This very compact optical system with an original design allows two groups of lenses to be moved perfectly coaxially over several millimeters. It is particularly recommended for applications requiring a constant alignment precision when moving the lenses. The perfect coaxiality of the lens holders is guaranteed by a common bore machined in a single operation. Numerous dimensional modifications allow a perfect adaptation to the optical design related to its application. Due to the use of perfectly adjusted ball cages, its low-friction translation mechanism is best suited for intense use and offers an unequalled lifetime without any particular maintenance.