小中大找到了:
“The rotation-free series of the Tecnai microscopes result for the majority of magnification and camera lengths in a fixed rotation angle between image and diffraction (dependent on the type of objective lens). The rotation angle is typically not zero (because that would result in a very restricted set of camera lengths available) but 60 or 90°. There may be a few camera lengths and images that do rotate (once again to make these available), typically at the extremes of magnification- and camera-length ranges (especially for energy-filter series).”