|
The Basics
|
• Every refractor has two main parts, a large lens to collect light from a distant object and a second smaller lens to magnify the image of the first lens.
• To “non-astronomers”, a refractor is the stereotypical telescope, a long thin tube you look directly through, like a paper towel roll.
• Lippershey's telescope magnified 3 times (or 3x). In 1609, Galileo built a telescope that magnified 30x, and became the first to turn such a device to the sky. Both telescopes had a ton of image distortion, or aberration, yet still yielded useful results.
|
A Deeper Look
|
• Some tech terms: the distance from the lens to the focal plane is the “focal length”; the ratio of the focal length to the objective lens diameter is the “focal ratio”; the ratio of the objective lens focal length to the eyepiece focal length is the magnification of the telescope.
• The first refractors had a single objective lens with spherical curvature. This caused much image distortion. And red, green, and blue light rays focused at different planes, a problem called “chromatic aberration”. To minimize these problems, these early telescopes needed large focal ratios, which meant even telescopes with a small objective lens were enormously long… ten to twenty feet or more.
• In the mid-1750s, a lawyer (!!) Chester Moore invented a refractor with a two-lens objective, each of which was made from a different kind of glass to partially correct for chromatic aberration. Today, all refractors have at least two lenses in the objective.
|
A Bit of History
|
Hans Lippershey called his new invention a “looker”. Galileo, the first to turn a refractor to the stars and planets, instead called it a perspicillum, then changed to telescopium in Latin and "telescopio" in Italian.
|
Personal View
|
You can imagine, I trust, what your spouse would say when you headed out into the night with your “looker” to gaze at the stars.
|
|
*** Highly Recommended ***
The "Swiss Army Knife" of lunar software. Track the phases, learn lunar topography, and plan your observing session. Learn more…
|
|
|
