An imaging optical device, in particular binoculars or a telescope, comprises, in addition to a casing, an optical system with at least two optical components, the distance of which relative to one another is adjustable for focus setting of the optical system. This adjustment is effected by an adjusting device, which is coupled with at least one of the two components. The position of the optical components relative to each other is detected and, by the aid of a processor, converted into a focal length of the optical system and then outputted as a focal length via an output device. In this way, the distance of an object sighted by the optical device can be determined conveniently.