At the most basic level, the aperture is the size of the “opening” through which your camera collects light, whereas f-stop is the way we measure the size of this opening. At times, the two terms can really be used interchangeably: “what aperture are you shooting?” or “what’s your f-stop?”. You’ll read later, however, why this doesn’t always make sense.

When the aperture is open all the way, your lens is letting in as much light as possible. When the aperture is closed all the way (well it’s never really closed all the way, just super small) your lens is letting in the smallest amount of light possible.

If that sounds too easy, let’s complicate things a tad. When speaking f-stops, what looks like a relatively low number (f/2.8 for example) corresponds to a large aperture , a high number (f/22, f/64) corresponds to a very small aperture.

You might have noticed that f-stops are expressed as fractions. To to put it in mathematical terms f-stop = (f) / (x), where f=the focal length of your lens (50mm, 18mm, etc…) and x is the number that we are familiar with, 2.8, 5.6, 11, 22, 64. Essentially, f/11 means that your aperture diameter is 1/11th the maximum possible size, given your lens. In terms of how much light is let in, these numbers are standardized on most lenses so that each number (2.8, 4, 5.6, 8, 11) lets in 1/2 the amount of light as the previous number.

Now remember the bit about being cautious when using the words “f-stop” and “aperture” interchangeably? Saying “large aperture” and “large f-stop” don’t really mean the same thing, so it’s best to think of the f-stop as a setting, and the aperture as the physical manifestation of that setting.

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