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The word “refractor” means a telescope whose principal focusing element is a lens. A refractor telescope is a type of optical telescope which is also referred to as a refracting telescope. Its curved primary – or largest – lens gathers light, bends it, and sends it back to a focal point where it is further modified by the use of an another set of lenses called the eyepiece. The curvature and size of the primary lens dictates the amount of distance needed to achieve the focal point. The larger it becomes, the longer it must become… and early refractor telescopes were huge affairs! Let’s take a look at the refractor’s history…
Refractor History – The refracting design was first used in spyglasses, then later in astronomical telescopes and telephoto camera lenses. These first spyglasses were designed by two men – Hans Lippershey and Zacharias Janssen. Of course, this type of technology has great military implications and it wasn’t long before several countries were putting their best opticians to work designing refractors for themselves. Thankfully Galileo Galilei heard about this new combination of lenses and what they could do – and independently designed his own refractor. While it only magnified the image about 30 times, rather than turn it towards incoming enemies, Galileo turned it towards the night sky and created the first astronomical telescope. By changing the convex, concave structure of the lens arrangements, other refractor telescopes were also developed, including the Keplerian telescope.
Refractor Design – While the refractor delivered incredibly sharp images, it wouldn’t be long until problems developed. In all image respects, the more light gathered means better views – and larger optics were needed to gather that light. Beginning glass-making processes were primitive and large lenses meant the introduction of air bubbles and defects. What’s worse, passing the electromagnetic spectrum through glass also meant the loss of some wavelengths and huge lenses bowed to the weight of gravity – further distorting the images. As time went on, astronomical refractor telescope designs changed as additives were combined with the lens elements to create ever better and more pure lenses. Opticians learned to combine lenses to reduce the focal length and compensate for optical errors. However, the refractor could never escape the weight of gravity! To this date, the largest achromatic refractor ever put into astronomical use is the 40-inch (1.02 m) Refractor, at Yerkes Observatory.
About Tammy Plotner
Tammy is a professional astronomy author, President Emeritus of Warren Rupp Observatory and retired Astronomical League Executive Secretary. She’s received a vast number of astronomy achievement and observing awards, including the Great Lakes Astronomy Achievement Award, RG Wright Service Award and the first woman astronomer to achieve Comet Hunter's Gold Status.
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