Eclipse photography dry run with sunspots

The time has come for serious practice for the total eclipse on August 21st from the Sand Hills of Nebraska. The very nice sunspot group, AR2665, provided a great opportunity to start today. There are only about two and a half minutes to capture both diamond rings, the inner corona and any flares, and high dynamic range (HDR) images of the full corona. I want to be handling the cameras on autopilot so that I can relax and enjoy the experience.

The solar corona is a highlight of the eclipse and extends up to a couple of degrees away from the Sun - far beyond the 1 degree field of view of my Questar telescope. I've decided to use a telephoto lens on my camera to get the field of view needed to capture the outer corona. The full setup is:

  • a Vixen Polarie star tracker
  • Sony a6300 (APS crop sensor, 24MP, mirrorless camera)
  • 2x teleconverter (optional)
  • vintage 200mm Vivitar telephoto prime manual focus lens
  • Thousand Oaks Nickle-Chrome glass solar filter

Today was my first time using this setup, and I wanted to try it with and without the teleconverter.

After sliding the solar filter on and off a couple of times, I decided too adjust the fitting tape. A looser fit makes for faster filter changes. There is no chance of the filter blowing off with the sun high overhead on eclipse day and the wide mounting band.

The teleconverter gives me a full frame equivalent focal length of 600 mm ( 2 x 200mm x 1.5 crop factor) with my crop sensor camera. We are well past the solar maximum of the sunspot cycle, so it is unlikely that the corona will be at its very largest. After viewing my test images, I've decided that the extra detail is worth the risk of loosing a bit of the outer corona. The image below is a processed 1:1 crop of the 600 mm equivilent focal length image.

The image blow shows the full field of view of the original 600 mm eq fl capture. Exposed ISO 100, f8 for 1/125 sec.

Finally this is the 300 mm eq. (200mm x 1.5) FOV image.

Content created: 2017-07-10




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