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Thread: Angle of view as it relates to the solar eclipse

  1. #11
    tgtaylor's Avatar
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    Re: Angle of view as it relates to the solar eclipse

    According to Schneider, the 360mm Symmar-S will provide 70 degree coverage at f22; the Rodenstock Apo-Sironar-S gives about 75 degree coverage at f11; except for the 120-SW, Nikon's lens provide for a 60 (f5.6) to 70 (f/22) degree coverage with the 120-SW gives 80 degree coverage at f/8 and 105 degree at F/22. I forget how it goes but you can guesstimate the arc in the sky by pointing one arm directly at the sun and keeping the other at 90 degrees (?) turn in the direction of solar travel.

    Thomas

  2. #12

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    Re: Angle of view as it relates to the solar eclipse

    Quote Originally Posted by couldabin View Post
    I plan to photograph the solar eclipse (weather-permitting) with both my 4x5 (210mm lens) and 8x10 (12" lens). From my viewing spot in Nebraska, the sun's azimuth will change nearly 80 degrees from start to finish. Does anyone know how to convert that to angle of view when the elevation is 60 degrees above the horizon? (It's not a simple calculation, since the vertical lines converge.) Thanks.
    This on-line calculator http://keisan.casio.com/exec/system/1224682277 will give you exactly the sun's azimuth and elevation (altitude)changes for your position, the time of the year and the length of your observation period. From these values you get the horizontal and vertical angles you need to cover by the angle of view of your lens (you have to calculate that from the FL of your lens and the film format you want to use).
    More problems wait for you on the way if you want to make a composite picture of the different eclipse phases on one single film frame, though.

  3. #13

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    Re: Angle of view as it relates to the solar eclipse

    No, the 12" goes on the 8x10. Yes, the sun's disc is roughly 0.5 degrees.

    Quote Originally Posted by Jim Noel View Post
    First, I would put the 12" lens on the 4x5. Even then you image is going to be quite small. The Sun and Moon each intercept an angle of only about 0.5 degrees.

  4. #14

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    Re: Angle of view as it relates to the solar eclipse

    No, I'm not mad. I live 2 hours from the center of totality, so I thought that might be a convenient viewing spot.

  5. #15

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    Re: Angle of view as it relates to the solar eclipse

    Thanks, but I think I didn't make my question sufficiently clear. Yes, the sun "moves" 0.25 degrees/minute. Totality at my viewing location will be 2:30. The duration of start of eclipse to end of eclipse is ~3 hours. Earth will rotate roughly 45 minutes during that period. But the azimuth changes nearly 80 degrees. I was asking how to convert that information to one that relates to the camera's angle of view. This is a calculation that would take into account the fact that azimuth is expressed at the horizon, but that all on the compass converge overhead.

  6. #16

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    Re: Angle of view as it relates to the solar eclipse

    Yes, I ended up doing this empirically -- the sun traverses the 4x5 view in ~2:15. I should be able to capture nearly 2/3rds of the event on the 4x5, but all of it (with about 8 min. to spare) with the 8x10. But I would like to know the trig involved.

  7. #17

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    Re: Angle of view as it relates to the solar eclipse

    Won't be in Lincoln, which will have 1:25 of totality.

  8. #18

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    Re: Angle of view as it relates to the solar eclipse

    Thanks, Ted. I was interested in finding out how to account for the fact that we have the azimuth for all relevant points in the event, but the event takes place at 52-61 degrees above the horizon. When you point your camera upwards, the angle of view covers something greater than the values implied by the azimuth -- point it directly overhead, for example, and the narrowest angle of view will capture the entire circle. I ended up simply timing it, which is effective for this but doesn't advance my ability to calculate such things in the future.

  9. #19

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    Re: Angle of view as it relates to the solar eclipse

    I think the relevant angles of view are determined by the focal length and film size. It's conventional to express the angle of view using the diagonal distance of the film, but that's of course the greatest angle the film can capture. The horizontal angle of view is less, and the vertical less still. My question related to the fact that the visual distance between two celestial objects (one with azimuth 100, one with azimuth 150), depends on their elevation, since all points converge directly overhead.

  10. #20

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    Re: Angle of view as it relates to the solar eclipse

    Quote Originally Posted by couldabin View Post
    Earth will rotate roughly 45 minutes during that period. But the azimuth changes nearly 80 degrees.
    Couldabin, I'm sorry you don't want to use the on-line calculator. To think that the Sun will change its azimuth with nearly 80 degrees in 45 minutes is nothing less than madness. I think you don't know at all what you're talking about.

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