What is Exposure?
The term exposure can refer to a number of different things in photography. Firstly, an image itself can be referred to as an exposure, for example, “I’m going to make an exposure now” or, “I need to brighten / darken my exposure.”
In this sense the meaning of “exposure” is simply an image that is captured in one single opening and closing of the shutter. You can have a long exposure or a short exposure, for example, depending on your shutter speed. However your lens’ aperture and your camera’s ISO also affect your exposure, causing it to be brighter or darker.
What is the Exposure Triangle?
The “exposure triangle” refers to the influence that each of the three camera / lens settings have on the other. If you simply want to make your exposure brighter or darker, then you would brighten or darken one or more of the three settings. A slower shutter speed, a higher ISO, or a wider aperture, for example, would all make your exposure brighter.
What is an EV Exposure Value and a Stop of Light?
The actual brightness of an exposure is measured in “stops”, or EVs. Generally speaking, one EV or stop is an amount of light that is either twice as bright or half as bright as the current amount of light. So if you increase your exposure by 1 EV, you are brightening that exposure to be twice as bright.
Exposure can also be a fixed measurement, however, an actual luminance value that has a fixed EV number assigned to it. For example, broad daylight is roughly EV 15, and the light of a full moon is roughly -2EV, or 17 EV’s darker than broad daylight.
For most photographers, the question “what is your exposure?” no longer correlates to a single EV number, however, but instead to the three settings in the exposure triangle.
Technical vs Creative Elements of Exposure
Exposure has both technical and creative elements; in fact, using exposure creatively is a key part of what makes good, artistic photographs. How you can use exposure creatively to achieve an artistic vision, and how you can become a master of exposure from a technical standpoint so that you achieve the best possible image quality. Whether you own a beginner camera or an advanced/professional camera, “nailing” your exposure can make a huge difference in the final result.
Creative Use Of Exposure
Okay, so, you understand what a stop of light is, and how the exposure triangle gives you different options in choosing the “right” exposure for a scene.
However, as we made sure to point out, there is no such thing as a single “perfect” exposure, since artistic vision must be taken into consideration.
The most common use of the exposure triangle is to keep your image brightness the same while achieving a different creative result. For example, aperture controls the depth of field, and if you want to achieve background blur, (shallow DOF) you would use a wide aperture and then adjust your shutter speed and/or ISO to keep the exposure brightness from changing. Oppositely, if you want everything in focus, you would use a small (narrow) aperture, and re-adjust your shutter speed and/or ISO to compensate. See the example below:
In the above image, the aperture was f/2 and f/22, so the shutter speed had to be dialed as well in order to keep the exposure consistent. Can you count how many stops this is? If you’re not sure, our article here on aperture will clear everything up!
As another example, if you are shooting action sports but your shutter speed is too slow and your subjects are blurring, you could use a faster (darker) shutter speed, while brightening your ISO and/or aperture by the same amount, to achieve the same final exposure yet with the action frozen.
Oppositely, if you intentionally want to blur something, you would have to use a small aperture, low ISO, and/or a very dark neutral density filter in order to achieve a long exposure .
Short/Fast exposure | Nikon D750, 1/60 sec, f/14, ISO 100
Before we wrap up this basic understanding of exposure, however, there is one element that has been ignored until now, which you might have noticed; we have often put the words “correct” or “right” in quotations when describing a proper exposure. This is because photography is an art form, of course, and “correct” is entirely subjective.
High-Key and Low-Key Images
Why isn’t there such a thing as one “correct” exposure for any given subject or scene? Because, sometimes, sheer creative inspiration will lead a photographer to create a much brighter or darker image than what would be considered “neutral.”
An image with more dark shadows than anything else is often called a Low-Key image, and an image with more bright highlights than anything else is often called a High-Key image. Often times this is because a scene itself was actually a dark and moody one, or a very bright one. Other times, creative use of exposure can have a profound result for even a “normal” scene.
Low-Key Exposure (Before Sunset)
1/10000 sec, f/1.4, ISO 100
High-Key Exposure (After Sunset)
1 sec, f/16, ISO 100
What is Exposure Compensation?
Exposure compensation is a camera function that allows you to brighten or darken your exposure by a specified amount while your camera is in any automatic exposure mode. In Aperture Priority exposure for example, the photographer sets the aperture (and usually the ISO) while the camera’s built-in light meter determines what the shutter speed should be in order to achieve a neutral exposure. If a neutral exposure is not what you desire, however, you would dial in positive EV compensation to make the exposure brighter, or negative EV compensation to make the exposure darker. Most modern cameras allow Exposure compensation to be dialed in as much as +/- 3-5 EV.
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