The Dozen Puzzle

At a recent Meetup, I was reminded of a pesky question that has long plagued me: why does film come in 12, 24, or 36 exposures?

I always shoot rolls of 36 exposure film. Of course, sometimes that roll takes awhile!

The upper limit is somewhat understandable. An arbitrary cartridge size was chosen by Oskar Barnack at Leica many moons ago (there are 12 lunar cycles in a solar year, and 12 hours ante and 12 hours post meridiem), and given the thickness of the film base, only a certain length of film would fit in the cartridge. That length is roughly five feet (there are 12 inches in a foot), and turns out to allow 36 exposures of film (each of which is 24x36mm (i.e., 12*2, and 12*3)).

Where do all these 12's come from? From the cellular to the social to the religious, 12 is everywhere:

  • 12 biochemical salts in every human cell
  • 12 ganglia in the human body
  • 12 cranial nerves
  • 12 ribs on the ribcage 
  • 12 finger bones on each hand
  • 12 basic hues in the color wheel
  • 12 jurors on a jury
  • 12 roses
  • 12 face cards in a card deck
  • 12 cans in a fridge pack
  • 12 eggs in a carton
  • 12 Tribes of Israel
  • 12 days of Christmas
  • 12 Apostles
  • 12 major gods of Olympus

Whether the result of Oskar Barnack's arms or a magical attraction to the number that's (literally) part of our DNA, 12 somehow works. It gives a sense of getting a great deal (the word itself stems from the Germanic compound "twalif," meaning "two-leftover"), and its divisors provide a lot of organizational flexibility (which is quite handy when cutting negatives).

The Leica M6 isn't the fastest film camera to load. Which is maybe why I pick longer rolls.

Because I've found no clear answer why film comes to us in 12, 24, and 36 increments—or why we think that's normal—I'm sure to spend some of the 24 hours of the day over the next 12 months pondering the question.

Happy New Year's to you all! And here's hoping your next 12 * 5 inches of film are your best images yet!