Exposure & Shutter Speed

Exposure

There are three factors that determine exposure.

• The light sensitivity or 'speed' of film - ISO.
• slow speeds need a lot of light and produce a high quality and detailed result
• fast speeds require less light, but the results can be grainy and will show less detail
• The size of the lens aperture
• a wide aperture allow in more light
• a small aperture allows in less light
• The amount of time the shutter remains open
• a fast shutter speed allows a small amount of light in
• a slow shutter speed allows a lot of light in

Shutter Speed

Shutter speed combined with aperture determines how much light reaches the film in the camera. Shutter speed also affects the way a moving or static subject is recorded

• Fast shutter speed = sharp and detailed image
• Slow shutter speed = blurred and impressionistic

Long exposures can lead to camera shake so a tripod is needed. If hand holding a shutter speed that is at least equivalent to the focal length of the lens is advised. This is because the longer the lens, the heavier it is so even a slight movement will translate as a big movement!

• 50mm lens - 1/60 or faster
• 90-135mm lens - 1/125 or faster
• 250mm lens - 1/250 or faster

Freezing action

• Use flash for an instant burst of light
• Use a fast shutter speed so NO movement is recorded - i.e. 1/1000

Creative control

• Use shutter speed to interpret a scene creatively
• Shoot a runner at 1/250 or 1/500 for a frozen image
• Shoot a runner at 1/60 if you want the figure to move slightly across the lens's field of view, which will create a clear image of the runner, but a blurred background

Panning

• Moving the camera while the shutter is still open
• Requires a speed of 1/30 or 1/60
• The nearer the moving object, the faster the shutter speed required
  

The image above of a boy playing on a merry-go-round was taken with an 18-70mm lens with an aperture of f8 and a shutter speed of 1/250. Here the action is frozen with the subject and background crisp and in detail.



This time - the same subject was shot at f27 at 1/15 sec. A slower shutter speed creates movement in the image as the shutter is still open while the image moves across the lens. A smaller aperture was required so that the image did not overexpose by letting in too much light while the shutter was open.