Data Assimilation In Models

An optical assembly, such as binoculars, having an objective and ocular lens system is focused by the axial displacement of at least one lens system on the optical axis. A manually operated actuator is translationally displaced on the binocular housing to impart the focusing movement. Preferably the actuator is a segment of flexible belt connected to a forked cam arrangement for actually displacing a focusing lens. The binocular housing along with the cam focusing lens system can be both aligned and retained in an operative mode by an elongated shaft extending through the segments of the binocular housing. The binocular housing is split and rotatable about the shaft within the range of movement of the flexible belt.