Pete,
Forget about what manufacturers/sellers claim as to what purposes specific eyepieces are suited to. Two of the most widely used "planetary" telescope eyepiece designs of all time, the plossl and the orthoscopic were originally designed for use in microscopes. It just so happened they worked very well in telescopes.
It's worth noting that Pentax produce very little in the way of "specialist" astronomical equipment. Four of the Pentax XW series are sold as "spotting scope" eyepieces and the other four are sold as "astronomical eyepieces". A pure marketing ploy as they are all essentially designed with similar design objectives and they all work equally as well for both purposes.
I own the 8.5mm Pentax XF. It is an excellent lunar/ planetary eyepiece. Of course it works equally as well in a spotting scope. It would also work very well in a microscope.
CS-John B
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