Have you ever talked about photography with someone ? Did you nod without understanding any terms that they use ? The photographic vocabulary is on every camera documentation, shops and forums. They look complicated and you feel bad having to ask for what they mean. 

Rest assured, these terms are not mystic and here are their explanation.


A diaphragm is a device that controls how much light goes through your camera lens when you take a picture. The more closed a diaphragm is, the less light you get and the darker the photo will be.

Just like the iris in your eye that open or close in regards of the quantity of light that you see.


You will only find captors on digital cameras. Indeed, it is an electronic component that convert the light flux into a numerical code. It replaces the film that are used in traditional photography. 


This is a mechanism that opens and closes during a specific amount of time when the light can reach the captor. It is close all the time, except when you take a picture. At that moment, you can actually hear it make the recognizable "click" of a camera.

F-number, F-stop, Relative Aperture

This F-number gives the diameter of the diaphragm as a function of the focal length of your lens. This parameter is unitless.


This is a number that informs us on the diaphragm's aperture. It basically characterizes how open the diaphragm is. Moreover the amount of light that can enter your camera is related to the area of this value. The area is a square function of the focal length divided by the f-number. 

Focal Length

The focal length is the distance between the lens to the captor for an infinite point of focus. It is given in millimeters. For instance, a 24mm lens will give you a wide field of view whereas a 400mm lens will create a zoom effect.


The sensitivity of your captor (or a photographic film) is described by the ISO. The lower this number is, the more sensitive it is and the more light will appear on your pictures. You may have noticed numbers such as 100 ISO, 200 ISO to 1600 ISO. It may seem magical and you may want to only use the 1600 ISO value to get more exposed images but the higher this number, the more noise you will see on your photographs. 

You are not the only one who wondered about those photography terms. Do everyone a favor and if you find someone who look puzzled when talking about diaphragm or aperture : spread the knowledge.