Patent ID: 8304704

Claim:
A method for performing autofocus, which comprises the steps of: performing one of patterning and spatially filtering light from a light emitter of a light source resulting in a generation of a light emitting light source pattern varying in a direction of an optical axis; masking the light emanating from the light emitting light source pattern with a minimum numerical aperture by a means for masking so that the light from each light source of the light emitting light source pattern which falls within the minimum numerical aperture is blocked from getting to a sample, and direct reflections from surfaces of the sample, which are outside a depth of field of an objective, being blocked as well; focusing the light on the sample via the objective resulting in a generation of a light pattern in the sample containing reflex areas at different positions in a direction perpendicular to the optical axis and further at different positions in the direction of the optical axis, thus a light intensity of the light pattern varies having at least two maxima in the direction of the optical axis; detecting a reflection of the light pattern spatially resolved via a detector; processing outputs of the detector for generating a positioning signal; and adjusting a focus of the objective in the sample depending on the positioning signal.