Refractor, Reflector and Dobsonian Telescopes

When someone mentions a name like Nicolaus Copernicus, Galileo Galilei, and Sir Isaac Newton a bell is sure to ring. The brilliant minds of our past that changed the world in the field of Astronomy as we now know will never be forgotten. Each one of these men made amazing discoveries about the cosmos that is the universe and with the exception of Copernicus; the findings which changed everything were done with a telescope. Fast forward to today, in the 21st century, with the incredible advancements in the astronomic telescopic field and with so many options on the market it is difficult to make a choice to choose the right telescope for an aspiring amateur astronomer.With a wide selection to choose from such as the reflecting telescopes, refracting telescopes, Catadioptric telescopes, and Dobsonian telescopes and many more variations it can be difficult for budding amateur astronomers just starting out to select which type of telescope is right for them. This brief intro into the history of the main 3 telescopes on the market today should give the aspiring astronomer what to expect, however this is not a guide for the best telescope, but rather so more of a dressed down history lesson of each telescope

Refractor Telescope

Refractor telescopes, also known as refracting telescopes or dioptric telescopes bend light to make parallel rays converge at a focal point. The refractor telescope design was predominantly used in spy glasses before its use in astronomical telescopes. The refractor telescope was the first kind of telescope invented. It utilises’ a glass lens as a medium to refract the rays of light to form an image. Incidentally, the first refracting telescopes invented was by none other than Galileo Galilei. He invented the first refractor telescope with one large glass lens as the objective and a smaller lens as the eyepiece or focal point. In order to be able to refract light the glass lens had to be shaped perfectly depending on the desired size of the image. The focal point would have a glass lens shaped in the opposite fashion of the objective to keep the image from being seen upside down. This design, being one of the first refractor telescope, has come to be known as none other than the Galilean telescope.

As brilliant as the Galilean telescope was, there is always room for improvement, hence in 1611, another astronomer by the name of Johannes Kepler created another variation of the refracting telescope based on the designs of the Galilean telescope. The Keplerian Telescope, as it came to be known, used convex lenses as opposed to Galileo’s version which used convex lenses.

This in essence gave the viewer a much wider field of view and much needed eye relief. The downside however being that the image would have been inverted. Other disadvantages of the refractor telescope was its’ lack of ability to filter aberrations of the non converged rays. These shortcomings sparked the invention of an achromatic refracting telescope and apochromatic refractors. Achromatic refractor telescopes are pretty self-explanatory. They are intended to display the image without color to mitigate aberrations. Apochromatic refractor telescopes on the other hand, are designed to bring three colors. The viewer would be able to see red, green, and blue wavelengths with minimal aberrations making the apochromatic refracting telescope highly preferable for its time.

Fast forward to the 21st century and refractor telescopes have advanced to such an extent that with the right telescope, viewing a picture clear Pluto through the lenses is not impossible. Also with the advent of technology, computerised goto refractor telescopes are now the norm.

Reflector Telescope

Reflector telescopes were a major improvement upon the refractor telescope which reflected light instead of refracting it. This was because Reflector Telescopes used curved mirrors to capture an image as opposed to the Refractor Telescopes which used lenses. Reflector telescopes were considered to be superior to the refractor telescope design because of the enhanced chromatic quality and potential for an enlarged viewing diameter. There were many proposed designs for a reflecting telescope in the 17th century but Sir Issac Newton is credited with the invention of the first successful working Reflector Telescope, which became known as the Newtonian Telescope

With the success of the Newtonian Telescope arose a number of notable reflector telescopes, albeit with a little variation, that emerged that continues to flourish to this day such as The Cassegrain, The Gregorian, The Ritchey-Chrétien and The Dall-Kirkham. Many of these designs and its’ variations are still applied in today’s’ more advance astronomical telescopes. The Gregorian reflector telescope design in particular can be found in famous modern telescopes such as the Magellan telescopes, the Giant Magellan Telescope, Vatican Advanced Technology Telescope, Large Binocular Telescope, and common assault rifle or sniper scopes. The most famous of them all being the mighty space telescope, Hubble.

Reflector Telescopes are some of the least expensive telescopes and a good starter telescope for today’s’ wannabe astronomers. It is the choice of scientists and professional astronomers alike.

Dobsonian Telescope

Dobsonian telescopes were developed in the 1960’s by John Dobson, an amateur astronomer. Having been fascinated by the Universe, John Dobson built his telescope, based on the Newtonian reflector telescope, out of every day common materials such as plywood and cardboard and is mostly, if not always alt-azimuth mounted. This simply meant that it had a simple two-axis mount for supporting and rotating the said telescope. This type of modified reflector telescope came to be known as the Dobsonian Telescope. Dobsonian Reflector telescopes are known for being great “deep sky” telescopes, mostly due to its’ large aperture. Not only are they efficient for viewing the deep skies of the universe, they are also very light in terms of mass in proportion to the diameter of the objective, in other words, the viewer will have a very large image without an immovable giant telescope. In addition, Dobsonian telescopes are very simple to put together, with the altazimuth mounts typically compact, light-weight, and easy to point, making it a preferred choice for astronomers of all levels. However, for every positive there is a negative and the Dobsonian telescopes is no exception. Due to its large aperture and its design which was optimized for deep sky penetration, an equatorial mount was left out of the design equation, thus a user must move the telescope manually every few minutes or so in order to compensate for the rotation of the Earth. Additionally, it also suffers from balance issues, this is due to the fact that since the Dobsonian Telescope is usually in a fixed relationship to its altitude bearings, an addition or subtraction of equipment’s such as finder scopes, and heavy eyepieces can render the unit useless until recalibrated. However, due to its’ ability to penetrate the deep dark skies, The Dobsonian Telescope still remains a firm favourite in the Astronomy community for the amateur and professional astronomers alike.