Effect of knife-edge skew on modulation transfer function measurement of charge-coupled device imagers employing a scanning knife edge

The scanning knife edge method is widely employed to measure the modulation transfer function (MTF) of solid state charge-coupled device (CCD) imagers. This paper presents a method to correct for the situation where the knife edge is skewed at a small angle with respect to the CCD. Experimental results for a time-delay-and-integration charge-coupled device (TDI-CCD) imager demonstrate that the knife-edge skew introduces a degradation in the measured MTF. A model to explain this effect and a quantitative method to correct for small-angle skew is presented. A good agreement between the model and experiment is obtained. In a TDI-CCD imaging system, the effect of small-angle skew is amplified and cannot be ignored.