16 Oct 09: Exposure control and exposure methods

Following our studio session with Andy today, John ran a class on exposure.

 Exposure is the amount of light receievd by the film or sensor and there is a range of possible scenarios based on 3 factors:

ISO controls how fast/slow the sensor records information.  This is turn affects the level of definition (quality).

Typically landscape photographers use slower speeds and sports photographers use fast speeds to freeze the action.

Aperture controls the intensity of light falling on the sensor and the depth of field.

Typically apertures range from 2.8  to 22.  The smaller the number means the larger the aperture and, hence, more light falling on the sensor.  A smaller aperture means that only the point of focus will be sharp and the foreground and background will be blurred.

Shutter speed controls the length of time for light to fall on the sensor and the amount of movement captured ie a fast shutter speed will freeze the image.

Typical speeds are from 1 second to 1/1000.  There is also a bulb setting which allows you to leave the shutter open for as long as the shutter button is held down - useful for fireworks etc.

Speed of sensor + intensity of light + time

control the exposure and combining these elements gives full creative control -

definition, depth of field, and movement are "bi-products".