RT Journal Article SR Electronic T1 CTFFIND4: Fast and accurate defocus estimation from electron micrographs JF bioRxiv FD Cold Spring Harbor Laboratory SP 020917 DO 10.1101/020917 A1 Alexis Rohou A1 Nikolaus Grigorieff YR 2015 UL http://biorxiv.org/content/early/2015/06/16/020917.abstract AB CTFFIND is a widely-used program for the estimation of objective lens defocus parameters from transmission electron micrographs. Defocus parameters are estimated by fitting a model of the microscope’s contrast transfer function (CTF) to an image’s amplitude spectrum. Here we describe modifications to the algorithm which make it significantly faster and more suitable for use with images collected using modern technologies such as dose fractionation and phase plates. We show that this new version preserves the accuracy of the original algorithm while allowing for higher throughput. We also describe a measure of the quality of the fit as a function of spatial frequency and suggest this can be used to define the highest resolution at which CTF oscillations were successfully modeled.