There may be times when you do not have access to light meters or the light
meter in your camera is not working. You can improve your chances of
taking usable exposures if you follow the f/16 rule. The f/16 rule is based on
the correct exposure for an average front-lighted subject under bright, sunny
To use the f/l6 rule:
Set the aperture of the camera to f/16.
Set the shutter speed on the camera to most closely approximate the
rated ISO of the film. For example, if the film is rated at ISO 125,
set the shutter speed at l/125 of a second.
The f/16 rule is a way to calculate alternate f/stops should environmental
conditions deteriorate. The following table lists different aperture settings
for daylight conditions.
Bright sun, light sand, or snow
Cloudy but bright
Overcast or open shade