What is Aperture and F-Stop?

What is aperture and f-stop?

Aperture (or Iris) is the ‘gate’ that blocks light from hitting the sensor. When you want more light in, you ‘open up’ the aperture. When you want less light in, you ‘close down’ or ‘stop down’ the aperture.

If you’re new to aperture, and don’t understand its relation to the shutter, ISO and exposure, please watch my simple explanation of the exposure triangle.

In this video I’ll explain the complex numbers (don’t worry, it’s easy) you’ll find on your lens:

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How to calculate the f-numbers of f-stop

It’s simple. Start with root 2 and raise it by an integer:

aperturesequence

Easy way to remember the numbers

When you first start using a lens, you won’t remember these numbers. Here’s an easy way:

Double the number!
0.7 1
1.4 2
2.8 4
5.6 8
11 16
22 32
44 64

If you notice, every second number is double or half the second number before or after it. E.g., if you start with f/1.4, then leaving one step, the next is f/2.8. 2.8 is double 1.4.

So, all you have to remember is 1 and 1.4, and you can easily calculate the remainder of the sequence. The only confusing bit is the jump from f/5.6 to f/11, which is not exactly double.

With a few hours of practice, this will be second nature.

A stop of light

Each jump is a stop of light. A stop isn’t an absolute standard, like a liter of water or a mile. A stop is a relative measurement.

When we say stop down by one stop, we’re saying halve the light. If we raise two stops, we’re quadrupling the light!

It takes some getting used to, but I hope my brief and simple system will help you remember and deal with the aperture and f-stop numbers. Please feel free to ask me anything in the comments below, and if you have a simpler way share it!

Exclusive Bonus: Download my free guide (with examples) on how to find the best camera angles for dialogue scenes when your mind goes blank.