Pentax Eyepieces – Observatory Quality

Back awhile ago I did a review on plossl eyepieces. In that article I was trying to reach for the average individual looking for a high quality eyepiece on a limited budget. This time I asked for an example of observatory quality eyepieces that I know some of our readers own and enjoy. Is there a difference between how a very expensive eyepiece behaves in average equipment as opposed to an average eyepiece? Is there a difference in how it behaves in observatory class equipment? Step inside and let’s take a look…

The reputation of certain eyepieces sometimes precedes itself and the case is certainly true when it comes to Pentax Eyepieces. Known widely for delivering superb color correction and outstanding contrast, I was very anxious for these beauties to arrive and put them to the test. In this case, I have asked for the Pentax XW series, which would put it in the Erfle category – alongside such popular brands as the Nagler, the Panoptic, the Ultima LX and the QX series. In dollar amounts, the Pentax figures roughly in the same category as the first two aforementioned products, and roughly three times more expensive than the last two. But is the performance worth the price?

High dispersion, low refraction lanthanum glass… These are great words, but nothing can match the precision machined quality of the outward appearance of a Pentax eyepiece. Absolutely nothing in its construction appears to be left to chance and I very much approved not only of how the body of the eyepieces appears to be “sealed”, but the fact that they have very positive grip surfaces and little safety grooves cut right into the barrel so they can’t accidentally fall out of the focuser. I can also see from examination that the insides are blackened to reduce internal reflections and that the eyepieces are fully threaded for filters… But how do they perform?

The last of the three eyepieces I asked to test was the Pentax 40mm XW 2″ Eyepiece. If you are looking for a true observatory quality eyepiece, look no further. Combined with aperture, the 40mm delivers a wide, true field that only marginally suffers from vignetting around the edges with fast focal ratio telescopes and virtually disappears as the focal length increases. Once again, we are talking about an eyepiece that was made to perform with eye sight limitations and with just a few minor adjustments, a total pinpoint panorama of stars can be yours. While I’ve used a lot of Erfle design eyepieces, this is perhaps the first low power, wide field Erfle that I’ve used that didn’t require me to hold my head just right to take in the view. With or without glasses…

My next step was to take this eyepiece arrangement and put them to the test in a true observatory telescope – a 31″ f/7. Eyepiece after eyepiece… Outstanding performance, perfect color correction and incredible eye relief. Is seeing believing? Yes and no. In my mind to deem something “observatory quality”, it has to measure up to the bar that I set for it – and that means the durability of use that an observatory eyepiece will go through in years of service. While I can field test an eyepiece for performance qualities, what I can’t tell you is what will happen to it ten years down the road. So… I investigated.

There’s a good reason why I admired the construction of the Pentax eyepieces when I first examined them – they are weather-proof. While you would not want to drop them in a bucket of water, these eyepieces are all rated JIS Class 4. Just what does that mean? It means that dust and particles sized 1.0mm in diameter or more cannot infiltrate. It means water splashed against the enclosure from any direction shall have no harmful effects. It means that by Pentax standards they actually sprayed these eyepieces down with a stream of water for 10 minutes and nothing reached the internal lenses. It means Pentax guarantees these eyepieces for life.

In the long run, Pentax eyepieces are an investment – a worthy investment in observatory quality.

The Pentax Eyepieces provided for this review were supplied by Oceanside Photo and Telescope.

7 Replies to “Pentax Eyepieces – Observatory Quality”

  1. Thanks for the review Tammy, I hope everyone enjoys your reviews as much as i do. They are very timely for me.

    I still do not have a delivery schedule for my Kennedy 24″ f3.6 (almost 1 1/2 years) so I have not yet ordered the Denk II bino’s, have been noodling the eyepiece issue. I have a pair of 19mm Panoptics and have decided on a pair of 13mm Ethos. With my old tired eyes I can use all the eye relief that i can get, the Pans are 13mm and the Ethos are 15mm which is good but the 20mm for the Pentax sounds like a winner. I may have to get a pair of the 20mm Pentax and sell the Pans. I will talk to OPT for their advice.

    All this means just fewer beans and hotdogs but the good news is that I’m losing weight on this diet. πŸ™‚


    ( I don’t feel tooo bad cluttering up the blog with my ramblings tonight, no one else seems to be around)

  2. Pretty much a spot on review and mirrors my feelings about the Pentax XW lineup – that is why I own 6 of them – 5mm through the 30mm =-)

    I first looked through a 10.5mm XL a few years back at a star party and just fell in love with it. The nice big eye lens, the adjustable eyecup, the awesome eye relief – wow, it was the most comfortable EP I ever used. And not an optical flaw to be seen – irregardless of what scope it was used in.

