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Celestron 10mm Axiom LX Eyepiece


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Background

Like many CN members my interest in astronomy, along with all things space-related, goes back to childhood. I had the obligatory "800X" 60mm no-name refractor on a rickety alt/az fork mount, but I wasn't terribly impressed with what I saw. So my interest lapsed for a couple of decades until I happened across one of the big telescope makers' Web sites and discovered how cheap[1] telescopes had become while I wasn't looking. That was a little over a year and a half ago, and I've been hooked ever since. My first scope, a 90mm Maksutov, led to a 80mm ED refractor, which in turn created an obvious need for a 10 inch truss Dobsonian.

The 80mm, a Celestron Onyx 80EDF f/6.25, has been my main instrument for most of the past year, and I've settled on the Zen-like solution of one eyepiece (the subject of this review), one Barlow (Orion Shorty Plus), and one extension tube to boost the Barlow's magnification. This lightweight kit does a nice job on almost everything a 80mm scope can be used for, and with very little fiddling around with eyepiece swaps. I do keep a 32mm Celestron Omni Plossl in the case for the rare huge object (read: M31 under dark skies), but I seldom use anything else since getting the Axiom earlier this year.

For whatever reason, the Axiom LX series hasn't generated much buzz in the CN forums other than jokes about how the 23mm and 31mm versions are apparently made of Neutronium due to their extreme weight—about three pounds for the 31mm! But questions about the shorter focal length versions attract almost no comments at all other than scattered and terse posts to the tune of "mine's pretty good".

Why? Are Celestron's Neutronium mushrooms best left in the astronomical produce section? Is a Non-Disclosure Agreement required for purchase? Are they just optical duds? Or do they just look too weird?

Having looked through and appreciated 7mm, 10mm, 15mm, and 19mm examples, I don't know why they don't have a larger following. But it's OK to be unpopular if you can deliver the goods. The 7mm and 15mm (the other two 1.25" oculars in the series) performed very much like my 10mm when I tried them out a few weeks ago, so my comments can probably be used as a rough guide for them as well.

First Impressions

Just to set things straight, the 10mm Axiom isn't made of Neutronium though it does feel like a solid billet of aluminum. There is some heft, but not the sort that causes a Dobsonian to emulate a medieval trebuchet if you remove it from the focuser. Fit and finish are very good: it looks like an expensive piece of gear with its silvery grey anodized body and gently scalloped black rubber grip ring around its waist.

The supplied caps are made of a soft elastomer, but the tapered shape of the eyepiece's eye lens end prevents the eye lens cap from staying on unless the eyepiece is vertical or nearly so. A rubber band is needed to keep everything together if you store one of these on its side.

The grip ring rotates to extend and retract the eyeguard from and into the body of the eyepiece. It's a neat feature and operates smoothly if a bit stiffly, but I suspect the design is responsible for making the eyepiece larger and heavier than it really needs to be. The marginally effective cap mentioned above becomes completely ineffective if the guard is extended at all, so don't plan on leaving the eyeguard in a preferred position if you want to store it with the caps on.

Ergonomics

In use, this is a comfortable eyepiece. Blackouts and kidney beaning are non-issues, and eye position isn't critical. Eye relief is stated at 13mm, and I believe it: it's long enough for comfort without my glasses, but it's impossible to see the whole field with my glasses on. The eye lens is about the same size as that of a garden variety 25mm Plossl, and on the whole it's about as easy to look through. My wife, who has some serious vision issues, has much less trouble with the 10mm Axiom than she does with anything shorter than a 20mm Plossl.

The eyeguard is effective in cutting out stray light and is easy to extend to the proper position for taking in the whole field. I like it better than the standard eyeguards found on most eyepieces and use it all the time.

The body/lens housing's girth is reasonable and doesn't cause me to turn my head to clear my ample nose.

In a brief side by side test with a 13T6 Nagler, I found the 15mm (the 10mm wasn't on hand) Axiom much less prone to blackouts and kidney beaning than the Nagler, and the Axiom's eye relief was notably more generous. There are some optical tradeoffs involved, so keep reading, but the Axiom was more pleasant ergonomically than its green lettered peer. My experience with my 10mm is much the same: I don't find myself straining to keep my eye in the proper position and kidney beans stay in the pantry where they belong.

