A microscope comprising a main objective having a lens assembly movable in the direction of the optical axis of the main objective for focal length change and comprising an illuminating unit with illumination deflector elements for deflecting an illuminating beam path for generating an illuminating beam path directed onto an object plane. The position of the illumination deflector elements is adjustable dependent on a focal length change of the main objective for centering the illumination, and the illumination deflector elements are designed as at least partly integrated into the movable lens assembly of the main objective. For this purpose, in particular a part of the lens surface of the movable lens assembly can be made reflective.