Sky-Watcher Skyliner-250PX Classic 254mm (10"") f/1200 Parabolic Dobsonian Telescope. These instruments offer an incredible aperture-to-price ratio. Popularized by John Dobson in the late 1970's, is a very simple but effective method of mounting a Newtonian Reflector. Fast and easy to set up, the Dobsonian mount consists of a box-type mounting which allows the telescope to pivot in altitude, while the box itself is rotated on a base in azimuth. The secret of the design is to correctly balance the optical tube and to use frictional materials, which allow it to move easily when nudged but to stay in position when not. The mount is designed to be driven by hand as opposed to slow motion controls. All Sky-Watcher Dobsonian models feature 0.5mm Ultra-Thin Secondary Mirror Supports to reduce diffraction spikes & light loss, and high quality Paraboloidal primary mirrors to eliminate spherical aberration.