Photography Cheat Sheet 1: What is aperture and how does it work?

What is aperture?

Definition: The aperture of a lens is the diameter of the diaphragm opening. It determines the amount of light that enters the camera and reaches the sensor.

Explanation: The camera aperture is a key factor in the exposure triangle (aperture-focal length-ISO), and also determines the depth of field.
The larger the aperture number, the less light will enter the camera, so more exposure time is needed, and/or larger ISO.
The smaller the aperture number, the more shallow the depth of field. A shallow DOF means that the area in focus is small, and your focused subject will be surrounded by a more or less blurry background.

How does aperture work? How to change the aperture.

The numbers written on your lens to indicate the aperture are called “f-stops“.
The act of narrowing down the aperture is often referred to as “stopping down” while opening it up is called “stopping up”. Each “stop” means that the light intensity changes by half from the previous stop.

The smaller the aperture value, the larger/wider the diaphragm opening, so more light enters the camera. Let’s see what happens with the diaphragm of the lens when the aperture changes:


Examples of what happens with the photo when you change the aperture:


A wide aperture also allows you to use a faster shutter speed, which is important when photographing fast-moving subjects or when hand-holding the camera.

Where is aperture number on my lens? How do I change the aperture?

If you have a DSLR, the aperture number will be written on the lens, and a white arrow will indicate the current aperture. To change it, rotate your lens ring to bring the arrow pointer to the desired f-stop number.

If you have a compact point-and-shoot camera, you can still choose your aperture in the same way if you set the camera to aperture priority mode. Or, you can change it from the menu, which is a different custom path for each camera manufacturer.

The F number representing the aperture can also be displayed as 1:nr instead of f/nr, and it is usually written like that on the lenses.


Not all cameras have the availability of the entire f-stops range. Lenses with larger apertures are usually faster. Also, lenses with wider apertures are more expensive than a normal lenses. Here’s what kind of lens do you need for a certain maximum aperture number:


This article is an excerpt from Complete Technical Photography Manual
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I started photography as a hobby in 2005, during college. My passion slowly became a more important part of my life since 2008. Because of using a combination of my photographic knowledge, with those of internet marketing, I like to call myself a "photomarketer".

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