In this test, a scene is illuminated that presents two planes. While one of them remains fixed, the other moves to positions further away from the focus in each model (see diagram).

While in model 1 both planes have a similar tone, due to being aligned and the focus affecting them similarly, the displacement of the mobile plane in models 2 and 3 causes it to gradually darken.

It is interesting to observe how the brightness of the fixed plane increases from model 1 to 2 due to the new incidence of light reflected from the moving plane on the left plane. However, between models 2 and 3, there is barely an increase, as the amount of light bounced from the moving plane does not change significantly with its displacement.

It is interesting to see how the brightness value that the plane acquires as it moves away from the light source and approaches the observer could be used to "measure" the distance or depth of it, as it is proportional.