The TeleVue Radians
Here's one area where beginners tend to go overboard. You don't really NEED more than 3 or 4 carefully chosen eyepieces, a barlow, and perhaps a filter or two, but most of us eventually wind up with collections, some of them quite impressive.
Eyepieces: The first accessory a newcomer buys is usually a new eyepiece. Below is a guide to various eyepiece designs.
Ramsden and Huygenian are 2-element eyepiece designs. While simple, they exhibit narrow fields of view, have numerous aberrations, and terrible edge correction. Generally supplied only with the least expensive telescopes. While not of much use visually, they make good solar projection eyepieces (i.e. you can risk 'em). About $25-$40.
The Kellner is a three element design that shows an acceptable 40-45 degree FOV, and good correction of spherical and chromatic aberration. Offshoots include the Meade MA, Celestron SMA, and Edumnd RKE. A decent general-purpose eyepiece for the price. About $30-$50.
Orthoscopic eyepieces were once considered the best for general use, but have lost some of their luster compared with newer Plossl designs. Using 4 elements, they are still popular for planetary work. They are well corrected throughout their 45 degree FOV. About $40-100.
The Plossl seems to be the most popular eyepiece design today. Using 4 or 5 elements, they are very well-corrected and have a wider (50-52 degree) FOV than Orthoscopics. However, some models are said to have shorter eye relief than Orthos. About $50-$150.
Erfles seem to have fallen out of favor these days. Using 6 elements, Erfles throw up a wide 60-65 degree FOV, with perhaps some minor aberrations near the edge. About $75-$150.
Newer designs, primarily from the efforts of TeleVue, are gaining in popularity. These include the 6 element, 67 degree FOV Panoptics (about $200-$400) and the 7-8 element, 82 degree FOV Naglers (about $175-$425). Both series are truly amazing. It is said that once you have looked through a Nagler, nothing else will be good enough for you. As a Nagler owner, I think they might have a point.
Sparked by the success of the TeleVue eyepieces, the Japanese have gotten into the act. The Meade Super Wides ($140-$300) and Ultra Wides ($170-$300) are virtual clones of the TeleVues. And Pentax's 6-7 element SMC-XL (about $250 each) are thought be some to exceed the performance of the TeleVues, especially at the lower focal lengths. Vixen's Lanthanums ($100-$200) and TeleVue's Radians ($250) throw out a generous 20 mm of eye relief regardless of focal length, and are a godsend to those who must wear glasses while observing.
Many observers find a barlow lens to be a valuable accessory. Inserted between the focuser and your eyepiece, a barlow will typically double or triple the magnification of any eyepiece. Thus, for $60-$100, you have effectively doubled the size of your eyepiece collection. Also, a barlow preserves the eye relief of your longer focal length eyepieces, thus reducing the amount of squinting you have to do.
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