Device for a layerwise manufacturing of a three-dimensional object and method for adjusting an optical system of the same

A device for manufacturing a three-dimensional object by a layer-wise solidification of a building material at positions in the respective layers corresponding to the object is provided. The device has an energy source that emits a beam for solidifying the building material, a scanner that selectively directs the beam to different positions in a building plane, and a deflection mirror that deflects the beam coming from the energy source to the scanner. The beam from the energy source to the scanner runs in a space secluded from the outside and an adjustment mechanism for the alignment of the deflection mirror is provided, which is adjustable from the outside of the secluded space.