GEOMAGNETIC STORM

Discussion in 'Photography Beginners' Forum' started by ElizaMM, Nov 5, 2017.

  1. ElizaMM

    ElizaMM TPF Noob!

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    Just read this: GEOMAGNETIC STORM PREDICTED: On Nov. 6th
    Are others aware of this and how do you prepare? Apparently, Auroras should visible as far south as Maine, Michigan, and Washington. We are a bit north of there at 45° north and have never seen anything from this location, after such announcements - maybe this week will be different. I will set up my tripod and set the camera to 1600ISO, F4 (largest possible), 20s. Any other suggestions would be appreciated.


     
  2. TCampbell

    TCampbell Been spending a lot of time on here!

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    Shoot it like any astro-image... wide angle lenses are best (at low focal ratio). Since the Earth is spinning, it will cause star trailing if the exposures are too long. You can calculate the time by using the "500 rule". This rule is meant for full-frame cameras (so you'd have to adjust it if using a crop-frame camera).

    The rule says that if the camera is on a stationary tripod (not tracking) then the longest exposure you can take before you start to notice the stars are elongating and start to form trails is found by dividing 500 by the focal length of your lens.

    So if you had a full-frame camera and, say, a 14mm lens (quite a wide angle for a full-frame camera) then 500 / 14 = 35.7. So roughly a 35 second exposure would work.

    If you have an APS-C sensor camera then you'd multiply your true focal length by the camera's crop-factor (1.6 for Canon or 1.5 for Nikon).

    So suppose you have a Nikon APS-C sensor camera and a 10mm lens... you'd multiply 10mm by the 1.5x crop factor to get 15. Then divide 500 by 15. That's just over 33 seconds.

    You can see how wide lenses have an advantage ... not just from viewing a bigger area of sky, but also from getting longer exposure times. Suppose you had a 50mm lens on an APS-C camera. 50 x 1.5 = 75. 500 / 75 = 6.66 seconds -- that's not very long.

    You can take longer exposures if the camera is on a "tracking" mount which compensates for the rotation of the Earth (e.g. a Sky Watcher "Star Adventurer" head or an iOptron "SkyTracker Pro" head, etc. These heads are meant to be aligned to the polar axis of the Earth so that as the Earth rotates from west to east, the head rotates from east to west at exactly the same rate ... cancelling out the rotation of the Earth and allowing for very long exposures which nice pinpoint sharp stars.
     
  3. ElizaMM

    ElizaMM TPF Noob!

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    Thanks for the info. I was all set up, but there was nothing to see in this area--just dark sky.
     
  4. benhasajeep

    benhasajeep No longer a newbie, moving up!

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    That's unfortunate. When I was younger we got to view the northern lights fairly often on good clear nights. Have not seen them in a very long time though.
     
  5. snowbear

    snowbear Big Furball Supporting Member

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    The only northern lights we get is the muddy lighting from DC.
     

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