Method and apparatus for automatically focusing

Details Method and apparatus for automatically focusing Method and apparatus for automatically focusing

1974-12-24

1976-02-10

Borchelt, Archie R.

Radiant energy

Inspection of solids or liquids by charged particles

Electron microscope type

315 31R, G01N 2300, G21K 700, H01K 3726

Patent

active

039379590

ABSTRACT:
The sum of the intensity changes of one polarity in the video signal is used as a signal indicative of the diameter of the electron beam irradiating a specimen. A storage counter which produces the signal indicative of the beam diameter is reset periodically in synchronism with the beam scan and two successive outputs of the counter are compared by a comparison circuit. The excitation current of the focusing lens is varied in synchronism with beam scan. The magnitude and polarity (increase or decrease) of the change in excitation current are controlled in response to the output of said comparison circuit to maximize the output of the storage counter.

REFERENCES:
patent: 3356792 (1967-12-01), Peters
patent: 3409799 (1968-11-01), Kurzweil, Jr. et al.
patent: 3436589 (1969-04-01), Gaskill, Jr. et al.

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