What is Exposure in Photography Explained
Robert Sullivan
Whether it's a snapshot or fine art photography, exposure of a picture is depends on how much light registers on the media (film or digital camera sensor) that gathers that light. The correct exposure of a picture is a product of the three factors that control how much light is gathered: aperture, Iso, and shutter speed. When these three variables are in the proper ratios, the proper exposure of pictures will result.
ISO is a measure of how sensitive the film or digital sensor is that is collecting the light. The lower the ISO number, the lower the sensitivity. The higher the ISO, the higher the sensitivity.
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 exactly what it sounds like. The length of time that the shutter is opened to collect light is called shutter speed. More light passes through the lens and onto the media the longer the shutter is opened.
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.
Changing the opening in the diameter of the diaphragm changes how much light passes through the lens and onto the light catching media whether it is film or a digital sensor. When changing the aperture the focus in the image captured is also changed. Smaller apertures such as f/8 and f/16 will result in more area in focus between foreground and background. Called depth of field, this is very important in the capturing of an image. Bigger apertures like f/1.8 and f2.8 narrow the depth of field so that most everything in the final picture will out of focus. This helps to highlight the subject in a dramatic way by leaving the subject in focus while distracting foreground and backgrounds remain out of focus.
Varying the length of time that the shutter is open will control how much light passes through the lens opening. This is called shutter speed. The longer the shutter remains open the more light will be collected by the sensor or film. Shutter speed also affects motion blur or lack of. When the shutter is open for longer periods, the moving parts of the image will begin to blur and the amount of blur increases the longer the shutter is open. Otherwise, opening the shutter for a shorter period of time results in freezing everything in the image in place. Faster moving objects require faster shutter speeds to capture them without motion blur, but less light is allowed through the lens when the shutter is opened for less time.
Correctly adjusting these settings will produce a properly exposed picture. Changing any of these factors requires adjustment to at least one of the other factors to assure proper exposure remains. Changing only one of the settings will change the amount of light that is collected by the camera and will affect the final exposure. If you increase the ISO which increases the sensitivity of the media without any other adjustment, you will get an overexposed image. To avoide this you will need to increase the shutter speed or reduce the size of the aperture. Using faster shutter speeds to freeze your child speeding by on a bicycle will give you an underexposed picture unless you increase the size of the aperture to collect more light or bump up the ISO so as to increase the sensitivity to the reduced amount of light gathered.
Together, these three factors result in whether or not the picture is properly exposed. A good photographer understands these factors and the effects that they have on the final image. He will use this knowledge and take care to ensure the proper settings are utilized to produce exactly what he wants before he ever presses the shutter release button.
About the Author:
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 nature picture he is the expert you have been looking for.
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