A zoom lens system includes a frontmost first lens unit having a negative optical power and a plurality of lens units on the rear side thereof. A leader member that is attached to a free end of a recording tape wound around a single reel accommodated in a case and that is pulled out from an opening formed in the case by an pull out member of a drive device is manufactured by metal injection molding of stainless steel. A system and method for sensing specific substances using the optical infrared emitterdetector of this invention in a sensor device is also provided.