Focal length measuring device and method

Abstract

A focal length measuring device, which is provided in a work device that performs work on a workpiece, and measures a focal length at which a lens provided in the work device is separated from the workpiece, includes: an image acquisition unit disposed in a movement path of light incident from the workpiece through the lens and configured to acquire an image from the workpiece; an image extraction unit configured to extract a plurality of first divided images from the image acquired by the image acquisition unit and select at least one second divided image having a sharpness greater than or equal to a preset reference from among the plurality of first divided images; and a focal length calculation unit configured to calculate a focal length of the workpiece from a position of each of the at least one second divided image selected by the image extraction unit, wherein the image acquisition unit is disposed to have a preset angle with respect to a direction perpendicular to the movement path of the light incident from the workpiece through the lens.