The imaging model of an optical camera without image aberration can be equivalently depicted by its conjugate nodal plane model. A pinhole camera model itself neglects aberration of corresponding equivalent model, and also fails to represent shift error of flat glass, tilt error of optical axis as well as image aberration of an actual optical system, all of these four factors give rise to image distortion. Based on this, utilizing the property of conjugate nodal plane, an geometry model of image distortion is presented. This model, which fits for pinhole cameras with chromatic aberration corrected, can analyze symmetric and asymmetric image distortion. The simulation of an actual optical system indicates that the relative radical distortion and relevant angle error both calculated by this model appears in the range of rational design parameters. In this model, four unknown parameters needed to be recognized are principal relevant parameters, tilt angle of optical axis and axial spherical aberration of flat glass. Theoretically, this geometric model can be used to correct image distortion, aiming at better precision of calibration of image distortion.
