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Telescope eyepieces

Filed Under Accessories, Astronomy, Telescopes 

telescope eyepiecesEyepieces are the part of the telescope that makes the image for your eye to see. The first half of the telescope is the lens or mirror, located at the front of back of the telescope’s tube, at the eyepiece is located at the side or back of the telescope’s tube.

On a refractor telescope, the eyepiece will sit in a focuser at the back of the telescope, which is a unit that is able to be moved in and out to focus the image that the telescope is looking at. The focuser unit comes in two standard sizes, 1.25 inches and 2 inches, before you buy your eyepieces, it is important to know which diameter eyepiece your focuser unit utilizes.

Calculating the power of the eyepiece that you will be using on your telescope requires some simple math. The primary lens or mirror in your telescope has a focal length, which is the distance that it takes for the light to be focused into a point; this is called FL. The eyepiece that you will look through also has a focal length, which is called fl. You need to convert the focal length of the primary lens or mirror and the focal length of the lens piece to millimeters, and then divide the focal length of the telescope by the focal length of the eyepiece (FL/fl). As an example, if your telescope had a 2000mm focal length (FL) and your eyepiece had a 20mm focal length (fl), the magnification would be 100x.

There are two main types of telescope eyepieces, Kellner eyepieces and Plossl eyepieces.

Kellner eyepieces utilize a three lens design, are fairly inexpensive and have good image quality from low to medium magnification.

Plossl eyepieces utilize at least a four lens design, where high quality eyepieces can become rather expensive. Plossl eyepieces are some of the most common on the market today and offer a relatively large field of view, however, also suffer from a very small amount of eye relief, which can lead to discomfort with excessive use.

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Comments

6 Responses to “Telescope eyepieces”

  1. Earl on June 28th, 2008 8:32 am

    good article, but don’t understand about eye relief

  2. admin on June 30th, 2008 4:16 am

    For more explanation about eye relief, please see this article :)

    http://www.telescopes.org/telescopes/eye-relief-and-why-it-matters

  3. calculating magnification of a telescope on August 1st, 2008 10:20 am

    [...] of back of the telescope??

  4. frank skroh on November 25th, 2008 8:28 pm

    Where can I obtain orthoscopic eeyepieces in 2 inch diameter?

  5. admin on November 30th, 2008 8:20 pm

    We will try and find this information for you :)

  6. David Stellwagen on September 9th, 2009 2:18 pm

    I know this is a tough question, but what two or three eyepieces would you recommend to use with the Orion Sky Quest 8? A 2x Barlow seems like a given, but with what? A 25 mm comes with it, but what do I complement that with? A 9 mm for detail? Or a mid 17mm? Thoughts? Any help or input would be greatly appreciated.

    DS

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