Abstract: A method for detecting lens cleanliness of a lens disposed in a flat-field optical path, the flat-field optical path including a light source, the lens, a camera, the light source is a narrow-band multispectral uniform surface light source, the camera's light-sensitive surface is disposed perpendicular to an optical axis of the lens and in the light position of the lens, the method including collecting the bright-field image data and dark-field image data in a plurality of spectra through the lens; for each pixel, performing a spectral differential flat-field correction operation to yield a plurality of spectral differentials; and displaying the spectral differentials in the form of a plurality of images to show a uniformity of each of the plurality of images, wherein a non-uniform area on each of the plurality of images is determined to have been caused by an impurity of the lens.

Abstract: A method for detecting lens cleanliness of a lens disposed in a flat-field optical path, the flat-field optical path including a light source, the lens, a camera, the light source is a narrow-band multispectral uniform surface light source, the camera's light-sensitive surface is disposed perpendicular to an optical axis of the lens and in the light position of the lens, the method including collecting the bright-field image data and dark-field image data in a plurality of spectra through the lens; for each pixel, performing a spectral differential flat-field correction operation to yield a plurality of spectral differentials; and displaying the spectral differentials in the form of a plurality of images to show a uniformity of each of the plurality of images, wherein a non-uniform area on each of the plurality of images is determined to have been caused by an impurity of the lens.