Back to Basics: Exposure Explained

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The Grand Tetons

Exposure is one of the first, and one of the most confusing, concepts that a budding photographer learns. All of the numbers, abbreviations, settings and relationships can be overwhelming at first. Here is a simple guide to help clarify things.

The Exposure Triangle:

The three elements of exposure – commonly referred to as “The Exposure Triangle” – are ISO, shutter speed, and aperture. These three elements work together to properly expose a photograph.

ISO is a measurement of the camera’s sensitivity to light. The term ISO first referred to film, but is now used in digital photography with reference to the camera sensor’s light sensitivity. ISO commonly ranges from 100 to 1600, with many cameras going as low as 50 and as high as 3200 and more. An ISO rating of 100 is less sensitive to light than an ISO rating of 800. The former would be used in brightly lit circumstances in order to prevent overexposure. The latter would be used in lower light conditions in order to prevent underexposure.

Shutter speed refers to how long the shutter remains open in order to expose the camera’s sensors and create the image. Shutter speeds on most cameras range from 1/8000th of a second to a full minute and more. Use a fast shutter speed in bright lighting in order to avoid overexposing the image, and use a slow shutter speed in dim light to avoid underexposure.

Aperture, also called “f-stop”, refers to the size of the lens opening when the picture is taken. The common range of apertures ranges from f/1.8 (large opening) to f/22 (small opening), lower or higher depending on the camera and lens used. The nomenclature can sometimes be counter-intuitive since a small number equals a large opening, and vice-versa. The larger the aperture, the more light is allowed into the camera to create the image.

Party people!

As you can see, the combination of ISO, shutter speed, and aperture are all about controlling the amount of light that is exposed to the camera’s sensors. There are some “rules of thumb” that can be applied in various circumstances in order to create a properly exposed photograph, though the best way to understand exposure is to simply practice. On a bright, sunny day, using an ISO 200, with a shutter speed of 1/250th of a second, and an aperture of f/16.0, will typically result in a properly exposed photograph. For indoor shots in dim light, use an ISO of 800, a shutter speed of 1/60th of a second (any slower and you’ll need to use a tripod), and an aperture of f/5.6 for a properly exposed shot.

Another good way to begin to understand exposure is to review the EXIF data on photographs posted to such sharing sites as Flickr. For example, the photograph of the Grand Tetons at the beginning of this article was shot at 1/400th of a second using ISO 200 and an aperture of f/11.0 – good settings for bright sunlight. The second photograph of the group of people was shot at 1/50th of a second using ISO 800 and an aperture of f/1.4 – good settings for a dim interior.

Photography is all about light. Understanding how to manipulate light will drastically improve the quality of your photographs.

Photo credits (all): Tiffany Joyce.

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