A Look at the Pentax XW 10 and
By John Mills
Browsing website ads for eyepieces can confound the
most hardened and experienced astronomer. Newcomers beware; it's a land
filled with multitudes of older designs endlessly re-shuffled and new species,
of titanic proportion and cost, roam the land. Sometimes, the astronomy
industry looks like an arena where manufacturers bout for dominance like
wild beasts for the few morsels of profit to be had. Reading the
ads, one is sometimes forced to mutter a line from a famous tune: "Endless
streams of mediocrity."
Take heart my friend! Learning the jargon and testing
equipment comes with the territory of this wonderful hobby. Like any other
interest, an investment of time doing careful research even becomes part
of the fun. Websites like Cloudy Nights have filled many a long, cold,
overcast evening with an unparalleled opportunity for us to communicate
and compare. It wasn't all that long ago that a club newsletter and the
latest issue of an astronomy periodical were the only real highlights to
be had each long, lonely wait between observing sessions and star parties.
We've come a very long way.
Before we enter the evaluation proper, I'd like to
add that that I'm not an optical expert but rather like most amateur hobbyists;
committed and enthusiastic. My family owns a 16" f/4.6 TeleKit truss dob
- no coma-corrector used.
The eyepiece box currently contains both the 10 and
14mm Pentax XW, a 28mm Meade 5000 SWA and a 12mm UO HD Orthoscopic. A used
and bruised 20mm Meade RG Erfle was recently added that's destined for
testing and a sample of the ever-present 25mm Meade MA, another twenty
+ year old, is kept for public sessions. (and sentimentality)
Most importantly, I have no affiliation whatsoever
with Pentax or any other astronomy company.
A Few Things
While there are many particulars involved in the design
of an eyepiece there are at first two basic, broad categories that must
be addressed. First and foremost, an ocular must do it's job - that of
rendering the truest, most faithful rendition of the object being observed. Second,
and for many of us this is about equal to the first, it must bring the
image to us in a comfortable, easily accessed manner.
Bringing about a happy marriage of these two formidable
criterion had in the past been something of a mystery; they even seemed
mutually exclusive. One only has to have the opportunity to look through
an older design like a 5mm Orthoscopic to understand that here is a true
image indeed, yet the fatigue often associated with having to "squint"
to see anything at all in the tiny eye lens makes observation, over a protracted
time, a short-lived chore. And, due to the short to nothing eye-relief,
keeping eyelash oils off the lens is about impossible without backing away;
which is a good practice anyway if the particular eyepiece allows for it.
In hot and cold weather, sweat and lens fogging just add to the inconvenience.
Enter the era of the premium wide-field eyepiece. Promises
of sweeping vistas are made with claims of long eye-relief all for the
price of what seems, well, a small mortgage! While it's true that advances
made through computer-aided design blended with "exotic" glass and coating
processes have propelled us into the universe in tantalizing new ways,
most eyepieces remain physically what they have essentially always been
- a machined metal housing containing ground, polished and coated glass
lenses. They have also become very expensive; a commodity in their own
and comfortable views
Since my start
in the hobby back in the early seventies I've owned and used more than a few
oculars. Memories of the obligatory .965" Ramsden or Kellner included
with that department store refractor have been happily forgotten - almost.
You see, first impressions, especially for a "Newbie," stay with
you forever and can slant your preferences for many years.
Where a new eyepiece
is concerned, there's nothing quite like opening that box the first time.
Again, first impressions are important and the XW's make a fine one indeed.
Even a cursory "look-see" tells you plainly that nothing has been
spared here. Everything about them, from the refreshing modern design and
first-class materials and construction, speak of supreme quality.
The rubberized outer housing is easy to grip and is
much like the armored rubber binoculars the military uses. You feel as
if this unit will be there for you when the going gets tough and the years
go by. Add to this the JIS Class 4 weatherproofing and there you have it
- a unique and beautiful piece of equipment. With a very large and extremely
well coated eye lens looking at you one is forced to conclude that it's
time to make coffee and roll the scope out.
Optical coatings seem to get special attention at Pentax
and the two XW units I'm looking at right now tell me so - the glass is
downright dark and flawless. To be sure, a very deep hue on a lens is generally
recognized as good and we have it here on both eye and field lens. Of course,
I can't see the partial coating Pentax has introduced between the cemented
lenses but the incredible, "contrasty", second-to-none views tell me something
In field use the Pentax XW does not disappoint. Again,
you are immediately impressed by the easily accessed, bright, crisp images.
