通过比较变形前后同一平面物体表面的两幅数字图像，二维数字图像相关方法可获得亚像素精度的像面位移（以像素为单位）和应变。但在实际测量中，变形物体表面的离面位移、相机传感器平面位置的微小改变以及镜头的成像畸变，都会使原先假设的物、像面位移间的线性对应关系不再严格成立，在某些情况下会引起不能忽略的测量误差。详细分析了被测物体的离面位移、相机自热和镜头畸变对二维数字图像相关方法位移和应变测量结果的影响。通过实验研究了3种典型的成像镜头（标准成像镜头、物方远心成像镜头和双远心成像镜头）对以上不利因素的抗干扰能力。实验显示高质量的双远心镜头不仅对被测物体表面的离面位移和相机自热不敏感，并且镜头畸变也小到可以忽略不计的程度，因此该镜头是高精度二维数字图像相关测量中的关键光学元件。

By comparing the two images recorded in different configurations on the same object surface, two-dimensional digital image correlation (2D-DIC) method produces full-field displacement with sub-pixel accuracy and full-field strains in the recorded images. In a practical measurement, however, various deteriorative factors, such as small out-of-plane motion of the test object surface, small out-of-plane motion of the sensor target and geometric distortion of the imaging lens may seriously impair the originally assumed linear correspondence between images displacement and object motions. In certain cases, these disadvantages may lead to significant errors in measuring displacements and strains. The measurement errors of 2D-DIC due to the above three unavoidable deteriorative factors are first described briefly. Then, the performances of three typical imaging lenses, including a standard lens, an object-side telecentric lens and a bilateral telecentric lens, against these three deteriorative factors are investigated experimentally using easy-to-implement static, out-of-plane and in-plane rigid body translation tests. A detailed examination reveals that a high-quality bilateral telecentric lens is not only insensitive to out-of-plane motions of the test object and the self-heating of a camera being used, but also demonstrates negligible lens distortion. So the bilateral lens is highly recommended for high accuracy 2D-DIC measurement.