Disclosed is an observation system including a first optical path capable of receiving first optical radiation emitted by a scene and including a first sensor configured to generate a first digital image from the first optical radiation; a second optical path capable of receiving second optical radiation and including a second sensor configured to generate a second digital image from the second optical radiation; a display configured to display a third digital image from the first and second digital images; a third optical path coupled to the display; and a fourth optical path connecting the first and third optical paths, the first optical path including an optical element configured to transmit a part of the first optical radiation to the fourth optical path.