That large eye-lens begs you to come and take a look. The 20mm eye relief
is truly plenty and is especially welcomed by the eyeglass wearer - myself
included. I even have room to spare and find myself twisting-up the ingenious
eyecup 2 or 3 turns. In comparing the similar adjustable eyecup design
of my Meade 28mm SWA, I'll confess I prefer the Meade in that it goes all
the way up or down in a single 180 degree turn. But, the XW is obviously
of a higher build quality - it looks nicer and has that durable, armored
binocular feel whereas the Meade has almost too simplistic an approach.
A well Balanced
Some prefer eyepieces only of 80 degree and above AFOV
such as that provided by the Tele Vue Nagler. Having owned Naglers of the
Type 4, 5 and 6 line I too have appreciated the wonderful impression of
"being there" that these superb eyepieces can provide. The Pentax XW is
a 70 degree product and yet having compared them to both the 12mm and 17mm
Type 4 Naglers I find myself thinking that the apparent field width difference
seems less than one would expect. The XW definitely purveys to the observer
that wonderful sense that you are a part of the scene, not just a distant
and removed observer. Here, though, I would echo what many before me have
said: That this is a very subjective and personal area of eyepiece evaluation.
Many other nuances come into play where one's impressions
of a view that a particular ocular provides are concerned. For instance,
in directly comparing the 12mm T4 with the 14 XW, I found that there is
quite a margin of difference in what I call, "view accessability." The
T4 provides a wider AFOV yet not without some restrictions - you must find
the exit pupil position and hold it tight. In doing so one finds that wonderful,
expansive view of the Nagler design. Now try to move your eyeball around
to see detail in the periphery and you'll encounter the infamous "kidney
bean." While the T4 gives a wider field overall, my eye can only utilize
the whole view while looking straight ahead. By comparison, the 14 XW is
completely forgiving in eye placement; The entire field is had at your
leisure without "blackout."
The saying, "wider is better" holds pretty much true
in considering AFOV - as long as it's a quality view. Aberrations
of differing kinds, lack of clarity or sharpness and tight eye relief are
gremlins that try hard to pop up any time you build an ocular. Stacking
multiple lenses to correct each successive problem can cause loss of precious
light. Astronomy, especially in the visual mode, is all about getting as
much of the cosmos into your eye as possible. For me, the ultra-long eye
relief combined with 70 degree apparent field served-up by the WX's is
quite spectacular and even preferable; it's very wide and engaging without
the inclusion of field area that is unusable or uncomfortable to see. My
"feeling" is that 70 degrees seems to offer the best opportunity for the
designer to find a beautiful balance between wide-field of view and all
other factors combined.
A note here for those of us who share our hobby with
the family, especially children. My two young boys love to use the XW's
because they are easy to use. Comments like, "Wow Daddy, I can really see
in this one!" are indication that Pentax has hit a homer.
We don't own the 20 XW but I've looked through a friend's
at length in our scope. While all of the XW's are definitely of the same
quality in every respect, there are some differences in how they function.
The 14 and 20 XW are, in my estimation, impossible to differentiate in
use. The "10" is different in that it's a little particular about eye placement.
There is no "bean" effect from moving your eye around to view the edges,
but moving or rocking your head - that is, getting your eyeball off-center,
will cause some darkening in the opposite direction. My personal feeling
is that this is not objectionable since the large eye lens and long eye
relief still offer a very healthy margin of comfort.
Pentax is a renowned Japanese optical company. To say
they are qualified to build us some eyepieces would be an understatement.
If you were to ask a company to design a new ocular for you it would probably
be Pentax or Tele Vue. Pentax cameras and ancillary equipment are some
of the finest made and as you probably know they have enjoyed an excellent
reputation for years in astronomy.
As a side note: The approach Pentax has taken in advertising
and promoting these fine eyepieces is unusual - they don't do much, if
any. This is kind of enticing in that we don't have any of the usual glossy
ads sprawling across the pages of every astronomy periodical. We're also
spared the circus sales pitch common to some companies. The downside here
is that most of us are techno - junkies who like the details even if we
have to sort through piles of junk to find them. You'll have to dig a little
to find any data on the XW's. Beware, some dealers don't get the facts
straight. Get a copy of the leaflet Pentax puts in the eyepiece box from
your dealer. It has the correct, basic technical data.
