04 May 2019

Solar Eclipse 2017 - HDR


By  Florian Bleymann


hereby I submit an image for the AAPOD. It’s a HDR picture oft he solar eclipse, from August 21, 2017. In the following lines you can read the technical and processing details and at the end why I have decided to process the image especially in this way. Image in appendix.

Recording date: August 21, 2017
Location: Corvallis, Oregon, USA
Lens:  Astro Professional ED Refractor (aperture:80mm, focal length: 560mm)
Camera: Canon EOS 700d
Gain (ISO): 100
 Details:   The picture is a HDR (hyigh dynamic range) of 12 pictures with different
exposure values. Values ins seconds:
1/1000, 1/500, 1/250, 1/125, 1/60, 1/30, 1/15, 1/8, 1/4, 1, 2

Before totality of the solar eclipse I used an ND 5.0 solar filter foil. I removed the filter immediatley after the begin oft he totality.
I started the image capturing with the HDR-bracketing function of Magic Lantern for my Canon EOS700d, triggered with a cable connected remote control.
The telescope, my ED80, was tracked with an older Meade LXD-75 parallactic mount (Polar Alignment for a perfect tracking was done early in the morning (03:00 AM on August 21, 2017)!
The image processing was time-consuming. I need 14 days of work in the evenings to finally work out this picture. My steps of image processing in overview:
1. First control in lightroom, minimal first sharpening for corona
2. Manual centering in Photoshop
3. Loading and Stacking in PixInsight 1.8
4. In PixInsight:
- DynamicCrop
- Color calibration
- Histogram transofrmation (wihtout masks after a lot of tries)
- HDRMultiscaleTransform with a scale of eight layers
- Curves transformation, adjustement of histogram
- Export to Tiff
5. Next steps in Photoshop:
- manual centering of hdr stack with stretched moon from 2 seconds exposure-time image from this stack
- stacking and transformation (the moon was shrunken in diameter – I had to correct it, due to sun light „blooming“ after 2 seconds ecposure time)
- sharpening, noise reduction

As you can see – a lot of work and iterations to work out such a picture.
I’ve done a lot of investigation on the internet. You can find a lot of solar eclipse pictures as reference. A lot of pictures are sharpened too much (my point of view), e.g. with a Larson Sekanina filter. But I’ve seen a lot of filter artifacts in the picture details.
After my first tries in image processing I decided to work out a more hamonic picture. The corona is a little bit more faint but harmonizes more with the sun/moon border and the background. The background looks a little bit more gray-blue after color calibration but comes more close tot he reality. All in all this harmonizes more with the embedded prominences but without loosing the glowing effect.
You can see the glowing from all perspectives! The glowing is changing when you change your viewing angle!!!
Therefore the picture shows a lot of part that you couldn’t see with your naked eyes but preserves also the visual impression during the total solar eclipse.

I hope you enjoy the picture like me and it will be chosen as an APOD.

If you have questions, don’t hesitate to contact me.

Yours faithfully,
and many greetings from Germany,

Florian Bleymann



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