Research on Optical System Focal Length Measurement Technology based on CCD Imaging Technology

This paper puts forward a new method to measure focal length of optical system automatically and intelligently.This method can meet the quirements of fast, high-precision measurement, which integrated CCD imaging technology, grating angular displacement measuring technology and digital image processing technology.With the combined measurement method,the system combine the measured optical system with additional lens into the Galileo telescope system(the measurement optical system is the concave lens) and Kepler telescope system(the measurement optical system is convex lens).The parallel light, given by porro board and the collimator in the system, goes through the whole telescope system, and the focal length of the measured lens is calculated by measuring the magnification of the telescope system.The system ingeniously converts the focal length measurement to the angle measurement of off-axis light.In the process of measurement, the Fibonacci search algorithm is used to realize the automatic focus system, and the sub-pixel edge detection algorithm is implied to realize the double clamp line alignment.The measured results of the focal length of the lens group show that, the measurement speed is fast with the proposed method, and the uncertainty can be up to 10-4 orders of magnitude in this paper.