Exposure

Just what is exposure?  Quite simply, it's the amount of light that is allowed to hit the photographic medium, whether it's film or the processor in a digital camera.

How Exposure is Controlled

Built-in Camera Programs

When left in auto, the camera itself sets the exposure.  You would think that should result in a perfect exposure every time.  The trouble is that the camera "reads" and adjusts itself to the lightest or darkest areas of the scene.  A shot with a lot of white, such as snow will end up over-exposed and one in deep shade will be underexposed.  Some of that can be repaired in photo editing software such as Nik or Photoshop, but if the whites are "blown out", meaning there are no or few individual pixels, it can't be rescued and far more involved editing is required.  To overcome this problem, most manufacturers have built in pre-sets such as snow, beach, action, sunset, landscape and a number of others, dependent on the sophistication of the camera.  If you want to exercise creative control and optimize the use of the camera, the idea is to avoid the pre-sets.

Aperture

Every camera has an aperture that controls the amount of light hitting the photographic medium, whether film or the processor in digital cameras.  In auto, the camera controls the aperture size dependent on how much light there is in a scene.  The result can be as described above.  So, just what is aperture?  Quite simply, it's a small hole in the camera and it works much like the pupil of the eye.  If it's dark, the aperture opens wide to let in more light; if bright, shrinks to let in less light.  This helps to control exposure. 

Shutter Speed

Aperture and shutter speed are related controls.  While the aperture controls the amount of light, the shutter controls how fast that light is allowed to hit the photographic medium.  A slower speed allows more light to reach the medium and a faster speed, less.  Once again, the camera itself can control the speed automatically or it can be manually set to slow or freeze action.  That ability can create interesting and dynamic effects.

ISO

The fourth factor, outside of filter use, controlling exposure is ISO, which means the International Organization for Standardization and descibes film speed.  This standard took the place of ASA and DIN.  Though digital cameras don't use film, of course and don't operate in the same way as a film ISO, they still use the term ISO to describe film speed.  Higher ISO ratings, such as 1600 are rated as faster and used in low light situations.  Lower ratings of 50, 100 or 200 are slower and are used in bright light, such as snow or beach shots.

Filters

Filters can also affect the exposure of a shot.  Neutral density or polarizers are what I call sunglasses for the camera and reduce the amount of light reaching the medium.  Dependent on the light source, the use of filters can require a larger aperture or a slower shutter speed.  They, like film speed can increase colour saturation or bring out detail through exposure that would otherwise be lost.

Upcoming

Applying ISO, aperture, shutter speed settings and how to use these to deveop creative control.