Sky-Watcher Skyliner-400P FlexTube 406mm (16"") f/1800 Parabolic Dobsonian Telescope. Sky Watcher patented FlexTube range of truss-tube Dobsonian models all feature collapsible OTA's, making them incredibly easy to transport and store, offering the ultimate flexibility for owning an otherwise large telescope. They all feature 2-part telescope tubes attached with 3-arm supports. When in use the tube is fully extended and each arm's axis is clamped to ensure a rigid, perfectly collimated, high-performance optical system. After use, the clamps can be loosened and the tube retracted into a convenient compact size. Owning a large telescope has never been so easy.