We use MeX but no, we haven't worked out how to determine epsilon either but I think the electron image working distance (as opposed to the z-axis height) 'should' be closer to 'pd' than 'wd' in the diagram. So far we've used relatively long working distances so epsilon is relatively small and we assume it's zero.
Hi Mike,
What is the "electron image working distance" and how is that different from the normal working distance? Just to be sure we are on the same page, I call the distance from the bottom of the objective lens to the sample surface, the working distance.
If you have a topographic standard it's obviously easy to test the settings. I haven't sketched it out or tested it to confirm but I think if the settings are wrong a flat surface would be modelled as curved.
Yes! That's exactly what I suggested the student to try. That is, put in an object of known size and shape and try to "back out" this so called epsilon distance from the instrument.
What gets me is that he's tried to ask Alicona what this epsilon distance should be (or how to measure it), but they don't respond. Also their manual (in the version 6.2 that we have), has several critical typos, so it's making it rather difficult to troubleshoot this problem.
Finally, why do we only get halfway reasonable results when specifying an absurd value of 1000mm (1 meter!) for the epsilon distance?