Optical reader and method of analyzing biological samples

An optical reader for analyzing biological samples arranged in the wells of a microplate, the optical reader comprising:

• a horizontal reading plane for receiving a microplate comprising a plurality of wells,
• an illuminating arrangement comprising a light source and being configured to illuminate the samples in the wells of the microplate,
• an imaging device arranged to receive light from the microplate,
• a beam splitter, which is arranged to direct part of the light from the illuminating arrangement towards the reading plane and to direct part of the light received from the microplate to the imaging device, and
• a lens system comprising at least one lens and being arranged between the beam splitter and the reading plane to focus the light received from the illuminating arrangement to a sample and to focus an image of the sample to the imaging device,
• wherein the optical reader is configured to transmit from the illuminating arrangement to the lens system only light having a specific polarization, and the optical reader comprises a polarizer that is arranged between the lens system and the imaging device and configured to block polarized light reflected from the surfaces of the lens system.