A projector apparatus includes: a light source, a digital micromirror device for modulating the light beams emitted from the light source into photo signals, an illuminating lens unit for guiding the light beams emitted from the light source towards the digital micromirror device, and an imaging lens unit for guiding and projecting the photo signals generated by the digital micromirror device. into an image. An aperture-controllable diaphragm is disposed in the apparatus, and defines an aperture. The diaphragm includes at least one adjustable blade for altering dimension of the aperture so as to adjust the brightness and contrast of the image.