A projection system and calibration method therefor relate to a light source configured to emit a light in response to an image data, an illumination optical system configured to steer the light, the illumination optical system including a first mirror and a second mirror, a digital micromirror device (DMD) including a plurality of micromirrors respectively configured to reflect the steered light to a filter as on-state light or to reflect the steered light as off-state light to a light dump; determining a deviation between an actual angle of orientation and an expected angle of orientation of the DMD; calculating a first amount of angle adjustment corresponding to the first mirror and a second amount of angle adjustment corresponding to the second mirror; and actuating the first mirror according to the first amount and the second mirror according to the second amount.