binoculars , one form of telescope , in accordance with the present invention have a lens frame drive responsive to manipulating a focusing ring . lens frames are driven to advance or withdrawn by means of the lens frame drive . the lens frames are driven to thrust from their positions of collapse to other positions , at which they enable observation , by manipulating the focusing ring . at this time , lens barriers covering the front surfaces of the lens frames are pressed by means of projections , and thus driven from positions at which they block objectives to other positions at which they free the objectives . withdrawal of the lens barriers and thrusting of the lens frames can be achieved merely by manipulating the focusing ring . changing the lens barriers from their positions of protection to their positions of withdrawal can be achieved with the simple manipulation .