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What is Exposure in Photography Explained

From fine art photography to point and shoot snapshots, exposure of a photograph is dependant on the amount of light that lands on the exposure media. Whether you are using film or digital cameras, the result is the same. Light is captured by a frame of film or the sensor in a digital camera and the proper exposure of your images depends on the settings of these three variables: Shutter speed, aperture, and ISO. The proper setting of these three variables will ensure proper exposure.

The measure of how sensitive the film or digital sensor is that is collecting the light is referred to as ISO. If the ISO number is lower, this means that the sensitivity is lower, and if the ISO is a higher number then the media is more sensitive to light.

The size of the hole that light passes through in the lens is called the aperture. Just like the pupil of the eye, the larger the hole, or aperture, the more light can enter through the lens and onto the media capturing it. Aperture is epressed as a ratio of focal length the size of the hole as adjusted by the diaphragm and is stated as f/(aperture value). If the aperture is f/2.8 it means that the focal length of the lens is 2.8 times the opening of the diaphragm. The smaller the aperture number, the larger the hole in the diaphragm. The larger the aperture number is, like f/8, the smaller the hole in the diaphragm.

Shutter speed is the easiest of the three variables to understand. It is as simple as it sounds. This is the amount of time that the shutter is open to collect light. The longer the shutter is opened, the more light is allowed to pass through the lens to be collected.

Each of these variables have other results or consequenses which, when fully understood and utilized, can be put to good use to create the desired image.

While all three variables are set with purpose, most photographers are concerned, first, with the ISO setting. Higher ISO settings result in more noise (or grain) which, for most film and digital cameras, increases signigicantly above ISO 400. For this reason, most film photographers use film with ISO ratings as low as conditions will allow, and similiarly, digital photographers set their camera to the lowest ISO settings that conditions will allow. Although noise or film grain is normally undesireable, there are times when they can be used creatively in a photograph to achieve desired results. Usually the ISO is determined first and is the last of the three variables to be changed.

Varying the aperture changes the diameter of the diaphragm which controls how much light can pass through the lens and onto the film or sensor. When varying the aperture the most noticable result in the final picture is how much of the scene is in focus. When a smaller aperture is used (higher numbers such as f/8 and f/16) more of the area from foreground to background is in apparent focus. This is called depth of field and is extremely important in the production of an image. Larger apertures (lower numbers such as f/1.8 and f2.8) narrow this depth of field which results in most everything in the image to be out of focus which brings attention to the in-focus subject in dramatic fashion and often eliminates distracting backgrounds.

Shutter speed regulates how much light passes through the lens by varying how long the shutter is open. Obviously, the longer the shutter is open the more light will pass through the lens on it's way to the film or sensor and vice versa. The side effect of shutter speed is motion blur or lack of. The longer the shutter is open the more the apparent moving parts of the image will blur. Blurring moving subjects or even the entire image using slow shutter speeds can be put to creative use and it often is. Other times a fast shutter speed is required when "freezing" a subject is the desired result.

When the values for these three variables are correctly determined and set accordingly, a well exposed image will be produced. After selecting these settngs, a change in any one of these variables calls for a compensating change in at least one or both of the others. Making a change in only one of the variables changes the amount of light that was will be captured by the sensor or film. If you choose to use a higher ISO film or setting then you will be increasing the sensitivity of that media which will result in an overexposer unless you reduce the amount of light that enters the lens by reducing the aperture or shutter speed. Using a faster shutter speed to freeze a passing race car will give you an underexposed image unless you increase sensitivity of the light collecting media by boosting the ISO or unless you open up the aperture to allow more light through the lens to compensate for the shorter duration that the shutter is open.

These three variables determine the exposure of the final photograph. And because of the side effects associated with these variables, a knowledgeable photographer knows what his desired result is and will determine each of these settings prior to pressing the shutter release button.

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Robert Sullivan is a Photographer and Artist who loves to find a great nature photo he lives in South Florida. If you are looking for a great picture of florida alligator he is the expert you have been looking for. This article is available as a unique content article with free reprint rights.

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