an actuator for moving {TAIL ~ either the pinhole plate} or the focusing lens to control the amount of the first portion of the focused laser beam passing through the pinholes for replaying a target track on {HEAD ~ the holographic medium}, 
an actuator for moving { TAIL ~ either the pinhole plate } or the focusing lens to control the amount of the first portion of the focused laser beam passing through the pinholes for replaying a target track on { HEAD ~ the holographic medium } ,
OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH