An observation optical system including an objective optical part which forms
an image of an object, an image inverting part which converts an image formed by
said objective optical part into an erect image, and an eyepiece optical part which
guides the erect image converted by said image inverting part to an observer. The
objective optical part has a first lens unit with a negative power and a second
lens unit with a positive power arranged from an object side in the order named,
and said second lens unit is movable in a direction including a component perpendicular
to an optical axis to stabilize an image.
