The exposure triangle is the foundation of photography. An intuitive understanding of exposure is crucial to advancing the art and business of photography. Modern digital cameras do a respectable job of balancing the three elements of the exposure triangle, capturing good pictures right out of the box using auto mode settings.
However, if you want to produce top quality images, shooting in priority or manual mode and a solid grasp of the basics of exposure are essential. Understanding exposure, not just how to obtain correct exposure but manipulating camera settings to capture light, is a vital step toward realizing your potential as a photographer.
In this article, we give an in-depth explanation of how the exposure triangle works, its three elements, how they interact to affect exposure and their importance to photography.
What is the Exposure Triangle?
As illustrated below in the exposure triangle chart, aperture, ISO, and shutter speed comprise the three elements of photography that impact exposure.
The exposure triangle is the framework for comprehending how light passes through the lens and is captured by the camera sensor. These three elements interact each time the shutter button is pressed and must be balanced to achieve a properly exposed photograph. A change to one setting necessitates adjustments to one or both of the other two to properly expose the image, maintaining balance in the exposure triangle.
The essence of photography is capturing light. Aperture, ISO, and shutter speed all play a role in capturing that light. In addition, each component of the exposure triangle impacts other aspects of photography, such as depth of field, noise, and sharpness.
It sounds complicated. But with a solid understanding of the exposure triangle and in-the-field practice, your skillset as a photographer expands.
Let’s start with a detailed look at each of the three important elements of capturing light, beginning with ISO.
What is ISO in the Exposure Triangle?
ISO is the International Organization for Standardization. This organization establishes standards that are internationally agreed upon by experts for best practices in manufacturing, process management, service providers, etc.
ISO in digital photography is a measurement of a camera’s sensitivity to light. And this measure of light sensitivity is standardized across the industry. So, ISO 200 means the same to Nikon, Canon, Sony, and all camera manufacturers.
Low ISO values indicate a lower sensitivity to light. This lower ISO value would be used in bright light. A high ISO refers to greater sensitivity to light, which is needed to acquire proper exposure for a low light shot.
Most camera models offer easy access to the ISO control, as in the photo below.
In the pre-digital age, ASA denoted film sensitivity. ASA, the American Standards Association is now the American National Standards Institute or ANSI.
ASA and ISO are essentially the same. A film camera with a roll of film that is ASA 400 performs the same as its digital counterpart with ISO 400.
ISO and Noise
The lowest ISO setting for most modern digital cameras is 50 or 100. ISO performance improves with each generation of digital sensor technology. So a camera performs at high ISO sensitivity with less noise.
The graphic below illustrates the relationship between ISO and noise.
Even some of the moderately priced cameras feature low noise performance with ISO settings up to 16000 or more. Some of the high-end cameras extend ISO to 200,000. This creates new possibilities for photographers, creating greater control over exposure settings.
Below is the detail of an image shot at a low ISO of 100, with resulting low noise.
A second image, a detail of the same object as above, shot in low light with an ISO of 10,000, shows a noticeable level of digital noise.
High ISO increases noise. As you dial up the ISO, the sensitivity of a digital camera’s sensor increases, but the noise also increases. So photographers strive to find a balance between sensitivity and noise in different lighting conditions while maintaining sharpness and detail in the images.
Recently, digital cameras have emerged that are ISO invariant. That means that the output from the camera’s sensor is consistent throughout the ISO range. So, even at high IOS settings, the image noise is low enough to be imperceptible.
Next on the exposure triangle: a look at the aperture.
How Aperture Controls Light in the Exposure Triangle
While ISO sets the camera’s sensitivity to light, aperture determines how much light arrives at the camera’s sensor.
A camera lens aperture performs much like the iris in the human eye, which expands or contracts according to the amount of light that is available. That amount of light, along with the camera’s sensitivity and how long the sensor is exposed to that light, determines how the image appears.
