Optimizing the phase shift and the cut-on periodicity of phase plates for TEM

► The effects on image quality of phase shift and cut-on periodicity of a phase plate are investigated. ► We derive formulas for the optimal phase shift as a function of the object parameters. ► The phase shift influences mostly the image contrast and less so the fidelity. ► The cut-on periodicity affects both the contrast and the fidelity of the image. ► Positive phase shift phase plates can provide better performance in certain applications.