Math: Exposure Tables

One of our first vexing problems was, “what settings do I use for manual exposures?” At first, we’d get a base setting from a published photo somewhere, and experiment by trial and error. Since we were just learning to use the equipment, and “trial and error” means looking at a digital camera LED, that was fine.

  • It took a long time for us to take a serious look at the Exposure Tables in the highly regarded Astrophotography for the Amateur, 2d edition, by Michael A. Covington. When we did, the tables were straightforward enough, for prime-focus photography. But what about filters? What would happen when we started using eyepiece projection, or afocal coupling? The extra lenses change total system magnification and f-ratio. And what if Mars were considerably closer, as it will be soon? The formulas are really intimidating; we haven’t done most of that math since high school.
  • We said, “Hey, we should be able to do all that in Perl!” And we did. Take a look in the Astronomy sidebar Permalinks for “Exposures – Easy” (canned scenarios), and “Exposures – Custom” (custom scenarios with bells and whistles). Enter your scenario in the HTML form, and print out the resulting photo exposure table for a happy night of viewing and photography! You’ll find notes and formulas to document and explain
  • what we’re doing, though if you get into this, we really recommend the Covington book!

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