When selecting eyepieces for your telescope consider the following;
1. You should buy as much quality as you can afford even if it means fewer oculars. Most beginning
amatuers are lured by high power claims when in fact the lower power eyepieces most often offer
the best views.
2. When selecting eyepieces consider the focal lengths that will yield power per inch in the ranges of
5, 10, 15, 20, 30, 40 and 50. If you have a limited budget, you might want to start with the 5
through 15 or 20 range first.
3. High quality eyepieces that offer wide flat fields of view are normally preferred.
4. As to design, Plossl and Orthoscopic are good at all powers, Nagler and Wide Field are good at medium
power and Wide Field and Erfle are good at low power.
A fine set of eyepieces could cost from $500 to well over $1,000. If you are serious about astronomy, I'd suggest you purchase the best eyepieces you can afford. If treated with care they will last a lifetime. (Note: Keep them clean by careful use and storage. Don't over over clean the optics as you may damage the anti-reflection coating or worse scratch the lens.) If you are a beginning astronomer, don't despair, you
can get good quality low power eyepieces from many sources at bargin prices. Check with a local astronomy club or buy a copy of Sky & Telescope or Astronomy magazine for more information on sources.
* The "Projection Magnification" formula in the table is set for the projection adaptor provided by Celestron for their C-8 telescope and my average eyepieces. (177.8 mm.) If you have a different setup
you will need to change the "X" value according to the following formula.
Projection Magnification = ( X - Fl of Eyepiece) / Fl of Eyepiece
where X is the distance between the eyepiece and the film plane.
This distance should be measured from the midpoint of the eyepiece lenses and not the eye lens, however for this calculation extreme accuracy is not especially critical.
Please feel free to pass Eyepiece Calculator on to anyone interested in astronomy. Comments or suggestions regarding Eyepiece Calculator can be directed to me at:
GEnie: J. FELBAB1
CompuServe: 76666,2437
AppleLink: N0793
Geneva
Zapf Chancery
Eyepiece Types
Eyepiece Types
Chicago
Geneva
ERFLE - Designed especially for a wide flat field. Excellent eyepiece for low power. Heavy, usually 6 or 7 elements.
KELLNER - Has achromatic eye lens for laterial color correction. A fair low power, inexpensive eyepiece especially for the beginning astronomer.
KONIG - An good design offering very wide field. Some curvature of field visable at edges. Short eye relief. Well priced, a good eyepiece.
ORTHOSCOPIC - Fully corrected for distortion. An excellent eyepiece at all powers but especially good for medium to hIgh power. Good eye relief.
PLOSSL - One of the best telescope eyepieces, it offers good field and eye relief. Inexpensive to manufacture.
NAGLER - A recent design, highly corrected offers maximum field and large exit pupil. Heavy (8 elements) and very expensive. Outstanding views and flat fields but very poor eye relief.
WIDE FIELD - Excellent field and good correction. Good eye relief. Very expensive.
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