What is a Stop of Light in Photography? How Aperture, Shutter Speed and ISO Affect Stops

You may have heard the term "stop of light." But what is it? A stop of light is simply a unit of measurement that helps photographers control the amount of light entering their camera. It's important to understand how aperture, shutter speed and ISO affect stops of light because they all work together to create the perfect exposure. In this blog post, we will explain what a stop of light is, and show you how to change the amount of light using aperture, shutter speed and ISO.

What are Stops of Light in photography?

Doubling or halving the light in an image is called a stop of light. A one-stop increase means the amount of light doubles. A one-stop decrease means the amount of light is halved. Digital cameras have the ability to change the light in increments. So, if you want to make a picture brighter, you would increase the light by one stop. If you wanted to make it darker, you would decrease the light by one stop.

How do Aperture, Shutter Speed and ISO Affect Stops of Light?

Aperture, shutter speed and ISO all affect the amount of light that enters your camera. They work together to create the perfect exposure.

Aperture and stops of light

Aperture is the size of the opening in the lens. The bigger the aperture, the more light enters the camera. The smaller the aperture, the less light enters the camera. To increase a stop of light with the aperture you would need to double the size of the opening. For example, if your aperture is f/16, you would need to make it f/11 to increase the light by one stop.

Shutter speed and stops of light

Shutter speed is how long the shutter is open for. The longer the shutter is open, the more light enters the camera. To increase a stop of light with shutter speed you would need to double the amount of time the shutter is open. For example, if your shutter speed is one second, you would need to make it two seconds to increase the light by one stop.

ISO and stops of light

ISO is how sensitive your camera sensor is to light. The higher the ISO, the more sensitive it is and the more light it collects. To increase a stop of light with ISO you would need to double the number. For example, if your ISO is 400, you would need to make it 800 to increase the light by one stop.

An Easy Way To Remember Those F Stop Numbers

If you're having trouble remembering the f stop numbers, here's an easy way to do it. The first thing to remember (this is important) is the lower the number, the wider the aperture opening will be and the more light that comes into your lens. So, f/16 is going to let less light in than f/11. To double the amount of light coming in, or move one full-stop up, you divide by 1.41. So starting at f/4, to go one full-stop up, you divide by 1.41 to get f/2.8. To move one full-stop down, you multiply by 1.41.

Below are the main sets of aperture numbers you need to know to have an understanding of each full stop of light.

f/2.8, f/4, f5.6, f/8, f11, f16, f22

These are all one-stop apart.

There are 1/3 stops and 1/2 stops that are a little more confusing, The cheat sheet below makes it easier for you to wrap your head around them! 

The Cheat Sheet above was put together by Digital Camera World

So what should I change if I want to adjust my exposure? Aperture, Shutter speed or ISO?

You need to decide what is important to you in the image you are taking. If you are shooting something that is fast-moving, then you may need a fast shutter speed to stop motion blur, in this case, you would not want to increase your shutter speed to let more light. If you wanted a shallow depth of field, then you will need a large aperture, if you wanted to let less light in then you would be better off increasing the shutter speed so you can keep the shallow depth of field.

One of the easiest ways to adjust your exposure in the field is to shoot in one of the auto modes, such as aperture priority or shutter priority and then use exposure compensation, which is usually a +/- button on your camera, to make the image lighter or darker.

It all comes down to what is important in your image, and each situation is different. That's why it's important to understand how each one works and how they affect your image.

I found the above diagram at Petapixel.com where you will find a really great article on the exposure triangle. 

Now that you understand how aperture, shutter speed and ISO affect stops of light, you can start experimenting with different settings to create the perfect exposure. Just remember, if you want to increase the light by one stop, you need to double the aperture, shutter speed or ISO. And if you want to decrease the light by one stop, you need to halve the aperture, shutter speed or ISO.