Photography Essentials Course
Chapter 3

Lesson 4: The Exposure Triangle

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IN THIS LESSON

The ‘Perfect’ Exposure

Ok, so this is what it comes down to; The Exposure Triangle.

The triangle is made up of 3 fundamental elements, one for each side of the triangle. It is the understanding that if one element changes so does one or both of the others to maintain a correct exposure. So, what are these elements?

You’re in luck as we’ve just covered them in the previous lessons. There are:

Aperture, Shutter Speed & ISO.


Understanding how these three elements interact allows photographers to make creative decisions and manipulate exposure to achieve the desired visual outcome for their photographs. Balancing the exposure triangle enables photographers to control the brightness, sharpness, and overall mood of their images.

Remember the very first lesson of this course? We talked about the importance of light. Each one of these elements relates to light control.

Aperture - You’re controlling the amount of light through the lens.

Shutter Speed - You’re controlling the amount of time the sensor or film is exposed to light.

ISO - You’re controlling how sensitive your sensor is to light.

Here is a situational example:

It is nighttime with just the moonlight for illumination and we want to capture a landscape. In this circumstance, I’d start with the aperture as this will provide depth of field and sharpness. It’s moonlit so let us go with f/11.

Now the aperture is set, let us move to another element. I’d go ISO. We know that if we increase the ISO too much it will introduce unwanted particles that will impact the quality. ISO 200 is very safe.

Now we have the aperture at f/11 and the ISO at 200, all we need to do now is change the final element, shutter speed.

The landscape is still with no movement so I don’t require a fast shutter speed (the reason why this element was last). What I will need to do is balance the aperture and ISO by having a slow shutter speed to allow enough light to expose correctly. Let us say we need a 10-second exposure for this image. Holding a camera completely still for 10 seconds is impossible so a tripod is needed. Now we can safely have a slower shutter speed without the risk of losing sharpness.

Voila, a well-balanced image.

  • Modern cameras have built-in exposure meters that indicate if the image is correctly exposed. This is displayed as a line made up of dashes at even increments. In the center of this line is usually 0 and this 0 is a ‘correct’ exposure.

    When changing your last element of the exposure triangle you can look at the meter to see if it is under or over-exposed. Simply change the value so the marker is in the middle at 0 and you should have a correctly exposed image.

  • Understanding the exposure triangle is fundamental to shooting in manual mode. Learn it and you will be able to correctly expose any circumstance.