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15mm Celestron Axiom LX


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My purpose in writing this review is, of course, to share my (rather limited) knowledge and experience with the community and, hopefully, make some future amateur astronomer's life a little easier. But my reason for choosing this particular eyepiece is simple: hardly anyone seems to have heard of it, and the whole Axiom LX series is a bit of a secret. But before we get into the meat of this review, a little background…

My name is Michael Daugherty. I've been observing since December of 2007, almost exclusively from a light polluted suburb of Youngstown, Ohio. The only telescope I have ever owned, and the one used for this evaluation, is a 12” f/4.9 Zhumell Dobsonian reflector. For a year I used only cheap Chinese Plössls, and loved them. My first experiment with wide-field eyepieces came in November of 2008 with the purchase of a used 17mm Baader Hyperion. It served me well for eight months, and then I decided it was time to try something different. Craving a wider field and lower magnification, I started seriously considering the 23mm Celestron Axiom LX. There was surprisingly little talk of this eyepiece and hardly anyone owned one, so I took the plunge and bought one sight-unseen. It turned out to be a good decision: I fell in love with the “Ax” after one observing session, and this was what eventually motivated me to trade up from my 17mm Hyperion to the 23mm's little brother, the 15mm Ax. There were even fewer people sharing their experiences with this eyepiece than with the 23mm, and as far as I knew no one in the local astronomy club owned one, so again I had to grit my teeth and pull the trigger on it without ever even having seen one. My wonderful experience with the 23mm Ax made me a little more confident about my decision, but it still came only after months of back-and-forthing and self-doubting. No matter how great the 23mm was, I still wasn't totally sure this was the right move.

In short, it was. There was no denying that the 15mm Ax was superior to the Hyperion overall, but it took me a little while longer to warm up to than the 23mm. I'll first give my initial impressions of the Ax and then break my thoughts down into several main areas that I think are important when choosing an eyepiece. Finally, there will be a short list of astronomical observations and a wrap-up at the end. Here we go…

First Impressions

As cheesy as it sounds, Celestron has obviously taken the saying, “You can only make a first impression once” to heart. All of the eyepieces in the Axiom LX series come in an attractive, and more importantly durable, box, which has heavy foam inside it that the eyepieces are packed inside of. It comes with two caps, one for the field lens and one for the eyelens, and although they look nice I'm not a big fan of the soft rubber they're made out of; if you're not careful you could easily knock one off or press it against a lens and make a smear on the glass. The cap for the eyelens is particularly prone to falling off, but this is due more to the odd shape of the eyepiece than the cap itself. An aftermarket bolt case might be a good thing to buy. As for the eyepiece itself, it's very well-built and, yes, I think it's pretty. The twist-up eyecup stays in place but isn't stiff or hard to adjust. I had a good feeling about this one before I popped it in the focuser.

Optical Quality

This is probably the biggest factor that people consider when buying a new eyepiece. Put simply, the 15mm Ax is optically excellent to my eyes.

The first thing that comes to my mind when evaluating the quality of a view through any eyepiece is sharpness. The Axiom shows beautiful pinpoint stars from the center of the field out to about 90% of the way to the field stop, and it doesn't really break down until about the last 5%. As far as I can tell the main aberration is coma, because the stars turn into points with tails pointing away from the center rather than bloated crosses or seagulls. For comparison, my Hyperion showed pinpoint stars out to only about 70% of the way to the field stop, and the dropoff in image quality was much more drastic. It was tolerable most of the time, but when looking at dense open clusters (some of my favorite targets), the view was frankly pretty disgusting.

Another consideration when judging an eyepiece's optical quality is lateral color, which manifests itself as a stretching and discoloration of bright stars when they're near the field stop. The amount of lateral color in the 15mm Axiom was surprising to me: any star brighter than about third magnitude stretches out and turns purple when it's only roughly 70% out from the center of the field. This is one area where the Hyperion clearly wins; I never noticed any lateral color when using that eyepiece. The 23mm Axiom has this defect as well, but only with stars brighter than about second magnitude, and more like 80% out from the center of the field of view. To be honest this isn't a deal-breaker for me. Some observers might find it objectionable, but unless you like viewing bright double stars at the edge of the field or trying to cram sprawling open clusters like M44 or M45 into a small field of view, it shouldn't be a problem in most cases.

Finally, pincushion distortion plays a minor role in my enjoyment of an eyepiece. I don't know the specific types of pincushion, which is more serious or even what exactly causes it, but the 15mm Ax has very little of it, just like its big brother. My old 17mm Hyperion showed a much larger amount of it, and even that didn't bother me except when panning around through rich starfields at high speeds. This point is hardly worth mention in my opinion, and I'd give the 15mm Axiom an “A” for optical quality.

Comfort

Amateur astronomy is not a hobby for the impatient; it often involves sitting in the cold, staring into an eyepiece and trying to pick out faint smudges from the background glow. Because of this, the comfort of an eyepiece is very important. The Axiom is easy to look through, if you don't wear glasses while observing.

