Eyepiece Design

The function of an eyepiece is to magnify the image from the telescope and project the image into your eye.

All makers have a variety of Kellner and/or Plossl offerings.  Typically, the upper end offerings from Meade, Celestron, Orion, etc., fall midway between their lower price offerings and the premium makers eyepieces.  When you get into the premium eyepieces Televue dominates the market, with Pentax also making some real quality eyepieces and University Optics periodically offering some premium glass. 

The best suggestion I can make is to attend some star parties and look through a variety of eyepieces.  What someone else loves may not work well for you and vice- versa.  Eyepiece selection can be a highly personal thing based on your vision and scope.   Unfortunately, I have found price is a key, though not absolute, indicator of image quality.

ER = Eye Relief
AFOV = Apparent Field of View

Abbe Erfle Ethos Huyghens
Kellner (SMA) Konig Lanthanum Nagler
Orthosopic Panoptic Pentax Plossl
Ramsden Radian    
Wide Angle Design      

Barrel Size

Eyepieces basically come in three standard barrel sizes or diameters, 0.965", 1.25" and 2". The smaller 0.965" are usually found on cheaper department store style telescopes and should be avoided if possible (Orion occasionally offers better eyepieces in 0.965"). Most amateur telescopes are equipped with 1.25" barrels, though many makers are now offering 2" focusers on many of their scopes - 2" focusers used to be found only found on the higher end telescopes.  A 2" eyepiece often offers an increased AFOV and a brighter image.   Adding a 2" adapter or diagonal my not realize the full brightness these eyepieces can offer, any smaller openings in the light path may cause a serious vignette.

Huyghens

Huyghens

ER: short, very short
AFOV: narrow
Invented by Christian Huyghens in the 1600's.  Two elements of the simplest compound design.  A lot of distortion and heavy chromatic aberration are normal.

Normally only found today with cheap, department store scopes with 0.96" eyepieces.  Often labeled with an "H", such as H10.

Back to Top

Ramsden

Ramsden

ER: short
AFOV: narrow
Created by Jesse Ramsden in the 18th century.  Another two element design of two plano-convex lenses, of the same focal length and glass, placed less than one focal length apart.  They are somewhat better optical quality than a Huyghens, but still falling short of the capabilities of today's scopes.  Chromatic aberration is often high.  Works fair in short f/l scopes.  Often labeled as "R".

 

Back to Top

Kellner

Kellner

ER: good to short
AFOV: 40
Designed by Carl Kellner in 1850.  First achromatic eyepiece, essentially an improved Ramsden.  Three element design includes a two element achromatic doublet in place of the Ramsden's single eye lens.  Sharp and bright at low to medium power.  Though they can suffer from internal reflections and poor edge performance, they are usually a good choice for smaller scopes in longer focal lengths.

Reverse Kellner is slightly better, though not many manufactures offer it.  Edmonds Scientific is the last offering I saw of it (RKE).

Another variation is the Super Modified Achromat (SMA).  Another slight improvement on the basic Kellner design, they are standard equipment on many lower cost scopes.

Back to Top

Ortho

Orthoscopic (Abbe)

ER: a little better than Kellner
AFOV: 40
Designed by Ernst Abbe in 1880.  Four element design, extremely low distortion.   Excellent sharpness, color correction and contrast.  Used to be the best eyepiece available, today there are many eyepieces with better eye relief and wider views, of comparable image quality.  Still one of the best choices for planetary viewing. 

Back to Top

Plossl

Plossl

ER: good, better than an Ortho
AFOV: 50
Originally designed by George Simon Plossl in 1860.  Four element design, generally two sets of doublets.  Excellent performance - high contrast and very good sharpness across the field.  Today, it is the first choice in affordable eyepieces, it may be all you really need.

Back to Top

Konig

Konig

ER: good
AFOV: 55 - 70
Designed in 1915.  The original design is a simplified Orthoscopic, with a leading doublet instead of a triplet.  At one time, they offered the best eye relief for a given magnification.  A traditional Konig has one less element than a Plossl.

