An improved disk cartridge has a light emitter and a light detector and a baffle plate disposed between the emitter and the detector. The detector functions to denote the presence of reflected light from a retroreflective marker disposed on a disk cartridge. The baffle plate acts as a filter to minimize the amount of light reflected from sources other than the retroreflective marker that is received by the detector. By minimizing the amount of light seen by the detector from sources other than the retroreflective marker, the retroreflective marker on a disk cartridge can be placed in close proximity to the emitter and detector. It is advantageous for a disk drive of compact design, such as those within a lap top computer.