J A Chapman 1962 J. Sci. Instrum. 39 273 doi:10.1088/0950-7671/39/6/305
J A Chapman
Show affiliationsA systematic but simple operational procedure for the correction of objective lens astigmatism in the Siemens Elmiskop I is described. Asymmetry in the Fresnel fringe at the edge of the image of a hole is expressed as a vector (the astigmatism vector). The direction of this vector is such that the angle it makes with a fixed reference line is twice the angular displacement of the fringe asymmetry from the same reference line; the magnitude is conveniently taken as the number of clicks of the fine focus controller over which incomplete fringes are visible. Astigmatism vectors defined in this way are shown to obey the law of vector addition and this leads to the procedure described; this procedure enables the required degree of correction to be achieved rapidly and with the minimum of effort. Other practical aspects of astigmatism correction are considered.
42.79.Bh Lenses, prisms and mirrors
07.78.+s Electron, positron, and ion microscopes; electron diffractometers
Issue 6 (June 1962)
Received 24 January 1962
J A Chapman 1962 J. Sci. Instrum. 39 273
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