Ocular (Eyepiece) Recommendations
By Chuck Hawks
The focal length of your telescope, as well as the focal length and apparent field of view (AFOV) of the ocular, determine both the actual field of view and the magnification of that view. For reasons of time and space, it is impossible to give specific ocular recommendations for telescopes of every focal length. What I can do is to make some specific recommendations of ocular lines and brands that have served me well. (Note: there are other brands and lines with which I am not familiar and therefore do not mention in this article, but that does not mean they aren't good.)
I can also suggest some appropriate ocular focal lengths for a couple of common telescope prime focal lengths with which I am personally familiar. These are: 900mm (common for various 80mm-105mm aperture refractors and 4.5" aperture reflectors) and 2000mm (the classic Celestron C8, Meade LX-10/50/200 and others). The recommendations in this article assume oculars with standard 1.25" diameter mounting barrels.
Recommended ocular types, brands and lines
Most amateur astronomers are using oculars that are widely available from the major telescope manufacturers, distributors and retailers. The common ocular brands include Celestron, Meade, Orion, TeleVue, Takahashi, Pentax, Burgess and Vixen; each of these brands offers multiple ocular lines. Major online retailers include the manufacturers/distributors themselves, as well as discount retailers specializing in telescopes and astronomical accessories, such as Optics Planet, Astronomics, Woodland Hills Telescope, Anacortes Telescope, OPT (Oceanside Photo & Telescope), Orion and others. Some of these retailers private label generic Chinese made eyepieces.
Usually the lower priced ocular lines from the top manufacturers are of conventional Orthoscopic or Plossl design, with the Plossl being the most popular ocular design today. These are four element oculars that offer good sharpness and contrast and, especially in medium and longer focal lengths, adequate apparent field and eye relief. The Ortho is a good design for high magnification lunar and planetary viewing, while the Plossl is preferred for deep space and general observing and offers greater eye relief and apparent field of view.
The TeleVue Plossl, Celestron Omni Series, Orion Sirius, Vixen NPL and Meade Series 4000 Super Plossl lines are widely distributed Plossl oculars. (The Meade Series 5000 "Plossls" are really Erfle type oculars; why Meade persists in deceptively calling them Plossl eyepieces is hard to understand.) Plossls generally perform well and are sold in a wide range of focal lengths from 4mm to 45mm in the common 1.25" barrel diameter size. The apparent field of view usually runs about 50-52 degrees (depending on brand) in all but the longest focal lengths. Short focal length Plossl oculars of conventional design have limited eye relief and a small ocular lens, however, which makes them hard to look through. There are better designs for short focal length oculars.
I have owned and used 1.25" Plossl's as short as 7.5mm and as long as 45mm. These days I feel that Plossls are best reserved for focal lengths above 15mm and they are most useful in focal lengths from 25mm to 45mm. I use long focal length Celestron and Tele Vue Plossls, but Vixen NPL and Meade Series 4000 Super Plossls are also well respected.
Celestron X-Cel LX oculars are available in the 18mm and 25mm sizes, in addition to shorter focal lengths. These six-element ED oculars offer excellent sharpness, flat field, 20mm eye relief and a very useable 55-degree apparent field of view. They cost more than Celestron Omni Plossl's, but are economical compared to other premium oculars and are worth every penny of their relatively modest price. Higher priced alternatives in medium focal length oculars include the TeleVue Panoptic (68-degree apparent field), Baader Planetarium Hyperion (68-degree apparent field), Vixen Lanthanum Wide (65-degree apparent field) and Vixen NLV (60-degree apparent field).
For shorter focal length oculars, meaning oculars of about 15mm and less, I prefer to spend the extra money for sophisticated designs with a wider apparent field of view and greater eye relief than offered by Ortho and Plossl oculars. I have used others in the past, but as I write these words I am using Tele Vue Radian and Burgess/TMB Planetary oculars in the short focal lengths. These deluxe oculars have a wide, but not excessive, apparent field (60-degrees) and long eye relief (20mm in the case of the Radian and 16mm in the case of the Planetary). They are much easier to look through than conventional Orthoscopic and Plossl oculars, especially for eyeglass wearers. Other good choices in short focal length oculars include the Pentax XF, Vixen Lanthanum Wide, Vixen NLV, Tele Vue Nagler, Baader Planetarium Hyperion and Celestron X-Cel LX lines.
Building a personal ocular system
When building your personal ocular system, you first need to decide what focal lengths and types best fit your needs. The telescope(s) you own and the viewing that you intend to do, along with any special requirements, should guide your selection. If you view while wearing eyeglasses, for example, you will need oculars that offer a generous amount of eye relief regardless of focal length; you might decide to eschew oculars with less than 20mm of eye relief. Having decided how many oculars you can afford, at approximately what focal lengths, you can then ponder the best way to acquire them.
I have built a reasonable collection of oculars over the years by "cherry picking" (mix and match) from different brands and lines. This is what happens if you base your selections on focal length, suitability for purpose and price without much regard for brand or line. The result is that in the short to medium focal lengths I now own 4mm, 7mm and 9mm Burgess/TMB Planetary oculars plus 8mm, 12mm, 14mm and 18mm Tele Vue Radians. In the longer focal lengths I am using a 25mm Celestron X-Cel, 32mm Tele Vue Plossl and 40mm Celestron Plossl. As a "catch all" ocular, I acquired a Tele Vue 8-24mm Click-Stop Zoom. This rather eclectic ocular collection does a pretty good job!
Rather than mix and match brands and lines, you might choose a favorite brand and select oculars from its various lines. For example, you could not go wrong by deciding to standardize on Tele Vue 1.25" oculars. You might decide to buy Nagler 6 oculars in the shortest focal lengths, such as 5mm and 7mm. You could switch to Radians for your 8mm, 12mm, 14mm and 18mm oculars. In the longer focal lengths, a 24mm Panoptic plus 32mm and 40mm Plossl oculars would serve nicely for deep sky viewing. You would be using different optical designs optimized for different purposes, but they would be similar in quality and appearance/graphics. The members of your local astronomy club would be impressed with your knowledge, discrimination and style.
It is worth noting that the Tele Vue Plossl, Celestron Omni Series Plossl, Baader Planetarium Hyperion and Meade Series 4000 Super Plossl eyepieces, among others, are available in a wide range of focal lengths, from short to long. Most of the oculars within these individual Tele Vue, Celestron, Orion and Meade lines are parfocal, meaning that they all come into sharp focus at the same distance, eliminating all but the most minor need for re-focusing. Years ago I had a complete set of first generation Celestron Plossl oculars, from 7.5mm to 45mm. Economic circumstances eventually forced the sale of my telescope and I foolishly sold my oculars along with it, thus learning an important, if bitter, lesson: never sell your oculars! If you want to stay with one brand and line for the sake of uniformity, the ocular lines mentioned in the first sentence of this paragraph might be worth considering.
Copyright 2009, 2011 by Chuck Hawks. All rights reserved.