to believe that early zoom lens designs of the sixties had and optical quality comparable to today's is ridiculous this ignores the progress on optical design of the past few decades early zoom designs typically consisted of three lens groups convergent divergent convergent the d group was fixed and the st and rd groups were mobile furthermore the st and rd group were rigidly linked so that a complex and difficult to manufacture non linear cam based group distance regulation mechanism wasn't needed the downside of the rigid linking was that such a design can limit optical aberrations only over a very limited focal length range the development of sophisticated complex non linearly driven four group based designs focusing variator compensator relay master is a fairly recent phenomenon that has been enabled by the development of new optical design techniques computation algorithms manufacturing e g lower cost aspherical lenses numerical control machines to manufacture precise non linear driving cams and material science e g glasses with anomalous dispersion characteristics