Celestron X-Cel Series Eyepieces

For many years Celestron's bread and butter eyepieces have been Plossls. The Omni line is their current Plossl offering and good oculars they are. (They are covered in an article you can find on the Astronomy and Photography index page.) The Plossl design uses four lens elements in two symmetrical groups. This apochromatic design provides a flat field, excellent sharpness, good contrast from center to edge, a reasonable apparent field of view (AFOV) of around 50 degrees and decent eye relief in medium and long focal lengths (from about 15mm and longer). The eye relief becomes limited, as does the exit pupil, in short focal length Plossls.

Because Plossl's tend to have rather small exit pupils in high magnification oculars and a short eye relief, viewing is difficult for most observers and practically impossible for eyeglass wearers. Ditto for orthoscopic oculars, another classic four-element design found in short focal length oculars.

Improvements in optical design and manufacturing technology have made it possible to manufacture short focal length oculars with a generous apparent field of view, extended eye relief, flat field, excellent sharpness from center to edge and an adequate exit pupil. Burgess/TMB Planetary and Tele Vue Radian eyepieces are two examples of such eyepieces recently reviewed on the Astronomy and Photography Information Guide. The X-Cel line is Celestron's entry in this upscale ocular arena.

The X-Cel design formula uses six elements, including extra low dispersion (ED) glasses for the most curved elements to minimize lateral color error (color fringing). All lens elements are fully multi-coated, edge-blackened and the eyepieces' internal barrel surfaces are flat black to help reduce internal reflections. The angular field of view of all X-Cel eyepieces is 55-degrees and the eye relief is 20mm, regardless of focal length. This puts them in the ballpark with the aforementioned Burgess/TMB and Tele Vue oculars. Celestron X-Cel eyepieces come with 1.25" mounting barrels in the following focal lengths: 2.3mm, 5mm, 8mm, 10mm, 12.5mm, 18mm and 25mm.

X-Cel eyepieces are manufactured by Celestron's partner in Red China. They come with hard chrome plated mounting barrels that include a wide safety notch to reduce the chance of loss if a star diagonal retaining screw should accidentally loosen. The mounting barrels are threaded to accept standard 1.25" filters. Their aluminum upper barrels are finished in an attractive matte black with a Celestron orange accent stripe and feature a wide, checkered, black rubber grip band. There is a rubber eye guard on the top of the ocular. Top and bottom caps and a protective plastic case are provided with every X-Cel eyepiece; it is a nice package. Here are some basic specifications for the X-Cel Series eyepieces:

Celestron's 2009 MSRP for X-Cel oculars is $86.99 ($102.95 list price) and online discount prices are considerably lower. Optics Planet (www.opticsplanet.com), for example, sells X-Cel's for only $56.45 each. That is a little over half the price of a Burgess/TMB Planetary and about ¼ of the price of a Radian. This is made possible by Celestron's manufacturing and marketing power.

The image through a Celestron X-Cel ocular is sharp and contrasty with little light scatter. The AFOV is sharp from center to edge and it is comfortably wide, without being so wide that you have to move your head around to see the entire field of view. (I prefer apparent AFOV's in the 55-70 degree range.) The rubber eye guard helps to exclude ambient light as well as protect the eye. Eyeglass wearers can fold back the eye guard.

I have come to prefer (reasonably) wide field, long eye relief oculars in the short and medium focal lengths. I own and use Burgess/TMB Planetary, Tele Vue Radian and Celestron X-Cel oculars in focal lengths from 25mm down to 5mm (the shortest focal length ocular I own). All three brands perform in an exemplary fashion.

Frankly, using my Mark I eyeballs, I cannot see much difference in the visual performance of the three brands. They are all easy to view through and they all work great in my Celestron Omni XLT 102ED refractor telescope. The Tele Vue Radian and Burgess/TMB Planetary oculars have slightly larger AFOV's than the Celestron X-Cel (60-degrees Vs. 55-degrees). The Celestron and Tele Vue have slightly greater eye relief than the Burgess/TMB (20mm Vs. 16mm). The Planetary and Radian oculars have deluxe pull-up or twist-up eye cups that the X-Cels lack. I can say that Celestron X-Cel oculars are a heck of a good deal for the price and that makes them my first recommendation in medium to short focal length eyepieces for the amateur astronomer on a budget.