An optical device is disclosed having a supporting bar with a twisted configuration. At least one lens is slidably connected to the supporting bar such that the lens rotates when slid longitudinally along the supporting bar. The optical device further comprises a nose piece connected to the supporting bar, which may be stationary or adjustable with respect to the supporting bar. As the lens or lenses are slid along the supporting bar, they achieve a continuously changing angle relative to the nosepiece.