On-line rapid testing of the optical transfer function

摘要

A new, simple method for on-line rapid testing of the optical transfer function (OTF) of camera lenses has been developed in which the digital fast Fourier transform method is employed using a linear array CCD for sampling the linear spread function (LSF) of the lens under test. The main advantage of the new method is that for the test of off-axis OTF neither the lens under test nor the collimator need to be rotated. Obviously, this method is different from the present complicated test methods. Therefore, this method is simple and easy to accomplish on-line automatic test of OTF. The time required for testing a nine-position OTF such as on-axis $POM@0.7 and $POM@1 viewfields in both meridional and sagittal planes is less than 2-3 min. An OTF testing formula relative to the testing factors has been established. Based on it, the testing accuracy of OTF is discussed with the idea of relative accuracy for the first time. The theoretical results are in agreement with the experiments. Precision is 1-2%. The relative errors of both the modulation transfer function (MTF) and phase transfer function (PTF), which change with spatial frequency f, are about 10% and 3% at f $EQ 50 c/mm, respectively.