How to Learn the Parts of a Telescope

Refractor Telescope Parts

• 1

  Set up the refractor telescope on its tripod mount so it may be walked around freely while observing the various parts. Walk around to the front of the telescope and observe the opening at the front, which is aimed toward an object to be viewed. Note that there is likely an extension protruding from a round piece of glass several inches deep inside of it. This shroud is called the "dew shield," and the large round glass lens within it is called the "objective lens."

• 2

  Walk around to the side of the telescope so the whole length of it may be viewed at once. The full length of the main body of the telescope is simply called the "optical tube" and the smaller scope sitting on top of the telescope with lenses on each end is called the "finder scope" used to assist in aiming the main tube correctly toward an object to be viewed in magnified form.

• 3

  Walk toward the rear of the telescope and observe that a metallic tube inserts into the rear of the telescope, which slides in and out of the telescope. This moving metal tube allows an object to be focused for clear viewing and is called the "draw tube."

• 4

  Observe the focusing mechanism composed of a shaft with two wheels on it, one on each side of the draw tube. These wheels are the "focus knobs," which are rotated to move the draw tube further into or out of the telescope. This manual movement of the draw tube is what permits the object being viewed to be focused for the sharpest observance.

• 5

  Draw your attention to the absolute rear of the telescope and make special note of an L-shaped elbow, where the lens is connected. The 90-degree elbow is called the "diagonal." A small reflective mirror is within this diagonal that bounces the light upward into the lens, which is the part that points straight up for viewing.

Reflector Telescope Parts

• 6

  Set up the reflector telescope onto its mount, base or tripod so it may be walked around freely. Walk around to the front of the telescope and observe the large hole in the front that is aimed toward the object being observed. This large opening has no objective lens in it like a refractor telescope does and simply allows light to travel to a large mirror at the rear of the telescope. The front opening is called the "aperture" of a reflector telescope.

• 7

  Look slightly above the aperture of the telescope, paying close attention to the exterior of the telescope body. The small tube that runs along the length of the main telescope body tube is the finder scope, which allows an easier way to aim the telescope toward an object to be viewed. Note another tube protruding upward from the telescope body itself at a 90-degree angle, which is the "eyepiece drawtube," while the part that slides into it is the lens itself. A shaft with two wheels on it is connected to the eyepiece-holding tube, and this is called the "focus knob," allowing for adjustment for the clearest view of the object being observed.

• 8

  Walk around to the rear of the reflector telescope and make note of a large metal or plastic ring at the rear with three thumbscrews protruding from it. The ring itself is what is holding the large mirror at the rear of the telescope, called the "primary mirror," which magnifies the light of an object while also reflecting it back toward the front of the telescope. The ring is called the "mirror cell," and the adjustable thumbscrews are called the "collimation screws." The collimation screws allow the rear mirror to be adjusted when necessary to make objects appear in the center of the eyepiece once a telescope is aimed at them. This process is called "collimation."

• 9

  Return to the front of the telescope and look into the front, or aperture, of the telescope and note that there are three or four arms connected to the interior part of the telescope body tube, with a small mirror assembly attached to it. The arms are called the "spider vanes" and the small mirror is called the "secondary mirror." The secondary mirror reflects the amplified light coming from the large primary mirror at the rear of the telescope and bounces all of that light upward into the lens where it is then focused and viewed.