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Originally Posted by 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.
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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.
Quote:
Originally Posted by Profiler
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?
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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.
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Originally Posted by Profiler
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?
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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.
Quote:
Originally Posted by Profiler
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.
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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