METHOD OF AUTOMATICALLY FOCUSING A CHARGED PARTICLE BEAM ON A SURFACE REGION OF A SAMPLE, METHOD OF CALCULATING A CONVERGING SET OF SHARPNESS VALUES OF IMAGES OF A CHARGED PARTICLE BEAM DEVICE AND CHARGED PARTICLE BEAM DEVICE FOR IMAGING A SAMPLE

A method of automatically focusing a charged particle beam on a surface region of a sample is provided. The method includes acquiring a plurality of images for a corresponding plurality of focusing strength values; calculating a plurality of sharpness values based on the plurality of images, the plurality of sharpness values are calculated with a sharpness function provided as a sum in a frequency space based on the plurality of images; and determining subsequent focusing strength values of the plurality of focusing strength values with a golden ratio search algorithm based one the calculated sharpness values.