The central beam should be perpendicular to what?

• A. The object and receptor.
• B. Only the receptor.
• C. Only the object.
• D. The surrounding room surfaces.

Answer: (A)

The central beam should be perpendicular to both the object and the image receptor. When the beam hits at right angles to the planes of both, the projection is true to size and shape, avoiding geometric distortion like elongation or foreshortening. If the beam isn’t perpendicular to either the object or the receptor, edges can appear stretched or shortened, and measurements become unreliable. The beam’s angle to room surfaces doesn’t affect the image, so perpendicularity to those surfaces is irrelevant.