An observation optical system for non flexible endoscopes 2 or 6, wherein {TAIL ~ said at least another relay lens module} which comprises negative lens elements comprises, in the vicinities of {HEAD ~ the center} of said relay lens module, at least two negative lens elements made of a glass material having an Abbes number not exceeding 40 
An observation optical system for non flexible endoscopes 2 or 6 , wherein { TAIL ~ said at least another relay lens module } which comprises negative lens elements comprises , in the vicinities of { HEAD ~ the center } of said relay lens module , at least two negative lens elements made of a glass material having an Abbes number not exceeding 40
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH