Approximate calculation of Collins’ formula and application research

In order to validate the approximate algorithm of Collins' formula,the diffraction images for a light wave that passes a thin lens from a quadrate aperture were evaluated numerically and compared with the experimental results.It is shown that the experimental results are in agreement with the computation results.Therefore,this approximate method is applied to the measurement of the lens focus,and the focus error between the approximate method and traditional method is less than 1%.