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As the fateful day draws closer, the United States will host a celestial event that comes once in three generations. I plan to witness this first hand at the exact center of greatest eclipse.

In the planning of this, I have immersed myself in the work of Eddington back in 1919, confirming Einstein’s General Theory of Relativity (and its explanations for gravity) was right.

I personally, could not just stand-by and just look at this event and not do something more. Knowing that failure, due to weather, equipment, and or other forces are stacked against me, I have to make an attempt because a chance like this will never present itself again in my lifetime.

My goal in coming here today is simple, I need some advice from someone who knows telescopes and cameras.

The equipment I plan on using is :

  • a 150 mm Celestron 6SE with an automatic GOTO mount, and an equatorial wedge.
  • The camera will be a Sony A 6000, with an adapter.

The field of view is large because of the 1500 mm focal of the telescope. I chose device because of a trade-off that has to be made, Eddington used a 100 mm refractor scope when conducting his experiment. With any shift in the apparent position of the stars behind the sun as Einstein predicted, the 150 mm telescope should, in theory, coupled with a camera that has a 24-megapixel sensor, have the necessary resolution to image this shift like Eddington's image. If any shift to the stars is to be captured, they will appear within close proximity surrounding the eclipse.

My problem is as follows, the telescope I will be using, will be the lens, and now the lens has only one f-stop. At f/10 and only having the ISO and shutter speed to work with, what exposure would I use ?

Knowing that a long exposure would only manage to capture the outer corona, and possibly engulfing and obscuring any stars that shift. Likewise, a shorter exposure would capture the inner corona and thus not image any stars at all.

I do however plan to bracket 5 stops (shutter speeds) to better my odd of catching any shift.

Would anyone have any other useful tips trick to further better my odds in my endeavor?

Thanks In advance

Bob Brooks

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    $\begingroup$ You might also consult with the Astrophotography forum at dpreview.com. Can't hurt. $\endgroup$ Commented Jun 8, 2017 at 23:28
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    $\begingroup$ This should be migrated to photo.SE , where the general topic of solar observation is discussed. $\endgroup$ Commented Jun 9, 2017 at 12:55
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    $\begingroup$ it's not clear whether you have any/much experience in astronomical photography, but from what you have said, I infer not very much. If that's the case, then worrying about exposure times may be not your biggest problem. The gravitational deflection is tiny, so you will need to have the telescope very accurately set up, since the exposure time will introduce errors greater than the the deflection you are trying to measure. $\endgroup$
    – Dr Chuck
    Commented Jun 9, 2017 at 23:43
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    $\begingroup$ While I applaud your desire to repeat Eddington's measurements, I strongly urge you to re-consider. You only have a few minutes of totality, don't waste them futzing around with a telescope & camera! By all means, set up the `scope and camera and let them do their thing on automatic, but please devote your personal attention to the most spectacular astronomical phenomenon that one can witness without leaving the planet. $\endgroup$
    – PM 2Ring
    Commented Jun 12, 2017 at 2:38
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    $\begingroup$ How did you get on? $\endgroup$
    – steveOw
    Commented Jan 29, 2020 at 2:30

1 Answer 1

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In light of the Apr, 8th, 2024 Eclipse in the US coming up, let me provide an answer, of how I would prepare for it:

  1. Using a planetarium program, have a look at which constellations the sun is passing at eclipse time.
  2. half a year up to a few month earlier to eclipse, take photos of the respective location in the sky.
  3. automate as much as possible using a program like Kstars/Ekos, N.I.N.A. or one of the commercial alternatives.

This way you have all the clear sky nights at your location to come up with the right exposure parameters and observation program. Given that the sun will be moving through the field of view quite fast, I would use 5s or 10s just as the Eddington expeditions did. I would adjust ISO to deal with that and get down to a photographic limiting magnitude of similar depth as the expeditions, which astrometry.net can tell you. Be prepared to change the ISO setting on the spot. Practice that well beforehand, so that you can do it with a blindfold on.

Using this approach, you will get photos of the same region of the sky with and with-out a big mass (the sun) present. This way you should also be able to take care of any distortions present in your instrument (aim at having the same orientation on both occasions).

Using the usual deep sky imaging stacking programs, you should be able to align the two pictures (i.e. on average) up to a tenth of a pixel and you should be able to measure differences in star positions using an astrometry program like Astrometrica.

Using the pixel pitch of 3.9 um of the Sony camera and the diameter of your scope, using the astronomy.tools ccd calculators the expected shift is roughly 3 pixels, so upping the diameter of your scope (increasing the angular resolution) and using a camera with corresponding smaller pixels will give you a larger signal, thus upping your odds of success.

BE CAREFUL: You will need to have a white-light solar filter for your scope for setting up your equipment before eclipse and during partial eclipse.

Have fun

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