Looking back over the article we see that the following
specifics have been discussed:
* Build quality / "Eyeball" coatings analysis
* Eye-relief / Comfort ("Approachability")
* AFOV comparison
* Manufacturer personality
Now, we'll consider whether the XW's are doing their
primary job; that of providing an honest rendition of the object being
observed. Here, the following come into our evaluation:
* Light transmission
* Distortion or aberration
Those of you who have used or own a Pentax XW know
that when it comes to light throughput they pretty much set the standard.
In comparing simpler eyepiece designs (Those with fewer lenses) such as
Tele Vue Plossls, I've been hard-pressed to say the XW's loose anything
at all on a perceptible level. That's saying a lot when you consider that
a "traditional" plossl has 4 lenses in two groups while both the 14 and
10 XW each have 7 lenses in 6 groups! For information's sake, the 20 XW
has 6 lenses in 4 groups and the others in the series vary from 6 to 8
Pentax has stated that visible light transmission is
98%, and having used them to reach into the depths of space for faint galaxies,
I would have to concur. Also, contrast is profound when compared to the
many other wide-fields I've looked through.
On sharpness they quite simply astound you. It is hard
to imagine that these are so sharp. This would defy the common thought
that an ocular with more than about 5 lenses will somehow become sloppy
of image handling. It's true that if you don't take care here that images
can become ever so "soft", making the quick-snap focusing pleasure of a
finely crafted eyepiece impossible. Pentax is paying more than adequate
attention to lens perfection which is readily attested by how "clean" they
focus an image.
My favorite test for sharpness is planetary observing.
Since Mars was near this season we put the 10 and 14 XW to the test in
the 16" TeleKit. Yes, the focus "snapped" in and the wonderful, wide
field made the swiftly moving God of War a pleasure to track and behold.
For comparison, the 12mm UO HD Ortho was inserted and again the focus process
came clean. Did the Ortho, a planetary observers dream by most anyone's
standard, give a better show? No, it didn't. The two eyepieces performed
extremely well without any preference for either - except that the XW has
eye relief and field to spare which helps in a dob.
The f/4.6 light
cone coming up from the TeleKit's primary mirror is a tough customer; it bullies
and humbles some very fine eyepieces. "Old tech" Erfles and the
like are a favorite of mine since they hearken me to my first years in the
hobby, yet they cower under the gaze of my mirror. The recently acquired "old" 20mm Meade RG Erfle also has about a 70 degree AFOV and optically it's quite
good. But, stars in the outer one third of the field stretch. I don't mind
that - as long as the eyepiece was inexpensive, which the RG was.
The XW's are truly
modern in that they address the needs of a "fast" scope. To my eyes,
star fields look flat and pristine in them. Minor field curvature was allowed
at the far edge yet as a tradeoff it is acceptable when you consider the benefits
of the total design. There is little or no appreciable chromatic aberration
or other aberration present.
One factor that
kept me back initially from purchasing an XW was the cost. At the time, it
took $339 US to walk-off with one. Since last year, they have retailed for
$299. Seeing the price go down on premium equipment is uncommon, yet I was
still shy and opted for a used 14 XW at $240. Like Mexican food, It wet my
appetite pretty bad after one try so I soon took-on the 10mm also.
No doubt that the venerable Nagler cut us loose from
the tyranny of the narrow past, setting a new world-class standard most
others have only yet modestly mimicked. I'm grateful that at least one
company, Pentax, has taken the Tele Vue challenge completely serious and
designed us a whole new breed of truly premium, perfection-quality eyepieces.
In doing so, they have provided us with some exciting new standards of
their own making; like modernization of the exterior and optical coating
technologies pushed into new territory. Meade has also recently offered
the Series 5000's. Their similar design to the XW would indicate that Pentax
is a force to be reckoned with. No ocular is perfect, yet the XW's come
as close as any - bar none in my humble opinion.
In recommending the Pentax XW's to you I hearken back
to my first year in astronomy - 1972. A TV commercial was heard then to
"Try it, you'll like it!"