Telescopes | Astronomy | Cosmos

Advantages and Disadvantages of Refractors

When one wishes to purchase a telescope, one can choose from two main types of telescope: refracting and reflecting telescopes. Refracting telescopes are the more traditional type of telescopes, which use two lenses (the objective lens and the eye lens) to collect, focus and magnify more light than the human eye can normally manage. Reflecting telescopes use a curved mirror (a parabolic mirror) to focus light onto a second mirror, which is then sent to the eye. For the purpose of this article, we will discuss the advantages and the disadvantages of the refracting telescope.

The refracting telescope uses lenses as its optical element. The use of lenses confers several advantages. Unlike reflecting telescopes, whose mirrors need to be recoated every few years, a refracting telescope’s glass lenses need little to no maintenance beyond the occasional wipe down with lens cloth. The lenses of refracting telescopes are also firmly set in place, so the telescope is more likely to survive minor accidents without an appreciable loss in picture quality. Having lenses that are firmly set in place also negates the need to have to constantly readjust the optical elements (a process known as collimation) to ensure the light is all going directly to the eye. All of these mean that refracting telescopes do not require anywhere near the maintenance a reflecting telescope would need. In addition, while the technology of refracting telescopes is older, it is also more refined, and so refracting telescopes will tend to be more reliable.

That said, refracting telescopes also possess their own set of disadvantages. The lenses which refracting telescopes use are made of glass, which means they must be painstakingly ground to the exact specifications required. This is costly in terms of time and skill required, and thus refracting telescopes will, on average, cost about five times as much as reflecting telescopes. In addition, the lenses of a refracting telescope will tend to be heavier than those of a reflecting telescope, because the telescope’s frame must be strong and the lens fittings sturdy in order to properly anchor the lenses in place. Finally, a refracting telescope’s lenses, though finely machined, are still prone to flaws such as chromatic aberrations, which is a discoloring of the image caused by imperfections in the lenses, and various other distortions. Though the engineering of the lenses is designed to minimize these flaws, they cannot be entirely eliminated from the design.

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