In order to extend the resolution available in electron tomograms, we have been experimenting with various deconvolution procedures that will ultimately enable correction of the focus gradient thereby allowing the resolution to be extended to beyond the first zero in the contrast transfer function (CTF). This effort requires first a determination of the amount of amplitude and phase contrast in the typical specimen used by us.

For the determination of the percentage of amplitude contrast a focus series of 19 images was taken at a magnification of 13500 on a CM300. The micrographs were digitized on a PDS scanner, the pixel size was 0.888 nm. After correction of translational shifts, rotations, and defocus dependent magnification differences the image restoration was carried out according to [1,2]. From the resulting complex wave function an averaged amplitude contrast amount of 18% was obtained for the stained specimen. The phase contrast part and amplitude contrast part are shown in Figs, 1b, and 1c, respectively, and can be compared with the micrograph taken at 960 nm underfocus (Fig. 1a).