The invention relates to an infrared camera comprising an optical zoom, characterized in that it comprises: —a matrix detector (5) comprising a cooled screen, a matrix able to detect infrared radiation; —a module (123) for modifying the focal length of the camera, the modifying module being able to vary the focal length of the camera so as to ensure the optical zoom function of the camera; and —an imager module (L4) able to ensure, for all the values of focal length of the camera: on the one hand the focusing of the infrared radiation on the matrix of the detector, and on the other hand the conjugation of the pupil of the camera on the cooled screen of the detector. The invention also relates to a method of observing a scene with the camera according to the invention.