Newtonian Telescope

Newtonian Telescopes

Bresser Messier N150

What is a Newtonian Telescope and why are they so good? Read on to find out why.

A Newtonian telescope is a simple set of optics usually on an equatorial mount. They are incredibly good and are great for amateurs and professional astronomers alike. They are also very economical compared to other telescopes.

The optical part of the telescope or OTA (Optical Tube Assembly) is the same as a Dobsonian reflector telescope. It consists of a primary parabolic mirror and a flat secondary mirror in an open-ended tube, with a focuser for an eyepiece set on the side. Light enters the tube, reflects off of the primary mirror at the base and is then focused onto the smaller flat secondary mirror and then finally, into an eyepiece. Simple!

Newtonian Telescope

Credit Skywatcher

Benefits of the Newtonian telescope

The benefit of this type of optical arrangement is the Newtonian telescopes light gathering ability. The more light gathered, equals more fainter objects to be seen.

Newtonian Telescopes have a big advantage over telescopes with lenses such as refractors and Cassegrain telescopes, as mirrors are a lot cheaper to make than lenses. Plus they can be a lot bigger!


Newtonian Telescopes are measured by the size of the diameter of their primary (big) mirror. Dobsonian sizes range from starter scopes of 6 inches up to 16 inches, but common Newtonian telescope sizes are 6 to 8 inches in diameter. They can be many times larger and less expensive to produce than scopes with lenses.

The second part of a Newtonian Telescope is the mount. Usually Newtonians come with an equatorial mount. These types of mount enable the telescope to follow the rotation of the sky with on axis parallel to the Earth’s axis of rotation. They can also be used in a basic manual mode which can be manually moved by hand in the Altitude (up/down) and Azimuth (left/right) axis.

The mount is usually a tripod with controls at the head or (mount). More so lately, some manufacturers have put GoTo systems with motors on some Newtonian mounts, this is critical for some long exposure astro photography, but not essential for visual observing as finding objects manually by star hopping or other manual methods helps you learn the sky better and can be fun.

Celestron Astromaster 130


Resist the urge to spend lots of money on small computerized scopes that will eventually never get used, as they can be too complicated or you may not see much through them apart from the brightest objects such as the Moon. A Newtonian is a great all-around telescope, and are available in all telescope stores. Please browse the excellent range of Newtonian Telescopes in the Meteorwatch Store

Sir Isaac Newton and the Newtonian Telescope

Sir Isaac Newton

The seventeenth century was a golden time for astronomy and telescopes. The very first refractors had began to appear on the scene and were improved by Galileo and so had the very first reflector telescopes. Like the predecessors of both models, the major flaw lay in shaping the optics correctly, and – like Galileo – Sir Isaac Newton was a far more advanced optician. While Galileo chose to work with lenses, Newton chose to work with concave mirrors to gather and focus light and his improved method came to be known as the Newtonian Reflector Telescope.


The first Newtonian Telescope appeared in about the year 1668, and introduced the one design manifestation that no one could figure out how to get around – once the light was gathered by the parabola and refocused back to a point on the focal plane, how did you view it without obstructing the light gathering source? Newton’s plan was simple and elegant. He simply introduced a very small, secondary mirror at the focal point and aligned it with the center of the parabola where most incoming parallel light rays are less effective. Held in place by thin vanes called the “spider” assembly, this secondary mirror captured the refocused light path in a non-magnified way and was aimed at a porthole on the top side of the optical tube. From there a series of lenses, called the eyepiece, is used to focus on the secondary mirror and study the image. The first practical working model of the Newtonian Telescope went into production in roughly the year 1689.

The Newtonian Telescope is a simple and elegant design which has endured through the years! Credit: Wikipedia