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Stargazing Formulas for camera obscura (correct sub forum?)

  1. Jan 27, 2017 #1
    Experiment / demonstration: Set up military surplus command tent as camera obscura / pinhole projector for observation of full soar eclipse.

    Problem: lacking in personal knowledge of the formula needed to determine correct focal length to hole diameter

    Solution: Request assistance from actual scientists instead of Brittanica and Wikipedia

    Thank you in advance for the help, I'll no doubt have further related questions on this project as I start attempting to do the maths.
  2. jcsd
  3. Jan 27, 2017 #2


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    The main driver of the size of the hole is the amount of light you will need, not so much the focus. Larger holes reduce the focus unless the hole is so small that optical effects blur it. The rule of thumb given in http://www.cameraobscuras.com/camera-obscura/faq/ is that the hole diameter should be 1/100th the distance from the hole to the image screen.
  4. Jan 28, 2017 #3
    TYVM, love the link!!

    Any warnings / advice on getting good photos & film of the event? (mostly wondering if the lower light levels will mess with photo quality)
  5. Jan 28, 2017 #4


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    Film can be sensitive to low light reciprocity error, where the exposure time has to be longer than the normal calculation. It happens fast and changes from full sunlight to night, so it would be tricky. Automated digital photography is probably easier.

    PS. I attended a meeting of the Fort Worth Astronomical Society where they were planning their trips. Someone here can probably give you a reference in your area. One of the recommendations from some avid eclipse chasers was to minimize the photography (or don't do any) during your first eclipse and just absorb the atmosphere. Apparently, it is very spooky and memorable. Save the photography for later eclipses.
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