What is the Exposure Triangle?

When shooting video, we are drawing images with light. But with cameras now so good in automatic modes, many operators just set their auto exposure and forget it. This is good enough for most of us.

For professional quality work, capturing and drawing light on a camera’s sensor requires knowing the fundamentals of exposing the triangle. This includes the camera’s shutter speed, aperture and ISO. Any change in one of these three corners of the triangle, means lower image quality.

Too long of an exposure means too much light hitting the sensor. This can “blow” the highlights. When the exposure is not enough, details are not properly visualized. “Clipping” of shadows means the image is underexposed to the point there are areas with no detail.

A proper exposure is one where the highlights and shadows all retain good detail.

In basic terms, exposure is the amount of light a camera’s digital sensor absorbs. Depending on the shot, the videographer sometimes wants more light in a scene than in others. For example, abundant light may be sought in a mid-day outdoor scene or little light in a dark room at night. This requires getting the exposure correct or neither scene will appear as you want it.

There are three key adjustments that determine exposure of a camera: shutter speed, aperture and the sensor’s sensitivity. Sensitivity is calculated in either ISO, ASA or gain — depending on the camera. When one of these measurements change, so do the others.

How does one arrive at the proper balance of exposure for a scene?

First, let’s deal with shutter speed — the fraction of a second that the sensor is exposed to light. As the shutter speed gets larger, the image gets darker

Then depth of field, which is how narrow an area is in focus. Larger apertures — numbers like 1.4 or 2.8 — let in additional light but also cut down on the range at which objects are in focus. Smaller aperture numbers like 16 or 22, let in less light but give a greater range of areas that are in focus.

Higher ISOs add noise to the video image. This is the result of digital gain and appears as unwanted artifacts in the picture. This noise comes when the camera makes guesses about data that it doesn’t have enough information to represent correctly.

When recording video, a camera records at 24, 25, 30, 50 or 60 frames per second. These frames are all still images shown in sequence. Don’t confuse the number of frames being shown each second with the shutter speed. Shutter speed is how long the aperture is open whenever it captures a frame.

Recording at 1/125th of a second means the camera is still shooting at 30 frames per second, only each frame represents 1/125th of a second of exposure to light.

Neutral density filters are important tools. To create a wide f-stop like f/1.8, pick a high shutter speed to make sure the exposure is correct. If the subject is moving, a high shutter speed might cause your video to jitter.

In this case, either lower your ISO or lower the amount of light. If you’ve hit the limit of your ISO, a neutral density filter is necessary. These filters dim the light. Open your f-stop to get a shallower depth of field without increasing your shutter speed.

For the most natural motion blur, it is best to set the shutter speed at double the frame rate. Intuitively, for 30 fps, this means about 1/60th of a second.

Cameras are optimized for a “native” ISO. This is usually 160. For best image results, stay as close as possible to this setting. To see how far you can deviate from this setting, do some tests and examine the footage critically.

Higher ISOs with large sensors can shoot with less noise free than smaller sensors. Beyond 1600 is capable with some higher end cameras.

Having a very shallow depth of field can cause focusing problems. When focus is critical, use a viewfinder magnifier or external monitor. Pre-pan shots carefully to smoothly follow people and keep them in focus as they move.

Mastering the exposure triangle is key to understanding video production.

The camera operator’s objective is to practice setting exposure manually balancing all three of these variables.

Having a good understanding of each part the exposure triangle is essential to making a proper exposure. Understand that moving one of the exposure elements requires a change in the others.

Which parameter gets priority over the others depends on what is being shot and how the videographer wishes to treat the subject. The exposure triangle is the artistic foundation of creative style. It is a basic that must be mastered before one can control visual images.

Writer at Broadcast Beat
Frank Beacham is a New York-based writer, director and producer who works in print, radio, television, film and theatre.

Beacham has served as a staff reporter and editor for United Press International, the Miami Herald, Gannett Newspapers and Post-Newsweek. His articles have appeared in the Los Angeles Times, Washington Post, the Village Voice and The Oxford American.

Beacham’s books, Whitewash: A Southern Journey through Music, Mayhem & Murder and The Whole World Was Watching; My Life Under the Media
Microscope are currently in publication. Two of his stories are currently being developed for television.

In 1985, Beacham teamed with Orson Welles over a six month period to develop a one-man television special. Orson Welles Solo was canceled after Mr. Welles died on the day principal photography was to begin.

In 1999, Frank Beacham was executive producer of Tim Robbins’ Touchstone feature film, Cradle Will Rock. His play, Maverick, about video with Orson Welles, was staged off-Broadway in New York City in 2019.
Frank Beacham
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