When a projector is not aligned perpendicular to the screen the display will appear wider at the top than the bottom. What is this called?

• A. Parallax error
• B. Keystoning
• C. Distortion
• D. Perspective shift

Answer: (B)

Keystoning describes the trapezoidal distortion you see when the projector isn’t perpendicular to the screen. When the lens is tilted relative to the screen, the projected image no longer forms a perfect rectangle; the top and bottom edges can end up with different widths, making the display appear wider at one end. This happens because the projection rays hit the screen at angles, warping the image geometry. To fix it, realign the projector so its lens is perpendicular to the screen, or use keystone correction (digital or optical) to compensate. Parallax error refers to viewing position differences, and distortion or perspective shift are broader terms that don’t specifically name this alignment-caused trapezoid.