Correction of Defocus and Astigmatism of an Electron Microscope
Original Publication Date: 1985-Sep-01
Included in the Prior Art Database: 2005-Feb-19
It is often necessary to measure defocus and astigmatism of an electron microscope. To do so, a Fourier transform of a white noise object was obtained. Another method for measuring defocus and astigmatism used image variance. The first technique is expensive and demands considerable processing and I/O overhead, while the second technique requires a specially constructed arithmetic unit capable of finding a covariance of two images. In order to eliminate these problems, a practical approach for determining defocus and astigmatism is to obtain information from an image histogram. The histogram can be obtained either on a host computer by summing image intensities, or through an image analyzer located directly in the frame store. The image analyzer is run at or near television rates.