CCD CAMERA CHARACTERIZATION FOR 400 KEV ELECTRON MICROSCOPY

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Glucose-embedded purple membranes were used as a test specimen to evaluate the reliability of phases retrieved from 400 kV spot-scan images acquired on a 1024x1024 slow-scan CCD camera made by Gatan. This specimen was chosen because it represents a broad class of low-contrast radiation-sensitive biological objects and its structure is well established. The amplitudes of computed reflections from these images were strongly damped by the modulation transfer function of the camera. Nevertheless, their phases on average were < 12-different from the reference data of Henderson up to 8.8
resolution, which corresponds to 0.8 of the Nyquist frequency of the camera. Similar results are also observed with a different camera made by Tietz with 100 kV electrons. These results confirm that CCD camera can be a viable recording medium that can replace photographic film for recording images of crystalline specimens such as purple membrane.