Pentax SMC XF 8.5mm and 12mm Eyepiece

[Simon Holmes]

I am wondering if there are any members who owns these Pentaxes.
Would like to hear from you guys.
How do you rate them for planetary viewing?
Are they worth a buy compared to the other brands like the Hyperion, Meade and the Vixen.
Heard they are good and comes with the expected Pentax quality and reputation.
Are these made in Japan or Taiwan??

[ausastronomer]

Hi,

I own the 8.5mm Pentax XF and an 8mm Televue Radian. I use them both in all my Scopes. The 8.5mm Pentax XF is an exceptionally high quality eyepiece and worth every single cent of it's price. It has excellent eye relief and optical performance. I would rate it as slightly superior to the TV Radian in all criteria. It is a clearly better eyepiece than the 8mm Hyperion.

They are made in Japan

Cheers,
John B

[Profiler]

Hello John B

While we are on the topic of Pentax XF series eyepieces do you have any thoughts or information you could share on the merits of the Pentax XF 6.5-19.5mm Zoom eyepiece?

Would you happen to know whether it is any better than the Baader Zoom for example?

[Richard Gamble]

Hi John,

In your honest opinion, which ones will you prefers, SMC or the NLV?
And from your considerable experience, what are the advantage of your choice over the other?

[Simon Holmes]

Thanks John for your input.
Is there any observable difference between the SMC XF and the XW, considering that the XW is almost twice the cost?
I am considering if, it is worth saving and waiting a bit longer to get the XW instead.Hope you can throw some of your experience our way, as you have used both version of these Pentaxes.

[ausastronomer]

I have never used this eyepiece, and the reports I have read indicate that it is a decent eyepiece but not great. From what I have read its performance deteriorates off axis.

To be honest I dislike zoom eyepieces for astronomy because in most cases the AFOV gets narrower as the focal length is increased. IMO, for all practical purposes it should be the opposite, where the AFOV gets wider as the focal length is increased and the magnification reduced. Further, zoom eyepieces are generally not quite the optical equal of fixed focal length eyepiecs. You need to understand that it is impossible to get a "zoom anything" close to perfection across the entire focal length range, particularly when the range is wide like it is in this particular case, unless you spend an enormous amount of money. That applies to eyepieces, binoculars, camera lenses and riflescopes. A fixed focal length camera lens will "always" outperform a zoom lens near the extremeties of the zoom range. This is the reason the Televue zooms have a very small zoom range. There are the odd good zoom eyepieces, but they are frightfully expensive. The Leica Zoom is exceptional.

http://www.apm-telescopes.net/en/product.html?info=3100&xf88e8=610fe99b086976784dcd962409f1 259b

It's also $1,200 landed in Australia.

Cheers,
John B

[Profiler]

Hello John

At the outset - thank you so much for your input - it is very much appreciated.

I have looked at the Pentax XW's which typically feature a 7 or 8 lens design (exception being the 20mm) versus the XF's which both feature a 6 lens design.

I am trying to decide whether it is worthwhile buying XF eyepieces or simply focusing on collecting a set of XWs.

Putting aside FOV and the magnifaction differences between the two series do the XF's optically (in terms of clarity/contrast in what may be seen etc) exhibit any superiority in performance over the XW's?

Is it fair to view the XF's as a physically smaller scaled down version of the XW's with comparatively smaller FOV or are they also slightly inferior (a poor-mans XW so-to-speak) in terms of their optics as well in comparison to the XW's?

One thing I can't seem to establish is whether the XF's do, in fact, incorporate lanthanum glass elements. On some websites the XF's are described as incorporating lanthanum whereas other sites are silent on this point. This is in contrast to descriptions about the XW's which are all clearly described as using lanthanum lens elements.

Thank you in advance for your time and advice.

[ausastronomer]

Hi Richard,

I haven't used the Vixen NLV's. I have used the Vixen LV's which the NLV's replaced. Most of the differences between the two I believe are just cosmetic. While Vixen might claim some extra bells and whistles, the reports I have read indicate there is no detectable optical difference between them. I rate the Vixen LV's as pretty decent eyepieces. While they have 20mm of eye relief their FOV is narrow, 45° in some focal length 50° in others. I find the optical performance of the LV's to be a touch behind the LVW's which have a wider FOV and cost more money. I find the LV's to have slightly reduced light throughput and contrast compared to the LVW's and top quality plossls or orthoscopics. I would also consider them to be a step behind the Pentax XF's, but keep in mind the Pentax XF only comes in 2 focal lengths, whereas the Vixen NLV's have a multitude of focal length choices. Not an eyepiece I will ever own but certainly an eyepiece that many people will be very happy with.

