Sky-Watcher Explorer 250P-DS OTA 10221

The heart of any Newtonian telescope is in the quality of its main mirror optics. The accuracy of the figure, the material they are made from and the coatings applied all play an important part. Sky-Watcher’s prowess and reputation for commercial mirror making is well known and one of the jewels in its crown. Sky-Watcher has demonstrated its unwavering ability to produce telescope mirrors of consistent high quality over decades. Parabolic (or Paraboloidal) mirrors are a complex shape so need to be well made to provide the high performance expected of them. A properly figured parabolic primary mirror will eliminate spherical aberrations by bringing the light rays to the same focal point. Sky-Watcher’s diffraction-limited parabolic primary mirrors will produce sharp, contrasty images that are full of detail.

The Explorer 250PDS primary and secondary mirrors are made from special Low-Expansion Borosilicate glass, similar to Pyrex. It has an exceptionally low coefficient of thermal expansion compared to regular glass types. In practice this means a quicker cool-down time to reach thermal equilibrium, and during the cool-down process the mirrors will maintain a better shape, reducing distortions, allowing you to start observing sooner.

The secondary mirror is held in place by four specially designed 0.5mm thin spider vane supports which are extremely rigid when tensioned. They serve to minimise obstruction to the light path, allowing the passage of more precious photons and keeping diffraction spikes to an absolute minimum.

Both primary and secondary mirrors are finished with Sky-Watcher’s RAQ™ Radiant Aluminium Quartz coatings, which include layers of aluminium, tantalum pentoxide and silicon dioxide for a brilliant, highly durable finish with 94% reflectivity that will last for years.

The colour scheme is not just an aesthetic. The OTA is tastefully finished in Sky-Watcher’s proprietary Black Diamond flecked metallic paintwork, and features, by design, complementary contrasting white painted surfaces. The white surfaces are a highly practical feature for providing more visibility, which can help prevent your expensive and carefully aligned telescope from being knocked accidentally in the dark.

With a tube weight of 14.4kg, this OTA would be a good match for the Sky-Watcher EQ6-R Pro, AZ-EQ6 Pro, CQ350i Pro, EQ8-R Pro or Wave-150i mountings