A microscope including an objective having a focal plane in a sample space, and an autofocus device comprising a light modulator for generating a luminous modulation object that is intensity-modulated periodically along one direction, an autofocus illumination optical unit that images the modulation object such that its image arises in the sample space, an autofocus camera, an autofocus imaging optical unit that images the image of the modulation object in the sample space onto the autofocus camera, a control device, which receives signals of the autofocus camera and determines an intensity distribution of the image of the modulation object and generates a focus control signal therefrom. The control device determines an intensity distribution of the image of a luminous comparison object imaged by the optical unit to correct the intensity distribution of the image of the modulation object with regard to reflectivity variations in the sample space.