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FAQ Refractor  The refracting
telescope is thought to have been invented in 1608 by Dutch optician Hans
Lippershey, who quite by accident discovered that magnified images were produced
when placing one lens in front of another. Hence, a refractor is a telescope
that takes advantage of the refraction of light through lenses to form images of
objects. There are several designs of refractors out on the market today, but
the most simple consists of just two lenses... the objective, or main
light-gathering lens, and the eyepiece, which magnifies the image. All other
variations invented through the years are still based on this simple design.
It is interesting to note that Galileo was the first astronomer to make serious regular telescopic observations with the refractor. He improved the simple design of Lippershey's telescope (which is why refractors are sometimes referred to as "Galilean" telescopes) as soon as he got word of the patent, and with that telescope (his first telescope magnified objects nine times, the second magnified images thirty times) made astounding discoveries that would lay the foundations for mathematical physics and prove Copernicus's heliocentric (Sun-centered) theory. Quite a history... There are two basic types of refractors on the market today, achromatic and apochromatic, plus one refractor-style spotting scope; the prismatic design. All three are covered below: TOP Achromatic Refractors This refractor type is the least expensive and is traditionally a two- or three-lens system made from crown and flint glass. These types of glass were developed in the 1880's to reduce "chromatic aberration", or color fringing around bright objects. While the 60mm altazimuth or equatorial refractor is a popular choice as a first telescope, consider spending a little more and investing in either an 80mm or 90mm refractor. The glass is usually of higher quality, the coatings are better and the additional light-gathering will allow you to see brighter images in greater detail than those produced through a smaller, mass-produced lens. TOP BRApochromatic Refractors The first apochromatic (also referred to as "APO") lens was invented by the German physicist, Abbe. Instead of basic two-element designs like the achromatic, the apochromatic refractor uses either three or four lenses, each made of a different material; a two-element lens, one of which is fluorite; or a newer two-element design of ED, or "extra-low dispersion" glass. The use of these newer materials and designs allows for a system which is virtually free of color fringing or chromatic aberration, which is the biggest obstacle to overcome when producing any refractor. Faster focal length refractors, while sought after because of their portability, also have the most stubborn color fringing, so the invention of the apochromatic design is a boon to those of us who want to take our refractor everywhere. Of course, apochromatic refractors are more expensive, but the views through them are exquisite, providing a velvety background and pinpoint star images. TOP "Prismatic" Spotting Scopes  Prismatic
spotting scopes use lenses to gather light just like your ordinary refractor,
but have an image-erecting prism built into them, placed just before the
eyepiece. This allows for a right-side-up, left-to-right correct view. The
eyepiece (the part that you look in) comes in two "flavors", either a "zoom" or
"fixed" design. The most popular of these two is the zoom spotting scope. This
type of scope has a magnification range built into it... usually somewhere
between 15 times to 60 times as far as your eye can see, and you control the
level of magnification by rotating a little knob or dial. The second type of
refracting spotting scope has a fixed magnification eyepiece attached to it.
Most of these scopes have additional, higher magnification eyepieces available
as optional equipment. Refracting spotting scopes are extremely portable and rugged (some are even waterproof), and attach at the bottom to a photographic tripod of any brand. If you don't have a tripod, make sure and get a sturdy one to help create a stable image. If you are interested in attaching a camera to your spotting scope, make sure this is an option. Some brands have the ability, some don't. If you have more than a passing interest in doing photography through your spotting scope, we recommend the second style mentioned in these pages... Catadioptric, otherwise known as Schmidt-Cassegrain or Maksutov spotting scopes, because of their larger light-gathering capacity and the stubbiness of the design, which helps assist even further in stability at high power. TOP Refractor Pro's & Con's Pro's:
AltazimuthTOP |
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