Monday, May 1, 2017

Eclipse Imaging #2 Ha-images with the moon covering the Sun

Well, this is what I bought my Lunt scope for :-)

I hope that these images provide some interesting detail (craters and mountains on the side of the moon against the sun with all it's surface details). And/or will make a good time lapse of the event. After reading more about it, the one thing I won't see here is the outer layers of the corona during totality (I would have to remove the filter for that ...)

So, the equipment I will use is:
  1. Lunt scope with automated pressure tuner
  2. Grasshopper camera from Point Grey
  3. MyT mount
  4. FlyCap software (from Point Grey)
Things to figure out:
  • For the sun surface vs. corona I need different exposure times. For my images so far, I took many images of the surface and then many images of the corona and then combined them. But here I need to take both at the same time. I.e. I need a program that can alternate between exposure times. Can FlyCap do that?
  • I also need different pressures for surface vs. corona. The app from Lunt to control the pressure can't do that and even if, I doubt that I could synchronize pressure alternation with exposure alternation.
    Maybe I need to write a script that triggers both (but need to find out if and what API the pressure tuner has)
  • How can the MyT mount track the sun over 2.5 hours?
    • TSX has a "sun tracking" speed. Need to try that out and how accurately it keeps the sun centered.
    • "proper" sun guiding solutions (like LuSol) might not work as the sun will be distorted.
  • Need to setup the Lunt scope side-by-side on the MyT mount
    • Need a better way to rotate the versa plate (without pinching the cables)
    • Need to route the RJ11 cable for the focuser through the mount
    • Need to run the whole setup from the NUC
Things I'll have to do onsite:
  • Accurately polar align the MyT mount (should not be a problem as I will use the MyT mount for astro imaging the nights before)
  • Focus and pressure tune as good as possible (I can do that the day before as I will keep the scope mounted)
  • That's it! This should be pretty easy! ... famous last words!!!
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Update 5/28:
I tried to track the Sun with "Sun tracking" enabled. It worked very well in RA, but in DEC, the mount went out by ~1 arcmin per hour. Which is expected as this only adjust the RA axis. But it should be enough for Ha imaging as I only need the body of the sun (I won't be able to see the corona around it). Maybe I will have to slightly adjust it once or twice to bring the sun back to the middle.

Update 6/12:

After trying a lot of things (Bahtinov mask, Hartmann mask, FireCapture...), I think the best way to focus is to do it manually. Use Live View of the camera, zoom into the edge of the sun and then carefully move the focuser into and out of focus until I find the right position.

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So, here is the plan for these images:

Before leaving for OSP:

  • Let camera run for the entirety of solar eclipse (before first contact and after fourth contact) - how much memory will I need? (might need to attach separate storage device)
  • Do I need to alternate exposures to capture surface and flares? Or can I stretch images enough to get flares?

At OSP before August 21:

  • Enter exact GPS coordinates from out site into TSX using the mobile GPS
On August 21:
  • Assuming that I have a great model and polar alignment from the previous nights, point the scope to sun. If necessary, center sun manually and synch into TSX.
  • Set tracking rates in TSX to sun.
  • Start Lunt compressor, set to ~9.5
  • Focus manually on outer sun.
  • Setup FireCapture
    • Set exposure time low enough that histogram peaks at 60% (should be able to leave gain at 0!)
    • Set delay between images to 1 second
    • Start recording