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The Exposure Triangle: Part 2 Aperture

There are three crucial components to creating every exposure…

ISO, Aperture and Shutter Speed

When taking a photo either in automatic or in full manual mode, there are three crucial components to creating every exposure. ISO,  Aperture and Shutter Speed. Each component influences the other and reducing one component means increasing another. When using automatic, the camera decides the setting for you, however if you want to take control and have more creativity with your photography, it is a good idea to understand how the exposure triangle works and switch to Manual or Semi Manual. This is Part 2 of a 3 part series of blog posts on the exposure triangle.

Part 2: Aperture

Aperture is the third component of the exposure triangle. It controls what is called the depth of field of a photo and is measured in f/stops (f/ is sometimes referred to focal ratio). What depth of field means is how much of the photo is in or out of focus. Aperture also affects the amount of light entering the camera. This is controlled by overlapping blades within the lens forming a circle to allow light through. The wider the aperture the larger the blade opening. A wide aperture of f/2.8 allows 4 times more light into the camera than an aperture of f/11. This is because the aperture blades with in the lens are open 4 times wider. Having a wide aperture in low light situations can be handy as it allows more light into the lens allowing a faster shutter speed.

Getting Creative

 If you take a photo of a flower in a garden and use a wide aperture like f/2.8, the flower will look in focus, but the background will be out of focus. This is referred to as a shallow or narrow depth of field as it only has a shallow pane of vision in focus and brings attention to the flower removing distractions. Having a shallow depth of field helps the viewer to focus on the main subject or part of the photo. If you were to take a photo of the same flower and used an aperture like f/11, the pane of vision would be wider allowing the flower and the background to be more in focus this is what is referred to as a wide depth of field. Now the flower doesn’t look so isolated. When trying this experiment, the closer the camera is to the flower, the more obvious the change.

Aperture is measured at f/1.4, f/2.0, f/2.8, f/4.0, f/5.6, f/8, f/11, f/16, f/22.

Changing up or down one aperture setting is also known as moving up or down one stop.


We can control the aperture by using full manual mode M to give us full creativity. Or if full manual sounds a bit scary, use the semi manual mode called Aperture Priority. This is Av  on a Canon or Pentax and A  on a Nikon or Sony. When starting out with photography the advantage of using the semi manual aperture priority mode is you only need to set the aperture and ISO, the camera sets the shutter speed itself. Just remember that a higher f/stop (f/11 or f/16) results in a wider depth of field, meaning more things will be in focus, but lower f/stop (f/2 or f/2.8) results in a shallow depth of field meaning more things will be out of focus.

Changing the aperture will affect one of the other two components of the exposure triangle because we are affectively changing the amount of light entering the camera. If we change our aperture from f/2.8 to f/11 like in the images above, we are stopping down by four stops. In other words an exposure of f/11 is four times darker than at f/2.8 and allowing four time less light to enter the camera. This will result in a very under exposed photo.

To overcome this our options are to change either the ISO or the shutter speed. In the images above I decided to keep the ISO at 200 because I wanted the image quality to remain high and not have any noise. ISO and noise are is explained in my blog regarding ISO. Since I wanted to keep the same ISO it left me with only one other option, to change my shutter speed. I needed to change the shutter speed four stops to have a correct exposure, from 1/50th of a second to 0.3 of a second. By doing this we increase the amount of light by four times, bringing the exposure back to normal.

By stopping down to a shutter speed of 0.3 of a second I needed to use a tripod to keep the image sharp. There is no way to hand hold a camera and take a sharp image at such a low shutter speed.

The exposure triangle is a very important concept to understand if we want to take control of our photography. By simply relying on our camera’s automatic mode we are very restricted and often cant’ take the creative and interesting photos that we visualise. Check out these other posts to learn more about the exposure triangle. The Exposure Triangle: Part 1 ISO and The Exposure Triangle: Part 3 Shutter Speed.


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