Exposure Factors For Beginners in Photography

Exposure of a photograph is a matter of how much light registers on the media (film or digital camera sensor) that collects that light. Proper exposure of a photograph depends on the three factors that control how much light is registered: ISO, aperture, and shutter speed. Combining these three variables in the proper proportions will result in the proper exposure of photographs.

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 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.

All three of these factors come with other benefits or drawbacks depending on how you look at it. These side effects can be put to creative use When fully understood and properly utilized.

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.

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.

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.

By: Robert Sullivan

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.

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