What are stops? Are they the same as f-stops? How are they measured? Are they the same for different exposure controls? Are they still useful now?
These are common questions for those just starting out in photography. They are good questions, and the exposure concepts surrounding them can be confusing. You have probably been told that a stop is a “doubling of light,” which of course is true. That is helpful, but it doesn’t show how stops really works and how they tie your exposure controls together.
What I want to show you in this article is how the concept of a stop acts as a common currency in exposure, and allows you to take complete control of it. Rather than being confusing, stops are really a simplification tool. Without stops, we’d have a hard time controlling our exposure between the three controls; aperture, shutter speed, and ISO.
Introduction
I’m using the term “common currency” to describe stops. To see what I mean, think about the barter system before we had money. If you sold chickens, I sold apples, and someone else sold bricks, how would we all trade? And what if the person selling the bricks didn’t value your chickens as much as I did? It was a mess, which is why the concept of money was developed. Now we all value our goods using money and we exchange money with each transaction. This has proven to be a remarkably useful tool, which is why it has stuck around for a few thousand years.
Similarly, in photography we faced trade-offs when it came to exposure. For example, how could we value a change in the size of the aperture versus lengthening the time of shutter speed? And then how would we value the sensitivity of the digital sensor (or film in the old days) as compared to these other two adjustments? It isn’t apples to apples. The concept of stops is how we square everything up.
View attachment 33222
