Wednesday, November 7, 2012

Eclipse 2012 - script design

I have now finalized the design of the pre-programmed sequence of images to be taken during totality. Recall that I will be using a Nikon D300 DSLR with a four inch f/6.4 refractor on an Astrotrac equatorial mount. This setup will be under fully automated PC control using the 'Eclipse Ochestrator' software.

In China (2009) I used a similar setup but failed to get good images because the time interval between images was too short, causing the camera to freeze up. This time I am using a camera recycle time of 0.8 seconds which I have previously found should avoid this problem.

My setup is quite heavy and on the limits of the mount capacity. Consequently, the whole thing is fairly prone to vibrations. To minimize the risk of shutter induced vibrations I'll use a mirror lock-up time of one second. Still, from previously testing, I do expect that a significant fraction of the shots will be blurred due to wind induced mount vibrations, so it is important to shoot as many images as possible.

Using the script wizard in Eclipse Orchestrator I can generate a rough initial script to see how many shots can be pressed in during each brief phase of the eclipse. The program also chooses reasonable exposure times based on the actual setup.

I tweaked the auto-generated script so that the Earthshine shots were centered on the deepest part of the eclipse. I could also press in one extra corona image series plus a few extra corona shots here and there. Click the image below to see an overview of what I'm going to attempt. When running the script with the camera connected I see that the exposure settings are updated correctly and that the camera does not lock up. Hurray!

Camera control script - click image above to get full size version
I chose to use ISO=200 for which Eclipse Orchestrator suggested these exposure times:

  • partial phase (with filter): 1/1250 sec.
  • diamond ring: 1/160 sec.
  • Baily's beads: 1/8000 sec.
  • chromosphere: 1/5000 sec.
  • prominences: 1/2500 sec.
  • Earthshine: 3 sec.
  • corona: 1/640, 1/200, 1/80, 1/30, 1/10, 1/4, 1/1.3 sec., corresponding to optimal coronal imaging at Rs=0.1-4.0
I hope that these times will prove to be OK!

Yesterday we approached Coonabarabran and on the way experienced the world's largest solar system drive. At the Jupiter stop, 22 km from Siding Spring Observatory, I couldn't resist attempting some serious observing!

Getting up close to Jupiter (click to get even closer!)

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