Point 2: Exposure

Intro

Framing your shot by subject placement and zoom affects the composition.  This is largely an aesthetic process without science behind it and is really in the eye of the photographer.  On the other side of the equation are the technical factors that ensure image is bright, sharp, free of noise, and a variety of other factors.

When your camera is set to "automatic" it is handling all the technical factors for you.  The magic boxes that are DSLRs nowadays are very adept at getting shots right in automatic.  However, there are lots of things that you can make the camera do that it may never choose to do when left to its own devices.  In fact, the true beauty of a DSLR is that you can take control of everything and alter the shot as you like.

The following sections have details on how you can adjust a variety of settings to get the most out of your camera, but there are a few terms that should be cleared up and some notes on how your camera operates.

Terminology

The most important term to know when adjusting a shot is exposure.  Exposure determines how brightly lit a shot is.  If a shot is under-exposed it is too dark, possibly to the point that some parts of the image are black without any details (shadow).  If a shot is over-exposed it is too bright, possibly to the point that some parts of the image are white without any details (highlight).  Regardless of anything else, if a shot is too far over or under exposed, it's junk.

Exposure is measured in whole or fractional "stops."  There is no real measuring point that a bright, sunny day is # stops, it is simply relative to itself.  So, if while taking a picture of people in sunny field a cloud rolls in, it may change the brightness by -1 stop.  It's helpful to know this measurement unit as adjustments to the camera can be measured in stops of how much light you are gaining or losing.

Exposure is balanced by three separate factors: 

1) How sensitive the image sensor is to light (ISO)

2) How much light the lens lets through (aperture)

3) How long the sensor has light shining on it (shutter speed)

While you can manually set each of these factors to determine exposure on your own, the following sections will look at each one individually and let the camera decide the best of the remaining settings.