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Home > Reviews > Eyepieces > Other > The Pentax Perplex

The Pentax Perplex
By Greg Nowell - 5/9/2006

The Pentax Perplex

Pentax offers some of the finest eyepieces on the market. Whether the telescope is a fast Newtonian, apochromatic refractor, or Schmidt Cassegrain, the view in the Pentax eyepiece is, in the view of many ardent users, the one to beat, and worrisome only in that it can become an addiction. Over the years the selection in my eyepiece box has gradually shifted away from premium competitors till it is now dominated by Pentax’s XL and XW lines. However, this is not an equipment review meant to preach the virtues of the product to skeptics, a task best left to Internet discussion groups. The Pentax Perplex is: why is this company making so many errors in marketing? I offer this critical essay as an admirer, owner, and user of the company’s products.

Televue is not just a maker of the dominant premier eyepiece brands but an integral member of the United States astronomical community. You can call Televue and without too much trouble get one of the Naglers on the phone.

By comparison, the telescope eyepiece division of Pentax is a subdivision of a large multinational corporation that is headquartered in Japan. Compared to other optical product lines, it is fair to say that the telescope eyepiece revenues must be minuscule. So I invite readers to picture supremely competent optical designers isolated by the dual factors of language and corporate structure from the American market and even, perhaps, without much of an idea of how amateur astronomers actually use eyepieces and what current trends are.

Let us consider, for example, the XW wide field line. The focal lengths offered are: 3.5mm, 5mm, 7mm, 10mm, 14mm, 20mm, 30mm, and 40mm.

This line makes two marketing errors. First, Pentax appears unaware of the common device known as “the Barlow.” When you consider the Pentax line from the perspective of a 2x Barlow owner you can pick out two sequences of note:

5mm, 10mm, 20mm, 40mm
and
3.5mm, 7mm, 14mm

Only the 30mm is “out of a 2x sequence.” In essence if you own a 2x Barlow you can buy the 40mm, 10mm, 14mm, and 3.5mm thereby economizing on three purchases. That’s a good financial deal but it cuts down on the incentive to buy eyepieces. If the sequence were staggered differently one can imagine selling eight eyepieces each of which, Barlowed 2x, would offer additional focal lengths, for eight unique Barlowed focal length options. But in the current series only the 3.5mm, 5mm, and 30mm do not Barlow to a focal length already available.

The Barlow needed would be two inch with an adapter for 1.25 inch, apochromatic to do justice to the color correction in the eyepieces, and 2x for general use. Such Barlows are available from Televue and Astro-physics. But we have to wonder: why doesn’t Pentax offer a high end Barlow for general use (2x) and at least one other option for short focal length scopes and imagers (typically 4 – 5x)? With amateur astrophotographers regularly doing spectacular work on the planets at effective focal lengths of f/30 to f/50 and higher, Pentax ought to be able to market excellent Barlow selections at least as readily as it markets its excellent eyepieces.

Our consideration of Barlow-related issues raises another interesting point about the Pentax XW line: the 30mm XW. Presumably Pentax opted against doubling the 14mm to a 28mm because they wanted a 30mm to compete against the famous 31mm Nagler: The 30 XW is cheaper, but at $500 approaches the same heady price range. Its 70 degrees does not match the 82 degrees of the $630 Nagler, but in crispness, definition, and contrast, it offers a spectacular alternative to the Big One. But why 30mm? The 30XW in Pentax’s own f/6.5 105mm telescope, soon to be marketed in the U.S., would yield 3.0 degrees field of view. The Nagler 31mm excels at the wide field game, and would yield 3.7 degrees. By shifting the specification from 30mm to 32mm Pentax could boost the hypothetical 32XW to a true field of 3.3 degrees, narrowing the field gap to less than half a degree’s difference. And the hypothetical 32XW would Barlow to 16mm, filling a hole in the available focal lengths.