Cheers,
John B

[ausastronomer]

Hi Simon,

The XW's step 7mm to 10mm, the XF is 8.5mm which is smack in the middle. The focal length difference is really too large to directly compare them. For instance in my 14" SDM the 8.5mm Pentax XF gives 190X compared to the 7mm and 10mm XW's which give 230X and 160X respectively. In my 18" Obsession the 8.5mm Pentax XF gives 250X. What I can tell you is that when I am after a medium/high power eyepiece the 8.5mm Pentax XF spends more time in the focuser than any other eyepiece I own, because its focal length is almost perfect for my two larger scopes. Having owned my Pentax XW's for about 9 years and my Pentax XF for almost 6 years, I can guarantee you that I feel the Pentax XF loses nothing to any other eyepiece, outside of a little bit of FOV and a couple of mm of eye relief. The eye relief on the XF is plenty for eyeglass wearers, but its a couple of mm less than the XW's which have 20mm of eye relief. The XF's are a lot smaller and lighter than the XW's. They are Japanese made and build quality is excellent.



Buy the eyepiece which provides you with the best focal length for your scope(s). The optical performance difference between them is miniscule, if there is one and not detectable because of the difference in focal length. You are paying more money for a physically larger eyepiece with a larger FOV and more eye relief. The XW's are also JIS Class 4 water resistant.

CAVEAT My comments refer to the 8.5mm Pentax XF only. I have not used the 12mm Pentax XF. I have had reports from some people who indicate it shows some field curvature in some scopes to some observers. I have also had reports from other observers that the 12mm Pentax XF is every bit as good as the 8.5mm Pentax XF. This may be telescope and user specific. The 8.5mm Pentax XF on the other hand has exhibited a beautiful flat field in every telescope I have tried it in.

Cheers,
John B

[ausastronomer]

The 8.5mm Pentax XF comes in a perfect focal length for my scopes. I will always have it and the 7mm and 10mm XW's, as they all get used a lot. Buy the focal lengths which suit your scope(s) and your observing style and don't be so worried about which set they come out of.



It's difficult to tell because of the difference in focal lengths but I am jamming them down the throat of some high class optics and I can't pick any difference in optical quality after making mental adjustments for the difference in focal lengths.



I wouldn't call the 8.5mm Pentax XF a poor man's anything. It is a top quality eyepiece in every respect IMO. The fact that it costs less money than some other premium eyepieces is just a bonus for mine. It is an excellent eyepiece in a compact light package.



The technicalities are all a bit academic for mine. While we like to think that what we buy uses the latest and greatest technology, it all comes back to how it performs IMO. I don't know what sort of glass the XF's use. What I do know is that my 8mm TV Radian uses Lanthanum Glass and the 8.5mm Pentax XF outperforms it by a small margin in every single optical performance criteria, so what glass the 8.5mm XF uses doesn't really matter IMO. The Pentax XF's use "unknown glass" and obviously have different coatings to the Pentax XW's which use Lanthanum Glass and partial phase coatings. But guess what? I can't pick any difference in optical performance between the XW's and the XF's. It is something we will never know because the focal lengths are different.

Cheers,
John B

[Profiler]

Thank you John - your input is very much appreciated.

I will offer one humble comment albeit possible correction to your comments purely informed by the item descriptions I seem to find on various websites.

In my own experience I have not come across any reference to Televue Radians or any Televue eyepieces as using/featuring lanthanum glass. Product descriptions are simply listed as 'ED' glass when anything is provided.

On many sites the item description for Pentax XF's state that they use lanthanum glass. On a few sites however the description of the glass in the XF series simply state that they use ED glass. However, on all sites that I have found the item description for the Pentax XW series are always clearly described as featuring lanthanum glass.

[rmcconachy]

John Rhodes is a Tele Vue employee and the company's representative on CloudyNights. In the following post he says "Our Radians were introduced in 1998, they use multiple fully multicoated Lanthanum elements in each one."

