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25 Oct 2021

Exposure Triangle

In photography, the exposure triangle explains how the shutter speed, ISO and aperture affect the exposure of an image.

Learning Exposure For Photography

The science behind photography is all about how a camera captures light, so understanding how to control exposure is essential to becoming a good photographer. In this video we're going to go over the 3 pillars of exposure that make up the exposure triangle. When you understand these 3 components, then you will have a mastery in both the technical and artistic aspects of photography.

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Understanding Exposure: Shutter Speed

The shutter speed controls the duration of light that reaches the sensor. When you take a picture the shutter door opens, revealing the sensor for a duration of time that you or the camera chooses, then closes. The duration is measured in seconds or fractions of seconds, for example: 10, 2, 1/200, 1/4000.

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When you are choosing a shutter speed you can choose whether you want to freeze or show motion. The higher the shutter speed to more frozen the action is going to, the slower the shutter speed the more evident the motion will be in your image.

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Understanding Exposure: Aperture

You can think of aperture as the pupil of the lens. By widening or narrowing itself, the aperture controls the amount of light that reaches the sensor. Aperture is measured in fractions or f-stops, like 1/2.8 or 1/4, but lenses will only show the denominator: 2.8, 4, 5.6, 8, etc. This is why the lower the aperture number, the wider the aperture gets.

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When you are choosing an aperture to shoot at, you are also controlling the depth of field. A wide aperture (f/1.4, f/2.8) creates a shallow depth of field, and a narrow aperture (f/8, f/16) creates a broad depth of field. In the image above observe how the background leafs fall into bokeh (the aesthetic quality of the out-of-focus areas) when shooting at f/2. Controlling the depth of field allows photographer another degree of control in their composition.

Understanding Exposure: ISO

ISO is a measurement representing the sensors sensitivity to light. The higher the ISO number the more sensitive your sensor will be to light, which means that at higher ISO's you would require less light to get to a proper exposure. This is useful in cases where you would want to use a higher shutter speed, or a narrow aperture. The downside to using higher ISO's is that your image will have more grain and noise in it. The higher the ISO, the more destructive the noise will be.

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Nowadays cameras are capable of achieving phenomenally high ISO's with little penalty from noise and grain. This means photographers now have more creative opportunities when shooting in the dark. The comparison above was shot with a Sony a7S, and although ISO 409600 is an unusable image, the ISO 102400 image looks fantastic.

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Exposure Triangle At Night

You may have heard of the exposure triangle (ISO, shutter speed, aperture), but how does it work when capturing images at night? Along with trying to get tack-sharp images, getting the right exposure while shooting at night is one of the biggest challenges to overcome.

When shooting at night, the elements within the exposure triangle will be pushed to the limit. The high ISO needed to capture an adequate amount of light will introduce plenty of grain/noise, the shallow aperture will limit the depth of field (luckily, the stars won’t be too affected by this in your image due to their distance and size; ultra-wide lenses with an f/2.8 aperture can appear sharp at night from infinite to 3-5 yards away while medium lenses with an f/1.4 aperture can appear sharp at night from infinite to 5-10 yards away), and slow shutter speed could cause motion blur (even when the camera is placed on a tripod) due to the earth’s rotation.

The downside of using a high ISO is the inability to cleanly make adjustments to the shadows during post. Dynamic range is limited, and this is one area where image quality can suffer. The downside for using a very slow shutter speed includes the introduction of thermal noise (which appears as tiny dots) and motion blur caused by the earth’s rotation (as mentioned before). While the star trails caused by the blur can be used for creative effect, they’re not always wanted.

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