If you look into a lens, you can probably see the metal blades of the aperture.
The lens has aperture settings called f-stops, indicating the size of the lens opening. A large opening in the aperture allows more light to enter. This would be an f-stop of f/1.4 or f/1.8. A very narrow opening allows less light into the camera, indicated by an f-stop of f/16 or f/22. A number of lenses go beyond f/22, and some lower than f/1.4.
The graph below illustrates the relationship between aperture sizes, f-number, and depth of field.
The low f-numbers indicate a wider opening of the lens, which allows more light to strike the camera sensor. Meanwhile, the higher f-stop numbers mean that the aperture is narrower and allows less light.
Aperture and Depth of Field
Depth of field is directly related to aperture values. It is that part of the photograph that is in sharp focus. As the f-stop number increases and the aperture narrows, the depth of field increases. A low f-stop number, with its wider aperture, reduces it.
Understanding this relationship facilitates the creative process. A landscape photographer might want the entire frame in sharp focus, choosing to shoot in the higher f-numbers. But a portrait photographer who wants a blurred background, or bokeh, prefers the narrow depth of field resulting from a low f-stop.
Each time the aperture is adjusted by one stop, it changes the amount of light passing through the lens and entering the camera by a factor of two. Changing the aperture from f/5.6 to f/4 doubles the amount of light. Moving from f/8 to f/11 reduces the amount of light by half.
Diffraction and the Sweet Spot
Diffraction is an anomaly that also relates to aperture size. This is a loss of image sharpness due to capturing light through a small opening. It is caused by the optical interference that occurs when the wavelength of light and the aperture opening is approximately the same size.
Most lenses are slightly soft at wide apertures, such as f/1.8. Then, at higher f-stop numbers, diffraction becomes a factor. For these reasons, photographers look for the sweet spot of a lens. That’s the aperture setting which delivers the sharpest image and as much light as required to achieve a good exposure. Typically, you’ll find it at around f/8 or f/11.
The final element of the exposure triangle is shutter speed.
How Shutter Speed Impacts the Image
Shutter speed controls how long the shutter remains open to allow light onto the sensor.
We measure shutter speed in fractions of a second or in seconds and occasionally minutes. A shutter speed of 1/60 second works in many situations. Capturing action, such as athletic events or wildlife photography, requires a much faster shutter speed. A setting of 1/1000 second or even faster may be required depending on the subject. Meanwhile, night photography demands slower shutter speeds, maybe 20 to 30 seconds or, in some situations, several minutes.
The graphic below shows the relationship between shutter speed and motion.
At any given shutter speed, the camera and lens work together with aperture and ISO to render an exposure. The three variables of shutter speed, aperture, and ISO combine in countless combinations to properly expose the image.
How Shutter Speed Captures a Moving Subject
Shutter speed determines many creative and artistic effects in photography. A slower shutter speed at night, with a sturdy tripod to support the camera, captures the lights of automobiles, but the vehicles disappear. We see that in the image below, which also renders a surreal effect to the clouds in the night sky.
You can stop motion with a fast shutter. The photo of the hummingbird below was exposed with a shutter speed of 1/1250 second. That setting captured the bird’s wings, which flap at 40 – 60 beats per second, with just a minimum of a blur. A faster speed, maybe 1/2000 second, would have produced a sharper image around the wing tips.
Extremes of Shutter Speed
Modern cameras come with shutter speeds as high as 1/8000 second; however, most models of DSLRs and mirrorless cameras list their fastest shutter speed as 1/4000 second. These extremely fast shutter speeds call for a wide aperture and a higher ISO setting.
The photo below shows how shutter speed can turn something as commonplace as water into an abstraction. The shutter speed of 1/3000 second captured this image of a splash fountain. And even though it was shot outdoors in bright sunshine, the ISO setting increased to 1100 to maintain perfect exposure.
