Newtonian · Dobsonian
305mm f/5 Dobsonian for serious deep-sky observing
Price in India
₹58,800
A 12" parabolic Newtonian on a Dobsonian base — the most aperture per rupee available, and the reason most experienced observers own one.
The Dobsonian is the cheapest way to put a large mirror under the sky. There is no tracking motor and no computer: you nudge it, and the simplicity is what lets the budget go into the mirror instead. This 12" model gathers enough light for galaxy structure that a smaller instrument only hints at, dozens of Virgo Cluster members in a single session, and planetary detail limited by the atmosphere rather than the optics. The Professional adds a dual-speed 10:1 micro focuser, an altitude clutch, an azimuth roller bearing and a tube balancing system over the Nightwatch — worth having if you observe at high magnification, where a single-speed focuser makes fine focus a fight.
Every figure below is calculated from this telescope's own specifications using standard optical formulae. None of it is a marketing number.
Light-gathering power
1898× the human eye
Compared to a dark-adapted 7mm pupil. This is what determines how faint an object you can detect.
Resolving power
0.38 arcseconds
The Dawes limit for this aperture — the finest detail the optics can theoretically separate.
Limiting magnitude
~14.9
The faintest star reachable under a genuinely dark sky. Expect two to three magnitudes worse from a city.
Maximum useful magnification
610×
Twice the aperture in millimetres. Atmospheric conditions usually impose a lower practical limit.
Magnification with 25mm eyepiece
61×
Your low-power, wide-field view — used for finding objects and framing large clusters.
Magnification with 10mm eyepiece
152×
The workhorse range for planets, lunar detail and globular clusters.
The optical ceiling for a 305mm aperture is about 610x. On a typical Indian night, atmospheric seeing — not the telescope — limits you to roughly 150x–200x. Most of your observing will happen between 61x and 152x, and the view will be brighter and sharper for it.
Why telescope magnification claims are misleading →No reviews for the GSO 12" Professional Dobsonian yet. We publish reviews only from people who actually bought the telescope from us, so this section stays empty until there is something real to put in it.
Own this telescope? Send us your reviewSpecifications on this page are taken from GSO's official product documentation. Derived figures — magnification, resolving power, limiting magnitude — are calculated from those specifications using standard formulae, and observing expectations reflect what this aperture realistically delivers under Indian skies.
View the manufacturer's official listing
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Considering more aperture? The GSO 16" Professional Dobsonian is the next step up at 406mm, for ₹1,50,600.
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