A method is provided for determining source-to-image distance (SID) setpoints in a digital radiographic imaging system. SID setpoints are determined during a setup and calibration procedure which includes generating x-ray beams while varying certain system parameters, such as the x-ray source position or the size of the collimator opening, and detecting and determining the size of the x-ray beams that impact on the digital detector. SID values and a separation gain constant can then be determined based on the calculated sizes of the detected x-ray beams and the feedback signals which are representative of the various system parameters that were varied (e.g., source position, collimator blade position, etc.) during the setup and calibration procedure. The separation gain constant and the calculated, empirical SID values can then be used to position the x-ray source at any user-selected SID based on position sensor feedback signals. The procedure also provides for a calibrated readout of the actual SID, which can be displayed to a user of the imaging system.