<http://www.cloudynights.com/ubbthreads/showflat.php?Cat=&Board=Eyepieces&Number=5290945&Forum=f75&Words=%2Bradian%20%2Blanthanum&Searchpage=0&Limit=2500&Main=5276100&Search=true&where=bodysub&Name=15300&daterange=1&newerval=10&newertype=y&olderval=&oldertype=&bodyprev=#Post5290945>

John is not Al or David Nagler but he ought to be a decent source IMHO.

[PlanetMan]

This is very interesting but is there any formal/official representation on this issue listed in specifications or marketing by Televue or some formal vendor/company selling its products? I think this is the point the previous post was trying to make.

Unfortunately, the US seems to be a rather litigious society and when, for example, something is stated/advertised to contain X but, in fact, doesn't lawsuits tend to quickly follow. Conversely, on the other hand - I can't imagine why such an obvious and beneficial marketing point wouldn't be clearly and formally stated in bold letters as it is with the Vixen LV's, NLVs, LVWs and apparently some Pentax EPs.

As we all know from recent news with twitter trolls the internet and its ilk seems to be something akin to the wild-west where the laws of most societies are unfortunately lacking in mechanisms for accountability on individuals etc.

However, if for example, a brochure or marketing specifications are formally made by a company which aren't correct etc - that is another story altogether.

Heck - I have never heard of circumstances where, for example, stockbrokers and speculators generate rumours through all sorts of mechanisms to influence financial perceptions in the public market.

Is anyone interested in buying some shares in Enron? I seem to recall having read somewhere that the company is making a huge come back :lol::lol::lol::lol::lol:

[ausastronomer]

Hi Profiler,

You are getting overly hung up on the construction of one or two elements, of eyepieces having 6 or more elements.

Here is a quote from Roland Christen on Astromart in 2007. Roland Christen designs and builds some of the worlds best Apochromatic refractors (Astro Physics). Roland is one of the worlds most respected opticians. Rolands' post was in response to a question about the Vixen FL102S Flourite doublet APO, which was also sold as the Celestron C102F. It is in fact a very high quality flourite doublet APO.



I want to emphasize this part of Roland's post:-



This brings me back to the question, "why are you so worried about whether or not an eyepiece has ONE or TWO Lanthanum glass elements when we have no clue what the other elements are made of. The material used in the construction of the other elements is infinitely more important than whether or not one or two elements are Lanthanum glass. This is purely the manufacturers' advertising hype to help them sell eyepieces. An eyepiece constructed from 4 elements of model aircraft grade perspex and two lanthanum glass elements isn't going to provide very good optical performance.

It all comes back to the fact that whatever glass Pentax uses in the construction of the XF series of eyepieces, it works very well.

Cheers,
John B

[Profiler]

Once again John thank you so much for the advice and to the contrary I immediately acted upon your wisdom and ordered both XF's.

Thanks once again!

[Simon Holmes]

It seems the lens are indeed made of lanthanum glass.
I was referring to the information from the Pentax website,

http://www.pentaxwebstore.com/product/9588

It says below,


High-refraction, low dispersion lanthanum glass to provide high resolution images with minimal aberrations


ion:



Overview (http://www.pentaxwebstore.com/product/9588#product)
Specifications (http://www.pentaxwebstore.com/product/9588#product)
Features (http://www.pentaxwebstore.com/product/9588#product)



Designed for use with Pentax PF 65 Series Spotting Scopes, provides 20x-60x magnification when used with them.
60 degree apparent field of view
Rubber eyepiece ring designed for viewing comfort
Also recommended for use with astronomical telescopes with 1 1/4" focuser
Pentax SMC full-surface multi-layer coated optics reduce glare while providing maximum light transmission and color quality
High-refraction, low dispersion lanthanum glass to provide high resolution images with minimal aberrations
Advanced computer simulation design technology to reduce internal reflections, producing brighter, clearer images.
Weatherproof construction for greater durability.



So, there should not be any doubt. Also, these eps are weatherproof....I am not sure if it means waterproof?

[Simon Holmes]

Hi Profiler,
I am thinking of ordering the XF8.5.
How much did you pay for them and from which seller?

[Profiler]

OPT has them for $179