To quickly summarize how we arrived at this point: The combination of good lighting, a suitable composition, and the right exposure either make an image outstanding or destroy it altogether. Having discussed lighting and the rules of composition, we’re ready to delve into the most technical of the three—exposure.
Most people new to digital photography keep their cameras in an automatic mode. But when you’re ready to get out of “auto mode” to make your own creative decisions and to have complete control over your photography, you’ll need an understanding of the basics of exposure.
The Basics of Exposure
Exposure, simply speaking, is the combination of three main variables that control the amount of light that is allowed to enter your digital camera’s sensor. These are:
- Aperture – the size of the opening in the lens when a picture is taken
- Shutter speed – the amount of time that the shutter is open
- ISO – the measure of a digital camera sensor’s sensitivity to light
The right combination of these variables is at the heart of every photo that has ever been taken by a camera—digital or film. They have complete and total control over how light enters your camera, reaches your light-sensitive sensor, and records the exposure.
Together, lens aperture, shutter speed, and ISO are collectively referred to as the exposure triangle.
The exposure triangle is a concept introduced by Bryan Peterson in his excellent book Understanding Exposure.
The exposure triangle explains how the individual aspects of exposure—aperture, shutter speed, and ISO—affect the final exposure of the photo. Each of these three aspects relate to light and how it enters and interacts with the camera.
The three elements of the exposure triangle interact together. For example, reducing the shutter speed by a stop (increased light) and narrowing the aperture by a stop (decreased light) will result in an identical exposure. However it may result in motion blur (due to decreased shutter speed) or deeper depth of field (due to narrower aperture).
This means that you can never really isolate just one of the elements alone but always need to have the others in the back of your mind.
Mastering the art of exposure is something that takes considerable practice. In many respects it’s a juggling act and even experienced photographers experiment and tweak their settings.
This is one of the most important technical concepts you can know in photography and it’s worth taking the time to learn and thoroughly understand.
I’m only in it for the exposure.