An arrow/circle object is placed in front of a bright light source, and this object is focused onto a distant screen by a 20cm convex lens, as seen in the photograph at the left. Inserting the prism inverts the image IN THE VERTICAL DIRECTION ONLY, as seen in the photograph at the center. Note that a pentaprism is used to invert the image in both directions simultaneously.
The optical arrangement is shown in the photograph at the right.
This technique is sometimes used in optical instruments.