Focusing method for the high-speed digitalisation of microscope slides and slide displacing device, focusing optics, and optical rangefinder

An apparatus for the scanning of a specimen on a microscope slide (4) comprising:

• a microscope having microscope optics with an objective and focus acquisition means for modifying the distance of the slide (4) from the objective;
• a high-resolution camera (1) for capturing a high-resolution image of a first image plane, the camera (1) being arranged along a first optical path connecting the camera (1) with an imaged portion of the slide and passing through said microscope optics;
• a beam splitting means (3) arranged in the first optical path for letting a first portion of a light beam coming from the microscope optics pass through to the camera (1) and directing a second portion of the light beam to a second optical path;
• a plurality of filters (8) arranged such as to further divide said second optical path into a plurality of secondary optical paths having different optical lengths;
• a plurality of image-capturing surfaces of at least one secondary camera (2) positioned along said plurality of secondary optical paths for the formation of a plurality of optical images of a plurality of image planes, said plurality of image-capturing surfaces being formed as distinct portions of a single camera;
• means for selecting a best focused image from said plurality of images captured of the plurality of image planes;
• and
• means for changing the first optical path via said focus acquisition means such that the resulting first image plane is identical with the image plane of the best focused image.