When changing from a selected area image of a specimen to a diffraction pattern, the strength of the intermediate lens is changed, producing an image rotation between the image and the diffraction pattern. This rotation is seen by photographing a crystal whose shape gives a clear indication of orientation. A molybdenum trioxide crystal is suitable for this purpose. Supported on a G400, 400 square mesh copper Gilder grid.
PELCO® Technical Notes, Image Rotation Molybdenum Trioxide Crystals, Product No. 625 (469KB PDF)
625 - Molybdenum Trioxide, on 3mm grid, each