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Message: <blockquote data-quote="henry link" data-source="post: 1497921" data-attributes="member: 6806">Frank,Look at the little Baader spotting scope in the photo here:<a href="http://www.baader-planetarium.com/pdf/hyperion_brief_description_e.pdf" target="_blank">http://www.baader-planetarium.com/pdf/hyperion_brief_description_e.pdf</a>It looks just like the Promaster scope and comes equipped with a Baader Hyperion Zoom eyepieces, which is one of the very best zooms. Naturally this has me wondering if the zoom eyepiece supplied with the Promaster is in fact the Baader zoom.The Pentax XW eyepieces are not a scaled design, so each one has different field curvature and astigmatism characteristics. Pentax used to have excellent technical data   for these eyepieces on its Japanese language website which included charts plotting astigmatism (also shows field curvature) and light transmission. Alas, that page seems to have disappeared. As I recall the 20mm and 14mm (I have that one) both have considerable field curvature, but the 14 has less astigmatism. Shorter focal lengths correct both pretty well. I don't know why you would see a lot more curvature in the Promaster than the Pentax 65mm. I think the Promaster focal length might be 360mm vs 390mm for the Pentax. Henry</blockquote>