Problem – Background is too dark

A common problem with flash photography is a background that is too dark. The foreground has the correct exposure but the background has simply become a black mass. Especially when using a direct flash (in contrast to indirect flash, the flash is pointed directly at the subject) many photographers have to grapple with this problem.  However, this is no camera defect but is instead contributed to basic principles of physics, the “law of quadric reciprocity”

Law of quadric reciprocity
The fact that a source of light’s level of brightness diminishes the further away the illuminated surface is, is well known. This effect can easily be observed when driving a car at night. While the first few meters are well lit, the brightness decreases with increasing distance. If the source of light’s beam angle remains the same, the light is distributed across a larger area if the distance is increased and therefore decreases its level of brightness.

This decrease in brightness in connection with increased distance is described using the law of quadric reciprocity. If you double the distance, brightness diminishes to a quarter of its original strength – double the distance again results in a reduction in brightness to 1/16 of its original brightness intensity. It is always the reciprocal value of the squared distance factor.

In flash photography, this results in the foreground of the image being correctly exposed while the background, if at a distance to the foreground, is too dark.

What options are there to solve this problem?

  • High ISO rate
  • Open diaphragm
  • Additional flash devices for the background
  • Set up additional light sources in the room or use the lighting available in the room
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