Optical Performance

It's a nice shiny aluminum mushroom that's easy to look through, but how about the images? Writing about how M42 looks through an eyepiece is a lot like the proverbial "dancing about architecture", so other than making some objective points about the Axiom's performance, I'll just say that the "porthole into space" effect is definitely there and that the images are very good indeed. Compared to my cheap but effective Omni Plossls, I can't detect any loss of sharpness or transmission due to the extra glass in the Axiom.

I did some brief tests at a recent star party with the 7mm Axiom in a Stellarvue 130mm f/6 apochromatic triplet pointed at Jupiter (under mediocre observing conditions, however) and saw very nicely resolved structure in the planet's disk. Swapping in various other eyepieces (8mm Ethos, T6 Naglers) didn't improve the views in that scope on that night, though it's possible better conditions would have revealed differences. Accounting for the more modest light gathering and resolution of my humble 80mm "semi-apo" doublet at home, my 10mm Axiom performs similarly.

Performance doesn't degrade noticeably in my recently acquired 10 inch f/4.7 Sky-Watcher truss Dobsonian, but it has been so cloudy lately that I must admit I haven't had much of a chance to look for defects.

I've favorably compared the Axioms to T6 Naglers in this review, but there are some drawbacks. For one thing, the 7-15mm Axioms all show some lateral color. This is most evident as a thin rind of lime green on the Moon's limb that comes and goes depending on eye position. Until I saw it in the Stellarvue apochromat, I chalked it up to my Onyx 80's less-than-perfect color correction. Stellarvue's Vic Maris was on hand and confirmed what I was seeing (he noted that the 19mm Axiom had less of this effect). In the same excellent telescope, there was no false color or fringing with either the T6 Naglers, 3-6mm Nagler Zoom, or the 8mm Ethos on the Moon or anywhere else. In practice, it's not obtrusive enough to bother me.

There is some mild ghosting on bright targets like Jupiter, but no more than a lot of other eyepieces I've looked through. More annoying, however, are the ever-present eye reflections I see when viewing these same targets. They can be distracting, to say the least, and may very well be a deal breaker for some people. It may also just be the peculiar shape of my eyes, or only present in the 10mm focal length, so try before you buy if you can.

The Axiom's field is completely usable in my Onyx 80. I don't hesitate to position an object near the edge and let it drift to the other edge to maximize viewing time with my alt/az mount. Planets exhibit a little less of the "football effect" near the edge in the Axiom than with my Omni Plossls. I don't know yet if this is true with my fast Dobsonian.

Performance with my Shorty Plus Barlow is very good despite the fact that there's 10 pieces of glass in the stack. This combination yields c. 110X with my Onyx 80, which is about as high as seeing here in suburban San Diego reliably permits. Adding a 2.2" long barrel extender between the eyepiece and Barlow bumps the magnification up to roughly 170X in the same scope, which is right around the 50X per inch rule of thumb for maximum magnification. If conditions support it, I get some terrific views of brighter objects. The Axiom may not be a Zeiss AOII, but it does pretty darned well.

Overall Impressions

Taking everything into account but leaving out cost, I prefer my 10mm Axiom to any of the other 82° AFOV eyepieces I've looked through: T6 Naglers, the Explore Scientific 82° series, Meade UWAs, etc. Factoring in the reasonable $179.00 street price of the Axioms makes them even more attractive. But everyone's tastes and scopes are different. I'm willing to sacrifice a little (but just a little) optical performance if it means I can stay at the eyepiece longer. You may have different priorities.

Pros
  • Nice price for a clean 82° AFOV
  • Fine build quality
  • Very good, if not the very best, optical performance
  • Excellent ergonomics, relatively insensitive to eye position
  • Useful retractable eye guard

Cons
  • Slight lateral color on the Moon and some other bright objects
  • Strong eye reflections on bright targets
  • Nearly useless eye lens cap
  • Probably larger and heavier than it needs to be

When my astro-toy budget recovers, my next two eyepieces will be the 7mm and 15mm Axioms, so I'm obviously pleased with them.

And, for the record, Celestron would strongly disclaim any relationship with me once they found out who I was and what I was up to. :-)

Footnote [1]: Yeah, the scope is cheap, but all stuff you want need for it really adds up.








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