中文摘要：

成像物镜具有两个独立的焦距，通过对空间物体成像并进行分析可获取其深度信息，此即双焦测距的原理。本文首先分析了图像主点坐标标定对双焦测距精度的影响，找到了双焦图像中两种相对于主点坐标的不变量，进而提出了基于此不变量的双焦测距算法，避免了繁琐的标定环节并提高了算法精度。与传统算法的实验对比表明了本文算法是正确可行的。

英文摘要：

The bifocus lens could produce images at the two independent focal length respectively and recovery the object＇s depth information according to the two bifocal images, which is the principle of depth estimating using bifocal lens. At first the principle of bifocal imaging and it＇s precision influenced by calibrating precision of principal point are analyzed, and two invariants of principal point are found in the two bifocal images. And then based on the two invariants a novel bifoeus depth-estimating algorithm is proposed to steer clear of the principal point calibration and improve the depth estimating precision. Experimental comparisons between the novel algorithm and the traditional algorithm illustrate that the novel algorithms is correct and feasible.