The present invention relates to a system for optically adjusting a computer-to-plate (CTP) imaging head which includes an a light source (104), optical fiber (124) for transmitting light emitted from the light source; an imaging lens (204) for focusing light emitted from a distal end of the optical fiber (128) on a substrate; wherein a portion of light striking the substrate is reflected back to the distal end of the optical fiber; a fiber optic coupler (116) in the optical fiber which transmits the reflected light to a light detector (112); wherein the light detector measures intensity of the reflected light; and a control unit configured to adjust the imaging head according to the intensity of the reflected light.