Improved glass and added lenses can create an eyepiece of extremely good quality, with an AFOV of up to 70, such as the University Optics Konig MK-70 series.

Back to Top

Erfle

Erfle

ER: good
AFOV: 60 - 70
Invented by Heinriche Erfle in 1921, then refined for military use in WW I.  Five or six elements.  Low power images can be outstanding, they tend to suffer edge softness at higher powers.  In reality, they are Plossl eyepieces with extra lenses.  At higher powers they tend to suffer from astigmatism.  Today, this design is found in good lower cost, wide-field eyepieces. 

Erfles remain popular due to the ease of use.

Back to Top

Lanthanum

ER: 20mm
AFOV: 45 - 50
Developed by Vixen of Japan.  Using Lanthanum optical glass they are remarkably free of false color and have a consistent 20mm eye relief.  AFOV is better than Ortho's and Kellner's, and a little shy of a modern Plossl.  Best performance is usually at higher powers.  Excellent for those that must wear eyeglasses.

Wide Field Lanthanum

ER: 20mm
AFOV: 65
5-group, 8-element design.  About the same performance as the standard Lanthanum, just a bigger AFOV.

Back to Top

Radian

ER: 20mm
AFOV: 60
Released by Al Nagler (Televue) in 1998, consisting of six elements in four groups.  Having Orthoscopic image quality(just a bit dimmer), the best offerings are in the shorter focal lengths, enabling eyeglass wearers to finally enjoy using a high-power eyepiece.

Back to Top

Pentax SMC XL

ER: 20mm
AFOV: 65
Combine the Televue Panoptic and Radian, and you have the Pentax SMC XL.  Five to six elements, in four groups.  The 14mm I have is as sharp as my 19mm Panoptic.   Pentax has discontinued the SMC XL line, but the replacement line is supposedly just as good. 

Back to Top

Panoptic

ER: fair, a tad tighter than a Plossl
AFOV: 68
Initial offerings by Al Nagler (Televue) in 1992.  A design of six elements in four groups provides the sharpest images of any eyepiece available, while offering the widest FOV in a 1.25" barrel. 

Back to Top

Nagler

ER: fair, close to a Plossl
AFOV: 82
Designed by Al Nagler (Televue) in 1979.   Up to eight elements of exotic high-index glass, in 4-5 groups, with excellent correction for astigmatism and other aberrations.  A negative doublet field lens increases magnification, followed by several positive groups.  Essentially, a Nagler is a Barlow combined with a long focal length eyepiece.

Often called a "Porthole in Space" they are usable by eyeglass wearers.  I find I have to move my head around to take in the entire AFOV.

While Nagler's have outstanding image quality, the price you pay, besides high cost, is weight and size.  The longer eyepieces are often mechanically unusable on many smaller scopes.

Back to Top

Ethos

ER: 15mm
AFOV: 100
Released in 2007.  The brainchild of David Nagler and Paul Dellechiaie, the design is not stated on Televue's website in 2008.  Size and weight are more than a comparable Nagler.  Reviews are very outstanding, the Nagler eyepieces may have finally been bested.  I'm almost afraid to try one.

Back to Top

SWA
UWA

SWA/UWA

Many companies offer various wide-angle eyepieces.  Many are of good quality, a few are a waste of money.  Quite often the pricing is the first clue, though it is not always a disqualifier.  A careful perusal of the web, or actual trial, can uncover the gems from the duds.

These two examples are the basis for the Pentax, Panoptic, Radian, and Nagler eyepieces, though they are a tad bit more involved/refined than these basic designs. 

Back to Top

Eyepieces   Equipment   Astronomy   Home

Copyright Notice:

This website and its content is copyrighted W Berglin 2001 - 2016. All rights reserved.
Any redistribution or reproduction of part or all of the contents in any form is prohibited other than the following:

- you may print or download material for your personal use
- you may use material from this website for non-commercial use if you acknowledge this website as the material's source

You may not, except with my express written permission, distribute or commercially exploit the content. Nor may you transmit it or store it in any other website or other form of electronic retrieval system.