On the long exposure side, camera manufacturers tend to set the limit at 30 seconds; however, with a Bulb Mode setting, the camera’s shutter is opened and closed manually. So you could hold the shutter open for hours to achieve even more motion blur.
Below, a longer shutter speed of 20 seconds, in daylight using a neutral density filter, captured the image of the fountain. The spouting water of the fountains takes on a silky, ghost-like appearance in this long exposure.
Shutter speed presents many opportunities for creativity. With a press of the shutter button, you can freeze motion with a higher shutter speed. With another exposure, you can create motion blur as you dial in slower shutter speeds.
Exposure Triangle Cheat Sheet
Now that you’ve been introduced to the exposure triangle definition and its three basic elements, a simple cheat sheet may help you remember.
Daniel Peters created the exposure triangle diagram that clearly states the relationship of shutter speed to motion, ISO to noise, and aperture to the depth of field.
How Manual and Priority Modes Affect the Exposure Triangle
Manual Mode gives the photographer full control over the camera. She or he adjusts the aperture, shutter speed, and ISO to achieve an exposure value according to conditions and the subject. The in-camera light meter provides a guide to the final exposure.
Manual Mode is cumbersome and can overwhelm the novice, but it allows the photographer to capture the scene exactly as wanted.
Look for M on the camera’s mode selector.
What is Shutter Priority Mode?
In this mode, the photographer manually selects the shutter speed, leaving the camera to automatically set the aperture and ISO. Shutter Priority Mode is most valuable for action photography. In other words, situations when you know you want a fast shutter speed to eliminate motion blur.
I use Shutter Priority for wildlife, and I shoot at 1/2000 second or faster. If I’m in good bright light, the ISO should stay within a reasonable range.
On the camera’s mode selector, Shutter Priority is labeled S on Nikon and Sony cameras and Tv on Canon models.
Aperture Priority
Another semi-automatic mode, Aperture Priority refers to manually selecting the aperture setting and determining how much light passes through the lens. This leaves shutter speed and ISO to the camera. Aperture priority gives the photographer control over the area of sharp focus, which is preferred by many professionals in landscape and still-life photography.
If a nice bokeh is part of the goal, set the camera to a wide aperture, capturing the subject in focus while delivering a soft background.
Sony and Nikon label Aperture Priority Mode A; Canon labels it Av on the mode selector.
Program Mode
The program mode sets the shutter speed and aperture according to available light, arriving at the proper exposure value. So the camera controls the primary elements of the exposure triangle but leaves other settings like focus area and metering mode to the photographer.
This is designated P on the mode selector.
ISO Priority Mode
Cameras do not have a specified ISO priority mode. Auto ISO can be turned on or off inside the camera. Accordingly, with Auto ISO activated, the camera automatically sets ISO, regardless of the mode selected. But with Auto ISO turned off, the photographer manually adjusts ISO, no matter what camera mode is selected.
Cinematography and Shutter Speed
Since most DSLRs and mirrorless cameras shoot video, we include a brief explanation of shutter speed as it relates to video.
A cinematic shutter speed of 1/48 second at 24 frames per second was the standard for film. Basically, the shutter stays open for twice as long as the video’s frame rate. To deviate from that results in increased motion blur or a jerky appearance.
Therefore, if you’re shooting video at 30 frames per second, set the shutter speed to 1/60 second. Many DSLR and mirrorless cameras default to 60 frames per second, which is the preferred frame rate; the ideal shutter speed is 1/120 second.
Exposure Triangle Conclusion
The relationship between ISO, aperture, and shutter is important and a little confusing. Adjustment to one component of the exposure triangle necessitates changes in one or both of the other parts. By understanding this relationship and its endless variations, you make the exposure triangle work for you.
Experiment with the camera’s settings and different modes. Discover what works for you in various situations. Also, as your skills improve, and you don’t think so much, you can concentrate on composition and creative ideas.
I hope this article helps. If you have any questions or comments about the exposure triangle, please write them down in the space below.
