Quote:
Originally Posted by 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?
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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.
Quote:
Originally Posted by Simon Holmes
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.
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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