” Lens6b-en ” by DrBob , licensed under CC BY-SA 3.0 ] [” Chromatic aberration lens diagram ” by Bob Mellish , licensed under CC BY-SA 3.0 Achromat Achromats take care of this to some degree apochromats (which are much-costlier) totally eliminate the problem (unless it is a poor set of lenses that make up the apochromat). Think of a lens as a prism (look at the edge of the lens) a single lens does indeed begin to break light into component wavelengths. This combination deals with the major refractor problem: color issues. Today’s modern quality refractors use either two ( achromat ) or three ( apochromat ) lenses for the objective. Their telescopes used double concave lenses, making for a long “optik stick.” And even though the parts of this simple lab telescope are inexpensive (the lenses are plastic), they are probably better than those used in early telescopes. The telescope you will assemble and test in lab is similar to the ones built by the Janssens, Lippershey, and Galileo, except for the eyepiece lens type. In modern telescopes the eyepiece can be changed, providing different power or magnification. An eyepiece might not be required for other “observers,” such as a camera, CCD, or spectroscope. Double concave means that both sides of the lens are curved inward, thus double (or two ) concave (or in ).Īgain, the eyepiece is required to focus and magnify the image for the human eye. The Galilean Refracting Telescope – a single lens each for the Objective and eyepiece [“The Galilean Refractor”, Florida State College at Jacksonville is licensed under CC BY 4.0Įarly telescopes such as the one invented by the Janssens and Lippershey 400 years ago, and the one used by Galileo astronomically, only used one lens for the objective, and a second double concave lens for the eyepiece. These sketches by Galileo are of the 1st and Last quarter moon.
Galileo’s observations of the Moon through the simple telescopes he made provided him with an unprecedented view. Other detectors can include cameras (both film and digital), video camera systems, spectroscopes, photomultiplier tubes (measures the amount of light incoming), etc. Your eye is one type of detector (shown in the telescope illustrations). You must use this lens or lens system - called the eyepiece - to focus and magnify for the eye. That is why you see a second, diverging lens (spreads the light out) on the left side of the below diagram. When the converging light reaches the end of the tube - its focus - the light must then be focused for the eye. The objective lens is a converging lens think of it as a magnifying glass (which it is!). As the light beam travels down the telescope tube (the solid barrel which holds the lenses), it converges or comes to a focus. Double convex refers to double (or two) convex (or out) . The objective shown here is a double convex lens that is both sides of the lens shape are outwardly curved. Why? Because if you show a solid beam of light incoming - what really happens - then you would not see the objective or any lens in a drawing because it would be blocked out by the “solid” line. For simplicity, the incoming light is shown as two (sometimes more) lines. Light - shown by the dashed lines and arrows enters the objective over the entire surface of the objective. The main lens which focuses the incoming image is called the objective . What you will see in these drawings is as if one took the telescope and cut it down the middle of the tube and lenses. Like with lenses and mirrors, when telescopes are shown as a drawing or illustration, they are more often shown as a cutaway or cross section. The refractor was first used astronomically by Galileo Galilei in 1609. The Refractor , believed to have been first invented by spectacle makers Hans and Zacharias Janssen, then independently Jan Lippershey of Holland in as early as 1595. The main part of this Lab is an introduction to the simple refracting telescope , using a combination of concave lenses. 29 The Telescope The Telescope Two of Galileo’s telescopes, now on display at the Science Museum in Florence, Italy.
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