Influence of camera exposure time on MTF measurements in not ideally linear systems

The theory of Modulation Transfer Function (MTF) measurements is based on the assumption of linear and shift invariant systems. However, most experimental setups partially violate these conditions due to nonlinearities in the image detector and the discrete sampling of the image. Nonlinearities in the image detection cause a dependence of the MTF measurement results on the actual image brightness and therefore the exposure time. Thus, the MTF measurement of not ideally linear systems shows a dependence of the intensity distribution of the test target, which needs to be considered in the measurement uncertainty budget. In this contribution the multi camera MTF measurement setup at PTB [1-2] is employed to demonstrate the influence of different exposure times on the recorded Line Spread Function (LSF) and its associated MTF. [1] Schake M., Schulz M., "Identification of aliasing effects in measurements of unknown MTFs," Proc. SPIE 11899 0H, (2021). [2] Schenker M., et al., “Effects of misalignments on the modulation transfer function measurement of camera lenses analyzed in optomechanical simulations,” Opt. Eng. 59(3),1 -17 (2020).