AUTOCOLLIMATION METHOD OF CHANGING FOCAL DISTANCE Russian patent published in 2014 - IPC G01M11/02 

FIELD: physics.

SUBSTANCE: method includes using an autocollimating flat mirror mounted in front of an optical lens surface situated last on the beam path from the focal plane. A radiation detector array with an imaging device is mounted in the same plane, close to the focal plane, with a radiation source. The autocollimation image of the radiation source, which is reflected from the flat mirror, is transferred to the plane of the radiation detector array. The rigidly fastened source-detector array assembly is moved towards or away from the lens. The focal plane is found by observing an image of the source on the display device based on one of known criteria of the quality of the image of the source. The source-detector array assembly is moved to the external position across the viewing field on an optical rail mounted perpendicular to the optical axis of the lens. By turning the flat mirror, the autocollimation image of the source is transferred to the plane of the detector array. Linear shift of the assembly relative to the optical axis d and the turning angle of the autocollimating mirror A are measured, and the focal distance of the lens f'=d/tgA is determined.

EFFECT: easy measurement of focal distances of long-focus lenses.

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