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. |
