一种数码相机的等效焦距测试方法

给出了一种焦距测试方法，用于测量数码相机电荷藕合器件（CCD）与传统光学相机相等效的焦距。分析数码相机CCD的设计特点，指出其在使用光学成像公式计算焦距时遇到的问题。设计两种测量CCD等效焦距的实验方法，分别利用物像距离与物像长度的比例关系和平行双目成像原理，得到与CCD焦距极值对应的等效焦距。由此计算等效焦距的换算比例，最终得出该数码相机所照任意一张照片的等效焦距。实验结果验证了数码相机生产厂所给出的CCD规格说明，表明该方法可以在一定的测量精度要求下，快速有效地标定数码相机焦距。

Equivalent Focal Length Estimation Method for Digital Camera

This paper proposes a new method for estimating the equivalent focal length of digital camera(DC) charge-coupled device(CCD) to the traditional optical camera.It analyzes the design characteristic of CCD and points out the problem in computing the focal length with the optic imaging formula.It designs two estimating experiments to obtain the focal length value corresponding to the minimum CCD focal length,from which the ratio of the CCD focal length to its optical equivalent is derived.Using this ratio,the equivalent optic focal length of any photo taken by this DC can be computed.The experimental result justifies the CCD product specification given by its manufacturer and shows that the method can calibrate DC effectively within certain range of the accuracy requirement.