The reason? Eye relief. This is the most important part of an eyepiece's ergonomics for me. While the 15mm Axiom doesn't have gobs of eye relief, I'd estimate it to be around 10mm. This is definitely not enough to take in the whole field while wearing glasses; I've tried. Fortunately I don't wear glasses while observing but this is something to keep in mind if you do. Earlier on I mentioned that it took me a little while longer to learn to love the 15mm than the 23mm, and this is the main reason why. Even though I don't wear glasses while observing, the need to keep my eye fairly close to the eyelens becomes somewhat of a problem when I Barlow the eyepiece. The higher power (200x in my scope) gives the image a tendency to shake if I rest my eye on the eyecup. The only way to solve this is to keep your eye hovering just above the eyecup, which takes a bit of practice. It's especially bothersome after using an extremely comfortable eyepiece like a Hyperion but isn't a big issue, especially if you're using a scope with a shorter focal length that will yield a lower magnification.

The other part of the ergonomics is the actual shape of the eyepiece. The Axiom's top is just about the right size for my face, not too big and not too small. This might vary from person to person but the twist-up eyecup makes it easy to find the position that best fits you. The eyelens, shown in the picture below, is the same size as that of the 23mm and gives a nice window to look through. The Ax gets a “B” from me for comfort.

Fit and Finish

I'll be honest: looks do not matter to me when selecting astronomy equipment. For what it's worth, though, I think the whole Axiom LX line is beautifully designed. The barrels are shiny chrome and the body of each eyepiece is a pretty metallic gray with a bit of red and orange thrown in. The lettering is deeply engraved so there's no chance of rubbing it off. They almost make the Hyperions look plain. Although not technically a part of its looks, the 15mm Axiom has a very manageable weight in a compact package. It's shorter than the 17mm Hyperion, about the same width and considerably lighter. This is an important consideration for Dob owners like me who need to keep their scopes balanced. For this purpose I use a freezer bag full of beans Velcroed to the back of the OTA. The only time it's necessary when using the 15mm Ax is when I put it in my heavy 2” Barlow and view objects close to the horizon. It's less than half the weight of the beastly 23mm and could fit inside it. More important than the looks and in my opinion more important than the weight is the mechanics of the eyepiece. There isn't much to say here; the twist-up eyecup works flawlessly and I love it. It isn't too stiff, too loose or greasy at all. The eyepiece has a great feel to it and gives off an air of quality. I rate the fit and finish at a solid “A.”

The Test

No matter how many opinions and numbers you read about a potential new piece of astro gear, no matter what it is, the most important part in your decision will come down to how it performs in the field. The following are a few notes from several different observing sessions with the 15mm Axiom including a variety of targets. The observing site was my suburban back yard which normally has a limiting magnitude of 5.0-5.3 but most of the observations were done under a full or nearly full moon.

U Cygni (8/31/09) – This carbon star showed a beautiful blood-red color in the 15mm.

NGC 6482 (8/31/09) – Faint (mag 11.5) galaxy in Hercules. Very small and quite faint, and just looked like a star with a slight fuzzy halo that disappeared with direct vision. Still fun to hunt down with a full moon overhead.

NGC 7027 (9/2/09) – Very interesting planetary nebula. Small and very bright with an obvious light green color. It was also elongated approximately north to south with two lobes which became more obviously separate with averted vision. There was a darker area between them. It was obviously nonstellar at 100x and great at 200x.

ε Lyrae (9/4/09) – Both components were split nicely at 100x, and at 200x there was plenty of black between the individual stars. Very nice view.

δ Cygni (9/4/09) – Easily split at 200x, companion strongly suspected at 100x.

NGC 40 (9/5/09) – A clearly defined circular area of nebulosity surrounding a faint central star.

NGC 7662 (9/5/09) – Obviously nonstellar at 100x, at 200x showed a large blue-gray disk with a dark nearly stellar spot in the center.

The slight increase in magnification over the 17mm Hyperion (100x vs. 88x) is noticeable to me and gives a more immersive experience. The much wider apparent field means you can frame objects in the Ax with just as much room to spare as with the Hyperion, at a higher magnification. The 3mm exit pupil in f/5 scopes is very nice, as it's big enough to give nice bright images but not so big that the background is too washed out, even with my light pollution. While I find the Hyperion more comfortable, the Axiom clearly wins in image quality and I think the wider field more than makes up for the shorter eye relief.

Wrap-Up

In case you're not interested in pages upon pages of analysis, here's the TL;DR version. The 15mm Axiom LX gives nice, crisp, widefield views with few aberrations. Although its eye relief is decent, if you wear glasses while observing you'll almost definitely want to consider something like a Hyperion, Panoptic or Vixen LVW. Aside from the somewhat short eye relief the Axiom is very user-friendly; the twist-up eyecup in particular is a very nice feature. If you're looking for a great eyepiece at a reasonable price, you should seriously consider this one. It's still a mystery to me why the Axiom LX line isn't more well-known.

Now for some thank-yous. I'd like to thank Phillip Creed, whose excellent review of the 23mm Axiom LX prompted me to snatch one up and become acquainted with these wonderful eyepieces. It was also Phil who told me it was lateral color I was seeing, which I had previously assumed was chromatic aberration. Also, a thank-you to Eurvin Jackson for giving his opinions on the Axioms, and of course the rest of the CN community for their ever-helpful advice and answers to my endless questions. And finally, thanks for reading. I hope you find this helpful.


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