This telescope has Newtonian optics, with a 1/8th
wave parabolic primary mirror located at the base of the metal
tube and a flat elliptical secondary mirror deflecting the light
cone to the rack and pinion focuser at the top of the tube.
The mounting is Dobsonian and is particularly suitable for beginners
or for those more advanced astronomers wanting the simplest
most trouble free mounting arrangement.
The telescope is robust, light weight, easy to manoeuvre and
simple to transport, fitting in the average car easily. It shows
all types of astronomical objects, planets, nebulae, open clusters,
globular clusters, stars and galaxies.
The 250mm diameter mirror collects 56 % more light than the
smaller 200 mm diameter mirror. With an f ratio of 5, the telescope
has a focal length of 1250 mm. The 25mm and 9mm Plossl eyepieces
provided as standard, will provide magnifications of x50 and
x139 respectively. These translate to fields of view of 60 and
22 minutes of arc, or approximately twice the diameter of the
full Moon and 72% of the diameter of the full Moon respectively.
The telescope will provide excellent viewing of the Moon and
planets; sharp views are helped by the small secondary mirror
and thin struts on the supporting spider. The Cassini division
in the rings of Saturn or the great red spot on Jupiter are
visible. Brighter nebulae and globular clusters are easily seen,
and from sites with darker skies, many galaxies and fainter
objects will be available. The limiting magnitude for discrete
stellar objects will typically be in the range magnitude 12.8
- 13.3.
The GSO 880 comes with a spring friction system. Even with
heavy accessories, the telescope will not move by itself, but
remains smooth in operation.
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The
new spring friction system avoids that the Dobsonian shifts by
itself, i. e. if the eyepiece is changed. Anyway, a sensitive
adjustment of the height is possible.