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Tutorial: What is Aperture?


There is bound to be someone who is going to point out something that isn’t technically accurate with this post, be it with my definitions or diagrams. So, before we start, I would like to state that my sole intention is to simplify, as far as possible, some of the fundamentals of photography. My intention is not to swamp the reader with technicalities but rather to outline the basic principles.


I am frequently approached by people who want to know how to get the most out of their shiny new camera. Many get stuck up on the material things like lenses and completely overlook the basics; Aperture, Shutter Speed and ISO.

These "Basics of Photography" blogs aim to be something that I can point them too. I hope that you may also find them useful.

What is Aperture?

In photography, the Aperture refers to the size of the opening of a diaphragm within the lens. Altering its size regulates the amount of light that is allowed to enter into the camera. This works much like the pupil of our eyes:


  • In a dimly lit environment, the pupil dilates (gets bigger), allowing for more light to reach the retina.
    This results in better vision for the given situation.

The same analogy can be used when describing Aperture:

  • When the Aperture is Opened, more light is allowed to reach the camera's sensor / film.
    An Open Aperture can also be referred to as a "Large Aperture."
  • When the Aperture is Closed, less light is allowed to reach the camera's sensor / film.
    A Closed Aperture can also be referred to as a "Small Aperture."


The size of the Aperture (the area of diaphragms opening) is measured in what are referred to as "F-Stops".
F-Stops are a scale of numbers for talking about how much light is being allowed through the aperture and into the camera.

With each f-number, the amount of light is either doubled or halved depending on whether one is going up or down the scale.


The order of these F-Numbers may seem pretty random. The reason is due to their calculation: (Focal Length) ÷ (Aperture Diameter) = F-Stop Number. Regardless, let's keep this post as simple.

Hopefully, you now have a pretty good understanding of what is meant by 'Aperture' and its role when it comes to regulating light. However, changing the Aperture also has an effect on what's known as ‘Depth of Field’.

If you haven't heard of Depth of Field or aren't comfortable with how Depth of Field works, be sure to read:
"Basics of Photography - Part 2: What is Depth of Field."


Up Next:
Basics of Photography - Part 2: What is Depth of Field