII filters, Astronomik RGB filters, QSI 683wsg camera. Mount: EQ8. Two part mosaic imaged from suburban Sydney.

Sulphur II: 41 x 14 minutes = 9.6 hours, Hydrogen alpha: 38 x 14 minutes = 8.9 hours, Oxygen III: 44 x 14 minutes = 10.3 hours, Red = 9 X 35 sec, Green = 11 x 30 sec, Blue = 9 x 40 sec.

Software: Nebulosity 4, PHD 2, PixInsight, Lightroom and Photoshop.
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Old 24-10-2020, 07:07 PM
Placidus (Mike and Trish)
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Gabriela Mistral, the Gem Cluster, and the faint surrounding nebulosity (top right of screen) came out very well.
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Old 25-10-2020, 11:00 AM
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pkinchington (Peter)
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Very interesting rendition. I like it.
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