What is Exposure?

The Exposure Triangle

Understanding Exposure

Underexposure occurs when the camera sensor is exposed to an insufficent amount of light. The resultant image will be dark and hard to make it out.

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An overexposed photo on the other hand, occurs when the camera sensor is exposed to too much light. The resultant image will look unnatural due to being too light.

In his higly recommended book, Understanding Exposure, Bryan Peterson illustrates the three main elements that need to be considered by calling them ‘the exposure triangle’.

The three elements are:

* Aperture: Aperture refers to the size of the opening in the lens when a picture is taken;

* Shutter Speed: Shutter speed is the amount of time that the shutter is open;

* ISO: ISO is the measure of a digital camera sensor’s sensitivity to light.

It is at the intersection of these three elements that an image’s exposure is created.

Most importantly – a change in one of the elements will impact the others. This means that you can't isolate just one of the elements without at least having the others in the back of your mind.

There are various metaphors that can be used to illustrate the digital photography exposure triangle, but this is the one I like the most:

Photography Exposure Metaphor

There are three ways to influence how fast and how full the bucket will be filled with water from a faucet.

* If you open the faucet all the way, more water will flow and the bucket will fill up faster. However, if you open the faucet only a little, less water will flow and it will take longer to fill the bucket. This faucet adjustment is like the camera's aperture;

* The length of time to allow the water to flow is like the shutter speed; and

* The pressure of the water is ISO.

Although not perfect, this metaphor illustrates the interconnectedness of aperture, shutter speed and ISO on your digital camera as it relates to light.

Exposure Management

One method would be to play it safe and let your camera's automatic settings take care of everything. However, even though you may get a visually accurate reproduction of the subject, your image may appear quite uninteresting. Your camera isn't infallible either. Sometimes incorrect exposure can be a direct result of your camera trying to compensate for low/high levels of light and incorrectly managing to do so.

Although riskier, it is infinitely more rewarding to manually expose the sensor to just enough light to properly reflect the mood of a subject.

Two digital function that can help you out along the way are:

* Exposure bracketing, and

* Histograms.

When working out what is exposure, keep trying, and if your first attempts aren't perfect, just take a deep breath and re-evaluate your settings one by one. Readjust and retake the image.

Over time, as you get more experienced, it will become easier to prevent over- and underexposed images under different lighting conditions.

Remember, many advanced photography techniques are mastered through constant experimentation.

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