STOPS AND F/STOPS
In addition to the words light and exposure you will also see the words stop and f/stop a lot. Always relating to exposure elements, stop and f/stop refer to the halving and doubling of light from one exposure choice to the next.
A stop is a relative change in the brightness or darkness of light. Specifically, a stop measures the doubling or halving of light. Imagine you have a series of light bulbs, all exactly the same. If you have two turned on and then turn on two more you have doubled the amount of light, or increased your light by one stop. If you go back to those original two light bulbs again and turn one off, you have halved the amount of light or decreased it by one stop.
The term f/stop typically refers to aperture, which is expressed as an f/number—for example, f/2.8 or f/4. As I talk about aperture in more detail (Chapter 3) or refer to different aperture choices throughout the book, you will see that information written as an f/number. Whenever you see that, you will know we are talking about the aperture of your lens.
Keep an eye on the technical asides throughout the next few chapters as they offer more detail about stops and how they work together. If you’re not quite ready for that much technical information yet, don’t worry. All you need to remember is that a stop refers to the amount of light and an f/stop refers to aperture, specifically.
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