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Originally Posted by OneOfOne
As noted by others in the group, the XW14 does appear to have a bit of field curvature, and I can confirm this myself in mine. I don't have an equivalent Stratus though, so I can comment on how the equivalent compares. The XW14 is not as "good" as the 7 or 10 though.
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You need to be a bit carefull there, jumping to conclusions based on a sample of 1 eyepiece in 1 scope. The 14mm Pentax XW shows worse field curvature in some scopes than in others. I have a 10"/F5 newt and an 18"/F4.5 newt. The field curvature in the 18"/F4.5 is hardly noticeable. This would appear surprising to some being of faster F-Ratio, but in fact field curvature seen in the eyepiece is not solely dependant on the F-Ratio of the scope it's used in, unlike coma and some other aberrations. We compared the views in the 18" scope between the 14mm Pentax XW and a 17mm Nagler T4 (both without a paracorr) at Kulnurra a couple of Saturdays ago and the Pentax gave a better view in just about every respect than the Nagler including field curvature and it's performance at the EOF. That wasn't just my opinion either BTW, there were about 6 other IIS forum members that all saw exactly the same thing. To be honest it wasn't even close. In fairness to the 17mm Nagler, I think its performance would have been improved a lot by the use of a paracorr, whereas the paracorr may not have been quite so beneficial in the Pentax.
CS-John B