The Exposure Triangle

Photography is all about light. The word is even derived from Greek roots which basically mean "drawing with light." In order to create a good photograph, it is essential to have the image properly exposed, which means that the camera has to capture the proper amount of light for the image to look good. If there is not enough light (under-exposed,) the image will be too dark, yet if the camera takes in too much light, the image will be burnt out and look very bright, or even just white (over-exposed.)

There are three elements that control the light entering a camera:

1. Aperture

2. Shutter speed

3. ISO (sometimes referred to as ASA, usually by older photographers)

The aperture is the opening in the lens through which the light enters the camera. When the shutter release button is clicked, the shutter opens and the light that comes through the aperture hits the sensor (or the film) and the photograph is captured. The wider the aperture, the more light gets in to the photo, the narrower the aperture, the less light gets in to the photo. The wider the aperture is, the less depth of field the photo has, meaning that only the photo's focal point will be in focus, while the rest of the photo is blurry. The narrower the aperture, the more depth of field the photo will have, meaning a greater area of the image will be in focus. Here's an image I've taken of Mama Chow in Sapa, Vietnam with a relatively shallow depth of field. It was taken using an F stop of 4.5. Notice how the background is blurry.

Shutter speed is the amount of time the shutter opens in order to let light in for the picture. Faster shutter speed can help "freeze" moments while slower shutter speeds can allow a feeling of movement. Here's an example of a shutter speed of 1/10th of a second, which was slow enough to make the image blurry which was what I wanted in order for the viewer to feel the speed and fast pace.

Combinations such as slow shutter speed and wide aperture, will result in too much light in the image, or an overexposed image. Fast shutter speed and narrow aperture can result in a lack of light, or an underexposed picture. In order to achieve proper exposure, we need to choose an appropriate combination of shutter speed and aperture. This can be done using a light meter, which most modern cameras have built in.

The third element is ISO - the sensor's sensitivity. Older readers may recall buying film which had numbers on it. You'd buy 100 if you were going to shoot in daylight, 400 if you were going to shoot on a cloudy day, 800 when shooting indoors etc. The higher the number, the more sensitive the sensor (or film) will be to light. The more sensitive the sensor is, the faster the photo is captured. Higher ISO would be better for environments with less light, as it would let us maintain a higher shutter speed. Higher ISO also means that you can use a narrower aperture, or use faster shutter speed and still have enough light to properly expose the photo. Lower ISO also means pictures with less "grain", while higher ISO will result in grainier images.

Here's an example of a photo I shot in a low-light environment with an extremely high ISO of 10,000. Can you see the grain?

Point-and-shoot cameras and cell phones generally automatically select the settings they feel will give the most accurate exposure. However, DSLRs, mirrorless and some high-end point-and-shoot cameras, allow the photographer to manually select aperture, shutter speed and ISO and give more creative options.

In my next few posts I will discuss each one of these settings separately and how and when each setting can be used to your benefit.

Keep up the good light!

Yehonathan