Trapezoidal Distortion in Projected Images

Trapezoidal distortion results when the projector lens axis and the screen axis do not coincide. Their difference is axial displacement which can be measured in degrees of arc or as the linear difference between the optimum and actual projector positions. The increased use of rear-screen systems with a shortened throw and two or more projectors makes the determination of the axial displacement limit a prime consideration in the system design. Using throw, screen width and axial displacement as independent variables, equations have been developed to permit specification of the trapezoidal distortion as a percentage of the projected image dimension. Based upon visual acuity criteria, it is recommended that 2% would be a reasonable maximum limit.