ISO 12233 slanted-edge method experiences errors using fast Fourier transform (FFT) in the camera modulation transfer function (MTF) measurement due to tilt angle errors in the knife-edge resulting in nonuniform sampling of the edge spread function (ESF). In order to resolve this problem, a modified slanted-edge method using nonuniform fast Fourier transform (NUFFT) for camera MTF measurement is proposed. Theoretical simulations for images with noise at a different nonuniform sampling rate of ESF are performed using the proposed modified slanted-edge method. It is shown that the proposed method successfully eliminates the error due to the nonuniform sampling of the ESF. An experimental setup for camera MTF measurement is established to verify the accuracy of the proposed method. The experiment results show that under different nonuniform sampling rates of ESF, the proposed modified slanted-edge method has improved accuracy for the camera MTF measurement compared to the ISO 12233 slanted-edge method.
Traditional slanted knife-edge method experiences large errors in the camera modulation transfer function (MTF) due to tilt angle error in the knife-edge resulting in non-uniform sampling of the edge spread function. In order to resolve this problem, a non –uniform sampling knife-edge method for camera MTF measurement is proposed. By applying a simple direct calculation of the Fourier transform of the derivative for the non-uniform sampling data, the camera super-sampled MTF results are obtained. Theoretical simulations for images with and without noise under different tilt angle errors are run using the proposed method. It is demonstrated that the MTF results are insensitive to tilt angle errors. To verify the accuracy of the proposed method, an experimental setup for camera MTF measurement is established. Measurement results show that the proposed method is superior to traditional methods, and improves the universality of the slanted knife-edge method for camera MTF measurement.
This paper describes an effective method for the measurements of large aperture sampling grating, the sampling
efficiency the sampling focal length and the sampling angle. By using a 351nm collimation laser source to scan the full
aperture of the sampling grating in every subregion, the diffraction power of “0” order and “+1” order can be obtained
synchronously by two standard integrating balls, And then by calculating the sampling efficiency of this subregion and
splicing the acquisition data, we can get the averaged grating sampling efficiency in the full aperture.Based on this
method, we can effectively eliminate the effect of the output instability of laser source, decrease the uncertainty of test
results. According to the fabrication principle of the sampling grating, measurements for the sampling focal length and
the sampling angle can be performed. Test rersults indicate that this method can be used to measure large aperture