OBJECTIVE WITH VARIABLE FOCAL DISTANCE (VARIANTS) Russian patent published in 1997 - IPC

FIELD: optical system. SUBSTANCE: objective has first and second positive groups of lenses and third negative group of lenses. All groups of lenses are mounted for movement along lens axis. In different variants of objective design definite relations between parameters are satisfied. Thus in first variant relations L_T / f_T < I,0 and f_T are realized, where f_T / f_W > 3,0 is maximum focal distance of objective; f_W is minimum focal distance of objective; L_T is distance between first surface of objective and plane of image at maximum focal distance of objective. EFFECT: more efficient optical system. 31 cl, 18 dwg