A scanning device for focusing a beam of rays in defined regions of a defined volume, comprising an input optics wherein the beam of rays penetrates first, having at least one first optical element; a focusing optics for focusing the beam of rays exiting from the input optics; and a deflecting device arranged between the first optical element and the focusing optics, for deflecting the beam of rays after it has passed through the first optical element, based on a position of the focus to be adjusted in lateral direction. In order to adjust the position of the focus of the beam of rays in the direction of the beam of rays, and optical element of the input optics can be displaced relative to the deflecting device.