    When I was upgrading my EP’s the next year, I did a lot of side by side comparisons between the Naglers, Radians, and Pentaxes. The Radians were almost as comfortable to use, but the Pentaxes were just a shade sharper. That was it, I was hooked!

    Last fall at the MidAtlantic Star Party, we had a 18″ Starmaster a 31mm Nagler, a 35mm Panoptic, and my 30mm Pentax – we did a side by side shootout with about 5 different observers using both with and without a parracor. All 3 gave exceptional views, but the Pentax kept coming out on top – again, comfort being a major consideration, but also how distortion free the view was: no pincushion effect, no issues with eye placement (kidney beaning), and no field curvature.

    Let me add one more comment to the review – that 20mm is the weakest of the EP’s in the lineup. Its got a bit of field curvature. Its more apparent the faster the scope, but its there. The 14mm also has it, but not nearly as noticeable as the 20mm. The rest of the lineup is dead on tight, fieldstop to fieldstop!!!

    I’ll probably pick up the 40mm next spring (bonus check time) but I don’t see the 3.5mm in my future. My 10″ scope gives me 250X with my 5mm and I can count on one hand the number of times seeing has been good enough to go much higher. I’ve still got a decent barlow and I can always barlow my 5mm or 7mm one those great nights. The Pentaxes do barlow well – no issues there.

    Thanks again for a nice writeup!!!

  3. you are very welcome.

    i wanted readers to know that i choose equipment because i like how it performs – not because of a brand name. while i admire televue – especially them plossls – i simply believe pentax has them beat in the erfle department. i mean no disrespect to mr. nagler’s design, but the pentax eyepieces don’t require optical correction to work in some scopes and that’s a bonus. there are simply some of us that have difficulty using certain types of eyepieces and finding the pentax was like finding a jewel…

    rapideye? if i had realized the eye relief was so incredible, i probably would have went more for the lower powers. it’s one thing to “read” that it has 20mm eye relief and it’s another to “see” it personally. again, a real bonus in pentax favor.

    as an aside, OPT has all pentax eyepieces currently on mark down and move ’em out while supplies last. this means free shipping and discounts aren’t in effect, so i was kinda’ afraid to mention it, but you guys are friends. πŸ˜‰

  4. “…are all rated JIS Class 4. Just what does that mean? It means that dust and particles sized 1.0mm in diameter or more cannot infiltrate.”

    >JIS Class 4 standards for a premium eyepiece are rubbish – particularly for dust ingress – a 1mm particle is pretty bloody big!

    I would damn well expect that a 1mm particle would go no where near to infiltrating an eyepiece’s internals, even on a $40 eyepiece! That’s like a new car coming with a guarantee that it will drive at least the first 100km with no breakdowns – not very lofty standards! Almost any piece of dirt, dust or grime is sub 1mm… On a premium eyepiece I think it should go without saying that the dust ingress at least should meet the criteria for JIS grade 5, and preferably 6.

    I’d never argue with the fact that Pentax eyepieces are the creme de la creme, but the JIS stats you quoted seem alarmingly sub-standard…

  5. PS –

    JIS Standards for dust ingress protection

    Grade 4

    Protected against solid foreign objects 1,0 mm diameter and greater.

    Grade 5

    Dust protected. Ingress of duct is not totally prevented, but dust shall not penetrate in a quantity to interfere with satisfactory operation of the apparatus or to impair safety.

    Grade 6

    Dust tight. No ingress of dust.

  6. “if i had realized the eye relief was so incredible, i probably would have went more for the lower powers. it’s one thing to “read” that it has 20mm eye relief and it’s another to “see” it personally.”

    That is one of the things that really hooked me on the lineup. A 10mm Plossl is a real pain to use. 10mm Ortho, same. Even the various Naglers get pretty tight at the higher powers.

    Being able to use a 5mm EP and have that nice big eye lens and very generous/comfortable eye relief is amazing!!! Its also great that they are all parafocal.

    I observe in high humidity – one of the added bonuses of the long eye relief is that they don’t fog up nearly as fast as other EP’s. I also have to clean eyelash oils off of them less often.

    Can you tell I’m a fanboy =-)

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