The Exposure Triangle with flash photography.

 The Exposure Triangle, as a concept and with the specific term, was first introduced in 1990 by Bryan Peterson in his book "Understanding Exposure."

While the relationship between aperture, shutter speed, and ISO (or film speed in the past) has been understood by photographers for much longer, Peterson was the first to formally define and popularize it as the "Exposure Triangle."

The exposure triangle is a fundamental concept in photography that explains the relationship between three key settings that control exposure: aperture, shutter speed, and ISO. Here’s a breakdown of each component and how using off-camera flash impacts them:

1. Aperture

• Aperture controls the size of the lens opening, letting in more or less light. It’s measured in f-stops (e.g., f/2.8, f/4, etc.).

• A wider aperture (e.g., f/2.8) lets in more light and creates a shallow depth of field, blurring the background.

• A narrower aperture (e.g., f/16) lets in less light and creates a deeper depth of field, keeping more of the image in focus.

2. Shutter Speed

• Shutter speed controls how long the camera’s sensor is exposed to light. It’s measured in seconds or fractions of a second (e.g., 1/200s, 1/1000s).

• Slower shutter speeds allow more light in, which is useful in low-light situations but can introduce motion blur.

• Faster shutter speeds let in less light but help freeze motion.

3. ISO

• ISO determines the camera sensor’s sensitivity to light. Lower ISO values (e.g., ISO 100) are less sensitive and result in less noise, while higher ISO values (e.g., ISO 1600) increase sensitivity but may add grain or noise.

When these three elements are balanced, you achieve a proper exposure. Changing one setting affects the others, so understanding their relationship is key to creating the exposure you want.

Using Off-Camera Flash

When you add an off-camera flash to the exposure triangle, you have an additional light source that can alter how you approach each component:

1. Aperture and Flash Power: Since aperture affects the amount of light hitting the sensor, a wider aperture can let in more of the flash’s light, resulting in brighter images. You can balance flash power and aperture to get the desired exposure while controlling depth of field.

2. Shutter Speed and Ambient Light: Shutter speed controls the ambient light exposure in flash photography but doesn’t affect flash power (up to the camera’s sync speed). By adjusting the shutter speed, you can control how much of the ambient light is captured, often darkening the background while keeping your subject lit by flash.

3. ISO and Overall Brightness: A higher ISO can make both flash and ambient light appear brighter in the photo. However, if you want to minimize ambient light while enhancing flash exposure, you might use a lower ISO.

By mastering the exposure triangle with off-camera flash, you can achieve a more dynamic and controlled lighting effect that isolates the subject, balances light, and emphasizes creative aspects such as depth, motion, and texture.