As in the next project we are dealing with controlling the strength of a colour I decided to research exposure further. The course notes tell us that “under-exposure produces a ‘stronger’ colour, and in professional photography this is quite a common technique”.
Exposure is the amount of light that falls onto the sensor of the camera during the process of taking a photograph. In modern cameras the exposure is usually set to automatic by default. Getting a 'correct' exposure means recording as much of the relevant information in the scene as possible.
Even when the exposure is 'correct' the problem with all cameras is that they cannot record the entire range of contrast (black to white) that the eye can see. Especially when you take into account that the eye is constantly adjusting to cope with high contrast. On a sunny day if you look into the shadows of a scene then into the bright areas, the iris in your eye will quickly adjust so you can see detail in both.
An exposure generally refers to a single shutter cycle. For example: a long exposure refers to a single, lengthened shutter cycle to capture enough low-intensity light, whereas a multiple exposure involves a series of relatively brief shutter cycles; effectively layering a series of photographs in one image. When undertaking the task of recording as much information as possible, the camera then tries to average out all the light levels and expose in accordance with this.
Auto Exposure Modes
Automatic exposure (AE) mode automatically calculates and adjusts exposure settings to as closely as possible match the subject's mid-tone, to the mid-tone of the photograph.
Manual Exposure
Using manual exposure allows you to make choices regarding 'aperture priority', 'shutter priority', 'exposure compensation' etc.
The amount of light falling on the sensor is affected by.
- The amount of light reflected from the scene. If you are photographing outdoors then there is little you can do about it.
- The 'shutter speed' which is the amount of time the shutter is open which is measured in fractions of a second.
- The 'aperture setting' which is the size of the hole through which the light enters (drawing comparisons with the iris of your eye) which is measured in 'f stops'.
- The ISO setting which is the 'sensitivity' of the sensor. The higher the ISO setting the less light is needed to make an exposure.
The advantage of manual exposure is that the settings do not keep changing as your scene changes.
Exposure compensation.
This is used to alter exposure from the value suggested by the camera; this in turn makes the image darker of lighter. It is most effective when it is used with center-weighting or spot metering.
Wikipedia
Nikon D90 manual.
The Photographer's Eye - Michael Freeman - Ilex - 2007
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