The ME F had its autofocus sensor inside the bottom of the mirror box. Twenty-five percent of the light from the lens' central image was siphoned through a semi-transparent reflex mirror and reflected off a piggy-backed secondary mirror to the AF module. In the module, beam splitter mirrors sent the light to fall on a two row, segmented, linear metal oxide semiconductor (MOS) silicon sensor. A microcomputer analyzed the sensor's subject contrast readings. Modern AF SLRs use similar, though much evolved, AF hardware; however, their AF software no longer analyze contrast.