Eyepieces

These are the most commonly desired accessories. Good eyepieces can make even a moderate quality instrument perform very well. When selecting eyepieces you must keep in mind several things. High magnification does not mean better images. As a matter of fact you need a fairly high quality instrument to benefit from anything much more than 150x. Even with high quality optics magnification should generally not exceed about 50x per inch of aperture, and often either the optics (for small diameter telescopes) or the atmospheric turbulence (for larger diameter optics) limit a good image to 20-30x per inch of aperture. Following is a list of some types of eyepieces and what they are worth in the used market:

Basic:

The most basic eyepieces are Ramsden (R) and Hyugenian (H). These are very simple, two lens eyepieces that usually accompany the wide range of small refractor telescopes in the small .965” diameter. These are usually not very good eyepieces due to their narrow fields of view and lack of color correction. When they are combined with refractor objectives, the false color fringes will seriously deteriorate good views in instruments less than f/12. Very short focal lengths (6mm or less) are practically worthless. The value of even the best of these eyepieces at reasonable focal lengths (9mm or more) is about $5-$15.

Good: A second generation of eyepieces improved false color, reduced spherical aberration and coma, gave a longer eye relief and produced marginally wider fields. These include Achromatic Ramsden (AR) , Kellner (K), Modified Achromatic (MA), Super Modified Achromatic (SMA), Symmetrical (SYM) and Revised Kellner (RKE). These are available with coated and uncoated lenses and are generally available in both .965” and 1 ¼” diameter, with a few also in 2” diameter. The table below gives an estimate of their value:

	.965”	1 ¼”	2”
Uncoated	$10-15	$15-20	$20-30
Coated	$15-25	$20-35	$30-50

Better:

The third generation of eyepieces took the improvements noted above even farther, some also reducing internal reflections. These include Orthoscopic (Or), Erfle (Er), Brandon and Plossl. The Orthoscopic eyepieces are optimized for high contrast and sharp images. They are excellent for high power, but are not well suited to wide fields. Erfles are optimized for wide fields of view for extended deep sky objects but the image degrades at the edges. RKE and Plossl eyepieces are well corrected for optical aberrations and that nicely balance width of field and eye relief. These general eyepieces are available in a wide range of focal lengths. The upper end of the price ranges shown below are for the best known Plossl designs as produced by TeleVue, Vixen, etc. as well as for the Brandons.

	.965”	1 ¼”	2”
Coated	$15-25	$25-40	$30-50
Multi-Coated	$25-30	$30-60	$50-90

Top-of-the-Line:

The latest generation uses complex designs that correct for all manner of special needs. Some result in sharp images across very wide fields, have large eye lenses even at short focal lengths, and can allow viewers with eyeglasses to use them with their glasses in place. These include, in relative order of cost, Konig, Ultrascopic, Super Plossl, Ultima, Lanthanum, Easy View, Super Wide, Ultra Wide, Nagler, Panoptic, XL and Radian. These are often large, heavy weight multicoated eyepieces, many of which cost more than a small telescope. For users with special needs or exacting requirements, however, they are well worth the cost.

1 ¼”	1 ¼&2”	2”
$50-120	$120-200	$200-300

Illuminated Reticle Eyepieces:

This group of eyepieces is specialized for photographic or visual measurement work. A fairly standard 1 1/4" eyepiece design, usually of the Modified Achromatic (MA), Orthoscopic (Or) or Plossl (PL) variety, is fitted with an etched flat lens with an edge-on light that illuminates the etched pattern. The etched pattern can be a single or double set of crosshairs or a more complex arrangement. The focal lengths of these eyepieces are generally in the 6mm to 12.5mm range for higher magnifications.

The purpose of most of these is to allow the user to fix a star in the eyepiece relative to the illuminated etching and then to make guiding corrections in the drive to keep the star stationary in the eyepiece. Other types of reticles may be designed to measure the angular seperation between double stars or their angular position with respect to one another. Some manufacturers have controls that allow you to move the reticle slightly to better match the crosshairs to a selected star. Often the light has variable brightness to match the brightness of the star being used as the guide star. The power for the light can be supplied by the telescope panel or a hanbox via a plug-in wire or by batteries attached directly to the eyepiece.

The cost of these eyepieces varies according to the eyepiece design, with the MA designs being cheaper than the Orthoscopic or Plossls. Typically the battery powered eyepieces are more expensive than the plug-in type, add $10 to the prices listed below. Be aware that there are some older Celestron battery powered units out there that it is hard to find batteries for.

Probably the most exotic of these eyepieces are the Celestron Micro Guide or Meade Astrometric models. The Celestron uses the orthoscopic design and the Meade the Modified Achromatic design. Both have a complex reticle that can be used for any of the above mentioned purposes.

MA plug-in	OR plug-in	Micro-Guide/Astrometric
$40-60	$50-70	$90-115