A stereolitography apparatus comprises a fixed vat (401) or a holder for receiving a removable vat for holding resin during stereolithographic 3D printing, and a radiation source (501) for generating radiation capable of polymerizing portions of said resin in said vat. (401). The apparatus comprises a shutter (502) between said radiation source (501) and said vat (401) for allowing only selected portions of the generated radiation to reach said resin, and a cooling channel (503) between said radiation source (501) and said shutter (502). The apparatus comprises a blower (504) configured to force coolant gas through said cooling channel (503).