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Pentax XW 10 & 14mm
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A Look at the Pentax XW 10 and 14
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 in General
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 right.
The Pentax XW Series:
Superb craftsmanship 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 is working.
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 70 Degrees
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.
Comparing three XW's
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.
About the Manufacturer
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.
The Evaluation Thus Far
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 lenses.
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 say:
"Try it, you'll like it!"