Abstract: A stereomicroscope comprising an objective lens system and eyepiece lens systems, the objective lens system comprising at least two lens units, permitting a working distance thereof by varying at least one airspace and having a concave surface at a location farthest from an object to be observed so as to minimize lowering of the magnification of the stereomicroscope and stereoscopic impressions of images observed through the stereomicroscope.

Abstract: A variable focal length lens system having, in the order from the object side, a first positive lens unit, a second positive lens unit and a third negative lens unit. In order to vary the focal length from the wide position to the tele position, the first positive lens unit and the third negative lens unit are moved jointly or independently toward the object side while the second positive lens unit is moved toward the object side at a lower speed than the first and third lens units. The variable focal length lens system satisfies the following conditions:0.5<.vertline.f.sub.3 /f.sub.W .vertline.<0.9 (1)1.3<.beta..sub.3W <2.0 (2)0.5<f.sub.2 /f.sub.W <1.3 (3)where f.sub.W is the focal length of the entire system at the wide position, f.sub.2 and f.sub.3 are the focal lengths of the second and third lens units, respectively, and .beta..sub.3W is the image magnification of the third lens unit at the wide position.