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 focusser 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 200mm diameter mirror collects 71 % more light than the
smaller 153 mm diameter mirror. With an f ratio of 6, the telescope
has a focal length of 1200 mm. The 25mm and 9mm Plossl eyepieces
provided as standard, will provide magnifications of x48 and
x133 respectively. These translate to fields of view of 63 and
23 minutes of arc, or approximately 2.1 times the diameter of
the full Moon and 75% 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
(55mm) and thin struts on the supporting spider. The Cassini
division in the rings of Saturn or the great red spot on Jupiter
are easily 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 12.5 - 13.0.
The GSO 680 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
secondary mirror only has a vignetting of 55 mm. Anyway, it is
not glued but mounted. The front adjusting element is made of
metal and allows a sensitive collimation. Screws can be reached
easily.
An
important improvement is the spider for the secondary mirror.
A view into the tube shows the low vignetting and the extremly
thin spider. But it is made solid. The mirror is mounted fix and
it is stable in adjustment. The former used thick struts caused
more diffraction phenomenon.