The present invention relates to an apparatus for varying a focal point of an optical system in a dental 3D-scanner, comprising: a lens unit with a lens being movable between a front reversal position and a rear reversal position to vary a position of a focal point with respect to a scan object; a guide unit for guiding a movement of the lens unit between the front reversal position and the rear reversal position along a guide axis being parallel to an optical axis of the lens; and a drive unit for driving the movement of the lens unit, said drive unit including a linear motor with an anchor and a stator, said anchor being movable along a drive axis of the drive unit that is parallel to the guide axis, said stator being affixed to the guide unit. The present invention further relates to a dental 3D-scanner for scanning a three-dimensional scan object.