Comparison of approaches and artefacts in the measurement of detector modulation transfer functions

► The modulation transfer function (MTF) of a CCD camera is measured using five different methods.
► Only methods that involve the use of a sharp aperture or holographic interference fringes work well.
► The use of a focused spot promises to be the best method in the future if it can be focused small enough.
► Apparently small errors in the measurement of the MTF can have a large effect on deconvoluted images.
► MTFs must be measured accurately if images are to be compared quantitatively with simulations.

In order to investigate the reproducibility of measurements of transmission electron microscope detector modulation transfer functions (MTFs) we measure the MTF of a charge-coupled device (CCD) camera using five different methods. MTFs derived from a sharp edge, a circular aperture and electron holographic interference fringes are found to agree closely with one other. The difficulty of obtaining accurate measurements of MTFs and the potential of using focused electron probes to make direct measurements of MTFs is discussed. We highlight the sensitivity of image contrast after deconvolution to small differences in the measured MTF.