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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.

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.

The simplest of the three factors to understand is the shutter speed. This is how long the shutter is open to allow light to pass through. More light passes through the lens the longer the shutter is opened and the media captures more light.

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.

The ISO setting is usually the first variable that is set and is normally the last variable to be changed because of the increase in film grain or digital noise the higher the ISO is set. For this reason, photographers usually use the lowest ISO possible to keep the noise and grain to a minimum. Sometimes, however, digital noise and film grain are used purposefully to create a desired outcome in the photograph.

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.

The three variables discussed here are everything that needs to be considered when determining exposure for an image. And if you understand the implications of each variable as it applies to the amount of light that is collected by the film or digital sensor, then you can learn to properly expose your images everytime. And, if you also understand and learn how and when to apply the different effects that each of these variables also brings to the table, then you will be able to explore countless creative possibilities with your photography.

Tags: Nature