Formulas for camera obscura (correct sub forum?)

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Discussion Overview

The discussion revolves around the setup of a camera obscura for observing a solar eclipse, specifically focusing on the formulas needed to determine the correct relationship between the focal length and the hole diameter. The scope includes practical applications and technical considerations related to photography during the eclipse.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant expresses a lack of knowledge regarding the formula for determining the correct focal length relative to the hole diameter in a camera obscura setup.
  • Another participant suggests that the size of the hole is primarily driven by the amount of light needed, rather than focusing, and cites a rule of thumb regarding hole diameter in relation to distance from the hole to the image screen.
  • A participant asks for advice on capturing good photos during the eclipse, particularly concerning the impact of lower light levels on photo quality.
  • Another participant notes that film can experience low light reciprocity error, which may complicate exposure calculations, and suggests that automated digital photography might be more manageable. They also share advice from eclipse chasers about prioritizing the experience over photography during the first eclipse.

Areas of Agreement / Disagreement

Participants present differing views on the importance of hole size versus light requirements, and there is no consensus on the best approach to photography during the eclipse. The discussion remains unresolved regarding the optimal setup and techniques for capturing images.

Contextual Notes

Limitations include potential missing assumptions about the specific conditions of the eclipse and the characteristics of the camera obscura setup. The discussion also reflects varying levels of experience and knowledge among participants.

Ravensong
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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.
 
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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.
 
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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)
 
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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