Good morning, John:
The field is round because the sample is the JEOL standard mount with a round disk of Si in the middle of the field, and the map is for Si only, thus making the rest of the field dark (the mount body is made of brass, so no Si in it). At the correct height, the X-ray map would look like a solid circle of green (in this example), with no 'vignette' at the lower left and upper right corners, and no apparent 'dark band' that you see migrating across the field in the animation. You would just see a dark arcing band across part of the field, depending on how out of focus the sample is (i.e., not on the sweet spot). The Z-height change is from about 12.838 mm (first frame in the animation) to about 9.500 mm in the last frame. The problem presented itself when we found out that the Z-height focal planes for the WD and ED systems were not coincident, even though they are supposed to be synchronous. At such extremes in Z-height, I would guess that the vignetting of the corners might be expected owing to the variation of the take-off angle, but what is most baffling to me is the appearance of the dark arcing band - I think this band may be an aperture ring that has shifted in the detector, but I'm not sure.
Best regards
Dan
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