It makes sense in my mind for Pentax to trim from the 82 degree mark established by the Nagler dynasty to the more modest 70 degrees of its own line. Wide field eyepieces have different focal lengths on and off axis to achieve the desired field, but at the price of softening the image a bit with higher magnification as you move off-axis. Trimming to 70 degrees gives the Pentax XW design room to concentrate on the luminance and contrast that are its distinguishing features and still leaves plenty of space for observers to enjoy stupendous views of wide field objects. There is a definite design choice at work here, a real tradeoff between different goals in eyepiece performance, and I think the market is better for having such distinct options. Competing against the 31mm Nagler is not a trivial proposition, but if one is going to do it, I would suggest applying the crystal clarity of the XW design to a 32mm focal length. In that hypothetical scenario, for $500 you get exquisite contrast and lose only four-tenths of a degree in true field of view to the $630 competitor.

If we turn to the growing market for binoviewers, we find an additional Pentax Perplex. People who like this company’s eyepieces are shown the door if they ask what to put into their binoviewers. The default focal length for a binoviewer is 20 to 22mm to get a wide field view without vignetting. But the Pentax 20mm’s girth dissuades people from trying it in their binoviewers. I have heard that dual 20mm eyepieces work for some owners; and some folks have suggested outfitting a binoviewer with dual Pentax zoom eyepieces. But zooms tend to give up field of view and, in my limited experience, never seem quite as good as dedicated eyepieces. By and large, it seems that Pentax is forfeiting the binoviewer market.

Why doesn’t Pentax have a reasonably widefield (perhaps 60 or 65 degrees) 20 or 21mm eyepiece available for the binoviewers of such companies as Astro-physics, Televue, and Denkmeier?

Why doesn’t Pentax, which is one of the world’s premier maker of binoculars, offer its own binoviewers for the wide range of scopes in use?

The Pentax Perplex continues if we look at promising entries into the high end apochromatic refractor market. The company has shown at the May 2006 Northeast Astronomy Forum (NEAF) three gorgeous refractors, a 100mm, 105mm and a 125mm, the latter two are f/6.4. They appear to be a Petzval-inspired design with a two element objective and a two lens arrangement half way down the tube for field flattening (i.e. not as low as the Televue NP101; more typical Petzval arrangements use a single lens lower down).

The 125mm features a helical focus whose diameter is the same as the optical tube. Apparently the 100mm will also have the helical focuser—I did not look at it closely at the show. The helical on the 125mm provides a very smooth focus that gives good grip for fast racking in and out and simultaneously allows for very fine focus with gentle nudges of the big ring. Precision markings (to return to an exact focus point) and a tight focus lock will aid the photographer. This is an innovative feature, and if adopted on both models it could be the trademark identity of the Pentax refractor line as it develops in the United States. But the 105mm has a rack and pinion focus. I find it regrettable that Pentax has not moved to a distinct look and design with its excellent helical on all the models; but perhaps this is a risky move. In any case as one who has his eye on the 105mm, I find it regrettable the that the helical focus apparently won’t be the default.

An f/6.4 high end apo with a custom design for field flattening is an enticing option in an era when Astro-physics has apparently abandoned the four inch fast apochromatic market for good. Even with Televue and Takahashi marketing options in the f/5 range, the consumer market can’t seem to have enough superbly built 4” fast scopes. Weirdly, the 105mm was at first on display in a 1.25 inch configuration, which one salesman suggested would be the standard default. We certainly would hope not! Here’s a fast scope with a field flattener that ought to mate perfectly with Pentax’s own exquisite 30XW and 40XW oculars for dazzling views of the milky way. It would be criminal neglect to have this thing arrive at your door, beautifully boxed, with pristine optics, a $4.2k price tag, and a 1.25” diagonal jammed in on the end. Surely the company will not plan on making customers buy an accessory to accept a two inch diagonal?

It is, of course, always difficult to second guess a corporation and its decisions. Perhaps there is a higher rationality behind these designs, of which I am unaware. The product line is awesome in its optical quality. But the underlying rationality, how the designs are intended to meet the actual needs of astronomers in the field and how the company intends to market its products as an integrated whole: this is not evident from a look at Pentax’s current and planned offerings. The company appears to make fantastic equipment and throw it out on the market with no eye to the principal competition, market trends in binoviewing and astrophotography, and with no particular consideration of how its own products mate with other high-end astronomy product offerings—neither those of its competitors, nor, more surprisingly, those of its own making. Which is why it is the Pentax Perplex.

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