Patent ID: 6157495
Filing Date: 2000-12-05
Classification: G02B

Abstract:
An afocal zoom lens system for stereoscopic microscopes comprising in order from the object side:a first lens unit having a positive refractive power;a second lens unit having a negative refractive power;a third lens unit having a refractive power; anda fourth lens unit having a negative refractive power,wherein said first lens unit and said fourth lens unit are stationary,said second lens unit is movable so as to vary an airspace reserved between the first lens unit and the second lens unit and an airspace reserved between the second lens unit and the third lens unit,said third lens unit is movable so as to vary an airspace reserved between the second lens unit and the third lens unit and an airspace reserved between the third lens unit and the fourth lens unit, andsaid afocal zoom lens system satisfies the following condition (1):0.6<f.sub.3 /f.sub.1 <0.7 (1)wherein the reference symbol f.sub.1 represents a focal length of the first lens unit and the reference symbol f.sub.3 designates a focal length of the third lens unit.