Scanning electron device

In a scanning electron device comprising:

• an electron gun for generating an electron beam;
• deflecting means, which in response to X and Y deflecting signals, deflect said electon beam in a two-dimensional raster over a specimen;
• a cathode ray tube having deflecting means which in response to X and Y deflecting signals scans an electron beam over the face of the cathode ray tube;
• a scanning signal generator generating normal condition X and Y deflecting signals for the cathode ray tube and the deflecting means for the scanning electon beam such that they are scanned in synchronism;
• a detector for detecting signals emanating from the specimen, the output of said detector being supplied to modulate the brightness of the beam scanning the cathode ray tube screen thus producing an image;
• a magnification circuit arranged between the signal generator and the electron beam deflecting means for varying the amplitude of the electron beam X and Y deflecting signals and thus the magnification of the image produced on the cathode ray tube;
• the improvement for enabling the simultaneous display of a low magnification image and a high magnification inset image simultaneously comprising
• a modifying circuit for producing X and Y inset image scan deflecting signals having amplitudes and d.c. signal levels different from the output of the scanning signal generator output signals but of the same frequency;
• switching means arranged between the magnification circuit and the scanning signal generator and between the magnification circuit and the modifying means for switching between normal condition deflecting signals produced by the scanning signal generator and inset image deflecting signals produced by the modifying circuit;
• and a switching signal generator for generating signals to control the switching means.