Fig. 5

Projection images recovered by iterative phase retrieval. a 2D projection image of microtubule samples recovered after Fourier transform of the image in Fig. 2a using a featureless tube for initial phase and after 100 cycles of iterative phase retrieval. b 2D projection image recovered after 100 cycles of iterative phase retrieval of the image shown in Fig. 2b. c 2D projection image recovered after 100 cycles of iterative phase retrieval of the image shown in Fig 2c. d 2D projection image recovered after 100 cycles of iterative phase retrieval of the image shown in Fig. 2d. These projection images shows increasing detail after each processing step. Both the average microtubule diameter of approximately 25 nm and sub-structures of 4 nm become visible when inverting the fitted diffraction image. White bars indicate 25 nm in the horizontal direction and 4 nm in the vertical direction. Blue represents low projection density whereas yellow is high projection density