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Telescopes and Accessories

This Article appeared in the November 23, 2012 edition of the Davis Enterprise.

By Vinita Domier

Special to the Enterprise

Join us Saturday evening, Dec. 8th, at 7:00 p.m., when we will discuss the different types of telescopes and accessories. For those interested in examining telescopes with thoughts of purchasing one for the holidays, we will have a variety of telescopes and binoculars set up for display at Explorit beginning at 6:00 p.m. We will also look at the stars in the night sky following the main program, weather permitting.

On a clear night far from city lights, we can see about 2000-3000 stars with our naked eyes. To see millions of stars, we need to use telescopes or binoculars. Telescopes work like our eyes. The image formed is upside-down and flipped right to left. The brain corrects the eyes’ image to its right orientation. In a telescope, the image’s orientation is usually not corrected.

There are three basic types of telescopes. Refracting (lens) telescopes use lenses to refract or bend light to produce an image. The primary convex objective lens (at the top of the telescope) collects and focuses light on the smaller eyepiece lens (at the base). It has excellent contrast but gets expensive and bulky with large diameter lenses. Reflecting (Newtonian) telescopes use mirrors to reflect light to produce an image. Light is collected by a concave primary mirror (at the base of the telescope) and reflected back to a flat secondary mirror (near the top of the scope), and then reflected on the eyepiece lens. It has medium contrast, is relatively inexpensive, but bulky as size increases. Combo (Schmidt-Cassegrain or Maksutov-Cassegrain) telescopes ‘fold’ light by using a combination of mirrors and lenses to form an image. Light is collected by a concave primary mirror (at the base of the telescope) and reflected back to a flat secondary mirror and correcting lens (at the top of the scope), and then reflected on the eyepiece lens. It has a condensed, portable tube and is less expensive than a big refractor. 

Eyepiece lenses focus the collected light to the eye, and determine the magnification, brightness, and contrast of the image. Eyepieces contain 2 to 5 lens elements with single or multiple anti-reflective coatings. The quality of an eyepiece is determined by its make, focal length, apparent field of view (width of the field of view), and eye relief (distance between eye and eyepiece lens).

Telescopes (a) collect light coming from a star, thus making it appear brighter – Light-gathering Power (proportional to the square of the diameter of the objective lens/primary mirror), (b) bring out details – Resolving Power (equal to the wavelength of light divided by the diameter of the objective/primary lens or mirror), and (c) enlarge a section of the sky – Magnifying Power (equal to the focal length of the eyepiece divided by the focal length of the objective/primary lens or mirror). The actual field of view is equal to the apparent field of view of the eyepiece divided by the telescope’s magnification.

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Explorit’s events:

• Winter Break: Explorit’s Beyond the Table exhibition will be open from 1:00 to 5:00 p.m. on December 22 – 23, December 26 – 31, and January 2 - 6.  We hope you will join us for some science fun and discovery over the holiday break.

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Explorit Science Center is located at 3141 5th St. For more information call (530) 756-0191 or visit http://www.explorit.org, or “like” us on Facebook at www.facebook.com/explorit.fb. 

 
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